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

We use Fermi-LAT data to analyse the faint gamma-ray source located at the centre of the Sagittarius (Sgr) dwarf spheroidal galaxy. In the 4FGL-DR3 catalogue, this source is associated with the globular cluster, M54. 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 the signal favours a dark matter mass of m χ = 29.6 ± 5.8 GeV and an annihilation cross section of |$\sigma v = (2.1 \pm 0.59) \times 10^{-26} \, \text{cm}^3$|  s−1 for the |$b \bar{b}$| channel (or m χ = 8.3 ± 3.8 GeV and |$\sigma v = (0.90 \pm 0.25) \times 10^{-26} \, \text{cm}^3$|  s−1 for the τ+τ− 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 Centre Gamma-Ray Excess. [ABSTRACT FROM AUTHOR]