Gas temperature profiles in galaxy clusters with Swift XRT: observations
  and capabilities to map near R200
  We investigate the possibility of using the X-ray telescope (XRT) on board
the Swift satellite to improve the current accuracy of the ICM temperature
measurements in the region close to the virial radius of nearby clusters. We
present the spectral analysis of the Swift XRT observations of 6 galaxy
clusters and their temperature profiles in the regions within 0.2-0.6 r200.
Four of them are nearby famous and very well studied objects (Coma, Abell 1795,
Abell 2029 and PKS0745-19). The remaining two, SWJ1557+35 and SWJ0847+13, at
redshift z=0.16 and z=0.36, were serendipitously observed by Swift-XRT. We
accurately quantify the temperature uncertainties, with particular focus on the
impact of the background scatter (both instrumental and cosmic). We extrapolate
these results and simulate a deep observation of the external region of Abell
1795 which is assumed here as a case study. In particular we calculate the
expected uncertainties in the temperature measurement as far as r200. We find
that, with a fairly deep observation (300 ks), the Swift XRT would be able to
measure the ICM temperature profiles in the external regions as far as the
virial radius, significantly improving the best accuracy among the previous
measurements. This can be achieved thanks to the unprecedented combination of
good PSF over the full field of view and very accurate control of the
instrumental background. Somehow unexpectedly we conclude that, among currently
operating telescope, the Swift-XRT is the only potentially able to improve the
current accuracy in plasma temperature measurement at the edges of the cluster
potential. This will be true until a newgeneration of low-background and large
field of view telescopes, aimed to the study of galaxy clusters, will operate.
These observations would be of great importance in developing the observing
strategy for suchmissions.
