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

March 2017 • 2017ApJ...837..167J

Authors • Jencson, Jacob E. • Kasliwal, Mansi M. • Johansson, Joel • Contreras, Carlos • Castellón, Sergio • Bond, Howard E. • Monson, Andrew J. • Masci, Frank J. • Cody, Ann Marie • Andrews, Jennifer E. • Bally, John • Cao, Yi • Fox, Ori D. • Gburek, Timothy • Gehrz, Robert D. • Green, Wayne • Helou, George • Hsiao, Eric • Morrell, Nidia • Phillips, Mark • Prince, Thomas A. • Simcoe, Robert A. • Smith, Nathan • Tinyanont, Samaporn • Williams, Robert

Abstract • 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 ≈ 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 (≈8400 km s-1), double-peaked emission line of He I at 1.083 μm, indicating an explosive origin. The NIR spectrum of SPIRITS 15c is similar to that of the Type IIb SN 2011dh at a phase of ≈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 ≳80 days, and we suggest a scenario similar to the low-luminosity Type IIP SN 2005cs obscured by A V ≈ 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 ≳18% of nearby core-collapse SNe are missed by currently operating optical surveys.


IPAC Authors

George Helou

IPAC Executive Director

Frank Masci

Senior Scientist