Abstract
An unidentified line at energy around 3.5 keV was detected in the spectra of dark matter-dominated objects. Recent work [1] used 30~Msec of XMM-Newton blank-sky observations to constrain the admissible line flux, challenging its dark matter decay origin. We demonstrate that these bounds are overestimated by more than an order of magnitude due to improper background modeling. Therefore, the dark matter interpretation of the 3.5~keV signal remains viable.
Highlights
An X-ray line at E 3.5 keV has been found in 2014 [2, 3]
As well as follow-up detections, have been reported, while non-detections have not ruled out the dark matter interpretation of the signal
Ref. [1] (DRS20 in what follows) recently reported bounds on the decay lifetime, which are about an order of magnitude below those required for dark matter interpretation
Summary
Model components Powerlaw Powerlaw Line @ 3.3 keV Line @ 3.68 keV Powerlaw Line @ 3.3 keV Line @ 3.68 keV Powerlaw Line @ 3.12 keV Line @ 3.3 keV Line @ 3.68 keV Line @ 3.9 keV. Our limits (“blue model”) are consistent with DSR20: strong constraints around 3.5 keV, lines at ∼ 3.3 and 3.68 keV detected with significance ≥ 3σ, consistently with significant weakening on the DRS20 limits at these energies. Such lines (Ar XVIII and S XVI complexes around 3.3 keV, and Ar XVII plus K XIX around 3.68 keV) are detected in astrophysical plasma both in galaxy clusters [2,6,7] and in our Galaxy [8,9,10,11].
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