Related papers: Diffuse Cluster-wide Radio Halos
We search for extended regions of radio emission not associated with Active Galactic Nuclei, known as 'relics', 'halos' and 'mini halo's, in a sample of 70 Abell clusters for which we have radio, optical and X-ray data. AGN can produce…
Giant Radio Halos (RH) are diffuse, Mpc-sized, synchrotron radio sources observed in a fraction of merging galaxy clusters. The current scenario for the origin of RHs assumes that turbulence generated during cluster mergers re-accelerates…
The underlying physics of giant and mini radio halos in galaxy clusters is still an open question. We find that mini halos (such as in Perseus and Ophiuchus) can be explained by radio-emitting electrons that are generated in hadronic cosmic…
The interaction of magnetic turbulence and relativistic particles is a important process for understanding particles propagation and acceleration in many astrophysical environments. Large-scale turbulence can be generated in the…
Non-thermal radio emission from cosmic ray electrons in the vicinity of merging galaxy clusters is an important tracer of cluster merger activity, and is the result of complex physical processes that involve magnetic fields, particle…
The recent evidences of the presence of magnetic fields and relativistic particles in galaxy clusters are reviewed. The existence of microG-level magnetic fields in cluster atmospheres appears well established from the detection of diffuse…
Context. The recent discovery of so-called mega radio halos as a new class of diffuse, steep-spectrum radio sources in clusters of galaxies has raised questions about the origin and the evolution of cluster-wide radio emission. Aims. We…
Giant radio halos are Mpc-scale diffuse radio sources associated with the central regions of galaxy clusters. The most promising scenario to explain the origin of these sources is that of turbulent re-acceleration, in which MeV electrons…
Radio relics are diffuse radio sources in galaxy clusters that are associated with merger shock waves. Detailed observations of radio relics in total intensity and in polarisation show complex structures on kiloparsec scales. The relation…
Recent observations of high energy (> 20 keV) X-ray emission in a few clusters extend and broaden our knowledge of physical phenomena in the intracluster space. This emission is likely to be nonthermal, probably resulting from Compton…
Relativistic electrons and magnetic fields permeate the intra-cluster medium (ICM) and manifest themselves as diffuse sources of synchrotron emission observable at radio wavelengths, namely radio halos and radio relics. Although there is…
The thermal plasma of galaxy clusters lost most of its information on how structure formation proceeded as a result of dissipative processes. In contrast, non-equilibrium distributions of cosmic rays (CR) preserve the information about…
In this paper, transient high energy events and their hosts are discussed with focus on signatures of radio synchrotron emission. Outstanding questions range from the origin of the two phases of radio emission in supernovae to the formation…
A radio bimodality is observed in galaxy clusters: a fraction of clusters host giant radio halos while the majority of clusters do not show evidence of diffuse cluster-scale radio emission. Present data clearly suggest that the radio…
About 1/3 of X-ray-luminous clusters show smooth, Mpc-scale radio emission, known as giant radio haloes. One promising model for radio haloes is Fermi-II acceleration of seed relativistic electrons by compressible turbulence. The origin of…
We present the first high resolution MHD simulation of cosmic-ray electron reacceleration by turbulence in cluster mergers. We use an idealised model for cluster mergers, combined with a numerical model for the injection, cooling and…
Galaxy clusters are unique laboratories to investigate turbulent fluid motions and large scale magnetic fields. Synchrotron radio halos at the center of merging galaxy clusters provide the most spectacular and direct evidence of the…
Galaxy clusters form through a sequence of mergers of smaller galaxy clusters and groups. Models of diffusive shock acceleration (DSA) suggest that in shocks that occur during cluster mergers, particles are accelerated to relativistic…
Several arguments have been presented in the literature to support the connection between radio halos and cluster mergers. The spectral index distributions of the halos in A665 and A2163 provide a new strong confirmation of this connection,…
Deep Very Large Array radio observations confirm the presence of halo and relic sources in six clusters of galaxies (A115, A520, A773, A1664, A2254, A2744) where a wide diffuse emission was previously found in the NRAO VLA Sky Survey. New…