A Hot Spot in Coma

Abstract

We study the temperature structure of the central part (r ≤ 18'≃ 0.7 h-150 Mpc) of the Coma Cluster of galaxies using ASCA data. Two different analysis methods produce results in good agreement with each other and reveal the presence of interesting structures in the gas temperature distribution. Globally, the average temperature in the center of the cluster is 9.0 ± 0.6 keV, which is in good agreement with previous results. Superimposed on this we find a cool area with temperatures of 4-6 keV associated with a filament of X-ray emission extending southeast from the cluster center and detected by Vikhlinin and coworkers. We also find a hot spot with a temperature of around 13 keV displaced north from the central peak of emission. The distribution of the gas temperatures and relative specific entropies suggests that the cool features are most likely gas stripped from a galaxy group centered on NGC 4874 and falling toward the core from outside, while the hot spot located " ahead " of this infalling gas is due to shock heating. Thus our results suggest that we are observing Coma during a minor merger with a small group of galaxies associated with NGC 4874 shortly before the initial core passage.