Spirits 16tn in ngc 3556: A heavily obscured and low-luminosity supernova at 8.8 mpc

Jacob E. Jencson, Mansi M. Kasliwal, Scott M. Adams, Howard E. Bond, Ryan M. Lau, Joel Johansson, Assaf Horesh, Kunal P. Mooley, Robert Fender, Kishalay De, Dónal O’Sullivan, Frank J. Masci, Ann Marie Cody, Nadia Blagorodnova, Ori D. Fox, Robert D. Gehrz, Peter A. Milne, Daniel A. Perley, Nathan Smith, Schuyler D. van Dyk

Research output: Contribution to journalArticlepeer-review


We present the discovery by the SPitzer InfraRed Intensive Transients Survey (SPIRITS) of a likely supernova (SN) in NGC 3556 (M108) at only 8.8 Mpc, which, despite its proximity, was not detected by optical searches. A luminous infrared (IR) transient at M[4.5] = −16.7 mag (Vega), SPIRITS 16tn is coincident with a dust lane in the inclined, star-forming disk of the host. Using observations in the IR, optical, and radio, we attempt to determine the nature of this event. We estimate AV ≈ 8–9 mag of extinction, placing it among the three most highly obscured IR-discovered SNe to date. The [4.5] light curve declined at a rate of 0.013 mag day−1, and the [3.6] − [4.5] color grew redder from 0.7 to & 1.0 mag by 184.7 days post discovery. Optical/IR spectroscopy shows a red continuum, but no clearly discernible features are evident, preventing a definitive spectroscopic classification. Deep radio observations constrain the radio luminosity of SPIRITS 16tn to Lν . 1024 erg s−1 Hz−1 between 3–15 GHz, excluding many varieties of radio core-collapse SNe. A type Ia SN is ruled out by the observed red IR color, and lack of features normally attributed to Fe-peak elements in the optical and IR spectra. SPIRITS 16tn was fainter at [4.5] than typical stripped-envelope SNe by ≈ 1 mag. Comparison of the spectral energy distribution (SED) to SNe II suggests SPIRITS 16tn was both highly obscured, and intrinsically dim, possibly akin to the low-luminosity SN 2005cs. We infer the presence of an IR dust echo powered by an initial peak luminosity of the transient of 5 × 1040 erg s−1 . Lpeak . 4 × 1043 erg s−1, consistent with the observed range for SNe II. This discovery illustrates the power of IR surveys to overcome the compounding effects of visible extinction and optically sub-luminous events in completing the inventory of nearby SNe.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Mar 1 2018


  • Dust
  • Extinction
  • Galaxies: individual (NGC 5336)
  • Supernovae: general
  • Supernovae: individual (SPIRITS 16tn)
  • Surveys

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