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

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

doi:10.1051/0004-6361/201117149

Cited by 95 publications

(136 citation statements)

References 115 publications

Supporting

Mentioning

119

Contrasting

Unclassified

Order By: Relevance

“…In particular, α 1.4 GHz 153 MHz = 1.50 ± 0.03 and α 1.4 GHz 153 MHz = 1.52 ± 0.05 for the observed (blue circles) and corrected (red stars) GMRT values (M10). This value is slightly flatter than reported in van Weeren et al 2011 in the frequency range 325 MHz-1.7 GHz, as our 153 MHz flux density measurement is below the extrapolation of their power-law.…”

Section: Radio Halo In a 697contrasting

confidence: 88%

“…The very steep spectrum radio halo in A 521 and A 697 holds at least down to 153 MHz. In particular, for the halo A 521 the slope of the spectrum is in the range α 1.4 GHz 153 MHz = 1.8−1.9 depending on whether the 610 MHz data point (which is known to suffer from major uncertainties) is included, while the spectral index we derived for A 697 with by adding the 153 MHz flux density measurement is α 1.4 GHz 153 MHz = 1.52 ± 0.05, slightly flatter than the previous measurements (M10; van Weeren et al 2011), though all values are still consistent with each other within the errors.…”

Section: Discussionmentioning

confidence: 58%

“…2), overlaid on the 325 MHz image at a similar resolution (from M10). The largest linear size of the radio halo is ∼1.3 Mpc, and its surface brightness is centrally peaked, as seen also at higher frequencies (see V08;van Weeren et al 2011). The surface brightness sensitivity of the 325 MHz image is ∼2-2.5 better than that at 153 MHz (assuming a spectral index of 1.6 for the radio halo, i.e.…”

Section: Radio Halo In a 697mentioning

confidence: 87%

“…Only recently, thanks to the very good imaging capabilities of the GMRT at low frequencies and to the advent of LOw Frequency ARray (LOFAR), it has become possible to perform high-sensitivity observations of halos and relics at sub-GHz frequencies down to 150 MHz and below, thus allowing us to probe the "low end" of the energy distribution of the relativistic electron population (e.g. van Weeren et al 2011;Kale & Dwarakanath 2009, 2010van Weeren et al 2012). This is essential for understanding the origin of these sources, since the acceleration mechanisms at play leave a clear imprint on the particle spectrum (and hence on the radio emission).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

153 MHz GMRT follow-up of steep-spectrum diffuse emission in galaxy clusters

Macario

Venturi

Intema

et al. 2013

A&A

Self Cite

View full text Add to dashboard Cite

Aims. We present new high-sensitivity 153 MHz Giant Meterwave Radio Telescope follow-up observations of the diffuse steepspectrum cluster radio sources in the galaxy clusters Abell 521, Abell 697, and Abell 1682. Abell 521 hosts a relic, and together with Abell 697 it also hosts a giant very steep-spectrum radio halo. Abell 1682 is a more complex system with candidate steep spectrum diffuse emission. Methods. We imaged the diffuse radio emission in these clusters at 153 MHz, and provided flux density measurements of all sources at this frequency. Our new flux density measurements, coupled with the existing data at higher frequencies, allowed us to study the total spectrum of the halos and relic over at least one order of magnitude in frequency. Results. Our images confirm the very steep "diffuse component" in Abell 1682. We found that the spectrum of the relic in Abell 521 can be fitted by a single power-law with α = 1.45 ± 0.02 from 153 MHz to 5 GHz. Moreover, we confirm that the halos in Abell 521 and Abell 697 have a very steep spectrum , with α = 1.8−1.9 and α = 1.52 ± 0.05, respectively. Even including of the 153 MHz flux density information, it is impossible to distinguish between power-law and curved spectra, as derived from homogeneous turbulent re-acceleration. The latter are favoured on the basis of simple energetic arguments, and we expect that LOFAR will finally unveil the spectral shape of radio halos below 100 MHz, thus providing clues on their origin.

show abstract

Section: Radio Halo In a 697contrasting

confidence: 88%

Section: Discussionmentioning

confidence: 58%

Section: Radio Halo In a 697mentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

153 MHz GMRT follow-up of steep-spectrum diffuse emission in galaxy clusters

Macario

Venturi

Intema

et al. 2013

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Clusters of galaxies: observational properties of the diffuse radio emission

Feretti

Giovannini

Govoni

et al. 2012

Astron Astrophys Rev

679

908

View full text Add to dashboard Cite

Clusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures. The luminous matter of clusters consists of galaxies and of an embedding intracluster medium (ICM), which has been heated to temperatures of tens of millions degrees, and thus is detected through its thermal emission in the soft X-ray regime. Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission.The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolutionary stage, and are crucial for a comprehensive physical description of the intracluster medium. They play an important role in the cluster formation and evolution.We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos. We discuss their classification and properties. We report published results up to date and obtain and discuss statistical properties. We present the properties of large-scale magnetic fields in clusters and in even larger structures: filaments connecting galaxy clusters. We summarize the current models of the origin of these cluster components, and outline the improvements that are expected in this area from future developments thanks to the new generation of radio telescopes.

show abstract

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

Cited by 95 publications

References 115 publications

153 MHz GMRT follow-up of steep-spectrum diffuse emission in galaxy clusters

153 MHz GMRT follow-up of steep-spectrum diffuse emission in galaxy clusters

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

Clusters of galaxies: observational properties of the diffuse radio emission

Contact Info

Product

Resources

About