X-RAY SPECTRAL OBSERVATIONS OF CLUSTERS OF GALAXIES UNDERGOING MERGEREVENTS

We have analyzed the HEAO 1 A2 observations of two clusters whose opti cal and X-ray isophotes are suggestive of merging subclusters, A119 an d A754, and find evidence of nonisothermal X-ray emission from both cl usters. The X-ray spectrum of both clusters, when fitted with a single isothermal model, shows residual soft X-ray emission. There is a stat istically significant reduction in chi2 (98% probability based on the F-test) when a second temperature component is added. If the asymmetri c isophotes seen in the soft X-ray image are indicative of merging sub clusters, then our analysis of the Einstein Imaging Proportional Count er (IPC) spectra and Solid State Spectrometer (SSS) observations of A7 54, which provide some spatial and spectral resolution, suggests that the two temperature components seen in the HEAO 1 A2 spectra are assoc iated with gas trapped in the subcluster potential wells. The implied subcluster isothermal masses suggest that a more massive cluster is ac creting a less massive companion in A754. The present observations can not rule out the alternative possibility that the cooler gas is associ ated with the outer cluster atmosphere rather than individual subclust ers, as appears to be the case for A119. Astro D observations will be necessary to distinguish between these two possibilities for both clus ters.