Radio multifrequency observations of galaxy clusters. The Abell 399$-$401 pair

Abstract

Galaxy clusters are assembled via merging of smaller structures, in a process that generates shocks and turbulence in the intra cluster medium and produces radio diffuse emission in the form of halos and relics. The cluster pair A399-A401 represents a special case: both clusters host a radio halo. Recent Low Frequency Array (LOFAR) observations at 140 MHz revealed the presence of a radio bridge connecting the two clusters along with two relic candidates. These relics include one South of A399 and the other in between the two clusters, in proximity of a shock front detected in X-ray observations. In this paper we present observations of the A399-A401 cluster pair at 1.7, 1.4, 1.2 GHz and 346 MHz from the Westerbork Synthesis Radio Telescope (WSRT). We detect the radio halo in the A399 cluster at 346 MHz, extending up to $\sim 650$ kpc and with a $125\pm 6$ mJy flux density. Its spectral index between 140 MHz and 346 MHz is $\alpha =1.75\pm 0.14$. The two candidate relics are also seen at 346 MHz and we determine their spectral indices to be $\alpha =1.10\pm 0.14$ and $\alpha =1.46\pm 0.14$. The low surface brightness bridge connecting the two clusters is below the noise level at 346 MHz, therefore we constrain the bridge average spectral index to be steep, i.e. $\alpha >1.5$ at 95% confidence level. This result favours the scenario where dynamically-induced turbulence is a viable mechanism to reaccelerate a population of mildly relativistic particles and amplify magnetic fields on scales of a few Mpcs. Key words: galaxies: clusters: general - galaxies: clusters: individual: Abell 399 - radio continuum: general

arXiv comment10 pages, 12 figures

References in corpus (34)

• A Cosmology Calculator for the World Wide Web
• Cosmic rays in galaxy clusters and their non-thermal emission
• The Temperature Structure of 30 Nearby Clusters Observed with ASCA. Similarity of Temperature Profiles
• Diffuse Radio Emission from Galaxy Clusters
• Post-correlation radio frequency interference classification methods
• A broadband flux scale for low frequency radio telescopes
• Cluster mergers and non-thermal phenomena: expectations from a statistical magneto-turbulent model
• Revisiting scaling relations for giant radio halos in galaxy clusters
• Radio signature of cosmological structure formation shocks
• GMRT Radio Halo Survey in galaxy clusters at z = 0.2 -- 0.4 I.The REFLEX sub--sample
• Foregrounds for observations of the cosmological 21 cm line: I. First Westerbork measurements of Galactic emission at 150 MHz in a low latitude field
• A radio ridge connecting two galaxy clusters in a filament of the cosmic web
• Evidence for particle re-acceleration in the radio relic in the galaxy cluster PLCKG287.0 +32.9
• Stochastic reacceleration of relativistic electrons by turbulent reconnection: a mechanism for cluster-scale radio emission ?
• Foregrounds for observations of the cosmological 21 cm line: II. Westerbork observations of the fields around 3C196 and the North Celestial Pole
• Turbulence and Particle Acceleration in Giant Radio Haloes: the Origin of Seed Electrons
• The Extended GMRT Radio Halo Survey II: Further results and analysis of the full sample
• Second order Fermi reacceleration mechanisms and large scale synchrotron radio emission in intra-cluster bridges
• Gas and galaxies in filament between clusters of galaxies: The study of A399-A401
• LOFAR discovery of an ultra-steep radio halo and giant head-tail radio galaxy in Abell 1132
• Testing cosmic-ray acceleration with radio relics: a high-resolution study using MHD and tracers
• LOFAR discovery of a double radio halo system in Abell 1758 and radio/X-ray study of the cluster pair
• Radio halos in a mass-selected sample of 75 galaxy clusters. II. Statistical analysis
• XMM-Newton observations of the binary cluster system Abell 399/401
• A double radio halo in the close pair of galaxy clusters Abell 399 and Abell 401
• Re-acceleration Model for Radio Relics with Spectral Curvature
• Properties of the cosmological filament between two clusters: A possible detection of a large-scale accretion shock by $Suzaku$
• Deep Westerbork observations of Abell 2256 at 350 MHz
• The X-ray Structure of A399 and A401: A Pre-Merging Cluster Pair
• Radio spectral study of the cluster of galaxies Abell 2255
• 153 MHz GMRT follow-up of steep-spectrum diffuse emission in galaxy clusters
• A giant radio bridge connecting two clusters in Abell 1758
• KAT-7 observations of a mass-selected sample of galaxy clusters
• Low-frequency integrated radio spectra of diffuse, steep-spectrum sources in galaxy clusters: palaeontology with the MWA and ASKAP

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