On the gamma-ray emission from the core of the Sagittarius dwarf galaxy

TL;DR

This study analyzes gamma-ray emissions from the Sagittarius dwarf galaxy's core using Fermi-LAT data, testing whether the emission is due to millisecond pulsars or dark matter annihilation, and finds results compatible with both hypotheses.

Contribution

It provides the first detailed spectral and spatial analysis of gamma-ray emission from Sagittarius dwarf galaxy, exploring both pulsar and dark matter origins with new constraints.

Findings

Source is point-like at low energies, consistent with pulsar emission.

Dark matter mass favored around 30 GeV for b quark channel.

Results align with gamma-ray constraints from other dwarf galaxies.

Abstract

We use data from the Large Area Telescope onboard the Fermi gamma-ray space telescope (Fermi-LAT) to analyze the faint gamma-ray source located at the center of the Sagittarius (Sgr) dwarf spheroidal galaxy. In the 4FGL-DR3 catalog, this source is associated with the globular cluster, M54, which is coincident with the dynamical center of this dwarf galaxy. We investigate the spectral energy distribution and spatial extension of this source, with the goal of testing two hypotheses: (1) the emission is due to millisecond pulsars within M54, or (2) the emission is due to annihilating dark matter from the Sgr halo. For the pulsar interpretation, we consider a two-component model which describes both the lower-energy magnetospheric emission and possible high-energy emission arising from inverse Compton scattering. We find that this source has a point-like morphology at low energies, consistent with magnetospheric emission, and find no evidence for a higher-energy component. For the dark matter interpretation, we find that this signal favors a dark matter mass of $m_{\chi} = 29.6 \pm 5.8$ GeV and an annihilation cross section of $\sigma v = (2.1 \pm 0.59) \times 10^{-26} \,\text{cm}^3/$s for the $b \bar{b}$ channel (or $m_{\chi} = 8.3 \pm 3.8$ GeV and $\sigma v = (0.90 \pm 0.25) \times 10^{-26} \, \text{cm}^3/$s for the $\tau^+ \tau^-$ channel), when adopting a J-factor of $J=10^{19.6} \, \text{GeV}^2 \, \text{cm}^{-5}$. This parameter space is consistent with gamma-ray constraints from other dwarf galaxies and with dark matter interpretations of the Galactic Center Gamma-Ray Excess.