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

Morgan, John S.; Macquart, Jean–Pierre; Chhetri, Rajan; Ekers, R. D.; Tingay, S. J.; Sadler, E. M.

doi:10.1017/pasa.2018.40

Cited by 21 publications

(27 citation statements)

References 82 publications

(96 reference statements)

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“…While these effects do not significantly effect the central portion of the primary lobe, the steep edges of the beam surrounding the nulls are susceptible to large power offsets, approaching ∼ 8dB, with pointing offsets as low as ∼ 1.5 • . This may be of particular import to observations conducted during the day, where clever observation techniques are used to place the sun in one of the primary beam nulls and achieve maximum attenuation (Morgan et al 2019). Positional offsets of the nulls could potentially introduce significant erroneous solar flux to such observations.…”

Section: Discussionmentioning

confidence: 99%

Dual Polarization Measurements of MWA Beampatterns at 137 MHz

Chokshi,

Line,

Barry

et al. 2021

Preprint

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The wide adoption of low-frequency radio interferometers as a tool for deeper and higher resolution astronomical observations has revolutionized radio astronomy. Despite their construction from static, relatively simple dipoles, the sheer number of distinct elements introduces new, complicated instrumental effects. Their necessary remote locations exacerbate failure rates, while electronic interactions between the many adjacent receiving elements can lead to non-trivial instrumental effects. The Murchison Widefield Array (MWA) employs phased array antenna elements (tiles), which improve collecting area at the expense of complex beam shapes. Advanced electromagnetic simulations have produced the Fully Embedded Element (FEE) simulated beam model which has been highly successful in describing the ideal beam response of MWA antennas. This work focuses on the relatively unexplored aspect of various in-situ, environmental perturbations to beam models and represents the first large-scale, in-situ, all-sky measurement of MWA beam shapes at multiple polarizations and pointings. Our satellite based beam measurement approach enables all-sky beam response measurements with a dynamic range of ∼ 50 dB, at 137 MHz.

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Section: Discussionmentioning

confidence: 99%

Dual Polarization Measurements of MWA Beampatterns at 137 MHz

Chokshi,

Line,

Barry

et al. 2021

Preprint

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“…Interferometric observations are not the only way of detecting compact structure at low frequencies. It is also possible to use observations of interplanetary scintillation (IPS), which are being carried out by the Murchison Widefield Array (MWA) in the southern hemisphere at 162 MHz (Morgan et al 2018;Chhetri et al 2018b,a;Sadler et al 2019;Morgan et al 2019), and by the Pushchino telescope in the north at 111 MHz (Tyul'bashev et al 2019(Tyul'bashev et al , 2020. The critical scale for sources to scintillate at these frequencies is ∼0.3 , well matched to the resolution of interferometric observations with International LOFAR.…”

Section: Introductionmentioning

confidence: 88%

Sub-arcsecond imaging with the International LOFAR Telescope: II. Completion of the LOFAR Long-Baseline Calibrator Survey

Jackson,

Badole,

Morgan

et al. 2021

Preprint

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The Low-Frequency Array (LOFAR) Long-Baseline Calibrator Survey (LBCS) was conducted between 2014 and 2019 in order to obtain a set of suitable calibrators for the LOFAR array. In this paper we present the complete survey, building on the preliminary analysis published in 2016 which covered approximately half the survey area. The final catalogue consists of 30006 observations of 24713 sources in the northern sky, selected for a combination of high low-frequency radio flux density and flat spectral index using existing surveys (WENSS, NVSS, VLSS, and MSSS). Approximately one calibrator per square degree, suitable for calibration of ≥ 200 km baselines is identified by the detection of compact flux density, for declinations north of 30 • and away from the Galactic plane, with a considerably lower density south of this point due to relative difficulty in selecting flat-spectrum candidate sources in this area of the sky. The catalogue contains indicators of degree of correlated flux on baselines between the Dutch core and each of the international stations, involving a maximum baseline length of nearly 2000 km, for all of the observations. Use of the VLBA calibrator list, together with statistical arguments by comparison with flux densities from lower-resolution catalogues, allow us to establish a rough flux density scale for the LBCS observations, so that LBCS statistics can be used to estimate compact flux densities on scales between 300 mas and 2 , for sources observed in the survey. The survey is used to estimate the phase coherence time of the ionosphere for the LOFAR international baselines, with median phase coherence times of about 2 minutes varying by a few tens of percent between the shortest and longest baselines. The LBCS can be used to assess the structures of point sources in lower-resolution surveys, with significant reductions in the degree of coherence in these sources on scales between 2 and 300 mas. The LBCS survey sources show a greater incidence of compact flux density in quasars than in radio galaxies, consistent with unified schemes of radio sources. Comparison with samples of sources from interplanetary scintillation (IPS) studies with the Murchison Widefield Array (MWA) shows consistent patterns of detection of compact structure in sources observed both interferometrically with LOFAR and using IPS.

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“…These findings motivated a 6-month long-observing campaign, described in detail by Morgan et al (2019). The analysis of these data is ongoing; however, much of the work so far has focused on determining the astrophysical nature of the sources detected.…”

Section: Interplanetary Scintillationmentioning

confidence: 96%

Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

Beardsley

Johnston‐Hollitt

Trott

et al. 2019

Publ. Astron. Soc. Aust.

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The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low frequency (80-300 MHz) southern sky. Since beginning operations in mid 2013, the MWA has opened a new observational window in the southern hemisphere enabling many science areas. The driving science objectives of the original design were to observe 21 cm radiation from the Epoch of Reionisation (EoR), explore the radio time domain, perform Galactic and extragalactic surveys, and monitor solar, heliospheric, and ionospheric phenomena. All together 60+ programs recorded 20,000 hours producing 146 papers to date. In 2016 the telescope underwent a major upgrade resulting in alternating compact and extended configurations. Other upgrades, including digital back-ends and a rapid-response triggering system, have been developed since the original array was commissioned. In this paper we review the major results from the prior operation of the MWA, and then discuss the new science paths enabled by the improved capabilities. We group these science opportunities by the four original science themes, but also include ideas for directions outside these categories.

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

Cited by 21 publications

References 82 publications

Dual Polarization Measurements of MWA Beampatterns at 137 MHz

Dual Polarization Measurements of MWA Beampatterns at 137 MHz

Sub-arcsecond imaging with the International LOFAR Telescope: II. Completion of the LOFAR Long-Baseline Calibrator Survey

Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

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