Radial Profile of the 3.55 keV line out to $R_{200}$ in the Perseus
  Cluster
  The recent discovery of the unidentified emission line at 3.55 keV in
galaxies and clusters has attracted great interest from the community. As the
origin of the line remains uncertain, we study the surface brightness
distribution of the line in the Perseus cluster since that information can be
used to identify its origin. We examine the flux distribution of the 3.55 keV
line in the deep Suzaku observations of the Perseus cluster in detail. The 3.55
keV line is observed in three concentric annuli in the central observations,
although the observations of the outskirts of the cluster did not reveal such a
signal. We establish that these detections and the upper limits from the
non-detections are consistent with a dark matter decay origin. However, absence
of positive detection in the outskirts is also consistent with some unknown
astrophysical origin of the line in the dense gas of the Perseus core, as well
as with a dark matter origin with a steeper dependence on mass than the dark
matter decay. We also comment on several recently published analyses of the
3.55 keV line.
