  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.
