Prediction of gamma-ray emission from Cygnus X-1, SS 433, and GRS 1915+105 after absorption

¹ Department of Informatics, University of Western Macedonia, Fourka Area, 52100 Kastoria, Greece
e-mail: th.papavasileiou@uowm.gr
² Department of MACE, University of Manchester, Sackville Street, George Begg Building, M1 3BB Manchester, UK

Received: 9 January 2023
Accepted: 4 April 2023

Abstract

Context. Stellar black hole X-ray binary stars (BHXRBs) are among the most luminous and powerful systems located in our Milky Way and in other galaxies of the Universe. Their jets are prominent sources of particles (e.g., neutrinos) and radiation emissions in energy ranges detectable by terrestrial and space telescopes, even from galaxies deep in the space. A significant factor, however, would be the photon absorption effect that occur due to scattering on the lower end of the energy radiation of the system’s surroundings.

Aims. We aim to study in detail and extract predictions for the emitted gamma-ray intensities and integral fluxes of the jets emanating from BHXRB systems Cygnus X-1, GRS 1915+105, and SS 433. Toward this end, we also investigate the severe effects of gamma-ray absorption that eradicate part of the produced intensity spectra. Furthermore, we explore the jet regions that are most likely to emit unabsorbed gamma-rays capable of reaching detectors on Earth. Our goal is to calculate the integral fluxes before and after absorption for the abovementioned systems and compare the results with the very-high-energy gamma-ray observations of sensitive telescopes such as the MAGIC, H.E.S.S., Fermi-LAT, and so on.

Methods. The implemented gamma-ray emission mechanisms initiate from the p − p scattering process inside the hadron-dominated jets following the well-known shock-wave particle acceleration. In addition, we estimate the optical depths of three absorption processes between gamma-ray photons and (i) accretion disk X-ray emission, (ii) black hole corona photons, and (iii) donor star thermal emission. We also examine the dependence of the absorption optical depths on various parameters, such as the disk’s temperature, coronal radius and, donor star luminosity.

Results. We find that disk absorption is dominant for distances of z < 10¹⁰ cm from the black hole, while the donor star absorption dominates for 10¹⁰ < z < 10¹² cm. Beyond that jet point, the absorption effects become significantly weaker. Cygnus X-1 presents the highest gamma-ray integral flux across the jet length, while GRS 1915+105 emits the least due to its weakly collimated jets. The jets of SS 433 emit gamma-rays only for z > 10¹⁰ cm due to severe disk absorption fueled by the system’s super-Eddington accretion limit.