A Caltech Library Service

Cluster merger shock constraints on particle acceleration and nonthermal pressure in the intracluster medium

Nakar, Ehud and Milosavljević, Miloš and Nagai, Daisuke (2008) Cluster merger shock constraints on particle acceleration and nonthermal pressure in the intracluster medium. Astrophysical Journal, 675 (1). pp. 126-135. ISSN 0004-637X. doi:10.1086/526409.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


X-ray observations of galaxy cluster merger shocks can be used to constrain nonthermal processes in the intracluster medium (ICM). The presence of nonthermal pressure components in the ICM, as well as the shock acceleration of particles and their escape, all affect shock jump conditions in distinct ways. Therefore, these processes can be constrained using X-ray surface brightness and temperature maps of merger shock fronts. Here we use these observations to place constraints on particle acceleration efficiency in intermediate Mach number (M ≈2-3) shocks and explore the potential to constrain the contribution of nonthermal components (e. g., cosmic rays, magnetic field, and turbulence) to ICM pressure in cluster outskirts. We model the hydrodynamic jump conditions in merger shocks discovered in the galaxy clusters A520 (M ≈2) and 1E 0657-56 (M ≈3) using a multifluid model comprising a thermal plasma, a nonthermal plasma, and a magnetic field. Based on the published X-ray spectroscopic data alone, we find that the fractional contribution of cosmic rays accelerated in these shocks is ~< 10% of the shock downstream pressure. Current observations do not constrain the fractional contribution of nonthermal components to the pressure of the undisturbed shock upstream. Future X-ray observations, however, have the potential to either detect particle acceleration in these shocks through its effect on the shock dynamics, or place a lower limit on the nonthermal pressure contributions in the undisturbed ICM. We briefly discuss implications formodels of particle acceleration in collisionless shocks and the estimates of galaxy cluster masses derived from X-ray and Sunyaev-Zel'dovich effect observations.

Item Type:Article
Related URLs:
URLURL TypeDescription
Nakar, Ehud0000-0002-4534-7089
Nagai, Daisuke0000-0002-6766-5942
Additional Information:© 2008 The American Astronomical Society. Received 2007 June 18; accepted 2007 October 2. The research was supported in part by the Sherman Fairchild Foundation. We would like to thank A. Konigl, E. Komatsu, A. Kravtsov, P. Kumar, Y. Rephaeli, and J. Scalo for helpful discussions.
Funding AgencyGrant Number
Sherman Fairchild FoundationUNSPECIFIED
Subject Keywords:cosmic rays; galaxies: clusters: general; galaxies: clusters: individual (A520, 1E 0657–06); intergalactic medium; shock waves; turbulence; X-rays: galaxies: clusters
Issue or Number:1
Record Number:CaltechAUTHORS:NAKapj08
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13424
Deposited By: Tony Diaz
Deposited On:27 May 2009 21:36
Last Modified:08 Nov 2021 22:37

Repository Staff Only: item control page