Observations of Extended Radio Emission in Clusters

Ferrari, Chiara; Govoni, F.; Schindler, S.; Bykov, A. M.; Rephaeli, Yoel

doi:10.1007/978-0-387-78875-3_6

Cited by 44 publications

(57 citation statements)

References 149 publications

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“…From the 1.4 GHz observations, Govoni et al (2001) determined the halo to be one of the most powerful known ( »Ṕ 2.6 10 1.4 GHz 25 W Hz −1 ). In the investigation by O07, the radio halo was found to have a patchy spectral index distribution in accordance with primary models (e.g., Ferrari et al 2008). A spatial correlation was also suggested between the halo regions with flattest spectral indices and those with the highest X-ray temperature.…”

Section: Previous Radio Studies Of Abell 2744mentioning

confidence: 55%

VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics

Pearce

Weeren

Andrade-Santos

et al. 2017

ApJ

117

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Cluster mergers leave distinct signatures in the intracluster medium (ICM) in the form of shocks and diffuse cluster radio sources that provide evidence for the acceleration of relativistic particles. However, the physics of particle acceleration in the ICM is still not fully understood. Here we present new 1-4 GHz Jansky Very Large Array (VLA) and archival Chandra observations of the HST Frontier Fields Cluster Abell2744. In our new VLA images, we detect the previously known ∼2.1Mpc radio halo and ∼1.5Mpc radio relic. We carry out a radio spectral analysis from which we determine the relic's injection spectral index to be a = - 1.12 0. 0.31 under the assumption of diffusive shock acceleration. We also find evidence for spectral steepening in the post-shock region. We do not find evidence for a significant correlation between the radio halo's spectral index and ICM temperature. In addition, we observe three new polarized diffuse sources and determine two of these to be newly discovered giant radio relics. These two relics are located in the southeastern and northwestern outskirts of the cluster. The corresponding integrated spectral indices measure −1.81±0.26 and −0.63±0.21 for the SE and NW relics, respectively. From an X-ray surface brightness profile we also detect a possible density jump of = -+ R 1.39 0.22 0.34 co-located with the newly discovered SE relic. This density jump would correspond to a shock front Mach number of  = -+ 1.26 0.15 0.25 .

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Section: Previous Radio Studies Of Abell 2744mentioning

confidence: 55%

VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics

Pearce

Weeren

Andrade-Santos

et al. 2017

ApJ

117

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“…Shocks in large scale structures have been investigated in a number of semi-analytical (Gabici & Blasi 2003;Berrington & Dermer 2003;Keshet et al 2003) and numerical works (Miniati et al 2001;Ryu et al 2003;Pfrommer et al 2007;Skillman et al 2008;Vazza et al2008;Molnar et al 2009). Observationally, merger shocks have been detected only in a few in a few nearby X-ray bright galaxy clusters Markevitch 2006;Solovyeva et al 2008), and may be possibly associated with single or double radio relics discovered in a number of galaxy clusters (e.g.…”

Section: Shock Propertiesmentioning

confidence: 99%

“…Ferrari et al 2008;Brunetti et al 2008;Cassano 2009, and references therein). Remarkably, the interplay between cosmic rays (CR) and turbulent magnetic fields may drive still poorly explored plasma processes that may potentially affect our simplified view of the IGM (Subramanian et al 2006;Schekochihin et al 2009;Brunetti & Lazarian 2007;Guo & Oh 2008).…”

Section: Introductionmentioning

confidence: 99%

Turbulent motions and shocks waves in galaxy clusters simulated with adaptive mesh refinement

Vazza

Brunetti

Kritsuk

et al. 2009

A&A

210

233

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We have implemented an adaptive mesh refinement criterion explicitly designed to increase spatial resolution around discontinuities in the velocity field in ENZO cosmological simulations. With this technique, shocks and turbulent eddies developed during the hierarchical assembly of galaxy clusters are followed with unprecedented spatial resolution, even at large distances from the clusters center. By measuring the spectral properties of the gas velocity field, its time evolution and the properties of shocks for a reference galaxy cluster, we investigate the connection between accretion processes and the onset of chaotic motions in the simulated intergalactic medium over a wide range of scales.

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“…Much less is known though about the physical properties and the origin of a non-thermal intra-cluster component (relativistic electrons with energies of 10 GeV spiralling in magnetic fields of few μGauss) that was discovered and studied mostly through deep radio observations (see e.g. Ferrari et al 2008, and references therein). However, it is now clear that the impact of the non-thermal component in the physics and thermo-dynamical evolution of galaxy clusters cannot be neglected anymore (e.g.…”

Section: Introductionmentioning

confidence: 99%

GMRT observations of the Ophiuchus galaxy cluster

Murgia¹,

Eckert

Govoni³

et al. 2010

A&A

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Aims. Observations with the Very Large Array telescope at 1477 MHz revealed the presence of a radio mini-halo surrounding the faint central point-like radio source in the Ophiuchus cluster of galaxies. In this work we present a study of the radio emission from this cluster of galaxies at lower radio frequencies. Methods. We observed the Ophiuchus cluster at 153, 240, and 614 MHz with the Giant Metrewave Radio Telescope. Results. The mini-halo is clearly detected at 153 and 240 MHz, the frequencies at which we reached the best sensitivity to the lowsurface brightness diffuse emission, while it is not detected at 610 MHz because of the too low signal-to-noise ratio at this frequency. The most prominent feature at low frequencies is a patch of diffuse steep spectrum emission located at about 5 south-east from the cluster centre. By combining these images with that at 1477 MHz, we derived the spectral index of the mini-halo. Globally, the minihalo has a low-frequency spectral index of α 153 240 1.4 ± 0.3 and an high-frequency spectral index of α 240 1477 1.60 ± 0.05. Moreover, we measure a systematic increase of the high-frequency spectral index with radius: the azimuthal radial average of α 240 1477 increases from about 1.3, at the cluster centre, up to about 2.0 in the mini-halo outskirts. Conclusions. The observed radio spectral index agrees with that obtained by modelling the non-thermal hard X-ray emission in this cluster of galaxies. We assume that the X-ray component arises from inverse-Compton scattering between the photons of the cosmic microwave background and a population of non-thermal electrons, which are isotropically distributed and whose energy spectrum is a power law with an index p. We derive that the electrons energy spectrum should extend from a minimum Lorentz factor of γ min 700 up to a maximum Lorentz factor of γ max 3.8 × 10 4 with an index p = 3.8 ± 0.4. The volume-averaged strength for a completely disordered intra-cluster magnetic field is B V 0.3 ± 0.1 μG.

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Observations of Extended Radio Emission in Clusters

Cited by 44 publications

References 149 publications

VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics

VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics

Turbulent motions and shocks waves in galaxy clusters simulated with adaptive mesh refinement

GMRT observations of the Ophiuchus galaxy cluster

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