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

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 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 in the dwarf's 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 identify no evidence of any higher energy component. For the dark matter interpretation, we find a best-fitting mass of 29 GeV and annihilation cross section of σv ~ 2.19 × 10^-26 cm³/s for the bb; channel (8.4 GeV and 0.90 × 10^-26 cm³/s for the ττ channel), when adopting a J-factor of J=10¹⁹ GeV² cm^-5. The cross section required to produce this emission could be reconciled with constraints from dwarf galaxies if the J-factor of the Sagitarrius dwarf is larger than this estimate by a factor of 2, such as could arise due to non-equilibrium effects.