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PROBING THE ENVIRONMENT OF GRAVITATIONAL-WAVE TRANSIENT SOURCES WITH TeV AFTERGLOW EMISSION

Recently, the Advanced Laser Interferometer Gravitational-wave Observatory 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 gamma-ray burst detected by GBM is in real association with GW150914. 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, originating from mergers of binary BHs that are similar to those in GW150914, could be detectable by ground-based Imaging Atmospheric Cherenkov Telescopes such as the Cherenkov Telescope Array (CTA) if the sources occur in a dense medium with a density of 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 it occurs in a dense medium with n ≳ 10 – 100 cm − 3 . Thus, TeV afterglow emission could 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.