A Study of Particle Transport in Young Pulsar Wind Nebulae

Abstract

The broadband emission of numerous pulsar wind nebula (PWNe) in our Galaxy can be well described by synchrotron radiation and inverse Compton scattering from relativistic particles, specifically electrons and positrons. However, the particle transport mechanism is still under debate. We use here a time-dependent model to investigate the particle transport process of the young PWN, while the particle cooling processes are also analyzed. Following applications of the model to six young PWNe, our results show that (1) the particle cooling process is dominated by adiabatic loss in the low-energy band but by synchrotron loss in the high-energy band; (2) the advection dominates the particle transport process in the low-energy band, whereas the advection and diffusion codominate in the high-energy band, indicating that both advection and diffusion play an important role in particle transport; and (3) the diffusion coefficient is (2–360) × 1024 cm2 s−1 at the electron energy of 1 TeV, i.e., about 3 orders of magnitude smaller than the value considered to be the average in the Galaxy. We conclude that a slow-diffusion mechanism may explain the multiband observation of the sample of six young PWNe considered in this study.