The effect of a circumstellar medium on the X-ray emission of young remnants of Type II supernovae

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Abstract
Many Type II supernovae explode in dense circumstellar media (CSM). We have investigated the subsequent dynamical evolution and non-equilibrium X-ray emission of the supernova remnant (SNR), using a spherically symmetric hydrodynamic code. The interaction of the supernova ejecta with the dense CSM leads to strong X-ray emission. An extraordinarily high X-ray luminosity of an SNR in NGC 4449 may be interpreted in terms of such an interaction. The interaction leads also to hardening of the X-ray spectrum, if electrons are not heated substantially at the collisionless shock front. After the blast shock breaks out of the CSM into the rarefied ambient medium, the SNR undergoes nearly unimpeded expansion, and the X-ray emission declines drastically. At this stage, the recombination exceeds the ionization, and the X-ray spectrum is characterized by strong recombination lines and continua. However, such spectra have not been observed in young SNRs. The CSM of those supernovae may be considerably less dense or more extended than the CSM of Type II–L supernovae such as SN 1979C and SN 1980K. Alternatively, the CSM of Type II supernovae may be highly inhomogeneous or asymmetric.

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