Observations of M31 and M33 with the Fermi Large Area Telescope: a galactic center excess in Andromeda?

Understand

The Fermi LAT has opened the way for comparative studies of cosmic rays (CRs) and high-energy objects in the Milky Way (MW) and in other, external, star-forming galaxies.

• Using 2 yr of observations with the Fermi LAT, local Group galaxy M31 was detected as a marginally extended gamma-ray source, while only an upper limit (UL) has been derived for the other nearby galaxy M33.
• We revisited the gamma-ray emission in the direction of M31 and M33 using more than 7 yr of LAT Pass 8 data in the energy range 0.1-100 GeV, presenting detailed morphological and spectral analyses.
• M33 remains undetected and we computed an UL for it.