Swift observation of Segue 1: constraints on sterile neutrino parameters in the darkest galaxy

TL;DR

This study uses Swift X-ray observations of the dark galaxy Segue 1 to set new constraints on sterile neutrino dark matter by searching for decay signals, finding none and thus limiting their possible properties.

Contribution

First X-ray constraints on sterile neutrino parameters in the highest dark matter density environment of Segue 1.

Findings

No spectral features detected that indicate sterile neutrino decay.

Established upper bounds on sterile neutrino mixing angles and masses.

Provided the most sensitive X-ray search in a high dark matter density region.

Abstract

Some extensions of standard particle physics postulate that dark matter may be partially composed of weakly interacting sterile neutrino particles that have so far eluded detection. We use a short (~5 ks) archival X-ray observation of Segue 1 obtained with the X-ray Telescope (XRT) onboard the Swift satellite to exclude the presence of sterile neutrinos in the 1.6 - 14 keV mass range down to a flux limit of 6 x 10^{-12} erg cm-2 s-1 within 67 pc of its centre. With an estimated mass-to-light ratio of ~3400 Msun/Lsun, Segue 1 is the darkest ultrafaint dwarf galaxy currently measured. Spectral analysis of the Swift XRT data fails to find any non-instrumental spectral feature possibly connected with the radiative decay of a dark matter particle. Accordingly, we establish upper bounds on the sterile neutrino parameter space based on the non-detection of emission lines in the spectrum. The present work provides the most sensitive X-ray search for sterile neutrinos in a region with the highest dark matter density yet measured.