The effect of the infrared excess from the Be star on inverse Compton gamma-ray production in PSR B1259-63/SS 2883

The binary system PSR B1259-63 consists of a 48-ms pulsar in a 3.4-yr orbit around a Be star, and unpulsed TeV gamma-ray emission has been detected near previous periastron passages. A likely source of the gamma-rays is the inverse Compton upscattering of target photons from the Be star by the ultrarelativistic electron/positron pulsar wind in the region of the plerion shock front. In this study, the effect of the infrared emission from the Be star's circumstellar disc on inverse Compton gamma-ray production in PSR B1259-63 is investigated by considering an isotropic photon/electron approximation. The modified photon density distribution is determined by using a curve of growth method fitted to previous optical and infrared observations. The inverse Compton scattering rate is calculated using the modified photon distribution and the exact scattering equation. It is shown that including the infrared emission increases the GeV gamma-ray flux by a factor of greater than or similar to 2.