Volume 625, May 2019
|Number of page(s)||5|
|Section||Letters to the Editor|
|Published online||17 May 2019|
Letter to the Editor
7.1 keV sterile neutrino dark matter constraints from a deep Chandra X-ray observation of the Galactic bulge Limiting Window
Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
2 Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
Accepted: 30 April 2019
Context. An unidentified emission line at 3.55 keV was recently 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 characterise 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 find tight constraints on the allowed flux for an additional line at 3.55 keV with a positive (∼1.5σ) best fit value FX3.55 keV ≈ (4.5 ± 3.5) × 10−7 cts cm−2 s−1. This would translate into a mixing angle of sin2(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 systematic uncertainties to derive tight constraints on the mixing angle of a 7.1 keV sterile neutrino DM candidate. The results highlight that the inner Milky Way will be a good target for DM searches with upcoming missions like eROSITA, XRISM, and ATHENA.
Key words: Galaxy: bulge / dark matter
© F. Hofmann and C. Wegg 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Open Access funding provided by Max Planck Society.
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