Evidence for Late-stage Eruptive Mass Loss in the Progenitor to SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission and a Rapidly Rising Luminous Transient

December 2019 • 2019ApJ...887..169H

Authors • Ho, Anna Y. Q. • Goldstein, Daniel A. • Schulze, Steve • Khatami, David K. • Perley, Daniel A. • Ergon, Mattias • Gal-Yam, Avishay • Corsi, Alessandra • Andreoni, Igor • Barbarino, Cristina • Bellm, Eric C. • Blagorodnova, Nadia • Bright, Joe S. • Burns, E. • Cenko, S. Bradley • Cunningham, Virginia • De, Kishalay • Dekany, Richard • Dugas, Alison • Fender, Rob P. • Fransson, Claes • Fremling, Christoffer • Goldstein, Adam • Graham, Matthew J. • Hale, David • Horesh, Assaf • Hung, Tiara • Kasliwal, Mansi M. • Kuin, N. Paul M. • Kulkarni, S. R. • Kupfer, Thomas • Lunnan, Ragnhild • Masci, Frank J. • Ngeow, Chow-Choong • Nugent, Peter E. • Ofek, Eran O. • Patterson, Maria T. • Petitpas, Glen • Rusholme, Ben • Sai, Hanna • Sfaradi, Itai • Shupe, David L. • Sollerman, Jesper • Soumagnac, Maayane T. • Tachibana, Yutaro • Taddia, Francesco • Walters, Richard • Wang, Xiaofeng • Yao, Yuhan • Zhang, Xinhan

Abstract • We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising (1.4 ± 0.1 mag hr-1) and luminous ({M}g,{peak}=-20 mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity ({L}bol}≳ 3× {10}44 {erg} {{{s}}}-1), the short rise time ({t}rise}=3 {days} in g band), and the blue colors at peak (g{--}r∼ -0.4) all resemble the high-redshift Ic-BL iPTF16asu, as well as several other unclassified fast transients. The early discovery of SN2018gep (within an hour of shock breakout) enabled an intensive spectroscopic campaign, including the highest-temperature ({T}eff}≳ {{40,000}} {{K}}) spectra of a stripped-envelope SN. A retrospective search revealed luminous ({M}g∼ {M}r≈ -14 mag) emission in the days to weeks before explosion, the first definitive detection of precursor emission for a Ic-BL. We find a limit on the isotropic gamma-ray energy release {E}γ ,{iso}< 4.9× {10}48 {erg}, a limit on X-ray emission {L}{{X}}< {10}40 {erg} {{{s}}}-1, and a limit on radio emission ν {L}ν ≲ {10}37 {erg} {{{s}}}-1. Taken together, we find that the early (< 10 {days}) data are best explained by shock breakout in a massive shell of dense circumstellar material (0.02 {M}) at large radii (3× {10}14 {cm}) that was ejected in eruptive pre-explosion mass-loss episodes. The late-time (> 10 {days}) light curve requires an additional energy source, which could be the radioactive decay of Ni-56.


IPAC Authors

Frank Masci

Senior Scientist

Ben Rusholme

Chief Engineer

Dave Shupe

Senior Scientist