University of Minnesota
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Robert Gehrz

A Systematic Study of Mid-Infrared Emission from Core-Collapse Supernovae with SPIRITS.
S.Tinyanont, M. M. Kasliwal, O. D. Fox, R. Lau, N. Smith, R. Williams, J. Jencson, D. Perley, D. Dykhoff, R. Gehrz, J. Johansson, S. D. Van Dyk, F. Masci, A. M. Cody, and T. Prince., 2016, ApJ, 833, 231.

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We present a systematic study of mid-infrared (mid-IR) emission from 141 nearby supernovae (SNe) observed with the InfraRed Array Camera (IRAC) on the Spitzer Space Telescope. These SNe reside in one of the 190 galaxies within 20 Mpc drawn from the ongoing three-year SPIRITS program. Both new SPIRITS observations and data from other programs available in the archive are used in this study. We detect 8 Type Ia SNe and 36 core-collapse SNe. All Type I SNe fade and become undetectable within 3 years of explosion. About 22±11% of Type II SNe continue to be detected at late-times with five events detected even two decades after discovery. Dust luminosity, temperature, and mass are obtained by fitting the spectral energy distributions using photometry with IRAC bands 1 and 2. The dust mass estimate is a lower limit as the dust cloud could be optically thick or there could be cooler dust hiding at longer wavelengths. The estimate also does not distinguish between pre-existing and newly produced dust. We observe warm dust masses between 10−2 and 10−6 M and dust temperatures from 200 K to 1280 K. We present detailed case studies of two extreme Type II-P SNe: SN 2011ja and SN 2014bi. SN 2011ja was over-luminous ([4.5] = −15.6 mag) at 900 days post-explosion accompanied by a monotonic growth of the dust mass. This suggests either an episode of dust formation similar to SN 2004et and SN 2004dj, or an intensifying CSM interactions heating up pre-existing dust. SN 2014bi showed a factor of 10 decrease in dust mass over one month suggesting either an episode of dust destruction or a fading source of dust heating. A re-brightening in the mid-IR light curve of the Type Ib SN 2014C coinciding with a rise in the dust mass indicates either an episode of dust production perhaps via CSM interactions or more pre-existing dust getting heated up by the CSM interactions. This observation adds to a small number of stripped-envelope SNe that have mid-IR excess as has been previously reported in the case of SN 2006jc. The observed dust mass and the location of the CSM interactions suggest that the CSM shell around SN 2014C is originated from an LBV-like eruption roughly 100 years before the explosion. We also report detections of SN 1974E, SN 1979C, SN 1980K, SN 1986J, and SN 1993J more than 20 years post-explosion. The number of outlying SNe identified in this work demonstrates the power of late time mid-IR observations of a large sample of SNe to identify events with unusual evolution.