On the Lack of X-ray Bright Type IIP Supernovae
  Type IIP Supernovae (SNe) are expected to arise from Red Supergiant stars (RSGs). These stars have observed mass-loss rates that span more than two orders of magnitude, from $< 10^{-6}$ solar masses yr$^{-1}$ to almost $ 10^{-4} $ solar masses yr$^{-1}$. Thermal bremsstrahlung X-ray emission from at least some IIP's should reflect the larger end of the high mass-loss rates. Strangely, no IIP SNe are seen where the X-ray luminosity is large enough to suggest mass-loss rates greater than about $ 10^{-5} $ solar masses yr$^{-1}$. We investigate if this could be due to absorption of the X-ray emission. After carefully studying all the various aspects, we conclude that absorption would not be large enough to prevent us from having detected X-ray emission from high mass-loss rate IIP's. This leads us to the conclusion that there may be an upper limit of $\sim 10^{-5} $ solar masses yr$^{-1}$ to the mass-loss rate of Type IIP progenitors, and therefore to the luminosity of RSGs that explode to form Type IIPs. This is turn suggests an upper limit of $\leq 19 $ solar masses for the progenitor mass of a Type IIP SN. This limit is close to that obtained by direct detection of IIP progenitors, as well as that suggested by recent stellar evolution calculations. Although the statistics need to be improved, many current indicators support the notion that RSGs above $\sim 19 $ solar masses do not explode to form Type IIP SNe. 
Vikram V. Dwarkadas (University of Chicago)
astro-ph.HE astro-ph.SR