ROSAT X-ray observations of the supernova remnant HB 21

HB 21 is one of the class of large diameter evolved supernova remnants. It was observed by the PSPC detector of the Rontgen-Satellit ROSAT, and the data have been taken during the survey phase of the ROSAT mission. The ROSAT x-ray image of HB 21 is presented here with angular resolution of 1 arcminute. It shows a centrally brightened form, in contrast to the radio image which is of irregular shell type form. The PSPC spectral analysis shows that HB 21 has no significant temperature variations. An interpretation of the x-ray observations is presented in terms of the White and Long (1991) solution for a blast wave propagating in an inhomogeneous interstellar medium.