  The standard model of particle physics assumes that neutrinos are massless,
although adding non-zeros is required by the experimentally established
phenomenon of neutrino oscillations requires neutrinos to have non-zero mass.
Sterile neutrinos (or right-handed neutrinos) are a good warm dark matter
candidate. We find that the excess of the intensity in the 8.7 keV line (at the
energy of the FeXXVI Ly$\gamma$ line) in the spectrum of the Galactic center
observed by the Suzaku X-ray mission cannot be explained by standard ionization
and recombination processes. We suggest that the origin of this excess is via
decays of sterile neutrinos with a mass of 17.4 keV and estimate the value of
the mixing angle. The estimated value of the mixing angle $\sin^2(2\theta)=(4.1
\pm 2.2)\times10^{-12}$ lies in the allowed region of the mixing angle of dark
matter sterile neutrino with a mass of 17-18 keV.
