A recent X-ray observation of the cluster 1E 0657 - 56 ( z = 0.296 ) with ASCA implied an unusually high temperature of \sim 17 keV .
Such a high temperature would make it the hottest known cluster and severely constrain cosmological models since , in a Universe with critical density ( \Omega = 1 ) the probability of observing such a cluster is only \sim 4 \times 10 ^ { -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 \sim 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 .
Using simulated data for a 12 keV cluster , we show that a high temperature of \sim 17 keV is artificially obtained if the true spectrum has a stronger low-energy cut-off than that for Galactic absorption only .
The apparent extra absorption may be astrophysical in origin , ( either intrinsic or line-of-sight ) , or it may be a problem with the low-energy CCD efficiency .
Although significantly lower than previous measurements , this temperature of kT \sim 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 signal-to-noise to that of the 1E 0657 - 56 data reported here .