On the high-energy protons regular acceleration in the Fermi Bubbles

Abstract

We propose the model of the global structure of the electromagnetic fields in the Fermi bubbles (FBs), which makes possible the proton regular acceleration up to ultra-high energies. The poloidal and the toroidal magnetic fields, as well as the radial electric field, turn to have a structure similar to fields that exist in jets ejected out from active galactic nuclei (AGN). A powerful source of relativistic particles observed in the centre of the Galaxy and associated with the rotating supermassive black hole (SMBH) Sgr A* can energize the FB and keeps its active for a long time. The absence of accretion onto a 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 BH can keep the FB activity. The regular FBs structure could be formed by inheritance from a relativistic jet that presumably existed in the active past of the Galaxy $ 10^7 $ years ago, or by processes near the Galaxy centre existing during the entire life cycle of the Galaxy. The acceleration of protons in electromagnetic fields of FB are found up to energies $ E_{max} \simeq 10^{17} $ eV, which explains the observed radiation of FB in the gamma range, as well as the emission of high-energy neutrinos.