Vol. 642
2. Astrophysical processes

A global model of particle acceleration at pulsar wind termination shocks

Pulsar wind nebulae are among the brightest Galactic nonthermal sources at high energies, up through TeV, testifying to the efficient acceleration of charged particles in the vicinity of the central neutron star. Determining how to reach the required energies has been a challenging problem for decades. This study uses a schematic but physically plausible representation of the latitude-dependent pulsar wind and magnetic field into which leptons (electron-positron) are injected. The time dependent flow forms a shock, whose structure rapidly becomes macroscopically turbulent. The simulation uses a fully relativistic particle-in-cell (PIC) code, Zeltron, to follow the diffusive particle energization through this tangle of filamented structures at the termination shock of the wind with its surrounding interstellar medium (ISM). The formation of the shock over time is a result of the simulation and it is not pre-imposed, hence the complex structure development can be followed. This is perhaps the most intriguing result of the modeling, that is to say the synchrotron emission in different energy ranges is diagnostic for the site of origin: The highest energy emission comes from the turbulent regions imbedded within shock cavities and it is boosted and beamed by the local bulk motions at the shock.