On the Origin of SN 2016hil—A Type II Supernova in the Remote Outskirts of an Elliptical Host

Creators: Irani, Ido; Schulze, Steve; Gal-Yam, Avishay; Lunnan, Ragnhild; Brink, Thomas G.; Zheng, WeiKang; Filippenko, Alexei V.; Yang, Yi; de Jaeger, Thomas; Nugent, Peter E.; Kasliwal, Mansi M.; Fremling, Christoffer; Neill, James Don; Rebbapragada, Umaa; Masci, Frank J.; Sollerman, Jesper; Yaron, Ofer

Abstract

Type II supernovae (SNe) stem from the core collapse of massive (>8 M ⊙) stars. Due to their short lifespan, we expect a very low rate of such events in elliptical hosts, where the star formation rate is low, and which are mostly comprised of an old stellar population. SN 2016hil (iPTF16hil) is an SN II located in the extreme outskirts of an elliptical galaxy at z = 0.0608 (projected distance 27.2 kpc). It was detected near peak (M_r ~ −17 mag) 9 days after the last non-detection. The event has some potentially peculiar properties: it presented an apparently double-peaked light curve, and its spectra suggest low metallicity content (Z < 0.4 Z ⊙). We place a tentative upper limit on the mass of a potential faint host at log M/M⊙ = 7.27^(+0.43)_(-0.24) using deep optical imaging from Keck/LRIS. In light of this, we discuss the possibility of the progenitor forming locally and other more exotic formation scenarios such as a merger or common-envelope evolution causing a time-delayed explosion. Further observations of the explosion site in the UV are needed in order to distinguish between the cases. Regardless of the origin of the transient, observing a population of such seemingly hostless SNe II could have many uses, including an estimate the amount of faint galaxies in a given volume, and tests of the prediction of a time-delayed population of core-collapse SNe in locations otherwise unfavorable for the detection of such events.

Additional Information

© 2019 The American Astronomical Society. Received 2019 April 11; revised 2019 September 26; accepted 2019 October 21; published 2019 December 16. We thank A. Ho and K. De for assistance with some of the observations. A.G.-Y. is supported by the EU via ERC grant No. 725161, the ISF, the BSF Transformative program, and a Kimmel award. A.V.F.'s supernova group at U.C. Berkeley is supported by the TABASGO Foundation, the Christopher R. Redlich Fund, Gary and Cynthia Bengier, and the Miller Institute for Basic Research in Science. T.d.J. is a Bengier Postdoctoral Fellow. R.L. is supported by a Marie Skłodowska-Curie Individual Fellowship within the Horizon 2020 European Union (EU) Framework Programme for Research and Innovation (H2020-MSCA-IF-2017-794467). 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 the National Aeronautics and Space Administration (NASA). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. 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. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work is based in part on observations obtained with the 48 inch Samuel Oschin Telescope and the 60 inch Telescope at the Palomar Observatory as part of the intermediate Palomar Transient Factory (iPTF) project, a scientific collaboration among the California Institute of Technology, Los Alamos National Laboratory, the University of Wisconsin, Milwaukee, the Oskar Klein Center, the Weizmann Institute of Science, the TANGO Program of the University System of Taiwan, and the Kavli Institute for the Physics and Mathematics of the Universe. The SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171.

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