The Entire Virial Radius of the Fossil Cluster RXJ1159+5531: I. Gas
  Properties
  Previous analysis of the fossil-group/cluster RXJ1159+5531 with X-ray
observations from a central Chandra pointing and an offset-North Suzaku
pointing indicate a radial intracluster medium (ICM) entropy profile at the
virial radius ($R_{\rm vir}$) consistent with predictions from gravity-only
cosmological simulations, in contrast to other cool-core clusters. To examine
the generality of these results, we present three new Suzaku observations that,
in conjunction with the North pointing, provide complete azimuthal coverage out
to $R_{\rm vir}$. With two new Chandra ACIS-I observations overlapping the
North Suzaku pointing, we have resolved $\gtrsim$50\% of the cosmic X-ray
background there. We present radial profiles of the ICM density, temperature,
entropy, and pressure obtained for each of the four directions. We measure only
modest azimuthal scatter in the ICM properties at $R_{\rm 200}$ between the
Suzaku pointings: 7.6\% in temperature and 8.6\% in density, while the
systematic errors can be significant. The temperature scatter, in particular,
is lower than that studied at $R_{\rm 200}$ for a small number of other
clusters observed with Suzaku. These azimuthal measurements verify that
RXJ1159+5531 is a regular, highly relaxed system. The well-behaved entropy
profiles we have measured for RXJ1159+5531 disfavor the weakening of the
accretion shock as an explanation of the entropy flattening found in other
cool-core clusters but is consistent with other explanations such as gas
clumping, electron-ion non-equilibrium, non-thermal pressure support, and
cosmic ray acceleration. Finally, we mention that the large-scale galaxy
density distribution of RXJ1159+5531 seems to have little impact on its gas
properties near $R_{\rm vir}$.
