SPIRITS: Uncovering Unusual Infrared Transients With Spitzer
astro-ph.HE
/ Authors
Mansi M. Kasliwal, John Bally, Frank Masci, Ann Marie Cody, Howard E. Bond, Jacob E. Jencson, Samaporn Tinyanont, Yi Cao, Carlos Contreras, Devin A. Dykhoff
and 37 more authors
Samuel Amodeo, Lee Armus, Martha Boyer, Matteo Cantiello, Robert L. Carlon, Alexander C. Cass, David Cook, David T. Corgan, Joseph Faella, Ori D. Fox, Wayne Green, Robert Gehrz, George Helou, Eric Hsiao, Joel Johansson, Rubab M. Khan, Ryan M. Lau, Norbert Langer, Emily Levesque, Peter Milne, Shazrene Mohamed, Nidia Morrell, Andy Monson
/ Abstract
We present an ongoing, systematic search for extragalactic infrared transients, dubbed SPIRITS --- SPitzer InfraRed Intensive Transients Survey. In the first year, using Spitzer/IRAC, we searched 190 nearby galaxies with cadence baselines of one month and six months. We discovered over 1958 variables and 43 transients. Here, we describe the survey design and highlight 14 unusual infrared transients with no optical counterparts to deep limits, which we refer to as SPRITEs (eSPecially Red Intermediate Luminosity Transient Events). SPRITEs are in the infrared luminosity gap between novae and supernovae, with [4.5] absolute magnitudes between -11 and -14 (Vega-mag) and [3.6]-[4.5] colors between 0.3 mag and 1.6 mag. The photometric evolution of SPRITEs is diverse, ranging from < 0.1 mag/yr to > 7 mag/yr. SPRITEs occur in star-forming galaxies. We present an in-depth study of one of them, SPIRITS 14ajc in Messier 83, which shows shock-excited molecular hydrogen emission. This shock may have been triggered by the dynamic decay of a non-hierarchical system of massive stars that led to either the formation of a binary or a proto-stellar merger.