Particle and Flames in Radiative and Magnetic Flows

October 11-15, 2010
Lyon, France

Contribution of J. Petri


Pulsars and their electromagnetic surrounding: an approach by PIC simulations




Neutron stars are end products of stellar evolution. Within the last few years, compact object astrophysics has greatly benefited from terrestrial based and space telescopes in the X- and gamma-ray ranges. However, these compact stars remain badly understood, especially in the high and ultrahigh-energy bands where particle acceleration, relativistic shocks and pulsed emission (MeV, GeV) occur. In this talk, in the first part, I will briefly review some problems related to our understanding of pulsars and then focus on their magnetosphere and wind. In a second part, I will show how to face some of these problems with help on numerical simulations like Particle-In-Cell codes (PIC) in order to model the plasma flow around those stars. I will show the existence of a peculiar structure of the magnetosphere called electrosphere, an example of non-neutral plasma in astrophysics. A detailed analysis has demonstrated that this geometry is unstable against some non-neutral plasma instabilities: the diocotron and magnetron instability. These results are then confirmed and extended by 2D electrostatic PIC simulations. Farther away from the neutron star, its magnetised wind can be subject to magnetic reconnection in the relativistic regime when crossing the termination shock. Reconnection is studied via 1D relativistic PIC simulations. To conclude, particle codes are especially useful and valuable tools to investigate the physics of neutron star magnetosphere in a self-consistent manner.