X-RAY OBSERVATIONS OF SUPERNOVA-REMNANTS AS DISTANCE INDICATORS

We investigate whether ROSAT observations of thermal X-ray emission fr om shell-type supernova remnants (SNRs) can be used to constrain their distances. The most critical assumption is that the initial kinetic e nergy (epsilon0) of a supernova (SN) explosion is a constant at epsilo n0 = 10(51) ergs; however, the derived distance (D) is only weakly dep endent on epsilon0 (D is-proportional-to epsilon0(0.4)). We evaluate t his technique by applying it to SNRs with independently determined dis tances, and our initial results indicate good agreement. We conclude t hat the ROSAT all-sky survey may be used to establish, for the first t ime, a set of good distance estimates to a large number of extended, s hell-type SNRs. The energy range of ROSAT is well suited for this purp ose, since most shell-type SNRs have thermal X-ray spectra which peak within the ROSAT PSPC energy range of 0.1-2.4 keV.