X-ray emission from supernovae in dense circumstellar matter environments: A search for collisionless shocks

TL;DR

This study investigates X-ray emissions from supernovae in dense circumstellar environments, finding evidence for collisionless shocks in some cases and suggesting shock breakout as a power source for certain supernova light curves.

Contribution

It provides observational evidence linking X-ray emissions to collisionless shocks and shock breakout in dense CSM for specific supernova types, advancing understanding of supernova explosion mechanisms.

Findings

Two supernovae show X-ray properties consistent with collisionless shocks.

Some supernovae's optical light curves are powered by shock breakout in CSM.

X-ray limits for other supernovae are inconclusive due to observational constraints.

Abstract

(Abridged). The optical light curve of some SNe may be powered by the outward diffusion of the energy deposited by the explosion shock in optically thick circumstellar matter (CSM). Recently, it was shown that the radiation-mediated and -dominated shock in an optically thick wind must transform into a collisionless shock and can produce hard X-rays. The X-rays are expected to peak at late times, relative to maximum visible light. Here we report on a search, using Swift and Chandra, for X-ray emission from 28 SNe that belong to classes whose progenitors are suspected to be embedded in dense CSM (IIn/Ibn/SLSN-I). Two SNe in our sample have X-ray properties that are roughly consistent with the expectation for X-rays from a collisionless shock in optically thick CSM. Therefore, we suggest that their optical light curves are powered by shock breakout in CSM. We show that two other events were too X-ray bright during the SN maximum optical light to be explained by the shock breakout model. We conclude that the light curves of some, but not all, type-IIn/Ibn SNe are powered by shock breakout in CSM. For the rest of the SNe in our sample, including all the SLSN-I events, our X-ray limits are not deep enough and were typically obtained at too early times to conclude about their nature. We argue that the optical light curves of SNe, for which the X-ray emission peaks at late times, are likely powered by the diffusion of shock energy from a dense CSM. We comment about the possibility to detect some of these events in radio.