We present photometry and spectroscopy of SN 2013fs and SN 2013fr in the first~100 d postexplosion. Both objects showed transient, relatively narrow Hα emission lines characteristic of SNe IIn, but later resembled normal SNe II-P or SNe II-L, indicative of fleeting interaction with circumstellar material (CSM). SN 2013fs was discovered within 8 h of explosion; one of the earliest SNe discovered thus far. Its light curve exhibits a plateau, with spectra revealing strong CSM interaction at early times. It is a less luminous version of the transitional SN IIn PTF11iqb, further demonstrating a continuum of CSM interaction intensity between SNe II-P and SNe IIn. It requires dense CSM within 6.5 × 1014 cm of the progenitor, from a phase of advanced pre-SN mass loss beginning shortly before explosion. Spectropolarimetry of SN 2013fs shows little continuum polarization (~0.5 per cent, consistent with zero), but noticeable line polarization during the plateau phase. SN 2013fr morphed from an SN IIn at early times to an SN II-L. After the first epoch, its narrow lines probably arose from host-galaxy emission, but the bright, narrow Hα emission at early times may be intrinsic to the SN. As for SN 2013fs, this would point to a short-lived phase of strong CSM interaction if proven to be intrinsic, suggesting a continuum between SNe IIn and SNe II-L. It is a low-velocity SN II-L like SN 2009kr, but more luminous. SN 2013fr also developed an infrared excess at later times, due to warm CSM dust that requires a more sustained phase of strong pre-SN mass loss.
Bibliographical noteFunding Information:
Observations using Steward Observatory facilities were obtained as part of the observing program AZTEC: Arizona Transient Exploration and Characterization, which receives support from NSF grant AST-1515559. This paper includes data obtained by the Supernova Spectropolarimetry Project, supported by the National Science Foundation through grant AST-1210599. The SN research of AVF's group at U.C. Berkeley is supported by Gary & Cynthia Bengier, the Richard & Rhoda Goldman Fund, the Christopher R. Redlich Fund, the TABASGO Foundation, NSF grant AST-1211916, and the Miller Institute for Basic Research in Science (U.C. Berkeley). 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. The Kast spectrograph at Lick Observatory resulted from a generous donation from Bill and Marina Kast. Research at Lick Observatory is partially supported by a generous gift from Google. Some observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. These results made use of Lowell Observatory's Discovery Channel Telescope. Lowell operates the DCT in partnership with Boston University, Northern Arizona University, the University of Maryland, and the University of Toledo. Partial support of the DCT was provided by Discovery Communications. LMI was built by Lowell Observatory using funds from NSF grant AST-1005313. We made use of Swift/UVOT data reduced by P. J. Brown and released in the Swift Optical/Ultraviolet SupernovaArchive (SOUSA). SOUSA is supported byNASA'sAstrophysics Data Analysis Program through grant NNX13AF35G. This work is based (in part) on observations collected at the European Organization for Astronomical Research in the Southern hemisphere, Chile as part of PESSTO (the Public ESO Spectroscopic Survey for Transient Objects Survey) ESO programs 188.D-3003 and 191.D-0935. Several of the spectra were retrieved from WiSEREP, the Weizmann interactive Supernova data REPository (http://wiserep.weizmann.ac.il). We are grateful to Isaac Shivvers and JeffSilverman for help with one of the Lick/Kast observations and reductions. We also thank U.C. Berkeley undergraduate students/visitors Andrew Bigley, Kevin Hayakawa, Heechan Yuk, Minkyu Kim, Kiera Fuller, Philip Lu, James Bradley, Haejung Kim, Chadwick Casper, Gary Li, Samantha Stegman, Kyle Blanchard, Erin Leonard, Jenifer Gross, Xianggao Wang, Stephen Taylor, and Sahana Kumar for their effort in taking Lick/Nickel data. We are grateful to the dedicated staffmembers of the observatories where data for this paper were obtained, Ryan Hofmann for his assistance with the IRAF apphot and daophot routines used in reducing the DCT/Kuiper data, Nancy Elias-Rosa for kindly providing comparison spectra of SN 2009r, and Kyle Boyer for assistance with figure corrections while the manuscript was being revised
© 2018 The Author(s).
- Circumstellar matter
- Stars: mass-loss
- Supernovae: general
- Supernovae: individual (SN 2013fs, SN 2013fr)