Thermal X-ray Emission from Centre-filled Supernova Remnants

Abstract

Two middle-aged supernova remnants, W44 (G34.6-0.5) and W28 (G6.4-0.1), have been studied using EINSTEIN IPC imaging data and EXOSAT ME spectra. Both remnants have a centre-filled X-ray morphology and a radio shell, but the X-ray spectra imply a thermal origin (in one case iron Ka line emission is revealed). Deprojection analyses of the X-ray images have been performed under simplfying assumptions and radial density distributions derived. These are inconsistent with a simple Sedov model, but are more similar to predictions of models involving evaporation of cold ISM clouds in the remnant centre.