Coupling Poynting-Robertson effect in mass accretion flow physics

Abstract

The physics of accretion onto compact objects has been experiencing for several decades by now a golden age in terms of theoretical knowledges and observational discoveries. Compact objects release the gravitational energy of the accreted matter in the form of persistent emission or thermonuclear type-I X-ray burst. This radiation field carries out energy and momentum that is transferred back to the interacting plasma inside the accretion disk. The radiation field entails a radiation pressure and a radiation drag force, which both can drastically change or even halt the whole mass transfer (especially when their intensity reaches the Eddington limit). The radiation drag force, known as Poynting-Robertson effect, acts as a dissipative force against the matter's orbital motion, removing very efficiently angular momentum and energy from it. To describe suitably the radiation processes around static compact objects, the Schwarzschild metric is usually employed. To this aim, I have developed a mathematical method for deriving a set of high-accurate approximate polynomial formulae to easily integrate photon geodesics in a Schwarzschild spacetime. Starting from the general relativistic treatment of the Poynting-Robertson effect led by Bini et al., I gave two fundamental contributions in such research field. In a first work, I proved through the introduction of an integrating factor that such effect admits a Lagrangian formulation, very peculiar propriety for a dissipative system in General Relativity. In the other work, I have extended the two dimensional general relativistic PR model in three dimensions. Once the theoretical apparatus has been developed, it is important to learn the state of art about the observational high-energy astrophysics. For such reasons, I focussed my energy on the data analysis of three accreting millisecond X-ray pulsars: IGR~J00291+5934, IGR~J18245-2452, and SAX~J1748.9-2021. This thesis offers innovative ideas in the field of radiation processes involving the Poynting-Robertson effect in high-energy astrophysics, opening thus up future interesting perspectives both in theoretical and observational physics. As conclusion, we propose possible further developments and applications.