Bulletin of the Astronomical Society of India
1Department of Astronomy, University of Maryland, College Park, MD 20742, USA
2Joint Space-Science Institute, University of Maryland, College Park, MD, 20742-2421, USA
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Many dynamically disturbed galaxy clusters exhibit diuse radio emission, which takes the form of cluster-wide synchrotron giant radio halos and peripheral Mpc-sized radio relics. Smaller-scale, diuse radio sources – called mini-halos – are found in the cool cores of a number of relaxed clusters. Halos and relics reveal a population of ultra-relativistic electrons coexisting with the intra-cluster thermal gas. The origin of these electrons is one of the most debated problems of cluster astrophysics. Significant improvement in our understanding of the properties of giant halos and of the physical mechanism behind their formation has been possible thanks to dedicated and extensive statistical studies such as the GMRT Radio Halo Survey and its ongoing extension. Because of their rarity, mini-halos are still poorly understood. Detailed radio spectral studies help to discriminate between various physical interpretations of mini-halos, but the information on their spectral properties is still scarce. Our recent spectral analysis of the mini-halo in RXJ 1720.1+2638 – the best-studied object of this class so far – has provided new insights on the origin of the synchrotron-emitting electrons in cluster cool cores.
Keywords :radio continuum: general – galaxies: clusters: general