# Electromagnetic Chirps from Neutron Star-Black Hole Mergers

## TL;DR

This paper models electromagnetic signals, specifically gamma-ray chirps, emitted during neutron star-black hole mergers, revealing a close correlation with gravitational wave signals and proposing detection methods.

## Contribution

It introduces a new simulation approach for electromagnetic signals from mergers, linking gamma-ray chirps to gravitational waveforms and suggesting detection strategies.

## Key findings

- Electromagnetic chirps mirror gravitational wave signals in frequency and amplitude.
- Relativistic effects modulate the gamma-ray light curve during mergers.
- Proposes matched filtering techniques for detecting electromagnetic chirps.

## Abstract

We calculate the electromagnetic signal of a gamma-ray flare coming from the surface of a neutron star shortly before merger with a black hole companion. Using a new version of the Monte Carlo radiation transport code Pandurata that incorporates dynamic spacetimes, we integrate photon geodesics from the neutron star surface until they reach a distant observer or are captured by the black hole. The gamma-ray light curve is modulated by a number of relativistic effects, including Doppler beaming and gravitational lensing. Because the photons originate from the inspiraling neutron star, the light curve closely resembles the corresponding gravitational waveform: a chirp signal characterized by a steadily increasing frequency and amplitude. We propose to search for these electromagnetic chirps using matched filtering algorithms similar to those used in LIGO data analysis.