  For the first time, we use the Gamma-ray Burst Monitor (GBM) on-board the
Fermi satellite to search for sterile neutrino decay lines in the energy range
10-25 keV corresponding to sterile neutrino mass range 20-50 keV. This energy
range has been out of reach of traditional X-ray satellites such as Chandra,
Suzaku, XMM-Newton, and gamma-ray satellites such as INTEGRAL. Furthermore, the
extremely wide field of view of the GBM opens a large fraction of the Milky Way
dark matter halo to be probed. We start with 1601 days worth of GBM data,
implement stringent data cuts, and perform two simple line search analyses on
the reduced data: in the first, the line flux is limited without background
modeling, and in the second, the background is modeled as a power-law. We find
no significant excess lines in both our searches. We set new limits on sterile
neutrino mixing angles, improving on previous limits by approximately an order
of magnitude. Better understanding of detector and astrophysical backgrounds,
as well as detector response, can further improve the limit.

High Energy Astrophysical Phenomena