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  • 1. Ackley, K.
    et al.
    Amati, L.
    Barbieri, C.
    Bauer, F. E.
    Benetti, S.
    Bernardini, M. G.
    Bhirombhakdi, K.
    Botticella, M. T.
    Branchesi, M.
    Brocato, E.
    Bruun, S. H.
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Campana, S.
    Cappellaro, E.
    Castro-Tirado, A. J.
    Chambers, K. C.
    Chaty, S.
    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 für Extraterrestrische Physik, Germany.
    Ciolfi, R.
    Coleiro, A.
    Copperwheat, C. M.
    Covino, S.
    Cutter, R.
    D'Ammando, F.
    D'Avanzo, P.
    De Cesare, G.
    D'Elia, V.
    Della Valle, M.
    Denneau, L.
    De Pasquale, M.
    Dhillon, V. S.
    Dyer, M. J.
    Elias-Rosa, N.
    Evans, P. A.
    Eyles-Ferris, R. A. J.
    Fiore, A.
    Fraser, M.
    Fruchter, A. S.
    Fynbo, J. P. U.
    Galbany, L.
    Gall, C.
    Galloway, D. K.
    Getman, F.
    Ghirlanda, G.
    Gillanders, J. H.
    Gomboc, A.
    Gompertz, B. P.
    Gonzalez-Fernandez, C.
    Gonzalez-Gaitan, S.
    Grado, A.
    Greco, G.
    Gromadzki, M.
    Groot, P. J.
    Gutierrez, C. P.
    Heikkila, T.
    Heintz, K. E.
    Hjorth, J.
    Hu, Y.-D.
    Huber, M. E.
    Inserra, C.
    Izzo, L.
    Japelj, J.
    Jerkstrand, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jin, Z. P.
    Jonker, P. G.
    Kankare, E.
    Kann, D. A.
    Kennedy, M.
    Kim, S.
    Klose, S.
    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).
    Kotak, R.
    Kuncarayakti, H.
    Lamb, G. P.
    Leloudas, G.
    Levan, A. J.
    Longo, F.
    Lowe, T. B.
    Lyman, J. D.
    Magnier, E.
    Maguire, K.
    Maiorano, E.
    Mandel, I.
    Mapelli, M.
    Mattila, S.
    McBrien, O. R.
    Melandri, A.
    Michalowski, M. J.
    Milvang-Jensen, B.
    Moran, S.
    Nicastro, L.
    Nicholl, M.
    Nicuesa Guelbenzu, A.
    Nuttal, L.
    Oates, S. R.
    O'Brien, P. T.
    Onori, F.
    Palazzi, E.
    Patricelli, B.
    Perego, A.
    Torres, M. A. P.
    Perley, D. A.
    Pian, E.
    Pignata, G.
    Piranomonte, S.
    Poshyachinda, S.
    Possenti, A.
    Pumo, M. L.
    Quirola-Vasquez, J.
    Ragosta, F.
    Ramsay, G.
    Rau, A.
    Rest, A.
    Reynolds, T. M.
    Rosetti, S. S.
    Rossi, A.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sabha, N. B.
    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).
    Salafia, O. S.
    Salmon, L.
    Salvaterra, R.
    Savaglio, S.
    Sbordone, L.
    Schady, P.
    Schipani, P.
    Schultz, A. S. 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). Max-Planck-Institut für Extraterrestrische Physik, Germany.
    Smartt, S. J.
    Smith, K. W.
    Smith, M.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Srivastav, S.
    Stanway, E. R.
    Starling, R. L. C.
    Steeghs, D.
    Stratta, G.
    Stubbs, C. W.
    Tanvir, N. R.
    Testa, V.
    Thrane, E.
    Tonry, J. L.
    Turatto, M.
    Ulaczyk, K.
    van der Horst, A. J.
    Vergani, S. D.
    Walton, N. A.
    Watson, D.
    Wiersema, K.
    Wiik, K.
    Wyrzykowski, 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).
    Yi, S.-X.
    Young, D. R.
    Observational constraints on the optical and near-infrared emission from the neutron star-black hole binary merger candidate S190814bv2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 643, article id A113Article in journal (Refereed)
    Abstract [en]

    Context. Gravitational wave (GW) astronomy has rapidly reached maturity, becoming a fundamental observing window for modern astrophysics. The coalescences of a few tens of black hole (BH) binaries have been detected, while the number of events possibly including a neutron star (NS) is still limited to a few. On 2019 August 14, the LIGO and Virgo interferometers detected a high-significance event labelled S190814bv. A preliminary analysis of the GW data suggests that the event was likely due to the merger of a compact binary system formed by a BH and a NS.

    Aims. In this paper, we present our extensive search campaign aimed at uncovering the potential optical and near infrared electromagnetic counterpart of S190814bv. We found no convincing electromagnetic counterpart in our data. We therefore use our non-detection to place limits on the properties of the putative outflows that could have been produced by the binary during and after the merger.

    Methods. Thanks to the three-detector observation of S190814bv, and given the characteristics of the signal, the LIGO and Virgo Collaborations delivered a relatively narrow localisation in low latency - a 50% (90%) credible area of 5 deg(2) (23 deg(2)) - despite the relatively large distance of 26752 Mpc. ElectromagNetic counterparts of GRAvitational wave sources at the VEry Large Telescope collaboration members carried out an intensive multi-epoch, multi-instrument observational campaign to identify the possible optical and near infrared counterpart of the event. In addition, the ATLAS, GOTO, GRAWITA-VST, Pan-STARRS, and VINROUGE projects also carried out a search on this event. In this paper, we describe the combined observational campaign of these groups.

    Results. Our observations allow us to place limits on the presence of any counterpart and discuss the implications for the kilonova (KN), which was possibly generated by this NS-BH merger, and for the strategy of future searches. The typical depth of our wide-field observations, which cover most of the projected sky localisation probability (up to 99.8%, depending on the night and filter considered), is r similar to 22 (resp. K similar to 21) in the optical (resp. near infrared). We reach deeper limits in a subset of our galaxy-targeted observations, which cover a total similar to 50% of the galaxy-mass-weighted localisation probability. Altogether, our observations allow us to exclude a KN with large ejecta mass M greater than or similar to 0.1 M-circle dot to a high (> 90%) confidence, and we can exclude much smaller masses in a sub-sample of our observations. This disfavours the tidal disruption of the neutron star during the merger.

    Conclusions. Despite the sensitive instruments involved in the campaign, given the distance of S190814bv, we could not reach sufficiently deep limits to constrain a KN comparable in luminosity to AT 2017gfo on a large fraction of the localisation probability. This suggests that future (likely common) events at a few hundred megaparsecs will be detected only by large facilities with both a high sensitivity and large field of view. Galaxy-targeted observations can reach the needed depth over a relevant portion of the localisation probability with a smaller investment of resources, but the number of galaxies to be targeted in order to get a fairly complete coverage is large, even in the case of a localisation as good as that of this event.

  • 2. Adams, S. M.
    et al.
    Blagorodnova, N.
    Kasliwal, M. M.
    Amanullah, Rahman
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Barlow, T.
    Bue, B.
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cao, Y.
    Cenko, S. B.
    Cook, D. O.
    Ferretti, Raphael
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fox, O. D.
    Fremling, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gezari, S.
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ho, A. Y. Q.
    Hung, Tiara
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Karamehmetoglu, Emir
    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.
    Kupfer, T.
    Laher, R. R.
    Masci, F. J.
    Miller, A. A.
    Neill, J. D.
    Nugent, P. 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).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walters, R.
    iPTF Survey for Cool Transients2018In: Publications of the Astronomical Society of the Pacific, ISSN 0004-6280, E-ISSN 1538-3873, Vol. 130, no 985, article id 034202Article in journal (Refereed)
    Abstract [en]

    We performed a wide-area (2000 deg2) g and I band experiment as part of a two month extension to the Intermediate Palomar Transient Factory. We discovered 36 extragalactic transients including iPTF17lf, a highly reddened local SN Ia, iPTF17bkj, a new member of the rare class of transitional Ibn/IIn supernovae, and iPTF17be, a candidate luminous blue variable outburst. We do not detect any luminous red novae and place an upper limit on their rate. We show that adding a slow-cadence I band component to upcoming surveys such as the Zwicky Transient Facility will improve the photometric selection of cool and dusty transients.

  • 3. 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.

  • 4.
    Ahrens, Maryon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Conrad, Jan M.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dumm, Jonathan P.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stanford University, USA.
    Rosswog, Stephan
    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).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. 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).
    Barbarino, Cristina
    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 Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Roy, Rupak
    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).
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Linnaeus University, Sweden.
    Morå, Knut
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wagner, Robert M.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Multi-messenger Observations of a Binary Neutron Star Merger2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 848, no 2, article id L12Article in journal (Refereed)
    Abstract [en]

    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of similar to 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of 40(-8)(+8) Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M-circle dot. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at similar to 40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over similar to 10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position similar to 9 and similar to 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

  • 5. Ahumada, Tomas
    et al.
    Anand, Shreya
    Coughlin, Michael W.
    Andreoni, Igor
    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).
    Kumar, Harsh
    Reusch, Simeon
    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).
    Stein, Robert
    Cenko, S. Bradley
    Kasliwal, Mansi M.
    Singer, Leo P.
    Dunwoody, Rachel
    Mangan, Joseph
    Bhalerao, Varun
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Burns, Eric
    Graham, Matthew J.
    Kaplan, David L.
    Perley, Daniel
    Almualla, Mouza
    Bloom, Joshua S.
    Cunningham, Virginia
    De, Kishalay
    Gatkine, Pradip
    Ho, Anna Y. Q.
    Karambelkar, Viraj
    Kong, Albert K. H.
    Yao, Yuhan
    Anupama, G. C.
    Barway, Sudhanshu
    Ghosh, Shaon
    Itoh, Ryosuke
    McBreen, Sheila
    Bellm, Eric C.
    Fremling, Christoffer
    Laher, Russ R.
    Mahabal, Ashish A.
    Riddle, Reed L.
    Rosnet, Philippe
    Rusholme, Ben
    Smith, Roger
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bissaldi, Elisabetta
    Fletcher, Corinne
    Hamburg, Rachel
    Mailyan, Bagrat
    Malacaria, Christian
    Roberts, Oliver
    In Search of Short Gamma-Ray Burst Optical Counterparts with the Zwicky Transient Facility2022In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 932, no 1, article id 40Article in journal (Refereed)
    Abstract [en]

    The Fermi Gamma-ray Burst Monitor (GBM) triggers on-board in response to ∼40 short gamma-ray bursts (SGRBs) per year; however, their large localization regions have made the search for optical counterparts a challenging endeavour. We have developed and executed an extensive program with the wide field of view of the Zwicky Transient Facility (ZTF) camera, mounted on the Palomar 48 inch Oschin telescope (P48), to perform target-of-opportunity (ToO) observations on 10 Fermi-GBM SGRBs during 2018 and 2020–2021. Bridging the large sky areas with small field-of-view optical telescopes in order to track the evolution of potential candidates, we look for the elusive SGRB afterglows and kilonovae (KNe) associated with these high-energy events. No counterpart has yet been found, even though more than 10 ground-based telescopes, part of the Global Relay of Observatories Watching Transients Happen (GROWTH) network, have taken part in these efforts. The candidate selection procedure and the follow-up strategy have shown that ZTF is an efficient instrument for searching for poorly localized SGRBs, retrieving a reasonable number of candidates to follow up and showing promising capabilities as the community approaches the multi-messenger era. Based on the median limiting magnitude of ZTF, our searches would have been able to retrieve a GW170817-like event up to ∼200 Mpc and SGRB afterglows to z = 0.16 or 0.4, depending on the assumed underlying energy model. Future ToOs will expand the horizon to z = 0.2 and 0.7, respectively.

  • 6. Alp, Dennis
    et al.
    Larsson, Josefin
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Indebetouw, Remy
    Jerkstrand, Anders
    Ahola, Antero
    Burrows, David
    Challis, Peter
    Cigan, Phil
    Cikota, Aleksandar
    Kirshner, Robert P.
    van Loon, Jacco Th.
    Mattila, Seppo
    Ng, C. -Y.
    Park, Sangwook
    Spyromilio, Jason
    Woosley, Stan
    Baes, Maarten
    Bouchet, Patrice
    Chevalier, Roger
    Frank, Kari A.
    Gaensler, B. M.
    Gomez, Haley
    Janka, Hans-Thomas
    Leibundgut, Bruno
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Marcaide, Jon
    Matsuura, Mikako
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sonneborn, George
    Staveley-Smith, Lister
    Zanardo, Giovanna
    Gabler, Michael
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wheeler, J. Craig
    The 30 Year Search for the Compact Object in SN 1987A2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 864, no 2, article id 174Article in journal (Refereed)
    Abstract [en]

    Despite more than 30 years of searching, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 10(-30) erg s(-1) cm(-2) Hz(-1) ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) to <4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency 77 is limited to <10(-11) eta(-1) M-circle dot yr(-1), which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P) is B less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.

  • 7. Anand, Shreya
    et al.
    Barnes, Jennifer
    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, Peopleʼs Republic of China.
    Kasliwal, Mansi M.
    Coughlin, Michael 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).
    De, Kishalay
    Fremling, Christoffer
    Corsi, Alessandra
    Ho, Anna Y. Q.
    Balasubramanian, Arvind
    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).
    Srinivasaragavan, Gokul P.
    Cenko, S. Bradley
    Ahumada, Tomás
    Andreoni, Igor
    Dahiwale, Aishwarya
    Das, Kaustav Kashyap
    Jencson, Jacob
    Karambelkar, Viraj
    Kumar, Harsh
    Metzger, Brian D.
    Perley, Daniel
    Sarin, Nikhil
    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).
    Schweyer, Tassilo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Sharma, Yashvi
    Sit, Tawny
    Stein, Robert
    Tartaglia, Leonardo
    Tinyanont, Samaporn
    Tzanidakis, Anastasios
    van Roestel, Jan
    Yao, Yuhan
    Bloom, Joshua S.
    Cook, David O.
    Dekany, Richard
    Graham, Matthew J.
    Groom, Steven L.
    Kaplan, David L.
    Masci, Frank J.
    Medford, Michael S.
    Riddle, Reed
    Zhang, Chaoran
    Collapsars as Sites of r-process Nucleosynthesis: Systematic Photometric Near-infrared Follow-up of Type Ic-BL Supernovae2024In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 962, no 1, article id 68Article in journal (Refereed)
    Abstract [en]

    One of the open questions following the discovery of GW170817 is whether neutron star (NS) mergers are the only astrophysical sites capable of producing r-process elements. Simulations have shown that 0.01–0.1 M of r-process material could be generated in the outflows originating from the accretion disk surrounding the rapidly rotating black hole that forms as a remnant to both NS mergers and collapsing massive stars associated with long-duration gamma-ray bursts (collapsars). The hallmark signature of r-process nucleosynthesis in the binary NS merger GW170817 was its long-lasting near-infrared (NIR) emission, thus motivating a systematic photometric study of the light curves of broad-lined stripped-envelope (Ic-BL) supernovae (SNe) associated with collapsars. We present the first systematic study of 25 SNe Ic-BL—including 18 observed with the Zwicky Transient Facility and 7 from the literature—in the optical/NIR bands to determine what quantity of r-process material, if any, is synthesized in these explosions. Using semi-analytic models designed to account for r-process production in SNe Ic-BL, we perform light curve fitting to derive constraints on the r-process mass for these SNe. We also perform independent light curve fits to models without the r-process. We find that the r-process-free models are a better fit to the light curves of the objects in our sample. Thus, we find no compelling evidence of r-process enrichment in any of our objects. Further high-cadence infrared photometric studies and nebular spectroscopic analysis would be sensitive to smaller quantities of r-process ejecta mass or indicate whether all collapsars are completely devoid of r-process nucleosynthesis.

  • 8. Anand, Shreya
    et al.
    Coughlin, Michael W.
    Kasliwal, Mansi M.
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Ahumada, Tomás
    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).
    Almualla, Mouza
    Andreoni, Igor
    Stein, Robert
    Foucart, Francois
    Singer, Leo P.
    Sollerman, Jesper
    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.
    Bolin, Bryce
    Caballero-García, M. D.
    Castro-Tirado, Alberto J.
    Cenko, S. Bradley
    De, Kishalay
    Dekany, Richard G.
    Duev, Dmitry A.
    Feeney, Michael
    Fremling, Christoffer
    Goldstein, Daniel A.
    Golkhou, V. Zach
    Graham, Matthew J.
    Guessoum, Nidhal
    Hankins, Matthew J.
    Hu, Youdong
    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).
    Kulkarni, S. R.
    Kumar, Harsh
    Laher, Russ R.
    Masci, Frank J.
    Mróz, Przemek
    Nissanke, Samaya
    Porter, Michael
    Reusch, Simeon
    Riddle, Reed
    Rosnet, Philippe
    Rusholme, Ben
    Serabyn, Eugene
    Sánchez-Ramírez, R.
    Rigault, Mickael
    Shupe, David L.
    Smith, Roger
    Soumagnac, Maayane T.
    Walters, Richard
    Valeev, Azamat F.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). California Institute of Technology, USA; Russian Academy of Sciences, Russia.
    Optical follow-up of the neutron star-black hole mergers S200105ae and S200115j2021In: Nature Astronomy, E-ISSN 2397-3366, Vol. 5, p. 46-53Article in journal (Refereed)
    Abstract [en]

    LIGO and Virgo's third observing run revealed the first neutron star-black hole (NSBH) merger candidates in gravitational waves. These events are predicted to synthesize r-process elements(1,2)creating optical/near-infrared 'kilonova' emission. The joint gravitational wave and electromagnetic detection of an NSBH merger could be used to constrain the equation of state of dense nuclear matter(3), and independently measure the local expansion rate of the Universe(4). Here, we present the optical follow-up and analysis of two of the only three high-significance NSBH merger candidates detected to date, S200105ae and S200115j, with the Zwicky Transient Facility(5). The Zwicky Transient Facility observed similar to 48% of S200105ae and similar to 22% of S200115j's localization probabilities, with observations sensitive to kilonovae brighter than -17.5 mag fading at 0.5 mag d(-1)in the g- and r-bands; extensive searches and systematic follow-up of candidates did not yield a viable counterpart. We present state-of-the-art kilonova models tailored to NSBH systems that place constraints on the ejecta properties of these NSBH mergers. We show that with observed depths of apparent magnitude similar to 22 mag, attainable in metre-class, wide-field-of-view survey instruments, strong constraints on ejecta mass are possible, with the potential to rule out low mass ratios, high black hole spins and large neutron star radii.

  • 9.
    Anderson, Brandon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Larsson, Stefan
    Li, L.
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ferretti, Raphael
    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).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    SUPPLEMENT: LOCALIZATION AND BROADBAND FOLLOW-UP OF THE GRAVITATIONAL-WAVE TRANSIENT GW150914 (2016, ApJL, 826, L13)2016In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 225, no 1, article id 8Article in journal (Refereed)
    Abstract [en]

    This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands.

  • 10.
    Anderson, Brandon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ferretti, Raphael
    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).
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    LOCALIZATION AND BROADBAND FOLLOW-UP OF THE GRAVITATIONAL-WAVE TRANSIENT GW 1509142016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 826, no 1, article id L13Article in journal (Refereed)
    Abstract [en]

    A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.

  • 11. Anderson, P.
    et al.
    Dessart, L.
    Gutiérrez, C. P.
    Krühler, T.
    Galbany, L.
    Jerkstrand, A.
    Smartt, S. J.
    Contreras, C.
    Morrell, N.
    Phillips, M. M.
    Stritzinger, M. D.
    Hsiao, E. Y.
    González-Gaitán, S.
    Agliozzo, C.
    Castellón, S.
    Chambers, K. C.
    Chen, T. -W.
    Flewelling, H.
    Gonzalez, C.
    Hosseinzadeh, G.
    Huber, M.
    Fraser, M.
    Inserra, C.
    Kankare, E.
    Mattila, S.
    Magnier, E.
    Maguire, K.
    Lowe, T. B.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sullivan, M.
    Young, D. R.
    Valenti, S.
    The lowest-metallicity type II supernova from the highest-mass red supergiant progenitor2018In: Nature Astronomy, E-ISSN 2397-3366, Vol. 2, no 7, p. 574-579Article in journal (Refereed)
    Abstract [en]

    Red supergiants have been confirmed as the progenitor stars of the majority of hydrogen-rich type II supernovae(1). However, while such stars are observed with masses > 25 M-circle dot (ref. (2)), detections of > 18 M-circle dot progenitors remain elusive(1). Red supergiants are also expected to form at all metallicities, but discoveries of explosions from low-metallicity progenitors are scarce. Here, we report observations of the type II supernova, SN 2015bs, for which we infer a progenitor metallicity of <= 0.1 Z(circle dot) from comparison to photospheric-phase spectral models(3), and a zero-age main-sequence mass of 17-25 M-circle dot through comparison to nebular-phase spectral models(4,5). SN 2015bs displays a normal 'plateau' light-curve morphology, and typical spectral properties, implying a red supergiant progenitor. This is the first example of such a high-mass progenitor for a 'normal' type II supernova, suggesting a link between high-mass red supergiant explosions and low-metallicity progenitors.

  • 12. Andreoni, I.
    et al.
    Ackley, K.
    Cooke, J.
    Acharyya, A.
    Allison, J. R.
    Anderson, G. E.
    Ashley, M. C. B.
    Baade, D.
    Bailes, M.
    Bannister, K.
    Beardsley, A.
    Bessell, M. S.
    Bian, F.
    Bland, P. A.
    Boer, M.
    Booler, T.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brown, I. S.
    Buckley, D. A. H.
    Chang, S. -W.
    Coward, D. M.
    Crawford, S.
    Crisp, H.
    Crosse, B.
    Cucchiara, A.
    Cupak, M.
    de Gois, J. S.
    Deller, A.
    Devillepoix, H. A. R.
    Dobie, D.
    Elmer, E.
    Emrich, D.
    Farah, W.
    Farrell, T. J.
    Franzen, T.
    Gaensler, B. M.
    Galloway, D. K.
    Gendre, B.
    Giblin, T.
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Green, J.
    Hancock, P. J.
    Hartig, B. A. D.
    Howell, E. J.
    Horsley, L.
    Hotan, A.
    Howie, R. M.
    Hu, L.
    Hu, Y.
    James, C. W.
    Johnston, S.
    Johnston-Hollitt, M.
    Kaplan, D. L.
    Kasliwal, M.
    Keane, E. F.
    Kenney, D.
    Klotz, A.
    Lau, R.
    Laugier, R.
    Lenc, E.
    Li, X.
    Liang, E.
    Lidman, C.
    Luvaul, L. C.
    Lynch, C.
    Ma, B.
    Macpherson, D.
    Mao, J.
    McClelland, D. E.
    McCully, C.
    Moller, A.
    Morales, M. F.
    Morris, D.
    Murphy, T.
    Noysena, K.
    Onken, C. A.
    Orange, N. B.
    Oslowski, S.
    Pallot, D.
    Paxman, J.
    Potter, S. B.
    Pritchard, T.
    Raja, W.
    Ridden-Harper, R.
    Romero-Colmenero, E.
    Sadler, E. M.
    Sansom, E. K.
    Scalzo, R. A.
    Schmidt, B. P.
    Scott, S. M.
    Seghouani, N.
    Shang, Z.
    Shannon, R. M.
    Shao, L.
    Shara, M. M.
    Sharp, R.
    Sokolowski, M.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Staff, J.
    Steele, K.
    Sun, T.
    Suntzeff, N. B.
    Tao, C.
    Tingay, S.
    Towner, M. C.
    Thierry, P.
    Trott, C.
    Tucker, B. E.
    Vaisanen, P.
    Krishnan, V. Venkatraman
    Walker, M.
    Wang, L.
    Wang, X.
    Wayth, R.
    Whiting, M.
    Williams, A.
    Williams, T.
    Wolf, C.
    Wu, C.
    Wu, X.
    Yang, J.
    Yuan, X.
    Zhang, H.
    Zhou, J.
    Zovaro, H.
    Follow Up of GW170817 and Its Electromagnetic Counterpart by Australian-Led Observing Programmes2017In: Publications Astronomical Society of Australia, ISSN 1323-3580, E-ISSN 1448-6083, Vol. 34, article id e069Article, review/survey (Refereed)
    Abstract [en]

    The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (similar to 2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.

  • 13. Andreoni, Igor
    et al.
    Coughlin, Michael W.
    Kool, Erik C.
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Kasliwal, Mansi M.
    Kumar, Harsh
    Bhalerao, Varun
    Carracedo, Ana Sagués
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Ho, Anna Y. Q.
    Pang, Peter T. H.
    Saraogi, Divita
    Sharma, Kritti
    Shenoy, Vedant
    Burns, Eric
    Ahumada, Tomás
    Anand, Shreya
    Singer, Leo P.
    Perley, Daniel A.
    De, Kishalay
    Fremling, U. C.
    Bellm, Eric C.
    Bulla, Mattia
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Crellin-Quick, Arien
    Dietrich, Tim
    Drake, Andrew
    Duev, Dmitry A.
    Goobar, Ariel
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Graham, Matthew J.
    Kaplan, David L.
    Kulkarni, S. R.
    Laher, Russ R.
    Mahabal, Ashish A.
    Shupe, David L.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Walters, Richard
    Yao, Yuhan
    Fast-transient Searches in Real Time with ZTFReST: Identification of Three Optically Discovered Gamma-Ray Burst Afterglows and New Constraints on the Kilonova Rate2021In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 918, no 2, article id 63Article in journal (Refereed)
    Abstract [en]

    The most common way to discover extragalactic fast transients, which fade within a few nights in the optical, is via follow-up of gamma-ray burst and gravitational-wave triggers. However, wide-field surveys have the potential to identify rapidly fading transients independently of such external triggers. The volumetric survey speed of the Zwicky Transient Facility (ZTF) makes it sensitive to objects as faint and fast fading as kilonovae, the optical counterparts to binary neutron star mergers, out to almost 200 Mpc. We introduce an open-source software infrastructure, the ZTF REaltime Search and Triggering, ZTFReST, designed to identify kilonovae and fast transients in ZTF data. Using the ZTF alert stream combined with forced point-spread-function photometry, we have implemented automated candidate ranking based on their photometric evolution and fitting to kilonova models. Automated triggering, with a human in the loop for monitoring, of follow-up systems has also been implemented. In 13 months of science validation, we found several extragalactic fast transients independently of any external trigger, including two supernovae with post-shock cooling emission, two known afterglows with an associated gamma-ray burst (ZTF20abbiixp, ZTF20abwysqy), two known afterglows without any known gamma-ray counterpart (ZTF20aajnksq, ZTF21aaeyldq), and three new fast-declining sources (ZTF20abtxwfx, ZTF20acozryr, ZTF21aagwbjr) that are likely associated with GRB200817A, GRB201103B, and GRB210204A. However, we have not found any objects that appear to be kilonovae. We constrain the rate of GW170817-like kilonovae to R < 900 Gpc(-3) yr(-1) (95% confidence). A framework such as ZTFReST could become a prime tool for kilonova and fast-transient discovery with the Vera Rubin Observatory.

  • 14. Andreoni, Igor
    et al.
    Goldstein, Daniel A.
    Kasliwal, Mansi M.
    Nugent, Peter E.
    Zhou, Rongpu
    Newman, Jeffrey A.
    Bulla, Mattia
    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).
    Foucart, Francois
    Hotokezaka, Kenta
    Nakar, Ehud
    Nissanke, Samaya
    Raaijmakers, Geert
    Bloom, Joshua S.
    De, Kishalay
    Jencson, Jacob E.
    Ward, Charlotte
    Ahumada, Tomas
    Anand, Shreya
    Buckley, David A. H.
    Caballero-Garcia, Maria D.
    Castro-Tirado, Alberto J.
    Copperwheat, Christopher M.
    Coughlin, Michael W.
    Cenko, S. Bradley
    Gromadzki, Mariusz
    Hu, Youdong
    Karambelkar, Viraj R.
    Perley, Daniel A.
    Sharma, Yashvi
    Valeev, Azamat F.
    Cook, David O.
    Fremling, U. Christoffer
    Kumar, Harsh
    Taggart, Kirsty
    Bagdasaryan, Ashot
    Cooke, Jeff
    Dahiwale, Aishwarya
    Dhawan, Suhail
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dobie, Dougal
    Gatkine, Pradip
    Golkhou, V. Zach
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Chaves, Andreas Guerra
    Hankins, Matthew
    Kaplan, David L.
    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).
    Mohite, Siddharth
    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
    Webb, Sara
    Zhang, Keming
    GROWTH on S190814bv: Deep Synoptic Limits on the Optical/Near-infrared Counterpart to a Neutron Star-Black Hole Merger2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 890, no 2, article id 131Article in journal (Refereed)
    Abstract [en]

    On 2019 August 14, the Advanced LIGO and Virgo interferometers detected the high-significance gravitational wave (GW) signal S190814bv. The GW data indicated that the event resulted from a neutron star-black hole (NSBH) merger, or potentially a low-mass binary BH merger. Due to the low false-alarm rate and the precise localization (23 deg(2) at 90%), S190814bv presented the community with the best opportunity yet to directly observe an optical/near-infrared counterpart to an NSBH merger. To search for potential counterparts, the GROWTH Collaboration performed real-time image subtraction on six nights of public Dark Energy Camera images acquired in the 3 weeks following the merger, covering >98% of the localization probability. Using a worldwide network of follow-up facilities, we systematically undertook spectroscopy and imaging of optical counterpart candidates. Combining these data with a photometric redshift catalog, we ruled out each candidate as the counterpart to S190814bv and placed deep, uniform limits on the optical emission associated with S190814bv. For the nearest consistent GW distance, radiative transfer simulations of NSBH mergers constrain the ejecta mass of S190814bv to be M-ej < 0.04 M-circle dot at polar viewing angles, or M-ej < 0.03 M-circle dot if the opacity is kappa < 2 cm(2)g(-1). Assuming a tidal deformability for the NS at the high end of the range compatible with GW170817 results, our limits would constrain the BH spin component aligned with the orbital momentum to be chi < 0.7 for mass ratios Q < 6, with weaker constraints for more compact NSs.

  • 15. Andreoni, Igor
    et al.
    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).
    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).
    Kasliwal, Mansi M.
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Ahumada, Tomás
    Coughlin, Michael W.
    Anand, Shreya
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. 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).
    Kaplan, David L.
    Loveridge, Tegan T.
    Karambelkar, Viraj
    Cooke, Jeff
    Bagdasaryan, Ashot
    Bellm, Eric C.
    Cenko, S. Bradley
    Cook, David O.
    De, Kishalay
    Dekany, Richard
    Delacroix, Alexandre
    Drake, Andrew
    Duev, Dmitry A.
    Fremling, Christoffer
    Golkhou, V. Zach
    Graham, Matthew J.
    Hale, David
    Kulkarni, S. R.
    Kupfer, Thomas
    Laher, Russ R.
    Mahabal, Ashish A.
    Masci, Frank J.
    Rusholme, Ben
    Smith, Roger M.
    Tzanidakis, Anastasios
    Sistine, Angela Van
    Yao, Yuhan
    Constraining the Kilonova Rate with Zwicky Transient Facility Searches Independent of Gravitational Wave and Short Gamma-Ray Burst Triggers2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 904, no 2, article id 155Article in journal (Refereed)
    Abstract [en]

    The first binary neutron star merger, GW170817, was accompanied by a radioactivity-powered optical/infrared transient called a kilonova. To date, no compelling kilonova has been found in all-sky optical surveys, independently of short gamma-ray burst and gravitational-wave triggers. In this work, we searched the first 23 months of the Zwicky Transient Facility (ZTF) data stream for candidate kilonovae in the form of rapidly evolving transients. We combined ZTF alert queries with forced point-spread-function photometry and nightly flux stacking to increase our sensitivity to faint and fast transients. Automatic queries yielded >11,200 candidates, 24 of which passed quality checks and selection criteria based on a grid of kilonova models tailored for both binary neutron star and neutron star-black hole mergers. None of the candidates in our sample was deemed a possible kilonova after thorough vetting. The sources that passed our selection criteria are dominated by Galactic cataclysmic variables. We identified two fast transients at high Galactic latitude, one of which is the confirmed afterglow of long-duration GRB.190106A, the other is a possible cosmological afterglow. Using a survey simulation code, we constrained the kilonova rate for a range of models including top-hat, linearly decaying light curves, and synthetic light curves obtained with radiative transfer simulations. For prototypical GW170817-like kilonovae, we constrain the rate to be R < 1775 Gpc(-3) yr(-1) (95% confidence). By assuming a population of kilonovae with the same geometry and composition of GW170817 observed under a uniform viewing angle distribution, we obtained a constraint on the rate of R.<.4029 Gpc(-3) yr(-1).

  • 16. Arcavi, Iair
    et al.
    Howell, D. Andrew
    Kasen, Daniel
    Bildsten, Lars
    Hosseinzadeh, Griffin
    McCully, Curtis
    Wong, Zheng Chuen
    Katz, Sarah Rebekah
    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).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Leloudas, Giorgos
    Fremling, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Nugent, Peter E.
    Horesh, Assaf
    Mooley, Kunal
    Rumsey, Clare
    Cenko, S. B. Radley
    Graham, Melissa L.
    Perley, Daniel A.
    Nakar, Ehud
    Shaviv, Nir J.
    Bromberg, Omer
    Shen, Ken J.
    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.
    Cao, Yi
    Wang, Xiaofeng
    Huang, Fang
    Rui, Liming
    Zhang, Tianmeng
    Li, Wenxiong
    Li, Zhitong
    Zhang, Jujia
    Valenti, Stefano
    Guevel, David
    Shappee, Benjamin
    Kochanek, Christopher S.
    Holoien, Thomas W. -S.
    Filippenko, Alexei V.
    Fender, Rob
    Nyholm, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yaron, Ofer
    Kasliwal, Mansi M. .
    Sullivan, Mark
    Lagorodnova, Nadja B.
    Walters, Richard S.
    Lunnan, Ragnhild
    Khazov, Danny
    Andreoni, Igor
    Laher, Russ R.
    Konidaris, Nick
    Wozniak, Przemek
    Bue, Brian
    Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star2017In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 551, no 7679, p. 210-213Article in journal (Refereed)
    Abstract [en]

    Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining(1). Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability(2-5). That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.

  • 17. Barbarino, C.
    et al.
    Dall'Ora, M.
    Botticella, M. T.
    Della Valle, M.
    Zampieri, L.
    Maund, J. R.
    Pumo, M. L.
    Jerkstrand, A.
    Benetti, S.
    Elias-Rosa, N.
    Fraser, M.
    Gal-Yam, A.
    Hamuy, M.
    Inserra, C.
    Knapic, C.
    LaCluyze, A. P.
    Molinaro, M.
    Ochner, P.
    Pastorello, A.
    Pignata, G.
    Reichart, D. E.
    Ries, C.
    Riffeser, A.
    Schmidt, B.
    Schmidt, M.
    Smareglia, R.
    Smartt, S. J.
    Smith, K.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sullivan, M.
    Tomasella, L.
    Turatto, M.
    Valenti, S.
    Yaron, O.
    Young, D.
    SN 2012ec: mass of the progenitor from PESSTO follow-up of the photospheric phase2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 448, no 3, p. 2312-2331Article in journal (Refereed)
    Abstract [en]

    We present the results of a photometric and spectroscopic monitoring campaign of SN 2012ec, which exploded in the spiral galaxy NGC 1084, during the photospheric phase. The photometric light curve exhibits a plateau with luminosity L = 0.9 x 10(42) erg s(-1) and duration similar to 90 d, which is somewhat shorter than standard Type II-P supernovae (SNe). We estimate the nickel mass M(Ni-56) = 0.040 +/- 0.015 M-circle dot from the luminosity at the beginning of the radioactive tail of the light curve. The explosion parameters of SN 2012ec were estimated from the comparison of the bolometric light curve and the observed temperature and velocity evolution of the ejecta with predictions from hydrodynamical models. We derived an envelope mass of 12.6 M-circle dot, an initial progenitor radius of 1.6 x 10(13) cm and an explosion energy of 1.2 foe. These estimates agree with an independent study of the progenitor star identified in pre-explosion images, for which an initial mass of M = 14-22 M-circle dot was determined. We have applied the same analysis to two other Type II-P SNe (SNe 2012aw and 2012A), and carried out a comparison with the properties of SN 2012ec derived in this paper. We find a reasonable agreement between the masses of the progenitors obtained from pre-explosion images and masses derived from hydrodynamical models. We estimate the distance to SN 2012ec with the standardized candle method (SCM) and compare it with other estimates based on other primary and secondary indicators. SNe 2012A, 2012aw and 2012ec all follow the standard relations for the SCM for the use of Type II-P SNe as distance indicators.

  • 18.
    Barbarino, Cristina
    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).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, C.
    Karamehmetoglu, E.
    Arcavi, I.
    Gal-Yam, A.
    Laher, R.
    Schulze, S.
    Wozniak, P.
    Yan, Lin
    Type Ic supernovae from the (intermediate) Palomar Transient Factory2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 651, article id A81Article in journal (Refereed)
    Abstract [en]

    Context. Type Ic supernovae represent the explosions of the most stripped massive stars, but their progenitors and explosion mechanisms remain unclear. Larger samples of observed supernovae can help characterize the population of these transients.

    Aims. We present an analysis of 44 spectroscopically normal Type Ic supernovae, with focus on the light curves. The photometric data were obtained over 7 years with the Palomar Transient Factory and its continuation, the intermediate Palomar Transient Factory. This is the first homogeneous and large sample of SNe Ic from an untargeted survey, and we aim to estimate explosion parameters for the sample.

    Methods. We present K-corrected Bgriz light curves of these SNe, obtained through photometry on template-subtracted images. We performed an analysis on the shape of the r-band light curves and confirmed the correlation between the rise parameter m 10 and the decline parameter m15. Peak r-band absolute magnitudes have an average of 17:71 +/- 0:85 mag. To derive the explosion epochs, we fit the r-band lightcurves to a template derived from a well-sampled light curve. We computed the bolometric light curves using r and g band data, g r colors and bolometric corrections. Bolometric light curves and Fe ii 5169 velocities at peak were used to fit to the Arnett semianalytic model in order to estimate the ejecta mass Mej, the explosion energy EK and the mass of radioactive nickel M(56Ni) for each SN.

    Results. Including 41 SNe, we find average values of hMej i = 4 :50 +/- 0 :79 M fi, hEK i = 1 :79 +/- 0 :29 X 1051 erg, and h M56Ni i = 0:19 X 0:03 M fi. The explosion-parameter distributions are comparable to those available in the literature, but our large sample also includes some transients with narrow and very broad light curves leading to more extreme ejecta masses values.

  • 19. Becker, A
    et al.
    Andra, 32
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Andra, 5
    Exploring the Outer Solar System with the ESSENCE Supernova Survey2008In: The Astrophysical Journal, Vol. 682, no 1, p. L53-L56Article in journal (Refereed)
    Abstract [en]

    We report the discovery and orbital determination of 14 trans-Neptunian objects (TNOs) from the ESSENCE Supernova Survey difference imaging data set. Two additional objects discovered in a similar search of the SDSS-II Supernova Survey database were recovered in this effort. ESSENCE repeatedly observed fields far from the solar system ecliptic (-21° < β < -5°), reaching limiting magnitudes per observation of I~23.1 and R~23.7. We examine several of the newly detected objects in detail, including 2003 UC414, which orbits entirely between Uranus and Neptune and lies very close to a dynamical region that would make it stable for the lifetime of the solar system. 2003 SS422 and 2007 TA418 have high eccentricities and large perihelia, making them candidate members of an outer class of TNOs. We also report a new member of the ``extended'' or ``detached'' scattered disk, 2004 VN112, and verify the stability of its orbit using numerical simulations. This object would have been visible to ESSENCE for only ~2% of its orbit, suggesting a vast number of similar objects across the sky. We emphasize that off-ecliptic surveys are optimal for uncovering the diversity of such objects, which in turn will constrain the history of gravitational influences that shaped our early solar system.

  • 20. Bellm, Eric C.
    et al.
    Kulkarni, Shrinivas R.
    Graham, Matthew J.
    Dekany, Richard
    Smith, Roger M.
    Riddle, Reed
    Masci, Frank J.
    Helou, George
    Prince, Thomas A.
    Adams, Scott 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).
    Barlow, Tom
    Bauer, James
    Beck, Ron
    Belicki, Justin
    Biswas, Rahul
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Blagorodnova, Nadejda
    Bodewits, Dennis
    Bolin, Bryce
    Brinnel, Valery
    Brooke, Tim
    Bue, Brian
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Burruss, Rick
    Cenko, S. Bradley
    Chang, Chan-Kao
    Connolly, Andrew
    Coughlin, Michael
    Cromer, John
    Cunningham, Virginia
    De, Kishalay
    Delacroix, Alex
    Desai, Vandana
    Duev, Dmitry A.
    Eadie, Gwendolyn
    Farnham, Tony L.
    Feeney, Michael
    Feindt, Ulrich
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flynn, David
    Franckowiak, Anna
    Frederick, S.
    Fremling, C.
    Gal-Yam, Avishay
    Gezari, Suvi
    Giomi, Matteo
    Goldstein, Daniel A.
    Golkhou, V. Zach
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Groom, Steven
    Hacopians, Eugean
    Hale, David
    Henning, John
    Ho, Anna Y. Q.
    Hover, David
    Howell, Justin
    Hung, Tiara
    Huppenkothen, Daniela
    Imel, David
    Ip, Wing-Huen
    Ivezic, Zeljko
    Jackson, Edward
    Jones, Lynne
    Juric, Mario
    Kasliwal, Mansi M.
    Kaspi, S.
    Kaye, Stephen
    Kelley, Michael S. P.
    Kowalski, Marek
    Kramer, Emily
    Kupfer, Thomas
    Landry, Walter
    Laher, Russ R.
    Lee, Chien-De
    Lin, Hsing Wen
    Lin, Zhong-Yi
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Giomi, Matteo
    Mahabal, Ashish
    Mao, Peter
    Miller, Adam A.
    Monkewitz, Serge
    Murphy, Patrick
    Ngeow, Chow-Choong
    Nordin, Jakob
    Nugent, Peter
    Ofek, Eran
    Patterson, Maria T.
    Penprase, Bryan
    Porter, Michael
    Rauch, Ludwig
    Rebbapragada, Umaa
    Reiley, Dan
    Rigault, Mickael
    Rodriguez, Hector
    van Roestel, Jan
    Rusholme, Ben
    van Santen, Jakob
    Schulze, S.
    Shupe, David L.
    Singer, Leo P.
    Soumagnac, Maayane T.
    Stein, Robert
    Surace, Jason
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Szkody, Paula
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Terek, Scott
    Van Sistine, Angela
    van Velzen, Sjoert
    Vestrand, W. Thomas
    Walters, Richard
    Ward, Charlotte
    Ye, Quan-Zhi
    Yu, Po-Chieh
    Yan, Lin
    Zolkower, Jeffry
    The Zwicky Transient Facility: System Overview, Performance, and First Results2019In: Publications of the Astronomical Society of the Pacific, ISSN 0004-6280, E-ISSN 1538-3873, Vol. 131, no 995, article id 018002Article in journal (Refereed)
    Abstract [en]

    The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg(2) field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and first scientific results from commissioning and the early survey. ZTF's public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope.

  • 21. Bellm, Eric C.
    et al.
    Wang, Yuankun
    van Roestel, Jan
    Phillipson, Rebecca A.
    Coughlin, Michael W.
    Tomsick, John A.
    Groom, Steven L.
    Healy, Brian
    Purdum, Josiah
    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).
    Bealo, Peter
    Lora, Stefano
    Muyllaert, Eddy
    Peretto, Ivo
    Schwendeman, Erik J.
    An Optically Discovered Outburst from XTE J1859+2262023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 956, no 1, article id 21Article in journal (Refereed)
    Abstract [en]

    Using the Zwicky Transient Facility, in 2021 February we identified the first known outburst of the black hole X-ray transient XTE J1859+226 since its discovery in 1999. The outburst was visible at X-ray, UV, and optical wavelengths for less than 20 days, substantially shorter than its full outburst of 320 days in 1999, and the observed peak luminosity was 2 orders of magnitude lower. Its peak bolometric luminosity was only 2 × 1035 erg s−1, implying an Eddington fraction of about 3 × 10−4. The source remained in the hard spectral state throughout the outburst. From optical spectroscopy measurements we estimate an outer disk radius of 1011 cm. The low observed X-ray luminosity is not sufficient to irradiate the entire disk, but we observe a surprising exponential decline in the X-ray light curve. These observations highlight the potential of optical and infrared synoptic surveys to discover low-luminosity activity from X-ray transients.

  • 22. Benetti, S.
    et al.
    Nicholl, M.
    Cappellaro, E.
    Pastorello, A.
    Smartt, S. J.
    Elias-Rosa, N.
    Drake, A. J.
    Tomasella, L.
    Turatto, M.
    Harutyunyan, A.
    Taubenberger, S.
    Hachinger, S.
    Morales-Garoffolo, A.
    Chen, T. -W
    Djorgovski, S. G.
    Fraser, M.
    Gal-Yam, A.
    Inserra, C.
    Mazzali, P.
    Pumo, M. 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).
    Valenti, S.
    Young, D. R.
    Dennefeld, M.
    Le Guillou, L.
    Fleury, M.
    Leget, P. -F
    The supernova CSS121015:004244+132827: a clue for understanding superluminous supernovae2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 441, no 1, p. 289-303Article in journal (Refereed)
    Abstract [en]

    We present optical photometry and spectra of the superluminous Type II/IIn supernova (SN) CSS121015: 004244+132827 (z = 0.2868) spanning epochs from -30 d (rest frame) to more than 200 d after maximum. CSS121015 is one of the more luminous SNe ever found and one of the best observed. The photometric evolution is characterized by a relatively fast rise to maximum (similar to 40 d in the SN rest frame), and by a linear post-maximum decline. The light curve shows no sign of a break to an exponential tail. A broad Ha is first detected at similar to+40 d (rest frame). Narrow, barely resolved Balmer and [O III] 5007 angstrom lines, with decreasing strength, are visible along the entire spectral evolution. The spectra are very similar to other superluminous supernovae (SLSNe) with hydrogen in their spectrum, and also to SN 2005gj, sometimes considered Type Ia interacting with H-rich circumstellar medium. The spectra are also similar to a subsample of H-deficient SLSNe. We propose that the properties of CSS121015 are consistent with the interaction of the ejecta with a massive, extended, opaque shell, lost by the progenitor decades before the final explosion, although a magnetar-powered model cannot be excluded. Based on the similarity of CSS121015 with other SLSNe (with and without H), we suggest that the shocked-shell scenario should be seriously considered as a plausible model for both types of SLSN.

  • 23. Bersten, Melina C.
    et al.
    Benvenuto, Omar G.
    Nomoto, Ken'ichi
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Folatelli, Gaston
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Benetti, Stefano
    Botticella, Maria Teresa
    Fraser, Morgan
    Kotak, Rubina
    Maeda, Keiichi
    Ochner, Paolo
    Tomasella, Lina
    THE TYPE IIb SUPERNOVA 2011dh FROM A SUPERGIANT PROGENITOR2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 757, no 1, article id 31Article in journal (Refereed)
    Abstract [en]

    A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star-with R similar to 200 R-circle dot-is needed to reproduce the early light curve (LC) of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star. From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be approximate to 2 M-circle dot, the explosion energy to be E = (6-10) x 10(50) erg, and the Ni-56 mass to be approximately 0.06 M-circle dot. The progenitor star was composed of a helium core of 3-4 M-circle dot and a thin hydrogen-rich envelope of approximate to 0.1M(circle dot) with a main-sequence mass estimated to be in the range of 12-15 M-circle dot. Our models rule out progenitors with helium-core masses larger than 8 M-circle dot, which correspond to M-ZAMS greater than or similar to 25M(circle dot). This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

  • 24. Betoule, M.
    et al.
    Kessler, R.
    Guy, J.
    Mosher, J.
    Hardin, D.
    Biswas, R.
    Astier, P.
    El-Hage, P.
    Konig, M.
    Kuhlmann, S.
    Marriner, J.
    Pain, R.
    Regnault, N.
    Balland, C.
    Bassett, B. A.
    Brown, P. J.
    Campbell, H.
    Carlberg, R. G.
    Cellier-Holzern, F.
    Cinabro, D.
    Conley, A.
    D'Andrea, C. B.
    DePoy, D. L.
    Doi, M.
    Ellis, R. S.
    Fabbro, S.
    Filippenko, A. V.
    Foley, R. J.
    Frieman, J. A.
    Fouchez, D.
    Galbany, L.
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gupta, R. R.
    Hill, G. J.
    Hlozek, R.
    Hogan, C. J.
    Hook, I. M.
    Howell, D. A.
    Jha, S. W.
    Le Guillou, L.
    EGENLeloudas, G.
    Lidrnan, C.
    Marshall, J. L.
    Moeller, A.
    Mourao, A. M.
    Neveu, J.
    Nichol, R.
    Olmstead, M. D.
    Palanque-Delabrouille, N.
    Perlinutter, S.
    Prieto, J. L.
    Pritchet, C. J.
    Richinond, M.
    Riess, A. G.
    Ruhlmann-Kleider, V.
    Sako, M.
    Sehahmaneche, K.
    Schneider, D. P.
    Smith, M.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sullivan, M.
    Walton, N. A.
    Wheeler, C. J.
    Improved cosmological constraints from a joint analysis of the SDSS-II and SNLS supernova samples2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 568, p. A22-Article in journal (Refereed)
    Abstract [en]

    Aims. We present cosmological constraints from a joint analysis of type la supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations. The dataset includes several low-redshift samples (z < 0.1), all three seasons from the SDSS-11 (0.05 < z < 0.4), and three years from SNLS (0.2 < z < 1), and it totals 740 spectroscopically confirmed type la supernovae with high quality light curves. Methods. We followed the methods and assumptions of the SNLS three-year data analysis except for the following important improvements: I) the addition of the full SDSS-II spectroscopically-confirmed SN la sample in both the training of the SALT2 light-curve model and in the Hubble diagram analysis (374 SNe); 2) intercalibration of the SNLS and SDSS surveys and reduced systematic uncertainties in the photometric calibration, performed blindly with respect to the cosmology analysis; and 3) a thorough investigation of systematic errors associated with the SALT2 modeling of SN la light curves. Results. We produce recalibrated SN la light curves and associated distances for the SDSS-II and SNLS samples. The large SOSS-II sample provides an effective, independent, low -z anchor for the Hubble diagram and reduces the systematic error from calibration systematics in the low -z SN sample. For a flat ACDM cosmology, we find Omega(m), = 0.295 0.034 (stat+sys), a value consistent with the most recent cosmic microwave background (CMB) measurement from the Planck and WMAP experiments. Our result is 1.8 sigma (stat+sys) different than the previously published result of SNLS three-year data. The change is due primarily to improvements in the SNLS photometric calibration. When combined with CMB constraints, we measure a constant dark energy equation of state parameter omega = -1.018 +/- 0,057 (sral+sys) for a fiat universe. Adding baryon acoustic oscillation distance measurements gives similar constraints: omega = 59 -1.027 0.055. Our supernova measurements provide the most stringent constraints to date on the nature of dark energy.

  • 25.
    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.

  • 26.
    Björnsson, Claes-Ingvar
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandberg, Andreas
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    The location of the Crab pulsar emission region: restrictions on synchrotron emission models2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 516, p. A65-Article in journal (Refereed)
    Abstract [en]

    Recent observations of the Crab pulsar show no evidence of a spectral break in the infrared regime. It is argued that the observations are consistent with a power-law spectrum in the whole observable infrared-optical range. This is taken as the starting point for evaluating of how self-consistent incoherent synchrotron models fare in a comparison with observations. Inclusion of synchrotron self-absorption proves important as does the restriction on the observed size of the emission region imposed by the relativistic beaming thought to define the pulse profile. It is shown that the observations can be used to derive two independent constraints on the distance from the neutron star to the emission region; in addition to a direct lower limit, an indirect measure is obtained from an upper limit to the magnetic field strength. Both of these limits indicate that the emission region is located at a distance considerably greater than the light cylinder radius. The implications of this result are discussed, and it is emphasized that, for standard incoherent synchrotron models to fit inside the light cylinder, rather special physical conditions need to be invoked.

  • 27. Blagorodnova, N.
    et al.
    Kotak, R.
    Polshaw, J.
    Kasliwal, M. M.
    Cao, Y.
    Cody, A. M.
    Doran, G. B.
    Elias-Rosa, N.
    Fraser, M.
    Fremling, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gonzalez-Fernandez, C.
    Harmanen, J.
    Jencson, J.
    Kankare, E.
    Kudritzki, R. -P.
    Kulkarni, S. R.
    Magnier, E.
    Manulis, I.
    Masci, F. J.
    Mattila, S.
    Nugent, P.
    Ochner, P.
    Pastorello, A.
    Reynolds, T.
    Smith, K.
    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).
    Terreran, G.
    Tomasella, L.
    Turatto, M.
    Vreeswijk, P. M.
    Wozniak, P.
    Zaggia, S.
    COMMON ENVELOPE EJECTION FOR A LUMINOUS RED NOVA IN M1012017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 834, no 2, article id 107Article in journal (Refereed)
    Abstract [en]

    We present the results of optical, near-infrared, and mid-infrared observations of M101 OT2015-1 (PSN J14021678+ 5426205), a luminous red transient in the Pinwheel galaxy (M101), spanning a total of 16 years. The light curve showed two distinct peaks with absolute magnitudes M-r <= -12.4 and M-r similar or equal to -12, on 2014 November 11 and 2015 February 17, respectively. The spectral energy distributions during the second maximum show a cool outburst temperature of approximate to 3700 K and low expansion velocities (approximate to -300 km s(-1)) for the H I, Ca II, Ba II, and K I lines. From archival data spanning 15-8 years before the outburst, we find a single source consistent with the optically discovered transient, which we attribute to being the progenitor; it has properties consistent with being an F-type yellow supergiant with L similar to 8.7 x 10(4) L-circle dot, T-eff approximate to 7000. K, and an estimated mass of M1= 18 +/- 1 M-circle dot. This star has likely just finished the H-burning phase in the core, started expanding, and is now crossing the Hertzsprung gap. Based on the combination of observed properties, we argue that the progenitor is a binary system, with the more evolved system overfilling the Roche lobe. Comparison with binary evolution models suggests that the outburst was an extremely rare phenomenon, likely associated with the ejection of the common envelope of a massive star. The initial mass of the primary fills the gap between the merger candidates V838 Mon (5-10 M-circle dot) and NGC. 4490-OT. (30M(circle dot)).

  • 28. Blondin, S
    et al.
    Andra, 3
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Andra, 27
    Time Dilation in Type Ia Supernova Spectra at High Redshift2008In: The Astrophysical Journal, Vol. 682, no 2, p. 724-736Article in journal (Refereed)
    Abstract [en]

    We present multiepoch spectra of 13 high-redshift Type Ia supernovae (SNe Ia) drawn from the literature, the ESSENCE and SNLS projects, and our own separate dedicated program on the ESO Very Large Telescope. We use the Supernova Identification (SNID) code of Blondin and Tonry to determine the spectral ages in the supernova rest frame. Comparison with the observed elapsed time yields an apparent aging rate consistent with the 1/(1+z) factor (where z is the redshift) expected in a homogeneous, isotropic, expanding universe. These measurements thus confirm the expansion hypothesis, while unambiguously excluding models that predict no time dilation, such as Zwicky's ``tired light'' hypothesis. We also test for power-law dependencies of the aging rate on redshift. The best-fit exponent for these models is consistent with the expected 1/(1+z) factor.

  • 29. Boles, T.
    et al.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Stritzinger, M.
    Hammer Holm, A.
    Jul Jensen, J.
    Paaske Drachmann, A.
    Juhl Hobert, M.
    Fynbo, J.
    Fraser, M.
    Wright, D.
    Kotak, R.
    Arcavi, I.
    Supernova 2012eg in NGC 1213 = Psn J03091697+38382072012Report (Other academic)