Improved Limits on Sterile Neutrino Dark Matter using Full-Sky Fermi Gamma-Ray Burst Monitor Data

TL;DR

This paper uses Fermi GBM data to set new upper limits on sterile neutrino dark matter decay lines in the 10-25 keV range, surpassing previous constraints and demonstrating the potential of wide-field gamma-ray observations.

Contribution

First to utilize Fermi GBM for sterile neutrino decay line searches in the 10-25 keV range, providing significantly improved upper limits on mixing angles.

Findings

No significant decay line detected.

Upper limits improved by about an order of magnitude in 25-40 keV range.

Wide field of view enables large-scale dark matter halo probing.

Abstract

A sterile neutrino of ~keV mass is a well motivated dark matter candidate. Its decay generates an X-ray line that offers a unique target for X-ray telescopes. For the first time, we use the Gamma-ray Burst Monitor (GBM) onboard the Fermi Gamma-Ray Space Telescope to search for sterile neutrino decay lines; our analysis covers the energy range 10-25 keV (sterile neutrino mass 20-50 keV), which is inaccessible to X-ray and gamma-ray satellites such as Chandra, Suzaku, XMM-Newton, and INTEGRAL. The extremely wide field of view of the GBM enables a large fraction of the Milky Way dark matter halo to be probed. After implementing careful data cuts, we obtain ~53 days of full sky observational data. We observe an excess of photons towards the Galactic Center, as expected from astrophysical emission. We search for sterile neutrino decay lines in the energy spectrum, and find no significant signal. From this, we obtain upper limits on the sterile neutrino mixing angle as a function of mass. In the sterile neutrino mass range 25-40 keV, we improve upon previous upper limits by approximately an order of magnitude. Better understanding of detector and astrophysical backgrounds, as well as detector response, will further improve the sensitivity of a search with the GBM.