A Radio View of the Bullet Cluster from 100 MHz to 9 GHz

Index Value

<p>We investigate a sample of 10 massive galaxy clusters for diffuse synchrotron emission. The shortlisted clusters are drawn from a sample of clusters observed with the South Pole Telescope (SPT) shown to have high Sunyaev-Zeldovich (SZ) signals.They are analysed for diffuse emission from the results of the Australia Telescope Compact Array (ATCA) archival data reduction. The focus then is on the cluster with the most prominent diffuse emission - the Bullet cluster. We used the Murchison Widefield Array Commissioning Survey (MWACS) data in conjunction with the ATCA images to derive the spectral behaviour of the Bullet cluster from 0.118 GHz to 8.896 GHz. In particular, we study the spectral properties of the known radio halo and radio relic. We search for spectral bending of this diffuse emission as seen in other clusters like the Coma cluster, A2256, A521 and A3256. We detect the radio relic at all frequencies in the cluster periphery. Polarised flux is detected for the relic at all frequencies except at 1.344 GHz and as expected the percentage polarisation increases with frequency. Our spectral index values of -1.08 ± 0.02 and -1.74 ± 0.22 for 2 regions of the radio relic agreed with the literature. We detect spectral flattening for a region in the radio relic at 4.532 GHz. This is a common spectral characteristic for a radio galaxy. This suggests that the source could be a recently dead radio galaxy. We discuss a scenario in which a dead radio galaxy supplying seed electrons for reacceleration and a merger process providing the required energy for the diffuse radio relic. We detect the radio halo at all frequencies and we derive a spectral index of -2.11±0.03 using our ATCA flux measurements. Our individual flux measurements at 1.344 and 2.1 GHz agree with the literature. However, we get a steeper ATCA spectral index value for the radio halo as compared to the existing value in the literature. We observe spectral flattening of the radio halo in the Bullet cluster at low frequencies between 0.180 GHz and 1.3 GHz. This is similar to the spectral property of the halo in clusters like the Coma cluster, A521 and A3256.</p>

A Radio View of the Bullet Cluster from 100 MHz to 9 GHz

10.26686/wgtn.17143319.v1 ◽

2021 ◽

Author(s):

◽

Raghav Srinivasan

Keyword(s):

Spectral Index ◽

Radio Galaxy ◽

Coma Cluster ◽

Diffuse Emission ◽

Low Frequencies ◽

Radio Halo ◽

Merger Process ◽

Flux Measurements ◽

Index Value

First look at the giant radio galaxy 3C 236 with LOFAR

10.1051/0004-6361/201935586 ◽

2019 ◽

Vol 628 ◽

pp. A69 ◽

Cited By ~ 2

Author(s):

A. Shulevski ◽

P. D. Barthel ◽

R. Morganti ◽

J. J. Harwood ◽

M. Brienza ◽

...

Keyword(s):

Spectral Index ◽

Radio Galaxy ◽

Ambient Medium ◽

Low Frequency ◽

Low Frequencies ◽

North West ◽

Link Type ◽

The North ◽

Morphological Differences ◽

Inner Region

We have examined the giant radio galaxy 3C 236 using LOFAR at 143 MHz down to an angular resolution of 7″, in combination with observations at higher frequencies. We used the low frequency data to derive spectral index maps with the highest resolution yet at these low frequencies. We confirm a previous detection of an inner hotspot in the north-west lobe and for the first time observe that the south-east lobe hotspot is in fact a triple hotspot, which may point to an intermittent source activity. Also, the spectral index map of 3C 236 shows that the spectral steepening at the inner region of the northern lobe is prominent at low frequencies. The outer regions of both lobes show spectral flattening, in contrast with previous high frequency studies. We derive spectral age estimates for the lobes, as well as particle densities of the IGM at various locations. We propose that the morphological differences between the lobes are driven by variations in the ambient medium density as well as the source activity history.

The GLEAM 200-MHz local radio luminosity function for AGN and star-forming galaxies

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.36 ◽

2021 ◽

Vol 38 ◽

Author(s):

T. M. O. Franzen ◽

N. Seymour ◽

E. M. Sadler ◽

T. Mauch ◽

S. V. White ◽

...

Keyword(s):

Spectral Index ◽

Luminosity Function ◽

Radio Continuum ◽

Radio Luminosity ◽

Low Frequencies ◽

Star Forming ◽

Wide Range ◽

Radio Luminosity Function ◽

Local Radio

Abstract The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a radio continuum survey at 76–227 MHz of the entire southern sky (Declination $<\!{+}30^{\circ}$ ) with an angular resolution of ${\approx}2$ arcmin. In this paper, we combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to construct a sample of 1 590 local (median $z \approx 0.064$ ) radio sources with $S_{200\,\mathrm{MHz}} > 55$ mJy across an area of ${\approx}16\,700\,\mathrm{deg}^{2}$ . From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73% are fuelled by an active galactic nucleus (AGN) and 27% by star formation. We present the local radio luminosity function for AGN and star-forming (SF) galaxies at 200 MHz and characterise the typical radio spectra of these two populations between 76 MHz and ${\sim}1$ GHz. For the AGN, the median spectral index between 200 MHz and ${\sim}1$ GHz, $\alpha_{\mathrm{high}}$ , is $-0.600 \pm 0.010$ (where $S \propto \nu^{\alpha}$ ) and the median spectral index within the GLEAM band, $\alpha_{\mathrm{low}}$ , is $-0.704 \pm 0.011$ . For the SF galaxies, the median value of $\alpha_{\mathrm{high}}$ is $-0.650 \pm 0.010$ and the median value of $\alpha_{\mathrm{low}}$ is $-0.596 \pm 0.015$ . Among the AGN population, flat-spectrum sources are more common at lower radio luminosity, suggesting the existence of a significant population of weak radio AGN that remain core-dominated even at low frequencies. However, around 4% of local radio AGN have ultra-steep radio spectra at low frequencies ( $\alpha_{\mathrm{low}} < -1.2$ ). These ultra-steep-spectrum sources span a wide range in radio luminosity, and further work is needed to clarify their nature.

The discovery of radio halos in the frontier fields clusters Abell S1063 and Abell 370

10.1051/0004-6361/201936953 ◽

2020 ◽

Vol 636 ◽

pp. A3 ◽

Cited By ~ 3

Author(s):

C. Xie ◽

R. J. van Weeren ◽

L. Lovisari ◽

F. Andrade-Santos ◽

A. Botteon ◽

...

Keyword(s):

Spectral Index ◽

Relativistic Electrons ◽

Synchrotron Emission ◽

Scaling Relation ◽

Diffuse Emission ◽

Very Large Array ◽

X Ray ◽

Radio Halo ◽

Radio Power ◽

Radio Halos

Context. Massive merging galaxy clusters often host diffuse megaparsec-scale radio synchrotron emission. This emission originates from relativistic electrons in the ionized intracluster medium. An important question is how these synchrotron emitting relativistic electrons are accelerated. Aims. Our aim is to search for diffuse emission in the Frontier Fields clusters Abell S1063 and Abell 370 and characterize its properties. While these clusters are very massive and well studied at some other wavelengths, no diffuse emission has been reported for these clusters so far. Methods. We obtained 325 MHz Giant Metrewave Radio Telescope (GMRT) and 1–4 GHz Jansky Very Large Array (VLA) observations of Abell S1063 and Abell 370. We complement these data with Chandra and XMM-Newton X-ray observations. Results. In our sensitive images, we discover radio halos in both clusters. In Abell S1063, a giant radio halo is found with a size of ∼1.2 Mpc. The integrated spectral index between 325 MHz and 1.5 GHz is −0.94 ± 0.08 and it steepens to −1.77 ± 0.20 between 1.5 and 3.0 GHz. This spectral steepening provides support for the turbulent reacceleration model for radio halo formation. Abell 370 hosts a faint radio halo mostly centered on the southern part of this binary merging cluster, with a size of ∼500−700 kpc. The spectral index between 325 MHz and 1.5 GHz is −1.10 ± 0.09. Both radio halos follow the known scaling relation between the cluster mass proxy Y500 and radio power, which is consistent with the idea that they are related to ongoing cluster merger events.

Signatures from a merging galaxy cluster and its AGN population: LOFAR observations of Abell 1682

10.1051/0004-6361/201935584 ◽

2019 ◽

Vol 627 ◽

pp. A176 ◽

Cited By ~ 3

Author(s):

A. O. Clarke ◽

A. M. M. Scaife ◽

T. Shimwell ◽

R. J. van Weeren ◽

A. Bonafede ◽

...

Keyword(s):

Active Galactic Nuclei ◽

Galaxy Cluster ◽

Galactic Nuclei ◽

Radio Galaxies ◽

Relativistic Electrons ◽

Diffuse Emission ◽

Low Frequencies ◽

Cluster Emission ◽

Radio Halo ◽

Merger Event

We present LOFAR data from 110–180 MHz of the merging galaxy cluster Abell 1682, alongside archival optical, radio, and X-ray data. Our images of 6 arcsec in resolution at low frequencies reveal new structures associated with numerous radio galaxies in the cluster. At a resolution of 20 arcsec we see diffuse emission throughout the cluster over hundreds of kiloparsecs, indicating particle acceleration mechanisms are in play as a result of the cluster merger event and powerful active galactic nuclei. We show that a significant part of the cluster emission is from an old radio galaxy with very steep spectrum emission (having a spectral index of α < −2.5). Furthermore, we identify a new region of diffuse steep-spectrum emission (α < −1.1) as a candidate for a radio halo which is co-spatial with the centre of the cluster merger. We suggest its origin as a population of old and mildly relativistic electrons left over from radio galaxies throughout the cluster which have been re-accelerated to higher energies by shocks and turbulence induced by the cluster merger event. We also note the discovery of six new giant radio galaxies in the vicinity of Abell 1682.

New giant radio sources and underluminous radio halos in two galaxy clusters

10.1051/0004-6361/201731174 ◽

2018 ◽

Vol 609 ◽

pp. A61 ◽

Cited By ~ 11

Author(s):

V. Cuciti ◽

G. Brunetti ◽

R. van Weeren ◽

A. Bonafede ◽

D. Dallacasa ◽

...

Keyword(s):

Radio Galaxy ◽

Recent Literature ◽

Radio Sources ◽

Diffuse Emission ◽

Very Large Array ◽

Radio Halo ◽

Mechanisms Of Formation ◽

Formation And Evolution ◽

Radio Power ◽

Radio Halos

Aims. The aim of this work is to analyse the radio properties of the massive and dynamically disturbed clusters Abell 1451 and Zwcl 0634.1+4750, especially focusing on the possible presence of diffuse emission. Methods. We present new Giant Metrewave Radio Telescope (GMRT) 320 MHz and Jansky Very Large Array (JVLA) 1.5 GHz observations of these two clusters. Results. We found that both Abell 1451 and Zwcl 0634.1+4750 host a radio halo with a typical spectrum (α ~ 1−1.3). Similarly to a few other cases reported in the recent literature, these radio halos are significantly fainter in radio luminosity with respect to the current radio power-mass correlations and they are smaller than classical giant radio halos. These underluminous sources might contribute to elucidating the complex mechanisms of formation and evolution of radio halos. Furthermore, we detected a candidate radio relic at large distance from the cluster centre in Abell 1451 and a peculiar head-tail (HT) radio galaxy in Zwcl 0634.1+4750, which might be interacting with a shock front.

Radio and X-ray Observations of the Restarted Radio Galaxy in the Galaxy Cluster CL 0838+1948

Galaxies ◽

10.3390/galaxies9040108 ◽

2021 ◽

Vol 9 (4) ◽

pp. 108

Author(s):

Simona Giacintucci ◽

Tracy Clarke ◽

Namir E. Kassim ◽

Wendy Peters ◽

Emil Polisensky

Keyword(s):

Radio Source ◽

Survey Data ◽

Radio Galaxy ◽

Galaxy Cluster ◽

Gas Emission ◽

Low Frequencies ◽

Nuclear Activity ◽

X Ray ◽

Hot Gas ◽

The Galaxy

We present VLA Low-band Ionosphere and Transient Experiment (VLITE) 338 MHz observations of the galaxy cluster CL 0838+1948. We combine the VLITE data with Giant Metrewave Radio Telescope 610 MHz observations and survey data. The central galaxy hosts a 250 kpc source whose emission is dominated by two large lobes at low frequencies. At higher frequencies, a pair of smaller lobes (∼30 kpc) is detected within the galaxy optical envelope. The observed morphology is consistent with a restarted radio galaxy. The outer lobes have a spectral index αout=1.6, indicating that they are old, whereas the inner lobes have αinn=0.6, typical for an active source. Spectral modeling confirms that the outer emission is a dying source whose nuclear activity switched off not more than 110 Myr ago. Using archival Chandra X-ray data, we compare the radio and hot gas emission. We find that the active radio source is contained within the innermost and X-ray brightest region, possibly a galactic corona. Alternatively, it could be the remnant of a larger cool core whose outer layers have been heated by the former epoch of activity that has generated the outer lobes.

The nature and likely redshift of GLEAM J0917–0012

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.35 ◽

2021 ◽

Vol 38 ◽

Author(s):

Guillaume Drouart ◽

Nick Seymour ◽

Jess W. Broderick ◽

José Afonso ◽

Rajan Chhetri ◽

...

Keyword(s):

Radio Galaxy ◽

Emission Lines ◽

Optical Data ◽

Space Observatory ◽

Very Large Array ◽

Original Interpretation ◽

Independent Confirmation ◽

Infrared Survey

Abstract We previously reported a putative detection of a radio galaxy at $z=10.15$ , selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The redshift of this source, GLEAM J0917–0012, was based on three weakly detected molecular emission lines observed with the Atacama Large Millimetre Array (ALMA). In order to confirm this result, we conducted deep spectroscopic follow-up observations with ALMA and the Karl Jansky Very Large Array (VLA). The ALMA observations targeted the same CO lines previously reported in Band 3 (84–115 GHz) and the VLA targeted the CO(4-3) and [CI(1-0)] lines for an independent confirmation in Q-band (41 and 44 GHz). Neither observation detected any emission lines, removing support for our original interpretation. Adding publicly available optical data from the Hyper Suprime-Cam survey, Widefield Infrared Survey Explorer (WISE), and Herschel Space Observatory in the infrared, as well as $<$ 10 GHz polarisation and 162 MHz inter-planetary scintillation observations, we model the physical and observational characteristics of GLEAM J0917–0012 as a function of redshift. Comparing these predictions and observational relations to the data, we are able to constrain its nature and distance. We argue that if GLEAM J0917–0012 is at $z<3,$ then it has an extremely unusual nature, and that the more likely solution is that the source lies above $z=7$ .

Thermal radio absorption as a tracer of the interaction of SNRs with their environments

10.1051/0004-6361/202141635 ◽

2021 ◽

Vol 653 ◽

pp. A62

Author(s):

G. Castelletti ◽

L. Supan ◽

W. M. Peters ◽

N. E. Kassim

Keyword(s):

Spectral Index ◽

Supernova Remnants ◽

Surrounding Medium ◽

Low Frequency ◽

Power Laws ◽

Line Of Sight ◽

Pulsar Wind Nebulae ◽

Very Large Array ◽

Thermal Absorption

We present new images and continuum spectral analysis for 14 resolved Galactic supernova remnants (SNRs) selected from the 74 MHz Very Large Array Low-Frequency Sky Survey Redux (VLSSr). We combine new integrated measurements from the VLSSr with, when available, flux densities extracted from the Galactic and Extragalactic All-Sky Murchison Widefield Array Survey and measurements from the literature to generate improved integrated continuum spectra sampled from ~15 MHz to ~217 GHz. We present the VLSSr images. When possible we combine them with publicly available images at 1.4 GHz, to analyse the resolved morphology and spectral index distribution across each SNR. We interpret the results and look for evidence of thermal absorption caused by ionised gas either proximate to the SNR itself, or along its line of sight. Three of the SNRs, G4.5+6.8 (Kepler), G28.6−0.1, and G120.1+1.4 (Tycho), have integrated spectra which can be adequately fit with simple power laws. The resolved spectral index map for Tycho confirms internal absorption which was previously detected by the Low Frequency Array, but it is insufficient to affect the fit to the integrated spectrum. Two of the SNRs are pulsar wind nebulae, G21.5−0.9 and G130.7+3.1 (3C 58). For those we identify high-frequency spectral breaks at 38 and 12 GHz, respectively. For the integrated spectra of the remaining nine SNRs, a low frequency spectral turnover is necessary to adequately fit the data. In all cases we are able to explain the turnover by extrinsic thermal absorption. For G18.8+0.3 (Kes 67), G21.8−0.6 (Kes 69), G29.7−0.3 (Kes 75), and G41.1−0.3 (3C 397), we attribute the absorption to ionised gas along the line of sight, possibly from extended H II region envelopes. For G23.3−0.3 (W41) the absorption can be attributed to H II regions located in its immediate proximity. Thermal absorption from interactions at the ionised interface between SNR forward shocks and the surrounding medium were previously identified as responsible for the low frequency turnover in SNR G31.9+0.0 (3C 391); our integrated spectrum is consistent with the previous results. We present evidence for the same phenomenon in three additional SNRs G27.4+0.0 (Kes 73), G39.2–0.3 (3C 396), and G43.3–0.2 (W49B), and derive constraints on the physical properties of the interaction. This result indicates that interactions between SNRs and their environs should be readily detectable through thermal absorption by future low frequency observations of SNRs with improved sensitivity and resolution.

Investigation of the WR 11 field at decimeter wavelengths

10.1051/0004-6361/201834971 ◽

2019 ◽

Vol 625 ◽

pp. A99 ◽

Cited By ~ 1

Author(s):

P. Benaglia ◽

S. del Palacio ◽

C. H. Ishwara-Chandra ◽

M. De Becker ◽

N. L. Isequilla ◽

...

Keyword(s):

Spectral Index ◽

Thermal Emission ◽

Mass Loss Rate ◽

High Energy ◽

Low Frequencies ◽

Nonthermal Radio ◽

Short Period ◽

Radiation Processes ◽

Period System ◽

The Individual

The massive binary system WR 11 (γ2-Velorum) has recently been proposed as the counterpart of a Fermi source. If this association is correct, this system would be the second colliding wind binary detected in GeV γ-rays. However, the reported flux measurements from 1.4 to 8.64 GHz fail to establish the presence of nonthermal (synchrotron) emission from this source. Moreover, WR 11 is not the only radio source within the Fermi detection box. Other possible counterparts have been identified in archival data, some of which present strong nonthermal radio emission. We conducted arcsec-resolution observations toward WR 11 at very low frequencies (150–1400 MHz) where the nonthermal emission – if existent and not absorbed – is expected to dominate. We present a catalog of more than 400 radio emitters, among which a significant portion are detected at more than one frequency, including limited spectral index information. Twenty-one of these radio emitters are located within the Fermi significant emission. A search for counterparts for this last group pointed at MOST 0808–471; this source is 2′ away from WR 11 and is a promising candidate for high-energy emission, having a resolved structure along 325–1390 MHz. For this source, we reprocessed archive interferometric data up to 22.3 GHz and obtained a nonthermal radio spectral index of − 0.97 ± 0.09. However, multiwavelength observations of this source are required to establish its nature and to assess whether it can produce (part of) the observed γ-rays. WR 11 spectrum follows a spectral index of 0.74 ± 0.03 from 150 to 230 GHz, consistent with thermal emission. We interpret that any putative synchrotron radiation from the colliding-wind region of this relatively short-period system is absorbed in the photospheres of the individual components. Notwithstanding, the new radio data allowed us to derive a mass-loss rate of 2.5 × 10−5 M⊙ yr−1, which, according to the latest models for γ-ray emission in WR 11, would suffice to provide the required kinetic power to feed nonthermal radiation processes.