The diffuse soft excess emission in the Coma cluster from the ROSAT
  All-Sky Survey
  RASS data near the North Galactic Pole was analyzed in order to study the
large-scale distribution of soft X-ray emission from the Coma cluster. These
RASS data constitute the only available X-ray observations of Coma that feature
an in situ -- temporally and spatially contiguous -- background, with unlimited
and continuous radial coverage. These unique characteristics of the RASS data
are used to deliver a final assessment on whether the soft excess previously
detected in the Coma cluster is due to background subtraction errors, or not.
This paper confirms the presence of soft X-ray excess associated with Coma, and
reports the detection of 1/4 keV band excess out to 5 Mpc from the cluster
center, the largest soft excess halo discovered to date. We propose that the
emission is related to filaments that converge towards Coma, and generated
either by non-thermal radiation caused by accretion shocks, or by thermal
emission from the filaments themselves.
