New Limits on the Dark Matter Lifetime from Dwarf Spheroidal Galaxies using Fermi-LAT

Matthew G. Baring, Tathagata Ghosh, Farinaldo S. Queiroz, Kuver Sinha

Published 2015-10-01Version 1

Dwarf spheroidal galaxies are promising targets for the indirect detection of dark matter through gamma-ray emission due to their proximity, lack of astrophysical backgrounds and high dark matter density. They are often used to place restrictive bounds on the dark matter annihilation cross section. In this letter, we analyze six years of Fermi-LAT gamma-ray data from 20 Dwarf Spheroidal galaxies that are satellites of the Milky Way, and derive for the first time in the literature from a stacked analysis, robust 95\% confidence level upper limits on the dark matter lifetime for several decay channels and dark matter masses between 10 GeV and 10 TeV. Our constraints from this ensemble, and from Reticulum II and Draco in particular, are among the most stringent and solid in the literature, and competitive with existing ones coming from the extragalactic gamma-ray background, galaxy clusters, AMS-02 cosmic ray data, Super-K and ICECUBE neutrino data, while rather insensitive to systematic uncertainties. In particular, we significantly improve existing limits for dark matter decaying into bb ($\mu\mu$) for DM masses below $\sim$ 100 (10) GeV, demonstrating that dwarf galaxies are compelling targets for constraining dark matter decay lifetimes.