Searching for the 3.5 keV Line in the Stacked Suzaku Observations of
  Galaxy Clusters
  We perform a detailed study of the stacked Suzaku observations of 47 galaxy
clusters, spanning a redshift range of 0.01-0.45, to search for the
unidentified 3.5 keV line. This sample provides an independent test for the
previously detected line. We detect only a 2sigma-significant spectral feature
at 3.5 keV in the spectrum of the full sample. When the sample is divided into
two subsamples (cool-core and non-cool core clusters), cool-core subsample
shows no statistically significant positive residuals at the line energy. A
very weak (2sigma-confidence) spectral feature at 3.5 keV is permitted by the
data from the non-cool core clusters sample. The upper limit on a neutrino
decay mixing angle from the full Suzaku sample is consistent with the previous
detections in the stacked XMM-Newton sample of galaxy clusters (which had a
higher statistical sensitivity to faint lines), M31, and Galactic Center at a
90% confidence level. However, the constraint from the present sample, which
does not include the Perseus cluster, is in tension with previously reported
line flux observed in the core of the Perseus cluster with XMM-Newton and
Suzaku.
