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  • 1. Bose, Subhash
    et al.
    Dong, Subo
    Kochanek, C. S.
    Pastorello, Andrea
    Katz, Boaz
    Bersier, David
    Andrews, Jennifer E.
    Prieto, J. L.
    Stanek, K. Z.
    Shappee, B. J.
    Smith, Nathan
    Kollmeier, Juna
    Benetti, Stefano
    Cappellaro, E.
    Chen, Ping
    Elias-Rosa, N.
    Milne, Peter
    Morales-Garoffolo, Antonia
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tomasella, L.
    Bilinski, Christopher
    Brimacombe, Joseph
    Frank, Stephan
    Holoien, T. W. -S.
    Kilpatrick, Charles D.
    Kiyota, Seiichiro
    Madore, Barry F.
    Rich, Jeffrey A.
    ASASSN-15nx: A Luminous Type II Supernova with a Perfect Linear Decline2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 862, no 2, article id 107Article in journal (Refereed)
    Abstract [en]

    We report a luminous Type II supernova, ASASSN-15nx, with a peak luminosity of M-v = -20 mag that is between those of typical core-collapse supernovae and super-luminous supernovae. The post-peak optical light curves show a long, linear decline with a steep slope of 2.5 mag (100 day)(-1) (i.e., an exponential decline in flux) through the end of observations at phase approximate to 260 day. In contrast, the light curves of hydrogen-rich supernovae (SNe II-P/L) always show breaks in their light curves at phase similar to 100 day, before settling onto Co-56 radioactive decay tails with a decline rate of about 1 mag (100 day)(-1). The spectra of ASASSN-15nx do not exhibit the narrow emission-line features characteristic of Type IIn SNe, which can have a wide variety of light-curve shapes usually attributed to strong interactions with a dense circumstellar medium (CSM). ASASSN-15nx has a number of spectroscopic peculiarities, including a relatively weak and triangular-shaped H alpha emission profile with no absorption component. The physical origin of these peculiarities is unclear, but the long and linear post-peak light curve without a break suggests a single dominant powering mechanism. Decay of a large amount of Ni-56 (M-Ni = 1.6 +/- 0.2 M-circle dot) can power the light curve of ASASSN-15nx, and the steep light-curve slope requires substantial gamma-ray escape from the ejecta, which is possible given a low-mass hydrogen envelope for the progenitor. Another possibility is strong CSM interactions powering the light curve, but the CSM needs to be sculpted to produce the unique light-curve shape and avoid producing SN IIn-like narrow emission lines.

  • 2. Dastidar, Raya
    et al.
    Misra, Kuntal
    Hosseinzadeh, G.
    Pastorello, A.
    Pumo, M. L.
    Valenti, S.
    McCully, C.
    Tomasella, L.
    Arcavi, I
    Elias-Rosa, N.
    Singh, Mridweeka
    Gangopadhyay, Anjasha
    Howell, D. A.
    Morales-Garoffolo, Antonia
    Zampieri, L.
    Kumar, Brijesh
    Turatto, M.
    Benetti, S.
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ochner, P.
    Sahu, D. K.
    Anupama, G. C.
    Pandey, S. B.
    SN 2015ba: a Type IIP supernova with a long plateau2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 479, no 2, p. 2421-2442Article in journal (Refereed)
    Abstract [en]

    We present optical photometry and spectroscopy from about a week after explosion to similar to 272 d of an atypical Type IIP supernova, SN 2015ba, which exploded in the edge-on galaxy IC 1029. SN 2015ba is a luminous event with an absolute V-band magnitude of -17.1 +/- 0.2 mag at 50 d since explosion and has a long plateau lasting for similar to 123 d. The distance to the SN is estimated to be 34.8 +/- 0.7 Mpc using the expanding photosphere and standard candle methods. High-velocity H Balmer components constant with time are observed in the late-plateau phase spectra of SN 2015ba, which suggests a possible role of circumstellar interaction at these phases. Both hydrodynamical and analytical modelling suggest a massive progenitor of SN 2015ba with a pre-explosion mass of 24-26 M-circle dot. However, the nebular spectra of SN 2015ba exhibit insignificant levels of oxygen, which is otherwise expected from a massive progenitor. This might be suggestive of the non-monotonical link between O-core masses and the zero-age main sequence mass of pre-supernova stars and/or uncertainties in the mixing scenario in the ejecta of supernovae.

  • 3. Fremling, C.
    et al.
    Ko, H.
    Dugas, A.
    Ergon, Mattias
    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).
    Bagdasaryan, 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).
    Belicki, J.
    Bellm, E.
    Blagorodnova, N.
    De, K.
    Dekany, R.
    Frederick, S.
    Gal-Yam, A.
    Goldstein, D. A.
    Golkhou, V. Z.
    Graham, M.
    Kasliwal, M.
    Kowalski, M.
    Kulkarni, S. R.
    Kupfer, T.
    Laher, R. R.
    Masci, F. J.
    Miller, A. A.
    Neill, J. D.
    Perley, D. A.
    Rebbapragada, U. D.
    Riddle, R.
    Rusholme, B.
    Schulze, S.
    Smith, R. M.
    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
    Yao, Y.
    ZTF18aalrxas: A Type IIb Supernova from a Very Extended Low-mass Progenitor2019In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 878, no 1, article id L5Article in journal (Refereed)
    Abstract [en]

    We investigate ZTF18aalrxas, a double-peaked Type IIb core-collapse supernova (SN) discovered during science validation of the Zwicky Transient Facility. ZTF18aalrxas was discovered while the optical emission was still rising toward the initial cooling peak (0.7 mag over 2 days). Our observations consist of multi-band (ultraviolet and optical) light curves (LCs), and optical spectra spanning from approximate to 0.7 to approximate to 480 days past the explosion. We use a Monte-Carlo based non-local thermodynamic equilibrium model that simultaneously reproduces both the Ni-56-powered bolometric LC and our nebular spectrum. This model is used to constrain the synthesized radioactive nickel mass (0.17 M-circle dot) and the total ejecta mass (1.7 M-circle dot) of the SN. The cooling emission is modeled using semi-analytical extended envelope models to constrain the progenitor radius (790-1050 R-circle dot) at the time of explosion. Our nebular spectrum shows signs of interaction with a dense circumstellar medium (CSM), and this spectrum is modeled and analyzed to constrain the amount of ejected oxygen (0.3-0.5 M-circle dot) and the total hydrogen mass (approximate to 0.15 M-circle dot) in the envelope of the progenitor. The oxygen mass of ZTF18aalrxas is consistent with a low (12-13 M-circle dot) zero-age main-sequence mass progenitor. The LCs and spectra of ZTF18aalrxas are not consistent with massive single-star SN Type IIb progenitor models. The presence of an extended hydrogen envelope of low mass, the presence of a dense CSM, the derived ejecta mass, and the late-time oxygen emission can all be explained in a binary model scenario.

  • 4. Hosseinzadeh, Griffin
    et al.
    Valenti, Stefano
    McCully, Curtis
    Howell, D. Andrew
    Arcavi, Iair
    Jerkstrand, Anders
    Guevel, David
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of California, USA; Steward Observatory, USA.
    Rui, Liming
    Mo, Jun
    Wang, Xiaofeng
    Huang, Fang
    Song, Hao
    Zhang, Tianmeng
    Itagaki, Koichi
    Short-lived Circumstellar Interaction in the Low-luminosity Type IIP SN 2016bkv2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 861, no 1, article id 63Article in journal (Refereed)
    Abstract [en]

    While interaction with circumstellar material is known to play an important role in Type. IIn supernovae (SNe), analyses of the more common SNe IIP and IIL have not traditionally included interaction as a significant power source. However, recent campaigns to observe SNe within days of explosion have revealed narrow emission lines of high-ionization species in the earliest spectra of luminous SNe II of all subclasses. These flash ionization features indicate the presence of a confined shell of material around the progenitor star. Here we present the first low-luminosity (LL) SN to show flash ionization features, SN 2016bkv. This SN peaked at M-V = -16 mag and has Ha expansion velocities under 1350 km s(-1) around maximum light, placing it at the faint/slow end of the distribution of SNe IIP (similar to SN 2005cs). The light-curve shape of SN 2016bkv is also extreme among SNe IIP. A very strong initial peak could indicate additional luminosity from circumstellar interaction. A very small fall from the plateau to the nickel tail indicates unusually large production of radioactive nickel compared to other LL SNe IIP. A comparison between nebular spectra of SN. 2016bkv and models raises the possibility that SN. 2016bkv is an electron-capture supernova.

  • 5. Li, Wenxiong
    et al.
    Wang, Xiaofeng
    Hu, Maokai
    Yang, Yi
    Zhang, Jujia
    Mo, Jun
    Chen, Zhihao
    Zhang, Tianmeng
    Benetti, Stefano
    Cappellaro, Enrico
    Elias-Rosa, Nancy
    Isern, Jordi
    Morales-Garoffolo, Antonia
    Huang, Fang
    Ochner, Paolo
    Pastorello, Andrea
    Reguitti, Andrea
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy.
    Terreran, Giacomo
    Tomasella, Lina
    Wang, Lifan
    Observations of Type Ia Supernova 2014J for Nearly 900 Days and Constraints on Its Progenitor System2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 882, no 1, article id 30Article in journal (Refereed)
    Abstract [en]

    We present extensive ground-based and Hubble Space Telescope (HST) photometry of the highly reddened, very nearby SN Ia 2014J in M82, covering the phases from 9 days before to about 900 days after the B-band maximum. SN 2014J is similar to other normal SNe Ia near the maximum light, but it shows flux excess in the B band in the early nebular phase. This excess flux emission can be due to light scattering by some structures of circum stellar materials located at a few 10(17) cm, consistent with a single-degenerate progenitor system or a double-degenerate progenitor system with mass outflows in the final evolution or magnetically driven winds around the binary system. At t similar to +300 to similar to +500 days past the B-band maximum, the light curve of SN 2014J shows a faster decline relative to the Ni-56 decay. That feature can be attributed to the significant weakening of the emission features around [Fe III] lambda 4700 and [Fe II] lambda 5200 rather than the positron escape, as previously suggested. Analysis of the HST images taken at t > 600 days confirms that the luminosity of SN 2014J maintains a flat evolution at the very late phase. Fitting the late-time pseudobolometric light curve with radioactive decay of Ni-56, Ni-57, and Fe-55 isotopes, we obtain the mass ratio Ni-57/Ni-56 as 0.035 +/- 0.011, which is consistent with the corresponding value predicted from the 2D and 3D delayed-detonation models. Combined with early-time analysis, we propose that delayed detonation through the single-degenerate scenario is most likely favored for SN 2014J.

  • 6.
    Nyholm, Anders
    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).
    Tartaglia, Leonardo
    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, Christoffer
    Blagorodnova, Nadia
    Filippenko, Alexei V.
    Gal-Yam, Avishay
    Howell, D. Andrew
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy.
    Kulkarni, Shrinivas R.
    Laher, Russ
    Leloudas, Giorgos
    Masci, Frank
    Kasliwal, Mansi M.
    Morå, Knut
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Moriya, Takashi J.
    Ofek, Eran O.
    Papadogiannakis, Seméli
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Quimby, Robert
    Rebbapragada, Umaa
    Schulze, Steve
    Type IIn supernova light-curve properties measured from an untargeted survey sampleManuscript (preprint) (Other academic)
    Abstract [en]

    We present a sample of supernovae Type IIn (SNe IIn) from the untargeted, magnitude-limited surveys of the Palomar Transient Factory (PTF) and its successor, iPTF. SNe IIn found and followed by the PTF/iPTF were used to select a sample of 42 events with useful constraints on the rise times as well as with available post-peak photometry. The SNe were discovered in 2009-2016 and have at least one low-resolution classification spectrum, as well as photometry from the P48 and P60 telescopes at Palomar Observatory. We study the light-curve properties of these SNe IIn using spline fits (for the peak and the declining portion) and template matching (for the rising portion). We find that the typical rise times are divided into fast and slow risers as 20±8 d and 50±15 d, respectively. The decline rates could possibly be divided into two groups, but this division has weak statistical significance. We find no significant correlation between the peak luminosity of SNe IIn and their rise times, but the more luminous SNe IIn are generally found to be more durable and the slowly rising SNe IIn are generally found to be slowly declining. The SNe in our sample were hosted by galaxies of absolute magnitude −22≲Mg≲−13 mag. The K-corrections at light-curve peak of the SNe in our sample are found to be within 0.2 mag for the observer's frame r-band, for SNe IIn at redshifts z<0.25. Applying K-corrections and including also ostensibly ``superluminous'' SNe IIn, we find that the peak magnitudes are Mrpeak=−19.18±1.32mag. We conclude that the occurrence of conspicuous light-curve bumps in SNe IIn, such as in iPTF13z, is limited to 1.4+14.6−1.0% of the SNe IIn. We also investigate a possible subtype of SNe IIn with a fast rise to a ≳50 d plateau followed by a slow, linear decline.

  • 7. Pastorello, A.
    et al.
    Chen, T. -W.
    Cai, Y. -Z.
    Morales-Garoffolo, A.
    Cano, Z.
    Mason, E.
    Barsukova, E. A.
    Benetti, S.
    Berton, M.
    Bose, S.
    Bufano, F.
    Callis, E.
    Cannizzaro, G.
    Cartier, R.
    Chen, Ping
    Dong, Subo
    Dyrbye, S.
    Elias-Rosa, N.
    Floers, A.
    Fraser, M.
    Geier, S.
    Goranskij, V. P.
    Kann, D. A.
    Kuncarayakti, H.
    Onori, F.
    Reguitti, A.
    Reynolds, T.
    Rivero Losada, Illa
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    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).
    Schweyer, T.
    Smartt, S. J.
    Tatarnikov, A. M.
    Valeev, A. F.
    Vogl, C.
    Wevers, T.
    de Ugarte Postigo, A.
    Izzo, L.
    Inserra, C.
    Kankare, E.
    Maguire, K.
    Smith, K. W.
    Stalder, B.
    Tartaglia, L.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Thone, C. C.
    Valerin, G.
    Young, D. R.
    The evolution of luminous red nova AT 2017jfs in NGC 44702019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 625, article id L8Article in journal (Refereed)
    Abstract [en]

    We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT 2017jfs. At peak, the object reaches an absolute magnitude of M-g = 15.46 +/- 0.15 mag and a bolometric luminosity of 5.5 x 10(41) erg s(-1). Its light curve has the double-peak shape typical of luminous red novae (LRNe), with a narrow first peak bright in the blue bands, while the second peak is longer-lasting and more luminous in the red and near-infrared (NIR) bands. During the first peak, the spectrum shows a blue continuum with narrow emission lines of H and Fe II. During the second peak, the spectrum becomes cooler, resembling that of a K-type star, and the emission lines are replaced by a forest of narrow lines in absorption. About 5 months later, while the optical light curves are characterized by a fast linear decline, the NIR ones show a moderate rebrightening, observed until the transient disappears in solar conjunction. At these late epochs, the spectrum becomes reminiscent of that of M-type stars, with prominent molecular absorption bands. The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust. We propose that the object is a common-envelope transient, possibly the outcome of a merging event in a massive binary, similar to NGC4490-2011OT1.

  • 8. Pastorello, A.
    et al.
    Reguitti, A.
    Morales-Garoffolo, A.
    Cano, Z.
    Prentice, S. J.
    Hiramatsu, D.
    Burke, J.
    Kankare, E.
    Kotak, R.
    Reynolds, T.
    Smartt, S. J.
    Bose, S.
    Chen, P.
    Congiu, E.
    Dong, S.
    Geier, S.
    Gromadzki, M.
    Hsiao, E. Y.
    Kumar, S.
    Ochner, P.
    Pignata, G.
    Tomasella, L.
    Wang, L.
    Arcavi, I
    Ashall, C.
    Callis, E.
    de Ugarte Postigo, A.
    Fraser, M.
    Hosseinzadeh, G.
    Howell, D. A.
    Inserra, C.
    Kann, D. A.
    Mason, E.
    Mazzali, P. A.
    McCully, C.
    Rodriguez, O.
    Phillips, M. M.
    Smith, K. W.
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Thone, C. C.
    Wevers, T.
    Young, D. R.
    Pumo, M. L.
    Lowe, T. B.
    Magnier, E. A.
    Wainscoat, R. J.
    Waters, C.
    Wright, D. E.
    A luminous stellar outburst during a long-lasting eruptive phase first, and then SN IIn 2018cnf2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 628, article id A93Article in journal (Refereed)
    Abstract [en]

    We present the results of the monitoring campaign of the Type IIn supernova (SN) 2018cnf (a.k.a. ASASSN-18mr). It was discovered about ten days before the maximum light (on MJD = 58 293.4 +/- 5.7 in the V band, with M-V = -18.13 +/- 0.15 mag). The multiband light curves show an immediate post-peak decline with some minor luminosity fluctuations, followed by a flattening starting about 40 days after maximum. The early spectra are relatively blue and show narrow Balmer lines with P Cygni profiles. Additionally, Fe II, O I, He I, and Ca II are detected. The spectra show little evolution with time and with intermediate-width features becoming progressively more prominent, indicating stronger interaction of the SN ejecta with the circumstellar medium. The inspection of archival images from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey has revealed a variable source at the SN position with a brightest detection in December 2015 at M-r = -14.66 +/- 0.17 mag. This was likely an eruptive phase from the massive progenitor star that started from at least mid-2011, and that produced the circumstellar environment within which the star exploded as a Type IIn SN. The overall properties of SN 2018cnf closely resemble those of transients such as SN 2009ip. This similarity favours a massive hypergiant, perhaps a luminous blue variable, as progenitor for SN 2018cnf.

  • 9. Prentice, S. J.
    et al.
    Ashall, C.
    Mazzali, P. A.
    Zhang, J. -J.
    James, P. A.
    Wang, X. -F.
    Vinko, J.
    Percival, S.
    Short, L.
    Piascik, A.
    Huang, F.
    Mo, J.
    Rui, L. -M.
    Wang, J. -G.
    Xiang, D. -F.
    Xin, Y. -X.
    Yi, W. -M.
    Yu, X. -G.
    Zhai, Q.
    Zhang, T. -M.
    Hosseinzadeh, G.
    Howell, D. A.
    McCully, C.
    Valenti, S.
    Cseh, B.
    Hanyecz, O.
    Kriskovics, L.
    Pal, A.
    Sarneczky, K.
    Sodor, A.
    Szakats, R.
    Szekely, P.
    Varga-Verebelyi, E.
    Vida, K.
    Bradac, M.
    Reichart, D. E.
    Sand, D.
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    SN 2016coi/ASASSN-16fp: an example of residual helium in a type Ic supernova?2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 478, no 3, p. 4162-4192Article in journal (Refereed)
    Abstract [en]

    The optical observations of Ic-4 supernova (SN) 2016coi/ASASSN-16fp, from similar to 2 to similar to 450 d after explosion, are presented along with analysis of its physical properties. The SN shows the broad lines associated with SNe Ic-3/4 but with a key difference. The early spectra display a strong absorption feature at similar to 5400 angstrom which is not seen in other SNe Ic-3/4 at this epoch. This feature has been attributed to He I in the literature. Spectral modelling of the SN in the early photospheric phase suggests the presence of residual He in a C/O dominated shell. However, the behaviour of the He I lines is unusual when compared with He-rich SNe, showing relatively low velocities and weakening rather than strengthening over time. The SN is found to rise to peak similar to 16 d after core-collapse reaching a bolometric luminosity of L-p similar to 3 x 10(42) erg s(-1). Spectral models, including the nebular epoch, show that the SN ejected 2.5-4M(circle dot) of material, with similar to 1.5M(circle dot) below 5000 km s(-1), and with a kinetic energy of (4.5-7) x 10(51) erg. The explosion synthesized similar to 0.14M(circle dot) of Ni-56. There are significant uncertainties in E(B - V)(host) and the distance, however, which will affect L-p and M-Ni. SN 2016coi exploded in a host similar to the Large Magellanic Cloud (LMC) and away from star-forming regions. The properties of the SN and the host-galaxy suggest that the progenitor had M-ZAMS of 23-28M(circle dot) and was stripped almost entirely down to its C/O core at explosion.

  • 10. Sand, D. J.
    et al.
    Graham, M. L.
    Botyanszki, J.
    Hiramatsu, D.
    McCully, C.
    Valenti, S.
    Hosseinzadeh, G.
    Howell, D. A.
    Burke, J.
    Cartier, R.
    Diamond, T.
    Hsiao, E. Y.
    Jha, S. W.
    Kasen, D.
    Kumar, S.
    Marion, G. H.
    Suntzeff, N.
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wheeler, J. C.
    Wyatt, S.
    Nebular Spectroscopy of the Blue Bump Type Ia Supernova 2017cbv2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 863, no 1, article id 24Article in journal (Refereed)
    Abstract [en]

    We present nebular phase optical and near-infrared spectroscopy of the Type Ia supernova (SN) 2017cbv. The early light curves of SN 2017cbv showed a prominent blue bump in the U, B, and g bands lasting for similar to 5 days. One interpretation of the early light curve is that the excess blue light is due to shocking of the SN ejecta against a nondegenerate companion star-a signature of the single degenerate scenario. If this is the correct interpretation, the interaction between the SN ejecta and the companion star could result in significant Ha (or helium) emission at late times, possibly along with other species, depending on the companion star and its orbital separation. A search for Ha emission in our +302 d spectrum yields a nondetection, with a L-H alpha < 8.0 x 10(35) erg s(-1) (given an assumed distance of D = 12.3 Mpc), which we verified by implanting simulated Ha emission into our data. We make a quantitative comparison to models of swept-up material stripped from a nondegenerate companion star and limit the mass of hydrogen that might remain undetected to M-H < 1 x 10(-4) M-circle dot. A similar analysis of helium star related lines yields a M-He < 5 x 10(-4) M-circle dot. Taken at face value, these results argue against a nondegenerate H- or He-rich companion in Roche lobe overflow as the progenitor of SN 2017cbv. Alternatively, there could be weaknesses in the envelope-stripping and radiative transfer models necessary to interpret the strong H and He flux limits.

  • 11.
    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).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Arcavi, I.
    Fremling, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). California Institute of Technology, USA.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Burke, J.
    Cenko, S. B.
    Andersen, O.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Andreoni, I.
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Blagorodova, N.
    Brink, T. G.
    Filippenko, A. V.
    Gal-Yam, A.
    Hiramatsu, D.
    Hosseinzadeh, G.
    Howell, D. A.
    de Jaeger, 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).
    McCully, C.
    Perley, D. A.
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Terreran, G.
    Valenti, S.
    Wang, X.
    Late-time observations of the extraordinary Type II supernova iPTF14hls2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 621, article id A30Article in journal (Refereed)
    Abstract [en]

    Aims. We study iPTF14hls, a luminous and extraordinary long-lived Type II supernova, which lately has attracted much attention and disparate interpretation.

    Methods. We have presented new optical photometry that extends the light curves up to more than three years past discovery. We also obtained optical spectroscopy over this period, and furthermore present additional space-based observations using Swift and HST.

    Results. After an almost constant luminosity for hundreds of days, the later light curve of iPTF14hls finally fades and then displays a dramatic drop after about 1000 d, but the supernova is still visible at the latest epochs presented. The spectra have finally turned nebular, and our very last optical spectrum likely displays signatures from the deep and dense interior of the explosion. A high-resolution HST image highlights the complex environment of the explosion in this low-luminosity galaxy.

    Conclusions. We provide a large number of additional late-time observations of iPTF14hls, which are (and will continue to be) used to assess the many different interpretations for this intriguing object. In particular, the very late (+1000 d) steep decline of the optical light curve is difficult to reconcile with the proposed central engine models. The lack of very strong X-ray emission, and the emergence of intermediate-width emission lines including [S II] that we propose originate from dense, processed material in the core of the supernova ejecta, are also key observational tests for both existing and future models.

  • 12. Yang, Sheng
    et al.
    Sand, David J.
    Valenti, Stefano
    Cappellaro, Enrico
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Department of Astronomy/Steward Observatory, USA.
    Wyatt, Samuel
    Corsi, Alessandra
    Reichart, Daniel E.
    Haislip, Joshua
    Kouprianov, Vladimir
    Optical Follow-up of Gravitational-wave Events during the Second Advanced LIGO/VIRGO Observing Run with the DLT40 Survey2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 875, no 1, article id 59Article in journal (Refereed)
    Abstract [en]

    We describe the gravitational-wave (GW) follow-up strategy and subsequent results of the Distance Less Than 40 Mpc survey (DLT40) during the second science run (O2) of the Laser Interferometer Gravitational-wave Observatory and Virgo collaboration (LVC). Depending on the information provided in the GW alert together with the localization map sent by the LVC, DLT40 would respond promptly to image the corresponding galaxies selected by our ranking algorithm in order to search for possible electromagnetic (EM) counterparts in real time. During the LVC O2 run, DLT40 followed 10 GW triggers, observing between similar to 20 and 100 galaxies within the GW localization area of each event. From this campaign, we identified two real transient sources within the GW localizations with an appropriate on-source time-one was an unrelated SN Ia (SN 2017cbv), and the other was the optical kilonova, AT 2017fgo/SSS17a/DLT17ck, associated with the binary neutron star (BNS) coalescence GW170817 (a.k.a gamma-ray burst GRB 170817A). We conclude with a discussion of the DLT40 survey's plans for the upcoming LVC O3 run, which include expanding our galaxy search fields out to D approximate to 65 Mpc to match the LVC's planned three-detector sensitivity for BNS mergers.

  • 13. Zhang, Kaicheng
    et al.
    Wang, Xiaofeng
    Zhang, Jujia
    Zhang, Tianmeng
    Benetti, S.
    Elias-Rosa, N.
    Huang, Fang
    Lin, Han
    Li, Linyi
    Li, Wenxiong
    Ochner, P.
    Pastorello, A.
    Rui, Liming
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tomasella, L.
    Siviero, A.
    Munari, U.
    Terreran, G.
    Song, Hao
    Taubenberger, S.
    Wheeler, J. Craig
    Xiang, Danfeng
    Zhao, Xulin
    Li, Hongbin
    Bai, Jinming
    Jiang, Xiaojun
    Shi, Jianrong
    Wu, Zhenyu
    SN 2014J in M82: new insights on the spectral diversity of Type Ia supernovae2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 481, no 1, p. 878-893Article in journal (Refereed)
    Abstract [en]

    We present extensive spectroscopic observations for one of the closest Type Ia supernovae (SNe Ia), SN 2014J discovered in M82, ranging from 10.4 d before to 473.2 d after B-band maximum light. The diffuse interstellar band features detected in a high-resolution spectrum allow an estimate of line-of-sight extinction as A(v) similar to 1.9 +/- 0.6 mag. Spectroscopically, SN 2014J can be put into the high-velocity (HV) subgroup in Wang's classification with a velocity of Si II lambda 6355 at maximum light of upsilon(0) = 1.22 +/- 0.01 x 10(4) km s(-1) but has a low velocity gradient (LVG, following Benetti's classification) of (v) over bar = 41 +/- 2 km s(-1) d(-1), which is inconsistent with the trend that HV SNe Ia generally have larger velocity gradients. We find that the HV SNe Ia with LVGs tend to have relatively stronger Si III (at similar to 4400 angstrom) absorptions in early spectra, larger ratios of S II lambda 5468 to S II lambda 5640, and weaker Si II 5972 absorptions compared to their counterparts with similar velocities but high velocity gradients. This shows that the HV+ LVG subgroup of SNe Ia may have intrinsically higher photospheric temperature, which indicates that their progenitors may experience more complete burning in the explosions relative to the typical HV SNe Ia.

  • 14. Zhang, Tianmeng
    et al.
    Wang, Xiaofeng
    Zhao, Xulin
    Xu, Dong
    Reguitti, Andrea
    Zhang, Jujia
    Pastorello, Andrea
    Tomasella, Lina
    Ochner, Paolo
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy.
    Benetti, Stefano
    Turatto, Massimo
    Harutyunyan, Avet
    Elias-Rosa, Nancy
    Huang, Fang
    Zhang, Kaicheng
    Chen, Juncheng
    Jiang, Zhaoji
    Ma, Jun
    Nie, Jundan
    Peng, Xiyan
    Zhou, Xu
    Zhou, Zhimin
    Zou, Hu
    Observations of a Fast-expanding and UV-bright Type Ia Supernova SN 2013gs2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 872, no 1, article id 14Article in journal (Refereed)
    Abstract [en]

    In this paper, we present extensive optical and ultraviolet (UV) observations of the type Ia supernova (SN Ia) 2013gs discovered during the Tsinghua-NAOC Transient Survey. The photometric observations in the optical show that the light curves of SN 2013gs are similar to those of normal SNe Ia, with an absolute peak magnitude of M-B = -19.25 +/- 0.15 mag and a post-maximum decline rate Delta m(15)(B) = 1.00 +/- 0.05 mag. Gehrels Swift Ultr-Violet/Optical Telescope observations indicate that SN 2013gs shows unusually strong UV emission (especially in the uvw1 band) at around the maximum light (M-uvw1 similar to -18.9 mag). The SN is characterized by relatively weak Fe II III absorptions at similar to 5000 angstrom in the early spectra and a larger expansion velocity (v(Si) similar to 13,000 km s(-1) around the maximum light) than the normal-velocity SNe Ia. We discuss the relation between the uvw1 - v color and some observables, including Si II velocity, line strength of Si II lambda 6355 and Fe II/III lines, and Delta m(15)(B). Compared to other fast-expanding SNe Ia, SN 2013gs exhibits Si and Fe absorption lines with similar strength and bluer uvw1 - v color. We briefly discussed the origin of the observed UV dispersion of SNe Ia.

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