Chernyshov D.O.,
Cheng, K.-S., Dogiel, V. A.

Fermi bubbles as sources of cosmic rays above 1 PeV


Fermi bubbles are giant gamma-ray structures extended north and south
of the Galactic center with characteristic size of order of 10 kpc
discovered by Fermi Large Area Telescope. Good correlation between radio
and gamma-ray emission in the region covered by Fermi bubbles implies the
presence of high-energy electrons in this area. Due to high energy losses
it is rather problematic to transfer relativistic electrons from the 
Galactic disk towards the Fermi bubbles. Therefore it is natural to assume
that these electrons are accelerated in-situ. Additionally this acceleration
mechanism should also affect protons. In particular it may re-accelerate
Galactic cosmic rays produced by supernova remnants. Unlike electrons
protons have huge life-times and therefore re-acceleration should not be a
local effect but affect the whole Galaxy. The effect may even be observed 
near the Earth. In our model we propose that hadronic CR below the “knee” 
of the observed CR spectrum are produced by Galactic supernova remnants 
distributed in the Galactic disk. Reacceleration of these particles in the 
Fermi Bubbles produces CRs above the knee. This model provides a natural 
explanation of the observed CR flux, spectral indexes, and matching of 
spectra at the knee.