Nonthermal phenomena in clusters of galaxies

Abstract

Recent observations of high energy (> 20 keV) X-ray emission in a few clusters of galaxies broaden our knowledge of physical phenomena in the intracluster space. This emission is likely to be nonthermal, probably resulting from Compton scattering of relativistic electrons by the cosmic microwave background (CMB) radiation. Direct evidence for the presence of relativistic electrons in some 50 clusters comes from measurements of extended radio emission in their central regions. We briefly review the main results from observations of extended regions of radio emission, and Faraday rotation measurements of background and cluster radio sources. The main focus of the review are searches for nonthermal X-ray emission conducted with past and currently operating satellites, which yielded appreciable evidence for nonthermal emission components in the spectra of a few clusters. This evidence is clearly not unequivocal, due to substantial observational and systematic uncertainties, in addition to virtually complete lack of spatial information. If indeed the emission has its origin in Compton scattering of relativistic electrons by the CMB, then the mean magnetic field strength and density of relativistic electrons in the cluster can be directly determined. Knowledge of these basic nonthermal quantities is valuable for the detailed description of processes in intracluster gas and for the origin of magnetic fields.

23 pages, 7 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 5; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeker

References in corpus (7)

• Observations of extended radio emission in clusters
• A deeper X-ray study of the core of the Perseus galaxy cluster: the power of sound waves and the distribution of metals and cosmic rays
• Particle acceleration mechanisms
• Nonthermal radiation mechanisms
• Nonthermal hard X-ray excess in the Coma cluster: resolving the discrepancy between the results of different PDS data analyses
• Analysis and Interpretation of Hard X-ray Emission from the Bullet Cluster (1E0657-56), the Most Distant Cluster of Galaxies Observed by RXTE
• South-West extension of the hard X-ray emission from the Coma cluster

Cited by in corpus (7)

• GMRT Radio Halo Survey in galaxy clusters at z = 0.2 -- 0.4. II.The eBCS clusters and analysis of the complete sample
• Diffuse radio emission from clusters in the MareNostrum Universe simulation
• Galaxy Clusters in the Swift/BAT era: Hard X-rays in the ICM
• Non-thermal processes in cosmological simulations
• Soft X-ray and extreme ultraviolet excess emission from clusters of galaxies
• Non-thermal emission in the core of Perseus: results from a long XMM-Newton observation
• Clusters of galaxies: setting the stage