The Exotic Type Ic Broad-Lined Supernova SN 2018gep: Blurring the Line Between Supernovae and Fast Optical Transients
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AuthorPritchard, T. A.; Bensch, Katarzyna; Thöne, Christina C.; García Benito, Rubén; Galbany González, Lluis; Kann, D. Alexander; De Ugarte Postigo, Antonio
Institute of Physics Publishing
Published version: T. A. Pritchard et al 2021 ApJ 915 121. [10.3847/1538-4357/ac00bc]
SponsorshipW.M. Keck Foundation; NASA under the Swift GI grant 1619152; Tess GI grant G03267; NYU Center for Cosmology and Particle Physics; New York University Research Challenge FundProgram; National Science Foundation (NSF) NSF - Office of the Director (OD) AST-1352405 National Science Foundation (NSF) AST-1911225 AST-1413260; Humboldt Faculty Fellowship; Center for Computational Astrophysics at the Flatiron institute; Spanish Government BES2014-069767 RyC-2012-09975 RyC-2012-09984; Juan de la Cierva Incorporacion fellowship IJCI-2015-26153 IJCI-2016-30940; "Transient Astrophysical Objects" project of the National Research, Development and Innovation Office (NKFIH), Hungary - European Union GINOP 2.3.2-15-2016-00033; National Research, Development & Innovation Office (NRDIO) - Hungary NKFI-K-131508 NKFI-KH-130526; Hungarian Academy of Sciences LP2018-7/2019; Orszagos Tudomanyos Kutatasi Alapprogramok (OTKA) 119993; National Natural Science Foundation of China (NSFC) 12033003 11633002 11761141001; National Basic Research Program of China 2016YFA0400803; Scholar Program of Beijing Academy of Science and Technology DZ:BS202002; European Commission 839090 PGC2018-095317-BC21; Spanish Ministry of Economy and Competitiveness AYA2016-77846-P; State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award SEV-2017-0709; National Aeronautics & Space Administration (NASA) 80NSSC19k1639; 19 Washington Square North Award AYA 2014-58381-P AYA201789384-P RTI2018-098104-J-I00 AYA2017-89384-P
In the last decade a number of rapidly evolving transients have been discovered that are not easily explained by traditional supernova models. We present optical and UV data on one such object, SN 2018gep, that displayed a fast rise with a mostly featureless blue continuum around peak, and evolved to develop broad features typical of an SN Ic-bl while retaining significant amounts of blue flux throughout its observations. This blue excess is most evident in its near-UV flux, which is over 4 mag brighter than other stripped-envelope supernovae, and is still visible in optical g-r colors. Its fast rise time of t (rise,V ) = 5.6 +/- 0.5 days puts it squarely in the emerging class of Fast Evolving Luminous Transients, or Fast Blue Optical Transients. With a peak absolute magnitude of M ( v ) = -19.53 +/- 0.23 mag it is on the extreme end of both the rise time and peak magnitude distribution for SNe Ic-bl. These observations are consistent with a simple SN Ic-bl model that has an additional form of energy injection at early times that drives the observed rapid, blue rise. We show that SN 2018gep and the literature SN iPTF16asu have similar photometric and spectroscopic properties and that they overall share many similarities with both SNe Ic-bl and Fast Evolving Transients. Based on our SN 2018gep host galaxy data we derive a number of properties, and we show that the derived host galaxy properties for both SN 2018gep and iPTF16asu are consistent with the SNe Ic-bl and gamma-ray burst/supernova sample while being on the extreme edge of the observed Fast Evolving Transient sample.