Anna Y.Q. Ho, California Institute of Technology
Daniel A. Goldstein, California Institute of Technology
Steve Schulze, Weizmann Institute of Science Israel
David K. Khatami, University of California, Berkeley
Daniel A. Perley, Liverpool John Moores University
Mattias Ergon, Stockholms universitet
Avishay Gal-Yam, Weizmann Institute of Science Israel
Alessandra Corsi, Texas Tech University
Igor Andreoni, California Institute of Technology
Cristina Barbarino, Stockholms universitet
Eric C. Bellm, University of Washington
Nadia Blagorodnova, Radboud University Nijmegen
Joe S. Bright, University of Oxford
E. Burns, NASA Goddard Space Flight Center
S. Bradley Cenko, NASA Goddard Space Flight Center
Virginia Cunningham, University of Maryland, College Park
Kishalay De, California Institute of Technology
Richard Dekany, California Institute of Technology
Alison Dugas, California Institute of Technology
Rob P. Fender, University of Oxford
Claes Fransson, Stockholms universitet
Christoffer Fremling, California Institute of Technology
Adam Goldstein, Huntsville Program Office
Matthew J. Graham, California Institute of Technology
David Hale, California Institute of Technology
Assaf Horesh, Hebrew University of Jerusalem
Tiara Hung, University of California, Santa Cruz
Mansi M. Kasliwal, California Institute of Technology
N. Paul M. Kuin, UCL Mullard Space Science Laboratory
S. R. Kulkarni, California Institute of Technology
Thomas Kupfer, Kavli Institute for Theoretical Physics
Ragnhild Lunnan, Stockholms universitet
Frank J. Masci, Infrared Processing & Analysis Center

Document Type


Publication Date



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 (Mg,peak = -20 mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity (Lbol ≳ 3 × 1044 erg s-1), the short rise time (trise = 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 (Teff ≳ 40,000 K) spectra of a stripped-envelope SN. A retrospective search revealed luminous (Mg ∼ Mr ≈ 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 LX < 1040 erg s-1, and a limit on radio emission ν Lν ≲ 1037 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 × 1014 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.

Publication Source (Journal or Book title)

Astrophysical Journal