Cosmic ray acceleration at supergalactic accretion shocks: A new upper energy limit due to a finite shock extension

Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland

Corresponding author: G. Siemieniec-Oziębło, grazyna@oa.uj.edu.pl

Received: 23 October 2001
Accepted: 18 February 2002

Abstract

Accretion flows onto supergalactic-scale structures are accompanied with large spatial scale shock waves. These shocks were postulated as possible sources of ultra-high energy cosmic rays. The highest particle energies were expected for perpendicular shock configuration in the so-called “Jokipii diffusion limit”, involving weakly turbulent conditions in the large-scale magnetic field imbedded in the accreting plasma. For such configuration we discuss the process limiting the highest energy that particles can obtain in the first-order Fermi acceleration process due to finite shock extensions to the sides, along and across the mean magnetic field. Cosmic ray outflow along the shock structure can substantially lower the upper energy limit for conditions considered for supergalactic shocks.