Multimessenger Constraints on Radiatively Decaying Axions from GW170817

TL;DR

This paper uses X-ray observations of GW170817 to set new constraints on axions with masses 1-400 MeV, improving existing bounds on their coupling to photons by analyzing decay-produced gamma-ray signals.

Contribution

It introduces a novel method to constrain radiatively decaying axions using multimessenger astrophysical data from neutron star mergers.

Findings

Excluded axion-photon couplings down to 5×10⁻¹¹ GeV⁻¹ for 1-400 MeV axion masses.

Provided the most stringent bounds to date in the 1-400 MeV mass range.

Demonstrated the method's applicability to other feebly-interacting particles decaying into photons.

Abstract

The metastable hypermassive neutron star produced in the coalescence of two neutron stars can copiously produce axions that radiatively decay into $\mathcal{O}(100)$~MeV photons. These photons can form a fireball with characteristic temperature smaller than $1\rm\, MeV$. By relying on X-ray observations of GW170817/GRB 170817A with CALET CGBM, Konus-Wind, and Insight-HXMT/HE, we present new bounds on the axion-photon coupling for axion masses in the range $1$-$400\,\rm MeV$. We exclude couplings down to $5\times 10^{-11}\,\rm GeV^{-1}$, complementing and surpassing existing constraints. Our approach can be extended to any feebly-interacting particle decaying into photons.