We present the results of an extensive observational campaign on the nearby Type Ibn SN 2015G, including data from radio through ultravioletwavelengths. SN2015Gwas asymmetric, showing late-time nebular lines redshifted by ~1000 km s-1. It shared many features with the prototypical SN Ibn 2006jc, including extremely strong He I emission lines and a late-time blue pseudo-continuum. The young SN 2015G showed narrow P-Cygni profiles of He I, but never in its evolution did it showany signature of hydrogen - arguing for a dense, ionized and hydrogenfree circumstellar medium moving outward with a velocity of ~1000 km s-1 and created by relatively recent mass-loss from the progenitor star. Ultraviolet through infrared observations show that the fading SN 2015G (which was probably discovered some 20 d post-peak) had a spectral energy distribution that was well described by a simple, single-component blackbody. Archival HST images provide upper limits on the luminosity of SN 2015G's progenitor, while non-detections of any luminous radio afterglow and optical non-detections of outbursts over the past two decades provide constraints upon its mass-loss history.
Bibliographical noteFunding Information:
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 NASA; the observatory was made possible by the generous financial support of the W. M. Keck Foundation. 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 and Jim Katzman Foundation and the TABASGO Foundation. Research at Lick Observatory is partially supported by a generous gift from Google. We are grateful to the staffs of Lick, Keck and the other observatories where we obtained data for their excellent assistance.
We thank K. Shen, C. Harris and J. Schwab for helpful discussions. We thank our referee, A. Pastorello, for his productive comments, which have improved this paper. A.V.F.’s supernova group at UC Berkeley is supported by US National Science Foundation (NSF) grant AST-1211916, Gary & Cynthia Bengier, the Richard & Rhoda Goldman Fund, the Christopher R. Redlich Fund, the TABASGO Foundation and the Miller Institute for Basic Research in Science (UC Berkeley). His work was conducted in part at the Aspen Center for Physics, which is supported by NSF grant PHY-1607611; he thanks the Center for its hospitality during the neutron stars workshop in June and July 2017. Support for HST programs GO-13683, GO-13797, GO-14149, AR-14295 and GO-14668 was provided by the National Aeronautics and Space Administration (NASA) through grants from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. The UCSC group is supported in part by NSF grant AST-1518052 and from fellowships from the Alfred P. Sloan Foundation and the David and Lucile Packard Foundation to RJF.
This work made use of Swift/UVOT data reduced by P. J. Brown for the Swift Optical/Ultraviolet Supernova Archive (SOUSA. SOUSA is supported by NASA’s Astrophysics Data Analysis Program through grant NNX13AF35G. This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. 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.
© 2017 The Authors.
- Stars: mass-loss
- Supernovae: individual: (SN 2015G)