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  • 1. 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.

  • 2. Blagorodnova, N.
    et al.
    Cenko, S. B.
    Kulkarni, S. R.
    Arcavi, I.
    Bloom, J. S.
    Duggan, G.
    Filippenko, A. V.
    Fremling, C.
    Horesh, A.
    Hosseinzadeh, G.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Levan, A.
    Masci, F. J.
    Nugent, P. E.
    Pasham, D. R.
    Veilleux, S.
    Walters, R.
    Yan, L.
    Zheng, W.
    The Broad Absorption Line Tidal Disruption Event iPTF15af: Optical and Ultraviolet Evolution2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 873, no 1, article id 92Article in journal (Refereed)
    Abstract [en]

    We present multiwavelength observations of the tidal disruption event (TDE) iPTF15af, discovered by the intermediate Palomar Transient Factory survey at redshift z = 0.07897. The optical and ultraviolet (UV) light curves of the transient show a slow decay over 5 months, in agreement with previous optically discovered TDEs. It also has a comparable blackbody peak luminosity of L-peak approximate to 1.5 x 10(44) erg s(-1). The inferred temperature from the optical and UV data shows a value of (3-5) x 10(4) K. The transient is not detected in X-rays up to L-X < 3 x 10(42) erg s(-1) within the first 5 months after discovery. The optical spectra exhibit two distinct broad emission lines in the He II region, and at later times also H alpha emission. Additionally, emission from [N III] and [O III] is detected, likely produced by the Bowen fluorescence effect. UV spectra reveal broad emission and absorption lines associated with high-ionization states of N V, C IV, Si IV, and possibly P V. These features, analogous to those of broad absorption line quasars (BAL QSOs), require an absorber with column densities N-H > 10(23) cm(-2). This optically thick gas would also explain the nondetection in soft X-rays. The profile of the absorption lines with the highest column density material at the largest velocity is opposite that of BAL QSOs. We suggest that radiation pressure generated by the TDE flare at early times could have provided the initial acceleration mechanism for this gas. Spectral UV line monitoring of future TDEs could test this proposal.

  • 3.
    Fremling, Christoffer
    et al.
    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.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kasliwal, M. M.
    Kulkarni, S. R.
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    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).
    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
    Cenko, S. B.
    Clubb, K.
    De Cia, A.
    Duggan, G.
    Filippenko, A.
    Gal-Yam, A.
    Graham, M. L.
    Horesh, A.
    Hosseinzadeh, G.
    Howell, D. A.
    Kuesters, D.
    Lunnan, Ragnhild
    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.
    Matheson, T.
    Nugent, P. E.
    Perley, D. A.
    Quimby, R. M.
    Saunders, C.
    Oxygen and helium in stripped-envelope supernovae2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 618, article id A37Article in journal (Refereed)
    Abstract [en]

    We present an analysis of 507 spectra of 173 stripped-envelope (SE) supernovae (SNe) discovered by the untargeted Palomar Transient Factory (PTF) and intermediate PTF (iPTF) surveys. Our sample contains 55 Type IIb SNe (SNe 45 Type Ib SNe (SNe IIb), 56 Type Ic SNe (SNe Ic), and 17 Type Ib/c SNe (SNe Ib/c). We have compared the SE SN subtypes via measurements of the pseudo-equivalent widths (pEWs) and velocities of the He I lambda lambda 5876, 7065 and O I lambda 7774 absorption lines. Consistent with previous work, we find that SNe Ic show higher pEWs and velocities in O I lambda 7774 compared to SNe IIb and Ib. The pEWs of the He I lambda lambda 5876, 7065 lines are similar in SNe Ib and IIb after maximum light. The He I lambda lambda 5876, 7065 velocities at maximum light are higher in SNe Ib compared to SNe IIb. We identify an anticorrelation between the He I lambda 7065 pEW and O I lambda 7774 velocity among SNe IIb and Ib. This can be interpreted as a continuum in the amount of He present at the time of explosion. It has been suggested that SNe Ib and Ic have similar amounts of He, and that lower mixing could be responsible for hiding He in SNe Ic. However, our data contradict this mixing hypothesis. The observed difference in the expansion rate of the ejecta around maximum light of SNe Ic (V-m root 2E(k)/M-ej approximate to 15 000 km s(-1)) and SNe Ib (V-m approximate to 9000 km s(-1)) would imply an average He mass difference of similar to 1.4 M-circle dot, if the other explosion parameters are assumed to be unchanged between the SE SN subtypes. We conclude that SNe Ic do not hide He but lose He due to envelope stripping.

  • 4.
    Fremling, Christoffer
    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).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fraser, M.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Valenti, S.
    Jerkstrand, A.
    Arcavi, I.
    Bufano, F.
    Elias Rosa, N.
    Filippenko, A. V.
    Fox, D.
    Gal-Yam, A.
    Howell, D. A.
    Kotak, R.
    Mazzali, P.
    Milisavljevic, D.
    Nugent, P. E.
    Nyholm, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pian, E.
    Smartt, S.
    PTF12os and iPTF13bvn. Two stripped-envelope supernovae from low-mass progenitors in NGC 58062016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 593, article id A68Article in journal (Refereed)
    Abstract [en]

    Context. We investigate two stripped-envelope supernovae (SNe) discovered in the nearby galaxy NGC 5806 by the (intermediate) Palomar Transient Factory [(i)PTF]. These SNe, designated PTF12os/SN 2012P and iPTF13bvn, exploded within ~520 days of one another at a similar distance from the host-galaxy center. We classify PTF12os as a Type IIb SN based on our spectral sequence; iPTF13bvn has previously been classified as Type Ib having a likely progenitor with zero age main sequence (ZAMS) mass below ~17 M. Because of the shared and nearby host, we are presented with a unique opportunity to compare these two SNe.

    Aims. Our main objective is to constrain the explosion parameters of iPTF12os and iPTF13bvn, and to put constraints on the SN progenitors. We also aim to spatially map the metallicity in the host galaxy, and to investigate the presence of hydrogen in early-time spectra of both SNe.

    Methods. We present comprehensive datasets collected on PTF12os and iPTF13bvn, and introduce a new automatic reference-subtraction photometry pipeline (FPipe) currently in use by the iPTF. We perform a detailed study of the light curves (LCs) and spectral evolution of the SNe. The bolometric LCs are modeled using the hydrodynamical code hyde. We analyze early spectra of both SNe to investigate the presence of hydrogen; for iPTF13bvn we also investigate the regions of the Paschen lines in infrared spectra. We perform spectral line analysis of helium and iron lines to map the ejecta structure of both SNe. We use nebular models and late-time spectroscopy to constrain the ZAMS mass of the progenitors. We also perform image registration of ground-based images of PTF12os to archival HST images of NGC 5806 to identify a potential progenitor candidate.

    Results. We find that our nebular spectroscopy of iPTF13bvn remains consistent with a low-mass progenitor, likely having a ZAMS mass of ~12M. Our late-time spectroscopy of PTF12os is consistent with a ZAMS mass of ~15M. We successfully identify a source in pre-explosion HST images coincident with PTF12os. The colors and absolute magnitude of this object are consistent between pre-explosion and late-time HST images, implying it is a cluster of massive stars. Our hydrodynamical modeling suggests that the progenitor of PTF12os had a compact He core with a mass of 3.25+ 0.77-0.56M at the time of the explosion, which had a total kinetic energy of 0.54+ 0.41-0.25 × 1051 erg and synthesized 0.063+ 0.020-0.011M of strongly mixed  56Ni. Spectral comparisons to the Type IIb SN 2011dh indicate that the progenitor of PTF12os was surrounded by a thin hydrogen envelope with a mass lower than 0.02M. We also find tentative evidence that the progenitor of iPTF13bvn could have been surrounded by a small amount of hydrogen prior to the explosion. This result is supported by possible weak signals of hydrogen in both optical and infrared spectra.

  • 5. Hosseinzadeh, Griffin
    et al.
    Arcavi, Iair
    Valenti, Stefano
    McCully, Curtis
    Howell, D. Andrew
    Johansson, Joel
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pastorello, Andrea
    Benetti, Stefano
    Cao, Yi
    Cenko, S. Bradley
    Clubb, Kelsey I.
    Corsi, Alessandra
    Duggan, Gina
    Elias-Rosa, Nancy
    Filippenko, Alexei V.
    Fox, Ori 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).
    Horesh, Assaf
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kasliwal, Mansi
    Marion, G. H.
    Ofek, Eran
    Sand, David
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zheng, WeiKang
    Fraser, Morgan
    Gal-Yam, Avishay
    Inserra, Cosimo
    Laher, Russ
    Masci, Frank
    Rebbapragada, Umaa
    Smartt, Stephen
    Smith, Ken W.
    Sullivan, Mark
    Surace, Jason
    Woźniak, Przemek
    Type Ibn Supernovae Show Photometric Homogeneity and Spectral Diversity at Maximum Light2017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 836, no 2, article id 158Article in journal (Refereed)
    Abstract [en]

    Type Ibn supernovae (SNe) are a small yet intriguing class of explosions whose spectra are characterized by low-velocity helium emission lines with little to no evidence for hydrogen. The prevailing theory has been that these are the core-collapse explosions of very massive stars embedded in helium-rich circumstellar material (CSM). We report optical observations of six new SNe Ibn: PTF11rfh, PTF12ldy, iPTF14aki, iPTF15ul, SN 2015G, and iPTF15akq. This brings the sample size of such objects in the literature to 22. We also report new data, including a near-infrared spectrum, on the Type Ibn SN 2015U. In order to characterize the class as a whole, we analyze the photometric and spectroscopic properties of the full Type Ibn sample. We find that, despite the expectation that CSM interaction would generate a heterogeneous set of light curves, as seen in SNe IIn, most Type Ibn light curves are quite similar in shape, declining at rates around 0.1 mag day(-1) during the first month after maximum light, with a few significant exceptions. Early spectra of SNe Ibn come in at least two varieties, one that shows narrow P Cygni lines and another dominated by broader emission lines, both around maximum light, which may be an indication of differences in the state of the progenitor system at the time of explosion. Alternatively, the spectral diversity could arise from viewing-angle effects or merely from a lack of early spectroscopic coverage. Together, the relative light curve homogeneity and narrow spectral features suggest that the CSM consists of a spatially confined shell of helium surrounded by a less dense extended wind.

  • 6.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Looking for the high-mass progenitors of stripped-envelope supernovae2018Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Stripped-envelope supernovae were thought to be the explosions of very massive stars (& 20 M) that lost their outer layers of hydrogen and/or helium in strong stellar winds. However, recent studies have highlighted that most stripped-envelope supernovae seem to be arising from rela- tively lower-mass progenitor stars in the 12 20 M(sun) range, creating a mystery about the fate of the higher-mass stars. In this licentiate thesis, we review our knowledge of stripped-envelope supernovae, and present the astrophysical problem of their missing high-mass progenitors. The thesis focuses on observations of unique and rare stripped-envelope supernovae classified with modern optical surveys such as the intermediate Palomar Transient Factory (iPTF) and the Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO). In these surveys we have discovered stripped-envelope supernovae with long-lasting broad lightcurves, which are thought to be a marker for highly massive (& 20 M[sun]) progenitor stars. Despite this exciting association, there are only a handful of existing examples of stripped- envelope supernovae with broad lightcurves published in the literature, not numerous enough to account for the missing high-mass stars.

    During our efforts, the first object we focused on was OGLE-2014-SN-131, a long-lasting supernova in the southern sky initially classified by PESSTO. We re-classified it as a supernova Type Ibn interacting with a helium-rich circumstellar environment. Unlike all other Type Ibn’s in the literature, OGLE-2014-SN-131 was found to have a long rise-time and large lightcurve broadness. By modeling its bolometric lightcurve, we concluded that OGLE-2014-SN-131 must have had an unusually massive progenitor star. Furthermore, since an ordinary radioactive- decay model could not reproduce the lightcurve, we investigated both a magnetar and circum- stellar interaction as potential powering scenarios and favored the latter due to the signatures of interaction present in the spectra. Next, we looked for similar objects in the supernova dataset of the iPTF, which contains over 200 stripped-envelope supernovae. Searching in a sub-sample of 100 well-observed supernovae, we identified 11 to have unusually broad lightcurves. We also constrained the distribution of lightcurve broadness for iPTF stripped-envelope supernovae. The 11 with broad lightcurves will be studied carefully in a forthcoming paper. The first part of this forthcoming paper, which describes the careful statistical identification of these super-novae, is included in this thesis. In it we identify that 10% of the iPTF stripped-envelope supernova sample have broad lightcurves, which a surprisingly high fraction given their rarity in the published literature. Finally, we evaluate whether our estimate of the fraction of broad stripped-envelope supernovae could help explain the missing high-mass progenitors, and con- clude that they can only be a small fraction of the missing high-mass progenitors.

  • 7.
    Karamehmetoglu, Emir
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    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).
    Wyrzykowski, L.
    Schmidl, S.
    Fraser, Morgan
    Fremling, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Greiner, J.
    Inserra, Cosimo
    Kostrzewa-Rutkowska, Z.
    Maguire, K.
    Smartt, S.
    Sullivan, M.
    Young, D. R.
    OGLE-2014-SN-131: A long-rising Type Ibn supernova from a massive progenitor2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 602, article id A93Article in journal (Refereed)
    Abstract [en]

    Context. Type Ibn supernovae (SNe Ibn) are thought to be the core-collapse explosions of massive stars whose ejecta interact with He-rich circumstellar material (CSM). Aims. We report the discovery of a SN Ibn, with the longest rise-time ever observed, OGLE-2014-SN-131. We discuss the potential powering mechanisms and the progenitor nature of this peculiar stripped-envelope (SE), circumstellar-interacting SN. Methods. Optical photometry and spectroscopy were obtained with multiple telescopes including VLT, NTT, and GROND. We compare light curves and spectra with those of other known SNe Ibn and Ibc. CSM velocities are derived from the spectral analysis. The SN light curve is modeled under di ff erent assumptions about its powering mechanism (56Ni decay, CSM-interaction, magnetar) in order to estimate the SN progenitor parameters. Results. OGLE-2014-SN-131 spectroscopically resembles SNe Ibn such as SN 2010al. Its peak luminosity and post-peak colors are also similar to those of other SNe Ibn. However, it shows an unprecedentedly long rise-time and a much broader light curve compared to other SNe Ibn. Its bolometric light curve can be reproduced by magnetar and CSM-interaction models, but not by a 56Ni-decay powering model. Conclusions. To explain the unusually long rise-time, the broad light curve, the light curve decline, and the spectra characterized by narrow emission lines, we favor a powering mechanism where the SN ejecta are interacting with a dense CSM. The progenitor of OGLE-2014-SN-131 was likely a Wolf-Rayet star with a mass greater than that of a typical SN Ibn progenitor, which expelled the CSM that the SN is interacting with.

  • 8.
    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.

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

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

  • 10.
    Roy, Rupak
    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).
    Silverman, J. M.
    Pastorello, A.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Drake, A.
    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
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kankare, E.
    Kumar, B.
    Cappellaro, E.
    Bose, S.
    Benetti, S.
    Filippenko, A. V.
    Valenti, S.
    Nyholm, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sutaria, F.
    Kumar, B.
    Pandey, S. B.
    Nicholl, M.
    Garcia-Alvarez, D.
    Tomasella, L.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Migotto, Katia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    SN 2012aa: A transient between Type Ibc core-collapse and superluminous supernovae2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, article id A67Article in journal (Refereed)
    Abstract [en]

    Context. Research on supernovae (SNe) over the past decade has confirmed that there is a distinct class of events which are much more luminous (by similar to 2 mag) than canonical core-collapse SNe (CCSNe). These events with visual peak magnitudes less than or similar to-21 are called superluminous SNe (SLSNe). The mechanism that powers the light curves of SLSNe is still not well understood. The proposed scenarios are circumstellar interaction, the emergence of a magnetar after core collapse, or disruption of a massive star through pair production. Aims. There are a few intermediate events which have luminosities between these two classes. They are important for constraining the nature of the progenitors of these two different populations and their environments and powering mechanisms. Here we study one such object, SN 2012aa. Methods. We observed and analysed the evolution of the luminous Type Ic SN 2012aa. The event was discovered by the Lick Observatory Supernova Search in an anonymous galaxy (z approximate to 0.08). The optical photometric and spectroscopic follow-up observations were conducted over a time span of about 120 days. Results. With an absolute V-band peak of similar to-20 mag, the SN is an intermediate-luminosity transient between regular SNe Ibc and SLSNe. SN 2012aa also exhibits an unusual secondary bump after the maximum in its light curve. For SN 2012aa, we interpret this as a manifestation of SN-shock interaction with the circumstellar medium (CSM). If we assume a Ni-56-powered ejecta, the quasi-bolometric light curve requires roughly 1.3 M-circle dot of Ni-56 and an ejected mass of similar to 14 M-circle dot. This also implies a high kinetic energy of the explosion, similar to 5.4 x 10(51) erg. On the other hand, the unusually broad light curve along with the secondary peak indicate the possibility of interaction with CSM. The third alternative is the presence of a central engine releasing spin energy that eventually powers the light curve over a long time. The host of SN 2012aa is a star-forming Sa/Sb/Sbc galaxy. Conclusions. Although the spectral properties of SN 2012aa and its velocity evolution are comparable to those of normal SNe Ibc, its broad light curve along with a large peak luminosity distinguish it from canonical CCSNe, suggesting that the event is an intermediate-luminosity transient between CCSNe and SLSNe at least in terms of peak luminosity. In comparison to other SNe, we argue that SN 2012aa belongs to a subclass where CSM interaction plays a significant role in powering the SN, at least during the initial stages of evolution.

  • 11.
    Taddia, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, Christoffer
    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).
    Corsi, A.
    Gal-Yam, A.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lunnan, R.
    Bue, B.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kasliwal, M.
    Vreeswijk, P. M.
    Wozniak, P. R.
    iPTF15dtg: a double-peaked Type Ic supernova from a massive progenitor2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 592, article id A89Article in journal (Refereed)
    Abstract [en]

    Context. Type Ic supernovae (SNe Ic) arise from the core-collapse of H-(and He-) poor stars, which could either be single Wolf-Rayet (WR) stars or lower-mass stars stripped of their envelope by a companion. Their light curves are radioactively powered and usually show a fast rise to peak (similar to 10-15 d), without any early (in the first few days) emission bumps (with the exception of broad-lined SNe Ic) as sometimes seen for other types of stripped-envelope SNe (e.g., Type IIb SN 1993J and Type Ib SN 2008D). Aims. We have studied iPTF15dtg, a spectroscopically normal SN Ic with an early excess in the optical light curves followed by a long (similar to 30 d) rise to the main peak. It is the first spectroscopically-normal double-peaked SN Ic to be observed. Our aim is to determine the properties of this explosion and of its progenitor star. Methods. Optical photometry and spectroscopy of iPTF15dtg was obtained with multiple telescopes. The resulting light curves and spectral sequence are analyzed and modeled with hydrodynamical and analytical models, with particular focus on the early emission. Results. iPTF15dtg is a slow rising SN Ic, similar to SN 2011bm. Hydrodynamical modeling of the bolometric properties reveals a large ejecta mass (similar to 10 M-circle dot) and strong Ni-56 mixing. The luminous early emission can be reproduced if we account for the presence of an extended (greater than or similar to 500 R-circle dot), low-mass (greater than or similar to 0.045 M-circle dot) envelope around the progenitor star. Alternative scenarios for the early peak, such as the interaction with a companion, a shock-breakout (SBO) cooling tail from the progenitor surface, or a magnetar-driven SBO are not favored. Conclusions. The large ejecta mass and the presence of H-and He-free extended material around the star suggest that the progenitor of iPTF15dtg was a massive (greater than or similar to 35 M-circle dot) WR star that experienced strong mass loss.

  • 12.
    Taddia, Francesco
    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).
    Fremling, C.
    Barbarino, Cristina
    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).
    Arcavi, I.
    Cenko, S. B.
    Filippenko, A.
    Gal-Yam, A.
    Hiramatsu, D.
    Hosseinzadeh, G.
    Howell, D. A.
    Kulkarni, S. R.
    Laher, R.
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). California Institute of Technology, USA.
    Masci, F.
    Nugent, P. E.
    Nyholm, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Perley, D. A.
    Quimby, R.
    Silverman, J. M.
    Analysis of broad-lined Type Ic supernovae from the (intermediate) Palomar Transient Factory2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 621, article id A71Article in journal (Refereed)
    Abstract [en]

    We study 34 Type Ic supernovae that have broad spectral features (SNe Ic-BL). This is the only SN type found in association with long-duration gamma-ray bursts (GRBs). We obtained our photometric data with the Palomar Transient Factory (PTF) and its continuation, the intermediate PTF (iPTF). This is the first large, homogeneous sample of SNe Ic-BL from an untargeted survey. Furthermore, given the high observational cadence of iPTF, most of these SNe Ic-BL were discovered soon after explosion. We present K-corrected Bgriz light curves of these SNe, obtained through photometry on template-subtracted images. We analyzed the shape of the r-band light curves, finding a correlation between the decline parameter Delta m(15) and the rise parameter Delta m-(10 ). We studied the SN colors and, based on g - r, we estimated the host-galaxy extinction for each event. Peak r-band absolute magnitudes have an average of -18.6 +/- 0.5 mag. We fit each r-band light curve with that of SN 1998bw (scaled and stretched) to derive the explosion epochs. We computed the bolometric light curves using bolometric corrections, r-band data, and g - r colors. Expansion velocities from Fen were obtained by fitting spectral templates of SNe Ic. Bolometric light curves and velocities at peak were fitted using the semianalytic Arnett model to estimate ejecta mass M-ej , explosion energy E-K and Ni-56 mass M( Ni-56) for each SN. We find average values of M-ej = 4 +/- 3 M-circle dot, E-K = (7 +/- 6) x 10(51) erg, and M( Ni-56) = 0.31 +/- 0.16 M-circle dot . The parameter distributions were compared to those presented in the literature and are overall in agreement with them. We also estimated the degree of Ni-56 mixing using scaling relations derived from hydrodynamical models and we find that all the SNe are strongly mixed. The derived explosion parameters imply that at least 21% of the progenitors of SNe Ic-BL are compatible with massive (>28 M-circle dot), possibly single stars, whereas at least 64% might come from less massive stars in close binary systems.

  • 13.
    Taddia, Francesco
    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).
    Fremling, C.
    Karamehmetoglu, Emir
    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).
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    West, Stuart
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gal-Yam, A.
    The luminous late-time emission of the type-Ic supernova iPTF15dtg-evidence for powering from a magnetar?2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 621, article id A64Article in journal (Refereed)
    Abstract [en]

    Context. The transient iPTF15dtg is a type-Ic supernova (SN) showing a broad light curve around maximum light, consistent with massive ejecta if we assume a radioactive-powering scenario.

    Aims. We aim to study the late-time light curve of iPTF15dtg, which turned out to be extraordinarily luminous for a stripped-envelope (SE) SN, and investigate possible powering mechanisms.

    Methods. We compare the observed light curves to those of other SE SNe and also to models for the (56) Co decay. We analyze and compare the spectra to nebular spectra of other SE SNe. We build a bolometric light curve and fit it with different models, including powering by radioactivity, magnetar powering, and a combination of the two.

    Results. Between 150 and 750 d post-explosion, the luminosity of iPTF15dtg declined by merely two magnitudes instead of the six magnitudes expected from Co-56 decay. This is the first spectroscopically regular SE SN found to show this behavior. The model with both radioactivity and magnetar powering provides the best fit to the light curve and appears to be the most realistic powering mechanism. An alternative mechanism might be circumstellar-medium (CSM) interaction. However, the spectra of iPTF15dtg are very similar to those of other SE SNe, and do not show signs of strong CSM interaction.

    Conclusions. The object iPTF15dtg is the first spectroscopically regular SE SN whose light curve displays such clear signs of a magnetar contributing to its late-time powering. Given this result, the mass of the ejecta needs to be revised to a lower value, and therefore the progenitor mass could be significantly lower than the previously estimated >35 M-circle dot.

  • 14.
    Taddia, Francesco
    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).
    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.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Quimby, R. M.
    Gal-Yam, A.
    Yaron, O.
    Kasliwal, M. M.
    Kulkarni, S. R.
    Nugent, P. E.
    Smadja, G.
    Tao, C.
    PTF11mnb: First analog of supernova 2005bf Long-rising, double-peaked supernova Ic from a massive progenitor2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 609, article id A106Article in journal (Refereed)
    Abstract [en]

    Aims. We study PTF11mnb, a He-poor supernova (SN) whose light curves resemble those of SN 2005bf, a peculiar double-peaked stripped-envelope (SE) SN, until the declining phase after the main peak. We investigate the mechanism powering its light curve and the nature of its progenitor star. Methods. Optical photometry and spectroscopy of PTF11mnb are presented. We compared light curves, colors and spectral properties to those of SN 2005bf and normal SE SNe. We built a bolometric light curve and modeled this light curve with the SuperNova Explosion Code (SNEC) hydrodynamical code explosion of a MESA progenitor star and semi-analytic models. Results. The light curve of PTF11mnb turns out to be similar to that of SN 2005bf until similar to 50 d when the main (secondary) peaks occur at -18.5 mag. The early peak occurs at similar to 20 d and is about 1.0 mag fainter. After the main peak, the decline rate of PTF11mnb is remarkably slower than what was observed in SN 2005bf, and it traces well the Co-56 decay rate. The spectra of PTF11mnb reveal a SN Ic and have no traces of He unlike in the case of SN Ib 2005bf, although they have velocities comparable to those of SN 2005bf. The whole evolution of the bolometric light curve is well reproduced by the explosion of a massive (M-ej = 7.8 M-circle dot), He-poor star characterized by a double-peaked Ni-56 distribution, a total Ni-56 mass of 0.59 M-circle dot, and an explosion energy of 2.2 x 10(51) erg. Alternatively, a normal SN Ib/c explosion (M(Ni-56) = 0.11 M-circle dot, E-K = 0.2 x 10(51) erg, M-ej = 1 M-circle dot) can power the first peak while a magnetar, with a magnetic field characterized by B = 5.0 x 10(14) G, and a rotation period of P = 18.1 ms, provides energy for the main peak. The early g-band light curve can be fit with a shock-breakout cooling tail or an extended envelope model from which a radius of at least 30 R-circle dot is obtained. Conclusions. We presented a scenario where PTF11mnb was the explosion of a massive, He-poor star, characterized by a double-peaked Ni-56 distribution. In this case, the ejecta mass and the absence of He imply a large ZAMS mass (similar to 85 M-circle dot) for the progenitor, which most likely was a Wolf-Rayet star, surrounded by an extended envelope formed either by a pre-SN eruption or due to a binary configuration. Alternatively, PTF11mnb could be powered by a SE SN with a less massive progenitor during the first peak and by a magnetar afterward.

  • 15. Whitesides, L.
    et al.
    Lunnan, Ragnhild
    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.
    Kasliwal, M. M.
    Perley, D. A.
    Corsi, A.
    Cenko, S. B.
    Blagorodnova, N.
    Cao, Y.
    Cook, D. O.
    Doran, G. B.
    Frederiks, D. 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).
    Hurley, K.
    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.
    Leloudas, G.
    Masci, F.
    Nugent, P. E.
    Ritter, A.
    Rubin, A.
    Savchenko, V.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Svinkin, D. S.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Vreeswijk, P.
    Wozniak, P.
    iPTF 16asu: A Luminous, Rapidly Evolving, and High-velocity Supernova2017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 851, no 2, article id 107Article in journal (Refereed)
    Abstract [en]

    Wide-field surveys are discovering a growing number of rare transients whose physical origin is not yet well understood. Here we present optical and UV data and analysis of intermediate Palomar Transient Factory (iPTF) 16asu, a luminous, rapidly evolving, high-velocity, stripped-envelope supernova ( SN). With a rest-frame rise time of just four. days and a peak absolute magnitude of M-g = -20.4 mag, the light curve of iPTF 16asu is faster and more luminous than that of previous rapid transients. The spectra of iPTF 16asu show a featureless blue continuum near peak that develops into an SN Ic-BL spectrum on the decline. We show that while the late-time light curve could plausibly be powered by Ni-56 decay, the early emission requires a different energy source. Nondetections in the X-ray and radio strongly constrain the energy coupled to relativistic ejecta to be at most comparable to the class of low-luminosity gamma-ray bursts (GRBs). We suggest that the early emission may have been powered by either a rapidly spinning-down magnetar or by shock breakout in an extended envelope of a very energetic explosion. In either scenario a central engine is required, making iPTF 16asu an intriguing transition object between superluminous SNe, SNe Ic-BL, and low-luminosity GRBs.

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