S E M I N A R IDepartament d'Astronomia i Astrofísica
Universitat de València
Magnetic field generation and particle acceleration in gamma ray bursts
Dr. Troels Haugboelle
Niels Bohr Institutet, Copenhaguen, Dinamarca
Seminari del departament d'Astronomia i Astrofísica
Divendres 11 març 2005
Gamma-ray bursts are among the most energetic events in the known universe. A highly relativistic fireball is ejected, in what is believed to be connected to the death of super massive stars. In most cases the burst itself is followed by an afterglow, emitted under deceleration as the fireball plunges through the circum-stellar media. To make the right interpretations from the afterglow observations, two things need to be determined and understood: 1) The origin and nature of the magnetic field in the fireball and 2) the particle velocity distribution function behind the shock. Both are necessary in existing afterglow models to account for what is believed to be synchrotron radiation. To answer these questions, we need to understand the microphysics at play in collisionless shocks. Using 3D particle-in-cell simulations we can gain insight in the microphysical processes that take place in such shocks. This talk presents the results of such computer experiments. It is shown how a Weibel-like two-stream plasma instability is able to create a strong transverse intermittent magnetic field and points to a connected mechanism for in situ particle acceleration in the shock-region.