Fermi bubbles: 10 kpc shocks from the Galactic Center?

Abstract

Data from the Fermi-LAT reveal two large gamma-ray bubbles, extending ∼50 degrees above and below the Galactic center, with a width of ∼40 degrees in longitude. The gamma-ray emission associated with these bubbles has a significantly harder spectrum (dN/dE ∼ E.2) than the IC emission from electrons in the Galactic disk, or the gammarays produced by decay of pions from proton-ISM collisions. There is no significant spatial variation in the spectrum or gamma-ray intensity within the bubbles, or between the north and south bubbles. The bubbles are spatially correlated with the hard-spectrum microwave excess known as the WMAP haze; the edges of the bubbles also line up with features in the ROSAT X-ray maps at 1.5 . 2 keV. We argue that these Galactic gamma-ray bubbles were most likely created by some large episode of energy injection in the Galactic center.