2 00 9 Probing the Pulsar Wind in the γ - ray Binary System PSR B 1259 - 63 / SS 2883

The spectral energy distribution from the X-ray to the very high energy regime (> 100 GeV) has been investigated for the γ-ray binary system PSR B125963/SS2883 as a function of orbital phase within the framework of a simple model of a pulsar wind nebula. The emission model is based on the synchrotron radiation process for the X-ray regime and the inverse Compton scattering process boosting stellar photons from the Be star companion to the very high energy (100GeV-TeV) regime. With this model, the observed temporal behavior can, in principle, be used to probe the pulsar wind properties at the shock as a function of the orbital phase. Due to theoretical uncertainties in the detailed microphysics of the acceleration process and the conversion of magnetic energy into particle kinetic energy, the observed X-ray data for the entire orbit are fit using two different methods. In the first method, the magnetization parameter and the Lorentz factor of the wind at the shock are allowed to vary for a given power law index characterizing the accelerated particles at the shock. In this case, the observed photon index ∼ 1.2 in the 1-10 keV energy band near periastron passage can be understood provided that (a) the electron energy distribution is described by a broken power law and (b) there is a break at an energy of about 8× 10 in units Academia Sinica Institute of Astrophysics and Astronomy-TIARA, P.O. Box 23-141, Taipei, 10617 Taiwan Academia Sinica Institute of Astrophysics and Astronomy/National Tsing Hua University-TIARA, Hsinchu Taiwan Northwestern University, Department of Physics and Astronomy, 2131 Tech Drive, Evanston, IL 60208