A recent X-ray observation of the cluster 1E0657-56 (z=0.296) with ASCA
implied an unusually high temperature of ~17 keV. Such a high temperature would
make it the hottest known cluster and severely constrain cosmological since, in
a Universe with critical density Omega=1 the probability of observing such a
cluster is only 4e-5. Here we test the robustness of this observational result
since it has such important implications. We analysed the data using a variety
of different data analysis methods and spectral analysis assumptions and find a
temperature of ~11-12 keV in all cases, except for one class of spectral fits.
These are fits in which the absorbing column density is fixed at the Galactic
value. We show that a high temperature of ~17 keV is artificially obtained if
the true spectrum has a stronger low- energy cut-off than that for Galactic
absorption only. The extra absorption may be astrophysical in origin, or it may
be a problem with the low-energy CCD efficiency. Although significantly lower
than previous measurements, this temperature of kT ~11-12 keV is still
relatively high since only a few clusters have been found to have temperatures
higher than 10 keV and the data therefore still present some difficulty for an
Omega=1 Universe. Our results will also be useful to anyone who wants to
estimate the systematic errors involved in different methods of background
subtraction of ASCA data for sources with similar S/N to that of the 1E0657-56
data reported here.Comment: 14 pages plus 2 figures. Latex with separate postscript figure files.
AASTEX 4.0 macro. Accepted for the Astrophysical Journal Letter
