High-Energy Radiation from Remnants of Neutron Star Binary Mergers

TL;DR

This paper explores high-energy emissions from neutron star merger remnants, proposing they are detectable sources of X-ray and gamma-ray radiation, potentially explaining some unidentified high-energy sources and contributing to ultra-high-energy cosmic rays.

Contribution

It introduces the idea that neutron star merger remnants can produce detectable high-energy emissions and may account for some unidentified gamma-ray sources and ultra-high-energy cosmic rays.

Findings

Remnants can produce X-ray synchrotron radiation detectable at 100 Mpc.

Inverse Compton gamma-ray emission from remnants is detectable by Fermi and CTA.

Merger remnants may explain some unidentified high-energy sources.

Abstract

We study high-energy emission from the mergers of neutron star binaries as electromagnetic counterparts to gravitational waves aside from short gamma-ray bursts. The mergers entail significant mass ejection, which interacts with the surrounding medium to produce similar but brighter remnants than supernova remnants in a few years. We show that electrons accelerated in the remnants can produce synchrotron radiation in X-rays detectable at $\sim 100$ Mpc by current generation telescopes and inverse Compton emission in gamma rays detectable by the \emph{Fermi} Large Area Telescopes and the Cherenkov Telescope Array under favorable conditions. The remnants may have already appeared in high-energy surveys such as the Monitor of All-sky X-ray Image and the \emph{Fermi} Large Area Telescope as unidentified sources. We also suggest that the merger remnants could be the origin of ultra-high-energy cosmic rays beyond the knee energy, $\sim 10^{15}$ eV, in the cosmic-ray spectrum.