On the high-energy proton regular acceleration in the Fermi bubbles

Abstract

ABSTRACT We propose a model of the global structure of the electromagnetic fields in the Fermi bubbles (FBs), which makes possible the proton regular acceleration up to ultrahigh energies. The poloidal and the toroidal magnetic fields, as well as the radial electric field, are found to have a structure similar to fields that exist in jets ejected out from active galactic nuclei. A powerful source of relativistic particles observed in the centre of the Galaxy and associated with the rotating supermassive black hole Sgr A* can energize the FB and keep it active for a long time. The absence of accretion on to a black hole (BH) and thus the absence of a relativistic jet does not mean that there is no loss of rotational energy of BH. In the case of FB, the energy lost by a BH can keep the FB activity going. The regular FB structure could be formed by inheritance from a relativistic jet that presumably existed in the active past of the Galaxy 107 yr ago, or by processes near the Galactic Centre existing during the entire life cycle of the Galaxy. The acceleration of protons in electromagnetic fields of FB is found up to energies Emax ≃ 1017 eV, which explains the observed radiation of FB in the gamma range, as well as the emission of high-energy neutrinos.