Probing the environment of gravitational wave transient sources with TeV afterglow emission

TL;DR

This paper predicts TeV gamma-ray afterglow emissions from gravitational wave sources like black hole and neutron star mergers, suggesting these emissions can reveal the density of their surrounding environment and aid understanding of their origins.

Contribution

It introduces calculations of high-energy gamma-ray emissions from wide-angle outflows of GW mergers, highlighting their detectability and environmental implications.

Findings

TeV emission from black hole mergers could be detected by CTA in dense media.

Neutron star mergers' TeV afterglow detectable if in very dense environments.

TeV afterglow emissions serve as probes of the GW transients' environments.

Abstract

Recently, Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) detected gravitational wave (GW) transients from mergers of binary black holes (BHs). The system may also produce a wide-angle, relativistic outflow if the claimed short GRB detected by GBM is in real association with GW 150914. It was suggested that mergers of double neutron stars (or neutron star-black hole binaries), another promising source of GW transients, also produce fast, wide-angle outflows. In this paper, we calculate the high-energy gamma-ray emission arising from the blast waves driven by these wide-angle outflows. We find that TeV emission arising from the inverse-Compton process in the relativistic outflow resulted from mergers of binary BHs similar to those in GW 150914 could be detectable by ground-based IACT telescopes such as Cherenkov Telescope Array (CTA) if the sources occur in { a dense medium with density $n > 0.3 cm^{-3}$}. For neutron star-neutron star (NS-NS) and NS-BH mergers, TeV emission from the wide-angle, mildly-relativistic outflow could be detected as well if they occur in a dense medium {with $n > 10-100 cm^{-3}$.} Thus TeV afterglow emission would be a useful probe of the environment of the GW transients, which could shed light on the evolution channels of the progenitors of GW transients.