1E0657-56: A Contender for the Hottest Known Cluster of Galaxies
  We identify the extended Einstein IPC X-ray source, 1E0657-56, with a previously unknown cluster of galaxies at a redshift of $z=0.296$. Optical CCD images show the presence of a gravitational arc in this cluster and galaxy spectra yield a cluster velocity dispersion of $1213^{+352}_{-191}$ km s$^{-1}$. X-ray data obtained with the ROSAT HRI and ASCA indicate that 1E0657-56 is a highly luminous cluster in which a merger of subclusters may be occurring. The temperature of the hot gas in 1E0657-56 is $\rm{kT}=17.4 \pm 2.5 keV$, which makes it an unusually hot cluster, with important cosmological implications. 
W. Tucker, P. Blanco, S. Rappoport, L. David, D. Fabricant, E.E.   Falco, W. Forman, A. Dressler, and M. Ramella