A ring around the heart of supernova remnant HB3

The discovery of bright ringlike Xray emission at the heart of the largesupernova remnant (SNR) HB3 has invoked many possible explanations for thisunique morphology including a second SNR, a presupernova circumstellar shell,or an unusual density distribution. However, previous observations of thisremnant have either suffered from significant flaring, or were taken by lowspatial and spectral resolution instruments. This makes it difficult tocharacterise the properties of this central emission, and determine the originof this unique morphology. Here we propose two XMMNewton observations of theheart of HB3 to map its bright central emission and some of its diffusesurroundings in an attempt to shed light on origin and nature this structure. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]