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  • 1. Aamer, Aysha
    et al.
    Nicholl, Matt
    Jerkstrand, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gomez, Sebastian
    Oates, Samantha R.
    Smartt, Stephen J.
    Srivastav, Shubham
    Leloudas, Giorgos
    Anderson, Joseph P.
    Berger, Edo
    de Boer, Thomas
    Chambers, Kenneth
    Chen, Ting-Wan
    Galbany, Lluís
    Gao, Hua
    Gompertz, Benjamin P.
    González-Bañuelos, Maider
    Gromadzki, Mariusz
    Gutiérrez, Claudia P.
    Inserra, Cosimo
    Lowe, Thomas B.
    Magnier, Eugene A.
    Mazzali, Paolo A.
    Moore, Thomas
    Müller-Bravo, Tomás E.
    Pursiainen, Miika
    Rest, Armin
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Smith, Ken W.
    Terwel, Jacco H.
    Wainscoat, Richard
    Young, David R.
    A precursor plateau and pre-maximum [O ii] emission in the superluminous SN2019szu: a pulsational pair-instability candidate2023In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 527, no 4, p. 11970-11995Article in journal (Refereed)
    Abstract [en]

    We present a detailed study on SN2019szu, a Type I superluminous supernova at z = 0.213 that displayed unique photometric and spectroscopic properties. Pan-STARRS and ZTF forced photometry show a pre-explosion plateau lasting ∼40 d. Unlike other SLSNe that show decreasing photospheric temperatures with time, the optical colours show an apparent temperature increase from ∼15 000 to ∼20 000 K over the first 70 d, likely caused by an additional pseudo-continuum in the spectrum. Remarkably, the spectrum displays a forbidden emission line (likely attributed to λλ7320,7330) visible 16 d before maximum light, inconsistent with an apparently compact photosphere. This identification is further strengthened by the appearances of [O III] λλ4959, 5007, and [O III] λ4363 seen in the spectrum. Comparing with nebular spectral models, we find that the oxygen line fluxes and ratios can be reproduced with ∼0.25 M of oxygen-rich material with a density of ∼10−15 g cm−3⁠. The low density suggests a circumstellar origin, but the early onset of the emission lines requires that this material was ejected within the final months before the terminal explosion, consistent with the timing of the precursor plateau. Interaction with denser material closer to the explosion likely produced the pseudo-continuum bluewards of ∼5500 Å. We suggest that this event is one of the best candidates to date for a pulsational pair-instability ejection, with early pulses providing the low density material needed for the formation of the forbidden emission line, and collisions between the final shells of ejected material producing the pre-explosion plateau.

  • 2. Agudo, I.
    et al.
    Chen, T. -W.
    Stockholm Univ, Oskar Klein Ctr, Dept Astron, AlbaNova, Stockholm, Sweden.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yang, S.
    Stockholm Univ, Oskar Klein Ctr, Dept Astron, AlbaNova, Stockholm, Sweden.
    Young, D. R.
    Panning for gold, but finding helium: Discovery of the ultra-stripped supernova SN 2019wxt from gravitational-wave follow-up observations2023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 675, article id A201Article in journal (Refereed)
    Abstract [en]

    We present the results from multi-wavelength observations of a transient discovered during an intensive follow-up campaign of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN 2019wxt, a young transient in a galaxy whose sky position (in the 80% GW contour) and distance (similar to SIM;150 Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transient's tightly constrained age, its relatively faint peak magnitude (M-i similar to -16.7 mag), and the r-band decline rate of similar to 1 mag per 5 days appeared suggestive of a compact binary merger. However, SN 2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of only similar to 0.1 M circle dot, with Ni-56 comprising similar to 20% of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitor channels that could give rise to the observed properties of SN 2019wxt and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling genuine electromagnetic counterparts to GW events from transients such as SN 2019wxt soon after discovery is challenging: in a bid to characterise this level of contamination, we estimated the rate of events with a volumetric rate density comparable to that of SN 2019wxt and found that around one such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500 Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns.

  • 3.
    Biswas, Rahul
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dhawan, Suhail
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Cambridge, UK.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bellm, Eric C.
    Dekany, Richard
    Drake, Andrew J.
    Duev, Dmitry A.
    Fremling, Christoffer
    Graham, Matthew
    Kim, Young-Lo
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kulkarni, Shrinivas R.
    Mahabal, Ashish A.
    Perley, Daniel
    Rigault, Mickael
    Rusholme, Ben
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm Univ, Oskar Klein Ctr, Dept Astron, SE-10691 Stockholm, Sweden.
    Shupe, David L.
    Smith, Matthew
    Walters, Richard S.
    Two c's in a pod: cosmology-independent measurement of the Type Ia supernova colour-luminosity relation with a sibling pair2022In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 509, no 4, p. 5340-5356Article in journal (Refereed)
    Abstract [en]

    Using Zwicky Transient Facility (ZTF) observations, we identify a pair of ‘sibling’ Type Ia supernovae (SNe Ia), i.e. hosted by the same galaxy at z = 0.0541. They exploded within 200 d from each other at a separation of 0.6arcsec0.6arcsec corresponding to a projected distance of only 0.6 kpc. Performing SALT2 light-curve fits to the gri ZTF photometry, we show that for these equally distant ‘standardizable candles’, there is a difference of 2 mag in their rest-frame B-band peaks, and the fainter supernova (SN) has a significantly red SALT2 colour c = 0.57 ± 0.04, while the stretch values x1 of the two SNe are similar, suggesting that the fainter SN is attenuated by dust in the interstellar medium of the host galaxy. We use these measurements to infer the SALT2 colour standardization parameter, β = 3.5 ± 0.3, independent of the underlying cosmology and Malmquist bias. Assuming the colour excess is entirely due to dust, the result differs by 2σ from the average Milky Way total-to-selective extinction ratio, but is in good agreement with the colour–brightness corrections empirically derived from the most recent SN Ia Hubble–Lemaitre diagram fits. Thus we suggest that SN ‘siblings’, which will increasingly be discovered in the coming years, can be used to probe the validity of the colour and light-curve shape corrections using in SN Ia cosmology while avoiding important systematic effects in their inference from global multiparameter fits to inhomogeneous data sets, and also help constrain the role of interstellar dust in SN Ia cosmology.

  • 4. Bruch, Rachel J.
    et al.
    Gal-Yam, Avishay
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Weizmann Institute of Science, Israel.
    Yaron, Ofer
    Yang, Yi
    Soumagnac, Maayane
    Rigault, Mickael
    Strotjohann, Nora L.
    Ofek, Eran
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Masci, Frank J.
    Barbarino, Cristina
    Ho, Anna Y. Q.
    Fremling, Christoffer
    Perley, Daniel
    Nordin, Jakob
    Cenko, S. Bradley
    Adams, S.
    Adreoni, Igor
    Bellm, Eric C.
    Blagorodnova, Nadia
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Burdge, Kevin
    De, Kishalay
    Dhawan, Suhail
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Drake, Andrew J.
    Duev, Dmitry A.
    Dugas, Alison
    Graham, Matthew
    Graham, Melissa L.
    Irani, Ido
    Jencson, Jacob
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Aarhus University, Denmark.
    Kasliwal, Mansi
    Kim, Young-Lo
    Kulkarni, Shrinivas
    Kupfer, Thomas
    Liang, Jingyi
    Mahabal, Ashish
    Miller, A. A.
    Prince, Thomas A.
    Riddle, Reed
    Sharma, Y.
    Smith, Roger
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Aarhus University, Denmark.
    Taggart, Kirsty
    Walters, Richard
    Yan, Lin
    A Large Fraction of Hydrogen-rich Supernova Progenitors Experience Elevated Mass Loss Shortly Prior to Explosion2021In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 912, no 1, article id 46Article in journal (Refereed)
    Abstract [en]

    Spectroscopic detection of narrow emission lines traces the presence of circumstellar mass distributions around massive stars exploding as core-collapse supernovae. Transient emission lines disappearing shortly after the supernova explosion suggest that the material spatial extent is compact and implies an increased mass loss shortly prior to explosion. Here, we present a systematic survey for such transient emission lines (Flash Spectroscopy) among Type II supernovae detected in the first year of the Zwicky Transient Facility survey. We find that at least six out of ten events for which a spectrum was obtained within two days of the estimated explosion time show evidence for such transient flash lines. Our measured flash event fraction (>30% at 95% confidence level) indicates that elevated mass loss is a common process occurring in massive stars that are about to explode as supernovae.

  • 5. Bruch, Rachel J.
    et al.
    Gal-Yam, Avishay
    Yaron, Ofer
    Chen, Ping
    Strotjohann, Nora L.
    Irani, Ido
    Zimmerman, Erez
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Weizmann Institute of Science, Israel.
    Yang, Yi
    Kim, Young-Lo
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rigault, Mickael
    Ofek, Eran
    Soumagnac, Maayane
    Masci, Frank J.
    Fremling, Christoffer
    Perley, Daniel
    Nordin, Jakob
    Cenko, S. Bradley
    Ho, Anna Y. Q.
    Adams, S.
    Adreoni, Igor
    Bellm, Eric C.
    Blagorodnova, Nadia
    Burdge, Kevin
    De, Kishalay
    Dekany, Richard G.
    Dhawan, Suhail
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Drake, Andrew J.
    Duev, Dmitry A.
    Graham, Matthew
    Graham, Melissa L.
    Jencson, Jacob
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Aarhus University, Denmark.
    Kasliwal, Mansi M.
    Kulkarni, Shrinivas
    Miller, A. A.
    Neill, James D.
    Prince, Thomas A.
    Riddle, Reed
    Rusholme, Benjamin
    Sharma, Y.
    Smith, Roger
    Sravan, Niharika
    Taggart, Kirsty
    Walters, Richard
    Yan, Lin
    The Prevalence and Influence of Circumstellar Material around Hydrogen-rich Supernova Progenitors2023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 952, no 2, article id 119Article in journal (Refereed)
    Abstract [en]

    Narrow transient emission lines (flash-ionization features) in early supernova (SN) spectra trace the presence of circumstellar material (CSM) around the massive progenitor stars of core-collapse SNe. The lines disappear within days after the SN explosion, suggesting that this material is spatially confined, and originates from enhanced mass loss shortly (months to a few years) prior to the explosion. We performed a systematic survey of H-rich (Type II) SNe discovered within less than 2 days from the explosion during the first phase of the Zwicky Transient Facility survey (2018–2020), finding 30 events for which a first spectrum was obtained within <2 days from the explosion. The measured fraction of events showing flash-ionization features (>36% at the 95% confidence level) confirms that elevated mass loss in massive stars prior to SN explosion is common. We find that SNe II showing flash-ionization features are not significantly brighter, nor bluer, nor more slowly rising than those without. This implies that CSM interaction does not contribute significantly to their early continuum emission, and that the CSM is likely optically thin. We measured the persistence duration of flash-ionization emission and find that most SNe show flash features for ≈5 days. Rarer events, with persistence timescales >10 days, are brighter and rise longer, suggesting these may be intermediate between regular SNe II and strongly interacting SNe IIn.

  • 6. Cano, Z.
    et al.
    Izzo, L.
    de Ugarte Postigo, A.
    Thöne, C. C.
    Krühler, T.
    Heintz, K. E.
    Malesani, D.
    Geier, S.
    Fuentes, C.
    Chen, T. -W.
    Covino, S.
    D'Elia, V.
    Fynbo, J. P. U.
    Goldoni, P.
    Gomboc, A.
    Hjorth, J.
    Jakobsson, P.
    Kann, D. A.
    Milvang-Jensen, B.
    Pugliese, G.
    Sánchez-Ramírez, R.
    Schulze, S.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tanvir, N. R.
    Wiersema, K.
    GRB 161219B/SN 2016jca: A low-redshift gamma-ray burst supernova powered by radioactive heating2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, article id A107Article in journal (Refereed)
    Abstract [en]

    Since the first discovery of a broad-lined type Ic supernova (SN) with a long-duration gamma-ray burst (GRB) in 1998, fewer than fifty GRB-supernovae (SNe) have been discovered. The intermediate-luminosity Swift GRB 161219B and its associated supernova SN 2016jca, which occurred at a redshift of z = 0.1475, represents only the seventh GRB-SN to have been discovered within 1 Gpc, and hence provides an excellent opportunity to investigate the observational and physical properties of these very elusive and rare type of SN. As such, we present optical to near-infrared photometry and optical spectroscopy of GRB 161219B and SN 2016jca, spanning the first three months since its discovery. GRB 161219B exploded in the disk of an edge-on spiral galaxy at a projected distance of 3.4 kpc from the galactic centre. GRB 161219B itself is an outlier in the E-p,E-i - E-gamma,E-iso plane, while SN 2016jca had a rest-frame, peak absolute V-band magnitude of M-V = -19.0 +/- 0.1, which it reached after 12.3 +/- 0.7 rest-frame days. We find that the bolometric properties of SN 2016jca are inconsistent with being powered solely by a magnetar central engine, and demonstrate that it was likely powered exclusively by energy deposited by the radioactive decay of nickel and cobalt into their daughter products, which were nucleosynthesised when its progenitor underwent core collapse. We find that 0.22 +/- 0.08 M-circle dot of nickel is required to reproduce the peak luminosity of SN 2016jca, and we constrain an ejecta mass of 5.8 +/- 0.3 M-circle dot and a kinetic energy of 5.1 +/- 0.8 x 10(52) erg. Finally, we report on a chromatic, pre-maximum bump in the g-band light curve, and discuss its possible origin.

  • 7. Chen, Ping
    et al.
    Gal-Yam, Avishay
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Post, Richard S.
    Liu, Chang
    Ofek, Eran O.
    Das, Kaustav K.
    Fremling, Christoffer
    Horesh, Assaf
    Katz, Boaz
    Kushnir, Doron
    Kasliwal, Mansi M.
    Kulkarni, Shri R.
    Liu, Dezi
    Liu, Xiangkun
    Miller, Adam A.
    Rose, Kovi
    Waxman, Eli
    Yang, Sheng
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Henan Academy of Sciences, People’s Republic of China.
    Yao, Yuhan
    Zackay, Barak
    Bellm, Eric C.
    Dekany, Richard
    Drake, Andrew J.
    Fang, Yuan
    Fynbo, Johan P. U.
    Groom, Steven L.
    Helou, George
    Irani, Ido
    Jegou du Laz, Theophile
    Liu, Xiaowei
    Mazzali, Paolo A.
    Neill, James D.
    Qin, Yu-Jing
    Riddle, Reed L.
    Sharon, Amir
    Strotjohann, Nora L.
    Wold, Avery
    Yan, Lin
    A 12.4-day periodicity in a close binary system after a supernova2024In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 625, no 7994, p. 253-258Article in journal (Refereed)
    Abstract [en]

    Neutron stars and stellar-mass black holes are the remnants of massive star explosions1. Most massive stars reside in close binary systems2, and the interplay between the companion star and the newly formed compact object has been theoretically explored3, but signatures for binarity or evidence for the formation of a compact object during a supernova explosion are still lacking. Here we report a stripped-envelope supernova, SN 2022jli, which shows 12.4-day periodic undulations during the declining light curve. Narrow Hα emission is detected in late-time spectra with concordant periodic velocity shifts, probably arising from hydrogen gas stripped from a companion and accreted onto the compact remnant. A new Fermi-LAT γ-ray source is temporally and positionally consistent with SN 2022jli. The observed properties of SN 2022jli, including periodic undulations in the optical light curve, coherent Hα emission shifting and evidence for association with a γ-ray source, point to the explosion of a massive star in a binary system leaving behind a bound compact remnant. Mass accretion from the companion star onto the compact object powers the light curve of the supernova and generates the γ-ray emission.

  • 8. Chen, Z. H.
    et al.
    Yan, Lin
    Kangas, T.
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Perley, D. A.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taggart, K.
    Hinds, K. R.
    Gal-Yam, A.
    Wang, X. F.
    Andreoni, I.
    Bellm, E.
    Bloom, J. S.
    Burdge, K.
    Burgos, A.
    Cook, D.
    Dahiwale, A.
    De, K.
    Dekany, R.
    Dugas, A.
    Frederik, S.
    Fremling, C.
    Graham, M.
    Hankins, M.
    Ho, A.
    Jencson, J.
    Karambelkar, V.
    Kasliwal, M.
    Kulkarni, S.
    Laher, R.
    Rusholme, B.
    Sharma, Y.
    Taddia, F.
    Tartaglia, L.
    Thomas, B. P.
    Tzanidakis, A.
    Van Roestel, J.
    Walter, R.
    Yang, Y.
    Yao, Y. H.
    Yaron, O.
    The Hydrogen-poor Superluminous Supernovae from the Zwicky Transient Facility Phase I Survey. I. Light Curves and Measurements2023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 943, no 1, article id 41Article in journal (Refereed)
    Abstract [en]

    During the Zwicky Transient Facility (ZTF) Phase I operations, 78 hydrogen-poor superluminous supernovae (SLSNe-I) were discovered in less than 3 yr, constituting the largest sample from a single survey. This paper (Paper I) presents the data, including the optical/UV light curves and classification spectra, while Paper II in this series will focus on the detailed analysis of the light curves and modeling. Our photometry is primarily taken by ZTF in the g, r, and i bands, and with additional data from other ground-based facilities and Swift. The events of our sample cover a redshift range of z = 0.06 − 0.67, with a median and 1σ error (16% and 84% percentiles) of zmed=0.265. The peak luminosity covers −22.8 mag ≤ Mg,peak ≤ −19.8 mag, with a median value of -21.48. The light curves evolve slowly with a mean rest-frame rise time of trise = 41.9 ± 17.8 days. The luminosity and timescale distributions suggest that low-luminosity SLSNe-I with a peak luminosity ∼−20 mag or extremely fast-rising events (<10 days) exist, but are rare. We confirm previous findings that slowly rising SLSNe-I also tend to fade slowly. The rest-frame color and temperature evolution show large scatters, suggesting that the SLSN-I population may have diverse spectral energy distributions. The peak rest-frame color shows a moderate correlation with the peak absolute magnitude, i.e., brighter SLSNe-I tend to have bluer colors. With optical and UV photometry, we construct the bolometric luminosity and derive a bolometric correction relation that is generally applicable for converting g, r-band photometry to the bolometric luminosity for SLSNe-I.

  • 9. Chen, Z. H.
    et al.
    Yan, Lin
    Kangas, T.
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Perley, D. A.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taggart, K.
    Hinds, K. R.
    Gal-Yam, A.
    Wang, X. F.
    De, K.
    Bellm, E.
    Bloom, J. S.
    Dekany, R.
    Graham, M.
    Kasliwal, M.
    Kulkarni, S.
    Laher, R.
    Neill, D.
    Rusholme, B.
    The Hydrogen-poor Superluminous Supernovae from the Zwicky Transient Facility Phase I Survey. II. Light-curve Modeling and Characterization of Undulations2023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 943, no 1, article id 42Article in journal (Refereed)
    Abstract [en]

    We present analysis of the light curves (LCs) of 77 hydrogen-poor superluminous supernovae (SLSNe I) discovered during the Zwicky Transient Facility Phase I operation. We find that the majority (67%) of the sample can be fit equally well by both magnetar and ejecta–circumstellar medium (CSM) interaction plus 56Ni decay models. This implies that LCs alone cannot unambiguously constrain the physical power sources for an SLSN I. However, 23% of the sample show inverted V-shape, steep-declining LCs or features of long rise and fast post-peak decay, which are better described by the CSM+Ni model. The remaining 10% of the sample favors the magnetar model. Moreover, our analysis shows that the LC undulations are quite common, with a fraction of 18%–44% in our gold sample. Among those strongly undulating events, about 62% of them are found to be CSM-favored, implying that the undulations tend to occur in the CSM-favored events. Undulations show a wide range in energy and duration, with median values (and 1σ errors) being as  and  days, respectively. Our analysis of the undulation timescales suggests that intrinsic temporal variations of the central engine can explain half of the undulating events, while CSM interaction (CSI) can account for the majority of the sample. Finally, all of the well-observed He-rich SLSNe Ib either have strongly undulating LCs or the LCs are much better fit by the CSM+Ni model. These observations imply that their progenitor stars have not had enough time to lose all of the He-envelopes before supernova explosions, and H-poor CSM are likely to present in these events.

  • 10. Das, Kaustav K.
    et al.
    Kasliwal, Mansi M.
    Fremling, Christoffer
    Yang, Sheng
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sit, Tawny
    De, Kishalay
    Tzanidakis, Anastasios
    Perley, Daniel A.
    Anand, Shreya
    Andreoni, Igor
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Brudge, K.
    Drake, Andrew
    Gal-Yam, Avishay
    Laher, Russ R.
    Karambelkar, Viraj
    Kulkarni, S. R.
    Masci, Frank J.
    Medford, Michael S.
    Polin, Abigail
    Reedy, Harrison
    Riddle, Reed
    Sharma, Yashvi
    Smith, Roger
    Yan, Lin
    Yang, Yi
    Yao, Yuhan
    Probing the Low-mass End of Core-collapse Supernovae Using a Sample of Strongly-stripped Calcium-rich Type IIb Supernovae from the Zwicky Transient Facility2023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 959, no 1, article id 12Article in journal (Refereed)
    Abstract [en]

    The fate of stars in the zero-age main-sequence (ZAMS) range ≈8–12 M is unclear. They could evolve to form white dwarfs or explode as electron-capture supernovae (SNe) or iron core-collapse SNe (CCSNe). Even though the initial mass function indicates that this mass range should account for over 40% of all CCSN progenitors, few have been observationally confirmed, likely due to the faintness and rapid evolution of some of these transients. In this paper, we present a sample of nine Ca-rich/O-poor Type IIb SNe detected by the Zwicky Transient Facility with progenitors likely in this mass range. These sources have a [Ca ii] λλ7291, 7324/[O i] λλ6300, 6364 flux ratio of ≳2 in their nebular spectra. Comparing the measured [O i] luminosity (≲1039 erg s−1) and derived oxygen mass (≈0.01 M) with theoretical models, we infer that the progenitor ZAMS mass for these explosions is less than 12 M. The ejecta properties (Mej ≲ 1 M and Ekin ∼ 1050 erg) are also consistent. The low ejecta mass of these sources indicates a class of strongly-stripped SNe that is a transition between the regular stripped-envelope SNe and ultra-stripped SNe. The progenitor could be stripped by a main-sequence companion and result in the formation of a neutron star−main sequence binary. Such binaries have been suggested to be progenitors of neutron star−white dwarf systems that could merge within a Hubble time and be detectable with LISA.

  • 11.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Strotjohann, Nora L.
    Yang, Sheng
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ofek, Eran O.
    Crellin-Quick, Arien
    De, Kishalay
    Drake, Andrew J.
    Fremling, Christoffer
    Gal-Yam, Avishay
    Ho, Anna Y. Q.
    Kasliwal, Mansi M.
    SN 2019zrk, a bright SN 2009ip analog with a precursor2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 666, article id A79Article in journal (Refereed)
    Abstract [en]

    We present photometric and spectroscopic observations of the Type IIn supernova SN 2019zrk (also known as ZTF 20aacbyec). The SN shows a > 100 day precursor, with a slow rise, followed by a rapid rise to M ≈ −19.2 in the r and g bands. The post-peak light-curve decline is well fit with an exponential decay with a timescale of ∼39 days, but it shows prominent undulations, with an amplitude of ∼1 mag. Both the light curve and spectra are dominated by an interaction with a dense circumstellar medium (CSM), probably from previous mass ejections. The spectra evolve from a scattering-dominated Type IIn spectrum to a spectrum with strong P-Cygni absorptions. The expansion velocity is high, ∼16 000 km s−1, even in the last spectra. The last spectrum ∼110 days after the main eruption reveals no evidence for advanced nucleosynthesis. From analysis of the spectra and light curves, we estimate the mass-loss rate to be ∼4 × 10−2M yr−1 for a CSM velocity of 100 km s−1, and a CSM mass of 1 M. We find strong similarities for both the precursor, general light curve, and spectral evolution with SN 2009ip and similar SNe, although SN 2019zrk displays a brighter peak magnitude. Different scenarios for the nature of the 09ip-class of SNe, based on pulsational pair instability eruptions, wave heating, and mergers, are discussed.

  • 12. Gal-Yam, A.
    et al.
    Bruch, R.
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Weizmann Institute of Science, Israel.
    Yang, Y.
    Perley, D. A.
    Irani, I.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Soumagnac, M. T.
    Yaron, O.
    Strotjohann, N. L.
    Zimmerman, E.
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kulkarni, S. R.
    Kasliwal, M. M.
    De, K.
    Yao, Y.
    Fremling, C.
    Yan, L.
    Ofek, E. O.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Filippenko, A. V.
    Zheng, W.
    Brink, T. G.
    Copperwheat, C. M.
    Foley, R. J.
    Brown, J.
    Siebert, M.
    Leloudas, G.
    Cabrera-Lavers, A. L.
    Garcia-Alvarez, D.
    Marante-Barreto, A.
    Frederick, S.
    Hung, T.
    Wheeler, J. C.
    Vinkó, J.
    Thomas, B. P.
    Graham, M. J.
    Duev, D. A.
    Drake, A. J.
    Dekany, R.
    Bellm, E. C.
    Rusholme, B.
    Shupe, D. L.
    Andreoni, I.
    Sharma, Y.
    Riddle, R.
    van Roestel, J.
    Knezevic, N.
    A WC/WO star exploding within an expanding carbon-oxygen-neon nebula2022In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 601, no 7892, p. 201-204Article in journal (Refereed)
    Abstract [en]

    The final fate of massive stars, and the nature of the compact remnants they leave behind (black holes and neutron stars), are open questions in astrophysics. Many massive stars are stripped of their outer hydrogen envelopes as they evolve. Such Wolf-Rayet stars(1) emit strong and rapidly expanding winds with speeds greater than 1,000 kilometres per second. A fraction of this population is also helium-depleted, with spectra dominated by highly ionized emission lines of carbon and oxygen (types WC/WO). Evidence indicates that the most commonly observed supernova explosions that lack hydrogen and helium (types Ib/Ic) cannot result from massive WC/WO stars(2,3), leading some to suggest that most such stars collapse directly into black holes without a visible supernova explosion(4). Here we report observations of SN 2019hgp, beginning about a day after the explosion. Its short rise time and rapid decline place it among an emerging population of rapidly evolving transients(5-8). Spectroscopy reveals a rich set of emission lines indicating that the explosion occurred within a nebula composed of carbon, oxygen and neon. Narrow absorption features show that this material is expanding at high velocities (greater than 1,500 kilometres per second), requiring a compact progenitor. Our observations are consistent with an explosion of a massive WC/WO star, and suggest that massive Wolf-Rayet stars may be the progenitors of some rapidly evolving transients.

  • 13. Ganot, Noam
    et al.
    Ofek, Eran O.
    Gal-Yam, Avishay
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Soumagnac, Maayane T.
    Morag, Jonathan
    Waxman, Eli
    Kulkarni, Shrinivas R.
    Kasliwal, Mansi M.
    Neill, James
    The GALEX-PTF Experiment. II. Supernova Progenitor Radius and Energetics via Shock-cooling Modeling2022In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 931, no 1, article id 71Article in journal (Refereed)
    Abstract [en]

    The radius and surface composition of an exploding massive star, as well as the explosion energy per unit mass, can be measured using early ultraviolet (UV) observations of core-collapse supernovae (CC SNe). We present the results from a simultaneous Galaxy Evolution Explorer (GALEX) and Palomar Transient Factory (PTF) search for early UV emission from SNe. We analyze five CC SNe for which we obtained near-UV (NUV) measurements before the first ground-based R-band detection. We introduce SOPRANOS, a new maximum likelihood fitting tool for models with variable temporal validity windows, and use it to fit the Sapir & Waxman shock-cooling model to the data. We report four Type II SNe with progenitor radii in the range of R* ≈ 600–1100 R⊙ and a shock velocity parameter in the range of vs* ≈ 2700–6000 km s−1 (E/M ≈ 2–8 × 1050 erg/M⊙) and one Type IIb SN with R* ≈ 210 R⊙ and vs* ≈ 11,000 km s−1 (E/M ≈ 1.8 × 1051 erg/M⊙). Our pilot GALEX/PTF project thus suggests that a dedicated, systematic SN survey in the NUV band, such as the wide-field UV explorer ULTRASAT mission, is a compelling method to study the properties of SN progenitors and SN energetics.

  • 14.
    Goobar, Ariel
    et al.
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Pearson Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Arendse, Nikki
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dhawan, Suhail
    Mörtsell, Edvard
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, Christoffer
    Yan, Lin
    Perley, Daniel
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Joseph, Rémy
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Hinds, K-Ryan
    Meynardie, William
    Andreoni, Igor
    Bellm, Eric
    Bloom, Josh
    Collett, Thomas E.
    Drake, Andrew
    Graham, Matthew
    Kasliwal, Mansi
    Kulkarni, Shri R.
    Lemon, Cameron
    Miller, Adam A.
    Neill, James D.
    Nordin, Jakob
    Pierel, Justin
    Richard, Johan
    Riddle, Reed
    Rigault, Mickael
    Rusholme, Ben
    Sharma, Yashvi
    Stein, Robert
    Stewart, Gabrielle
    Townsend, Alice
    Vinko, Jozsef
    Wheeler, J. Craig
    Wold, Avery
    Uncovering a population of gravitational lens galaxies with magnified standard candle SN Zwicky2023In: Nature Astronomy, E-ISSN 2397-3366, Vol. 7, no 9, p. 1098-1107Article in journal (Refereed)
    Abstract [en]

    Detecting gravitationally lensed supernovae is among the biggest challenges in astronomy. It involves a combination of two very rare phenomena: catching the transient signal of a stellar explosion in a distant galaxy and observing it through a nearly perfectly aligned foreground galaxy that deflects light towards the observer. Here we describe how high-cadence optical observations with the Zwicky Transient Facility, with its unparalleled large field of view, led to the detection of a multiply imaged type Ia supernova, SN Zwicky, also known as SN 2022qmx. Magnified nearly 25-fold, the system was found thanks to the standard candle nature of type Ia supernovae. High-spatial-resolution imaging with the Keck telescope resolved four images of the supernova with very small angular separation, corresponding to an Einstein radius of only θE = 0.167″ and almost identical arrival times. The small θE and faintness of the lensing galaxy are very unusual, highlighting the importance of supernovae to fully characterize the properties of galaxy-scale gravitational lenses, including the impact of galaxy substructures.

  • 15. Ho, Anna Y. Q.
    et al.
    Kulkarni, S. R.
    Perley, Daniel A.
    Cenko, S. Bradley
    Corsi, Alessandra
    Schulze, Steve
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gal-Yam, Avishay
    Anand, Shreya
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bellm, Eric C.
    Bruch, Rachel J.
    Burns, Eric
    De, Kishalay
    Dekany, Richard
    Delacroix, Alexandre
    Duev, Dmitry A.
    Frederiks, Dmitry D.
    Fremling, Christoffer
    Goldstein, Daniel A.
    Golkhou, V. Zach
    Graham, Matthew J.
    Hale, David
    Kasliwal, Mansi M.
    Kupfer, Thomas
    Laher, Russ R.
    Martikainen, Julia
    Masci, Frank J.
    Neill, James D.
    Ridnaia, Anna
    Rusholme, Ben
    Savchenko, Volodymyr
    Shupe, David L.
    Soumagnac, Maayane T.
    Strotjohann, Nora L.
    Svinkin, Dmitry S.
    Taggart, Kirsty
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yan, Lin
    Zolkower, Jeffry
    SN 2020bvc: A Broad-line Type Ic Supernova with a Double-peaked Optical Light Curve and a Luminous X-Ray and Radio Counterpart2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 902, no 1, article id 86Article in journal (Refereed)
    Abstract [en]

    We present optical, radio, and X-ray observations of SN 2020bvc (=ASASSN-20bs, ZTF 20aalxlis), a nearby (z = 0.0252; d.=.114Mpc) broad-line (BL) Type Ic supernova (SN) and the first double-peaked Ic-BL discovered without a gamma-ray burst (GRB) trigger. Our observations show that SN 2020bvc shares several properties in common with the Ic-BL SN 2006aj, which was associated with the low-luminosity gamma-ray burst (LLGRB) 060218. First, the 10 GHz radio luminosity (L-radio approximate to 10(37) erg s(-1)) is brighter than ordinary core-collapse SNe but fainter than LLGRB SNe such as SN 1998bw (associated with LLGRB 980425). We model our VLA observations (spanning 13-43 days) as synchrotron emission from a mildly relativistic (v greater than or similar to 0.3c) forward shock. Second, with Swift and Chandra, we detect X-ray emission (L-X approximate to 10(41) erg s(-1)) that is not naturally explained as inverse Compton emission or part of the same synchrotron spectrum as the radio emission. Third, high-cadence (6x night(-1)) data from the Zwicky Transient Facility (ZTF) show a double-peaked optical light curve, the first peak from shock cooling of extended low-mass material (mass M-e < 10(-2) M-circle dot at radius R-e > 10(12) cm) and the second peak from the radioactive decay of 56Ni. SN 2020bvc is the first double-peaked Ic-BL SN discovered without a GRB trigger, so it is noteworthy that it shows X-ray and radio emission similar to LLGRB SNe. For four of the five other nearby (z less than or similar to 0.05) Ic-BL SNe with ZTF high-cadence data, we rule out a first peak like that seen in SN 2006aj and SN 2020bvc, i.e., that lasts approximate to 1 day.and reaches a peak luminosity M approximate to -18. Follow-up X-ray and radio observations of Ic-BL SNe with well-sampled early optical light curves will establish whether double-peaked optical light curves are indeed predictive of LLGRB-like X-ray and radio emission.

  • 16. Ho, Anna Y. Q.
    et al.
    Perley, Daniel A.
    Gal-Yam, Avishay
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Das, Kaustav K.
    Dobie, Dougal
    Yao, Yuhan
    Fremling, Christoffer
    Adams, Scott
    Anand, Shreya
    Andreoni, Igor
    Bellm, Eric C.
    Bruch, Rachel J.
    Burdge, Kevin B.
    Castro-Tirado, Alberto J.
    Dahiwale, Aishwarya
    De, Kishalay
    Dekany, Richard
    Drake, Andrew J.
    Duev, Dmitry A.
    Graham, Matthew J.
    Helou, George
    Kaplan, David L.
    Karambelkar, Viraj
    Kasliwal, Mansi M.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kulkarni, S. R.
    Mahabal, Ashish A.
    Medford, Michael S.
    Miller, A. A.
    Nordin, Jakob
    Ofek, Eran
    Petitpas, Glen
    Riddle, Reed
    Sharma, Yashvi
    Smith, Roger
    Stewart, Adam J.
    Taggart, Kirsty
    Tartaglia, Leonardo
    Tzanidakis, Anastasios
    Winters, Jan Martin
    A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients2023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 949, no 2, article id 120Article in journal (Refereed)
    Abstract [en]

    We present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 day < t (1/2) < 12 days, of which 28 have blue (g - r less than or similar to -0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had predominantly featureless spectra and luminous radio emission: AT2018lug (The Koala) and AT2020xnd (The Camel). Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad H alpha in emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (eight) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 24 of the transients. All X-ray and radio observations resulted in nondetections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs and use ZTF's SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate.

  • 17. Ho, Anna Y. Q.
    et al.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Omand, Conor M. B.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pessi, Priscila Jael
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zheng, WeiKang
    Minutes-duration optical flares with supernova luminosities2023In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 623, no 7989, p. 927-931Article in journal (Refereed)
    Abstract [en]

    In recent years, certain luminous extragalactic optical transients have been observed to last only a few days. Their short observed duration implies a different powering mechanism from the most common luminous extragalactic transients (supernovae), whose timescale is weeks. Some short-duration transients, most notably AT2018cow, show blue optical colours and bright radio and X-ray emission. Several AT2018cow-like transients have shown hints of a long-lived embedded energy source, such as X-ray variability, prolonged ultraviolet emission, a tentative X-ray quasiperiodic oscillation and large energies coupled to fast (but subrelativistic) radio-emitting ejecta. Here we report observations of minutes-duration optical flares in the aftermath of an AT2018cow-like transient, AT2022tsd (the ‘Tasmanian Devil’). The flares occur over a period of months, are highly energetic and are probably nonthermal, implying that they arise from a near-relativistic outflow or jet. Our observations confirm that, in some AT2018cow-like transients, the embedded energy source is a compact object, either a magnetar or an accreting black hole. 

  • 18. Hoeflich, Peter
    et al.
    Yang (杨轶), Yi
    Baade, Dietrich
    Cikota, Aleksandar
    Maund, Justyn R.
    Mishra, Divya
    Patat, Ferdinando
    Patra, Kishore C.
    Wang, Lifan
    Wheeler, J. Craig
    Filippenko, Alexei V.
    Gal-Yam, Avishay
    Schulze, Steven
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    The core normal Type Ia supernova 2019np – an overall spherical explosion with an aspherical surface layer and an aspherical 56Ni core 2023In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 520, no 1, p. 560-582Article in journal (Refereed)
    Abstract [en]

    Optical spectropolarimetry of the normal thermonuclear supernova (SN) 2019np from −14.5 to +14.5 d relative to B-band maximum detected an intrinsic continuum polarization (pcont) of 0.21 ± 0.09 per cent at the first epoch. Between days −11.5 and  +0.5, pcont remained ∼0 and by day +14.5 was again significant at 0.19 ± 0.10 per cent. Not considering the first epoch, the dominant axis of SiII λ6355 was roughly constant staying close the continuum until both rotated in opposite directions on day  +14.5. Detailed radiation-hydrodynamical simulations produce a very steep density slope in the outermost ejecta so that the low first-epoch pcont ≈ 0.2 per cent nevertheless suggests a separate structure with an axis ratio ∼2 in the outer carbon-rich (3.5–4) × 10−3 M. Large-amplitude fluctuations in the polarization profiles and a flocculent appearance of the polar diagram for the CaII near-infrared triplet (NIR3) may be related by a common origin. The temporal evolution of the polarization spectra agrees with an off-centre delayed detonation. The late-time increase in polarization and the possible change in position angle are also consistent with an aspherical 56Ni core. The pcont and the absorptions due to SiII λ6355 and CaII NIR3 form in the same region of the extended photosphere, with an interplay between line occultation and thermalization producing p. Small-scale polarization features may be due to small-scale structures, but many could be related to atomic patterns of the quasi-continuum; they hardly have an equivalent in the total-flux spectra. We compare SN 2019np to other SNe and develop future objectives and strategies for SN Ia spectropolarimetry.

  • 19. Irani, I.
    et al.
    Prentice, S. J.
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Weizmann Institute of Science, Israel.
    Gal-Yam, A.
    Teffs, Jacob
    Mazzali, Paolo
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gonzalez, E. P.
    Taggart, K.
    De, Kishalay
    Fremling, Christoffer
    Perley, Daniel A.
    Strotjohann, Nora L.
    Kasliwal, Mansi M.
    Howell, A.
    Dhawan, Suhail
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Cambridge, UK.
    Tzanidakis, Anastasios
    Hiramatsu, Daichi
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Anderson, J. P.
    Müller-Bravo, T. E.
    Dekany, Richard
    Gromadzki, Mariusz
    Carini, Roberta
    Galbany, L.
    Drake, Andrew J.
    Burke, Jamison
    Pellegrino, Craig
    Della Valle, Massimo
    Medford, Michael S.
    Rusholme, Ben
    Young, D. R.
    Gutiérrez, Claudia P.
    Inserra, Cosimo
    Omer, Rafia
    Shupe, David L.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Shin, Kyung Min
    Yaron, Ofer
    McCully, Curtis
    Nicholl, Matt
    Riddle, Reed
    Less Than 1% of Core-collapse Supernovae in the Local Universe Occur in Elliptical Galaxies2022In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 927, no 1, article id 10Article in journal (Refereed)
    Abstract [en]

    We present observations of three core-collapse supernovae (CCSNe) in elliptical hosts, detected by the Zwicky Transient Facility Bright Transient Survey (BTS). SN 2019ape is a SN Ic that exploded in the main body of a typical elliptical galaxy. Its properties are consistent with an explosion of a regular SN Ic progenitor. A secondary g-band light-curve peak could indicate interaction of the ejecta with circumstellar material (CSM). An Ha-emitting source at the explosion site suggests a residual local star formation origin. SN 2018fsh and SN 2020uik are SNe II which exploded in the outskirts of elliptical galaxies. SN 2020uik shows typical spectra for SNe II, while SN 2018fsh shows a boxy nebular Ha profile, a signature of CSM interaction. We combine these 3 SNe with 7 events from the literature and analyze their hosts as a sample. We present multi-wavelength photometry of the hosts, and compare this to archival photometry of all BTS hosts. Using the spectroscopically complete BTS, we conclude that 0.3%(+0.3)(-0.1) of all CCSNe occur in elliptical galaxies. We derive star formation rates and stellar masses for the host galaxies and compare them to the properties of other SN hosts. We show that CCSNe in ellipticals have larger physical separations from their hosts compared to SNe Ia in elliptical galaxies, and discuss implications for star-forming activity in elliptical galaxies.

  • 20. Irani, Ido
    et al.
    Chen, Ping
    Morag, Jonathan
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Gal-Yam, Avishay
    Strotjohann, Nora L.
    Yaron, Ofer
    Zimmerman, Erez A.
    Sharon, Amir
    Perley, Daniel A.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tohuvavohu, Aaron
    Das, Kaustav K.
    Kasliwal, Mansi M.
    Bruch, Rachel
    Brink, Thomas G.
    Zheng, Weikang
    Filippenko, Alexei V.
    Patra, Kishore C.
    Vasylyev, Sergiy S.
    Yang, Yi
    Graham, Matthew J.
    Bloom, Joshua S.
    Mazzali, Paolo
    Purdum, Josiah
    Laher, Russ R.
    Wold, Avery
    Sharma, Yashvi
    Lacroix, Leander
    Medford, Michael S.
    SN 2022oqm-A Ca-rich Explosion of a Compact Progenitor Embedded in C/O Circumstellar Material2024In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 962, no 2, article id 109Article in journal (Refereed)
    Abstract [en]

    We present the discovery and analysis of SN 2022oqm, a Type Ic supernova (SN) detected <1 day after the explosion. The SN rises to a blue and short-lived (2 days) initial peak. Early-time spectral observations of SN 2022oqm show a hot (40,000 K) continuum with high ionization C and O absorption features at velocities of 4000 km s−1, while its photospheric radius expands at 20,000 km s−1, indicating a pre-existing distribution of expanding C/O material. After ∼2.5 days, both the spectrum and light curves evolve into those of a typical SN Ic, with line velocities of ∼10,000 km s−1, in agreement with the evolution of the photospheric radius. The optical light curves reach a second peak at t ≈ 15 days. By t = 60 days, the spectrum of SN 2022oqm becomes nearly nebular, displaying strong Ca ii and [Ca ii] emission with no detectable [O i], marking this event as Ca-rich. The early behavior can be explained by 10−3M of optically thin circumstellar material (CSM) surrounding either (1) a massive compact progenitor such as a Wolf–Rayet star, (2) a massive stripped progenitor with an extended envelope, or (3) a binary system with a white dwarf. We propose that the early-time light curve is powered by both the interaction of the ejecta with the optically thin CSM and shock cooling (in the massive star scenario). The observations can be explained by CSM that is optically thick to X-ray photons, is optically thick in the lines as seen in the spectra, and is optically thin to visible-light continuum photons that come either from downscattered X-rays or from the shock-heated ejecta. Calculations show that this scenario is self-consistent.

  • 21. Kangas, T.
    et al.
    Yan, Lin
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Omand, Conor M. B.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Andreoni, I.
    Burruss, R.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Drake, A. J.
    Fremling, C.
    Gal-Yam, A.
    Graham, M. J.
    Groom, S. L.
    Lezmy, J.
    Mahabal, A. A.
    Masci, F. J.
    Perley, D.
    Riddle, R.
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). INAF - Osservatorio Astronomico di Padova, Italy.
    Yao, Y.
    The Zwicky Transient Facility phase I sample of hydrogen-rich superluminous supernovae without strong narrow emission lines2022In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 516, no 1, p. 1193-1218Article in journal (Refereed)
    Abstract [en]

    We present a sample of 14 hydrogen-rich superluminous supernovae (SLSNe II) from the Zwicky Transient Facility (ZTF) between 2018 and 2020. We include all classified SLSNe with peaks Mg < −20 mag with observed broad but not narrow Balmer emission, corresponding to roughly 20 per cent of all hydrogen-rich SLSNe in ZTF phase I. We examine the light curves and spectra of SLSNe II and attempt to constrain their power source using light-curve models. The brightest events are photometrically and spectroscopically similar to the prototypical SN 2008es, while others are found spectroscopically more reminiscent of non-superluminous SNe II, especially SNe II-L. 56Ni decay as the primary power source is ruled out. Light-curve models generally cannot distinguish between circumstellar interaction (CSI) and a magnetar central engine, but an excess of ultraviolet (UV) emission signifying CSI is seen in most of the SNe with UV data, at a wide range of photometric properties. Simultaneously, the broad H α profiles of the brightest SLSNe II can be explained through electron scattering in a symmetric circumstellar medium (CSM). In other SLSNe II without narrow lines, the CSM may be confined and wholly overrun by the ejecta. CSI, possibly involving mass lost in recent eruptions, is implied to be the dominant power source in most SLSNe II, and the diversity in properties is likely the result of different mass loss histories. Based on their radiated energy, an additional power source may be required for the brightest SLSNe II, however – possibly a central engine combined with CSI.

  • 22. Karambelkar, Viraj R.
    et al.
    Kasliwal, Mansi M.
    Maguire, Kate
    Anand, Shreya G.
    Andreoni, Igor
    De, Kishalay
    Drake, Andrew
    Duev, Dmitry A.
    Graham, Matthew J.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Laher, Russ R.
    Magee, Mark R.
    Mahabal, Ashish A.
    Medford, Michael S.
    Perley, Daniel
    Rigault, Mickael
    Rusholme, Ben
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sharma, Yashvi
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tzanidakis, Anastasios
    Walters, Richard
    Yao, Yuhan
    Faintest of Them All: ZTF 21aaoryiz/SN 2021fcg-Discovery of an Extremely Low Luminosity Type Iax Supernova2021In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 921, no 1, article id L6Article in journal (Refereed)
    Abstract [en]

    We present the discovery of ZTF 21aaoryiz/SN 2021fcg-an extremely low luminosity Type Tax supernova. SN 2021fcg was discovered by the Zwicky Transient Facility in the star-forming galaxy IC0512 at a distance of approximate to 27 Mpc. It reached a peak absolute magnitude of M-r = -12.66 +/- 0.20 mag, making it the least luminous thermonuclear supernova discovered to date. The E(B - V) contribution from the underlying host galaxy is unconstrained. However, even if it were as large as 0.5 mag, the peak absolute magnitude would be M-r = -13.78 +/- 0.20 mag-still consistent with being the lowest-luminosity SN. Optical spectra of SN 2021fcg taken at 37 and 65 days post-maximum show strong [Ca II], Ca II, and Na I D emission and several weak [Fe II] emission lines. The [Ca II] emission in the two spectra has extremely low velocities of approximate to 1300 and 1000 km s(-1), respectively. The spectra very closely resemble those of the very low luminosity Type Tax supernovae SN 2008 ha, SN 2010ae, and SN 2019gsc taken at similar phases. The peak bolometric luminosity of SN 2021fcg is approximate to 2.5(-0.3)(+1.5) x 10(40) erg s(-1), which is a factor of 3 lower than that for SN 2008 ha. The bolometric lightcurve of SN 2021fcg is consistent with a very low ejected nickel mass (M-Ni approximate to 0.8(-0.5)(+0.4) x 10(-3) M-circle dot). The low luminosity and nickel mass of SN 2021fcg pose a challenge to the picture that low-luminosity SNe Tax originate from deflagrations of near-M-ch hybrid carbon-oxygen-neon white dwarfs. Instead, the merger of a carbon-oxygen and oxygen-neon white dwarf is a promising model to explain SN 2021fcg.

  • 23.
    Karamehmetoglu, Emir
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Aarhus University, Denmark.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Aarhus University, Denmark.
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Feindt, Ulrich
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, C.
    Gal-Yam, A.
    Kasliwal, M. M.
    Petrushevska, T.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Stritzinger, M. D.
    Zapartas, E.
    A population of Type Ibc supernovae with massive progenitors Broad lightcurves not uncommon in (i)PTF2023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 678, article id A87Article in journal (Refereed)
    Abstract [en]

    If high-mass stars (≳20 − 25 M) are the progenitors of stripped-envelope (SE) supernovae (SNe), their massive ejecta should lead to broad, long-duration lightcurves. Instead, literature samples of SE SNe have reported relatively narrow lightcurves corresponding to ejecta masses between 1 − 4 M that favor intermediate-mass progenitors (≲20 − 25 M). Working with an untargeted sample from a single telescope to better constrain their rates, we searched the Palomar Transient Factory (PTF) and intermediate-PTF (iPTF) sample of SNe for SE SNe with broad lightcurves. Using a simple observational marker of g- or r-band lightcurve stretch compared to a template to measure broadness, we identified eight significantly broader Type Ibc SNe after applying quantitative sample selection criteria. The lightcurves, broad-band colors, and spectra of these SNe are found to evolve more slowly relative to typical Type Ibc SNe, proportional with the stretch parameter. Bolometric lightcurve modeling and their nebular spectra indicate high ejecta masses and nickel masses, assuming radioactive decay powering. Additionally, these objects are preferentially located in low-metallicity host galaxies with high star formation rates, which may account for their massive progenitors, as well as their relative absence from the literature. Our study thus supports the link between broad lightcurves (as measured by stretch) and high-mass progenitor stars in SE SNe with independent evidence from bolometric lightcurve modeling, nebular spectra, host environment properties, and photometric evolution. In the first systematic search of its kind using an untargeted sample, we used the stretch distribution to identify a higher than previously appreciated fraction of SE SNe with broad lightcurves (∼13%). Correcting for Malmquist and lightcurve duration observational biases, we conservatively estimate that a minimum of ∼6% of SE SNe are consistent with high-mass progenitors. This result has implications for the progenitor channels of SE SNe, including late stages of massive stellar evolution, the origin of the observed oxygen fraction in the universe, and formation channels for stellar-mass black holes.

  • 24.
    Kool, Erik C.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pearson Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Moldón, Javier
    Moriya, Takashi J.
    Mattila, Seppo
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Chomiuk, Laura
    Pérez-Torres, Miguel
    Harris, Chelsea
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Graham, Matthew
    Yang, Sheng
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Henan Academy of Sciences, China.
    Perley, Daniel A.
    Strotjohann, Nora Linn
    Fremling, Christoffer
    Gal-Yam, Avishay
    Lezmy, Jeremy
    Maguire, Kate
    Omand, Conor M. B.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Smith, Mathew
    Andreoni, Igor
    Bellm, Eric C.
    Bloom, Joshua S.
    De, Kishalay
    Groom, Steven L.
    Kasliwal, Mansi M.
    Masci, Frank J.
    Medford, Michael S.
    Park, Sungmin
    Purdum, Josiah
    Reynolds, Thomas M.
    Riddle, Reed
    Robert, Estelle
    Ryder, Stuart D.
    Sharma, Yashvi
    Stern, Daniel
    A radio-detected type Ia supernova with helium-rich circumstellar material2023In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 617, no 7961, p. 477-482Article in journal (Refereed)
    Abstract [en]

    Type Ia supernovae (SNe Ia) are thermonuclear explosions of degenerate white dwarf stars destabilized by mass accretion from a companion star1, but the nature of their progenitors remains poorly understood. A way to discriminate between progenitor systems is through radio observations; a non-degenerate companion star is expected to lose material through winds2 or binary interaction3 before explosion, and the supernova ejecta crashing into this nearby circumstellar material should result in radio synchrotron emission. However, despite extensive efforts, no type Ia supernova (SN Ia) has ever been detected at radio wavelengths, which suggests a clean environment and a companion star that is itself a degenerate white dwarf star4,5. Here we report on the study of SN 2020eyj, a SN Ia showing helium-rich circumstellar material, as demonstrated by its spectral features, infrared emission and, for the first time in a SN Ia to our knowledge, a radio counterpart. On the basis of our modelling, we conclude that the circumstellar material probably originates from a single-degenerate binary system in which a white dwarf accretes material from a helium donor star, an often proposed formation channel for SNe Ia (refs. 6,7). We describe how comprehensive radio follow-up of SN 2020eyj-like SNe Ia can improve the constraints on their progenitor systems.

  • 25. Levan, Andrew J.
    et al.
    Malesani, Daniele B.
    Gompertz, Benjamin P.
    Nugent, Anya E.
    Nicholl, Matt
    Oates, Samantha R.
    Perley, Daniel A.
    Rastinejad, Jillian
    Metzger, Brian D.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Stanway, Elizabeth R.
    Inkenhaag, Anne
    Zafar, Tayyaba
    Agüí Fernández, J. Feliciano
    Chrimes, Ashley A.
    Bhirombhakdi, Kornpob
    de Ugarte Postigo, Antonio
    Fong, Wen-fai
    Fruchter, Andrew S.
    Fragione, Giacomo
    Fynbo, Johan P. U.
    Gaspari, Nicola
    Heintz, Kasper E.
    Hjorth, Jens
    Jakobsson, Pall
    Jonker, Peter G.
    Lamb, Gavin P.
    Mandel, Ilya
    Mandhai, Soheb
    Ravasio, Maria E.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tanvir, Nial R.
    A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy2023In: Nature Astronomy, E-ISSN 2397-3366, Vol. 7, no 8, p. 976-985Article in journal (Refereed)
    Abstract [en]

    The majority of long-duration (>2 s) gamma-ray bursts (GRBs) arise from the collapse of massive stars, with a small proportion created from the merger of compact objects. Most of these systems form via standard stellar evolution pathways. However, a fraction of GRBs may result from dynamical interactions in dense environments. These channels could also contribute substantially to the samples of compact object mergers detected as gravitational wave sources. Here we report the case of GRB 191019A, a long GRB (a duration of T90 = 64.4 ± 4.5 s), which we pinpoint close (⪅100 pc projected) to the nucleus of an ancient (>1 Gyr old) host galaxy at z = 0.248. The lack of evidence for star formation and deep limits on any supernova emission disfavour a massive star origin. The most likely route for progenitor formation is via dynamical interactions in the dense nucleus of the host. The progenitor, in this case, could be a compact object merger. These may form in dense nuclear clusters or originate in a gaseous disc around the supermassive black hole. Identifying, to the best of our knowledge, a first example of a dynamically produced GRB demonstrates the role that such bursts may have in probing dense environments and constraining dynamical fractions in gravitational wave populations.

  • 26. Liu, Chang
    et al.
    Miller, Adam A.
    Boos, Samuel J.
    Shen, Ken J.
    Townsley, Dean M.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Harvey, Luke
    Maguire, Kate
    Pearson Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Brink, Thomas G.
    Burgaz, Umut
    Dimitriadis, Georgios
    Filippenko, Alexei V.
    Hall, Saarah
    Hinds, K-Ryan
    Hoffman, Andrew
    Karambelkar, Viraj
    Kilpatrick, Charles D.
    Perley, Daniel
    Pichay, Neil
    Sears, Huei
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stein, Robert
    Terwel, Jacco H.
    Zheng, Weikang
    Graham, Matthew J.
    Kasliwal, Mansi M.
    Lacroix, Leander
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics. Sorbonne Université, France.
    Purdum, Josiah
    Rusholme, Benjamin
    Wold, Avery
    SN 2022joj: A Peculiar Type Ia Supernova Possibly Driven by an Asymmetric Helium-shell Double Detonation2023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 958, no 2, article id 178Article in journal (Refereed)
    Abstract [en]

    We present observations of SN 2022joj, a peculiar Type Ia supernova discovered by the Zwicky Transient Facility. SN 2022joj exhibits an unusually red g ZTF - r ZTF color at early times and a rapid blueward evolution afterward. Around maximum brightness, SN 2022joj shows a high luminosity ( MgZTF,max similar or equal to-19.7 mag), a blue broadband color (g ZTF - r ZTF similar or equal to -0.2 mag), and shallow Si ii absorption lines, consistent with those of overluminous, SN 1991T-like events. The maximum-light spectrum also shows prominent absorption around 4200 angstrom, which resembles the Ti ii features in subluminous, SN 1991bg-like events. Despite the blue optical-band colors, SN 2022joj exhibits extremely red ultraviolet minus optical colors at maximum luminosity (u - v similar or equal to 0.6 mag and uvw1 - v similar or equal to 2.5 mag), suggesting a suppression of flux at similar to 2500-4000 angstrom. Strong C ii lines are also detected at peak. We show that these unusual spectroscopic properties are broadly consistent with the helium-shell double detonation of a sub-Chandrasekhar mass (M similar or equal to 1 M circle dot) carbon/oxygen white dwarf from a relatively massive helium shell (M s similar or equal to 0.04-0.1 M circle dot), if observed along a line of sight roughly opposite to where the shell initially detonates. None of the existing models could quantitatively explain all the peculiarities observed in SN 2022joj. The low flux ratio of [Ni ii] lambda 7378 to [Fe ii] lambda 7155 emission in the late-time nebular spectra indicates a low yield of stable Ni isotopes, favoring a sub-Chandrasekhar mass progenitor. The significant blueshift measured in the [Fe ii] lambda 7155 line is also consistent with an asymmetric chemical distribution in the ejecta, as is predicted in double-detonation models.

  • 27. Liu, Chang
    et al.
    Miller, Adam A.
    Polin, Abigail
    Nugent, Anya E.
    De, Kishalay
    Nugent, Peter E.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gal-Yam, Avishay
    Fremling, Christoffer
    Anand, Shreya
    Andreoni, Igor
    Blanchard, Peter
    Brink, Thomas G.
    Dhawan, Suhail
    Filippenko, Alexei V.
    Maguire, Kate
    Schweyer, Tassilo
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sears, Huei
    Sharma, Yashvi
    Graham, Matthew J.
    Groom, Steven L.
    Hale, David
    Kasliwal, Mansi M.
    Masci, Frank J.
    Purdum, Josiah
    Racine, Benjamin
    Sollerman, Jesper
    Kulkarni, Shrinivas R.
    SN 2020jgb: A Peculiar Type Ia Supernova Triggered by a Helium-shell Detonation in a Star-forming Galaxy2023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 946, no 2, article id 83Article in journal (Refereed)
    Abstract [en]

    The detonation of a thin (less than or similar to 0.03 M (circle dot)) helium shell (He-shell) atop a similar to 1 M (circle dot) white dwarf (WD) is a promising mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker He-shells and less massive WDs may explain some recently observed peculiar SNe Ia. We present observations of SN 2020jgb, a peculiar SN Ia discovered by the Zwicky Transient Facility (ZTF). Near maximum brightness, SN 2020jgb is slightly subluminous (ZTF g-band absolute magnitude -18.7 mag less than or similar to M ( g ) less than or similar to -18.2 mag depending on the amount of host-galaxy extinction) and shows an unusually red color (0.2 mag less than or similar to g (ZTF) - r (ZTF) less than or similar to 0.4 mag) due to strong line-blanketing blueward of similar to 5000 angstrom. These properties resemble those of SN 2018byg, a peculiar SN Ia consistent with an He-shell double detonation (DDet) SN. Using detailed radiative transfer models, we show that the optical spectroscopic and photometric evolution of SN 2020jgb is broadly consistent with a similar to 0.95-1.00 M (circle dot) (C/O core + He-shell) progenitor ignited by a greater than or similar to 0.1 M (circle dot) He-shell. However, one-dimensional radiative transfer models without non-local-thermodynamic-equilibrium treatment cannot accurately characterize the line-blanketing features, making the actual shell mass uncertain. We detect a prominent absorption feature at similar to 1 mu m in the near-infrared (NIR) spectrum of SN 2020jgb, which might originate from unburnt helium in the outermost ejecta. While the sample size is limited, we find similar 1 mu m features in all the peculiar He-shell DDet candidates with NIR spectra obtained to date. SN 2020jgb is also the first peculiar He-shell DDet SN discovered in a star-forming dwarf galaxy, indisputably showing that He-shell DDet SNe occur in both star-forming and passive galaxies, consistent with the normal SN Ia population.

  • 28.
    Lunnan, Ragnhild
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yan, Lin
    Perley, D. A.
    Schulze, S.
    Taggart, K.
    Gal-Yam, A.
    Fremling, C.
    Soumagnac, M. T.
    Ofek, E.
    Adams, S. M.
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bellm, E. C.
    De, K.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Frederick, S.
    Golkhou, V. Z.
    Graham, M. J.
    Hallakoun, N.
    Ho, A. Y. Q.
    Kasliwal, M. M.
    Kaspi, S.
    Kulkarni, S. R.
    Laher, R. R.
    Masci, F. J.
    Nunez, F. Pozo
    Rusholme, B.
    Quimby, R. M.
    Shupe, D. L.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    van Roestel, J.
    Yang, Y.
    Yao, Yuhan
    Four (Super)luminous Supernovae from the First Months of the ZTF Survey2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 901, no 1, article id 61Article in journal (Refereed)
    Abstract [en]

    We present photometry and spectroscopy of four hydrogen-poor luminous supernovae discovered during the 2-month long science commissioning and early operations of the Zwicky Transient Facility (ZTF) survey. Three of these objects, SN 2018bym (ZTF18aapgrxo), SN 2018avk (ZTF18aaisyyp), and SN 2018bgv (ZTF18aavrmcg), resemble typical SLSN-I spectroscopically, while SN 2018don (ZTF18aajqcue) may be an object similar to SN 2007bi experiencing considerable host galaxy reddening, or an intrinsically long-lived, luminous, and red SN Ic. We analyze the light curves, spectra, and host galaxy properties of these four objects and put them in context of the population of SLSN-I. SN 2018bgv stands out as the fastest-rising SLSN-I observed to date, with a rest-frame g-band rise time of just 10 days from explosion to peak—if it is powered by magnetar spin-down, the implied ejecta mass is only 1 M . SN 2018don also displays unusual properties—in addition to its red colors and comparatively massive host galaxy, the light curve undergoes some of the strongest light-curve undulations postpeak seen in an SLSN-I, which we speculate may be due to interaction with circumstellar material. We discuss the promises and challenges of finding SLSNe in large-scale surveys like ZTF given the observed diversity in the population.

  • 29. Maguire, Kate
    et al.
    Magee, Mark R.
    Leloudas, Giorgos
    Miller, Adam A.
    Dimitriadis, Georgios
    Pursiainen, Miika
    Bulla, Mattia
    De, Kishalay
    Gal-Yam, Avishay
    Perley, Daniel A.
    Fremling, Christoffer
    Karambelkar, Viraj R.
    Nordin, Jakob
    Reusch, Simeon
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Terreran, Giacomo
    Yang, Yi
    Bellm, Eric C.
    Groom, Steven L.
    Kasliwal, Mansi M.
    Kulkarni, Shrinivas R.
    Lacroix, Leander
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Masci, Frank J.
    Purdum, Josiah N.
    Sharma, Yashvi
    Smith, Roger
    SN 2020udy: an SN Iax with strict limits on interaction consistent with a helium-star companion2023In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 525, no 1, p. 1210-1228Article in journal (Refereed)
    Abstract [en]

    Early observations of transient explosions can provide vital clues to their progenitor origins. In this paper, we present the nearby Type Iax (02cx-like) supernova (SN), SN 2020udy, that was discovered within hours (∼7 h) of estimated first light. An extensive data set of ultra-violet, optical, and near-infrared observations was obtained, covering out to ∼150 d after explosion. SN 2020udy peaked at −17.86 ± 0.43 mag in the r band and evolved similarly to other ‘luminous’ SNe Iax, such as SNe 2005hk and 2012Z. Its well-sampled early light curve allows strict limits on companion interaction to be placed. Main-sequence companion stars with masses of 2 and 6 M are ruled out at all viewing angles, while a helium-star companion is allowed from a narrow range of angles (140–180° away from the companion). The spectra and light curves of SN 2020udy are in good agreement with those of the ‘N5def’ deflagration model of a near Chandrasekhar-mass carbon–oxygen white dwarf. However, as has been seen in previous studies of similar luminosity events, SN 2020udy evolves slower than the model. Broad-band linear polarization measurements taken at and after peak are consistent with no polarization, in agreement with the predictions of the companion-star configuration from the early light-curve measurements. The host galaxy environment is low metallicity and is consistent with a young stellar population. Overall, we find the most plausible explosion scenario to be the incomplete disruption of a CO white dwarf near the Chandrasekhar-mass limit, with a helium-star companion.

  • 30. Miller, A. A.
    et al.
    Magee, M. R.
    Polin, A.
    Maguire, K.
    Zimmerman, E.
    Yao, Y.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, S.
    Perley, D. A.
    Kromer, M.
    Dhawan, Suhail
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Andreoni, I
    Bellm, E. C.
    De, K.
    Dekany, R.
    Delacroix, A.
    Fremling, C.
    Gal-Yam, A.
    Goldstein, D. A.
    Golkhou, V. Z.
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Graham, M. J.
    Irani, I.
    Kasliwal, M. M.
    Kaye, S.
    Kim, Y-L
    Laher, R. R.
    Mahabal, A. A.
    Masci, F. J.
    Nugent, P. E.
    Ofek, E.
    Phinney, E. S.
    Prentice, S. J.
    Riddle, R.
    Rigault, M.
    Rusholme, B.
    Schweyer, Tassilo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Shupe, D. L.
    Soumagnac, M. T.
    Terreran, G.
    Walters, R.
    Yan, L.
    Zolkower, J.
    Kulkarni, S. R.
    The Spectacular Ultraviolet Flash from the Peculiar Type Ia Supernova 2019yvq2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 898, no 1, article id 56Article in journal (Refereed)
    Abstract [en]

    Early observations of Type Ia supernovae (SNe Ia) provide essential clues for understanding the progenitor system that gave rise to the terminal thermonuclear explosion. We present exquisite observations of SN 2019yvq, the second observed SN Ia, after iPTF 14atg, to display an early flash of emission in the ultraviolet (UV) and optical. Our analysis finds that SN 2019yvq was unusual, even when ignoring the initial flash, in that it was moderately underluminous for an SN Ia ( mag at peak) yet featured very high absorption velocities ( km s−1 for Si ii λ6355 at peak). We find that many of the observational features of SN 2019yvq, aside from the flash, can be explained if the explosive yield of radioactive 56Ni is relatively low (we measure ) and it and other iron-group elements are concentrated in the innermost layers of the ejecta. To explain both the UV/optical flash and peak properties of SN 2019yvq we consider four different models: interaction between the SN ejecta and a nondegenerate companion, extended clumps of 56Ni in the outer ejecta, a double-detonation explosion, and the violent merger of two white dwarfs. Each of these models has shortcomings when compared to the observations; it is clear additional tuning is required to better match SN 2019yvq. In closing, we predict that the nebular spectra of SN 2019yvq will feature either H or He emission, if the ejecta collided with a companion, strong [Ca ii] emission, if it was a double detonation, or narrow [O i] emission, if it was due to a violent merger.

  • 31. Parrag, Eleonora
    et al.
    Inserra, Cosimo
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Anderson, Joseph
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max-Planck-Institut fur Extraterrestrische Physik, Germany.
    Leloudas, Giorgios
    Galbany, Lluis
    Gutiérrez, Claudia P.
    Hiramatsu, Daichi
    Kankare, Erkki
    Müller-Bravo, Tomás E.
    Nicholl, Matt
    Pignata, Giuliano
    Cartier, Regis
    Gromadzki, Mariusz
    Kozyreva, Alexandra
    Rau, Arne
    Burke, Jamison
    Howell, D. Andrew
    McCully, Curtis
    Pellegrino, Craig
    SN 2019hcc: a Type II supernova displaying early Oɪɪ lines2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 506, no 4, p. 4819-4840Article in journal (Refereed)
    Abstract [en]

    We present optical spectroscopy together with ultraviolet, optical, and near-infrared photometry of SN 2019hcc, which resides in a host galaxy at redshift 0.044, displaying a sub-solar metallicity. The supernova spectrum near peak epoch shows a ‘w’ shape at around 4000 Å which is usually associated with O II lines and is typical of Type I superluminous supernovae. SN 2019hcc post-peak spectra show a well-developed H α P-Cygni profile from 19 d past maximum and its light curve, in terms of its absolute peak luminosity and evolution, resembles that of a fast-declining Hydrogen-rich supernova (SN IIL). The object does not show any unambiguous sign of interaction as there is no evidence of narrow lines in the spectra or undulations in the light curve. Our TARDIS spectral modelling of the first spectrum shows that carbon, nitrogen, and oxygen (CNO) at 19 000 K reproduce the ‘w’ shape and suggests that a combination of non-thermally excited CNO and metal lines at 8000 K could reproduce the feature seen at 4000 Å. The Bolometric light-curve modelling reveals that SN 2019hcc could be fit with a magnetar model, showing a relatively strong magnetic field (B > 3 × 1014 G), which matches the peak luminosity and rise time without powering up the light curve to superluminous luminosities. The high-energy photons produced by the magnetar would then be responsible for the detected Oɪɪ lines. As a consequence, SN 2019hcc shows that a ‘w’ shape profile at around 4000 Å, usually attributed to O II, is not only shown in superluminous supernovae and hence it should not be treated as the sole evidence of the belonging to such a supernova type. 

  • 32. Pasham, Dheeraj R.
    et al.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yang, Sheng
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    The Birth of a Relativistic Jet Following the Disruption of a Star by a Cosmological Black Hole2023In: Nature Astronomy, E-ISSN 2397-3366, Vol. 7, no 1, p. 88-104Article in journal (Refereed)
    Abstract [en]

    A black hole can launch a powerful relativistic jet after it tidally disrupts a star. If this jet fortuitously aligns with our line of sight, the overall brightness is Doppler boosted by several orders of magnitude. Consequently, such on-axis relativistic tidal disruption events have the potential to unveil cosmological (redshift z > 1) quiescent black holes and are ideal test beds for understanding the radiative mechanisms operating in super-Eddington jets. Here we present multiwavelength (X-ray, UV, optical and radio) observations of the optically discovered transient AT 2022cmc at z = 1.193. Its unusual X-ray properties, including a peak observed luminosity of ≳1048 erg s−1, systematic variability on timescales as short as 1,000 s and overall duration lasting more than 30 days in the rest frame, are traits associated with relativistic tidal disruption events. The X-ray to radio spectral energy distributions spanning 5–50 days after discovery can be explained as synchrotron emission from a relativistic jet (radio), synchrotron self-Compton (X-rays) and thermal emission similar to that seen in low-redshift tidal disruption events (UV/optical). Our modelling implies a beamed, highly relativistic jet akin to blazars but requires extreme matter domination (that is, a high ratio of electron-to-magnetic-field energy densities in the jet) and challenges our theoretical understanding of jets.

  • 33. Perley, Daniel A.
    et al.
    Ho, Anna Y. Q.
    Yao, Yuhan
    Fremling, Christoffer
    Anderson, Joseph P.
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kumar, Harsh
    Anupama, G. C.
    Barway, Sudhanshu
    Bellm, Eric C.
    Bhalerao, Varun
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Duev, Dmitry A.
    Galbany, Lluís
    Graham, Matthew J.
    Gromadzki, Mariusz
    Gutiérrez, Claudia P.
    Ihanec, Nada
    Inserra, Cosimo
    Kasliwal, Mansi M.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kulkarni, S. R.
    Laher, Russ R.
    Masci, Frank J.
    Neill, James D.
    Nicholl, Matt
    Pursiainen, Miika
    van Roestel, Joannes
    Sharma, Yashvi
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walters, Richard
    Wiseman, Philip
    Real-time discovery of AT2020xnd: a fast, luminous ultraviolet transient with minimal radioactive ejecta2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 508, no 4, p. 5138-5147Article in journal (Refereed)
    Abstract [en]

    The many unusual properties of the enigmatic AT2018cow suggested that at least some subset of the empirical class of fast blue optical transients (FBOTs) represents a genuinely new astrophysical phenomenon. Unfortunately, the intrinsic rarity and fleeting nature of these events have made it difficult to identify additional examples early enough to acquire the observations necessary to constrain theoretical models. We present here the Zwicky Transient Facility discovery of AT2020xnd (ZTF20acigmel, the 'Camel') at z = 0.243, the first unambiguous AT2018cow analogue to be found and confirmed in real time. AT2018cow and AT2020xnd share all key observational properties: a fast optical rise, sustained high photospheric temperature, absence of a second peak attributable to ejection of a radioactively heated stellar envelope, extremely luminous radio, millimetre, and X-ray emission, and a dwarf-galaxy host. This supports the argument that AT2018cow-like events represent a distinct phenomenon from slower-evolving radio-quiet supernovae, likely requiring a different progenitor or a different central engine. The sample properties of the four known members of this class to date disfavour tidal disruption models but are consistent with the alternative model of an accretion powered jet following the direct collapse of a massive star to a black hole. Contextual filtering of alert streams combined with rapid photometric verification using multiband imaging provides an efficient way to identify future members of this class, even at high redshift.

  • 34. Perley, Daniel A.
    et al.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Yao, Yuhan
    Fremling, Christoffer
    Gal-Yam, Avishay
    Ho, Anna Y. Q.
    Yang, Yi
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Irani, Ido
    Yan, Lin
    Andreoni, Igor
    Baade, Dietrich
    Bellm, Eric C.
    Brink, Thomas G.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cikota, Aleksandar
    Coughlin, Michael W.
    Dahiwale, Aishwarya
    Dekany, Richard
    Duev, Dmitry A.
    Filippenko, Alexei
    Hoeflich, Peter
    Kasliwal, Mansi M.
    Kulkarni, S. R.
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Masci, Frank J.
    Maund, Justyn R.
    Medford, Michael S.
    Riddle, Reed
    Rosnet, Philippe
    Shupe, David L.
    Strotjohann, Nora Linn
    Tzanidakis, Anastasios
    Zheng, WeiKang
    The Type Icn SN 2021csp: Implications for the Origins of the Fastest Supernovae and the Fates of Wolf-Rayet Stars2022In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 927, no 2, article id 180Article in journal (Refereed)
    Abstract [en]

    We present observations of SN 2021csp, the second example of a newly identified type of supernova (SN) hallmarked by strong, narrow, P Cygni carbon features at early times (Type Icn). The SN appears as a fast and luminous blue transient at early times, reaching a peak absolute magnitude of −20 within 3 days due to strong interaction between fast SN ejecta (v ≈ 30,000 km s−1) and a massive, dense, fast-moving C/O wind shed by the WC-like progenitor months before explosion. The narrow-line features disappear from the spectrum 10–20 days after explosion and are replaced by a blue continuum dominated by broad Fe features, reminiscent of Type Ibn and IIn supernovae and indicative of weaker interaction with more extended H/He-poor material. The transient then abruptly fades ∼60 days post-explosion when interaction ceases. Deep limits at later phases suggest minimal heavy-element nucleosynthesis, a low ejecta mass, or both, and imply an origin distinct from that of classical Type Ic SNe. We place SN 2021csp in context with other fast-evolving interacting transients, and discuss various progenitor scenarios: an ultrastripped progenitor star, a pulsational pair-instability eruption, or a jet-driven fallback SN from a Wolf–Rayet (W-R) star. The fallback scenario would naturally explain the similarity between these events and radio-loud fast transients, and suggests a picture in which most stars massive enough to undergo a W-R phase collapse directly to black holes at the end of their lives.

  • 35. Pessi, T.
    et al.
    Prieto, J. L.
    Anderson, J. P.
    Galbany, L.
    Lyman, J. D.
    Kochanek, C.
    Dong, S.
    Forster, F.
    González-Díaz, R.
    Gonzalez-Gaitan, S.
    Gutiérrez, C. P.
    Holoien, T. W. -S.
    James, P. A.
    Jiménez-Palau, C.
    Johnston, E. J.
    Kuncarayakti, H.
    Rosales-Ortega, F.
    Sánchez, S. F.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Shappee, B.
    A characterization of ASAS-SN core-collapse supernova environments with VLT+MUSE I. Sample selection, analysis of local environments, and correlations with light curve properties2023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 677, article id A28Article in journal (Refereed)
    Abstract [en]

    Context. The analysis of core-collapse supernova (CCSN) environments can provide important information on the life cycle of massive stars and constrain the progenitor properties of these powerful explosions. The MUSE instrument at the Very Large Telescope (VLT) enables detailed local environment constraints of the progenitors of large samples of CCSNe. Using a homogeneous SN sample from the All-Sky Automated Survey for Supernovae (ASAS-SN) survey, an untargeted and spectroscopically complete transient survey, has enabled us to perform a minimally biased statistical analysis of CCSN environments.

    Aims. We analyze 111 galaxies observed by MUSE that hosted 112 CCSNe – 78 II, nine IIn, seven IIb, four Ic, seven Ib, three Ibn, two Ic-BL, one ambiguous Ibc, and one superluminous SN – detected or discovered by the ASAS-SN survey between 2014 and 2018. The majority of the galaxies were observed by the All-weather MUse Supernova Integral field Nearby Galaxies (AMUSING) survey. Here we analyze the immediate environment around the SN locations and compare the properties between the different CCSN types and their light curves.

    Methods. We used stellar population synthesis and spectral fitting techniques to derive physical parameters for all H II regions detected within each galaxy, including the star formation rate (SFR), Hα equivalent width (EW), oxygen abundance, and extinction.

    Results. We found that stripped-envelope supernovae (SESNe) occur in environments with a higher median SFR, Hα EW, and oxygen abundances than SNe II and SNe IIn/Ibn. Most of the distributions have no statistically significant differences, except between oxygen abundance distributions of SESNe and SNe II, and between Hα EW distributions of SESNe and SNe II. The distributions of SNe II and IIn are very similar, indicating that these events explode in similar environments. For the SESNe, SNe Ic have higher median SFRs, Hα EWs, and oxygen abundances than SNe Ib. SNe IIb have environments with similar SFRs and Hα EWs to SNe Ib, and similar oxygen abundances to SNe Ic. We also show that the postmaximum decline rate, s, of SNe II correlates with the Hα EW, and that the luminosity and the Δm15 parameter of SESNe correlate with the oxygen abundance, Hα EW, and SFR at their environments. This suggests a connection between the explosion mechanisms of these events to their environment properties.

  • 36. Petrushevska, T.
    et al.
    Leloudas, G.
    Ilić, D.
    Bronikowski, M.
    Charalampopoulos, P.
    Jaisawal, G. K.
    Paraskeva, E.
    Pursiainen, M.
    Rakić, N.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Taggart, K.
    Wedderkopp, C. K.
    Anderson, J. P.
    de Boer, T.
    Chambers, K.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Damljanović, G.
    Fraser, M.
    Gao, H.
    Gomboc, A.
    Gromadzki, M.
    Ihanec, N.
    Maguire, K.
    Marčun, B.
    Müller-Bravo, T. E.
    Nicholl, M.
    Onori, F.
    Reynolds, T. M.
    Smartt, S. J.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Smith, K. W.
    Wevers, T.
    Wyrzykowski, Ł.
    The rise and fall of the iron-strong nuclear transient PS16dtm2023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 669, article id A140Article in journal (Refereed)
    Abstract [en]

    Context. Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centers of galaxies – nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN). Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN.

    Aims. Here, we study PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy, which has been proposed to be a TDE candidate. Our aim is to study the spectroscopic and photometric properties of PS16dtm, in order to better understand the outbursts originating in NLSy1 galaxies.

    Methods. Our extensive multiwavelength follow-up that spans around 2000 days includes photometry and spectroscopy in the UV/optical, as well as mid-infrared (MIR) and X-ray observations. Furthermore, we improved an existing semiempirical model in order to reproduce the spectra and study the evolution of the spectral lines.

    Results. The UV/optical light curve shows a double peak at ∼50 and ∼100 days after the first detection, and it declines and flattens afterward, reaching preoutburst levels after 2000 days of monitoring. The MIR light curve rises almost simultaneously with the optical, but unlike the UV/optical which is approaching the preoutburst levels in the last epochs of our observations, the MIR emission is still rising at the time of writing. The optical spectra show broad Balmer features and the strongest broad Fe II emission ever detected in a nuclear transient. This broad Fe II emission was not present in the archival preoutburst spectrum and almost completely disappeared +1868 days after the outburst. We found that the majority of the flux of the broad Balmer and Fe II lines is produced by photoionization. We detect only weak X-ray emission in the 0.5−8 keV band at the location of PS16dtm, at +848, +1130, and +1429 days past the outburst. This means that the X-ray emission continues to be lower by at least an order of magnitude, compared to archival, preoutburst measurements.

    Conclusions. We confirm that the observed properties of PS16dtm are difficult to reconcile with normal AGN variability. The TDE scenario continues to be a plausible explanation for the observed properties, even though PS16dtm shows differences compared to TDE in quiescent galaxies. We suggest that this event is part of a growing sample of TDEs that show broad Balmer line profiles and Fe II complexes. We argue that the extreme variability seen in the AGN host due to PS16dtm may have easily been misclassified as a CLAGN, especially if the rising part of the light curve had been missed. This implies that some changing look episodes in AGN may be triggered by TDEs. Imaging and spectroscopic data of AGN with good sampling are needed to enable testing of possible physical mechanisms behind the extreme variability in AGN.

  • 37. Prentice, S. J.
    et al.
    Ashall, C.
    James, P. A.
    Short, L.
    Mazzali, P. A.
    Bersier, D.
    Crowther, P. A.
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Chen, T. -W.
    Copperwheat, C. M.
    Darnley, M. J.
    Denneau, L.
    Elias-Rosa, N.
    Fraser, M.
    Galbany, L.
    Gal-Yam, A.
    Harmanen, J.
    Howell, D. A.
    Hosseinzadeh, G.
    Inserra, C.
    Kankare, E.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lamb, G. P.
    Limongi, M.
    Maguire, K.
    McCully, C.
    Olivares E., F.
    Piascik, A. S.
    Pignata, G.
    Reichart, D. E.
    Rest, A.
    Reynolds, T.
    Rodríguez, Ó.
    Saario, J. L. O.
    Schulze, S.
    Smartt, S. J.
    Smith, K. W.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stalder, B.
    Sullivan, M.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Valenti, S.
    Vergani, S. D.
    Williams, S. C.
    Young, D. R.
    Investigating the properties of stripped-envelope supernovae; what are the implications for their progenitors?2019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 485, no 2, p. 1559-1578Article in journal (Refereed)
    Abstract [en]

    We present observations and analysis of 18 stripped-envelope supernovae observed during 2013-2018. This sample consists of five H/He-rich SNe, sixH-poor/He-rich SNe, three narrow lined SNe Ic, and four broad lined SNe Ic. The peak luminosity and characteristic time-scales of the bolometric light curves are calculated, and the light curves modelled to derive Ni-56 and ejecta masses (M-Ni and M-cj). Additionally, the temperature evolution and spectral line velocity curves of each SN are examined. Analysis of the [O I] line in the nebular phase of eight SNe suggests their progenitors had initial masses < 20 M-circle dot. The bolometric light curve properties are examined in combination with those of other SE events from the literature. The resulting data set gives the M-ej distribution for 80 SE-SNe, the largest such sample in the literature to date, and shows that SNe Ib have the lowest median M-ej, followed by narrow-lined SNe Ic, H/He-rich SNe, broad-lined SNe Ic, and finally gamma-ray burst SNe. SNe Ic-6/7 show the largest spread of M-ej ranging from similar to 1.2-11 M-circle dot, considerably greater than any other subtype. For all SE-SNe <M-ej> = 2.8 +/- 1.5 M-circle dot which further strengthens the evidence that SE-SNe arise from low-mass progenitors which are typically <5 M-circle dot at the time of explosion, again suggesting M-ZAMS < 25 M-circle dot. The low <M-ej> and lack of clear bimodality in the distribution implies < 30 M-circle dot progenitors and that envelope stripping via binary interaction is the dominant evolutionary pathway of these SNe.

  • 38. Prentice, S. J.
    et al.
    Inserra, C.
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Nicholl, M.
    Mazzali, P. A.
    Vergani, S. D.
    Galbany, L.
    Anderson, J. P.
    Ashall, C.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Deckers, M.
    Mancheño, M. Delgado
    Díaz, R. González
    González-Gaitán, S.
    Gromadzki, M.
    Gutiérrez, C. P.
    Harvey, L.
    Kozyreva, A.
    Magee, M. R.
    Maguire, K.
    Müller-Bravo, T. E.
    Muñoz Torres, S.
    Pessi, P. J.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Teffs, J.
    Terwel, J. H.
    Young, D. R.
    Transitional events in the spectrophotometric regime between stripped envelope and superluminous supernovae2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 508, no 3, p. 4342-4358Article in journal (Refereed)
    Abstract [en]

    The division between stripped-envelope supernovae (SE-SNe) and superluminous supernovae (SLSNe) is not well-defined in either photometric or spectroscopic space. While a sharp luminosity threshold has been suggested, there remains an increasing number of transitional objects that reach this threshold without the spectroscopic signatures common to SLSNe. In this work, we present data and analysis on four SNe transitional between SE-SNe and SLSNe; the He-poor SNe 2019dwa and 2019cri, and the He-rich SNe 2019hge and 2019unb. Each object displays long-lived and variable photometric evolution with luminosities around the SLSN threshold of Mr < −19.8 mag. Spectroscopically however, these objects are similar to SE-SNe, with line velocities lower than either SE-SNe and SLSNe, and thus represent an interesting case of rare transitional events.

  • 39. Pursiainen, M.
    et al.
    Leloudas, G.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Charalampopoulos, P.
    Angus, C. R.
    Anderson, J. P.
    Bauer, F.
    Chen, T.-W.
    Galbany, L.
    Gromadzki, M.
    Gutiérrez, C. P.
    Inserra, C.
    Lyman, J.
    Müller-Bravo, T. E.
    Nicholl, M.
    Smartt, S. J.
    Tartaglia, L.
    Wiseman, P.
    Young, D. R.
    SN 2023emq: A Flash-ionized Ibn Supernova with Possible C iii Emission2023In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 959, no 1, article id L10Article in journal (Refereed)
    Abstract [en]

    SN 2023emq is a fast-evolving transient initially classified as a rare Type Icn supernova (SN), interacting with a H- and He-free circumstellar medium (CSM) around maximum light. Subsequent spectroscopy revealed the unambiguous emergence of narrow He lines, confidently placing SN 2023emq in the more common Type Ibn class. Photometrically, SN 2023emq has several uncommon properties regardless of its class, including its extreme initial decay (faster than >90% of Type Ibn/Icn SNe) and sharp transition in the decline rate from 0.20 to 0.07 mag day−1 at +20 days. The bolometric light curve can be modeled as CSM interaction with 0.32M of ejecta and 0.12M of CSM, with 0.006M of nickel, as expected of fast, interacting SNe. Furthermore, broadband polarimetry at +8.7 days (P = 0.55% ± 0.30%) is consistent with spherical symmetry. A discovery of a transitional Type Icn/Ibn SN would be unprecedented and would give valuable insights into the nature of mass loss suffered by the progenitor just before death, but we favor an interpretation that SN 2023emq is a Type Ibn SN that exhibited flash-ionized features in the earliest spectrum, as the features are not an exact match with other Type Icn SNe to date. However, the feature at 5700 Å, in the region of C iii and N ii emission, is significantly stronger in SN 2023emq than in the few other flash-ionized Type Ibn SNe, and if it is related to C iii, it possibly implies a continuum of properties between the two classes.

  • 40. Reusch, Simeon
    et al.
    Stein, Robert
    Kowalski, Marek
    van Velzen, Sjoert
    Franckowiak, Anna
    Lunardini, Cecilia
    Murase, Kohta
    Winter, Walter
    Miller-Jones, James C. A.
    Kasliwal, Mansi M.
    Gilfanov, Marat
    Garrappa, Simone
    Paliya, Vaidehi S.
    Ahumada, Tomás
    Anand, Shreya
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bellm, Eric C.
    Brinnel, Valéry
    Buson, Sara
    Cenko, S. Bradley
    Coughlin, Michael W.
    De, Kishalay
    Dekany, Richard
    Frederick, Sara
    Gal-Yam, Avishay
    Gezari, Suvi
    Giroletti, Marcello
    Graham, Matthew J.
    Karambelkar, Viraj
    Kimura, Shigeo S.
    Kong, Albert K. H.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Laher, Russ R.
    Medvedev, Pavel
    Necker, Jannis
    Nordin, Jakob
    Perley, Daniel A.
    Rigault, Mickael
    Rusholme, Ben
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Schweyer, Tassilo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Singer, Leo P.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Strotjohann, Nora Linn
    Sunyaev, Rashid
    van Santen, Jakob
    Walters, Richard
    Zhang, B. Theodore
    Zimmerman, Erez
    Candidate Tidal Disruption Event AT2019fdr Coincident with a High-Energy Neutrino2022In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 128, no 22, article id 221101Article in journal (Refereed)
    Abstract [en]

    The origins of the high-energy cosmic neutrino flux remain largely unknown. Recently, one high-energy neutrino was associated with a tidal disruption event (TDE). Here we present AT2019fdr, an exceptionally luminous TDE candidate, coincident with another high-energy neutrino. Our observations, including a bright dust echo and soft late-time x-ray emission, further support a TDE origin of this flare. The probability of finding two such bright events by chance is just 0.034%. We evaluate several models for neutrino production and show that AT2019fdr is capable of producing the observed high-energy neutrino, reinforcing the case for TDEs as neutrino sources.

  • 41. Rossi, A.
    et al.
    Frederiks, D. D.
    Kann, D. A.
    De Pasquale, M.
    Pian, E.
    Lamb, G.
    D'Avanzo, P.
    Izzo, L.
    Levan, A. J.
    Malesani, D. B.
    Melandri, A.
    Nicuesa Guelbenzu, A.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Strausbaugh, R.
    Tanvir, N. R.
    Amati, L.
    Campana, S.
    Cucchiara, A.
    Ghirlanda, G.
    Della Valle, M.
    Klose, S.
    Salvaterra, R.
    Starling, R. L. C.
    Stratta, G.
    Tsvetkova, A. E.
    Vergani, S. D.
    D'Ai, A.
    Burgarella, D.
    Covino, S.
    D'Elia, V.
    de Ugarte Postigo, A.
    Fausey, H.
    Fynbo, J. P. U.
    Frontera, F.
    Guidorzi, C.
    Heintz, K. E.
    Masetti, N.
    Maiorano, F.
    Mundell, C. G.
    Oates, S. R.
    Page, M. J.
    Palazzi, E.
    Palmerio, J.
    Pugliese, G.
    Rau, A.
    Saccardi, A.
    Sbarufatti, B.
    Svinkin, D. S.
    Tagliaferri, G.
    van der Horst, A. J.
    Watson, D. J.
    Ulanov, M.
    Wiersema, K.
    Xu, D.
    Zhang, J.
    A blast from the infant Universe: The very high-z GRB210905A2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 665, article id A125Article in journal (Refereed)
    Abstract [en]

    We present a detailed follow-up of the very energetic GRB 210905A at a high redshift of z = 6.312 and its luminous X-ray and optical afterglow. Following the detection by Swift and Konus-Wind, we obtained a photometric and spectroscopic follow-up in the optical and near-infrared (NIR), covering both the prompt and afterglow emission from a few minutes up to 20 Ms after burst. With an isotropic gamma-ray energy release of Eiso = 1.27−0.19+0.20 × 1054 erg, GRB 210905A lies in the top ∼7% of gamma-ray bursts (GRBs) in the Konus-Wind catalogue in terms of energy released. Its afterglow is among the most luminous ever observed, and, in particular, it is one of the most luminous in the optical at t ≳ 0.5 d in the rest frame. The afterglow starts with a shallow evolution that can be explained by energy injection, and it is followed by a steeper decay, while the spectral energy distribution is in agreement with slow cooling in a constant-density environment within the standard fireball theory. A jet break at ∼46.2 ± 16.3 d (6.3 ± 2.2 d rest-frame) has been observed in the X-ray light curve; however, it is hidden in the H band due to a constant contribution from the host galaxy and potentially from a foreground intervening galaxy. In particular, the host galaxy is only the fourth GRB host at z > 6 known to date. By assuming a number density n = 1 cm−3 and an efficiency η = 0.2, we derived a half-opening angle of 8.4 ° ±1.0°, which is the highest ever measured for a z ≳ 6 burst, but within the range covered by closer events. The resulting collimation-corrected gamma-ray energy release of ≃1 × 1052 erg is also among the highest ever measured. The moderately large half-opening angle argues against recent claims of an inverse dependence of the half-opening angle on the redshift. The total jet energy is likely too large to be sustained by a standard magnetar, and it suggests that the central engine of this burst was a newly formed black hole. Despite the outstanding energetics and luminosity of both GRB 210905A and its afterglow, we demonstrate that they are consistent within 2σ with those of less distant bursts, indicating that the powering mechanisms and progenitors do not evolve significantly with redshift.

  • 42. Rossi, A.
    et al.
    Rothberg, B.
    Palazzi, E.
    Kann, D. A.
    D'Avanzo, P.
    Amati, L.
    Klose, S.
    Perego, A.
    Pian, E.
    Guidorzi, C.
    Pozanenko, A. S.
    Savaglio, S.
    Stratta, G.
    Agapito, G.
    Covino, S.
    Cusano, F.
    D'Elia, V.
    De Pasquale, M.
    Della Valle, M.
    Kuhn, O.
    Izzo, L.
    Loffredo, E.
    Masetti, N.
    Melandri, A.
    Minaev, P. Y.
    Nicuesa Guelbenzu, A.
    Paris, D.
    Paiano, S.
    Plantet, C.
    Rossi, F.
    Salvaterra, R.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Veillet, C.
    Volnova, A. A.
    The Peculiar Short-duration GRB 200826A and Its Supernova2022In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 932, no 1, article id 1Article in journal (Refereed)
    Abstract [en]

    Gamma-ray bursts (GRBs) are classified into long and short events. Long GRBs (LGRBs) are associated with the end states of very massive stars, while short GRBs (SGRBs) are linked to the merger of compact objects. GRB 200826A was a peculiar event, because by definition it was an SGRB, with a rest-frame duration of similar to 0.5 s. However, this event was energetic and soft, which is consistent with LGRBs. The relatively low redshift (z = 0.7486) motivated a comprehensive, multiwavelength follow-up campaign to characterize its host, search for a possible associated supernova (SN), and thus understand the origin of this burst. To this aim we obtained a combination of deep near-infrared (NIR) and optical imaging together with spectroscopy. Our analysis reveals an optical and NIR bump in the light curve whose luminosity and evolution are in agreement with several SNe associated to LGRBs. Analysis of the prompt GRB shows that this event follows the E-p,E-i-E-iso relation found for LGRBs. The host galaxy is a low-mass star-forming galaxy, typical of LGRBs, but with one of the highest star formation rates, especially with respect to its mass (log M-*/M-circle dot = 8.6, SFR similar to 4.0 M-circle dot yr(-1)). We conclude that GRB 200826A is a typical collapsar event in the low tail of the duration distribution of LGRBs. These findings support theoretical predictions that events produced by collapsars can be as short as 0.5 s in the host frame and further confirm that duration alone is not an efficient discriminator for the progenitor class of a GRB.

  • 43.
    Sagués Carracedo, Ana
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A very luminous jet from the disruption of a star by a massive black hole2022In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 612, no 7940, p. 430-434Article in journal (Refereed)
    Abstract [en]

    Tidal disruption events (TDEs) are bursts of electromagnetic energy that are released when supermassive black holes at the centres of galaxies violently disrupt a star that passes too close1. TDEs provide a window through which to study accretion onto supermassive black holes; in some rare cases, this accretion leads to launching of a relativistic jet2,3,4,5,6,7,8,9, but the necessary conditions are not fully understood. The best-studied jetted TDE so far is Swift J1644+57, which was discovered in γ-rays, but was too obscured by dust to be seen at optical wavelengths. Here we report the optical detection of AT2022cmc, a rapidly fading source at cosmological distance (redshift z = 1.19325) the unique light curve of which transitioned into a luminous plateau within days. Observations of a bright counterpart at other wavelengths, including X-ray, submillimetre and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron ‘afterglow’, probably launched by a supermassive black hole with spin greater than approximately 0.3. Using four years of Zwicky Transient Facility10 survey data, we calculate a rate of 0.02+0.04−0.01 Gpc−3 yr−1 for on-axis jetted TDEs on the basis of the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X-ray and radio observations11. Correcting for the beaming angle effects, this rate confirms that approximately 1 per cent of TDEs have relativistic jets. Optical surveys can use AT2022cmc as a prototype to unveil a population of jetted TDEs.

  • 44.
    Sarin, Nikhil
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Heavy-element production in a compact object merger observed by JWST2024In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 626, p. 737-741Article in journal (Refereed)
    Abstract [en]

    The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs)1, sources of high-frequency gravitational waves (GWs)2 and likely production sites for heavy-element nucleosynthesis by means of rapid neutron capture (the r-process)3. Here we present observations of the exceptionally bright GRB 230307A. We show that GRB 230307A belongs to the class of long-duration GRBs associated with compact object mergers4,5,6 and contains a kilonova similar to AT2017gfo, associated with the GW merger GW170817 (refs. 7,8,9,10,11,12). We obtained James Webb Space Telescope (JWST) mid-infrared imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns, which we interpret as tellurium (atomic mass A = 130) and a very red source, emitting most of its light in the mid-infrared owing to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create r-process elements across a broad atomic mass range and play a central role in heavy-element nucleosynthesis across the Universe.

  • 45. Schady, P.
    et al.
    Yates, R. M.
    Christensen, L.
    De Cia, A.
    Rossi, A.
    D'Elia, V
    Heintz, K. E.
    Jakobsson, P.
    Laskar, T.
    Levan, A.
    Salvaterra, R.
    Starling, R. L. C.
    Tanvir, N. R.
    Thöne, C. C.
    Vergani, S.
    Wiersema, K.
    Arabsalmani, M.
    Chen, H. -W
    De Pasquale, M.
    Fruchter, A.
    Fynbo, J. P. U.
    García-Benito, R.
    Gompertz, B.
    Hartmann, D.
    Kouveliotou, C.
    Milvang-Jensen, B.
    Palazzi, E.
    Perley, D. A.
    Piranomonte, S.
    Pugliese, G.
    Savaglio, S.
    Sbarufatti, B.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Tagliaferri, G.
    Postigo, A. de Ugarte
    Watson, D.
    Wiseman, P.
    Comparing emission- and absorption-based gas-phase metallicities in GRB host galaxies at z =2-4 using JWST2024In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 529, no 3, p. 2807-2831Article in journal (Refereed)
    Abstract [en]

    Much of what is known of the chemical composition of the universe is based on emission line spectra from star-forming galaxies. Emission-based inferences are, nevertheless, model-dependent and they are dominated by light from luminous star-forming regions. An alternative and sensitive probe of the metallicity of galaxies is through absorption lines imprinted on the luminous afterglow spectra of long gamma ray bursts (GRBs) from neutral material within their host galaxy. We present results from a JWST/NIRSpec programme to investigate for the first time the relation between the metallicity of neutral gas probed in absorption by GRB afterglows and the metallicity of the star-forming regions for the same host galaxy sample. Using an initial sample of eight GRB host galaxies at z = 2.1–4.7, we find a tight relation between absorption and emission line metallicities when using the recently proposed 𝑅^ metallicity diagnostic (±0.2 dex). This agreement implies a relatively chemically homogeneous multiphase interstellar medium and indicates that absorption and emission line probes can be directly compared. However, the relation is less clear when using other diagnostics, such as R23 and R3. We also find possible evidence of an elevated N/O ratio in the host galaxy of GRB 090323 at z = 4.7, consistent with what has been seen in other z > 4 galaxies. Ultimate confirmation of an enhanced N/O ratio and of the relation between absorption and emission line metallicities will require a more direct determination of the emission line metallicity via the detection of temperature-sensitive auroral lines in our GRB host galaxy sample.

  • 46. Schulze, Steve
    et al.
    Yaron, Ofer
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Leloudas, Giorgos
    Gal, Amit
    Wright, Angus H.
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gal-Yam, Avishay
    Ofek, Eran O.
    Perley, Daniel A.
    Filippenko, Alexei
    Kasliwal, Mansi M.
    Kulkarni, Shrinivas R.
    Neill, James D.
    Nugent, Peter E.
    Quimby, Robert M.
    Sullivan, Mark
    Strotjohann, Nora Linn
    Arcavi, Iair
    Ben-Ami, Sagi
    Bianco, Federica
    Bloom, Joshua S.
    De, Kishalay
    Fraser, Morgan
    Fremling, Christoffer U.
    Horesh, Assaf
    Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kelly, Patrick L.
    Knezevic, Nikola
    Knezevic, Sladjana
    Maguire, Kate
    Nyholm, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Papadogiannakis, Seméli
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Petrushevska, Tanja
    Rubin, Adam
    Yan, Lin
    Yang, Yi
    Adams, Scott M.
    Bufano, Filomena
    Clubb, Kelsey
    Foley, Ryan J.
    Green, Yoav
    Harmanen, Jussi
    Ho, Anna Y. Q.
    Hook, Isobel M.
    Hosseinzadeh, Griffin
    Howell, D. Andrew
    Kong, Albert K. H.
    Kotak, Rubina
    Matheson, Thomas
    McCully, Curtis
    Milisavljevic, Dan
    Pan, Yen-Chen
    Poznanski, Dovi
    Shivvers, Isaac
    van Velzen, Sjoert
    Verbeek, Kars K.
    The Palomar Transient Factory Core-collapse Supernova Host-galaxy Sample. I. Host-galaxy Distribution Functions and Environment Dependence of Core-collapse Supernovae2021In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 255, no 2, article id 29Article in journal (Refereed)
    Abstract [en]

    Several thousand core-collapse supernovae (CCSNe) of different flavors have been discovered so far. However, identifying their progenitors has remained an outstanding open question in astrophysics. Studies of SN host galaxies have proven to be powerful in providing constraints on the progenitor populations. In this paper, we present all CCSNe detected between 2009 and 2017 by the Palomar Transient Factory. This sample includes 888 SNe of 12 distinct classes out to redshift z approximate to 1. We present the photometric properties of their host galaxies from the far-ultraviolet to the mid-infrared and model the host-galaxy spectral energy distributions to derive physical properties. The galaxy mass function of Type Ic, Ib, IIb, II, and IIn SNe ranges from 10(5) to 10(11.5) M (circle dot), probing the entire mass range of star-forming galaxies down to the least-massive star-forming galaxies known. Moreover, the galaxy mass distributions are consistent with models of star-formation-weighted mass functions. Regular CCSNe are hence direct tracers of star formation. Small but notable differences exist between some of the SN classes. Type Ib/c SNe prefer galaxies with slightly higher masses (i.e., higher metallicities) and star formation rates than Type IIb and II SNe. These differences are less pronounced than previously thought. H-poor superluminous supernovae (SLSNe) and SNe Ic-BL are scarce in galaxies above 10(10) M (circle dot). Their progenitors require environments with metallicities of < 0.4 and < 1 solar, respectively. In addition, the hosts of H-poor SLSNe are dominated by a younger stellar population than all other classes of CCSNe. Our findings corroborate the notion that low metallicity and young age play an important role in the formation of SLSN progenitors.

  • 47. Sfaradi, Itai
    et al.
    Horesh, Assaf
    Fender, Rob
    Green, David A.
    Williams, David R. A.
    Bright, Joe
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    A Late-time Radio Flare Following a Possible Transition in Accretion State in the Tidal Disruption Event AT 2019azh2022In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 933, no 2, article id 176Article in journal (Refereed)
    Abstract [en]

    We report here radio follow-up observations of the optical tidal disruption event (TDE) AT 2019azh. Previously reported X-ray observations of this TDE showed variability at early times and a dramatic increase in luminosity, by a factor of ∼10, about 8 months after optical discovery. The X-ray emission is mainly dominated by intermediate hard-soft X-rays and is exceptionally soft around the X-ray peak, which is LX ∼ 1043 erg s−1. The high cadence 15.5 GHz observations reported here show an early rise in radio emission followed by an approximately constant light curve, and a late-time flare. This flare starts roughly at the time of the observed X-ray peak luminosity and reaches its peak about 110 days after the peak in the X-ray, and a year after optical discovery. The radio flare peaks at νLν ∼ 1038 erg s−1, a factor of two higher than the emission preceding the flare. In light of the late-time radio and X-ray flares, and the X-ray spectral evolution, we speculate a possible transition in the accretion state of this TDE, similar to the observed behavior in black hole X-ray binaries. We compare the radio properties of AT 2019azh to other known TDEs, and focus on the similarities to the late-time radio flare of the TDE ASASSN-15oi.

  • 48. Sharma, Yashvi
    et al.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, Christoffer
    Kulkarni, Shrinivas R.
    De Kishalay, Kishalay
    Irani, Ido
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Strotjohann, Nora Linn
    Gal-Yam, Avishay
    Maguire, Kate
    Perley, Daniel A.
    Bellm, Eric C.
    Kool, Erik C.
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Brink, Thomas G.
    Bruch, Rachel
    Deckers, Maxime
    Dekany, Richard
    Dugas, Alison
    Filippenko, Alexei V.
    Goldwasser, Samantha
    Graham, Matthew J.
    Graham, Melissa L.
    Groom, Steven L.
    Hankins, Matt
    Jencson, Jacob
    Pearson Johansson, Joel
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Karambelkar, Viraj
    Kasliwal, Mansi M.
    Masci, Frank J.
    Medford, Michael S.
    Neill, James D.
    Nir, Guy
    Riddle, Reed L.
    Rigault, Mickael
    Schweyer, Tassilo
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Terwel, Jacco H.
    Yan, Lin
    Yang, Yi
    Yao, Yuhan
    A Systematic Study of Ia-CSM Supernovae from the ZTF Bright Transient Survey2023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 948, no 1, article id 52Article in journal (Refereed)
    Abstract [en]

    Among the supernovae (SNe) that show strong interaction with a circumstellar medium (CSM), there is a rare subclass of Type Ia supernovae, SNe Ia-CSM, which show strong narrow hydrogen emission lines much like SNe IIn but on top of a diluted Type Ia spectrum. The only previous systematic study of this class identified 16 SNe Ia-CSM, eight historic and eight from the Palomar Transient Factory (PTF). Now using the successor survey to PTF, the Zwicky Transient Facility (ZTF), we have classified 12 additional SNe Ia-CSM through the systematic Bright Transient Survey (BTS). Consistent with previous studies, we find these SNe to have slowly evolving optical light curves with peak absolute magnitudes between -19.1 and -21, spectra having weak H ss and large Balmer ldecrements of similar to 7. Out of the 10 SNe from our sample observed by NEOWISE, nine have 3 sigma detections, with some SNe showing a reduction in the red wing of Ha, indicative of newly formed dust. We do not find our SN Ia-CSM sample to have a significantly different distribution of equivalent widths of He I.5876 than SNe IIn as observed in Silverman et al. The hosts tend to be late-type galaxies with recent star formation. We derive a rate estimate of 29+(27)(21) Gpc(-3) yr(-1) for SNe Ia-CSM, which is similar to 0.02%-0.2% of the SN Ia rate. We also identify six ambiguous SNe IIn/Ia-CSM in the BTS sample and including them gives an upper limit rate of 0.07%-0.8%. This work nearly doubles the sample of well-studied Ia-CSM objects in Silverman et al., increasing the total number to 28.

  • 49. Short, P.
    et al.
    Lawrence, A.
    Nicholl, M.
    Ward, M.
    Reynolds, T. M.
    Mattila, S.
    Yin, C.
    Arcavi, I
    Carnall, A.
    Charalampopoulos, P.
    Gromadzki, M.
    Jonker, P. G.
    Kim, S.
    Leloudas, G.
    Mandel, I
    Onori, F.
    Pursiainen, M.
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Villforth, C.
    Wevers, T.
    Delayed appearance and evolution of coronal lines in the TDE AT2019qiz2023In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 525, no 1, p. 1568-1587Article in journal (Refereed)
    Abstract [en]

    Tidal disruption events (TDEs) occur when a star gets torn apart by a supermassive black hole as it crosses its tidal radius. We present late-time optical and X-ray observations of the nuclear transient AT2019qiz, which showed the typical signs of an optical-UV transient class commonly believed to be TDEs. Optical spectra were obtained 428, 481, and 828 rest-frame days after optical light-curve peak, and a UV/X-ray observation coincided with the later spectrum. The optical spectra show strong coronal emission lines, including [Fe VII], [Fe X], [Fe XI], and [Fe XIV]. The Fe lines rise and then fall, except [Fe XIV] that appears late and rises. We observe increasing flux of narrow H α and H β and a decrease in broad H α flux. The coronal lines have full width at half-maximum ranging from ∼150−300 km s−1, suggesting they originate from a region between the broad- and narrow-line emitting gas. Between the optical flare and late-time observation, the X-ray spectrum softens dramatically. The 0.3–1 keV X-ray flux increases by a factor of ∼50, while the hard X-ray flux decreases by a factor of ∼6. Wide-field Infrared Survey Explorer fluxes also rose over the same period, indicating the presence of an infrared echo. With AT2017gge, AT2019qiz is one of two examples of a spectroscopically confirmed optical-UV TDE showing delayed coronal line emission, supporting speculations that Extreme Coronal Line Emitters in quiescent galaxies can be echos of unobserved past TDEs. We argue that the coronal lines, narrow lines, and infrared emission arise from the illumination of pre-existing material likely related to either a previous TDE or active galactic nucleus activity.

  • 50.
    Sollerman, Jesper
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yang, Sheng
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Perley, D.
    Schulze, Steve
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, C.
    Kasliwal, M.
    Shin, K.
    Racine, B.
    Maximum luminosities of normal stripped-envelope supernovae are brighter than explosion models allow2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 657, article id A64Article in journal (Refereed)
    Abstract [en]

    Context. Stripped-envelope supernovae (SE SNe) of Type Ib and Type Ic are thought to be the result of explosions of massive stars that have lost their outer envelopes. The favored explosion mechanism is via core-collapse, with the shock later revived by neutrino heating. However, there is an upper limit to the amount of radioactive Ni-56 that such models can accommodate. Recent studies in the literature point to a tension between the maximum luminosity from such simulations and the observations.

    Aims. We used a well-characterized sample of SE SNe from the Zwicky Transient Facility (ZTF) Bright Transient Survey (BTS) to scrutinize the observational caveats regarding estimates of the maximum luminosity (and thus the amount of ejected radioactive nickel) for the sample members.

    Methods. We employed the strict selection criteria for the BTS to collect a sample of spectroscopically classified normal Type Ibc SNe, for which we used the ZTF light curves to determine the maximum luminosity. We culled the sample further based on data quality, shape of the light curves, distances, and colors. Then we examined the uncertainties that may affect the measurements. The methodology of the sample construction based on this BTS sample can be used for other future investigations.

    Results. We analyzed the observational data, consisting of optical light curves and spectra, for the selected sub-samples. In total, we used 129 Type Ib or Type Ic BTS SNe with an initial rough luminosity distribution peaking at M-r = -17.61 +/- 0.72, and where 36% are apparently brighter than the theoretically predicted maximum brightness of M-r = -17.8. When we further culled this sample to ensure that the SNe are normal Type Ibc with good LC data within the Hubble flow, the sample of 94 objects gives M-r = -17.64 +/- 0.54. A main uncertainty in absolute magnitude determinations for SNe is the host galaxy extinction correction, but the reddened objects only get more luminous after corrections. If we simply exclude red objects, or those with unusual or uncertain colors, then we are left with 14 objects at M-r = -17.90 +/- 0.73, whereof a handful are most certainly brighter than the suggested theoretical limit. The main result of this study is thus that normal SNe Ibc do indeed reach luminosities above 10(426) erg s(-1), which is apparently in conflict with existing explosion models.

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