Radio and gamma-ray constraints on dark matter annihilation in the Galactic center

TL;DR

This paper uses radio and gamma-ray observations of the Galactic center to set new, more stringent limits on dark matter annihilation cross sections, focusing on electron-positron production and their resulting emissions.

Contribution

It provides the first combined analysis of radio and gamma-ray data to constrain dark matter annihilation, reducing dependence on magnetic field assumptions.

Findings

Constraints on dark matter cross section are an order of magnitude stronger than previous limits.

For 10 GeV dark matter, the cross section must be below a few times 10^-25 cm^3 s^-1.

The analysis is robust against variations in magnetic field assumptions.

Abstract

We determine upper limits on the dark matter (DM) self-annihilation cross section for scenarios in which annihilation leads to the production of electron--positron pairs. In the Galactic centre (GC), relativistic electrons and positrons produce a radio flux via synchroton emission, and a gamma ray flux via bremsstrahlung and inverse Compton scattering. On the basis of archival, interferometric and single-dish radio data, we have determined the radio spectrum of an elliptical region around the Galactic centre of extent 3 degrees semi-major axis (along the Galactic plane) and 1 degree semi-minor axis and a second, rectangular region, also centered on the GC, of extent 1.6 degrees x 0.6 degrees. The radio spectra of both regions are non-thermal over the range of frequencies for which we have data: 74 MHz -- 10 GHz. We also consider gamma-ray data covering the same region from the EGRET instrument (about GeV) and from HESS (around TeV). We show how the combination of these data can be used to place robust constraints on DM annihilation scenarios, in a way which is relatively insensitive to assumptions about the magnetic field amplitude in this region. Our results are approximately an order of magnitude more constraining than existing Galactic centre radio and gamma ray limits. For a DM mass of m_\chi =10 GeV, and an NFW profile, we find that the velocity-averaged cross-section must be less than a few times 10^-25 cm^3 s^-1.