Gamma-Ray Flashes from Dark Photons in Neutron Star Mergers

TL;DR

This paper explores how dark photons emitted during neutron star mergers could produce detectable gamma-ray signals, offering a new way to probe dark matter models with upcoming telescopes.

Contribution

It introduces the concept of dark photon emission as a source of gamma-ray signals from neutron star mergers, providing calculations of expected luminosities and observational signatures.

Findings

Dark photon signals can produce gamma-ray luminosities >10^46 ergs.

Signals are approximately isotropic and thermal, distinguishable from typical short gamma-ray bursts.

Parameter space for dark photons in the 1-100 MeV range can be probed with current and future detectors.

Abstract

In this letter we begin the study of visible dark sector signals coming from binary neutron star mergers. We focus on dark photons emitted in the 10 ms - 1 s after the merger, and show how they can lead to bright transient gamma-ray signals. The signal will be approximately isotropic, and for much of the interesting parameter space will be close to thermal, with an apparent temperature of about $100$ keV. These features can be used to distinguish the dark photon signal from the expected short gamma-ray bursts produced in neutron star mergers, which are beamed in a small angle and non-thermal. We calculate the expected signal strength and show that for dark photon masses in the $1-100$ MeV range it can easily lead to total luminosities larger than $10^{46}$ ergs for much of the unconstrained parameter space. This signal can be used to probe a large fraction of the unconstrained parameter space motivated by freeze-in dark matter scenarios with interactions mediated by a dark photon in that mass range. We also comment on future improvements when proposed telescopes and mid-band gravitational detectors become operational.