A LOFAR view into the stormy environment of the galaxy cluster 2A0335+096

Galaxie

Turbulent magnetic fields in the merging galaxy cluster MACS J0717.5+3745

Large scale structure and cosmolog

Understanding the radio relic emission in the galaxy cluster MACS J0717.5+3745: spectral analysis

Large scale structure and cosmolog

Source finding in linear polarization for LOFAR, and SKA predecessor surveys, using Faraday moments

Contains fulltext : 180901.pdf (publisher's version ) (Open Access

A 'MeerKAT-meets-LOFAR' study of the complex multi-component (mini-)halo in the extreme sloshing cluster Abell 2142

International audienceClusters of galaxies are turbulent environments, whether merging systems with a turbulent intracluster medium (ICM) or relaxed systems sloshing within the potential well. In many such clusters, diffuse radio sources associated with the ICM are found: radio haloes and mini-haloes. Abell 2142 is a rich cluster undergoing extreme core sloshing, generating four cold fronts and a complex multi-component radio halo. Recent work revealed three halo components which span 2.4 Mpc. Particle acceleration on such scales is poorly understood, and requires high-quality multi-frequency data to understand. We use new deep MeerKAT L-band (1283 MHz) observations, combined with LOFAR HBA (143 MHz) data and X-ray data from XMM-Newton and Chandra to study the spectrum of the halo and the connection between the thermal and non-thermal components of the ICM. We detect the third halo component for the first time at 1283 MHz and confirm its ultra-steep spectrum nature, recovering $\alpha_{\rm H3, total} = -1.68 \pm 0.10$. All components follow power-law spectra which steepen toward the cluster outskirts. We profile the halo along three directions, finding evidence of asymmetry and spectral steepening perpendicular to the main axis of the cluster. Our thermal/non-thermal investigation shows sub-linear correlations that are steeper at 1283 MHz than 143 MHz, and we find different connections in different components of the halo. We find both a moderate anti-correlation (H1, the core) and positive correlation (H2, the ridge) between radio spectral index and X-ray temperature. Our results are broadly consistent with an interpretation of inhomogeneous turbulent (re-)acceleration. However, the anti-correlation between radio spectral index and X- ray temperature in the cluster core is challenging to explain; the presence of three cold fronts and a generally lower temperature may provide the foundations of an explanation

LOFAR discovery of radio emission in MACS J0717.5+3745

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Spectral analysis of spatially resolved 3C295 (sub-arcsecond resolution) with the International LOFAR Telescope

3C295 is a bright, compact steep spectrum source with a well-studied integrated radio spectral energy distribution (SED) from 132 MHz to 15 GHz. However, spatially resolved spectral studies have been limited due to a lack of high resolution images at low radio frequencies. These frequencies are crucial for measuring absorption processes, and anchoring the overall spectral modelling of the radio SED. In this paper, we use International LOw-Frequency ARray (LOFAR) Telescope (ILT) observations of 3C295 to study its spatially resolved spectral properties with sub-arcsecond resolution at 132 MHz. Combining our new 132 MHz observation with archival data at 1.6 GHz, 4.8 GHz, and 15 GHz, we are able to carry out a resolved radio spectral analysis. The spectral properties of the hotspots provides evidence for low frequency flattening. In contrast, the spectral shape across the lobes is consistent with a Jaffe-Perola spectral ageing model. Using the integrated spectral information for each component, we then fitted low-frequency absorption models to the hotspots, finding that both free-free absorption and synchrotron self-absorption models provide a better fit to the data than a standard power law. Although we can say there is low-frequency absorption present in the hotspots of 3C295, future observations with the Low Band Antenna of the ILT at 55 MHz may allow us to distinguish the type of absorption

A LOFAR view into the stormy environment of the galaxy cluster 2A0335+096

Context. Radio observations represent a powerful probe of the physics occurring in the intracluster medium (ICM) because they trace the relativistic cosmic rays in the cluster magnetic fields, or within galaxies themselves. By probing the low-energy cosmic rays, low-frequency radio observations are especially interesting because they unveil emission powered by low-efficiency particle acceleration processes, which are believed to play a crucial role in the origin of diffuse radio emission. Aims. We investigate the origin of the radio mini-halo at the centre of the galaxy cluster 2A0335+096 and its connection to the central galaxy and the sloshing cool core. We also study the properties of the head-tail galaxy GB6 B0335+096 hosted in the cluster to explore the life cycle of the relativistic electrons in its radio tails. Methods. We used new LOw Frequency ARray (LOFAR) observations from the LOFAR Two-meter Sky Survey at 144 MHz to map the low-frequency emission with a high level of detail. The new data were combined with archival Giant Metrewave Radio Telescope and Chandra observations to carry out a multi-wavelength study. Results. We have made the first measurement of the spectral index of the mini-halo (α = −1.2 ± 0.1 between 144 MHz and 1.4 GHz) and the lobes of the central source (α ≃ −1.5 ± 0.1 between 144 and 610 MHz). Based on the low-frequency radio emission morphology with respect to the thermal ICM, we propose that the origin of the diffuse radio emission is linked to the sloshing of the cool core. The new data reveal the presence of a megaparsec-long radio tail associated with GB6 B0335+096. The observed projected length is a factor 3 longer than the expected cooling length, with evidence of flattening in the spectral index trend along the tail. Therefore, we suggest that the electrons towards the end of the tail are kept alive by the ICM gentle re-acceleration

A MeerKAT-meets-LOFAR study of MS 1455.0 + 2232: a 590 kiloparsec 'mini'-halo in a sloshing cool-core cluster

Large scale structure and cosmolog