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 kT = 17.4 \pm~ { } 2.5 keV , which makes it an unusually hot cluster , with important cosmological implications .