Decaying dark matter search with NuSTAR deep sky observations

TL;DR

This study uses NuSTAR deep sky observations to search for decaying dark matter in the 6-40 keV range, improving constraints on decay times and identifying potential spectral lines, with implications for sterile neutrino dark matter.

Contribution

It provides new constraints on dark matter decay times and masses, especially for sterile neutrinos, using NuSTAR's high sensitivity and large aperture observations.

Findings

Improved constraints on dark matter decay time by up to an order of magnitude.

Detected four unidentified spectral lines, possibly due to systematics or astrophysical sources.

Imposed an upper bound of 20 keV on sterile neutrino dark matter mass.

Abstract

We present the results of the search for decaying dark matter with particle mass in the 6-40 keV range with NuSTAR deep observations of COSMOS and ECDFS empty sky fields. We show that main contribution to the decaying dark matter signal from the Milky Way galaxy comes through the aperture of the NuSTAR detector, rather than through the focusing optics. High sensitivity of the NuSTAR detector, combined with the large aperture and large exposure times of the two observation fields allow us to improve previously existing constraints on the dark matter decay time by up to an order of magnitude in the mass range 10-30 keV. In the particular case of the nuMSM sterile neutrino dark matter, our constraints impose an upper bound m<20 keV on the dark matter particle mass. We report detection of four unidentified spectral lines in our data set. These line detections are either due to the systematic effects (uncertainties of calibrations of the NuSTAR detectors) or have an astrophysical origin. We discuss different possibilities for testing the nature of the detected lines.