Draft version January 18, 2016Preprint typeset using L A T E X style emulateapj v. 5/2/11RAPIDLY RISING TRANSIENTS IN THE SUPERNOVA - SUPERLUMINOUS SUPERNOVA GAPIair Arcavi 1,2 , William M. Wolf 3 , D. Andrew Howell 1,3 , Lars Bildsten 2,3 , Giorgos Leloudas 4,5 ,Delphine Hardin 6 , Szymon Prajs 7 , Daniel A. Perley 5 , Gilad Svirski 8 , Avishay Gal-Yam 4 , Boaz Katz 4 ,Curtis McCully 2,3 , S. Bradley Cenko 9,10 , Chris Lidman 11 , Mark Sullivan 7 , Stefano Valenti 2,3 , Pierre Astier 6 ,Cristophe Balland 6 , Ray G. Carlberg 13 , Alex Conley 14 , Dominique Fouchez 15 , Julien Guy 6 , Reynald Pain 6 ,Nathalie Palanque-Delabrouille 16 , Kathy Perrett 17 , Chris J. Pritchet 18 , Nicolas Regnault 6 , James Rich 16 andVanina Ruhlmann-Kleider 161 Las Cumbres Observatory Global Telescope, 6740 Cortona Dr, Suite 102, Goleta, CA 93111, USA iarcavi@lcogt.net2 Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106, USA3 Department of Physics, University of California, Santa Barbara, CA 93106, USA4 Department of Particle Physics and Astrophysics, The Weizmann Institute of Science, Rehovot, 76100, Israel5 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark6 LPNHE, CNRS-IN2P3 and University of Paris VI & VII, F-75005 Paris, France7 School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK8 Racah Institute for Physics, The Hebrew University, Jerusalem 91904, Israel9 Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771, USA10 Joint Space-Science Institute, University of Maryland, College Park, MD 20742, USA11 Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia12 University of Paris-Sud, Orsay, F-91405, France13 Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H8, Canada14 Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309-389, USA15 Aix Marseille Universit´ e, CNRS/IN2P3, CPPM UMR 7346, 13288, Marseille, France16 DSM/IRFU/SPP, CEA-Saclay, F-91191 Gif-sur-Yvette, France17 DRDC Ottawa, 3701 Carling Avenue, Ottawa, ON K1A 0Z4, Canada and18 Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6, CanadaDraft version January 18, 2016ABSTRACTWe present observations of four rapidly rising (t rise ≈ 10d) transients with peak luminosities be-tween those of supernovae (SNe) and superluminous SNe (M peak ≈ −20) - one discovered and followedby the Palomar Transient Factory (PTF) and three by the Supernova Legacy Survey (SNLS). Thelight curves resemble those of SN2011kl, recently shown to be associated with an ultra-long-durationgamma ray burst (GRB), though no GRB was seen to accompany our SNe. The rapid rise to a lumi-nous peak places these events in a unique part of SN phase space, challenging standard SN emissionmechanisms. Spectra of the PTF event formally classify it as a Type II SN due to broad Hα emission,but an unusual absorption feature, which can be interpreted as either high velocity Hα (though deeperthan in previously known cases) or Si II (as seen in Type Ia SNe), is also observed. We f i nd thatexisting models of white dwarf detonations, CSM interaction, shock breakout in a wind (or steeperCSM) and magnetar spindown can not readily explain the observations. We consider the possibilitythat a “Type 1.5 SN” scenario could be the origin of our events. More detailed models for these kindsof transients and more constraining observations of future such events should help better determinetheir nature.Subject headings: supernovae: individual (PTF10iam, SNLS04D4ec, SNLS05D2bk, SNLS06D1hc,Dougie)1. INTRODUCTIONSupernovae (SNe), the explosive deaths of stars, areobserved to occur in a variety of types and a spreadof luminosities. Most notable is the division into corecollapse SNe (Types Ib/c and II; see Filippenko 1997for a review), which are associated with the deaths ofmassive (M & 8M ? ) stars, and Type Ia SNe, associ-ated with the thermonuclear disruptions of white dwarfs(Hoyle & Fowler 1960; Hansen & Wheeler 1969, Nomoto1982a,b; Nomoto, Thielemann & Yokoi 1984; Branch etal. 1985; see Nugent et al. 2011 for the most directobservational evidence of this association). Recently, athird class of explosions has been identif i ed, superlumi-nous SNe (SLSNe), characterized by their high luminos-ity at peak (e.g. Quimby et al. 2007; Smith et al. 2007;Ofek et al. 2007; Gal-Yam et al. 2009; Pastorello etal. 2010; Quimby et al. 2011; see Gal-Yam 2012 for areview). These events likely originate in massive stars,but clear progenitor scenarios for SLSNe have yet to bedetermined.An open question related to the possible connection be-tween core collapse SNe and SLSNe is whether the appar-ent lack of “intermediate” events (i.e. SNe with peak ab-solute magnitudes in the range −19 to −21; Fig. 1) is realor just a selection ef f ect. Arcavi et al. (2014) searchedfor such events in the spectroscopically conf i rmed H-richcore collapse sample from the Palomar Transient Factory(PTF; Rau et al. 2009; Law et al. 2009). Three eventswere found in the centers of non-starforming galaxies,and turned out to be tidal disruptions of stars by super-massive black holes (Arcavi et al. 2014). A fourth event,PTF10iam, was shown to be signif i cantly of f set from itshost center, was in a starforming galaxy and displayed afaster rise to peak magnitude.arXiv:1511.00704v2 [astro-ph.CO] 15 Jan 2016
