Astron. Astrophys. Suppl. Ser.
Volume 138, Number 3, September 1999Gamma-Ray Bursts in the Afterglow Era Contents Rome, November 3-6, 1998
|Page(s)||549 - 550|
|Published online||15 September 1999|
Particle acceleration at ultra-relativistic shocks
Gamma-ray burst afterglow spectra and UHECRs
Astronomical Institute, Utrecht University, P.O. Box 80 000, 3508 TA Utrecht, Netherlands
2 Max–Planck–Institut für Kernphysik, Postfach 10 39 80, 69029 Heidelberg, Germany
Send offprint request to: Y.A. Gallant
Accepted: 26 January 1999
We consider particle acceleration of the Fermi type at the ultra-relativistic shock bounding an expanding relativistic fireball. We distinguish between the initial shock crossing cycle, in which particles can gain a large factor in energy, and subsequent crossing cycles, where the energy typically only doubles. We show that repeated shock crossings yield a power-law spectrum of accelerated particles with index , compatible with afterglow observations. We suggest that ultra-high-energy cosmic rays (UHECRs) might be produced by the initial boost in a relativistic fireball expanding into a pulsar wind bubble created by the progenitor system.
Key words: acceleration of particles / relativity / shock waves / gamma-rays: bursts / cosmic rays
© European Southern Observatory (ESO), 1999