  We present a Chandra, Suzaku and Rosat study of the hot Intra Group Medium
(IGrM) of the relaxed fossil group/ poor cluster RXJ1159+5531. This group
exhibits an advantageous combination of flat surface brightness profile, high
luminosity and optimal distance, allowing the gas to be detected out to the
virial radius (Rvir=R108=1100 kpc) in a single Suzaku pointing, while the
complementary Chandra data reveal a round morphology and relaxed IGrM image
down to kpc scales. We measure the IGrM entropy profile over 3 orders of
magnitude in radius, including 3 data bins beyond 0.5R200 with azimuthal
coverage (>30%). We find no evidence that the profile flattens at large scales
(>R500), and when corrected for the enclosed gas fraction, the entropy profile
is very close to the predictions from self-similar structure formation
simulations, as seen in massive clusters. Within Rvir, we measure a baryon
fraction of 0.17+/-0.02, consistent with the Cosmological value. These results
are in sharp contrast to the gas behaviour at large scales recently reported in
the Virgo and Perseus clusters, and indicate that substantial gas clumping
cannot be ubiquitous near Rvir, at least in highly evolved (fossil) groups.
