scholarly journals A study of halo and relic radio emission in merging clusters using the Murchison Widefield Array

2017 ◽  
pp. stx155 ◽  
Author(s):  
L. T. George ◽  
K. S. Dwarakanath ◽  
M. Johnston-Hollitt ◽  
H. T. Intema ◽  
N. Hurley-Walker ◽  
...  
Keyword(s):  
Radio Emission ◽  
Murchison Widefield Array

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

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.

scholarly journals Murchison Widefield Array detection of steep-spectrum, diffuse, non-thermal radio emission within Abell 1127

2020 ◽  
Vol 37 ◽  
Author(s):  
S. W. Duchesne ◽  
M. Johnston-Hollitt ◽  
Z. Zhu ◽  
R. B. Wayth ◽  
J. L. B. Line
Keyword(s):  
Radio Emission ◽  
Galaxy Clusters ◽  
Phase Ii ◽  
Thermal Emission ◽  
Low Frequency ◽  
Radio Spectrum ◽  
Discrete Source ◽  
Thermal Radio ◽  
Thermal Radio Emission ◽  
Murchison Widefield Array

Abstract Diffuse, non-thermal emission in galaxy clusters is increasingly being detected in low-frequency radio surveys and images. We present a new diffuse, steep-spectrum, non-thermal radio source within the cluster Abell 1127 found in survey data from the Murchison Widefield Array (MWA). We perform follow-up observations with the ‘extended’ configuration MWA Phase II with improved resolution to better resolve the source and measure its low-frequency spectral properties. We use archival Very Large Array S-band data to remove the discrete source contribution from the MWA data, and from a power law model fit we find a spectral index of –1.83±0.29 broadly consistent with relic-type sources. The source is revealed by the Giant Metrewave Radio Telescope at 150 MHz to have an elongated morphology, with a projected linear size of 850 kpc as measured in the MWA data. Using Chandra observations, we derive morphological estimators and confirm quantitatively that the cluster is in a disturbed dynamical state, consistent with the majority of phoenices and relics being hosted by merging clusters. We discuss the implications of relying on morphology and low-resolution imaging alone for the classification of such sources and highlight the usefulness of the MHz to GHz radio spectrum in classifying these types of emission. Finally, we discuss the benefits and limitations of using the MWA Phase II in conjunction with other instruments for detailed studies of diffuse, steep-spectrum, non-thermal radio emission within galaxy clusters.

High fidelity spectroscopic imaging at low radio frequencies to estimate plasma parameters of solar coronal mass ejections at higher coronal heights

2021 ◽  
Author(s):  
Devojyoti Kansabanik ◽  
Surajit Mondal ◽  
Divya Oberoi ◽  
Angelos Vourlidas
Keyword(s):  
Radio Emission ◽  
Coronal Mass Ejections ◽  
Large Scale ◽  
Dynamic Range ◽  
High Dynamic Range ◽  
Physical Parameters ◽  
Plasma Parameters ◽  
Radio Imaging ◽  
Gyrosynchrotron Emission ◽  
Murchison Widefield Array

<p>Coronal Mass Ejections (CMEs) are large-scale explosive eruptions of magnetised plasma from the Sun into the Heliosphere. Measuring the physical parameters of CMEs is crucial for understanding their physics and for assessing their geo-effectiveness. Radio observations offer the most direct means for estimating these plasma parameters when gyrosynchrotron (GS) emission is detected from the CME plasma. However, since the first detection by Bastian et al.2001, only a handful of studies have successfully detected GS emission from CME plasma. This is usually attributed to the challenges involved in obtaining the high dynamic range imaging required for observing this faint gyrosynchrotron emission in the vicinity of active solar emissions.</p><p>The newly developed imaging pipeline (Mondal et al., 2019) designed for the data from Murchison Widefield Array (MWA) marks a significant improvement in metrewave solar radio imaging. Our work suggests that we should now be able to routinely detect GS emission from CME plasma. We present an example where we have successfully detected radio emission from CME plasma and modelled it as GS emission, leading to reliable estimates of CME magnetic field as well as the distribution of energetic electrons (Mondal et al. 2020). In a different example we are able to detect the radio emission from the CME plasma out to as far as 8.3 solar radii. We find that the observed spectra are not always consistent with simple GS models. This highlights that more complicated physics might be at play and points to the need for building more detailed models for interpreting these emissions. We hope that with the availability of polarimetric imaging capability, which we are in the process of developing, this technique will provide a robust way to routinely measure CME magnetic fields along with its other physical parameters. We note that these are the weakest detections of GS emissions from CME plasma reported yet.</p>

scholarly journals MURCHISON WIDEFIELD ARRAY LIMITS ON RADIO EMISSION FROM ANTARES NEUTRINO EVENTS

2016 ◽  
Vol 820 (2) ◽  
pp. L24 ◽  
Author(s):  
S. Croft ◽  
D. L. Kaplan ◽  
S. J. Tingay ◽  
T. Murphy ◽  
M. E. Bell ◽  
...  
Keyword(s):  
Radio Emission ◽  
Murchison Widefield Array

scholarly journals The radio/gamma-ray connection from 120 MHz to 230 GHz

2016 ◽  
Author(s):  
Marcello Giroletti ◽  
Filippo D'Ammando ◽  
Monica Orienti ◽  
Rocco Lico
Keyword(s):  
Radio Emission ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Low Frequency ◽  
High Energy ◽  
Physical Parameters ◽  
Radiation Emission ◽  
Spatial Features ◽  
Murchison Widefield Array ◽  
Radio Band

Radio loud active galactic nuclei are composed of different spatial features, each one characterized by different spectral properties in the radio band. Among them, blazars are the most common class of sources detected at gamma-rays by \fermi, and their radio emission is dominated by the flat spectrum compact core. In this contribution, we explore the connection between emission at high energy revealed by \fermi\ and at radio frequency. Taking as a reference the strong and very highly significant correlation found between gamma rays and cm-$\lambda$ radio emission, we explore different behaviours found as we change the energy range in gamma rays and in radio, therefore changing the physical parameters of the zones involved in the radiation emission. We find that the correlation weakens when we consider (1) gamma rays of energy above 10 GeV (except for high synchrotron peaked blazars) or (2) low frequency radio data taken by the Murchison Widefield Array; on the other hand, the correlation strengthens when we consider mm-$\lambda$ data taken by ALMA.

scholarly journals The High Time and Frequency Resolution Capabilities of the Murchison Widefield Array

2015 ◽  
Vol 32 ◽  
Author(s):  
S. E. Tremblay ◽  
S. M. Ord ◽  
N. D. R. Bhat ◽  
S. J. Tingay ◽  
B. Crosse ◽  
...  
Keyword(s):  
Radio Emission ◽  
Time Resolution ◽  
High Time ◽  
Frequency Resolution ◽  
High Time Resolution ◽  
Radio Bursts ◽  
Radio Telescopes ◽  
Initial Design ◽  
Imaging Telescope ◽  
Murchison Widefield Array

AbstractThe science cases for incorporating high time resolution capabilities into modern radio telescopes are as numerous as they are compelling. Science targets range from exotic sources such as pulsars, to our Sun, to recently detected possible extragalactic bursts of radio emission, the so-called fast radio bursts (FRBs). Originally conceived purely as an imaging telescope, the initial design of the Murchison Widefield Array (MWA) did not include the ability to access high time and frequency resolution voltage data. However, the flexibility of the MWA’s software correlator allowed an off-the-shelf solution for adding this capability. This paper describes the system that records the 100 μs and 10 kHz resolution voltage data from the MWA. Example science applications, where this capability is critical, are presented, as well as accompanying commissioning results from this mode to demonstrate verification.

scholarly journals A DEEP SEARCH FOR PROMPT RADIO EMISSION FROM THE SHORT GRB 150424A WITH THE MURCHISON WIDEFIELD ARRAY

2015 ◽  
Vol 814 (2) ◽  
pp. L25 ◽  
Author(s):  
D. L. Kaplan ◽  
A. Rowlinson ◽  
K. W. Bannister ◽  
M. E. Bell ◽  
S. D. Croft ◽  
...  
Keyword(s):  
Radio Emission ◽  
Murchison Widefield Array

scholarly journals Murchison Widefield Array rapid-response observations of the short GRB 180805A

2021 ◽  
Vol 38 ◽  
Author(s):  
G. E. Anderson ◽  
P. J. Hancock ◽  
A. Rowlinson ◽  
M. Sokolowski ◽  
A. Williams ◽  
...  
Keyword(s):  
Radio Emission ◽  
Gamma Ray ◽  
Response Times ◽  
Low Frequency ◽  
Rapid Response ◽  
Gamma Ray Burst ◽  
Upper Limit ◽  
Emission Models ◽  
Murchison Widefield Array ◽  
Prompt Emission

Abstract Here we present stringent low-frequency (185 MHz) limits on coherent radio emission associated with a short-duration gamma-ray burst (SGRB). Our observations of the short gamma-ray burst (GRB) 180805A were taken with the upgraded Murchison Widefield Array (MWA) rapid-response system, which triggered within 20s of receiving the transient alert from the Swift Burst Alert Telescope, corresponding to 83.7 s post-burst. The SGRB was observed for a total of 30 min, resulting in a $3\sigma$ persistent flux density upper limit of 40.2 mJy beam–1. Transient searches were conducted at the Swift position of this GRB on 0.5 s, 5 s, 30 s and 2 min timescales, resulting in $3\sigma$ limits of 570–1 830, 270–630, 200–420, and 100–200 mJy beam–1, respectively. We also performed a dedispersion search for prompt signals at the position of the SGRB with a temporal and spectral resolution of 0.5 s and 1.28 MHz, respectively, resulting in a $6\sigma$ fluence upper-limit range from 570 Jy ms at DM $=3\,000$ pc cm–3 ( $z\sim 2.5$ ) to 1 750 Jy ms at DM $=200$ pc cm–3 ( $z\sim 0.1)$ , corresponding to the known redshift range of SGRBs. We compare the fluence prompt emission limit and the persistent upper limit to SGRB coherent emission models assuming the merger resulted in a stable magnetar remnant. Our observations were not sensitive enough to detect prompt emission associated with the alignment of magnetic fields of a binary neutron star just prior to the merger, from the interaction between the relativistic jet and the interstellar medium (ISM) or persistent pulsar-like emission from the spin-down of the magnetar. However, in the case of a more powerful SGRB (a gamma-ray fluence an order of magnitude higher than GRB 180805A and/or a brighter X-ray counterpart), our MWA observations may be sensitive enough to detect coherent radio emission from the jet-ISM interaction and/or the magnetar remnant. Finally, we demonstrate that of all current low- frequency radio telescopes, only the MWA has the sensitivity and response times capable of probing prompt emission models associated with the initial SGRB merger event.

scholarly journals Constraining coherent low-frequency radio flares from compact binary mergers

2019 ◽  
Vol 489 (3) ◽  
pp. 3316-3333 ◽  
Author(s):  
A Rowlinson ◽  
G E Anderson
Keyword(s):  
Neutron Star ◽  
Radio Emission ◽  
Gamma Ray ◽  
Low Frequency ◽  
Binary Neutron Star ◽  
Compact Binary ◽  
Binary Mergers ◽  
Wave Emission ◽  
Murchison Widefield Array ◽  
Response Modes

ABSTRACT The presence and detectability of coherent radio emission from compact binary mergers (containing at least one neutron star) remains poorly constrained due to large uncertainties in the models. These compact binary mergers may initially be detected as short gamma-ray bursts or via their gravitational wave emission. Several radio facilities have developed rapid response modes enabling them to trigger on these events and search for this emission. For this paper, we constrain this coherent radio emission using the deepest available constraints for GRB 150424A, which were obtained via a triggered observation with the Murchison Widefield Array. We then expand this analysis to determine the properties of magnetar merger remnants that may be formed via a general population of binary neutron star mergers. Our results demonstrate that many of the potential coherent emission mechanisms that have been proposed for such events can be detected or very tightly constrained by the complementary strategies used by the current generation of low-frequency radio telescopes.

scholarly journals Low-Frequency Spectral Energy Distributions of Radio Pulsars Detected with the Murchison Widefield Array

2017 ◽  
Vol 34 ◽  
Author(s):  
Tara Murphy ◽  
David L. Kaplan ◽  
Martin E. Bell ◽  
J. R. Callingham ◽  
Steve Croft ◽  
...  
Keyword(s):  
Radio Emission ◽  
Low Frequency ◽  
Spectral Energy ◽  
Radio Pulsars ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Measured Flux ◽  
Murchison Widefield Array ◽  
Continuum Radio ◽  
Good Agreement

AbstractWe present low-frequency spectral energy distributions of 60 known radio pulsars observed with the Murchison Widefield Array telescope. We searched the GaLactic and Extragalactic All-sky Murchison Widefield Array survey images for 200-MHz continuum radio emission at the position of all pulsars in the Australia Telescope National Facility (ATNF) pulsar catalogue. For the 60 confirmed detections, we have measured flux densities in 20 × 8 MHz bands between 72 and 231 MHz. We compare our results to existing measurements and show that the Murchison Widefield Array flux densities are in good agreement.

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