Fermi Gamma-ray Space Telescope

Developing of a specialized Particle-In-Cell code to study Pulsar Magnetospheres

G. Brambilla
C. Kalapotharakos, A. N. Timokhin, A. K. Harding, D. Kazanas

Abstract:

Thanks to Fermi, we know more about pulsar ?-ray emission than a decade ago, but the exact mechanism(s) remains elusive. Models of so-called magnetospheric gaps, where particles are accelerated up to ultrarelativistic energies by electric field and emit high energy radiation, have been used to reproduce the variety of light curves seen by Fermi with various degrees of success. Gap models, besides being electrodynamically inconsistent, have serious difficulties in explaining luminosity, spectra, and light curve features at the same time. It became clear that understanding pulsar emission mechanism(s) requires construction of a global self-consistent model of the magnetosphere accounting for the microphysics of particle acceleration and pair creation. MHD models were successful explaining the general magnetosphere structure and the emission, but are not self-consistent either. The Particle-In-Cell (PIC) technique is the most promising way to connect micro- and macro- physics. In PIC codes the currents and fields are generated by many individual super-particles, each accounting for many of the real particles; these particles can also emit photons depending on their acceleration by the (consistent) electric field. The first attempts of applying PIC codes to the pulsar problem have been encouraging. In our group we are developing a PIC code suited to study pulsar magnetospheres. I will describe the goals of the project, its limitations and early results.