Low-frequency radio emission in the massive galaxy cluster MACSJ0717.5 + 3745

Context. Extended synchrotron radio sources are often observed in merging galaxy clusters. Studies of the extended emission help us to understand the mechanisms in which the radio emitting particles gain their relativistic energies. Aims. We examine the possible acceleration mechanisms of the relativistic particles that are responsible for the extended radio emission in the merging galaxy cluster Abell 520. Methods. We performed new 145 MHz observations with the LOw Frequency ARay (LOFAR) and combined these with archival Giant Metrewave Radio Telescope (GMRT) 323 MHz and Very Large Array (VLA) 1.5 GHz data to study the morphological and spectral properties of extended cluster emission. The observational properties are discussed in the framework of particle acceleration models associated with cluster merger turbulence and shocks. Results. In Abell 520, we confirm the presence of extended (760 × 950 kpc2) synchrotron radio emission that has been classified as a radio halo. The comparison between the radio and X-ray brightness suggests that the halo might originate in a cocoon rather than from the central X-ray bright regions of the cluster. The halo spectrum is roughly uniform on the scale of 66 kpc. There is a hint of spectral steepening from the SW edge towards the cluster centre. Assuming diffusive shock acceleration (DSA), the radio data are suggestive of a shock Mach number of ℳSW = 2.6−0.2+0.3 that is consistent with the X-ray derived estimates. This is in agreement with the scenario in which relativistic electrons in the SW radio edge gain their energies at the shock front via acceleration of either thermal or fossil electrons. We do not detect extended radio emission ahead of the SW shock that is predicted if the emission is the result of adiabatic compression. An X-ray surface brightness discontinuity is detected towards the NE region that may be a counter shock of Mach number ℳNEX = 1.52±0.05. This is lower than the value predicted from the radio emission which, assuming DSA, is consistent with ℳNE = 2.1 ± 0.2. Conclusions. Our observations indicate that the radio emission in the SW of Abell 520 is likely effected by the prominent X-ray detected shock in which radio emitting particles are (re-)accelerated through the Fermi-I mechanism. The NE X-ray discontinuity that is approximately collocated with an edge in the radio emission hints at the presence of a counter shock.

Download Full-text

Diffuse radio emission in the galaxy cluster SPT-CL J2031−4037: a steep-spectrum intermediate radio halo?

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa002 ◽

2020 ◽

Vol 493 (1) ◽

pp. L28-L32 ◽

Cited By ~ 1

Author(s):

Ramij Raja ◽

Majidul Rahaman ◽

Abhirup Datta ◽

Jack O Burns ◽

H T Intema ◽

...

Keyword(s):

Radio Emission ◽

Spectral Index ◽

Low Frequency ◽

Galaxy Cluster ◽

Transition System ◽

Cluster Galaxy ◽

Radio Halo ◽

Spectrum Radio ◽

Upper Limits ◽

The Galaxy

ABSTRACT The advent of sensitive low-frequency radio observations has revealed a number of diffuse radio objects with peculiar properties that are challenging our understanding of the physics of the intracluster medium. Here, we report the discovery of a steep-spectrum radio halo surrounding the central brightest cluster galaxy (BCG) in the galaxy cluster SPT-CL J2031−4037. This cluster is morphologically disturbed yet has a weak cool core, an example of a cool-core/non-cool-core transition system, which harbours a radio halo ∼0.7 Mpc in size. The halo emission detected at 1.7 GHz is less extended compared to that in the 325 MHz observation, and the spectral index of the part of the halo visible at the 325 MHz to 1.7 GHz frequencies was found to be −1.35 ± 0.07. Also, P1.4 GHz was found to be 0.77 × 1024 W Hz−1, which falls in the region where radio mini-haloes, halo upper limits and ultra-steep-spectrum (USS) haloes are found in the P1.4 GHz–LX plane. Additionally, simulations presented in the paper provide support for the scenario of the steep spectrum. The diffuse radio emission found in this cluster may be a steep-spectrum ‘intermediate’ or ‘hybrid’ radio halo that is transitioning into a mini-halo.

Download Full-text

Ultra-steep spectrum emission in the merging galaxy cluster Abell 1914

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833992 ◽

2019 ◽

Vol 622 ◽

pp. A22 ◽

Cited By ~ 6

Author(s):

S. Mandal ◽

H. T. Intema ◽

T. W. Shimwell ◽

R. J. van Weeren ◽

A. Botteon ◽

...

Keyword(s):

Low Frequency ◽

Galaxy Cluster ◽

Diffuse Emission ◽

Radio Observations ◽

Very Large Array ◽

Radio Halo ◽

The Galaxy ◽

Distinct Source ◽

Relativistic Particles ◽

Massive Galaxy

A number of radio observations have revealed the presence of large synchrotron-emitting sources associated with the intra-cluster medium. There is strong observational evidence that the emitting particles have been (re-)accelerated by shocks and turbulence generated during merger events. The particles that are accelerated are thought to have higher initial energies than those in the thermal pool but the origin of such mildly relativistic particles remains uncertain and needs to be further investigated. The galaxy cluster Abell 1914 is a massive galaxy cluster in which X-ray observations show clear evidence of merging activity. We carried out radio observations of this cluster with the LOw Frequency ARay (LOFAR) at 150 MHz and the Giant Metrewave Radio Telescope (GMRT) at 610 MHz. We also analysed Very Large Array (VLA) 1.4 GHz data, archival GMRT 325 MHz data, CFHT weak lensing data and Chandra observations. Our analysis shows that the ultra-steep spectrum source (4C38.39; α ≲ −2), previously thought to be part of a radio halo, is a distinct source with properties that are consistent with revived fossil plasma sources. Finally, we detect some diffuse emission to the west of the source 4C38.39 that could belong to a radio halo.

Download Full-text

Low-frequency radio study of MACS clusters at 610 and 235 MHz using the GMRT

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1965 ◽

2019 ◽

Vol 489 (1) ◽

pp. 446-458 ◽

Cited By ~ 4

Author(s):

Surajit Paul ◽

Sameer Salunkhe ◽

Abhirup Datta ◽

Huib T Intema

Keyword(s):

Radio Emission ◽

Radio Source ◽

High Speed ◽

High Redshift ◽

Low Frequency ◽

Dual Band ◽

Radio Jets ◽

Peripheral Location ◽

Massive Galaxy ◽

Massive Cluster

Abstract Studies have shown that mergers of massive galaxy clusters produce shocks and turbulence in the intracluster medium, these events possibly creating radio relics, as well as radio haloes. Here we present Giant Metrewave Radio Telescope (GMRT) dual-band (235- and 610-MHz) radio observations of four such clusters from the MAssive Cluster Survey (MACS) catalogue. We report the discovery of a very faint, diffuse, elongated radio source with a projected size of about 0.5 Mpc in cluster MACSJ0152.5−2852. We also confirm the presence of a radio-relic-like source (about 0.4 Mpc, previously reported at 325 MHz) in cluster MACSJ0025.4−1222. Proposed relics in both these clusters are found apparently inside the virial radius, instead of at their usual peripheral location, while no radio haloes are detected. These high-redshift clusters (z = 0.584 and 0.413) are among the earliest merging systems detected from cluster radio emission. In cluster MACSJ1931.8-2635, we found a radio mini-halo and an interesting highly bent pair of radio jets. Also, we present here a maiden study of low-frequency (GMRT 235- and 610-MHz) spectral and morphological signatures of the previously known radio cluster MACSJ0014.3−3022 (Abell 2744). This cluster hosts a relatively flat spectrum ($\alpha ^{610}_{235}\sim -1.15$), giant (∼1.6 Mpc each) halo–relic structure and a nearby high-speed ($1769\pm ^{148}_{359}$ km s−1) merger shock ($\mathcal {M}=2.02\pm ^{0.17}_{0.41}$) originating from a possible second merger in the cluster.

Download Full-text

Characterizing the radio emission from the binary galaxy cluster merger Abell 2146

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834025 ◽

2019 ◽

Vol 622 ◽

pp. A21 ◽

Cited By ~ 4

Author(s):

D. N. Hoang ◽

T. W. Shimwell ◽

R. J. van Weeren ◽

H. J. A. Röttgering ◽

A. Botteon ◽

...

Keyword(s):

Particle Acceleration ◽

Radio Emission ◽

Low Frequency ◽

Galaxy Cluster ◽

Relativistic Electrons ◽

Extended Source ◽

Very Large Array ◽

Radio Halo ◽

Extended Radio ◽

Relativistic Particles

Context. Collisions of galaxy clusters generate shocks and turbulence in the intra-cluster medium (ICM). The presence of relativistic particles and magnetic fields is inferred through the detection of extended synchrotron radio sources such as haloes and relics and implies that merger shocks and turbulence are capable of (re-)accelerating particles to relativistic energies. However, the precise relationship between merger shocks, turbulence, and extended radio emission is still unclear. Studies of the most simple binary cluster mergers are important to help understand the particle acceleration in the ICM. Aims. Our main aim is to study the properties of the extended radio emission and particle acceleration mechanism(s) associated with the generation of relativistic particles in the ICM. Methods. We measure the low-frequency radio emission from the merging galaxy cluster Abell 2146 with LOFAR at 144 MHz. We characterize the spectral properties of the radio emission by combining these data with data from archival Giant Metrewave Radio Telescope (GMRT) at 238 MHz and 612 MHz and Very Large Array (VLA) at 1.5 GHz. Results. We observe extended radio emission at 144 MHz behind the NW and SE shocks. Across the NW extended source, the spectral index steepens from −1.06 ± 0.06 to −1.29 ± 0.09 in the direction of the cluster centre. This spectral behaviour suggests that a relic is associated with the NW upstream shock. The precise nature of the SE extended emission is unclear. It may be a radio halo bounded by a shock or a superposition of a relic and halo. At 144 MHz, we detect a faint emission that was not seen with high-frequency observations, implying a steep (α < −1.3) spectrum nature of the bridge emission. Conclusions. Our results imply that the extended radio emission in Abell 2146 is probably associated with shocks and turbulence during cluster merger. The relativistic electrons in the NW and SE may originate from fossil plasma and thermal electrons, respectively.

Download Full-text

The GLEAM 4-Jy Sample: The brightest radio-sources in the southern sky

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320003476 ◽

2019 ◽

Vol 15 (S356) ◽

pp. 375-375

Author(s):

Sarah White

Keyword(s):

Radio Emission ◽

Active Galactic Nuclei ◽

Visual Inspection ◽

Low Frequency ◽

Galactic Nuclei ◽

Radio Sources ◽

Relativistic Jets ◽

The Galaxy ◽

Murchison Widefield Array ◽

Past Activity

AbstractLow-frequency radio emission allows powerful active galactic nuclei (AGN) to be selected in a way that is unaffected by dust obscuration and orientation of the jet axis. It also reveals past activity (e.g. radio lobes) that may not be evident at higher frequencies. Currently, there are too few “radio-loud” galaxies for robust studies in terms of redshift-evolution and/or environment. Hence our use of new observations from the Murchison Widefield Array (the SKA-Low precursor), over the southern sky, to construct the GLEAM 4-Jy Sample (1,860 sources at S151MHz > 4 Jy). This sample is dominated by AGN and is 10 times larger than the heavily relied-upon 3CRR sample (173 sources at S178MHz > 10 Jy) of the northern hemisphere. In order to understand how AGN influence their surroundings and the way galaxies evolve, we first need to correctly identify the galaxy hosting the radio emission. This has now been completed for the GLEAM 4-Jy Sample – through repeated visual inspection and extensive checks against the literature – forming a valuable, legacy dataset for investigating relativistic jets and their interplay with the environment.

Download Full-text

IDCS J1426.5+3508: THE MOST MASSIVE GALAXY CLUSTER ATz> 1.5

The Astrophysical Journal ◽

10.3847/0004-637x/817/2/122 ◽

2016 ◽

Vol 817 (2) ◽

pp. 122 ◽

Cited By ~ 20

Author(s):

Mark Brodwin ◽

Michael McDonald ◽

Anthony H. Gonzalez ◽

S. A. Stanford ◽

Peter R. Eisenhardt ◽

...

Keyword(s):

Galaxy Cluster ◽

Massive Galaxy

Download Full-text

Discovery of a Large-Scale Filament Connected to the Massive Galaxy Cluster MACS J0717.5+3745 at z = 0.55

The Astrophysical Journal ◽

10.1086/422750 ◽

2004 ◽

Vol 609 (2) ◽

pp. L49-L52 ◽

Cited By ~ 81

Author(s):

H. Ebeling ◽

E. Barrett ◽

D. Donovan

Keyword(s):

Large Scale ◽

Galaxy Cluster ◽

Massive Galaxy

Download Full-text

Low frequency radio counterparts of HESS J1731−347 a.k.a SNR G353.6−0.7

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317004689 ◽

2017 ◽

Vol 12 (S331) ◽

pp. 201-205

Author(s):

A. J. Nayana ◽

Poonam Chandra

Keyword(s):

Radio Emission ◽

Radio Telescope ◽

Supernova Remnants ◽

Low Frequency ◽

High Energy ◽

Spectral Indices ◽

Thermal Radio Emission ◽

Very High Energy ◽

Γ Rays ◽

Very High

AbstractHESS J1731−347 a.k.a. SNR G353.6−0.7 is one of the five known very high energy (VHE, Energy > 0.1 TeV) shell-type supernova remnants. We carried out Giant Metrewave Radio Telescope (GMRT) observations of this TeV SNR in 1390, 610 and 325 MHz bands. We detected the 325 and 610 MHz radio counterparts of the SNR G353.6−0.7 (Nayana et al. 2017). We also determined the spectral indices of individual filaments and our values are consistent with the non-thermal radio emission. We compared the radio morphology with that of VHE emission. The peak in radio emission corresponds to the faintest feature in the VHE emission. We explain this anti-correlated emission in a possible leptonic origin of the VHE γ-rays.

Download Full-text