X-RAYS FROM THE EXPLOSION SITE: 15 YEARS OF LIGHT CURVES OF SN 1993J

We present a comprehensive analysis of the X-ray light curves of supernova (SN) 1993J in a nearby galaxy M81. This is the only SN other than SN 1987 Lambda, which is so extensively followed in the X-ray bands. Here, we report on SN 1993J observations with 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, Chandra, and XMM-Newton observations from 1993 April to 2006 August. In this paper, we report the X-ray light curves of SN 1993J, extending up to 15 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.