Rescued from oblivion: detailed analysis of archival Spitzer data of SN 1993J

SN 1993J is one of the best-studied supernovae (SNe) with an extensive, decade-long multi-wavelength dataset published in various papers; however, its detailed late-time mid-infrared (mid-IR) analysis is still missing from the literature. Mid-IR data provides numerous advantages, in particular it follows not only the continuously cooling SN ejecta but also late-time dust formation and circumstellar interaction processes. We carried out a detailed analysis on archive mid-IR Spitzer data of SN 1993J. We present the late-time evolution of the SN and also provide evidence that its observed late-time mid-IR excess can be described by the presence of two-component local dust. Furthermore, we investigated the origin of this excess and examined both the newly-formed and the collisonally/ radiatively heated pre-existing dust scenarios as well. We came to the conclusion that the source of the components can be either newly-formed dust grains (assumed to be located both in the unshocked inner ejecta and in the outer cold dense shell - just as seen in the Cassiopeia A remnant and also assumed in other dust-forming SNe in a few years after explosion), or heating of pre-existing dust via ongoing CSM interaction.