An XMM-Newton study of the mixed-morphology supernova remnant W28

We perform an XMM-Newton study of the mixed-morphology supernova remnant (MMSNR) W28. The X-ray spectrum arising from the northeastern shell consists of a thermal component plus a non-thermal power-law component with a hard photon index (~1.5). Non-thermal bremsstrahlung is the most favourible origin of the hard X-ray emission. The gas in the SNR interior is centrally peaked and best described by a two-temperature thermal model. We found a non-uniform absorption column density and temperature profile for the central gas, indicating that the remnant is evolving in a non-uniform environment with denser material in the east. We argue that the cloudlet evaporation is an indispensable process to explain both the spectral properties and the clumpiness in the X-ray emission.