Vikram

Even after several decades of study, the progenitor stars of supernovae (SNe) have proven difficult to identify. The identification of progenitors has generally been the purview of optical astronomy, aided in part by stellar evolution models. But observations at other
wavelengths can also provide several hints about the progenitors.

We have aggregated together data available in the literature, or analysed by us, to compute the lightcurves of almost all young SNe (days to years after explosion) that have been detected in X-rays. Currently we have about 60 SNe spanning all the various types, but the database is expanding rapidly. The lightcurves themselves span 12 orders of magnitude in luminosity. We use this library of lightcurves and spectra to explore the diversity of SNe, the characteristics of the environment into which they are expanding, and the implications for their progenitors. X-ray spectra can provide insight into the density structure, composition and metallicity of the surrounding medium, and the ionization level, through the spectra themselves as well as the X-ray absorption. Since core-collapse SNe expand mainly in environments created by the progenitor star mass-loss, this can provide crucial information about the nature of the progenitor star, and its mass-loss parameters in the decades or centuries before its death. We explore all SN types, with emphasis on Type IIP and Type IIn SNe. IIPs have the lowest X-ray luminosities, which is surprising given the high mass-loss rate, and low velocity, winds expected from their red supergiant (RSG) progenitors, and therefore the high density medium into which IIP SNe are expected to expand into. We show that the low X-ray luminosity sets a limit on the mass-loss rate, and thereby initial mass of a RSG star which can become a Type IIP progenitor. This initial mass limit, of about 19 solar masses, is consistent with that obtained via direct optical progenitor identification. IIns are observed to have high X-ray luminosities in general, but their light curves are very diverse, with some of them tending to fall off very steeply. We explore the implications of this behaviour.