A double radio relic in the merging galaxy cluster ZwCl 0008.8+5215

Weeren, R. J. van; Hoeft, M.; Röttgering, H. J. A.; Brüggen, M.; Intema, H. T.; Velzen, S. van

doi:10.1051/0004-6361/201016185

Cited by 69 publications

(112 citation statements)

References 67 publications

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“…If the relic is seen under a viewing angle of 30 • from edge-on it is located at a true distance of ∼0.5 Mpc from the cluster center. This is about a factor of two closer to the cluster center than most of the double radio relic clusters (e.g., Röttgering et al 1997;Bagchi et al 2006;Bonafede et al 2009;van Weeren et al 2011b). Together with the flat radio spectrum this is consistent with the fact that the relic in A2256 is seen at a relatively early stage in the merger, approximately half of the time after core passage compared to some of the double radio relic clusters.…”

Section: Radio Relicsupporting

confidence: 68%

First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

Weeren¹,

Röttgering²,

Rafferty³

et al. 2012

A&A

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Abell 2256 is one of the best known examples of a galaxy cluster hosting large-scale diffuse radio emission that is unrelated to individual galaxies. It contains both a giant radio halo and a relic, as well as a number of head-tail sources and smaller diffuse steep-spectrum radio sources. The origin of radio halos and relics is still being debated, but over the last years it has become clear that the presence of these radio sources is closely related to galaxy cluster merger events. Here we present the results from the first LOFAR low band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our knowledge, the image presented in this paper at 63 MHz is the deepest ever obtained at frequencies below 100 MHz in general. Both the radio halo and the giant relic are detected in the image at 63 MHz, and the diffuse radio emission remains visible at frequencies as low as 20 MHz. The observations confirm the presence of a previously claimed ultra-steep spectrum source to the west of the cluster center with a spectral index of −2.3 ± 0.4 between 63 and 153 MHz. The steep spectrum suggests that this source is an old part of a head-tail radio source in the cluster. For the radio relic we find an integrated spectral index of −0.81 ± 0.03, after removing the flux contribution from the other sources. This is relatively flat which could indicate that the efficiency of particle acceleration at the shock substantially changed in the last ∼0.1 Gyr due to an increase of the shock Mach number. In an alternative scenario, particles are re-accelerated by some mechanism in the downstream region of the shock, resulting in the relatively flat integrated radio spectrum. In the radio halo region we find indications of low-frequency spectral steepening which may suggest that relativistic particles are accelerated in a rather inhomogeneous turbulent region.

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Section: Radio Relicsupporting

confidence: 68%

First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

Weeren¹,

Röttgering²,

Rafferty³

et al. 2012

A&A

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“…The elongated structure does not show any morphological feature typical of radio relics such as high brightness filamentary structures or a transverse flux asymmetry (see e.g. van Weeren et al 2011). We conclude that its classification as a radio relic is very unlikely.…”

Section: Radio Imagesmentioning

confidence: 87%

“…In addition, diffuse radio sources classified as radio relics are detected in cluster peripheral regions (see e.g. Giovannini & Feretti 2004;and van Weeren et al 2011). These sources are not directly associated with the activity of individual galaxies and are related to physical properties of the whole cluster.…”

Section: Introductionmentioning

confidence: 99%

A giant radio halo in the low luminosity X-ray cluster Abell 523

Giovannini

Feretti

Girardi

et al. 2011

A&A

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Context. Radio halos are extended and diffuse non-thermal radio sources present at the cluster center, not obviously associated with any individual galaxy. A strong correlation has been found between the cluster X-ray luminosity and the halo radio power.Aims. We observe and analyze the diffuse radio emission present in the complex merging structure Abell 523, classified as a low luminosity X-ray cluster, to discuss its properties in the context of the halo total radio power versus X-ray luminosity correlation. Methods. We reduced VLA archive observations at 1.4 GHz to derive a deep radio image of the diffuse emission, and compared radio, optical, and X-ray data. Results. Low-resolution VLA images detect a giant radio halo associated with a complex merging region. The properties of this new halo agree with those of radio halos in general discussed in the literature, but its radio power is about a factor of ten higher than expected on the basis of the cluster X-ray luminosity. Conclusions. Our study of this giant radio source demonstrates that radio halos can also be present in clusters with a low X-ray luminosity. Only a few similar cases have so far been found. This result suggests that this source represents a new class of objects, that cannot be explained by classical radio halo models. We suggest that the particle reacceleration related to merging processes is very efficient and/or the X-ray luminosity is not a good indicator of the past merging activity of a cluster.

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“…We recently discovered two large radio relics in the NVSS and WENSS surveys (van Weeren et al 2010(van Weeren et al , 2011a. Interestingly, these relics remained unnoticed for about 15 years.…”

Section: Introductionmentioning

confidence: 99%

“…A few clusters host so-called double relics systems (van Weeren et al 2011a;van Weeren et al 2010;Bonafede et al 2009b;van Weeren et al 2009a;Venturi et al 2007;Feretti et al 2005;Bagchi et al 2006;Röttgering et al 1997), with both relics located symmetrically about to the cluster center and along the merger axis, as indicated by X-ray observations of the thermal ICM. Another class of diffuse filamentary radio sources in clusters are radio "phoenices".…”

Section: Introductionmentioning

confidence: 99%

Radio continuum observations of new radio halos and relics from the NVSS and WENSS surveys

Weeren

Brüggen

Röttgering

et al. 2011

A&A

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Context. Radio halos and relics are diffuse radio sources found in galaxy clusters showing significant substructure at X-ray wavelengths. These sources provide important information about non-thermal processes taking place in the intracluster medium (ICM). Until now only a few dozen relics and halos are known, while models predict that a much larger number of these sources exist. In this paper we present the results of an extensive observing campaign to search for new diffuse radio sources in galaxy clusters. Aims. The aim of the observations is to create a large sample of diffuse radio sources in galaxy clusters that help to understand the formation of radio relics and halos and can be used to probe the physical conditions of the ICM. Methods. We carried out radio continuum observations with the Westerbork Synthese Radio Telescope (WSRT), Giant Metrewave Radio Telescope (GMRT) and Very Large Array (VLA) of clusters with diffuse radio emission visible in NVSS and WENSS survey images. Optical images were taken with the William Herschel and Isaac Newton Telescope (WHT, INT). Results. We discovered 6 new radio relics, including a probable double relic system, and 2 radio halos. In addition, we confirm the presence of diffuse radio emission in four galaxy clusters. By constructing a sample of 35 radio relics we find that relics are mostly found along the major axis of the X-ray emission from the ICM, while their orientation is perpendicular to this axis. We also compared the X-ray luminosity and redshift distributions of clusters with relics to an X-ray selected sample from the NORAS and REFLEX surveys. We find tentative evidence for an increase of the cluster's relic fraction with X-ray luminosity and redshift. The major and minor axis ratio distribution of the ICM for clusters with relics is broader than that of the NORAS-REFLEX sample. Conclusions. The location and orientation of radio relics with respect to the ICM elongation is consistent with the scenario that relics trace merger shock waves.

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A double radio relic in the merging galaxy cluster ZwCl 0008.8+5215

Cited by 69 publications

References 67 publications

First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

A giant radio halo in the low luminosity X-ray cluster Abell 523

Radio continuum observations of new radio halos and relics from the NVSS and WENSS surveys

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