We have identified a progenitor candidate in archival Hubble Space Telescope (HST) images for the Type Ic supernova (SN Ic) SN 2017ein in NGC 3938, pinpointing the candidate's location via HST Target of Opportunity imaging of the SN itself. This would be the first identification of a stellar-like object as a progenitor candidate for any SN Ic to date. We also present observations of SN 2017ein during the first ∼49 days since explosion. We find that SN 2017ein most resembles the well-studied SN Ic SN 2007gr. We infer that SN 2017ein experienced a total visual extinction of A V ≈ 1.0-1.9 mag, predominantly because of dust within the host galaxy. Although the distance is not well known, if this object is the progenitor, it was likely of high initial mass, ∼47-48 M o if a single star, or ∼60-80 M o if in a binary system. However, we also find that the progenitor candidate could be a very blue and young compact cluster, further implying a very massive (>65 M o) progenitor. Furthermore, the actual progenitor might not be associated with the candidate at all and could be far less massive. From the immediate stellar environment, we find possible evidence for three different populations; if the SN progenitor was a member of the youngest population, this would be consistent with an initial mass of ∼57 M o. After it has faded, the SN should be reobserved at high spatial resolution and sensitivity, to determine whether the candidate is indeed the progenitor.
Bibliographical noteFunding Information:
We thank the referee for a careful review that improved this manuscript. We also thank Ylva Götberg, Selma de Mink, and J. J. Eldridge for helpful discussions regarding SN Ic progenitor models, and Monica Tosi regarding stellar clusters in nearby galaxies. We appreciate comments on the paper provided by Jorick Vink, Scott Adams, Or Graur, and Kathryn Grasha. Andrew Dolphin modified Dolphot to accept WFPC2 frames that have been flagged for cosmic-ray hits with AstroDrizzle. We are grateful to UC Berkeley undergraduate students Sanyum Channa, Nick Choksi, Edward Falcon, Goni Halevi, Julia Hestenes, Ben Jeffers, and Samantha Stegman for helping obtain some of the Lick Nickel data. We kindly thank Thomas de Jaeger for assistance with some of the Kast observations. Support for program GO-14645 was provided by the National Aeronautics and Space Administration (NASA) through a grant from the Space Telescope Science Institute (STScI), and this work is based in part on observations made with the NASA/ ESA Hubble Space Telescope, obtained from the Data Archive at STScI, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. Partial support for N.S.ʼs supernova and transient research group at the University of Arizona was provided by NSF grant AST-1515559. Support for A.V.F.ʼs supernova research group at UC Berkeley has been provided by U.S. NSF grant AST-1211916, the TABASGO Foundation, the Christopher R. Redlich Fund, and the Miller Institute for Basic Research in Science (UC Berkeley). This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. PyRAF is a product of the Space Telescope Science Institute, which is operated by AURA for NASA.
We thank the Lick Observatory staff for their expert assistance. KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScope Corporation, Lick Observatory, the NSF, the University of California, the Sylvia & Jim Katzman Foundation, and the TABASGO Foundation. A major upgrade of the Kast Spectrograph on the Shane 3m telescope at Lick Observatory was made possible through generous gifts from the Heising-Simons Foundation, as well as William and Marina Kast.
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- binaries: general
- galaxies: individual (NGC 3938)
- galaxies: stellar content
- stars: massive
- supernovae: individual (SN 2017ein)