X-rays from the explosion site: Fifteen years of light curves of SN 1993J

TL;DR

This paper provides a detailed 15-year analysis of X-ray light curves from supernova SN 1993J, revealing the evolution of shock emissions and their relation to optical lines, supported by hydrodynamic simulations.

Contribution

It offers the first comprehensive long-term X-ray light curve analysis of SN 1993J, combining multiple observatories and confirming the reverse shock origin through hydrodynamic modeling.

Findings

X-ray flux declines follow a t^{-1} law after 5 years.

Soft X-ray emission dominates after a few hundred days.

Hα luminosity correlates with X-ray emission, indicating plasma clumps.

Abstract

We present a comprehensive analysis of the X-ray light curves of SN 1993J in a nearby galaxy M81. This is the only supernova other than SN 1987A, which is so extensively followed in the X-ray bands. Here we report on SN 1993J observations with the {\it Chandra} in the year 2005 and 2008, and Swift observations in 2005, 2006 and 2008. We combined these observations with all available archival data of SN 1993J, which includes ROSAT, ASCA, {\it Chandra}, and XMM-{\it Newton} observations from 1993 April to 2006 August. In this paper we report the X-ray light curves of SN 1993J, extending up to fifteen years, in the soft (0.3--2.4 keV), hard (2--8 keV) and combined (0.3--8 keV) bands. The hard and soft-band fluxes decline at different rates initially, but after about 5 years they both undergo a $t^{-1}$ decline. The soft X-rays, which are initially low, start dominating after a few hundred days. We interpret that most of the emission below 8 keV is coming from the reverse shock which is radiative initially for around first 1000-2000 days and then turn into adiabatic shock. Our hydrodynamic simulation also confirms the reverse shock origin of the observed light curves. We also compare the H$\alpha$ line luminosity of SN 1993J with its X-ray light curve and note that the H$\alpha$ line luminosity has a fairly high fraction of the X-ray emission, indicating presence of clumps in the emitting plasma.