Abstract
Optically thin accretion plasmas can reach ion temperatures Ti ≥ 1010 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 γ-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 (Ṁc2) and can be increased for heavier compositions up to 10−3. The efficiency of transformation of the kinetic energy of the outflow into high energy (≥100 MeV) γ-rays through the production and decay of π0-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.
Highlights
Hard X-ray emission from compact X-ray binary systems is a distinct signature of a hot plasma accreting onto a black hole
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 γ-ray lines
In the advection dominated accretion flow (ADAF) regime, CNO and heavier nuclei are destroyed before reaching the last stable orbit
Summary
Hard X-ray emission from compact X-ray binary systems is a distinct signature of a hot plasma accreting onto a black hole. Later developments have shown that the SLE model is thermally unstable (see, e.g., Abramowicz et al 1995, 2000) and that the advection of heat plays an important role in the viscous and thermal stability of the plasma (see, e.g., Ichimaru 1977; Paczynski & Bisnovatyi-Kogan 1981; Abramowicz et al 1988, 1995; Narayan & Popham 1993; Narayan & Yi 1994; Chen et al 1995) Another group of very hot and optically thin accretion disk solutions is linked to the so-called advection-dominated accretion flows (ADAF) Narayan & Yi (1994, 1995a,b). We present the results of our study of the γ-ray emission related to two-temperature accretion plasma within the framework of the ADAF and SLE models For this task, we utilize a massive nuclear reaction network and the recent parametrizations of π-meson production cross sections at low (close to the kinematic threshold) energies. We discuss the efficiency of evaporation of free neutrons from the disk and the maximum amount of the secondary Li, Be, and B nuclei produced in the ADAF accretion plasma
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