Constraints on the sub-pc environment of the nearby Type Iax SN 2014dt from deep X-ray and radio observations

We present X-ray and radio observations of what may be the closest Type Iax supernova (SN) to date, SN 2014dt (d = 12.3-19.3 Mpc), and provide tight constraints on the radio and X-ray emission. We infer a specific radio luminosity LR < (1.0-2.4) × 1025 erg s-1 Hz-1 at a frequency of 7.5 GHz and a X-ray luminosity LX < 1.4 × 1038 erg s-1 (0.3-10 keV) at ~38- 48 d post-explosion. We interpret these limits in the context of Inverse Compton (IC) emission and synchrotron emission from a population of electrons accelerated at the forward shock of the explosion in a power-law distribution Ne(γe) α γe-p with p = 3. Our analysis constrains the progenitor system mass-loss rate to be M < 5.0 × 10-6M⊙ yr-1 at distances r ≤ 1016 cm for an assumed wind velocity vw = 100 km s-1, and a fraction of post-shock energy into magnetic fields and relativistic electrons of ϵB = 0.01 and ϵe = 0.1, respectively. This result rules out some of the parameter space of symbiotic giant star companions, and it is consistent with the low mass-loss rates expected from He-star companions. Our calculations also show that the improved sensitivity of the next-generation Very Large Array (ngVLA) is needed to probe the very low-density media characteristic of He stars that are the leading model for binary stellar companions of white dwarfs giving origin to Type Iax SNe.