# Detecting Gravitational Self Lensing from Stellar-Mass Binaries Composed of Black Holes or Neutron Stars

## TL;DR

This paper proposes detecting electromagnetic signatures of stellar-mass compact-object binaries through gravitational lensing effects in X-ray observations, which can identify progenitors of gravitational wave sources and reveal otherwise hidden populations.

## Contribution

It introduces the concept of observing periodic lensing flares caused by binary components, offering a new method to study compact-object binaries before they merge.

## Key findings

- Periodic lensing flares could be detected with future X-ray missions like Lynx.
- Non-detection constrains the population of EM bright compact-object binaries.
- Lensing signatures can identify binaries that are progenitors of LIGO-detectable mergers.

## Abstract

We explore a unique electromagnetic signature of stellar-mass compact-object binaries long before they are detectable in gravitational waves. We show that gravitational lensing of light emitting components of a compact-object binary, by the other binary component, could be detectable in the nearby universe. This periodic lensing signature could be detected from present and future X-ray observations, identifying the progenitors of binaries that merge in the LIGO band, and also unveiling populations that do not merge, thus providing a tracer of the compact-object binary population in an enigmatic portion of its life. We argue that periodically repeating lensing flares could be observed for ~100 ksec orbital-period binaries with the future Lynx X-ray mission, possibly concurrent with gravitational wave emission in the LISA band. Binaries with longer orbital periods could be more common and be detectable as single lensing flares, though with reliance on a model for the flare that can be tested by observations of succeeding flares. Non-detection of such events, even with existing X-ray observations, will help to constrain the population of EM bright compact-object binaries.