The Galactic Wind Haze and its $\gamma$-spectrum

Abstract

We study the possibility that the gamma ray emission in the Fermi bubbles observed is produced by cosmic ray electrons with a spectrum similar to Galactic cosmic rays. We argue that the cosmic ray electrons steepen near 1 TeV from $E^{-3}$ to about $E^{-4.2}$, and are partially secondaries derived from the knee-feature of normal cosmic rays. We speculate that the observed feature at $\sim 130$ GeV could essentially be due to inverse Compton emission off a pair-production peak on top of a turn-off in the $\gamma$ ray spectrum at $\sim 130$ GeV. It suggests that the knee of normal cosmic rays is the same everywhere in the Galaxy. A consequence could be that all supernovae contributing give the same cosmic ray spectrum, with the knee feature given by common stellar properties; in fact, this is consistent with the supernova theory proposed by Bisnovatyi-Kogan (1970), a magneto-rotational mechanism, if massive stars converge to common properties in terms of rotation and magnetic fields just before they explode.

Comments: 16 pages, 2 figures, more discussions added