Self-Lensing in Eclipsing X-ray Binary Systems

TL;DR

This study explores the potential of gravitational self-lensing in eclipsing X-ray binary systems to measure compact object masses, highlighting its advantages and optimal conditions for detection.

Contribution

It models the amplification curves and identifies conditions under which self-lensing signals are strongest, proposing a new observational method for compact object detection.

Findings

Self-lensing signals are strongest with small companion stars, like in LMXBs.

Evolved massive stars can produce detectable signals.

Lensing signals are stronger at larger binary separations, opposite to other methods.

Abstract

This project examines the feasibility of using gravitational lensing to measure the mass of compact objects in eclipsing X-ray binary (XRB) systems. We investigate which kind of XRB would be most conducive for viewing the effect, by modeling the amplification curves and determining if any feature of an XRB system could potentially hinder observation of such a signal. We examine the effect of accretion disks and stellar winds, as well as the compact object mass, binary separation, and companion spectral type. Generally speaking, the lensing signal is strongest for when the angular size subtended by the companion is small, favoring relatively compact companion stars (LMXBs) although evolved massive stars (such as certain WR stars) have signals that are feasibly detectable. Interestingly, the self-lensing signal is stronger in binaries with large separations, which is the exact opposite of the case for all other techniques. Thus, a dedicated self-lensing survey would complement X-ray and radial-velocity techniques, by extending the parameter space for discovery of compact objects. Simultaneously, a self-lensing survey offers the possibility of revealing the large population of non-accreting compact objects in galactic binary systems.