Radio halo and relic candidates from the NRAO VLA Sky Survey

Giovannini, G.; Tordi, Massimiliano; Feretti, L.

doi:10.1016/s1384-1076(99)00018-4

Cited by 311 publications

(409 citation statements)

References 26 publications

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“…The extended emission at the cluster center, reported by Harris et al (1980) and also visible in the NVSS image ) is at the limit of significance in our map at 90 cm. This implies that this feature cannot have a steep spectral index between 90 and 20 cm (α 20 90 < 0.7) and confirms the suggestion of Giovannini et al (1999) that the radio emission might be the blend of many bright cluster galaxies in this region, rather than a diffuse halo. The diffuse emission detected in the NVSS in the eastern peripheral region ) cannot be seen in the 90 cm image because of the too low angular resolution.…”

Section: Notes On Individual Clusters Without Diffuse Sourcessupporting

confidence: 84%

Halo and relic sources in clusters of galaxies

2000

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New images of 7 radio halos and relics, obtained with the Very Large Array at 20 or 90 cm, are presented here. The existence of a cluster-wide radio halo in the clusters A 665 and CL 0016+16 is confirmed. Both these clusters share the properties of the other clusters with radio halos, i.e. are luminous in X-rays, have high temperature, and show recent merger processes. No diffuse sources are detected in a sample of clusters showing at least a tailed radio galaxy within 300 kpc from the cluster center, indicating that the connection between tailed radio galaxies and halos is not relevant. For these clusters we give limits to the surface brightness and to the angular size of possible undetected diffuse sources. : 98.65.Cw; 98.65.Hb; 98.70.Dk; 98.70.Qy PACS

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Section: Notes On Individual Clusters Without Diffuse Sourcessupporting

confidence: 84%

Halo and relic sources in clusters of galaxies

2000

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“…We assume some proportional relation (e.g. equipartition) between the energies of the magnetic field and non-thermal electrons Allen & Fabian (1998), except 1ES 0657 − 55.8 data from Liang et al (2000) b Data for Coma from Kim et al (1990); A 2256, A 2163, A 1914 and A 2744 from Giovannini et al (1999); 1ES 0657 − 55.8 from Liang et al (2000); A 2219 from Bacchi et al (2003). c Approximate largest angular extent.…”

Section: Hard X-ray and Radio Emissionmentioning

confidence: 99%

Nonthermal Radiation Mechanisms

2008

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In this paper we review the possible radiation mechanisms for the observed non-thermal emission in clusters of galaxies, with a primary focus on the radio and hard X-ray emission. We show that the difficulty with the non-thermal, non-relativisitic Bremsstrahlung model for the hard X-ray emission, first pointed out by Petrosian (2001) using a cold target approximation, is somewhat alleviated when one treats the problem more exactly by including the fact that the background plasma particle energies are on average a factor of 10 below the energy of the non-thermal particles. This increases the lifetime of the non-thermal particles, and as a result decreases the extreme energy requirement, but at most by a factor of three. We then review the synchrotron and so-called inverse Compton emission by relativistic electrons, which when compared with observations can constrain the value of the magnetic field and energy of relativistic electrons. This model requires a low value of the magnetic field which is far from the equipartition value. We briefly review the possibilities of gammaray emission and prospects for GLAST observations. We also present a toy model of the non-thermal electron spectra that are produced by the acceleration mechanisms discussed in an accompanying paper.

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“…Radio halos are preferentially found in high X-ray luminosity clusters (Giovannini et al 1999) and a tentative correlation was found between the radio luminosity of halos and X-ray temperature of cluster gas (Liang et al 2000). Recently, we have observed a number of clusters with relatively low temperature (kT x < 7 keV) to test if this correlation still holds and whether there is a switch-on temperature for radio halo production.…”

Section: Properties Of Radio Halosmentioning

confidence: 99%

“…1) with the addition of A2199 (Kempner & Sarazin 2000) and A3667 (Ekers private comm.). We also attempted to test the theory that merging is the essential ingredient in halo production, since so far all the known radio halos are detected in non-cooling flow, merging clusters (Giovannini et al 1999). For this reason, we chose to observe with the ATCA a strong cooling flow cluster (i.e.…”

Section: Properties Of Radio Halosmentioning

confidence: 99%

Diffuse Cluster-Wide Radio Halos

Liang

2002

Highlights astron.

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Abstract. We will discuss the properties and origins of halos and relics including estimates of the cluster magnetic fields, and present results for a few recently discovered halos and relics. The electrons in the suprathermal high energy tail of the thermal gas distribution are likely to provide the seed particles for acceleration through mergers and turbulences to relativistic energies. These relativistic particles are then responsible for the synchrotron emission of the halos.

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Radio halo and relic candidates from the NRAO VLA Sky Survey

Cited by 311 publications

References 26 publications

Halo and relic sources in clusters of galaxies

Halo and relic sources in clusters of galaxies

Nonthermal Radiation Mechanisms

Diffuse Cluster-Wide Radio Halos

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