A search for infrared emission from core-collapse supernovae at the transitional phase

Most of the observational studies of supernova (SN) explosions are limited to early phases (<a few years after the explosion) of extragalactic SNe and observations of SN remnants (>100yr) in our Galaxy or very nearby galaxies. SNe at the epoch between these two, which we call the "transitional" phase, have not been explored in detail except for several extragalactic SNe including SN1987A in the Large Magellanic Cloud. We present theoretical predictions for the infrared (IR) dust emissions by several mechanisms; emission from dust formed in the SNejecta, light echo by circumstellar (CS) and interstellar (IS) dust, and emission from shocked CS dust. We search for IR emission from six core-collapse SNe at the transitional phase in the nearby galaxies NGC1313, NGC6946, and M101 by using the data taken with the AKARI satellite and Spitzer. Among six targets, we detect the emission from SN1978K in NGC1313. SN1978K is associated with 1.3 × 10^-3 M _⊙ of silicate dust. We show that, among several mechanisms, the shocked CS dust is the most probable emission source to explain the IR emission observed for SN1978K. IR emission from the other five objects is not detected. Our current observations are sensitive to IR luminosity of >10³⁸ erg s^-1, and the non-detection of SN1962M excludes the existence of the shocked CS dust for a high gas mass-loss rate of ∼10^-4 M _⊙ yr^-1. Observations of SNe at the transitional phase with future IR satellites will fill the gap of IR observations of SNe with the age of 10-100yr, and give a new opportunity to study the CS and IS environments of the progenitor, and possibly dust formation in SNe.