Consistency of dark matter interpretations of the 3.5 keV X-ray line

Tentative evidence of a 3.5 keV X-ray line has been found in the stacked spectra of galaxy clusters, individual clusters, the Andromeda galaxy and the galactic center, leading to speculation that it could be due to decays of metastable dark matter such as sterile neutrinos. However searches for the line in other systems such as dwarf satellites of the Milky Way have given negative or ambiguous results. We reanalyze both the positive and negative searches from the point of view that the line is due to inelastic scattering of dark matter to an excited state that subsequently decays---the mechanism of excited dark matter (XDM). Unlike the metastable dark matter scenario, XDM gives a stronger signal in systems with higher velocity dispersions, such as galaxy clusters. We show that the predictions of XDM can be consistent with null searches from dwarf satellites, while the signal from the closest individual galaxies can be detectable having a flux consistent with that from clusters. We discuss the impact of our new fits to the data for two specific realizations of XDM.
Comment: 14 pages, 10 figures; v.2. corrected error in M31 field of view; main results unchanged; v.3. incorporated results from arXiv:1411.0050, improved fig. 1, added references; v.4. changed title for journal, added references, clarified role of XDM parameters; v.5. fixed typos, content matches published version