7.1 keV sterile neutrino dark matter constraints from a deepChandraX-ray observation of the Galactic bulge Limiting Window

Abstract

Context. Recently an unidentified emission line at 3.55 keV has been detected in X-ray spectra of clusters of galaxies. The line has been discussed as a possible decay signature of 7.1 keV sterile neutrinos, which have been proposed as a dark matter (DM) candidate. Aims. We aim to further constrain the line strength and its implied mixing angle under the assumption that all DM is made of sterile neutrinos.Methods. The X-ray observations of the Limiting Window (LW) towards the Galactic bulge (GB) offer a unique dataset for exploring DM lines. We characterize the systematic uncertainties of the observation and the fitted models with simulated X-ray spectra. In addition we discuss uncertainties of indirect DM column density constraints towards the GB to understand systematic uncertainties in the assumed DM mass in the field of view of the observation. Results. We found tight constraints on the allowed flux for an additional line at 3.55 keV with a positive (∼ 1.5σ) best fit value F 3.55keV X ≈ (4.5 ± 3.5) × 10 −7 cts cm −2 s −1 . This would translate into a mixing angle of sin 2 (2Θ) ≈ (2.3 ± 1.8) × 10 −11 which, while consistent with some recent results, is in tension with earlier detections. Conclusions. We used a very deep dataset with well understood systematics to derive tight constraints on the mixing angle of a 7.1 keV sterile neutrino DM. The results highlight that the inner Milky Way will be a good target for DM searches with upcoming missions like eROSITA, XRISM, and ATHENA.

NuSTAR tests of sterile-neutrino dark matter: New Galactic bulge observations and combined impact

“…Space-based x-ray observatories such as HEAO-1 [59], Chandra [60,61], XMM-Newton [59,[62][63][64], Suzaku [39,65], Fermi-GBM [40], and INTEGRAL [41,66] have provided the most robust constraints on the χ → ν þ γ decay rate for m χ ≃ 1-100 keV. The observation of an unknown x-ray line at E ≃ 3.5 keV ("the 3.5-keV line") in several analyses [34][35][36] has led to much interest, as well as many follow-up analyses using different instruments and astrophysical targets [30,38,39,63,64,[67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83]. Some suggest that the 3.5-keV line may be a signature of sterileneutrino DM [84] or other DM candidates [85][86][87][88][89]; alternatively, modeling systematics [69,71] or novel astrophysical processes [90,<...>…”

The XMM Cluster Survey: new evidence for the 3.5-keV feature in clusters is inconsistent with a dark matter origin

“…Furthermore, an analysis of Chandra observations of the GC reported no detection of a 3.5-keV feature (Riemer-Sørensen 2016). Other searches for a 3.5-keV feature have analysed the spectra of the Galactic bulge (Hofmann & Wegg 2019); individual galaxies (Anderson, Churazov & Bregman 2015;Jeltema & Profumo 2016;Ruchayskiy et al 2016); galaxy stacks (Malyshev, Neronov & Eckert 2014); and Xray blank sky observations of the Milky Way (Dessert, Rodd & Safdi 2020).…”

The lensing properties of subhaloes in massive elliptical galaxies in sterile neutrino cosmologies

“…Sterile neutrinos are expected to decay into X-rays at a rate that is accessible to constraint/detection by X-ray observatories, particularly if the sterile neutrino mass is larger than 2 keV (Abazajian, Fuller & Patel 2001a;Abazajian, Fuller & Tucker 2001b). An unexplained X-ray line detected at an energy of 3.55 keV in stacked observations of galaxy clusters (Bulbul et al 2014), M31 (Boyarsky et al 2014), the Galactic Centre (Boyarsky et al 2015;Hofmann & Wegg 2019), and the Milky Way (MW) halo outskirts (Boyarsky et al 2018;Cappelluti et al 2018) counts the decay of a 7.1 keV sterile neutrino among its possible sources. As one of the most promising, although not uncontentious (see Anderson, Churazov & Bregman 2015;Jeltema & Profumo 2016;Ruchayskiy et al 2016), indirect dark matter detection signals, it constitutes a viable dark matter candidate, and is especially well suited to further study because the particle physics parameters that determine the X-ray decay signal also set the structure formation properties.…”