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1. Surveillance of Space using Passive Radar and the Murchison Widefield Array

Author: Palmer, James E., Hennessy, Brendan, Rutten, Mark, Merrett, David, Tingay, Steven, Kaplan, David, Tremblay, Steven, Ord, Stephen M., Morgan, John, and Wayth, Randall B.
Subjects: Electrical Engineering and Systems Science - Signal Processing, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: In this paper we build upon recent work in the radio astronomy community to experimentally demonstrate the viability of passive radar for Space Situational Awareness. Furthermore, we show that the six state parameters of objects in orbit may be measured and used to perform orbit characterisation/estimation., Comment: Published in: 2017 IEEE Radar Conference (RadarConf) URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7944483&isnumber=7944108
Published: 2019
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2. Wavelet-Based Characterization of Small-Scale Solar Emission Features at Low Radio Frequencies

Author: Suresh, Akshay, Sharma, Rohit, Oberoi, Divya, Das, Srijan B., Pankratius, Victor, Timar, Brian, Lonsdale, Colin J., Bowman, Judd D., Briggs, Frank, Cappallo, Roger J., Corey, Brian E., Deshpande, Avinash A., Emrich, David, Goeke, Robert, Greenhill, Lincoln J., Hazelton, Bryna J., Johnston-Hollitt, Melanie, Kaplan, David L., Kasper, Justin C., Kratzenberg, Eric, Lynch, Mervyn J., McWhirter, S. Russell, Mitchell, Daniel A., Morales, Miguel F., Morgan, Edward, Ord, Stephen M., Prabu, Thiagaraj, Rogers, Alan E. E., Roshi, Anish, Shankar, N. Udaya, Srivani, K. S., Subrahmanyan, Ravi, Tingay, Steven J., Waterson, Mark, Wayth, Randall B., Webster, Rachel L., Whitney, Alan R., Williams, Andrew, and Williams, Christopher L.
Subjects: Astrophysics - Solar and Stellar Astrophysics
Abstract: Low radio frequency solar observations using the Murchison Widefield Array have recently revealed the presence of numerous weak, short-lived and narrow-band emission features, even during moderately quiet solar conditions. These non-thermal features occur at rates of many thousands per hour in the 30.72 MHz observing bandwidth, and hence, necessarily require an automated approach for their detection and characterization. Here, we employ continuous wavelet transform using a mother Ricker wavelet for feature detection from the dynamic spectrum. We establish the efficacy of this approach and present the first statistically robust characterization of the properties of these features. In particular, we examine distributions of their peak flux densities, spectral spans, temporal spans and peak frequencies. We can reliably detect features weaker than 1 SFU, making them, to the best of our knowledge, the weakest bursts reported in literature. The distribution of their peak flux densities follows a power law with an index of -2.23 in the 12-155 SFU range, implying that they can provide an energetically significant contribution to coronal and chromospheric heating. These features typically last for 1-2 seconds and possess bandwidths of about 4-5 MHz. Their occurrence rate remains fairly flat in the 140-210 MHz frequency range. At the time resolution of the data, they appear as stationary bursts, exhibiting no perceptible frequency drift. These features also appear to ride on a broadband background continuum, hinting at the likelihood of them being weak type-I bursts., Comment: 15 pages, 14 figures, Accepted for publication in ApJ
Published: 2016
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3. GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey I: A low-frequency extragalactic catalogue

Author: Hurley-Walker, Natasha, Callingham, Joseph R., Hancock, Paul J., Franzen, Thomas M. O., Hindson, Luke, Kapinska, Anna D., Morgan, John, Offringa, Andre R., Wayth, Randall B., Wu, Chen, Zheng, Q., Murphy, Tara, Bell, Martin E., Dwarakanath, K. S., For, Bi-Qing, Gaensler, Bryan M., Johnston-Hollitt, Melanie, Lenc, Emil, Procopio, Pietro, Staveley-Smith, Lister, Ekers, Ron, Bowman, Judd D., Briggs, Frank, Cappallo, R. J., Deshpande, Avinash A., Greenhill, Lincoln, Hazelton, Brynah J., Kaplan, David L., Lonsdale, Colin J., McWhirter, S. R., Mitchell, Daniel A., Morales, Miguel F., Morgan, Edward, Oberoi, Divya, Ord, Stephen M., Prabu, T., Shankar, N. Udaya, Srivani, K. S., Subrahmanyan, Ravi, Tingay, Steven J., Webster, Rachel L., Williams, Andrew, and Williams, Christopher L.
Subjects: Astrophysics - Astrophysics of Galaxies
Abstract: 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 $5\sigma$, 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., Comment: 30 pages, 18 figures, 6 tables, published in Monthly Notices of the Royal Astronomical Society
Published: 2016
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4. A Digital-Receiver for the Murchison Widefield Array

Author: Prabu, Thiagaraj, Srivani, K. S., Roshi, D. Anish, Kamini, P. A., Madhavi, S., Emrich, David, Crosse, Brian, Williams, Andrew J., Waterson, Mark, Deshpande, Avinash A., Shankar, N. Udaya, Subrahmanyan, Ravi, Briggs, Frank H., Goeke, Robert F., Tingay, Steven J., Johnston-Hollitt, Melanie, R, Gopalakrishna M, Morgan, Edward H., Pathikulangara, Joseph, Bunton, John D., Hampson, Grant, Williams, Christopher, Ord, Stephen M., Wayth, Randall B., Kumar, Deepak, Morales, Miguel F., deSouza, Ludi, Kratzenberg, Eric, Pallot, D., McWhirter, Russell, Hazelton, Bryna J., Arcus, Wayne, Barnes, David G., Bernardi, Gianni, Booler, T., Bowman, Judd D., Cappallo, Roger J., Corey, Brian E., Greenhill, Lincoln J., Herne, David, Hewitt, Jacqueline N., Kaplan, David L., Kasper, Justin C., Kincaid, Barton B., Koenig, Ronald, Lonsdale, Colin J., Lynch, Mervyn J., Mitchell, Daniel A., Oberoi, Divya, Remillard, Ronald A., Rogers, Alan E., Salah, Joseph E., Sault, Robert J., Stevens, Jamie B., Tremblay, S. E., Webster, Rachel L., Whitney, Alan R., and Wyithe, Stuart B.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: An FPGA-based digital-receiver has been developed for a low-frequency imaging radio interferometer, the Murchison Widefield Array (MWA). The MWA, located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia, consists of 128 dual-polarized aperture-array elements (tiles) operating between 80 and 300\,MHz, with a total processed bandwidth of 30.72 MHz for each polarization. Radio-frequency signals from the tiles are amplified and band limited using analog signal conditioning units; sampled and channelized by digital-receivers. The signals from eight tiles are processed by a single digital-receiver, thus requiring 16 digital-receivers for the MWA. The main function of the digital-receivers is to digitize the broad-band signals from each tile, channelize them to form the sky-band, and transport it through optical fibers to a centrally located correlator for further processing. The digital-receiver firmware also implements functions to measure the signal power, perform power equalization across the band, detect interference-like events, and invoke diagnostic modes. The digital-receiver is controlled by high-level programs running on a single-board-computer. This paper presents the digital-receiver design, implementation, current status, and plans for future enhancements., Comment: 14 pages, 7 figures
Published: 2015
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5. Serendipitous discovery of a dying Giant Radio Galaxy associated with NGC 1534, using the Murchison Widefield Array

Author: Hurley-Walker, Natasha, Johnston-Hollitt, Melanie, Ekers, Ron, Hunstead, Richard, Sadler, Elaine M., Hindson, Luke, Hancock, Paul, Bernardi, Gianni, Bowman, Judd D., Briggs, Frank, Cappallo, Roger, Corey, Brian, Deshpande, Avinash A., Emrich, David, Gaensler, Bryan M., Goeke, Robert, Greenhill, Lincoln, Hazelton, Bryna J., Hewitt, Jacqueline, Kaplan, David L., Kasper, Justin, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, Mitchell, Daniel, McWhirter, Russell, Morales, Miguel, Morgan, Edward, Oberoi, Divya, Offringa, Andre, Ord, Stephen, Prabu, Thiagaraj, Rogers, Alan, Roshi, Anish, Shankar, Udaya, Srivani, K., Subrahmanyan, Ravi, Tingay, Steven, Waterson, Mark, Wayth, Randall B., Webster, Rachel, Whitney, Alan, Williams, Andrew, and Williams, Chris
Subjects: Astrophysics - Astrophysics of Galaxies
Abstract: Recent observations with the Murchison Widefield Array at 185~MHz have serendipitously unveiled a heretofore unknown giant and relatively nearby ($z = 0.0178$) radio galaxy associated with NGC\,1534. The diffuse emission presented here is the first indication that NGC\,1534 is one of a rare class of objects (along with NGC\,5128 and NGC\,612) in which a galaxy with a prominent dust lane hosts radio emission on scales of $\sim$700\,kpc. We present details of the radio emission along with a detailed comparison with other radio galaxies with disks. NGC1534 is the lowest surface brightness radio galaxy known with an estimated scaled 1.4-GHz surface brightness of just 0.2\,mJy\,arcmin$^{-2}$. The radio lobes have one of the steepest spectral indices yet observed: $\alpha=-2.1\pm0.1$, and the core to lobe luminosity ratio is $<0.1$\%. We estimate the space density of this low brightness (dying) phase of radio galaxy evolution as $7\times10^{-7}$\,Mpc$^{-3}$ and argue that normal AGN cannot spend more than 6\% of their lifetime in this phase if they all go through the same cycle., Comment: 12 pages, 7 figures, accepted MNRAS
Published: 2014
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6. The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14,110 Compact Radio Sources over 6,100 Square Degrees

Author: Hurley-Walker, Natasha, Morgan, John, Wayth, Randall B., Hancock, Paul J., Bell, Martin E., Bernardi, Gianni, Bhat, Ramesh, Briggs, Frank, Deshpande, Avinash A., Ewall-Wice, Aaron, Feng, Lu, Hazelton, Bryna J., Hindson, Luke, Jacobs, Daniel C., Kudryavtseva, David L. Kaplan Nadia, Lenc, Emil, McKinley, Benjamin, Mitchell, Daniel, Pindor, Bart, Procopio, Pietro, Oberoi, Divya, Offringa, André, Ord, Stephen, Riding, Jennifer, Bowman, Judd D., Cappallo, Roger, Corey, Brian, Emrich, David, Gaensler, B. M., Goeke, Robert, Greenhill, Lincoln, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kasper, Justin, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, Russell, Morales, Miguel F., Morgan, Edward, Prabu, Thiagaraj, Rogers, Alan, Roshi, Anish, Shankar, Udaya, Srivani, K., Subrahmanyan, Ravi, Tingay, Steven, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, Andrew, and Williams, Chris
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: 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., Comment: 22 pages, 18 figures, accepted to PASA
Published: 2014
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7. Study of Redshifted HI from the Epoch of Reionization with Drift scan

Author: Paul, Sourabh, Sethi, Shiv K., Subrahmanyan, Ravi, Shankar, N. Udaya, Dwarakanath, K. S., Deshpande, Avinash A., Bernardi, Gianni, Bowman, Judd D., Briggs, Frank, Cappallo, Roger J., Corey, Brian E., Emrich, David, Gaensler, Bryan M., Goeke, Robert F., Greenhill, Lincoln J., Hazelton, Bryna J., Hewitt, Jacqueline N., Johnston-Hollitt, Melanie, Kaplan, David L., Kasper, Justin C., Kratzenberg, Eric, Lonsdale, Colin J., Lynch, Mervyn J., McWhirter, S. Russell, Mitchell, Daniel A., Morales, Miguel F., Morgan, Edward H., Oberoi, Divya, Ord, Stephen M., Prabu, Thiagaraj, Rogers, Alan E. E., Roshi, Anish A., Srivani, K. S., Tingay, Steven J., Wayth, Randall B., Waterson, Mark, Webster, Rachel L., Whitney, Alan R., Williams, Andrew J., and Williams, Christopher L.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The detection of the Epoch of Reionization (EoR) in the redshifted 21-cm line is a challenging task. Here we formulate the detection of the EoR signal using the drift scan strategy. This method potentially has better instrumental stability as compared to the case where a single patch of sky is tracked. We demonstrate that the correlation time between measured visibilities could extend up to 1-2 hr for an interferometer array such as the Murchison Widefield Array (MWA), which has a wide primary beam. We estimate the EoR power based on cross-correlation of visibilities across time and show that the drift scan strategy is capable of the detection of the EoR signal with comparable/better signal-to-noise as compared to the tracking case. We also estimate the visibility correlation for a set of bright point sources and argue that the statistical inhomogeneity of bright point sources might allow their separation from the EoR signal., Comment: 23 pages, 14 figures, accepted for publication in ApJ
Published: 2014
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8. A study of fundamental limitations to statistical detection of redshifted HI from the epoch of reionization

Author: Thyagarajan, Nithyanandan, Shankar, N. Udaya, Subrahmanyan, Ravi, Arcus, Wayne, Bernardi, Gianni, Bowman, Judd D., Briggs, Frank, Bunton, John D., Cappallo, Roger J., Corey, Brian E., deSouza, Ludi, Emrich, David, Gaensler, Bryan M., Goeke, Robert F., Greenhill, Lincoln J., Hazelton, Bryna J., Herne, David, Hewitt, Jacqueline N., Johnston-Hollitt, Melanie, Kaplan, David L., Kasper, Justin C., Kincaid, Barton B., Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin J., Lynch, Mervyn J., McWhirter, S. Russell, Mitchell, Daniel A., Morales, Miguel F., Morgan, Edward H., Oberoi, Divya, Ord, Stephen M., Pathikulangara, Joseph, Remillard, Ronald A., Rogers, Alan E. E., Roshi, Anish A., Salah, Joseph E., Sault, Robert J., Srivani, K. S., Stevens, Jamie B., Thiagaraj, Prabu, Tingay, Steven J., Wayth, Randall B., Waterson, Mark, Webster, Rachel L., Whitney, Alan R., Williams, Andrew J., Williams, Christopher L., and Wyithe, J. Stuart B.
Subjects: Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: In this paper we explore for the first time the relative magnitudes of three fundamental sources of uncertainty, namely, foreground contamination, thermal noise and sample variance in detecting the HI power spectrum from the Epoch of Reionization (EoR). We derive limits on the sensitivity of a Fourier synthesis telescope to detect EoR based on its array configuration and a statistical representation of images made by the instrument. We use the Murchison Widefield Array (MWA) configuration for our studies. Using a unified framework for estimating signal and noise components in the HI power spectrum, we derive an expression for and estimate the contamination from extragalactic point-like sources in three-dimensional k-space. Sensitivity for EoR HI power spectrum detection is estimated for different observing modes with MWA. With 1000 hours of observing on a single field using the 128-tile MWA, EoR detection is feasible (S/N > 1 for $k\lesssim 0.8$ Mpc$^{-1}$). Bandpass shaping and refinements to the EoR window are found to be effective in containing foreground contamination, which makes the instrument tolerant to imaging errors. We find that for a given observing time, observing many independent fields of view does not offer an advantage over a single field observation when thermal noise dominates over other uncertainties in the derived power spectrum., Comment: 19 pages, 14 figures (19 figures in total including subfigures), 2 appendices, in press for publication in ApJ
Published: 2013
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9. Science with the Murchison Widefield Array

Author: Bowman, Judd D., Cairns, Iver, Kaplan, David L., Murphy, Tara, Oberoi, Divya, Staveley-Smith, Lister, Arcus, Wayne, Barnes, David G., Bernardi, Gianni, Briggs, Frank H., Brown, Shea, Bunton, John D., Burgasser, Adam J., Cappallo, Roger J., Chatterjee, Shami, Corey, Brian E., Coster, Anthea, Deshpande, Avinash, deSouza, Ludi, Emrich, David, Erickson, Philip, Goeke, Robert F., Gaensler, B. M., Greenhill, Lincoln J., Harvey-Smith, Lisa, Hazelton, Bryna J., Herne, David, Hewitt, Jacqueline N., Johnston-Hollitt, Melanie, Kasper, Justin C., Kincaid, Barton B., Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin J., Lynch, Mervyn J., Matthews, Lynn D., McWhirter, S. Russell, Mitchell, Daniel A., Morales, Miguel F., Morgan, Edward H., Ord, Stephen M., Pathikulangara, Joseph, Thiagaraj, Prabu, Remillard, Ronald A., Robishaw, Timothy, Rogers, Alan E. E., Roshi, Anish A., Salah, Joseph E., Sault, Robert J., Shankar, N. Udaya, Srivani, K. S., Stevens, Jamie B., Subrahmanyan, Ravi, Tingay, Steven J., Wayth, Randall B., Waterson, Mark, Webster, Rachel L., Whitney, Alan R., Williams, Andrew J., Williams, Christopher L., and Wyithe, J. Stuart B.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics
Abstract: Significant 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 epoch of reionisation 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., Comment: Updated with revisions. 32 pages including figures and references. Submitted to PASA
Published: 2012
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10. Fast Holographic Deconvolution: a new technique for precision radio interferometry

Author: Sullivan, Ian, Morales, Miguel, Hazelton, Bryna, Arcus, Wayne, Barnes, David, Bernardi, Gianni, Briggs, Frank, Bowman, Judd D., Bunton, John, Cappallo, Roger, Corey, Brian, Deshpande, Avinash, deSouza, Ludi, Emrich, David, Gaensler, B. M., Goeke, Robert, Greenhill, Lincoln, Herne, David, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kaplan, David, Kasper, Justin, Kincaid, Barton, Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, Russell, Mitchell, Daniel, Morgan, Edward, Oberoi, Divya, Ord, Stephen, Pathikulangara, Joseph, Prabu, Thiagaraj, Remillard, Ron, Rogers, Alan, Roshi, Anish, Salah, Joseph, Sault, Robert, Shankar, Udaya, Srivani, K., Stevens, Jamie, Subrahmanyan, Ravi, Tingay, Steven, Wayth, Randall, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, Andrew, Williams, Chris, and Wyithe, Stuart
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Extragalactic Astrophysics
Abstract: We introduce the Fast Holographic Deconvolution method for analyzing interferometric radio data. Our new method is an extension of A-projection/software-holography/forward modeling analysis techniques and shares their precision deconvolution and widefield polarimetry, while being significantly faster than current implementations that use full direction-dependent antenna gains. Using data from the MWA 32 antenna prototype, we demonstrate the effectiveness and precision of our new algorithm. Fast Holographic Deconvolution may be particularly important for upcoming 21 cm cosmology observations of the Epoch of Reionization and Dark Energy where foreground subtraction is intimately related to the precision of the data reduction., Comment: ApJ accepted
Published: 2012
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11. Direction-Dependent Polarised Primary Beams in Wide-Field Synthesis Imaging

Author: Mitchell, Daniel A., Wayth, Randall B., Bernardi, Gianni, Greenhill, Lincoln J., and Ord, Stephen M.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Extragalactic Astrophysics
Abstract: The process of wide-field synthesis imaging is explored, with the aim of understanding the implications of variable, polarised primary beams for forthcoming Epoch of Reionisation experiments. These experiments seek to detect weak signatures from redshifted 21cm emission in deep residual datasets, after suppression and subtraction of foreground emission. Many subtraction algorithms benefit from low side-lobes and polarisation leakage at the outset, and both of these are intimately linked to how the polarised primary beams are handled. Building on previous contributions from a number of authors, in which direction-dependent corrections are incorporated into visibility gridding kernels, we consider the special characteristics of arrays of fixed dipole antennas operating around 100-200 MHz, looking towards instruments such as the Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Arrays (HERA). We show that integrating snapshots in the image domain can help to produce compact gridding kernels, and also reduce the need to make complicated polarised leakage corrections during gridding. We also investigate an alternative form for the gridding kernel that can suppress variations in the direction-dependent weighting of gridded visibilities by 10s of dB, while maintaining compact support., Comment: 15 pages, 4 figures. Accepted for publication in JAI
Published: 2012

12. Low Frequency Imaging of Fields at High Galactic Latitude with the Murchison Widefield Array 32-Element Prototype

Author: Williams, Christopher L., Hewitt, Jacqueline N., Levine, Alan M., de Oliveira-Costa, Angelica, Bowman, Judd D., Briggs, Frank H., Gaensler, B. M., Hernquist, Lars L., Mitchell, Daniel A., Morales, Miguel F., Sethi, Shiv K., Subrahmanyan, Ravi, Sadler, Elaine M., Arcus, Wayne, Barnes, David G., Bernardi, Gianni, Bunton, John D., Cappallo, Roger C., Crosse, Brian W., Corey, Brian E., Deshpande, Avinash, deSouza, Ludi, Emrich, David, Goeke, Robert F., Greenhill, Lincoln J., Hazelton, Bryna J., Herne, David, Kaplan, David L., Kasper, Justin C., Kincaid, Barton B., Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin J., Lynch, Mervyn J., McWhirter, S. Russell, Mitchell, %Daniel A., Morales, %Miguel F., Morgan, Edward H., Oberoi, Divya, Ord, Stephen M., Pathikulangara, Joseph, Prabu, Thiagaraj, Remillard, Ronald A., Rogers, Alan E. E., Roshi, Anish A., Salah, Joseph E., Sault, Robert J., Shankar, N. Udaya, Srivani, K. S., Stevens, Jamie B., Tingay, Steven J., Wayth, Randall B., Waterson, Mark, Webster, Rachel L., Whitney, Alan R., Williams, Andrew J., and Wyithe, J. Stuart B.
Subjects: Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: The Murchison Widefield Array (MWA) is a new low-frequency, wide field-of-view radio interferometer under development at the Murchison Radio-astronomy Observatory (MRO) in Western Australia. We have used a 32-element MWA prototype interferometer (MWA-32T) to observe two 50-degree diameter fields in the southern sky in the 110 MHz to 200 MHz band in order to evaluate the performance of the MWA-32T, to develop techniques for epoch of reionization experiments, and to make measurements of astronomical foregrounds. We developed a calibration and imaging pipeline for the MWA-32T, and used it to produce ~15' angular resolution maps of the two fields. We perform a blind source extraction using these confusion-limited images, and detect 655 sources at high significance with an additional 871 lower significance source candidates. We compare these sources with existing low-frequency radio surveys in order to assess the MWA-32T system performance, wide field analysis algorithms, and catalog quality. Our source catalog is found to agree well with existing low-frequency surveys in these regions of the sky and with statistical distributions of point sources derived from Northern Hemisphere surveys; it represents one of the deepest surveys to date of this sky field in the 110 MHz to 200 MHz band., Comment: 20 pages, 6 tables, 12 figures. 1 online-only machine readable table. Submitted to ApJ
Published: 2012
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13. First Spectroscopic Imaging Observations of the Sun at Low Radio Frequencies with the Murchison Widefield Array Prototype

Author: Oberoi, Divya, Matthews, Lynn D., Cairns, Iver H., Emrich, David, Lobzin, Vasili, Lonsdale, Colin J., Morgan, Edward H., Prabu, T., Vedantham, Harish, Wayth, Randall B., Williams, Andrew, Williams, Christopher, White, Stephen M., Allen, G., Arcus, Wayne, Barnes, David, Benkevitch, Leonid, Bernardi, Gianni, Bowman, Judd D., Briggs, Frank H., Bunton, John D., Burns, Steve, Cappallo, Roger C., Clark, M. A., Corey, Brian E., Dawson, M., DeBoer, David, De Gans, A., deSouza, Ludi, Derome, Mark, Edgar, R. G., Elton, T., Goeke, Robert, Gopalakrishna, M. R., Greenhill, Lincoln J., Hazelton, Bryna, Herne, David, Hewitt, Jacqueline N., Kamini, P. A., Kaplan, David L., Kasper, Justin C., Kennedy, Rachel, Kincaid, Barton B., Kocz, Jonathan, Koeing, R., Kowald, Errol, Lynch, Mervyn J., Madhavi, S., McWhirter, Stephen R., Mitchell, Daniel A., Morales, Miguel F., Ng, A., Ord, Stephen M., Pathikulangara, Joseph, Rogers, Alan E. E., Roshi, Anish, Salah, Joseph E., Sault, Robert J., Schinckel, Antony, Shankar, N. Udaya, Srivani, K. S., Stevens, Jamie, Subrahmanyan, Ravi, Thakkar, D., Tingay, Steven J., Tuthill, J., Vaccarella, Annino, Waterson, Mark, Webster, Rachel L., and Whitney, Alan R.
Subjects: Astrophysics - Solar and Stellar Astrophysics
Abstract: We present the first spectroscopic images of solar radio transients from the prototype for the Murchison Widefield Array (MWA), observed on 2010 March 27. Our observations span the instantaneous frequency band 170.9-201.6 MHz. Though our observing period is characterized as a period of `low' to `medium' activity, one broadband emission feature and numerous short-lived, narrowband, non-thermal emission features are evident. Our data represent a significant advance in low radio frequency solar imaging, enabling us to follow the spatial, spectral, and temporal evolution of events simultaneously and in unprecedented detail. The rich variety of features seen here reaffirms the coronal diagnostic capability of low radio frequency emission and provides an early glimpse of the nature of radio observations that will become available as the next generation of low frequency radio interferometers come on-line over the next few years., Comment: 15 pages, 5 figures, accepted for publication in Astrophysical Journal Letters. Movies for figures 4 and 5 available at http://www.mwatelescope.org/info/mwa_proto.html
Published: 2011
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14. The Murchison Widefield Array

Author: Mitchell, Daniel A., Greenhill, Lincoln J., Ord, Stephen M., Bernardi, Gianni, Wayth, Randall B., Edgar, Richard G., Clark, Michael A., Dal, Kevin, Pfister, Hanspeter, Gleadow, Stewart J., Arcus, W., Briggs, F. H., Benkevitch, L., Bowman, J. D., Bunton, J. D., Burns, S., Cappallo, R. J., Corey, B. E., de Oliveira-Costa, A., Desouza, L., Doeleman, S. S., Derome, M. F., Emrich, D., Glossop, M., Goeke, R., Krishna, M. R. Gopala, Hazelton, B., Herne, D. E., Hewitt, J. N., Kamini, P. A., Kaplan, D. L., Kasper, J. C., Kincaid, B. B., Kocz, J., Kowald, E., Kratzenberg, E., Kumar, D., Lonsdale, C. J., Lynch, M. J., Madhavi, S., Matejek, M., McWhirter, S. R., Morales, M. F., Morgan, E., Oberoi, D., Pathikulangara, J., Prabu, T., Rogers, A., Salah, J. E., Sault, R. J., Shankar, N. Udaya, Srivani, K. S., Stevens, J., Tingay, S. J., Vaccarella, A., Waterson, M., Webster, R. L., Whitney, A. R., Williams, A., and Williams, C.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Widefield Array to employ a simple RFI blanking scheme and still calibrate visibilities and form images in the FM radio band. The techniques described are running autonomously in our calibration and imaging software, which is currently being used to process an FM-band survey of the entire southern sky., Comment: Accepted for publication in Proceedings of Science [PoS(RFI2010)016]. 6 pages and 3 figures. Presented at RFI2010, the Third Workshop on RFI Mitigation in Radio Astronomy, 29-31 March 2010, Groningen, The Netherlands
Published: 2010

15. The Problems and the Solutions of the Metacomputing Experiment in SC99

Author: Pickles, Stephen, Costen, Fumie, Brooke, John, Gabriel, Edgar, Müller, Matthias, Resch, Michael, Ord, Stephen, Goos, Gerhard, editor, Hartmanis, Juris, editor, van Leeuwen, Jan, editor, Bubak, Marian, editor, Afsarmanesh, Hamideh, editor, Hertzberger, Bob, editor, and Williams, Roy, editor
Published: 2000
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16. The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14,110 Compact Radio Sources over 6,100 Square Degrees

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Hurley-Walker, Natasha, Morgan, John, Wayth, Randall B., Hancock, Paul J., Bell, Martin E., Bernardi, Gianni, Bhat, Ramesh, Briggs, Frank, Deshpande, Avinash A., Ewall-Wice, Aaron Michael, Feng, Lu, Hazelton, Bryna J., Hindson, Luke, Jacobs, Daniel C., Kaplan, David L., Kudryavtseva, Nadia, Lenc, Emil, McKinley, Benjamin, Mitchell, Daniel, Pindor, Bart, Procopio, Pietro, Oberoi, Divya, Offringa, Andre, Ord, Stephen, Riding, Jennifer, Bowman, Judd D., Cappallo, Roger, Corey, Brian, Emrich, David, Gaensler, B. M., Goeke, Robert F, Greenhill, Lincoln, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kasper, Justin, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, Russell, Morales, Miguel F., Morgan, Edward H, Prabu, Thiagaraj, Rogers, Alan, Roshi, Anish, Shankar, Udaya, Srivani, K., Subrahmanyan, Ravi, Tingay, Steven, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, Andrew, Williams, Chris, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Hurley-Walker, Natasha, Morgan, John, Wayth, Randall B., Hancock, Paul J., Bell, Martin E., Bernardi, Gianni, Bhat, Ramesh, Briggs, Frank, Deshpande, Avinash A., Ewall-Wice, Aaron Michael, Feng, Lu, Hazelton, Bryna J., Hindson, Luke, Jacobs, Daniel C., Kaplan, David L., Kudryavtseva, Nadia, Lenc, Emil, McKinley, Benjamin, Mitchell, Daniel, Pindor, Bart, Procopio, Pietro, Oberoi, Divya, Offringa, Andre, Ord, Stephen, Riding, Jennifer, Bowman, Judd D., Cappallo, Roger, Corey, Brian, Emrich, David, Gaensler, B. M., Goeke, Robert F, Greenhill, Lincoln, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kasper, Justin, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, Russell, Morales, Miguel F., Morgan, Edward H, Prabu, Thiagaraj, Rogers, Alan, Roshi, Anish, Shankar, Udaya, Srivani, K., Subrahmanyan, Ravi, Tingay, Steven, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, Andrew, and Williams, Chris
Abstract: We present the results of an approximately 6,100 deg[superscript 2] 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 [superscript -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. Keywords: surveys; radio continuum; general - surveys - techniques; interferometric
Published: 2020

17. The SKA Science Data Processor (SDP): final design and getting ready for the construction phase

Author: Guzman, Juan Carlos and Ord, Stephen
Abstract: The Square Kilometre Array (SKA) project is an international effort to build the world's largest radio telescope, led by the SKA Organisation based at the Jodrell Bank Observatory near Manchester, UK. The SKA will conduct transformational science to improve our understanding of the Universe and the laws of fundamental physics, monitoring the sky in unprecedented detail and mapping it hundreds of times faster than any current facility. On 12 March 2019, members of 7 countries signed the international treaty that marks the beginning of the establishment of the SKA Observatory as the intergovernmental organisation responsible of the delivery and operations of this new radio telescope. Currently almost all the elements of the SKA have completed its design work and the project is now moving towards the construction phase. The Science Data Processor (SDP) element finished its engineering design work at the end of March 2019 completing almost 5 years of designing the computing software and hardware systems responsible of processing the vast amount of data coming from the telescopes (~ 5 Tb/s). It is estimated that the SDP will produce and distribute approx. 1 PB of science-ready products per day to astronomers across the globe. This sheer amount of processing capability will be made possible by dedicated High Performance Computing (HPC) platforms deployed in Australia and South Africa for a combined peak processing power of approx. 250 PFLOPS. This design effort was completed by the SDP consortium, a collaboration of astrophysicists, engineers and computer scientists working in 11 countries worldwide and led by the University of Cambridge. This paper will present a status of the SKA project, a summary of the SDP design work and what lies ahead towards the construction phase.
Published: 2019
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18. NASA Facts: Edison Demonstration of Spacecraft Networks (EDSN) Mission

Author: Ord, Stephen, Yost, Bruce D, and Petro, Andrew J
Subjects: Communications And Radar
Abstract: NASA's Edison Demonstration of Smallsat Networks (EDSN) mission will launch and deploy a swarm of 8 cubesats into a loose formation approximately 500 km above Earth. EDSN will develop technology to send multiple, advanced, yet affordable nanosatellites into space with cross-link communications to enable a wide array of scientific, commercial, and academic research. Other goals of the mission include lowering the cost and shortening the development time for future small spacecraft.
Published: 2013

19. Innovation in Substance Misuse Services: The contribution of the health care assistant

Author: Ord, Stephen and Sims, John
Published: 2006

20. The Problems and the Solutions of the Metacomputing Experiment in SC99

Author: Pickles, Stephen, primary, Costen, Fumie, additional, Brooke, John, additional, Gabriel, Edgar, additional, Müller, Matthias, additional, Resch, Michael, additional, and Ord, Stephen, additional
Published: 2000
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21. Are we There Yet? Experiences from Developing and Commissioning the High Performance Computing (HPC) System for the ASKAP Telescope.

Author: Guzman, Juan C., Bastholm, Eric, Raja, Wasim, Whiting, Matthew, Mitchell, Daniel, Voronkov, Max, and Ord, Stephen
Published: 2019

22. Design Book nostalgia.

Author: ORD, STEPHEN
Subjects: BOOK design, NOSTALGIA, INTERNET searching
Abstract: As a longtime subscriber, I fondly remember the Design editions you used to produce. - STEPHEN ORD, London, Ont., Canada Editor's note: You're in luck. [Extracted from the article]
Published: 2023

23. CHIPS: The Cosmological H i Power Spectrum Estimator

Author: Trott, Cathryn, Pindor, B., Procopio, P., Wayth, Randall, Mitchell, D., McKinley, B., Tingay, Steven, Barry, N., Beardsley, A., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Carroll, P., Oliveira-Costa, A., Dillon, J., Ewall-Wice, A., Feng, L., Greenhill, L., Hazelton, B., Hewitt, J., Hurley-Walker, Natasha, Johnston-Hollitt, M., Jacobs, D., Kaplan, D., Kim, H., Lenc, E., Line, J., Loeb, A., Lonsdale, C., Morales, M., Morgan, E., Neben, A., Thyagarajan, N., Oberoi, D., Offringa, A., Ord, Stephen, Paul, S., Pober, J., Prabu, T., Riding, J., Shankar, N., Sethi, S., Srivani, K., Subrahmanyan, R., Sullivan, I., Tegmark, M., Webster, R., Williams, Andrew, Williams, C., Wu, C., Wyithe, J., Trott, Cathryn, Pindor, B., Procopio, P., Wayth, Randall, Mitchell, D., McKinley, B., Tingay, Steven, Barry, N., Beardsley, A., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Carroll, P., Oliveira-Costa, A., Dillon, J., Ewall-Wice, A., Feng, L., Greenhill, L., Hazelton, B., Hewitt, J., Hurley-Walker, Natasha, Johnston-Hollitt, M., Jacobs, D., Kaplan, D., Kim, H., Lenc, E., Line, J., Loeb, A., Lonsdale, C., Morales, M., Morgan, E., Neben, A., Thyagarajan, N., Oberoi, D., Offringa, A., Ord, Stephen, Paul, S., Pober, J., Prabu, T., Riding, J., Shankar, N., Sethi, S., Srivani, K., Subrahmanyan, R., Sullivan, I., Tegmark, M., Webster, R., Williams, Andrew, Williams, C., Wu, C., and Wyithe, J.
Abstract: © 2016. The American Astronomical Society. All rights reserved. Detection of the cosmological neutral hydrogen signal from the Epoch of Reionization (EoR) and estimation of its basic physical parameters are principal scientific aims of many current low-frequency radio telescopes. Here we describe the Cosmological H i Power Spectrum Estimator (CHIPS), an algorithm developed and implemented with data from the Murchison Widefield Array, to compute the two-dimensional and spherically-averaged power spectrum of brightness temperature fluctuations. The principal motivations for CHIPS are the application of realistic instrumental and foreground models to form the optimal estimator, thereby maximizing the likelihood of unbiased signal estimation, and allowing a full covariant understanding of the outputs. CHIPS employs an inverse-covariance weighting of the data through the maximum likelihood estimator, thereby allowing use of the full parameter space for signal estimation ("foreground suppression"). We describe the motivation for the algorithm, implementation, application to real and simulated data, and early outputs. Upon application to a set of 3 hr of data, we set a 2s upper limit on the EoR dimensionless power at Mpc-1 of mK2 in the redshift range z = [6.2-6.6], consistent with previous estimates.
Published: 2016

24. Simultaneous observations of giant pulses from the Crab pulsar, with the Murchison Widefield Array and Parkes radio telescope: implications for the giant pulse emission mechanism

Author: Oronsaye, S., Ord, Stephen, Bhat, Ramesh, Tremblay, Steven, McSweeney, Sam, Tingay, Steven, Van Straten, W., Jameson, A., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Deshpande, A., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Kaplan, D., Lonsdale, C., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Prabu, T., Shankar, N., Srivani, K., Subrahmanyan, R., Wayth, Randall, Webster, R., Williams, A., Williams, C., Oronsaye, S., Ord, Stephen, Bhat, Ramesh, Tremblay, Steven, McSweeney, Sam, Tingay, Steven, Van Straten, W., Jameson, A., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Deshpande, A., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Kaplan, D., Lonsdale, C., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Prabu, T., Shankar, N., Srivani, K., Subrahmanyan, R., Wayth, Randall, Webster, R., Williams, A., and Williams, C.
Abstract: We report on observations of giant pulses from the Crab pulsar performed simultaneously with the Parkes radio telescope and the incoherent combination of the Murchison Widefield Array (MWA) antenna tiles. The observations were performed over a duration of approximately one hour at a center frequency of 1382 MHz with 340 MHz bandwidth at Parkes, and at a center frequency of 193 MHz with 15 MHz bandwidth at the MWA. Our analysis has led to the detection of 55 giant pulses at the MWA and 2075 at Parkes above a threshold of 3.5σ and 6.5σ, respectively. We detected 51% of the MWA giant pulses at the Parkes radio telescope, with spectral indices in the range of-3.6 > α > -4.9 (Sv μ ∝ Va). We present a Monte Carlo analysis supporting the conjecture that the giant pulse emission in the Crab is intrinsically broadband, the less than 100% correlation being due to the relative sensitivities of the two instruments and the width of the spectral index distribution. Our observations are consistent with the hypothesis that the spectral index of giant pulses is drawn from normal distribution of standard deviation 0.6, but with a mean that displays an evolution with frequency from −3.00 at 1382 MHz, to −2.85 at 192 MHz.
Published: 2015

25. Modelling of the spectral energy distribution of Fornax A: leptonic and hadronic production of high-energy emission from the radio lobes

Author: McKinley, B., Yang, R., López-Caniego, M., Briggs, F., Hurley-Walker, N., Wayth, Randall, Offringa, A., Crocker, R., Bernardi, G., Procopio, P., Gaensler, B., Tingay, Steven, Johnston-Hollitt, M., McDonald, M., Bell, M., Bhat, N., Bowman, J., Cappallo, R., Corey, B., Deshpande, A., Emrich, D., Ewall-Wice, A., Feng, L., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Hindson, L., Jacobs, D., Kaplan, D., Kasper, J., Kratzenberg, E., Kudryavtseva, N., Lenc, E., Lonsdale, C., Lynch, M., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Pindor, B., Prabu, T., Riding, J., Rogers, A., Roshi, D., Shankar, N., Srivani, K., Subrahmanyan, R., Waterson, M., Webster, R., Whitney, A., Williams, A., Williams, C., McKinley, B., Yang, R., López-Caniego, M., Briggs, F., Hurley-Walker, N., Wayth, Randall, Offringa, A., Crocker, R., Bernardi, G., Procopio, P., Gaensler, B., Tingay, Steven, Johnston-Hollitt, M., McDonald, M., Bell, M., Bhat, N., Bowman, J., Cappallo, R., Corey, B., Deshpande, A., Emrich, D., Ewall-Wice, A., Feng, L., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Hindson, L., Jacobs, D., Kaplan, D., Kasper, J., Kratzenberg, E., Kudryavtseva, N., Lenc, E., Lonsdale, C., Lynch, M., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Pindor, B., Prabu, T., Riding, J., Rogers, A., Roshi, D., Shankar, N., Srivani, K., Subrahmanyan, R., Waterson, M., Webster, R., Whitney, A., Williams, A., and Williams, C.
Abstract: We present new low-frequency observations of the nearby radio galaxy Fornax A at 154 MHz with the Murchison Widefield Array, microwave flux-density measurements obtained from WMAP and Planck data, and γ-ray flux densities obtained from Fermi data. We also compile a comprehensive list of previously published images and flux-density measurements at radio, microwave and X-ray energies. A detailed analysis of the spectrum of Fornax A between 154 and 1510 MHz reveals that both radio lobes have a similar spatially averaged spectral index, and that there exists a steep-spectrum bridge of diffuse emission between the lobes. Taking the spectral index of both lobes to be the same, we model the spectral energy distribution of Fornax A across an energy range spanning 18 orders of magnitude, to investigate the origin of the X-ray and γ-ray emission. A standard leptonic model for the production of both the X-rays and γ-rays by inverse-Compton scattering does not fit the multiwavelength observations. Our results best support a scenario where the X-rays are produced by inverse-Compton scattering and the γ-rays are produced primarily by hadronic processes confined to the filamentary structures of the Fornax A lobes.
Published: 2015

26. Limits on low-frequency radio emission from southern exoplanets with the Murchison Widefield Array

Author: Murphy, T., Bell, M., Kaplan, D., Gaensler, B., Offringa, A., Lenc, E., Hurley-Walker, N., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Deshpande, A., Emrich, D., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Johnston-Hollitt, M., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Rogers, A., Roshi, D., Shankar, N., Srivani, K., Subrahmanyan, R., Tingay, Steven, Waterson, M., Wayth, Randall, Webster, R., Whitney, A., Williams, A., Williams, C., Murphy, T., Bell, M., Kaplan, D., Gaensler, B., Offringa, A., Lenc, E., Hurley-Walker, N., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Deshpande, A., Emrich, D., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Johnston-Hollitt, M., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Rogers, A., Roshi, D., Shankar, N., Srivani, K., Subrahmanyan, R., Tingay, Steven, Waterson, M., Wayth, Randall, Webster, R., Whitney, A., Williams, A., and Williams, C.
Abstract: We present the results of a survey for low-frequency radio emission from 17 known exoplanetary systems with the Murchison Widefield Array. This sample includes 13 systems that have not previously been targeted with radio observations. We detected no radio emission at 154 MHz, and put 3σ upper limits in the range 15.2–112.5 mJy on this emission. We also searched for circularly polarized emission and made no detections, obtaining 3σ upper limits in the range 3.4–49.9 mJy. These are comparable with the best low-frequency radio limits in the existing literature and translate to luminosity limits of between 1.2 × 1014 and 1.4 × 1017 W if the emission is assumed to be 100 per cent circularly polarized. These are the first results from a larger program to systematically search for exoplanetary emission with the MWA.
Published: 2015

27. Foregrounds in wide-field Redshifted 21 cm power spectra

Author: Thyagarajan, N., Jacobs, D., Bowman, J., Barry, N., Beardsley, A., Bernardi, G., Briggs, F., Cappallo, R., Carroll, P., Corey, B., Oliveira-Costa, A., Dillon, J., Emrich, D., Ewall-Wice, A., Feng, L., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Hurley-Walker, N., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kim, H., Kittiwisit, P., Kratzenberg, E., Lenc, E., Line, J., Loeb, A., Lonsdale, C., Lynch, Mervyn, McKinley, B., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Neben, A., Oberoi, D., Offringa, A., Ord, Stephen, Paul, S., Pindor, B., Pober, J., Prabu, T., Procopio, P., Riding, J., Rogers, A., Roshi, A., Shankar, N., Sethi, S., Srivani, K., Subrahmanyan, R., Sullivan, I., Tegmark, M., Tingay, Steven, Trott, C., Waterson, M., Wayth, Randall, Webster, R., Whitney, A., Williams, A., Williams, C., Wu, C., Wyithe, J., Thyagarajan, N., Jacobs, D., Bowman, J., Barry, N., Beardsley, A., Bernardi, G., Briggs, F., Cappallo, R., Carroll, P., Corey, B., Oliveira-Costa, A., Dillon, J., Emrich, D., Ewall-Wice, A., Feng, L., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Hurley-Walker, N., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kim, H., Kittiwisit, P., Kratzenberg, E., Lenc, E., Line, J., Loeb, A., Lonsdale, C., Lynch, Mervyn, McKinley, B., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Neben, A., Oberoi, D., Offringa, A., Ord, Stephen, Paul, S., Pindor, B., Pober, J., Prabu, T., Procopio, P., Riding, J., Rogers, A., Roshi, A., Shankar, N., Sethi, S., Srivani, K., Subrahmanyan, R., Sullivan, I., Tegmark, M., Tingay, Steven, Trott, C., Waterson, M., Wayth, Randall, Webster, R., Whitney, A., Williams, A., Williams, C., Wu, C., and Wyithe, J.
Abstract: Detection of 21 cm emission of H I from the epoch of reionization, at redshifts z > 6, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the H I signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic pitchfork signature on the “foreground wedge” in Fourier delay space. Based on these results, we propose that selective down-weighting of data based on antenna spacing and time can mitigate foreground contamination substantially by a factor of ∼100 with negligible loss of sensitivity.
Published: 2015

28. Real-time imaging of density ducts between the plasmasphere and ionosphere

Author: Loi, S., Murphy, T., Cairns, I., Menk, F., Waters, C., Erickson, P., Trott, C., Hurley-Walker, Natasha, Morgan, John, Lenc, E., Offringa, A., Bell, M., Ekers, R., Gaensler, B., Lonsdale, C., Feng, L., Hancock, Paul, Kaplan, D., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Deshpande, A., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Mcwhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Shankar, N., Srivani, K., Subrahmanyan, R., Tingay, Steven, Wayth, Randall, Webster, R., Williams, A., Williams, C., Loi, S., Murphy, T., Cairns, I., Menk, F., Waters, C., Erickson, P., Trott, C., Hurley-Walker, Natasha, Morgan, John, Lenc, E., Offringa, A., Bell, M., Ekers, R., Gaensler, B., Lonsdale, C., Feng, L., Hancock, Paul, Kaplan, D., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Deshpande, A., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Mcwhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Shankar, N., Srivani, K., Subrahmanyan, R., Tingay, Steven, Wayth, Randall, Webster, R., Williams, A., and Williams, C.
Abstract: Ionization of the Earth's atmosphere by sunlight forms a complex, multilayered plasma environment within the Earth's magnetosphere, the innermost layers being the ionosphere and plasmasphere. The plasmasphere is believed to be embedded with cylindrical density structures (ducts) aligned along the Earth's magnetic field, but direct evidence for these remains scarce. Here we report the first direct wide-angle observation of an extensive array of field-aligned ducts bridging the upper ionosphere and inner plasmasphere, using a novel ground-based imaging technique. We establish their heights and motions by feature tracking and parallax analysis. The structures are strikingly organized, appearing as regularly spaced, alternating tubes of overdensities and underdensities strongly aligned with the Earth's magnetic field. These findings represent the first direct visual evidence for the existence of such structures.
Published: 2015

29. The spectral variability of the GHz-peaked spectrum radio source PKS 1718-649 and a comparison of absorption models

Author: Tingay, Steven, Macquart, Jean-Pierre, Collier, J., Rees, G., Callingham, J., Stevens, J., Carretti, E., Wayth, Randall, Wong, G., Trott, C., McKinley, B., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Deshpande, A., Emrich, D., Gaensler, B., Goeke, R., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Rogers, A., Roshi, A., Shankar, N., Srivani, K., Subrahmanyan, R., Waterson, M., Webster, R., Whitney, A., Williams, A., Williams, C., Tingay, Steven, Macquart, Jean-Pierre, Collier, J., Rees, G., Callingham, J., Stevens, J., Carretti, E., Wayth, Randall, Wong, G., Trott, C., McKinley, B., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Deshpande, A., Emrich, D., Gaensler, B., Goeke, R., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Rogers, A., Roshi, A., Shankar, N., Srivani, K., Subrahmanyan, R., Waterson, M., Webster, R., Whitney, A., Williams, A., and Williams, C.
Abstract: Using the new wideband capabilities of the ATCA, we obtain spectra for PKS 1718-649, a well-known gigahertzpeaked spectrum radio source. The observations, between approximately 1 and 10 GHz over 3 epochs spanning approximately 21 months, reveal variability both above the spectral peak at ~3 GHz and below the peak. The combination of the low- and high-frequency variability cannot be easily explained using a single absorption mechanism, such as free-free absorption or synchrotron self-absorption. We find that the PKS 1718-649 spectrum and its variability are best explained by variations in the free-free optical depth on our line of sight to the radio source at low frequencies (below the spectral peak) and the adiabatic expansion of the radio source itself at high frequencies (above the spectral peak). The optical depth variations are found to be plausible when X-ray continuum absorption variability seen in samples of active galactic nuclei is considered. We find that the cause of the peaked spectrum in PKS 1718-649 is most likely due to free-free absorption. In agreement with previous studies, we find that the spectrum at each epoch of observation is best fit by a free-free absorption model characterized by a power-law distribution of free-free absorbing clouds. This agreement is extended to frequencies below the 1 GHz lower limit of the ATCA by considering new observations with Parkes at 725 MHz and 199 MHz observations with the newly operational Murchison Widefield Array. These lower frequency observations argue against families of absorption models (both free-free and synchrotron self-absorption) that are based on simple homogenous structures.
Published: 2015

30. The Low-Frequency Environment of the Murchison Widefield Array: Radio-Frequency Interference Analysis and Mitigation

Author: Offringa, A., Wayth, Randall, Hurley-Walker, N., Kaplan, D., Barry, N., Beardsley, A., Bell, M., Bernardi, G., Bowman, J., Briggs, F., Callingham, J., Cappallo, R., Carroll, P., Deshpande, A., Dillon, J., Dwarakanath, K., Ewall-Wice, A., Feng, L., For, B., Gaensler, B., Greenhill, L., Hancock, P., Hazelton, B., Hewitt, J., Hindson, L., Jacobs, D., Johnston-Hollitt, M., Kapinska, A., Kim, H., Kittiwisit, P., Lenc, E., Line, J., Loeb, A., Lonsdale, C., McKinley, B., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Morgan, J., Neben, A., Oberoi, D., Ord, Stephen, Paul, S., Pindor, B., Pober, J., Prabu, T., Procopio, P., Riding, J., Shankar, N., Sethi, S., Srivani, K., Staveley-Smith, L., Subrahmanyan, R., Sullivan, I., Tegmark, M., Thyagarajan, N., Tingay, Steven, Trott, C., Webster, R., Williams, A., Williams, C., Wu, C., Wyithe, J., Zheng, Q., Offringa, A., Wayth, Randall, Hurley-Walker, N., Kaplan, D., Barry, N., Beardsley, A., Bell, M., Bernardi, G., Bowman, J., Briggs, F., Callingham, J., Cappallo, R., Carroll, P., Deshpande, A., Dillon, J., Dwarakanath, K., Ewall-Wice, A., Feng, L., For, B., Gaensler, B., Greenhill, L., Hancock, P., Hazelton, B., Hewitt, J., Hindson, L., Jacobs, D., Johnston-Hollitt, M., Kapinska, A., Kim, H., Kittiwisit, P., Lenc, E., Line, J., Loeb, A., Lonsdale, C., McKinley, B., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Morgan, J., Neben, A., Oberoi, D., Ord, Stephen, Paul, S., Pindor, B., Pober, J., Prabu, T., Procopio, P., Riding, J., Shankar, N., Sethi, S., Srivani, K., Staveley-Smith, L., Subrahmanyan, R., Sullivan, I., Tegmark, M., Thyagarajan, N., Tingay, Steven, Trott, C., Webster, R., Williams, A., Williams, C., Wu, C., Wyithe, J., and Zheng, Q.
Abstract: The Murchison Widefield Array is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array. We describe the automated radio-frequency interference detection strategy implemented for the Murchison Widefield Array, which is based on the aoflagger platform, and present 72–231 MHz radio-frequency interference statistics from 10 observing nights. Radio-frequency interference detection removes 1.1% of the data. Radio-frequency interference from digital TV is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After radio-frequency interference detection and excision, almost all data can be calibrated and imaged without further radio-frequency interference mitigation efforts, including observations within the FM and digital TV bands. The results are compared to a previously published Low-Frequency Array radio-frequency interference survey. The remote location of the Murchison Widefield Array results in a substantially cleaner radio-frequency interference environment compared to Low-Frequency Array’s radio environment, but adequate detection of radio-frequency interference is still required before data can be analysed. We include specific recommendations designed to make the Square Kilometre Array more robust to radio-frequency interference, including: the availability of sufficient computing power for radio-frequency interference detection; accounting for radio-frequency interference in the receiver design; a smooth band-pass response; and the capability of radio-frequency interference detection at high time and frequency resolution (second and kHz-scale respectively).
Published: 2015

31. The Murchison Widefield Array Correlator

Author: Ord, Stephen, Crosse, B., Emrich, D., Pallot, D., Wayth, Randall, Clark, M., Tremblay, S., Arcus, W., Barnes, D., Bell, M., Bernardi, G., Bhat, N., Bowman, J., Briggs, F., Bunton, J., Cappallo, R., Corey, B., Deshpande, A., deSouza, L., Ewell-Wice, A., Feng, L., Goeke, R., Greenhill, L., Hazelton, B., Herne, D., Hewitt, J., Hindson, L., Hurley-Walker, N., Jacobs, D., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Kudryavtseva, N., Lenc, E., Lonsdale, C., Lynch, Mervyn, McKinley, B., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Offringa, A., Pathikulangara, J., Pindor, B., Prabu, T., Procopio, P., Remillard, R., Riding, J., Rogers, A., Roshi, A., Salah, J., Sault, R., Shankar, N., Srivani, K., Stevens, J., Subrahmanyan, R., Tingay, Steven, Waterson, M., Webster, R., Whitney, A., Williams, A., Williams, C., Wyithe, J., Ord, Stephen, Crosse, B., Emrich, D., Pallot, D., Wayth, Randall, Clark, M., Tremblay, S., Arcus, W., Barnes, D., Bell, M., Bernardi, G., Bhat, N., Bowman, J., Briggs, F., Bunton, J., Cappallo, R., Corey, B., Deshpande, A., deSouza, L., Ewell-Wice, A., Feng, L., Goeke, R., Greenhill, L., Hazelton, B., Herne, D., Hewitt, J., Hindson, L., Hurley-Walker, N., Jacobs, D., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Kudryavtseva, N., Lenc, E., Lonsdale, C., Lynch, Mervyn, McKinley, B., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Offringa, A., Pathikulangara, J., Pindor, B., Prabu, T., Procopio, P., Remillard, R., Riding, J., Rogers, A., Roshi, A., Salah, J., Sault, R., Shankar, N., Srivani, K., Stevens, J., Subrahmanyan, R., Tingay, Steven, Waterson, M., Webster, R., Whitney, A., Williams, A., Williams, C., and Wyithe, J.
Abstract: The Murchison Widefield Array is a Square Kilometre Array Precursor. The telescope is located at the Murchison Radio–astronomy Observatory in Western Australia. The MWA consists of 4 096 dipoles arranged into 128 dual polarisation aperture arrays forming a connected element interferometer that cross-correlates signals from all 256 inputs. A hybrid approach to the correlation task is employed, with some processing stages being performed by bespoke hardware, based on Field Programmable Gate Arrays, and others by Graphics Processing Units housed in general purpose rack mounted servers. The correlation capability required is approximately 8 tera floating point operations per second. The MWA has commenced operations and the correlator is generating 8.3 TB day−1 of correlation products that are subsequently transferred 700 km from the MRO to Perth (WA) in real-time for storage and offline processing. In this paper, we outline the correlator design, signal path, and processing elements and present the data format for the internal and external interfaces.
Published: 2015

32. A digital-receiver for the Murchison Widefield Array

Author: Prabu, T., Srivani, K., Roshi, D., Kamini, P., Madhavi, S., Emrich, D., Crosse, B., Williams, A., Waterson, M., Deshpande, A., Shankar, N., Subrahmanyan, R., Briggs, F., Goeke, R., Tingay, Steven, Johnston-Hollitt, M., R, G., Morgan, E., Pathikulangara, J., Bunton, J., Hampson, G., Williams, C., Ord, Stephen, Wayth, Randall, Kumar, D., Morales, M., DeSouza, L., Kratzenberg, E., Pallot, D., McWhirter, R., Hazelton, B., Arcus, W., Barnes, D., Bernardi, G., Booler, T., Bowman, J., Cappallo, R., Corey, B., Greenhill, L., Herne, D., Hewitt, J., Kaplan, D., Kasper, J., Kincaid, B., Koenig, R., Lonsdale, C., Lynch, Mervyn, Mitchell, D., Oberoi, D., Remillard, R., Rogers, A., Salah, J., Sault, R., Stevens, J., Tremblay, S., Webster, R., Whitney, A., Wyithe, S., Prabu, T., Srivani, K., Roshi, D., Kamini, P., Madhavi, S., Emrich, D., Crosse, B., Williams, A., Waterson, M., Deshpande, A., Shankar, N., Subrahmanyan, R., Briggs, F., Goeke, R., Tingay, Steven, Johnston-Hollitt, M., R, G., Morgan, E., Pathikulangara, J., Bunton, J., Hampson, G., Williams, C., Ord, Stephen, Wayth, Randall, Kumar, D., Morales, M., DeSouza, L., Kratzenberg, E., Pallot, D., McWhirter, R., Hazelton, B., Arcus, W., Barnes, D., Bernardi, G., Booler, T., Bowman, J., Cappallo, R., Corey, B., Greenhill, L., Herne, D., Hewitt, J., Kaplan, D., Kasper, J., Kincaid, B., Koenig, R., Lonsdale, C., Lynch, Mervyn, Mitchell, D., Oberoi, D., Remillard, R., Rogers, A., Salah, J., Sault, R., Stevens, J., Tremblay, S., Webster, R., Whitney, A., and Wyithe, S.
Abstract: An FPGA-based digital-receiver has been developed for a low-frequency imaging radio interferometer, the Murchison Widefield Array (MWA). The MWA, located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia, consists of 128 dual-polarized aperture-array elements (tiles) operating between 80 and 300 MHz, with a total processed bandwidth of 30.72 MHz for each polarization. Radio-frequency signals from the tiles are amplified and band limited using analog signal conditioning units; sampled and channelized by digital-receivers. The signals from eight tiles are processed by a single digital-receiver, thus requiring 16 digital-receivers for the MWA. The main function of the digital-receivers is to digitize the broad-band signals from each tile, channelize them to form the sky-band, and transport it through optical fibers to a centrally located correlator for further processing. The digital-receiver firmware also implements functions to measure the signal power, perform power equalization across the band, detect interference-like events, and invoke diagnostic modes. The digital-receiver is controlled by high-level programs running on a single-board-computer. This paper presents the digital-receiver design, implementation, current status, and plans for future enhancements.
Published: 2015

33. Quantifying ionospheric effects on time-domain astrophysics with the Murchison Widefield Array

Author: Loi, S., Murphy, T., Bell, M., Kaplan, D., Lenc, E., Offringa, A., Hurley-Walker, Natasha, Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Deshpande, A., Emrich, David, Gaensler, B., Goeke, R., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Rogers, A., Roshi, A., Udaya Shankar, N., Srivani, K., Subrahmanyan, R., Tingay, Steven, Waterson, M., Wayth, Randall, Webster, R., Whitney, A., Williams, Andrew, Williams, C., Loi, S., Murphy, T., Bell, M., Kaplan, D., Lenc, E., Offringa, A., Hurley-Walker, Natasha, Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Deshpande, A., Emrich, David, Gaensler, B., Goeke, R., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Rogers, A., Roshi, A., Udaya Shankar, N., Srivani, K., Subrahmanyan, R., Tingay, Steven, Waterson, M., Wayth, Randall, Webster, R., Whitney, A., Williams, Andrew, and Williams, C.
Abstract: © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Refraction and diffraction of incoming radio waves by the ionosphere induce time variability in the angular positions, peak amplitudes and shapes of radio sources, potentially complicating the automated cross-matching and identification of transient and variable radio sources. In this work, we empirically assess the effects of the ionosphere on data taken by the Murchison Widefield Array (MWA) radio telescope. We directly examine 51 h of data observed over 10 nights under quiet geomagnetic conditions (global storm index Kp < 2), analysing the behaviour of short-time-scale angular position and peak flux density variations of around ten thousand unresolved sources. We find that while much of the variation in angular position can be attributed to ionospheric refraction, the characteristic displacements (10-20 arcsec) at 154 MHz are small enough that search radii of 1-2 arcmin should be sufficient for crossmatching under typical conditions. By examining bulk trends in amplitude variability, we place upper limits on the modulation index associated with ionospheric scintillation of 1-3 per cent for the various nights. For sources fainter than ~1 Jy, this variation is below the image noise at typical MWA sensitivities. Our results demonstrate that the ionosphere is not a significant impediment to the goals of time-domain science with the MWA at 154 MHz.
Published: 2015

34. A digital-receiver for the MurchisonWidefield Array

Author: Prabu, Thiagaraj, primary, Srivani, K. S., additional, Roshi, D. Anish, additional, Kamini, P. A., additional, Madhavi, S., additional, Emrich, David, additional, Crosse, Brian, additional, Williams, Andrew J., additional, Waterson, Mark, additional, Deshpande, Avinash A., additional, Shankar, N. Udaya, additional, Subrahmanyan, Ravi, additional, Briggs, Frank H., additional, Goeke, Robert F., additional, Tingay, Steven J., additional, Johnston-Hollitt, Melanie, additional, R, Gopalakrishna M, additional, Morgan, Edward H., additional, Pathikulangara, Joseph, additional, Bunton, John D., additional, Hampson, Grant, additional, Williams, Christopher, additional, Ord, Stephen M., additional, Wayth, Randall B., additional, Kumar, Deepak, additional, Morales, Miguel F., additional, deSouza, Ludi, additional, Kratzenberg, Eric, additional, Pallot, D., additional, McWhirter, Russell, additional, Hazelton, Bryna J., additional, Arcus, Wayne, additional, Barnes, David G., additional, Bernardi, Gianni, additional, Booler, T., additional, Bowman, Judd D., additional, Cappallo, Roger J., additional, Corey, Brian E., additional, Greenhill, Lincoln J., additional, Herne, David, additional, Hewitt, Jacqueline N., additional, Kaplan, David L., additional, Kasper, Justin C., additional, Kincaid, Barton B., additional, Koenig, Ronald, additional, Lonsdale, Colin J., additional, Lynch, Mervyn J., additional, Mitchell, Daniel A., additional, Oberoi, Divya, additional, Remillard, Ronald A., additional, Rogers, Alan E., additional, Salah, Joseph E., additional, Sault, Robert J., additional, Stevens, Jamie B., additional, Tremblay, S., additional, Webster, Rachel L., additional, Whitney, Alan R., additional, and Wyithe, Stuart B., additional
Published: 2015
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35. Serendipitous discovery of a dying Giant Radio Galaxy associated with NGC 1534, using the Murchison Widefield Array

Author: Hurley-Walker, Natasha, primary, Johnston-Hollitt, Melanie, additional, Ekers, Ron, additional, Hunstead, Richard, additional, Sadler, Elaine M., additional, Hindson, Luke, additional, Hancock, Paul, additional, Bernardi, Gianni, additional, Bowman, Judd D., additional, Briggs, Frank, additional, Cappallo, Roger, additional, Corey, Brian, additional, Deshpande, Avinash A., additional, Emrich, David, additional, Gaensler, Bryan M., additional, Goeke, Robert, additional, Greenhill, Lincoln, additional, Hazelton, Bryna J., additional, Hewitt, Jacqueline, additional, Kaplan, David L., additional, Kasper, Justin, additional, Kratzenberg, Eric, additional, Lonsdale, Colin, additional, Lynch, Mervyn, additional, Mitchell, Daniel, additional, McWhirter, Russell, additional, Morales, Miguel, additional, Morgan, Edward, additional, Oberoi, Divya, additional, Offringa, André, additional, Ord, Stephen, additional, Prabu, Thiagaraj, additional, Rogers, Alan, additional, Roshi, Anish, additional, Shankar, Udaya, additional, Srivani, K., additional, Subrahmanyan, Ravi, additional, Tingay, Steven, additional, Waterson, Mark, additional, Wayth, Randall B., additional, Webster, Rachel, additional, Whitney, Alan, additional, Williams, Andrew, additional, and Williams, Chris, additional
Published: 2015
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36. The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14 110 Compact Radio Sources over 6 100 Square Degrees

Author: Hurley-Walker, Natasha, Morgan, John, Wayth, Randall, Hancock, Paul, Bell, M., BERNARDI, G., Bhat, Ramesh, Briggs, F., Deshpande, A., Ewall-Wice, A., Feng, L., Hazelton, B., Hindson, L., Jacobs, D., KAPLAN, D., Kudryavtseva, Nadia, Lenc, E., McKinley, B., Mitchell, D., Pindor, B., Procopio, P., Oberoi, D., Offringa, A., Ord, Stephen, Riding, J., Bowman, J., Cappallo, R., Corey, B., Emrich, David, Gaensler, B., Goeke, R., Greenhill, L., Hewitt, J., Johnston-Hollitt, M., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, R., Morales, M., Morgan, E., Prabu, T., Rogers, A., Roshi, A., Shankar, U., Srivani, K., Subrahmanyan, R., Tingay, Steven, Waterson, Mark, Webster, R., Whitney, A., Williams, Andrew, Williams, C., Hurley-Walker, Natasha, Morgan, John, Wayth, Randall, Hancock, Paul, Bell, M., BERNARDI, G., Bhat, Ramesh, Briggs, F., Deshpande, A., Ewall-Wice, A., Feng, L., Hazelton, B., Hindson, L., Jacobs, D., KAPLAN, D., Kudryavtseva, Nadia, Lenc, E., McKinley, B., Mitchell, D., Pindor, B., Procopio, P., Oberoi, D., Offringa, A., Ord, Stephen, Riding, J., Bowman, J., Cappallo, R., Corey, B., Emrich, David, Gaensler, B., Goeke, R., Greenhill, L., Hewitt, J., Johnston-Hollitt, M., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, R., Morales, M., Morgan, E., Prabu, T., Rogers, A., Roshi, A., Shankar, U., Srivani, K., Subrahmanyan, R., Tingay, Steven, Waterson, Mark, Webster, R., Whitney, A., Williams, Andrew, and Williams, C.
Abstract: We 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: theMWACS. 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 centredon 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.
Published: 2014

37. Study of redshifted H I from the epoch of reionization with drift scan

Author: Paul, S., Sethi, S., Subrahmanyan, R., Udaya Shankar, N., Dwarakanath, K., Deshpande, A., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Emrich, David, Gaensler, B., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Rogers, A., Roshi, A., Srivani, K., Tingay, Steven, Wayth, Randall, Webster, R., Whitney, A., Williams, Andrew, Williams, C., Paul, S., Sethi, S., Subrahmanyan, R., Udaya Shankar, N., Dwarakanath, K., Deshpande, A., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Emrich, David, Gaensler, B., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Prabu, T., Rogers, A., Roshi, A., Srivani, K., Tingay, Steven, Wayth, Randall, Webster, R., Whitney, A., Williams, Andrew, and Williams, C.
Abstract: The detection of the Epoch of Reionization (EoR) in the redshifted 21-cm line is a challenging task. Here we formulate the detection of the EoR signal using the drift scan strategy. This method potentially has better instrumental stability as compared to the case where a single patch of sky is tracked. We demonstrate that the correlation time between measured visibilities could extend up to 1-2 hr for an interferometer array such as the Murchison Widefield Array (MWA), which has a wide primary beam. We estimate the EoR power based on cross-correlation of visibilities across time and show that the drift scan strategy is capable of the detection of the EoR signal with comparable/better signal-to-noise as compared to the tracking case. We also estimate the visibility correlation for a set of bright point sources and argue that the statistical inhomogeneity of bright point sources might allow their separation from the EoR signal.
Published: 2014

38. High time resolution radio astronomy with low-frequency interferometric arrays

Author: Bhat, N., Ord, Stephen, Tremblay, S., Tingay, Steven, Deshpande, A., Van Straten, W., Bhat, N., Ord, Stephen, Tremblay, S., Tingay, Steven, Deshpande, A., and Van Straten, W.
Abstract: High time resolution applications of radio astronomy including pulsars and fast radio bursts are proving to be incredibly scientifically rewarding in terms of the depth and breadth of new physics and astrophysics they unveil. While the use of large single-dish type instruments has been dominating the field over the past decades, with the emergence of several next-generation radio facilities including the Square Kilometre Array (SKA) pre-cursors and pathfinders, it becomes imperative to develop and master suitable high time resolution functionalities that are effective for interferometric instruments. The Murchison Widefield Array (MWA) - the low-frequency pre-cursor to the SKA - provides excellent opportunities to help realise the related goals. This paper will describe the high time resolution mode being developed for the MWA and highlight early science results, including the lowest-frequency scintillation observations of the millisecond pulsar PSR J0437-4715.
Published: 2014

39. Observing the Sun with the Murchison Widefield Array

Author: Oberoi, D., Sharma, R., Bhatnagar, S., Lonsdale, C., Matthews, L., Cairns, I., Tingay, Steven, Benkevitch, L., Donea, A., White, S., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Deshpande, A., Emrich, D., Gaensler, B., Goeke, R., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kratzenberg, E., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Offringa, A., Ord, Stephen, Prabu, T., Rogers, A., Roshi, A., Salah, J., Shankar, N., Srivani, K., Subrahmanyan, R., Waterson, M., Wayth, Randall, Webster, R., Whitney, A., William, A., Williams, C., Oberoi, D., Sharma, R., Bhatnagar, S., Lonsdale, C., Matthews, L., Cairns, I., Tingay, Steven, Benkevitch, L., Donea, A., White, S., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R., Corey, B., Deshpande, A., Emrich, D., Gaensler, B., Goeke, R., Greenhill, L., Hazelton, B., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kratzenberg, E., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Offringa, A., Ord, Stephen, Prabu, T., Rogers, A., Roshi, A., Salah, J., Shankar, N., Srivani, K., Subrahmanyan, R., Waterson, M., Wayth, Randall, Webster, R., Whitney, A., William, A., and Williams, C.
Abstract: The Sun has remained a difficult source to image for radio telescopes, especially at the low radio frequencies. Its morphologically complex emission features span a large range of angular scales and the emission mechanisms involved, span a wide range in brightness temperatures. In addition, time and frequency synthesis, the key tool used by most radio interferometers to build up information about the source being imaged is not effective for solar imaging, because many of the features of interest are short lived and change dramatically over small fractional bandwidths. Building on the advances in radio frequency technology, digital signal processing and computing, the kind of instruments needed to simultaneously capture the evolution of solar emission in time, frequency, morphology and polarization over a large spectral span with the requisite imaging fidelity, and time and frequency resolution have only recently begun to appear. Of this class of instruments, the Murchison Widefield Array (MWA) is best suited for solar observations. The MWA has now entered a routine observing phase and here we present some early examples from MWA observations.
Published: 2014

40. STUDY OF REDSHIFTED H I FROM THE EPOCH OF REIONIZATION WITH DRIFT SCAN

Author: Paul, Sourabh, primary, Sethi, Shiv K., additional, Subrahmanyan, Ravi, additional, Shankar, N. Udaya, additional, Dwarakanath, K. S., additional, Deshpande, Avinash A., additional, Bernardi, Gianni, additional, Bowman, Judd D., additional, Briggs, Frank, additional, Cappallo, Roger J., additional, Corey, Brian E., additional, Emrich, David, additional, Gaensler, Bryan M., additional, Goeke, Robert F., additional, Greenhill, Lincoln J., additional, Hazelton, Bryna J., additional, Hewitt, Jacqueline N., additional, Johnston-Hollitt, Melanie, additional, Kaplan, David L., additional, Kasper, Justin C., additional, Kratzenberg, Eric, additional, Lonsdale, Colin J., additional, Lynch, Mervyn J., additional, McWhirter, S. Russell, additional, Mitchell, Daniel A., additional, Morales, Miguel F., additional, Morgan, Edward H., additional, Oberoi, Divya, additional, Ord, Stephen M., additional, Prabu, Thiagaraj, additional, Rogers, Alan E. E., additional, Roshi, Anish A., additional, Srivani, K. S., additional, Tingay, Steven J., additional, Wayth, Randall B., additional, Waterson, Mark, additional, Webster, Rachel L., additional, Whitney, Alan R., additional, Williams, Andrew J., additional, and Williams, Christopher L., additional
Published: 2014
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41. The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14 110 Compact Radio Sources over 6 100 Square Degrees

Author: Hurley-Walker, Natasha, primary, Morgan, John, additional, Wayth, Randall B., additional, Hancock, Paul J., additional, Bell, Martin E., additional, Bernardi, Gianni, additional, Bhat, Ramesh, additional, Briggs, Frank, additional, Deshpande, Avinash A., additional, Ewall-Wice, Aaron, additional, Feng, Lu, additional, Hazelton, Bryna J., additional, Hindson, Luke, additional, Jacobs, Daniel C., additional, Kaplan, David L., additional, Kudryavtseva, Nadia, additional, Lenc, Emil, additional, McKinley, Benjamin, additional, Mitchell, Daniel, additional, Pindor, Bart, additional, Procopio, Pietro, additional, Oberoi, Divya, additional, Offringa, André, additional, Ord, Stephen, additional, Riding, Jennifer, additional, Bowman, Judd D., additional, Cappallo, Roger, additional, Corey, Brian, additional, Emrich, David, additional, Gaensler, B. M., additional, Goeke, Robert, additional, Greenhill, Lincoln, additional, Hewitt, Jacqueline, additional, Johnston-Hollitt, Melanie, additional, Kasper, Justin, additional, Kratzenberg, Eric, additional, Lonsdale, Colin, additional, Lynch, Mervyn, additional, McWhirter, Russell, additional, Morales, Miguel F., additional, Morgan, Edward, additional, Prabu, Thiagaraj, additional, Rogers, Alan, additional, Roshi, Anish, additional, Shankar, Udaya, additional, Srivani, K., additional, Subrahmanyan, Ravi, additional, Tingay, Steven, additional, Waterson, Mark, additional, Webster, Rachel, additional, Whitney, Alan, additional, Williams, Andrew, additional, and Williams, Chris, additional
Published: 2014
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42. Low-Frequency Observations of the Moon with the Murchison Widefield Array

Author: McKinley, B., Briggs, Frank, Kaplan, D., Greenhill, L., Bernardi, G., Bowman, Judd, de Oliveira-Costa, A., Tingay, Steven, Gaensler, B., Oberoi, Divya, Johnston-Hollitt, M., Arcus, Wayne, Barnes, D., Bunton, John, Cappallo, Roger, Corey, Brian, Deshpande, Avinash, DeSouza, Ludi, Emrich, D., Goeke, Robert, Hazelton, Bryna, Herne, David, Hewitt, Jacqueline, Kasper, Justin, Kincaid, Barton, Koenig, R., Kratzenberg, Eric, Lonsdale, Colin, McWhirter, S., Mitchell, D., Morales, Miguel, Morgan, Edward, Ord, Stephen, Pathikulangara, Joseph, Prabu, T., Remillard, Ron, Rogers, Alan, Roshi, Anish, Salah, J., Sault, Robert, Shankar, N Udaya, Srivani, K., Stevens, J., Subrahmanyan, R., Wayth, R., Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, A., Williams, C., Wyithe, J., McKinley, B., Briggs, Frank, Kaplan, D., Greenhill, L., Bernardi, G., Bowman, Judd, de Oliveira-Costa, A., Tingay, Steven, Gaensler, B., Oberoi, Divya, Johnston-Hollitt, M., Arcus, Wayne, Barnes, D., Bunton, John, Cappallo, Roger, Corey, Brian, Deshpande, Avinash, DeSouza, Ludi, Emrich, D., Goeke, Robert, Hazelton, Bryna, Herne, David, Hewitt, Jacqueline, Kasper, Justin, Kincaid, Barton, Koenig, R., Kratzenberg, Eric, Lonsdale, Colin, McWhirter, S., Mitchell, D., Morales, Miguel, Morgan, Edward, Ord, Stephen, Pathikulangara, Joseph, Prabu, T., Remillard, Ron, Rogers, Alan, Roshi, Anish, Salah, J., Sault, Robert, Shankar, N Udaya, Srivani, K., Stevens, J., Subrahmanyan, R., Wayth, R., Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, A., Williams, C., and Wyithe, J.
Abstract: A new generation of low-frequency radio telescopes is seeking to observe the redshifted 21 cm signal from the epoch of reionization (EoR), requiring innovative methods of calibration and imaging to overcome the difficulties of wide-field low-frequency radio interferometry. Precise calibration will be required to separate the expected small EoR signal from the strong foreground emission at the frequencies of interest between 80 and 300 MHz. The Moon may be useful as a calibration source for detection of the EoR signature, as it should have a smooth and predictable thermal spectrum across the frequency band of interest. Initial observations of the Moon with the Murchison Widefield Array 32 tile prototype show that the Moon does exhibit a similar trend to that expected for a cool thermally emitting body in the observed frequency range, but that the spectrum is corrupted by reflected radio emission from Earth. In particular, there is an abrupt increase in the observed flux density of the Moon within the internationally recognized frequency modulated (FM) radio band. The observations have implications for future low-frequency surveys and EoR detection experiments that will need to take this reflected emission from the Moon into account. The results also allow us to estimate the equivalent isotropic power emitted by the Earth in the FM band and to determine how bright the Earth might appear at meter wavelengths to an observer beyond our own solar system.
Published: 2013

43. A study of fundamental limitations to statistical detection of redshifted H I from the epoch of reionization

Author: Thyagarajan, Nithyanandan, Udaya Shankar, N., Subrahmanyan, Ravi, Arcus, Wayne, Bernardi, Gianni, Bowman, Judd, Briggs, Frank, Bunton, John, Cappallo, Roger, Corey, Brian, deSouza, Ludi, Emrich, David, Gaensler, Brian, Goeke, Robert, Greenhill, Lincoln, Hazelton, Bryna, Herne, David, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kaplan, David, Kasper, Justin, Kincaid, Barton, Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, S. Russell, Mitchell, Daniel, Morales, Miguel, Morgan, Edward, Oberoi, Divya, Ord, Stephen, Pathikulangara, Joseph, Remillard, Ronald, Rogers, Alan, Roshi, D. Anish, Salah, Joseph, Sault, Robert, Srivani, K., Stevens, Jamie, Thiagaraj, Prabu, Tingay, Steven, Wayth, Randall, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, Andrew, Williams, Christopher, Wyithe, J. Stuart, Thyagarajan, Nithyanandan, Udaya Shankar, N., Subrahmanyan, Ravi, Arcus, Wayne, Bernardi, Gianni, Bowman, Judd, Briggs, Frank, Bunton, John, Cappallo, Roger, Corey, Brian, deSouza, Ludi, Emrich, David, Gaensler, Brian, Goeke, Robert, Greenhill, Lincoln, Hazelton, Bryna, Herne, David, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kaplan, David, Kasper, Justin, Kincaid, Barton, Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, S. Russell, Mitchell, Daniel, Morales, Miguel, Morgan, Edward, Oberoi, Divya, Ord, Stephen, Pathikulangara, Joseph, Remillard, Ronald, Rogers, Alan, Roshi, D. Anish, Salah, Joseph, Sault, Robert, Srivani, K., Stevens, Jamie, Thiagaraj, Prabu, Tingay, Steven, Wayth, Randall, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, Andrew, Williams, Christopher, and Wyithe, J. Stuart
Abstract: In this paper, we explore for the first time the relative magnitudes of three fundamental sources of uncertainty, namely, foreground contamination, thermal noise, and sample variance, in detecting the H I power spectrum from the epoch of reionization (EoR). We derive limits on the sensitivity of a Fourier synthesis telescope to detect EoR based on its array configuration and a statistical representation of images made by the instrument. We use the Murchison Widefield Array (MWA) configuration for our studies. Using a unified framework for estimating signal and noise components in the H I power spectrum, we derive an expression for and estimate the contamination from extragalactic point-like sources in three-dimensional k-space. Sensitivity for EoR H I power spectrum detection is estimated for different observing modes with MWA. With 1000 hr of observing on a single field using the 128 tile MWA, EoR detection is feasible (S/N > 1 for k <~ 0.8 Mpc−1). Bandpass shaping and refinements to the EoR window are found to be effective in containing foreground contamination, which makes the instrument tolerant to imaging errors. We find that for a given observing time, observing many independent fields of view does not offer an advantage over a single field observation when thermal noise dominates over other uncertainties in the derived power spectrum.
Published: 2013

44. The Murchison Widefield Array: The Square Kilometre Array Precursor at Low Radio Frequencies

Author: Tingay, Steven, Emrich, David, Ord, Stephen, Booler, Tom, Crosse, Brian, Wayth, Randall, Tremblay, Steven, Pallot, Dave, Colegate, Timothy, Kudryavtseva, Nadia, Goeke, R., Bowman, J., Mitchell, D., Morales, M., Lonsdale, C., Colegate, T., Wicenec, A., Arcus, W., Barnes, D., Bernardi, G., Briggs, F., Burns, S., Bunton, J., Cappallo, R., Corey, B., Deshpande, A., Desouza, L., Gaensler, B., Greenhill, L., Hall, P., Hazelton, B., Herne, D., Hewitt, J., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Lynch, M., McKinley, B., McWhirter, S., Morgan, E., Oberoi, D, Pathikulangara, J., Prabu, T., Remillard, R., Rogers, A., Roshi, A., Salah, J., Sault, R., Udaya-Shankar, N., Schlagenhaufer, F., Srivani, K., Stevens, J., Subrahmanyan, R., Waterson, M., Webster, R., Whitney, A., Williams, A., Williams, C., Wyithe, J., Tingay, Steven, Emrich, David, Ord, Stephen, Booler, Tom, Crosse, Brian, Wayth, Randall, Tremblay, Steven, Pallot, Dave, Colegate, Timothy, Kudryavtseva, Nadia, Goeke, R., Bowman, J., Mitchell, D., Morales, M., Lonsdale, C., Colegate, T., Wicenec, A., Arcus, W., Barnes, D., Bernardi, G., Briggs, F., Burns, S., Bunton, J., Cappallo, R., Corey, B., Deshpande, A., Desouza, L., Gaensler, B., Greenhill, L., Hall, P., Hazelton, B., Herne, D., Hewitt, J., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Lynch, M., McKinley, B., McWhirter, S., Morgan, E., Oberoi, D, Pathikulangara, J., Prabu, T., Remillard, R., Rogers, A., Roshi, A., Salah, J., Sault, R., Udaya-Shankar, N., Schlagenhaufer, F., Srivani, K., Stevens, J., Subrahmanyan, R., Waterson, M., Webster, R., Whitney, A., Williams, A., Williams, C., and Wyithe, J.
Abstract: The Murchison Widefield Array (MWA) is one of three Square Kilometre Array Precursor telescopes and is located at the Murchison Radio-astronomy Observatory in the Murchison Shire of the mid-west of Western Australia, a location chosen for its extremely low levels of radio frequency interference. The MWA operates at low radio frequencies, 80–300 MHz, with a processed bandwidth of 30.72 MHz for both linear polarisations, and consists of 128 aperture arrays (known as tiles) distributed over a ~3-km diameter area. Novel hybrid hardware/software correlation and a real-time imaging and calibration systems comprise the MWA signal processing backend. In this paper, the as-built MWA is described both at a system and sub-system level, the expected performance of the array is presented, and the science goals of the instrument are summarised.
Published: 2013

45. The giant lobes of Centaurus A observed at 118MHz with the Murchison Widefield Array

Author: McKinley, B., Briggs, F., Gaensler, B., Feain, I., Bernardi, G., Wayth, Randall, Johnston-Hollitt, M., Offringa, A., Arcus, Wayne, Barnes, D., Bowman, J., Bunton, J., Capallo, R., Corey, B., Deshpande, A., deSouza, L., Emrich, David, Goeke, R., Greenhill, L., Hazelton, B., Herne, David, Hewitt, J., Kaplan, David, Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Pathikulangara, J., Prabu, T., Remillard, R., Rogers, A., Roshi, D., Salah, J., Sault, R., Udaya Shankar, N., Srivani, K., Stevens, J., Subrahmanyan, R., Tingay, Steven, Waterson, Mark, Webster, R., Whitney, A., Williams, Andrew, Williams, C., Wyithe, J., McKinley, B., Briggs, F., Gaensler, B., Feain, I., Bernardi, G., Wayth, Randall, Johnston-Hollitt, M., Offringa, A., Arcus, Wayne, Barnes, D., Bowman, J., Bunton, J., Capallo, R., Corey, B., Deshpande, A., deSouza, L., Emrich, David, Goeke, R., Greenhill, L., Hazelton, B., Herne, David, Hewitt, J., Kaplan, David, Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Pathikulangara, J., Prabu, T., Remillard, R., Rogers, A., Roshi, D., Salah, J., Sault, R., Udaya Shankar, N., Srivani, K., Stevens, J., Subrahmanyan, R., Tingay, Steven, Waterson, Mark, Webster, R., Whitney, A., Williams, Andrew, Williams, C., and Wyithe, J.
Abstract: We present new wide-field observations of Centaurus A (Cen A) and the surrounding region at 118MHz with the Murchison Widefield Array (MWA) 32-tile prototype, with which we investigate the spectral-index distribution of Cen A’s giant radio lobes. We compare our images to 1.4 GHz maps of Cen A and compute spectral indices using temperature–temperature plots and spectral tomography. We find that the morphologies at 118MHz and 1.4 GHz match very closely apart from an extra peak in the southern lobe at 118 MHz, which provides tentative evidence for the existence of a southern counterpart to the northern middle lobe of Cen A. Our spatially averaged spectral indices for both the northern and southern lobes are consistent with previous analyses, however we find significant spatial variation of the spectra across the extent of each lobe. Both the spectral-index distribution and the morphology at low radio frequencies support a scenario of multiple outbursts of activity from the central engine. Our results are consistent with inverse-Compton modelling of radio and gamma-ray data that support a value for the lobe age of between 10 and 80 Myr.
Published: 2013

46. A survey for transients and variables with the Murchison Widefield Array 32-tile prototype at 154 MHz

Author: Trott, Cathryn, Hurley-Walker, Natasha, Wayth, Randall, Macquart, Jean-Pierre, Arcus, Wayne, Emrich, David, Herne, David, Lynch, Mervyn, Ord, Stephen, Tingay, Steven, Waterson, Mark, Williams, Andrew, Bell, M., Murphy, T., Kaplan, D., Hancock, P., Gaensler, B., Banyer, J., Bannister, K., Barnes, D., Bernardi, G., Bowman, J., Briggs, F., Bunton, J., Cappallo, R., Corey, B., Deshpande, A., deSouza, L., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Johnston-Hollitt, M., Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Lonsdale, C., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Pathikulangara, J., Prabu, T., Remillard, R., Rogers, A., Roshi, A., Salah, J., Sault, R., Udaya Shankar, N., Srivani, K., Stevens, J., Subrahmanyan, R., Webster, R., Whitney, A., Williams, C., Wyithe, J., Trott, Cathryn, Hurley-Walker, Natasha, Wayth, Randall, Macquart, Jean-Pierre, Arcus, Wayne, Emrich, David, Herne, David, Lynch, Mervyn, Ord, Stephen, Tingay, Steven, Waterson, Mark, Williams, Andrew, Bell, M., Murphy, T., Kaplan, D., Hancock, P., Gaensler, B., Banyer, J., Bannister, K., Barnes, D., Bernardi, G., Bowman, J., Briggs, F., Bunton, J., Cappallo, R., Corey, B., Deshpande, A., deSouza, L., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Johnston-Hollitt, M., Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Lonsdale, C., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Pathikulangara, J., Prabu, T., Remillard, R., Rogers, A., Roshi, A., Salah, J., Sault, R., Udaya Shankar, N., Srivani, K., Stevens, J., Subrahmanyan, R., Webster, R., Whitney, A., Williams, C., and Wyithe, J.
Abstract: We present a search for transient and variable radio sources at 154 MHz with the Murchison Widefield Array 32-tile prototype. Fifty-one images were obtained that cover a field of view of 1430 deg2 centred on Hydra A. The observations were obtained over three days in 2010 March and three days in 2011 April and May. The mean cadence of the observations was 26 minutes and there was additional temporal information on day and year timescales. We explore the variability of a sample of 105 low frequency radio sources within the field. Four bright (S > 6 Jy) candidate variable radio sources were identified that displayed low levels of short timescale variability (26 minutes). We conclude that this variability is likely caused by simplifications in the calibration strategy or ionospheric effects. On the timescale of one year we find two sources that show significant variability. We attribute this variability to either refractive scintillation or intrinsic variability. No radio transients were identified and we place an upper limit on the surface density of sources p < 7.5 × 10-5 deg-2 with flux densities > 5.5 Jy, and characteristic timescales of both 26 minutes and one year.
Published: 2013

47. Science with the Murchison Widefield Array

Author: Arcus, Wayne, Emrich, David, Herne, David, Lynch, Mervyn, Ord, Stephen, Tingay, Steven, Wayth, Randall, Waterson, Mark, Bowman, Judd, Cairns, Iver, Kaplan, David, Murphy, Tara, Oberoi, Divya, Staveley-Smith, Lister, Barnes, David, Bernardi, Gianni, Briggs, Frank, Brown, Shea, Bunton, John, Burgasser, Adam, Cappallo, Roger, Chatterjee, Shami, Corey, Brian, Coster, Anthea, Deshpande, Avinash, DeSouza, Ludi, Erickson, Philip, Goeke, Robert, Gaensler, B.M., Greenhill, Lincoln, Harvey-Smith, Lisa, Hazelton, Bryna, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kasper, Justin, Kincaid, Barton, Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin, Matthews, Lynn, McWhirter, S. Russell, Mitchell, Daniel, Morales, Miguel, Morgan, Edward, Pathikulangara, Joseph, Prabu, Thiagaraj, Remillard, Ronald, Robishaw, Timothy, Rogers, Alan, Roshi, Anish, Salah, Joseph, Sault, Robert, Udaya Shankar, N., Srivani, K.S., Stevens, Jamie, Subrahmanyan, Ravi, Webster, Rachel, Whitney, Alan, Williams, Andrew, Williams, Christopher, Wyithe, J. Stuart, Arcus, Wayne, Emrich, David, Herne, David, Lynch, Mervyn, Ord, Stephen, Tingay, Steven, Wayth, Randall, Waterson, Mark, Bowman, Judd, Cairns, Iver, Kaplan, David, Murphy, Tara, Oberoi, Divya, Staveley-Smith, Lister, Barnes, David, Bernardi, Gianni, Briggs, Frank, Brown, Shea, Bunton, John, Burgasser, Adam, Cappallo, Roger, Chatterjee, Shami, Corey, Brian, Coster, Anthea, Deshpande, Avinash, DeSouza, Ludi, Erickson, Philip, Goeke, Robert, Gaensler, B.M., Greenhill, Lincoln, Harvey-Smith, Lisa, Hazelton, Bryna, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kasper, Justin, Kincaid, Barton, Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin, Matthews, Lynn, McWhirter, S. Russell, Mitchell, Daniel, Morales, Miguel, Morgan, Edward, Pathikulangara, Joseph, Prabu, Thiagaraj, Remillard, Ronald, Robishaw, Timothy, Rogers, Alan, Roshi, Anish, Salah, Joseph, Sault, Robert, Udaya Shankar, N., Srivani, K.S., Stevens, Jamie, Subrahmanyan, Ravi, Webster, Rachel, Whitney, Alan, Williams, Andrew, Williams, Christopher, and Wyithe, J. Stuart
Abstract: Significant 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.
Published: 2013

48. Fast Holographic Deconvolution: A New Technique for Precision Radio Interferometry

Author: Sullivan, I., Morales, M., Hazelton, B., Arcus, Wayne, Barnes, D., Bernardi, G., Briggs, F., Bowman, J., Bunton, J., Cappallo, R., Corey, B., Deshpande, A., DeSouza, L., Emrich, David, Gaensler, B., Goeke, R., Greenhill, L., Herne, David, Hewitt, J., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morgan, E., Oberoi, D., Ord, Stephen, Pathikulangara, J., Prabu, T., Remillard, R., Rogers, A., Salah, J., Sault, R., Shankar, N., Srivani, K., Stevens, J., Subrahmanyan, R., Tingay, Steven, Wayth, Randall, Waterson, Mark, Webster, R., Whitney, A., Sullivan, I., Morales, M., Hazelton, B., Arcus, Wayne, Barnes, D., Bernardi, G., Briggs, F., Bowman, J., Bunton, J., Cappallo, R., Corey, B., Deshpande, A., DeSouza, L., Emrich, David, Gaensler, B., Goeke, R., Greenhill, L., Herne, David, Hewitt, J., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Mitchell, D., Morgan, E., Oberoi, D., Ord, Stephen, Pathikulangara, J., Prabu, T., Remillard, R., Rogers, A., Salah, J., Sault, R., Shankar, N., Srivani, K., Stevens, J., Subrahmanyan, R., Tingay, Steven, Wayth, Randall, Waterson, Mark, Webster, R., and Whitney, A.
Abstract: We introduce the Fast Holographic Deconvolution method for analyzing interferometric radio data. Our new method is an extension of A-projection/software-holography/forward modeling analysis techniques and shares their precision deconvolution and wide-field polarimetry, while being significantly faster than current implementations that use full direction-dependent antenna gains. Using data from the MWA 32 antenna prototype, we demonstrate the effectiveness and precision of our new algorithm. Fast Holographic Deconvolution may be particularly important for upcoming 21 cm cosmology observations of the Epoch of Reionization and Dark Energy where foreground subtraction is intimately related to the precision of the data reduction.
Published: 2012

49. Realisation of a low frequency SKA Precursor: The Murchison Widefield Array

Author: Tingay, Steven, Emrich, David, Ord, Stephen, Crosse, Brian, Arcus, Wayne, Colegate, Timothy, Hall, Peter, Herne, David, Lynch, Mervyn, Schlagenhaufer, Franz, Tremblay, Steven, Wayth, Randall, Waterson, Mark, Williams, Andrew, Tingay, Steven, Emrich, David, Ord, Stephen, Crosse, Brian, Arcus, Wayne, Colegate, Timothy, Hall, Peter, Herne, David, Lynch, Mervyn, Schlagenhaufer, Franz, Tremblay, Steven, Wayth, Randall, Waterson, Mark, and Williams, Andrew
Abstract: The Murchison Widefield Array is a low frequency (80 - 300 MHz) SKA Precursor, comprising 128 aperture array elements distributed over an area of 3 km diameter. The MWA is located at the extraordinarily radio quiet Murchison Radioastronomy Observatory in the mid-west of Western Australia, the selected home for the Phase 1 and Phase 2 SKA low frequency arrays. The MWA science goals include: 1) detection of fluctuations in the brightness temperature of the diffuse redshifted 21 cm line of neutral hydrogen from the epoch of reionisation; 2) studies of Galactic and extragalactic processes based on deep, confusion-limited surveys of the full sky visible to the array; 3) time domain astrophysics through exploration of the variable radio sky; and 4) solar imaging and characterisation of the heliosphere and ionosphere via propagation effects on background radio source emission. This paper will focus on a brief discussion of the as-built MWA system, highlighting several novel characteristics of the instrument, and a brief progress report (as of June 2012) on the final construction phase. Practical completion of the MWA is expected in November 2012, with commissioning commencing from approximately August 2012 and operations commencing near mid 2013. A brief description of recent science results from the MWA prototype instrument is given.
Published: 2012

50. Low-Frequency Imaging of Fields at High Galactic Latitude with the Murchison Widefield Array 32 Element Prototype

Author: Williams, C., Hewitt, J., Levine, A., de Oliveira-Costa, A., Bowman, Judd, Briggs, Frank, Gaensler, B., Hernquist, Lars, Mitchell, D., Morales, Miguel, Sethi, S., Subrahmanyan, R., Sadler, E., Arcus, Wayne, Barnes, David, Bernardi, G., Bunton, John, Cappallo, Roger, Crosse, B., Corey, Brian., Deshpande, Avinash, DeSouza, Ludi, Emrich, D., Goeke, Robert, Greenhill, L., Hazelton, Bryna, Herne, David, Kaplan, D., Kasper, Justin, Kincaid, Barton, Koenig, R., Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, S., Morgan, Edward, Oberoi, Divya, Ord, Stephen, Pathikulangara, Joseph, Prabu, T., Remillard, Ron, Rogers, Alan, Roshi, Anish, Salah, J., Sault, R., Shankar, N Udaya, Srivani, K., Stevens, J., Tingay, Steven, Wayth, Randall, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, A., Wyithe, J., Williams, C., Hewitt, J., Levine, A., de Oliveira-Costa, A., Bowman, Judd, Briggs, Frank, Gaensler, B., Hernquist, Lars, Mitchell, D., Morales, Miguel, Sethi, S., Subrahmanyan, R., Sadler, E., Arcus, Wayne, Barnes, David, Bernardi, G., Bunton, John, Cappallo, Roger, Crosse, B., Corey, Brian., Deshpande, Avinash, DeSouza, Ludi, Emrich, D., Goeke, Robert, Greenhill, L., Hazelton, Bryna, Herne, David, Kaplan, D., Kasper, Justin, Kincaid, Barton, Koenig, R., Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, S., Morgan, Edward, Oberoi, Divya, Ord, Stephen, Pathikulangara, Joseph, Prabu, T., Remillard, Ron, Rogers, Alan, Roshi, Anish, Salah, J., Sault, R., Shankar, N Udaya, Srivani, K., Stevens, J., Tingay, Steven, Wayth, Randall, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, A., and Wyithe, J.
Abstract: The Murchison Widefield Array (MWA) is a new low-frequency, wide-field-of-view radio interferometer under development at the Murchison Radio-astronomy Observatory in Western Australia. We have used a 32 element MWA prototype interferometer (MWA-32T) to observe two 50 degrees diameter fields in the southern sky, covering a total of similar to 2700 deg(2), in order to evaluate the performance of the MWA-32T, to develop techniques for epoch of reionization experiments, and to make measurements of astronomical foregrounds. We developed a calibration and imaging pipeline for the MWA-32T, and used it to produce similar to 15' angular resolution maps of the two fields in the 110-200 MHz band. We perform a blind source extraction using these confusion-limited images, and detect 655 sources at high significance with an additional 871 lower significance source candidates. We compare these sources with existing low-frequency radio surveys in order to assess the MWA-32T system performance, wide-field analysis algorithms, and catalog quality. Our source catalog is found to agree well with existing low-frequency surveys in these regions of the sky and with statistical distributions of point sources derived from Northern Hemisphere surveys; it represents one of the deepest surveys to date of this sky field in the 110-200 MHz band.
Published: 2012

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