Nuclear γ-ray emission from very hot accretion flows

Optically thin accretion plasmas can reach ion temperatures T-i >= 10(10) K and thus trigger nuclear reactions. Using a large nuclear interactions network, we studied the radial evolution of the chemical composition of the accretion flow toward the black hole and computed the emissivity in nuclear gamma-ray lines. In the advection dominated accretion flow (ADAF) regime, CNO and heavier nuclei are destroyed before reaching the last stable orbit. The overall luminosity in the de-excitation lines for a solar composition of plasma can be as high as few times 10(-5) the accretion luminosity ((M) over dotc(2)) and can be increased for heavier compositions up to 10(-3). The e ffi ciency of transformation of the kinetic energy of the outflow into high energy (>= 100 MeV) gamma-rays through the production and decay of pi(0)-mesons can be higher, up to 10 2 of the accretion luminosity. We show that in the ADAF model up to 15% of the mass of accretion matter can "evaporate" in the form of neutrons.