Gamma-rays from the pulsar wind nebulae

Abstract

We investigate the radiation processes inside supernova remnants which are powered by young pulsars. Using a recent model for particle acceleration by the pulsar wind nebulae (PWNe), in which positrons gain energy in the process of resonant scattering by the heavy nuclei, we construct a time-dependent radiation model for the PWNe. In this model, the spectra of relativistic particles, injected inside the nebula, depend on time due to the evolution of the pulsar parameters. Applying a simple model for the evolution of the PWNa, the equilibrium spectra of leptons and nuclei inside the nebula are determined as a function of time, taking into account the energy losses of particles on dierent processes and their escape from the nebula. We calculate the multiwavelength photon spectra produced by leptons and nuclei and compare them with the observations of the PWNe for which TeV-ray emission has been reported, i.e. the Crab Nebula, the Vela Supernova Remnant, and the nebula around PSR 1706-44. It is found that the emission from the Crab Nebula can be well fitted by the composition of the -ray emission produced by leptons (below10 TeV) and nuclei (10 TeV). The model is further tested by successful fitting of the high energy spectrum from the Vela SNR. In this case, the observed-ray emission is mainly due to leptons and the contribution of-rays from decay of neutral pions, produced in collision of nuclei, is significantly lower. However, the considered model does not give good fitting to the emission from PSR1706-44 for the likely parameters of this source, unless an additional target for relativistic leptons is present inside the nebula, e.g. the thermal infrared emission. Based on the knowledge obtained from these fittings, we predict the -ray fluxes in the TeV energy range from other PWNe, which are promissing TeV-ray sources due to their similarities to the -ray nebulae, i.e. MSH15-52 (PSR 1509-58), 3C58 (PSR J0205+6449), and CTB80 (PSR 1951+32). Possible detection of these sources by the new generation of Cherenkov telescopes is discussed.