In this work we revise the estimate of dark matter (DM) decay signals from dwarf galaxies in the Milky Way. They are ideal for indirect DM searches, since they are known to be DM dominated systems. We test both warm and cold DM candidates, i.e. sterile neutrinos decaying into X-ray photons and a heavier DM candidate decaying into gamma rays.
We analyze the sensitivity to such a signal for both ground- and space-based detectors: Athena, XRISM and eROSITA for X-rays and HAWC and CTA for very-high-energy gamma rays. We consider sterile neutrinos with masses between 4-20 keV and masses for the heavier DM candidate in the range of 200 TeV to 20 PeV, decaying via a $b\bar{b}$ or a $\tau^+\tau^-$ channel.
We make projections for future dwarf galaxies that would be newly discovered with the Vera Rubin Observatory Legacy Survey of Space and Time, which will further improve the expected sensitivity to DM decays both in the keV and TeV mass ranges. Our results show that all of these X-ray telescopes will be able to critically assess the claim of 7 keV sterile neutrino decays from stacked galaxy clusters and nearby galaxies, reaching sensitivities of $\sin^2(2\theta)\sim10^{-12}-10^{-13}$.
For TeV dark matter, both HAWC and CTA will be sensitive to DM lifetimes of $10^{27}-10^{28}$ seconds.