Pulsed Gamma-Ray emission from the Crab

摘要

It is generally believed that pulsars eject ultrarelativistic electron-positron winds. The wind originates close to the light cylinder and carries the entire rotation energy of the pulsar to large distances. This leads to the formation of extended regions filled with non-thermal particles (pulsar wind nebulae). There are a few factors which make direct observations of the pulsar winds wind to a complicated task. In particular, dominant contributions from the nebula and the pulsar can hide the wind signal. Since the pulsar wind is expected to be cold, no strong synchrotron emission is produced in the wind zone. In fact, the only mechanism for pulsar wind to produce a detectable non-thermal emission is the inverse Compton scattering. It has been suggested that the recently-observed very high energy pulsed gamma-rays emitted by the Crab pulsar are best explained by the inverse Compton emission at illumination of the wind by X-ray photons from the pulsar magnetosphere. This finding provides precise localization of the site of the wind acceleration at R_w ≈ 30 light cylinders from the pulsar, and a measurement of the wind Lorentz factor (Γ_w = (5 - 7) × 10~5). In this paper we study the consistency of the suggested scenario against a few problematic issues. We discuss the implications measurements of the shape of the pulse shape measured in the VHE regime. Also, we study whether the obtained wind parameters are consistent with the radio flux of the Crab Nebula.