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Using the Murchison Widefield Array (MWA), the low-frequency Square Kilometre Array (SKA1 LOW) precursor located in Western Australia, we have completed the GaLactic and Extragalactic All-sky MWA (GLEAM) survey, and present the resulting extragalactic catalogue, utilising the first year of observations. The catalogue covers 24,831 square degrees, over declinations south of $+30^circ$ and Galactic latitudes outside $10^circ$ of the Galactic plane, excluding some areas such as the Magellanic Clouds. It contains 307,455 radio sources with 20 separate flux density measurements across 72--231MHz, selected from a time- and frequency- integrated image centred at 200MHz, with a resolution of $approx 2$. Over the catalogued region, we estimate that the catalogue is 90% complete at 170mJy, and 50% complete at 55mJy, and large areas are complete at even lower flux density levels. Its reliability is 99.97% above the detection threshold of $5sigma$, which itself is typically 50mJy. These observations constitute the widest fractional bandwidth and largest sky area survey at radio frequencies to date, and calibrate the low frequency flux density scale of the southern sky to better than 10%. This paper presents details of the flagging, imaging, mosaicking, and source extraction/characterisation, as well as estimates of the completeness and reliability. All source measurements and images are available online (http://www.mwatelescope.org/science/gleam-survey). This is the first in a series of publications describing the GLEAM survey results.
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This work makes available a further 2,860deg$^2$ of the GLEAM survey, covering half of the accessible Galactic Plane, across twenty frequency bands sampling $72-231$MHz, with resolution $4-2$. Unlike previous GLEAM data releases, we used multi-scale clean to better deconvolve large-scale Galactic structure. For the Galactic longitude ranges $345^circ < l < 67^circ$, $180^circ < l < 240^circ$, we provide a compact source catalogue of 22,037 components selected from a 60-MHz bandwidth image centred at 200-MHz, with RMS noise $approx10-20$mJy beam$^{-1}$ and position accuracy better than $2$. The catalogue has a completeness of 50% at $approx120$mJy, and a reliability of 99.86%. It covers Galactic latitudes $1^circleq|b|leq10^circ$ toward the Galactic Centre and $|b|leq10^circ$ for other regions, and is available from Vizier; images covering $|b|leq10^circ$ for all longitudes are made available on the GLEAM VO server and SkyView.
We describe the parameters of a low-frequency all-sky survey of compact radio sources using Interplanetary Scintillation (IPS), undertaken with the Murchison Widefield Array (MWA). While this survey gives important complementary information to low-resolution survey such as the MWA GLEAM survey, providing information on the subarsecond structure of every source, a survey of this kind has not been attempted in the era of low-frequency imaging arrays such as the MWA and LOFAR. 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 IPS measurements at any point on the celestial sphere and we show that at 160MHz, reasonable results can be obtained within 30deg of the ecliptic (2{pi} str: half the sky). We also suggest some observational strategies and describe the first such survey, the MWA Phase I IPS survey. Finally we analyse the potential of the recently-upgraded MWA and discuss the potential of the SKA-low to use IPS to probe sub-mJy flux density levels at sub-arcsecond angular resolution.
We have compiled a catalogue of HII regions detected with the Murchison Widefield Array (MWA) between 72 and 231MHz. The multiple frequency bands provided by the MWA allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in HII regions. We detect 302 HII regions between 260 < l < 340 and report on the positions, sizes, peak, integrated flux density, and spectral indices of these HII regions. By identifying the point at which HII regions transition from the optically thin to thick regime we derive the physical properties including the electron density, ionised gas mass and ionising photon flux, towards 61 HII regions. This catalogue of HII regions represents the most extensive and uniform low frequency survey of HII regions in the Galaxy to date.
We present the results of an approximately 6,100 square degree 104--196MHz radio sky survey performed with the Murchison Widefield Array during instrument commissioning between 2012 September and 2012 December: the Murchison Widefield Array Commissioning Survey (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 < Right Ascension (RA) < 8.5 h, -58 deg < Declination (Dec) < -14 deg 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, with reduced sensitivity near the field boundaries and bright sources. We describe the data reduction strategy, based upon mosaiced 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.
We present a calibration component for the Murchison Widefield Array All-Sky Virtual Observatory (MWA ASVO) utilising a newly developed PostgreSQL database of calibration solutions. Since its inauguration in 2013, the MWA has recorded over thirty-four petabytes of data archived at the Pawsey Supercomputing Centre. According to the MWA Data Access policy, data become publicly available eighteen months after collection. Therefore, most of the archival data are now available to the public. Access to public data was provided in 2017 via the MWA ASVO interface, which allowed researchers worldwide to download MWA uncalibrated data in standard radio astronomy data formats (CASA measurement sets or UV FITS files). The addition of the MWA ASVO calibration feature opens a new, powerful avenue for researchers without a detailed knowledge of the MWA telescope and data processing to download calibrated visibility data and create images using standard radio-astronomy software packages. In order to populate the database with calibration solutions from the last six years we developed fully automated pipelines. A near-real-time pipeline has been used to process new calibration observations as soon as they are collected and upload calibration solutions to the database, which enables monitoring of the interferometric performance of the telescope. Based on this database we present an analysis of the stability of the MWA calibration solutions over long time intervals.
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