The Exotic Type Ic Broad-Lined Supernova SN 2018gep: Blurring the Line Between Supernovae and Fast Optical Transients Pritchard, T. A. Bensch, Katarzyna Thöne, Christina C. García Benito, Rubén Galbany González, Lluis Kann, D. Alexander De Ugarte Postigo, Antonio Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. T.P. acknowledges support from NASA under the Swift GI grant 1619152, the Tess GI grant G03267, from the NYU Center for Cosmology and Particle Physics, from a 19 Washington Square North Award awarded to M.M, and in part by a grant from the New York University Research Challenge FundProgram. M.M. and the SNYU group have been supported by the NSF CAREER award AST-1352405, by the NSF award AST1413260, and by a Humboldt Faculty Fellowship. M.M. is grateful for her sabbatical stay supported by the Center for Computational Astrophysics at the Flatiron institute and for the hospitality of the Max-Planck Institute for Astronomy, Heidelberg, during which some of this work was accomplished. K.B. acknowledges financial support from the Ministerio de Economia y Competitividad through the Spanish grant BES2014-069767. K.B., C.T. and A.d.U.P. acknowledge support from the Spanish research project AYA2017-89384-P. C.T. acknowledges support from funding associated to a Ramon y Cajal fellowship RyC-2012-09984. A.d.U.P. acknowledges support from funding associated to a Ramon y Cajal fellowship RyC-2012-09975. L.I. acknowledges support from funding associated to a Juan de la Cierva Incorporacion fellowship IJCI-2016-30940. D.A.K. acknowledges support from the Spanish research projects AYA 2014-58381-P, AYA201789384-P, from Juan de la Cierva Incorporacion fellowship IJCI-2015-26153, and from Spanish National Project research project RTI2018-098104-J-I00 (GRBPhot). J.V. and his research group at Konkoly Observatory is supported by the "Transient Astrophysical Objects" GINOP 2.3.2-15-2016-00033 project of the National Research, Development and Innovation Office (NKFIH), Hungary, funded by the European Union. K.V. and L.K. thank the financial support from the National Research, Development and Innovation Office (NKFIH), Hungary, under grants NKFI-K-131508 and NKFI-KH-130526. A.B. and K.V. are supported by the Lendulet program grant LP2018-7/2019 of the Hungarian Academy of Sciences. T.N.D. also acknowledges the support of the Hungarian OTKA grant No. 119993. The work of X.W. was funded by the National Science Foundation of China (NSFC grants 12033003, 11633002, and 11761141001), the Major State Basic Research Development Program (grant No. 2016YFA0400803), and the Scholar Program of Beijing Academy of Science and Technology (DZ:BS202002). L.G. was funded by the European Union's Horizon 2020 research and innovation program under the Marie SklodowskaCurie grant agreement No. 839090. This work has been partially supported by the Spanish grant PGC2018-095317-BC21 within the European Funds for Regional Development (FEDER). R.G.B. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness through grant AYA2016-77846-P and from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709). These observations made use of the LCO network. D.A.H., C.P., D.H., and J.B. are supported by NSF Grant AST-1911225 and NASA Grant 80NSSC19k1639. 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. 2021-09-15T09:08:26Z 2021-09-15T09:08:26Z 2020-08-10 info:eu-repo/semantics/article Published version: T. A. Pritchard et al 2021 ApJ 915 121. [10.3847/1538-4357/ac00bc] http://hdl.handle.net/10481/70213 10.3847/1538-4357/ac00bc eng info:eu-repo/grantAgreement/EC/H2020/839090 http://creativecommons.org/licenses/by-nc-nd/3.0/es/ info:eu-repo/semantics/openAccess Atribución-NoComercial-SinDerivadas 3.0 España Institute of Physics Publishing