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

Abstract

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. We aim to further constrain the line strength and its implied mixing angle under the assumption that all DM is made of sterile neutrinos. 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. We found tight constraints on the allowed flux for an additional line at 3.55 keV with a positive ($\sim 1.5\sigma$) best fit value ${\mathrm{F}}_{\mathrm{X}}^{3.55keV}\approx (4.5\pm 3.5)\times 10^{-7}\mathrm{cts}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$. This would translate into a mixing angle of $\mathrm{si}{\mathrm{n}}^2(2\Theta )\approx (2.3\pm 1.8)\times 10^{-11}$ which, while consistent with some recent results, is in tension with earlier detections. 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.

5 pages, 3 figures, accepted A&A Letter

References in corpus (11)

• The Local Dark Matter Density
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• Discrete sources as the origin of the Galactic X-ray ridge emission
• Contour binning: a new technique for spatially-resolved X-ray spectroscopy applied to Cassiopeia A
• New Constraints on Sterile Neutrino Dark Matter from $NuSTAR$ M31 Observations
• The Galactic Centre Chimney
• Hitomi constraints on the 3.5 keV line in the Perseus galaxy cluster
• Constraints on decaying Dark Matter from XMM-Newton observations of M31
• MOA-II Galactic Microlensing Constraints: The Inner Milky Way has a Low Dark Matter Fraction and a Near Maximal Disk
• Laboratory measurements compellingly support charge-exchange mechanism for the 'dark matter' $\sim$3.5 keV X-ray line
• Decaying dark matter search with NuSTAR deep sky observations

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