scholarly journals Interplanetary Scintillation with the Murchison Widefield Array V: An all-sky survey of compact sources using a modern low-frequency radio telescope

2019 ◽  
Vol 36 ◽  
Author(s):  
J. S. Morgan ◽  
J.-P. Macquart ◽  
R. Chhetri ◽  
R. D. Ekers ◽  
S. J. Tingay ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Low Frequency ◽  
Radio Sources ◽  
Interplanetary Scintillation ◽  
Complementary Information ◽  
Imaging Arrays ◽  
Sky Survey ◽  
Murchison Widefield Array ◽  
Celestial Sphere ◽  
Compact Sources

AbstractWe describe the parameters of a low-frequency all-sky survey of compact radio sources using Interplanetary Scintillation, undertaken with the Murchison Widefield Array. While this survey gives important complementary information to low-resolution survey, providing information on the sub-arsecond structure of every source, a survey of this kind has not been attempted in the era of low-frequency imaging arrays such as the Murchison Widefield Array and LOw Frequency Array. Here we set out the capabilities of such a survey, describing the limitations imposed by the heliocentric observing geometry and by the instrument itself. We demonstrate the potential for Interplanetary Scintillation measurements at any point on the celestial sphere and we show that at 160 MHz, reasonable results can be obtained within 30° of the ecliptic (2π str: half the sky). We also suggest some observational strategies and describe the first such survey, the Murchison Widefield Array Phase I Interplanetary Scintillation survey. Finally we analyse the potential of the recently upgraded Murchison Widefield Array and discuss the potential of the Square Kilometre Array-low to use Interplanetary Scintillation to probe sub-mJy flux density levels at sub-arcsecond angular resolution.

scholarly journals The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14 110 Compact Radio Sources over 6 100 Square Degrees

2014 ◽  
Vol 31 ◽  
Author(s):  
Natasha Hurley-Walker ◽  
John Morgan ◽  
Randall B. Wayth ◽  
Paul J. Hancock ◽  
Martin E. Bell ◽  
...  
Keyword(s):  
Flux Density ◽  
Noise Level ◽  
Angular Resolution ◽  
Low Frequency ◽  
Radio Sources ◽  
Reduction Strategy ◽  
Sky Survey ◽  
Field Boundaries ◽  
Murchison Widefield Array ◽  
Finding Method

AbstractWe present the results of an approximately 6 100 deg2 104–196 MHz radio sky survey performed with the Murchison Widefield Array during instrument commissioning between 2012 September and 2012 December: the MWACS. The data were taken as meridian drift scans with two different 32-antenna sub-arrays that were available during the commissioning period. The survey covers approximately 20.5 h < RA < 8.5 h, − 58° < Dec < −14°over three frequency bands centred on 119, 150 and 180 MHz, with image resolutions of 6–3 arcmin. The catalogue has 3 arcmin angular resolution and a typical noise level of 40 mJy beam− 1, with reduced sensitivity near the field boundaries and bright sources. We describe the data reduction strategy, based upon mosaicked snapshots, flux density calibration, and source-finding method. We present a catalogue of flux density and spectral index measurements for 14 110 sources, extracted from the mosaic, 1 247 of which are sub-components of complexes of sources.

scholarly journals High resolution VLBI observations of the nuclei of bright galaxies and quasars at 327 MHz

1986 ◽  
Vol 119 ◽  
pp. 169-170
Author(s):  
S. Ananthakrishnan ◽  
V.K. Kulkarni
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
The Other ◽  
Radio Sources ◽  
Interplanetary Scintillation ◽  
Ss 433 ◽  
Vlbi Observations ◽  
Nearby Galaxies ◽  
Compact Sources ◽  
3C 120

An intercontinental VLBI experiment at 327 MHz involving the Ooty Radio Telescope and telescopes at Jodrell Bank, Westerbork, Torun and Crimea was carried out during December 8–12, 1983. The purpose of the experiment was to (i) establish the feasibility of performing MKII VLBI observations from India and (ii) to study the low frequency structure of nearby galaxies, quasars and some other well known radio sources at metre wavelengths. The sources observed were NGC 262, 315, 1052, 1068, 1265, 1275, 4151, 4486, 7674 and 3C 120; PKS 1055+018, 1148−001 and CTA 102; 3C 237 and SS 433. The bright NGC galaxies chosen were selected from an Interplanetary Scintillation survey of 150 nearby galaxies (Bagri and Ananthakrishnan 1983); they were found to have a flux density greater than about 0.2 Jy in subarcsec components at 327 MHz and have high frequency VLBI observations. The quasars chosen are amongst the most compact sources known at metrewavelengths. The other objects were the well known sources which have been studied extensively at higher frequencies.

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 A Comparison of the Structures of 3CR Quasars and Blank Field Radio Sources

1982 ◽  
Vol 97 ◽  
pp. 435-436 ◽  
Author(s):  
F. N. Owen ◽  
J. J. Puschell ◽  
R. A. Laing
Keyword(s):  
Radio Source ◽  
Structural Properties ◽  
Low Frequency ◽  
Radio Sources ◽  
Blank Field ◽  
Sky Survey

The purpose of this communication is to update our knowledge of the radio structural properties of quasars and blank field radio sources (blank field ≡ any radio source without an identification on the Palomar Sky Survey prints). The quasar sample consists of all sources (25) with angular sizes greater than 10 arcsec in the list of Jodrell Bank quasars observed by Owen, Porcas and Neff (1978). The blank fields consist of 16 3CR sources also with structures >10 arcsec based on Cambridge 5 km telescope observations. The sources were selected in low-frequency surveys; their emission at ν < 1 GHz is dominated by extended components with steep spectra. Thus, both samples should be oriented randomly in space except for a slight bias to be in the plane of the sky.

scholarly journals LOFAR observations of the XMM-LSS field

2019 ◽  
Vol 622 ◽  
pp. A4 ◽  
Author(s):  
C. L. Hale ◽  
W. Williams ◽  
M. J. Jarvis ◽  
M. J. Hardcastle ◽  
L. K. Morabito ◽  
...  
Keyword(s):  
Large Scale ◽  
Angular Resolution ◽  
Low Frequency ◽  
Primary Beam ◽  
Electromagnetic Spectrum ◽  
Radio Sources ◽  
Spectral Indices ◽  
The North ◽  
True Source ◽  
Scale Calibration

We present observations of the XMM Large-Scale Structure (XMM-LSS) field observed with the LOw Frequency ARray (LOFAR) at 120–168 MHz. Centred at a J2000 declination of −4.5°, this is a challenging field to observe with LOFAR because of its low elevation with respect to the array. The low elevation of this field reduces the effective collecting area of the telescope, thereby reducing sensitivity. This low elevation also causes the primary beam to be elongated in the north-south direction, which can introduce side lobes in the synthesised beam in this direction. However the XMM-LSS field is a key field to study because of the wealth of ancillary information, encompassing most of the electromagnetic spectrum. The field was observed for a total of 12 h from three four-hour LOFAR tracks using the Dutch array. The final image presented encompasses ∼27 deg2, which is the region of the observations with a >50% primary beam response. Once combined, the observations reach a central rms of 280μJy beam−1at 144 MHz and have an angular resolution of 7.5 × 8.5″. We present our catalogue of detected sources and investigate how our observations compare to previous radio observations. This includes investigating the flux scale calibration of these observations compared to previous measurements, the implied spectral indices of the sources, the observed source counts and corrections to obtain the true source counts, and finally the clustering of the observed radio sources.

A discussion on infared astronomy - A far infrared sky survey

1969 ◽  
Vol 264 (1150) ◽  
pp. 267-271 ◽  
Keyword(s):  
Milky Way ◽  
Angular Resolution ◽  
Thermal Emission ◽  
Far Infrared ◽  
The Moon ◽  
Sky Survey ◽  
Upper Limits ◽  
Celestial Sphere ◽  
Thick Source ◽  
Thin Source

A balloon-borne instrument for making far infrared sky surveys with 2° angular resolution is described. In two initial flights at a wavelength of 320 μm approximately half of the celestial sphere including most of the northern milky way was surveyed. The thermal emission of the moon was alone detected. The upper limit to the flux from other sources was 3 x 10-12 W cm-2 in the 300 to 360 μm band, or approximately 2 x 10-23 W cm-2 Hz-1. A blackbody (optically thick) source 2° or greater in diameter yielding this flux would have a temperature of 10 °K. A warmer, small or optically thin source providing this much radiation in the Rayleigh-Jeans tail of the Plank distribution would have a temperature averaged over the 2° beam of 0.6 °K. These observations can be used to set upper limits to the opacity and temperature of interstellar grains.

scholarly journals Science with the Murchison Widefield Array

2013 ◽  
Vol 30 ◽  
Author(s):  
Judd D. Bowman ◽  
Iver Cairns ◽  
David L. Kaplan ◽  
Tara Murphy ◽  
Divya Oberoi ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Early Universe ◽  
Western Australia ◽  
Space Weather ◽  
Time Domain ◽  
Angular Resolution ◽  
Low Frequency ◽  
Performance Properties ◽  
Square Kilometre Array ◽  
Murchison Widefield Array

AbstractSignificant new opportunities for astrophysics and cosmology have been identified at low radio frequencies. The Murchison Widefield Array is the first telescope in the southern hemisphere designed specifically to explore the low-frequency astronomical sky between 80 and 300 MHz with arcminute angular resolution and high survey efficiency. The telescope will enable new advances along four key science themes, including searching for redshifted 21-cm emission from the EoR in the early Universe; Galactic and extragalactic all-sky southern hemisphere surveys; time-domain astrophysics; and solar, heliospheric, and ionospheric science and space weather. The Murchison Widefield Array is located in Western Australia at the site of the planned Square Kilometre Array (SKA) low-band telescope and is the only low-frequency SKA precursor facility. In this paper, we review the performance properties of the Murchison Widefield Array and describe its primary scientific objectives.

scholarly journals The MWA long baseline Epoch of reionisation survey—I. Improved source catalogue for the EoR 0 field

2021 ◽  
Vol 38 ◽  
Author(s):  
C. R. Lynch ◽  
T. J. Galvin ◽  
J. L. B. Line ◽  
C. H. Jordan ◽  
C. M. Trott ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Low Frequency ◽  
Calibration Model ◽  
Spectral Measurements ◽  
Long Baseline ◽  
Source Models ◽  
Extended Sources ◽  
Murchison Widefield Array ◽  
Foreground Calibration ◽  
Good Agreement

Abstract One of the principal systematic constraints on the Epoch of Reionisation (EoR) experiment is the accuracy of the foreground calibration model. Recent results have shown that highly accurate models of extended foreground sources, and including models for sources in both the primary beam and its sidelobes, are necessary for reducing foreground power. To improve the accuracy of the source models for the EoR fields observed by the Murchison Widefield Array (MWA), we conducted the MWA Long Baseline Epoch of Reionisation Survey (LoBES). This survey consists of multi-frequency observations of the main MWA EoR fields and their eight neighbouring fields using the MWA Phase II extended array. We present the results of the first half of this survey centred on the MWA EoR0 observing field (centred at RA (J2000) $0^\mathrm{h}$ , Dec (J2000) $-27^{\circ}$ ). This half of the survey covers an area of 3 069 degrees $^2$ , with an average rms of 2.1 mJy beam–1. The resulting catalogue contains a total of 80 824 sources, with 16 separate spectral measurements between 100 and 230 MHz, and spectral modelling for 78 $\%$ of these sources. Over this region we estimate that the catalogue is 90 $\%$ complete at 32 mJy, and 70 $\%$ complete at 10.5 mJy. The overall normalised source counts are found to be in good agreement with previous low-frequency surveys at similar sensitivities. Testing the performance of the new source models we measure lower residual rms values for peeled sources, particularly for extended sources, in a set of MWA Phase I data. The 2-dimensional power spectrum of these data residuals also show improvement on small angular scales—consistent with the better angular resolution of the LoBES catalogue. It is clear that the LoBES sky models improve upon the current sky model used by the Australian MWA EoR group for the EoR0 field.

scholarly journals Angular clustering of point sources at 150 MHz in the TGSS survey

2019 ◽  
Vol 485 (4) ◽  
pp. 5891-5896 ◽  
Author(s):  
Sandeep Rana ◽  
Jasjeet S Bagla
Keyword(s):  
Correlation Function ◽  
Power Law ◽  
Low Frequency ◽  
Point Sources ◽  
Radio Sources ◽  
Redshift Distribution ◽  
Intensity Mapping ◽  
Flux Limit ◽  
Sky Survey ◽  
Angular Correlation Function

Abstract We study the angular clustering of point sources in The GMRT (Giant Metrewave Radio Telescope) Sky Survey (TGSS). The survey at 150 MHz with δ &gt; −53.5° has a sky coverage of 3.6π steradians, i.e. $90{{\ \rm per\ cent}}$ of the whole sky. We created subsamples by applying different total flux thresholds limit (Sflux ≫ 5σ) for good completeness and measured the angular correlation function ω(θ) of point sources at large scales (≥1°). We find that the amplitude of angular clustering is higher for brighter subsamples; this indicates that higher threshold flux samples are hosted by massive haloes and cluster strongly: this conclusion is based on the assumption that the redshift distribution of sources does not change with flux and this is supported by models of radio sources. We compare our results with other low-frequency studies of clustering of point sources and verify that the amplitude of clustering varies with the flux limit. We quantify this variation as a power-law dependence of the amplitude of correlation function with the flux limit. This dependence can be used to estimate foreground contamination due to clustering of point sources for low-frequency H i intensity mapping surveys for studying the epoch of reionization.

scholarly journals Radio and optical observations of “optically quiet quasars”

1986 ◽  
Vol 119 ◽  
pp. 113-115
Author(s):  
W. D. Cotton ◽  
F. N. Owen ◽  
M. J. Mahoney
Keyword(s):  
Large Particle ◽  
Low Frequency ◽  
Optical Emission ◽  
Optical Observations ◽  
Radio Sources ◽  
Optical Counterpart ◽  
Vlbi Observations ◽  
Compact Radio Source ◽  
Weak Magnetic Fields ◽  
Sky Survey

In recent years a number of very steep spectrum, compact radio sources have been discovered (e.g. Cotton 1983, Cotton and Owen 1985, Ulvestad 1985) which have no optical counterpart to the limit of the Palomar Sky Survey. VLBI observations of a number of these have confirmed the very compact (<10 mas) nature of several of these sources. Analysis of the available data in terms of the standard synchrotron modal suggest that they contain very weak magnetic fields, large particle densities and may emit detectable infrared and optical emission by inverse Campton scattering in the compact radio source (Cotton 1983). This paper will report on an analysis including new VLBI observations, infrared and optical imaging at KPNO and low frequency radio observations at CLRO of a number of these objects.

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