X-ray emission from galactic supernova remnants.

X-ray emission from galactic supernova remnants X-ray images and spectra are used to determine the structure and physical conditions of shock heated interstellar gas and stellar ejecta within three galactic supernova remnants (SNRs). Parameters describing the initial supernova explosions (total energy, ejected mass) and ambient interstellar medium (density, homogeneity) are then derived. The interior density of the "middle-aged" SNR W44 is found to be fairly uniform, and inconsistent with the standard Sedov model, but similar to that predicted by models in which thermal conduction and/or heating and evaporation of engulfed, cold, interstellar clouds are important. This expanding bubble of hot, high pressure gas is likely to be an example of the formation of the hot component of interstellar medium, as detected in the vicinity of the Sun. In addition, it is likely that the SNR has collided with a nearby dense molecular cloud. The SNR W49B is found to be probably the remnant of a Type II supernova which occurred in a relatively dense medium 2000-5000 years ago. The abundance of hot iron in the ejecta is consistent with the cosmic value. The youngest SNR studied, SN1006, is found to be the remnant of a Type I supernova which occurred in a region of low, but fairly uniform (to within a factor of 2), interstellar density. Emission from reverse shocked ejecta may be most prominent in a limited area of the SNR, explaining a discrepancy between previous X-ray spectra of the remnant. A common result in all three SNRs is the detection of hot gas at their centres; the likely effects of a reverse shock and thermal conduction within SNRs are emphasized.