An Excess of Mid-infrared Emission from the Type Iax SN 2014dt

Supernovae Type Iax (SNe Iax) are less energetic and less luminous than typical thermonuclear explosions. A suggested explanation for the observed characteristics of this subclass is a binary progenitor system consisting of a CO white dwarf primary accreting from a helium star companion. A single-degenerate explosion channel might be expected to result in a dense circumstellar medium (CSM), although no evidence for such a CSM has yet been observed for this subclass. Here we present recent Spitzer observations of the SN Iax 2014dt obtained by the SPIRITS program nearly one year post-explosion that reveal a strong mid-IR excess over the expected fluxes of more normal SNe Ia. This excess is consistent with 10^-5{M}_⊙ of newly formed dust, which would be the first time that newly formed dust has been observed to form in a Type Ia. The excess, however, is also consistent with a dusty CSM that was likely formed in pre-explosion mass-loss, thereby suggesting a single degenerate progenitor system. Compared to other SNe Ia that show significant shock interaction (SNe Ia-CSM) and interacting core-collapse events (SNe IIn), this dust shell in SN 2014dt is less massive. We consider the implications that such a pre-existing dust shell has for the progenitor system, including a binary system with a mass donor that is a red giant, a red supergiant, or an asymptotic giant branch star.