Cosmic ray acceleration and non-thermal radiative losses around black holes: the eects of magnetic reconnection

Cosmic Ray (CR) acceleration is still challenging in high energy astrophysics. The first-order Fermi mechanism within magnetic reconnection layers has been demonstrated to be a powerful CR accelerator in recent studies. In this work we have investigated this acceleration process in the nuclear region of radio-galaxies and microquasars, considering fast magnetic reconnection events in the coronal region between the field lines of the black hole (BH) magnetosphere and the lines arising from the inner accretion disk. We found that specially the very high energy gamma-ray emission, whose location is still not well determined from current observations of these sources, may be originated through this mechanism in the nuclear region around the black hole. We employed both Lepontic and hadronic models to interpret the observed non-thermal emission from radio to gamma-rays resulting from interactions of the accelerated particles by magnetic reconnection with the surrounding matter, radiation and magnetic fields. We compared the calculated acceleration rate from numerical simulations with the proper radiative cooling rates obtaining the maximum particle energy and then reconstructed the spectral energy distribution (SED) for a few microquasars and radio galaxies for which there is emission detected up to TeV energies, namely, the microquasars Cyg X-1 and Cyg X-3, and the radio-galaxies Cen A, Per A, M87 and IC 310. We found that the calculated SEDs are consistent with the observations. We have shown that the TeV emission is produced by the photo-meson process in both class of sources.

We have also considered the same acceleration model occurring in the core region of luminous AGNs in general to investigate the origin of the recently detected high energy extragalactic neutrinos by the IceCube experiment. We found that the decay of charged pions produced by photo-meson process using the accelerated protons via magnetic reconnection around the black holes of these sources located between redshifts z = 0 and 5 can explain the observed diffuse neutrino flux.

The results of this study on cosmic ray acceleration and non-thermal radiative processes strengthen recent findings that suggest that the VHE emission in microquasars and low luminosity AGNs in general may be originated in the core of these sources. Furthermore, these results may help to constrain particle acceleration, emission processes and space distribution models for comparison with high resolution observations of the coming new instruments, especially the gamma-ray observatory Cherenkov Telescope Array (CTA) which will be built around 2020 and will have 10 times more sensitivity at the very high energies than the current gamma-ray detectors.