Gamma-ray and neutrino flares produced by protons accelerated on an accretion disc surface in active galactic nuclei

Abstract

We discuss the consequences of almost rectilinear acceleration of protons to extremely high energies in a reconnection region on the surface of an accretion disc that surrounds a central black hole in an active galaxy. The protons produce γ-rays and neutrinos in interactions with the disc radiation as considered in several previous papers. However, in this model the secondary γ-rays can initiate cascades in the magnetic and radiation fields above the disc. We compute the spectra of γ-rays and neutrinos emerging from regions close to the disc surface. Depending on the parameters of the reconnection regions, this model predicts the appearance of γ-ray and neutrino flares if protons take most of the energy from the reconnection region. In contrast, if leptons take most of the energy, they produce pure γ-ray flares. The γ-ray spectrum expected in the case of hadronic cascading is compared with the spectrum observed during the flare in 1991 June from 3C 279. The neutrino flares that should accompany these γ-ray flares may be detected by future large-scale neutrino telescopes sensitive at ∼ 105 TeV.