RE-ACCELERATION OF NON-THERMAL PARTICLES AT WEAK COSMOLOGICAL SHOCK WAVES
- Department of Earth Sciences, Pusan National University, Pusan 609-735 (Korea, Republic of)
- Department of Astronomy and Space Science, Chungnam National University, Daejeon (Korea, Republic of)
We examine diffusive shock acceleration (DSA) of the pre-existing as well as freshly injected populations of non-thermal, cosmic-ray (CR) particles at weak cosmological shocks. Assuming simple models for thermal leakage injection and Alfvenic drift, we derive analytic, time-dependent solutions for the two populations of CRs accelerated in the test-particle regime. We then compare them with the results from kinetic DSA simulations for shock waves that are expected to form in intracluster media and cluster outskirts in the course of large-scale structure formation. We show that the test-particle solutions provide a good approximation for the pressure and spectrum of CRs accelerated at these weak shocks. Since the injection is extremely inefficient at weak shocks, the pre-existing CR population dominates over the injected population. If the pressure due to pre-existing CR protons is about 5% of the gas thermal pressure in the upstream flow, the downstream CR pressure can absorb typically a few to 10% of the shock ram pressure at shocks with a Mach number M {approx}< 3, yet the re-acceleration of CR electrons can result in a substantial synchrotron emission behind the shock. The enhancement in synchrotron radiation across the shock is estimated to be about a few to several for M {approx} 1.5 and 10{sup 2}-10{sup 3} for M {approx} 3, depending on the detail model parameters. The implication of our findings for observed bright radio relics is discussed.
- OSTI ID:
- 21576690
- Journal Information:
- Astrophysical Journal, Vol. 734, Issue 1; Other Information: DOI: 10.1088/0004-637X/734/1/18; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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