The Murchison Widefield Array Correlator

Ord, S. M.; Crosse, B.; Emrich, D.; Pallot, D.; Wayth, R. B.; Clark, Michael A.; Tremblay, S. E.; Arcus, W.; Barnes, David G.; Bell, M. E.; Bernardi, G.; Bhat, N. D. R.; Bowman, Judd D.; Briggs, F.; Bunton, John D.; Cappallo, R. J.; Corey, B. E.; Deshpande, A. A.; deSouza, L.; Ewell-Wice, A.; Lü, Feng; Goeke, R.; Greenhill, L. J.; Hazelton, B. J.; Herne, D.; Hewitt, Jacqueline N.; Hindson, L.; Hurley‐Walker, N.; Jacobs, Daniel; Johnston‐Hollitt, M.; Kaplan, D. L.; Kasper, J. C.; Kincaid, B. B.; Koenig, R.; Kratzenberg, E.; Kudryavtseva, N. A.; Lenc, E.; Lonsdale, Colin J.; Lynch, M. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Oberoi, D.; Offringa, A. R.; Pathikulangara, J.; Pindor, B.; Prabu, T.; Procopio, P.; Remillard, Ron; Riding, J.; Rogers, A. E. E.; Roshi, A.; Salah, J. E.; Sault, R. J.; Shankar, N. Udaya; Srivani, K. S.; Stevens, J.; Subrahmanyan, R.; Tingay, S. J.; Waterson, M.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.; Wyithe, J. Stuart B.

doi:10.1017/pasa.2015.5

Cited by 47 publications

(35 citation statements)

References 17 publications

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“…Only the upper half, centred at 162 MHz, is discussed here. The data were correlated in real-time on site, using the standard MWA correlator (Ord et al 2015) with the maximum available time resolution of 0.5 s.…”

Section: Observations and Initial Data Reductionmentioning

confidence: 99%

Interplanetary scintillation studies with the Murchison Widefield Array – II. Properties of sub-arcsecond compact sources at low radio frequencies

Chhetri

Morgan

Ekers

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We report the first astrophysical application of the technique of wide-field Interplanetary Scintillation (IPS) with the Murchison Widefield Array (MWA). This powerful technique allows us to identify and measure sub-arcsecond compact components in lowfrequency radio sources across large areas of sky without the need for long-baseline interferometry or ionospheric calibration. We present the results of a five-minute observation of a 30×30 deg 2 MWA field at 162 MHz with 0.5 second time resolution. Of the 2550 continuum sources detected in this field, 302 (12 per cent) show rapid fluctuations caused by IPS. We find that at least 32% of bright low-frequency radio sources contain a sub-arcsec compact component that contributes over 40% of the total flux density. Perhaps surprisingly, peaked-spectrum radio sources are the dominant population among the strongly-scintillating, low-frequency sources in our sample. While gamma-ray AGN are generally compact, flat-spectrum radio sources at higher frequencies, the 162 MHz properties of many of the Fermi blazars in our field are consistent with a compact component embedded within more extended low-frequency emission. The detection of a known pulsar in our field shows that the wide-field IPS technique is at the threshold of sensitivity needed to detect new pulsars using image plane analysis, and scaling the current MWA sensitivity to that expected for SKA-low implies that large IPS-based pulsar searches will be feasible with SKA. Calibration strategies for the SKA require a better knowledge of the space density of compact sources at low radio frequencies, which IPS observations can now provide.

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Section: Observations and Initial Data Reductionmentioning

confidence: 99%

Interplanetary scintillation studies with the Murchison Widefield Array – II. Properties of sub-arcsecond compact sources at low radio frequencies

Chhetri

Morgan

Ekers

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Each of these elements is an array of 4×4 dual-polarisation dipoles. Details of the MWA design are available in Lonsdale et al (2009) and Tingay et al (2013), the description of the correlator in Ord et al (2015), and the key science targets in Bowman et al (2013). The data used here come from MWA observations on 3 November 2014 from 06:12:02-06:16:02 UT, taken under the solar observing proposal G0002.…”

Section: Observations and State Of The Sunmentioning

confidence: 99%

4D Data Cubes from Radio-Interferometric Spectroscopic Snapshot Imaging

Mohan

Oberoi

2017

Sol Phys

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The new generation of low radio-frequency interferometric arrays have enabled the imaging of the solar corona at high spectro-temporal resolutions and sensitivity. In this article we introduce and implement a formalism to generate flux density and brightness temperature ($T_{\mathrm B}$) maps from such images, using independently obtained disc-integrated solar flux density dynamic spectra. These images collectively generate a 4D data cube, with axes spanning angular coordinates ($\theta,\phi$), frequency ($\nu$) and time ($t$). This 4D data cube is the most informative data product which can be generated from interferometric radio data. It will allow us to track solar emission simultaneously in these four dimensions. We also introduce SPatially REsolved Dynamic Spectra (SPREDS), named in analogy to the usual dynamic spectra. For any arbitrary region, ($\theta_i,\phi_j$), in the maps, these 2D projections of the 4D data cube correspond to the dynamic spectrum of emission arising from there. We show examples of these data products using observations from the Murchison Widefield Array (MWA). These are also the first calibrated solar maps from the MWA

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“…Visibilities were produced using the standard MWA correlator (Ord et al 2015) and cotter (Offringa et al 2015). For our calibrator observations, this included 8-s time averaging and RFI flagging using the aoflagger algorithm (Offringa et al 2012).…”

Section: Murchison Widefield Array (Mwa)mentioning

confidence: 99%

Type III Solar Radio Burst Source Region Splitting due to a Quasi-separatrix Layer

McCauley

Cairns

Morgan

et al. 2017

ApJ

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We present low-frequency (80-240 MHz) radio imaging of type III solar radio bursts observed by the Murchison Widefield Array (MWA) on 2015/09/21. The source region for each burst splits from one dominant component at higher frequencies into two increasingly-separated components at lower frequencies. For channels below ∼132 MHz, the two components repetitively diverge at high speeds (0.1-0.4 c) along directions tangent to the limb, with each episode lasting just ∼2 s. We argue that both effects result from the strong magnetic field connectivity gradient that the burst-driving electron beams move into. Persistence mapping of extreme ultraviolet (EUV) jets observed by the Solar Dynamics Observatory reveals quasi-separatrix layers (QSLs) associated with coronal null points, including separatrix dome, spine, and curtain structures. Electrons are accelerated at the flare site toward an open QSL, where the beams follow diverging field lines to produce the source splitting, with larger separations at larger heights (lower frequencies). The splitting motion within individual frequency bands is interpreted as a projected time-of-flight effect, whereby electrons traveling along the outer field lines take slightly longer to excite emission at adjacent positions. Given this interpretation, we estimate an average beam speed of 0.2 c. We also qualitatively describe the quiescent corona, noting in particular that a disk-center coronal hole transitions from being dark at higher frequencies to bright at lower frequencies, turning over around 120 MHz. These observations are compared to synthetic images based on the Magnetohydrodynamic Algorithm outside a Sphere (MAS) model, which we use to flux-calibrate the burst data.

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The Murchison Widefield Array Correlator

Cited by 47 publications

References 17 publications

Interplanetary scintillation studies with the Murchison Widefield Array – II. Properties of sub-arcsecond compact sources at low radio frequencies

Interplanetary scintillation studies with the Murchison Widefield Array – II. Properties of sub-arcsecond compact sources at low radio frequencies

4D Data Cubes from Radio-Interferometric Spectroscopic Snapshot Imaging

Type III Solar Radio Burst Source Region Splitting due to a Quasi-separatrix Layer

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