scholarly journals Discovery of a Steep-spectrum Low-luminosity Pulsar with the Murchison Widefield Array

2021 ◽  
Vol 911 (2) ◽  
pp. L26
Author(s):  
N. A. Swainston ◽  
N. D. R. Bhat ◽  
M. Sokolowski ◽  
S. J. McSweeney ◽  
S. Kudale ◽  
...  
Keyword(s):  
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 GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey III: South Galactic Pole data release

2021 ◽  
Vol 38 ◽  
Author(s):  
T. M. O. Franzen ◽  
N. Hurley-Walker ◽  
S. V. White ◽  
P. J. Hancock ◽  
N. Seymour ◽  
...  
Keyword(s):  
Large Scale ◽  
Angular Resolution ◽  
Beam Model ◽  
Spectral Variability ◽  
Extragalactic Source ◽  
Automated Algorithm ◽  
Data Release ◽  
Murchison Widefield Array ◽  
Source Populations ◽  
One Year

Abstract We present the South Galactic Pole (SGP) data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. These data combine both years of GLEAM observations at 72–231 MHz conducted with the Murchison Widefield Array (MWA) and cover an area of 5 113 $\mathrm{deg}^{2}$ centred on the SGP at $20^{\mathrm{h}} 40^{\mathrm{m}} < \mathrm{RA} < 05^{\mathrm{h}} 04^{\mathrm{m}}$ and $-48^{\circ} < \mathrm{Dec} < -2^{\circ} $ . At 216 MHz, the typical rms noise is ${\approx}5$ mJy beam–1 and the angular resolution ${\approx}2$ arcmin. The source catalogue contains a total of 108 851 components above $5\sigma$ , of which 77% have measured spectral indices between 72 and 231 MHz. Improvements to the data reduction in this release include the use of the GLEAM Extragalactic catalogue as a sky model to calibrate the data, a more efficient and automated algorithm to deconvolve the snapshot images, and a more accurate primary beam model to correct the flux scale. This data release enables more sensitive large-scale studies of extragalactic source populations as well as spectral variability studies on a one-year timescale.

scholarly journals The giant lobes of Centaurus A observed at 118 MHz with the Murchison Widefield Array

2013 ◽  
Vol 436 (2) ◽  
pp. 1286-1301 ◽  
Author(s):  
B. McKinley ◽  
F. Briggs ◽  
B. M. Gaensler ◽  
I. J. Feain ◽  
G. Bernardi ◽  
...  
Keyword(s):  
Murchison Widefield Array ◽  
Centaurus A

scholarly journals The nature and likely redshift of GLEAM J0917–0012

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 ◽  
Murchison Widefield 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 $z=7$ .

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

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 ◽  
Murchison Widefield 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.

scholarly journals Extragalactic megahertz-peaked spectrum radio sources at milliarcsecond scales

2019 ◽  
Vol 628 ◽  
pp. A56 ◽  
Author(s):  
M. A. Keim ◽  
J. R. Callingham ◽  
H. J. A. Röttgering
Keyword(s):  
Magnetic Field ◽  
Spectral Characteristics ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Long Baseline ◽  
Spectrum Radio ◽  
Spectral Peaks ◽  
Murchison Widefield Array ◽  
Very Long Baseline Array ◽  
Field Strengths

Extragalactic peaked-spectrum radio sources are thought to be the progenitors of larger, radio-loud active galactic nuclei (AGN). Synchrotron self-absorption (SSA) has often been identified as the cause of their spectral peak. The identification of new megahertz-peaked spectrum sources from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey provides an opportunity to test how radio sources with spectral peaks below 1 GHz fit within this evolutionary picture. We observed six peaked-spectrum sources selected from the GLEAM survey, three that have spectral characteristics which violate SSA and three that have spectral peaks below 230 MHz, with the Very Long Baseline Array at 1.55 and 4.96 GHz. We present milliarcsecond resolution images of each source and constrain their morphology, linear size, luminosity, and magnetic field strength. Of the sources that are resolved by our study, the sources that violate SSA appear to be compact doubles, while the sources with peak frequencies below 230 MHz have core-jet features. We find that all of our sources are smaller than expected from SSA by factors of ≳20. We also find that component magnetic field strengths calculated from SSA are likely inaccurate, differing by factors of ≳5 from equipartition estimates. The calculated equipartition magnetic field strengths more closely resemble estimates from previously studied gigahertz-peaked spectrum sources. Exploring a model of the interaction between jets and the interstellar medium, we demonstrate that free-free absorption (FFA) can accurately describe the linear sizes and peak frequencies of our sources. Our findings support the theory that there is a fraction of peaked-spectrum sources whose spectral peaks are best modeled by FFA, implying our understanding of the early stages of radio AGN is incomplete.

scholarly journals The development of non-coherent passive radar techniques for space situational awareness with the Murchison Widefield Array

2020 ◽  
Vol 37 ◽  
Author(s):  
Steve Prabu ◽  
Paul J. Hancock ◽  
Xiang Zhang ◽  
Steven J. Tingay
Keyword(s):  
Situational Awareness ◽  
Signal To Noise Ratio ◽  
Space Station ◽  
Passive Radar ◽  
Space Situational Awareness ◽  
Direct Path ◽  
Orbital Parameters ◽  
Ratio Spectrum ◽  
Murchison Widefield Array ◽  
Future Work

Abstract The number of active and non active satellites in Earth orbit has dramatically increased in recent decades, requiring the development of novel surveillance techniques to monitor and track them. In this paper, we build upon previous non-coherent passive radar space surveillance demonstrations undertaken using the Murchison Widefield Array (MWA). We develop the concept of the Dynamic Signal to Noise Ratio Spectrum (DSNRS) in order to isolate signals of interest (reflections of FM transmissions of objects in orbit) and efficiently differentiate them from direct path reception events. We detect and track Alouette-2, ALOS, UKube-1, the International Space Station, and Duchifat-1 in this manner. We also identified out-of-band transmissions from Duchifat-1 and UKube-1 using these techniques, demonstrating the MWA’s capability to look for spurious transmissions from satellites. We identify an offset from the locations predicted by the cataloged orbital parameters for some of the satellites, demonstrating the potential of using MWA for satellite catalog maintenance. These results demonstrate the capability of the MWA for Space Situational Awareness and we describe future work in this area.

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
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