Gamma ray radiation in Spider Binary system

Abstract

Pulsars are some of the most fantastic and intriguing celestial bodies to study with the tools of modern astrophysics. As a fast-spinning neutron star and strong magnetic dipole, extensive studies reveal unique magnetospheric physics responsible for high energy emissions and particle outflow. Spider pulsar systems are a class of binaries comprising consisting of a millisecond pulsar and a low-mass companion that is continuously irradiated by the intense pulsar wind. Two categories of spider binaries have been found, 'redbacks' and 'black widows', which are divided by companion mass. Besides the presence of radio pulsar eclipses, data from multiple research and facilities, including Fermi-LAT, have shown a clear high emission pattern in the X-ray and gamma-ray ranges which result from the pulsar spin-down and intra-binary shocks. This research focuses on how high-energy emission from the pulsar wind impacts the companion's atmosphere and subsequent evolution in spider pulsar systems through the Compton scattering mechanism. Aiming at finding the deposition depth of high-energy photons in the stellar envelopes, Monte Carlo simulations have been performed for various evolutionary snapshots in low-mass X-ray binaries which are leading to the formation of spider binaries using the 'Module of experimental astrophysics(MESA)'. We calculated the penetration depth of gamma-ray photons sampled from 'typical' observational pulsar data taken from the 4FGL-DR2 Fermi catalog between 50 MeV and 100 GeV. In the simulations, the first-order mean free path is calculated, showing that before the companion's structure is altered, gamma-ray photons can penetrate only the very top atmosphere of the companion star. We also investigate how extra heat deposited a different depths - shallow convection zone, intermediate transition region, and deep into the radiative zone - affects the stellar structure. Combined with the heating effect, a self-consistent penetration mechanism has been developed. The energy deposited by gamma-ray photons should cause radius inflation, leading to higher mass loss efficiency and altering the entire evolution track.

Date of Award	31 Dec 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Keith (Supervisor) & Rene Breton (Supervisor)