Fermi bubbles as sources of cosmic rays above 1 PeV

¹ I.E.Tamm Theoretical Physics Division of P.N.Lebedev Institute of Physics, Leninskii pr. 53, 119991 Moscow, Russia
² Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong, China
³ Institute of Astronomy, National Central University, Jhongli, Taoyuan, Taiwan, R.O.C.
⁴ Moscow Institute of Physics and Technology, 141700 Moscow Region, Dolgoprudnii, Russia
⁵ Department of Physics and Center for Complex Systems, National Central University, Jhongli, Taoyuan, Taiwan, R.O.C.

^a e-mail: chernyshov@lpi.ru
^b e-mail: hrspksc@hku.hk
^c e-mail: dogiel@lpi.ru
^d e-mail: cmko@astro.ncu.edu.tw

Published online: 26 June 2017

Abstract

Fermi bubbles are giant gamma-ray structures extended north and south of the Galactic center with characteristic sizes of the order of 10 kpc discovered by the 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 toward 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 cosmic rays (CR) below the “knee” of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Re-acceleration of these particles in Fermi Bubbles produces CRs above the knee. This model provides a natural explanation of the observed CR flux, spectral indices, and matching of spectra at the knee.