[Paper Review] Coupling Poynting-Robertson Effect in Mass Accretion Flow Physics

Vittorio De Falco|arXiv (Cornell University)|Jan 1, 2017

Gas Dynamics and Kinetic Theory15 references4 citations

TL;DR

This thesis develops a general relativistic framework for the Poynting-Robertson (PR) effect in accretion flows around compact objects, introducing a Lagrangian formulation for the dissipative PR force and extending the 2D model to 3D spacetime. It applies this formalism to analyze X-ray data from three accreting millisecond pulsars, revealing how radiation drag influences mass transfer and orbital evolution in strong gravitational fields.

ABSTRACT

In my doctoral thesis, I have focussed my attention on radiation processes in high-energy astrophysics connected with the accretion flow physics around compact objects. Generally, a radiation field beside to exert an outward radiation pressure, there is also the presence of a radiation drag force, which both can drastically change or even halt the motion of the surrounding matter. 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. The thesis is organised in three parts: (1) for ray-tracing purposes, 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; (2) I gave two fundamental contributions in the field of the general relativistic treatment of the Poynting-Robertson effect (Lagrangian formulations and extension of the model in three dimensions); (3) I reduced the data 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.

Motivation & Objective

• To develop a high-accuracy, polynomial-based method for integrating photon geodesics in Schwarzschild spacetime to model radiation transport in accretion flows.
• To establish a Lagrangian formulation for the general relativistic Poynting-Robertson effect, a rare property for a dissipative force in GR.
• To extend the 2D general relativistic PR model to three dimensions, enabling more realistic simulations of radiation drag in 3D accretion disk dynamics.
• To analyze observational data from three accreting millisecond X-ray pulsars (IGR J00291+5934, IGR J18245–2452, SAX J1748.9–2021) to assess the impact of radiation drag on mass accretion.
• To explore the implications of radiation drag near the Eddington limit and its role in halting or modifying accretion flow dynamics in compact object systems.

Proposed method

• Derives approximate polynomial formulae for photon geodesics in Schwarzschild spacetime using a mathematical method based on series expansion and integrating factors.
• Applies the general relativistic treatment of the Poynting-Robertson effect as developed by Bini et al., incorporating radiation pressure and drag forces in curved spacetime.
• Introduces an integrating factor to demonstrate that the dissipative PR force admits a Lagrangian formulation in GR, a non-trivial result for a non-conservative system.
• Extends the 2D PR model to 3D by modeling test particle orbits in Schwarzschild spacetime under the influence of radiation drag in three spatial dimensions.
• Identifies a critical hypersurface in 3D where the PR force transitions from inward to outward radial drift, indicating a dynamical bifurcation point.
• Performs spectral and timing analysis on INTEGRAL and Swift observations of three accreting millisecond X-ray pulsars to extract constraints on burst properties and accretion behavior.

Experimental results

Research questions

• RQ1 Can the Poynting-Robertson effect in general relativity be formulated in a Lagrangian framework despite being a dissipative force?
• RQ2 How does the 3D general relativistic Poynting-Robertson effect modify orbital evolution and angular momentum loss in accretion disks around compact objects?
• RQ3 What are the observable signatures of radiation drag in the X-ray light curves and burst properties of accreting millisecond pulsars?
• RQ4 How does the Eddington limit influence the efficiency of radiation drag in halting or altering mass accretion flows?
• RQ5 What are the implications of the critical hypersurface in 3D PR dynamics for the stability and structure of accretion disks?

Key findings

• The Poynting-Robertson effect in general relativity admits a Lagrangian formulation through the introduction of an integrating factor, resolving a long-standing theoretical challenge.
• The 3D extension of the PR model reveals a critical hypersurface in spacetime where the radial drift of particles reverses, indicating a non-trivial dynamical transition in accretion flow behavior.
• The developed polynomial approximation for photon geodesics enables high-accuracy integration of light bending, time delay, and solid angle in Schwarzschild spacetime, suitable for astrophysical modeling.
• Analysis of the 2015 outburst of IGR J00291+5934 shows a type-I X-ray burst with a peak luminosity consistent with Eddington-limited emission, suggesting strong radiation drag effects.
• The 2013 outburst of IGR J18245–2452 exhibits broad-band X-ray and soft gamma-ray emission, with timing features indicating possible radiation pressure modulation consistent with PR-driven mass transfer.
• The study demonstrates that radiation drag via the Poynting-Robertson effect can significantly alter orbital decay and angular momentum loss in compact accretion systems, especially near the Eddington limit.