Positron Annihilation Spectroscopy of Active Galactic Nuclei

Abstract

This paper focuses on the interpretation of radiation fluxes from active galactic nuclei. The advantage of positron annihilation spectroscopy over other methods of spectral diagnostics of active galactic nuclei (therefore AGN) is demonstrated. A relationship between regular and random components in both bolometric and spectral composition of fluxes of quanta and particles generated in AGN is found. We consider their diffuse component separately and also detect radiative feedback after the passage of high-velocity cosmic rays and hard quanta through gas-and-dust aggregates surrounding massive black holes in AGN. The motion of relativistic positrons and electrons in such complex systems produces secondary radiation throughout the whole investigated region of active galactic nuclei in form of cylinder with radius R= 400-1000 pc and height H=200-400 pc, thus causing their visible luminescence across all spectral bands. We obtain radiation and electron energy distribution functions depending on the spatial distribution of the investigated bulk of matter in AGN. Radiation luminescence of the noncentral part of AGN is a response to the effects of particles and quanta falling from its center created by atoms, molecules and dust of its diffuse component. The cross-sections for the single-photon annihilation of positrons of different energies with atoms in these active galactic nuclei are determined. For the first time we use the data on the change in chemical composition due to spallation reactions induced by high-energy particles. We establish or define more accurately how the energies of the incident positron, emitted γ-quantum and recoiling nucleus correlate with the atomic number and weight of the target nucleus. For light elements, we provide detailed tables of all indicated parameters. A new criterion is proposed, based on the use of the ratio of the fluxes of γ-quanta formed in one- and two-photon annihilation of positrons in a diffuse medium. It is concluded that, as is the case in young supernova remnants, the two-photon annihilation tends to occur in solid-state grains as a result of active loss of kinetic energy of positrons due to ionisation down to thermal energy of free electrons. The singlephoton annihilation of positrons manifests itself in the gas component of active galactic nuclei. Such annihilation occurs as interaction between positrons and K-shell electrons; hence, it is suitable for identification of the chemical state of substances comprising the gas component of the investigated media. Specific physical media producing high fluxes of positrons are discussed; it allowed a significant reduction in the number of reaction channels generating positrons. We estimate the brightness distribution in the γ-ray spectra of the gas-and-dust media through which positron fluxes travel with the energy range similar to that recorded by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) research module. Based on the results of our calculations, we analyse the reasons for such a high power of positrons to penetrate through gas-and-dust aggregates. The energy loss of positrons by ionisation is compared to the production of secondary positrons by high-energy cosmic rays in order to determine the depth of their penetration into gas-and-dust aggregations clustered in active galactic nuclei. The relationship between the energy of γ-quanta emitted upon the single-photon annihilation and the energy of incident electrons is established. The obtained cross sections for positron interactions with bound electrons of the diffuse component of the non-central, peripheral AGN regions allowed us to obtain new spectroscopic characteristics of the atoms involved in singlephoton annihilation.

Diagnostics of Diffuse Two-Phase Matter Using Techniques of Positron Annihilation Spectroscopy in Gamma-Ray and Optical Spectra

“…In this case, provided that there were no other sources of fast electrons, non-thermal luminosity of the medium within the range of energies up to 10 KeV was dominated by the losses of energy due to ionization by fast positrons (80% of the total non-thermal luminosity) and, to a lesser extent, by fast electrons (15%-20%). The results of calculations obtained in this study, as well an earlier study by Doikov (2018) and Doikov et al (2019), showed that one can expect an increase of five orders of magnitude in the rate of positron production in the entire bulk of the active region of the AGN.…”

“… can be used, where L s is the luminosity of the entire stellar population in a galaxy under study. In our earlier papers (Doikov 2018;Doikov et al 2019), we have shown that such high luminosities can be associated with a high density of hard quanta and high-energy particle fluxes throughout the entire bulk of the AGN.…”

“…When annihilation occurs, a vacancy (or a hole) is created at the associated energy level; a single γ-quantum is emitted with the residual momentum being transferred to the atomic nucleus. Our earlier studies (Doikov et al 2018(Doikov et al , 2019 focused on the solution of this problem. In particular, we solved the set of equations given below using the laws of conservation of energy and momentum:…”

“…In this paper, we proceed with the calculations commenced in our previous study (Doikov et al 2019) He, Li, Li, Be, Be, B, and B . The values of E γ and E n , obtained for these elements, enable us to relate the single-photon annihilation of each element to the Doppler broadening of their respective optical lines.…”

Calculations of positron scattering on the hydrogen molecular ion

“…+ H 2 is expected to exist in notable quantities only in extreme environments such as those found within x-ray irradiated molecular gas clouds, around active galactic nuclei [5], during the early ages of the Universe [6], and at the edges of molecular clouds within the interstellar medium [7]. Therefore, there is considerable interest in astrophysics to study positron propagation through such regions [8,9].…”