SPIRITS 15c and SPIRITS 14buu: Two Obscured Supernovae in the Nearby Star-forming Galaxy IC 2163

SPitzer InfraRed Intensive Transients Survey-SPIRITS-is an ongoing survey of nearby galaxies searching for infrared (IR) transients with Spitzer/IRAC. We present the discovery and follow-up observations of one of our most luminous (M-[4.5] = -17.1 +/- 0.4 mag, Vega) and reddest ([3.6] - [4.5] = 3.0 +/- 0.2 mag) transients, SPIRITS 15c. The transient was detected in a dusty spiral arm of IC. 2163 (D approximate to 35.5 Mpc). Pre-discovery ground-based imaging revealed an associated, shorter-duration transient in the optical and near-IR (NIR). NIR spectroscopy showed a broad (approximate to 8400 km s(-1)), double-peaked emission line of He I at 1.083 mu m, indicating an explosive origin. The NIR spectrum of SPIRITS 15c is similar to that of the Type IIb SN 2011dh at a phase of approximate to 200 days. Assuming an A(V) = 2.2 mag of extinction in SPIRITS 15c provides a good match between their optical light curves. The NIR light curves, however, show some minor discrepancies when compared with SN 2011dh, and the extreme [3.6]-[4.5] color has not been previously observed for any SN IIb. Another luminous (M-4.5 = -16.1 +/- 0.4 mag) event, SPIRITS 14buu, was serendipitously discovered in the same galaxy. The source displays an optical plateau lasting greater than or similar to 80 days, and we suggest a scenario similar to the low-luminosity Type. IIP SN 2005cs obscured by A(V) approximate to 1.5 mag. Other classes of IR-luminous transients can likely be ruled out in both cases. If both events are indeed SNe, this may suggest that greater than or similar to 18% of nearby core-collapse SNe are missed by currently operating optical surveys.National Science Foundation [DGE-1144469]; NASA through Space Telescope Science Institute [GO-13935, GO-14258]; NASA [NAS 5-26555]; United States Air Force; U.S. Department of Energy Office of ScienceThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu