Evidence of Fermi bubbles around M31

M. S. Pshirkov; V. V. Vasiliev; K. A. Postnov

doi:10.1093/mnrasl/slw045

paper

Evidence of Fermi bubbles around M31

arXiv:1603.07245 · doi:10.1093/mnrasl/slw045

Abstract

Gamma-ray haloes can exist around galaxies due to the interaction of escaping galactic cosmic rays with the surrounding gas. We have searched for such a halo around the nearby giant spiral Andromeda galaxy M31 using almost 7 years of Fermi LAT data at energies above 300 MeV. The presence of a diffuse gamma-ray halo with total photon flux $2.6 \pm 0.6 \times 1 0^{- 9}$ cm $^{- 2}$ ~s $^{- 1}$ , corresponding to a luminosity (0.3-100 GeV) of $(3.2 \pm 0.6) \times 1 0^{38}$ erg s $^{- 1}$ (for a distance of 780~kpc) was found at a 5.3 $σ$ confidence level. The halo form does not correspond to the extended baryonic HI disc of M31, as would be expected in hadronic production of gamma photons from cosmic ray interaction, nor it is spherically symmetric, as could be in the case of dark matter annihilation. The best-fit halo template corresponds to two 6-7.5 kpc bubbles symmetrically located perpendicular to the M31 galactic disc, similar to the 'Fermi bubbles' found around the Milky Way centre, which suggests the past activity of the central supermassive black hole or a star-formation burst in M31.

arXiv comment8 pages, 8 figures, strongly revised and extended version of 1501.03460. Accepted to MNRAS Letters. arXiv admin note: substantial text overlap with arXiv:1501.03460

Evidence of Fermi bubbles around M31

Abstract

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