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Abstract

The inverse Compton (IC) scattering of electrons accelerated at the pulsar wind termination shock is believed to be responsible for TeV gamma-ray signal recently reported from the binary system PSR B1259-63. While this process can explain the energy spectrum of the observed TeV emission, the gamma-ray fluxes detected by HESS do not agree with the published predictions of the TeV lightcurve. In this paper we study evolution of the energy spectra of relativistic electrons under different assumptions about the acceleration and energy-loss rates, and the impact of these processes on the lightcurve of IC gamma-rays. We demonstrate that the observed lightcurve can be explained (i) by adiabatic losses which dominate over the entire trajectory of the pulsar, or (ii) by the "early" cutoffs in the energy spectra of electrons due to the enhanced rate of Compton losses close to the periastron. The Compton cooling of the electron-positron pulsar wind contributes to the decrease of the nonthermal power released in the accelerated electrons after the wind termination, and thus to the reduction of the IC and synchrotron components of radiation close to the periastron. Although this effect alone cannot explain the observed TeV and X-ray lightcurves, the Comptonization of the cold ultrarelativistic wind leads to the formation of gamma-radiation with a specific line-type energy spectrum. While the HESS data already constrain the Lorentz factor of the wind, $\Gamma \le 10^6$, future observations of this object with GLAST should allow a deep probe of the wind Lorentz factor in the range between $10^4$ and $10^6$.