2019ApJ...882..112X

In our search for γ-ray emission from Be X-ray binaries from the analysis of the data obtained with the Large Area Telescope onboard the Fermi Gamma-Ray Space Telescope, we find likely detection of GRO J1008-57. The binary has an orbital period of 249.48 days, and it is only significantly detected in its orbital phase 0.8-0.9 (>4σ). Further light-curve analysis indicates that the detection is probably largely due to an emitting event in one orbital cycle around year 2012-2013, following a giant X-ray outburst of the source. This property of having occasional γ-ray emitting events is similar to that seen in another high-mass X-ray binary (HMXB) 4U 1036-56. However, models considering possible γ-ray emission from an accreting neutron star have difficulty in explaining the observed ∼10³⁴ erg s^–1 luminosity of the source, unless the distance was largely overestimated. Further observational studies are required, in order to more clearly establish the high-energy emission properties of GRO J1008-57 or similar HMXBs and find clues for understanding how γ-ray emission is produced from them.