The very steep spectrum radio halo in Abell 697

Macario, G.; Venturi, T.; Brunetti, G.; Dallacasa, D.; Giacintucci, S.; Cassano, R.; Bardelli, S.; Athreya, R.

doi:10.1051/0004-6361/201014109

Cited by 65 publications

(84 citation statements)

References 53 publications

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“…those with "normal" (α ∼ 1.2 ÷ 1.3) spectrum, tend to have sizes and shapes similar at all frequencies, and the "low frequency haloes", i.e. those with very steep spectra (α ≥ 1.6) show increasing size at decreasing frequency, as is the case for A 697 (see Macario et al 2010, and van Weeren et al 2011a, it is possible that this difference is the result of the limited sensitivity of the current interferometers. The improved sensitivity of the EVLA at GHz frequencies and of the LOFAR below 240 MHz will allow us to carefully address this point, and explore the possibility that the dependence of the size with frequency is the result of the radial spectral steepening.…”

Section: Size Versus Frequencymentioning

confidence: 92%

“…While it is still possible that the 610 MHz flux density measurements are underestimated (see Macario et al 2010), a check on the S-E ridge does not suggest any missing flux at 610 MHz. The spectral index for this feature between 240 MHz and 610 MHz is consistent with that reported in V08 between 610 MHz and 1.4 GHz (NVSS).…”

Section: A 1682: a Very Complex Clustermentioning

confidence: 97%

“…The legend to Col. 5 is: GRH = giant radio halo 2 ; RH = radio halo; Rel = relic. Four clusters in Table 1 have been published in dedicated works: A 521 Brunetti et al 2008), A 697 (Macario et al 2010), A 781 (Venturi et al 2011a), and RXCJ 2003.5-2323). In this paper we present the remaining clusters, and we incorporate all the clusters in Table 1 in the discussion.…”

Section: The Cluster Samplementioning

confidence: 99%

“…So A&A 551, A24 (2013) References. a) This paper; b) Giacintucci et al (2008); c) Brunetti et al (2008); d) Dallacasa et al (2009); e) Macario et al (2010); f) Venturi et al (2011a); g) Venturi et al (2011b); h) Mazzotta et al (2011); i) Giacintucci et al (2009). far a spatial connection between a X-ray shock, or candidate, and cluster-scale radio emission in the form of a distinct radio relic, or an edge in the radio halo structure, has only been reported for a handful of clusters: the Bullet cluster (Markevitch et al 2002), A 520 (Markevitch et al 2005); A 754 (Macario et al 2011a); A 3667 (Finoguenov et al 2010;Akamatsu et al 2012); A 521 Bourdin et al 2012); RXCJ 1314.5-2515 . A census of the relics studied so far is given in van Weeren et al (2011a); and a review of our knowledge of shocks and of the related radio emission has been recently given in Markevitch (2010).…”

Section: Introductionmentioning

confidence: 99%

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Low frequency follow up of radio haloes and relics in the GMRT Radio Halo Cluster Survey

Venturi

Giacintucci

Dallacasa

et al. 2013

A&A

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Aims. To gain insight into the origin of diffuse radio sources in galaxy clusters and their connection with cluster merger processes, we performed GMRT low frequency observations of the radio haloes, relics and new candidates belonging to the GMRT radio Halo cluster sample first observed at 610 MHz. Our main aim was to investigate their observational properties and integrated spectra at frequencies below 610 MHz. Methods. High sensitivity imaging was performed using the GMRT at 325 MHz and 240 MHz. The properties of the diffuse emission in each cluster were compared to our 610 MHz images and/or literature information available at other frequencies, in order to derive the integrated spectra over a wide frequency range. Results. Cluster radio haloes form a composite class in terms of spectral properties. Beyond the classical radio haloes, whose spectral index α is in the range ∼1.2 ÷ 1.3 (S ∝ ν −α ), we found sources with α ∼ 1.6 ÷ 1.9. This result supports the idea that the spectra of the radiating particles in radio haloes is not universal and that inefficient mechanisms of particle acceleration are responsible for their origin. We also found a variety of brightness distributions, i.e. both centrally peaked and clumpy haloes. Even though the thermal and relativistic plasma tend to occupy the same cluster volume, in some cases a positional shift between the radio and X-ray peaks of emission is evident. Our observations also revealed diffuse cluster sources that cannot be easily classified as either haloes or relics. New candidate relics were found in A 1300 and in A 1682, and in some clusters "bridges" of radio emission have been detected, connecting the relic and radio halo emission. Finally, by combining our new data with information in the literature, we derived the Log L X -Log P 325 MHz correlation for radio haloes, and investigated the possible correlation of the spectral index of radio haloes with the temperature of the intracluster medium.

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Section: Size Versus Frequencymentioning

confidence: 92%

Section: A 1682: a Very Complex Clustermentioning

confidence: 97%

Section: The Cluster Samplementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Low frequency follow up of radio haloes and relics in the GMRT Radio Halo Cluster Survey

Venturi

Giacintucci

Dallacasa

et al. 2013

A&A

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“…In particular, an unrealistic amount of energy in the form of relativistic protons would be required by secondary models to explain radio halos with very steep spectra (Brunetti 2004;Pfrommer & Enßlin 2004;Brunetti et al 2008;Macario et al 2010;van Weeren et al 2011a). On the other hand, if turbulence plays an important role for the origin of these giant sources, a large number of steep spectrum radio halos is expected to glow up at low radio frequencies Brunetti et al 2008).…”

Section: Introductionmentioning

confidence: 99%

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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Radio observations of Planck clusters

Kale

2013

Astron Nachr

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Recently, a number of new galaxy clusters have been detected by the ESA-Planck satellite, the South Pole Telescope and the Atacama Cosmology Telescope using the Sunyaev-Zel'dovich effect. Several of the newly detected clusters are massive, merging systems with disturbed morphology in the X-ray surface brightness. Diffuse radio sources in clusters, called giant radio halos and relics, are direct probes of cosmic rays and magnetic fields in the intra-cluster medium. These radio sources are found to occur mainly in massive merging clusters. Thus, the new SZ-discovered clusters are good candidates to search for new radio halos and relics. We have initiated radio observations of the clusters detected by Planck with the Giant Metrewave Radio Telescope. These observations have already led to the detection of a radio halo in PLCKG171.9-40.7, the first giant halo discovered in one of the new Planck clusters. Galaxy cluster surveysGalaxy clusters are the most massive (masses ∼ 10 14 − 10 15 M ⊙ ) gravitationally bound objects in the present Universe, with dark matter dominating the gravity. The baryonic matter in clusters consists of hot (10 7 − 10 8 K) intracluster medium (ICM) and galaxies. Large surveys in optical and X-ray bands have resulted in discoveries of thousands of clusters (eg. Abell et al 1980;Bohringer et al 2004). These surveys rely on the surface brightness of the emission from stars in the galaxies (optical band) and on the thermal X-ray emission from the ICM for the detections of clusters. These result in 'flux-limited' catalogues of sources. Another signal that is used to detect clusters is the thermal Sunyaev Zel'dovich effect (SZ) -the spectral distortion of Cosmic Microwave Background (CMB) caused by inverse Compton scattering with the ICM (Sunyaev and Zel'dovich 1972). This signal is independent of redshift and the integrated thermal SZ effect is expected to trace cluster mass with low scatter There are a number of clusters discovered by these telescopes that have been confirmed by deep X-ray and optical observations. Notably, the Planck collaboration has published confirmation of 51 new galaxy clusters (Planck collaboration 2011a(Planck collaboration , 2011b(Planck collaboration , 2011c(Planck collaboration , 2012a(Planck collaboration , 2012b. The vali-⋆ Corresponding author: e-mail: rkale@ira.inaf.it dation of the cluster candidates was carried out by snapshot observations in X-rays with the XMM Newton. These newly discovered clusters were earlier missed by the blind all sky X-ray surveys such as with the ROSAT due to their low surface brightness. This is evident from the fact that the new clusters have flat electron density profiles (Planck collaboration 2011a) as compared to the clusters that were detected in surveys by the ROSAT. Thus apart from being massive, the newly discovered clusters using the SZ are likely to be merging systems with disturbed ICM. Radio observations of clustersRadio observations are the main probes of non-thermal activities in galaxy clusters. They lead to discove...

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The very steep spectrum radio halo in Abell 697

Cited by 65 publications

References 53 publications

Low frequency follow up of radio haloes and relics in the GMRT Radio Halo Cluster Survey

Low frequency follow up of radio haloes and relics in the GMRT Radio Halo Cluster Survey

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

Radio observations of Planck clusters

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