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
Creators: name: Ho, Anna Y. Q.
name: Goldstein, Daniel A.
name: Schulze, Steve
name: Khatami, David K.
name: Perley, Daniel A.
name: Ergon, Mattias
name: Gal-Yam, Avishay
name: Corsi, Alessandra
name: Andreoni, Igor
name: Barbarino, Cristina
name: Bellm, Eric C.
name: Blagorodnova, Nadia
name: Bright, Joe S.
name: Burns, Eric
name: Cenko, S. Bradley
name: Cunningham, Virginia
name: De, Kishalay
name: Dekany, Richard
name: Dugas, Alison
name: Fender, Rob P.
name: Fransson, Claes
name: Fremling, Christoffer
name: Goldstein, Adam
name: Graham, Matthew J.
name: Hale, David
name: Horesh, Assaf
name: Hung, Tiara
name: Kasliwal, Mansi M.
name: Kuin, N. Paul M.
name: Kulkarni, Shri R.
name: Kupfer, Thomas
name: Lunnan, Ragnhild
name: Masci, Frank J.
name: Ngeow, Chow-Choong
name: Nugent, Peter E.
name: Ofek, Eran O.
name: Patterson, Maria T.
name: Petitpas, Glen
name: Rusholme, Ben
name: Sai, Hanna
name: Sfaradi, Itai
name: Shupe, David L.
name: Sollerman, Jesper
name: Soumagnac, Maayane T.
name: Tachibana, Yutaro
name: Taddia, Francesco
name: Walters, Richard
name: Wang, Xiaofeng
name: Yao, Yuhan
name: Zhang, Xinhan
Publisher: name: arXiv
Year: 2019
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising ($1.4\pm0.1$ mag/hr) and luminous ($M_{g,\mathrm{peak}}=-20$ mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity ($L_{\mathrm{bol}} \gtrsim 3 \times 10^{44}$ erg $\mathrm{sec}^{-1}$), the short rise time ($t_{\mathrm{rise}}= 3$ days in $g$-band), and the blue colors at peak ($g-r\sim-0.4$) 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 ($T_{\mathrm{eff}}\gtrsim40,000$ K) spectra of a stripped-envelope SN. A retrospective search revealed luminous ($M_g \sim M_r \approx -14\,$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 $E_\mathrm{γ,iso}&lt;4.9 \times 10^{48}$ erg, a limit on X-ray emission $L_{\mathrm{X}} &lt; 10^{40}\,$erg sec$^{-1}$, and a limit on radio emission $νL_ν\lesssim 10^{37}\,$erg sec$^{-1}$. Taken together, we find that the early ($&lt;10\,$days) data are best explained by shock breakout in a massive shell of dense circumstellar material ($0.02\,M_\odot$) at large radii ($3 \times 10^{14}\,$cm) that was ejected in eruptive pre-explosion mass-loss episodes. The late-time ($&gt;10$ days) light curve requires an additional energy source, which could be the radioactive decay of Ni-56.
description: Accepted to ApJ on 1 Oct 2019. In this version, we made minor corrections and removed extraneous references