B. Crosse

Curtin University

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Co-Authors

S. J. Tingay

International Centre for Radio Astronomy Research

A. Williams

Florida Atlantic University

R. B. Wayth

International Centre for Radio Astronomy Research

M. Johnston‐Hollitt

International Centre for Radio Astronomy Research

D. Emrich

International Centre for Radio Astronomy Research

D. L. Kaplan

University of Wisconsin–Milwaukee

D. Pallot

International Centre for Radio Astronomy Research

M. F. Morales

University of Washington

M. Walker

Monash Health

D. Kenney

Curtin University

Cooperative Institutions

Centre National de la Recherche Scientifique

507

California Institute of Technology

343

Consejo Nacional de Investigaciones Científicas y Técnicas

285

Goddard Space Flight Center

225

Université Paris Cité

198

National Institute for Astrophysics

198

University of Alaska Anchorage

178

Clark Atlanta University

177

Universidad Nacional de La Plata

175

University of Buenos Aires

167

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The Engineering Development Array: A Low Frequency Radio Telescope Utilising SKA Precursor Technology

Publications of the Astronomical Society of Australia (2017)

R. B. Wayth M. Sokołowski T. Booler B. Crosse D. Emrich

We describe the design and performance of the Engineering Development Array (EDA), which is a low frequency radio telescope comprising 256 dual-polarisation dipole antennas working as a phased-array. The EDA was conceived of, developed, and deployed in just 18 months via re-use of Square Kilometre Array (SKA) precursor technology and expertise, specifically from the Murchison Widefield Array (MWA) radio telescope. Using drift scans and a model for the sky brightness temperature at low frequencies, we have derived the EDA's receiver temperature as a function of frequency. The EDA is shown to be sky-noise limited over most of the frequency range measured between 60 and 240 MHz. By using the EDA in interferometric mode with the MWA, we used calibrated visibilities to measure the absolute sensitivity of the array. The measured array sensitivity matches very well with a model based on the array layout and measured receiver temperature. The results demonstrate the practicality and feasibility of using MWA-style precursor technology for SKA-scale stations. The modular architecture of the EDA allows upgrades to the array to be rolled out in a staged approach. Future improvements to the EDA include replacing the second stage beamformer with a fully digital system, and to transition to using RF-over-fibre for the signal output from first stage beamformers.

Radio Astronomy

10.1017/pasa.2017.27

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Citations (16)

Comparing Redundant and Sky-model-based Interferometric Calibration: A First Look with Phase II of the MWA

The Astrophysical Journal (2018)

Wenqing Li Jonathan Pober B. J. Hazelton N. Barry M. F. Morales

Abstract Interferometric arrays seeking to measure the 21 cm signal from the epoch of reionization (EOR) must contend with overwhelmingly bright emission from foreground sources. Accurate recovery of the 21 cm signal will require precise calibration of the array, and several new avenues for calibration have been pursued in recent years, including methods using redundancy in the antenna configuration. The newly upgraded Phase II of Murchison Widefield Array (MWA) is the first interferometer that has large numbers of redundant baselines while retaining good instantaneous UV coverage. This array therefore provides a unique opportunity to compare redundant calibration with sky-model-based algorithms. In this paper, we present the first results from comparing both calibration approaches with MWA Phase II observations. For redundant calibration, we use the package OMNICAL and produce sky-based calibration solutions with the analysis package Fast Holographic Deconvolution (FHD). There are three principal results: (1) We report the success of OMNICAL on observations of ORBComm satellites, showing substantial agreement between redundant visibility measurements after calibration. (2) We directly compare OMNICAL calibration solutions with those from FHD and demonstrate that these two different calibration schemes give extremely similar results. (3) We explore improved calibration by combining OMNICAL and FHD. We evaluate these combined methods using power spectrum techniques developed for EOR analysis and find evidence for marginal improvements mitigating artifacts in the power spectrum. These results are likely limited by the signal-to-noise ratio in the 6 hr of data used, but they suggest future directions for combining these two calibration schemes.

10.3847/1538-4357/aad3c3

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Citations (51)

The low frequency receivers for SKA 1-low: Design and verification

P. Benthem Marchei Gerbers J.G. Bij de Vaate Stefan Wynholds J. E. Bast

The initial phase of the Square Kilometre Array (SKA) [1] is represented by a ~10% instrument and construction should start in 2018. SKA 1-Low, a sparse Aperture Array (AA) covering the frequency range 50 to 350 MHz, will be part of this. This instrument will consist of 512 stations, each hosting 256 antennas creating a total of 131,072 antennas. A first verification system towards SKA 1-Low, Aperture Array Verification System 1 (AAVSl), is being deployed and validated in 2017.

Aperture (computer memory)

Square (algebra)

10.23919/ursigass.2017.8104992

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Citations (6)

The Aperture Array Verification System 1: System overview and early commissioning results.

arXiv (Cornell University) (2021)

P. Benthem R. B. Wayth Eloy de Lera Acedo Kristian Zarb Adami M. Alderighi

The design and development process for the Square Kilometre Array (SKA) radio telescope, the Low Frequency Aperture Array component, was progressed during the SKA pre-construction phase by an international consortium, with the goal of meeting requirements for a critical design review. As part of the development process a full-sized prototype SKA Low station was deployed, the Aperture Array Verification System 1 (AAVS1). We provide a system overview and describe the commissioning results of AAVS1, which is a low frequency radio telescope with 256 dual-polarisation log-periodic dipole antennas working as a phased array. A detailed system description is provided, including an in-depth overview of relevant sub-systems, ranging from hardware, firmware, software, calibration,and control sub-systems. Early commissioning results cover initial bootstrapping, array calibration, stability testing, beam-forming,and on-sky sensitivity validation. Lessons learned are presented, along with future developments.

Firmware

Aperture (computer memory)

Installation

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The Murchison Widefield Array Correlator

Publications of the Astronomical Society of Australia (2015)

S. M. Ord B. Crosse D. Emrich D. Pallot R. B. Wayth

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.

Aperture (computer memory)

Radio Astronomy

Murchison meteorite

10.1017/pasa.2015.5

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Citations (43)

A High Time-resolution Study of the Millisecond Pulsar J2241−5236 at Frequencies Below 300 MHz

The Astrophysical Journal (2019)

D. Kaur N. D. R. Bhat S. E. Tremblay R. M. Shannon S. J. McSweeney

Abstract One of the major challenges for pulsar timing array (PTA) experiments is the mitigation of the effects of the turbulent interstellar medium (ISM) from timing data. These can potentially lead to measurable delays and/or distortions in the pulse profiles and scale strongly with the inverse of the radio frequency. Low-frequency observations are therefore highly appealing for characterizing them. However, in order to achieve the necessary time resolution to resolve profile features of short-period millisecond pulsars, phase-coherent dedispersion is essential, especially at frequencies below 300 MHz. We present the lowest-frequency (80–220 MHz), coherently dedispersed detections of one of the most promising pulsars for current and future PTAs, PSR J2241–5236, using our new beamformer software for the MWA’s voltage capture system, which reconstructs the time series at a much higher time resolution of ∼1 μ s by resynthesizing the recorded voltage data at 10 kHz/100 μ s native resolutions. Our data reveal a dual-precursor type feature in the pulse profile that is either faint or absent in high-frequency observations from Parkes. The resultant high-fidelity detections have enabled dispersion measure determinations with very high precision, of the order of (2–6) × 10 −6 , owing to the microsecond level timing achievable for this pulsar at the MWA’s low frequencies. This underscores the usefulness of low-frequency observations for probing the ISM toward PTA pulsars and informing optimal observing strategies for PTA experiments.

Millisecond

10.3847/1538-4357/ab338f

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Citations (7)

Upper limits on low-frequency emission from FRBs 200914 and 200919 from SKA-Low prototype stations

The astronomer's telegram (2020)

M. Sokołowski N. D. R. Bhat R. B. Wayth J. W. Broderick David Minchin

Source

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MWA tied-array processing III: Microsecond time resolution via a polyphase synthesis filter

Publications of the Astronomical Society of Australia (2020)

S. J. McSweeney S. M. Ord D. Kaur N. D. R. Bhat Bradley W. Meyers

A new high time resolution observing mode for the Murchison Widefield Array (MWA) is described, enabling full polarimetric observations with up to 30.72 MHz of bandwidth and a time resolution of ~0.8 $μ$s. This mode makes use of a polyphase synthesis filter to "undo" the polyphase analysis filter stage of the standard MWA's Voltage Capture System (VCS) observing mode. Sources of potential error in the reconstruction of the high time resolution data are identified and quantified, with the S/N loss induced by the back-to-back system not exceeding -0.65 dB for typical noise-dominated samples. The system is further verified by observing three pulsars with known structure on microsecond timescales.

Polyphase system

Microsecond

10.1017/pasa.2020.24

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Citations (9)

No Low-frequency Emission from Extremely Bright Fast Radio Bursts

The Astrophysical Journal Letters (2018)

M. Sokołowski N. D. R. Bhat Jean‐Pierre Macquart R. M. Shannon K. W. Bannister

Abstract We present the results of a coordinated campaign conducted with the Murchison Widefield Array (MWA) to shadow fast radio bursts (FRBs) detected by the Australian Square Kilometre Array Pathfinder (ASKAP) at 1.4 GHz, which resulted in simultaneous MWA observations of seven ASKAP FRBs. We de-dispersed the 24 × 1.28 MHz MWA images across the 170–200 MHz band taken at 0.5 s time resolution at the known dispersion measures (DMs) and arrival times of the bursts and searched both within the ASKAP error regions (typically ∼10′ × 10′), and beyond (4° × 4°). We identified no candidates exceeding a 5 σ threshold at these DMs in the dynamic spectra. These limits are inconsistent with the mean fluence scaling of α = −1.8 ± 0.3 ( , where ν is the observing frequency) that is reported for ASKAP events, most notably for the three high-fluence ( Jy ms) FRBs 171020, 180110, and 180324. Our limits show that pulse broadening alone cannot explain our non-detections, and that there must be a spectral turnover at frequencies above 200 MHz. We discuss and constrain parameters of three remaining plausible spectral break mechanisms: free–free absorption, intrinsic spectral turnover of the radiative processes, and magnification of signals at ASKAP frequencies by caustics or scintillation. If free–free absorption were the cause of the spectral turnover, we constrain the thickness of the absorbing medium in terms of the electron temperature, T , to <0.03 ( T /10 4 K) −1.35 pc for FRB 171020.

10.3847/2041-8213/aae58d

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Citations (31)

Hunting for Radio Emission from the Intermittent Pulsar J1107-5907 at Low Frequencies

The Astrophysical Journal (2018)

Bradley W. Meyers S. E. Tremblay N. D. R. Bhat Chris Flynn Vivek Gupta

Abstract Rare intermittent pulsars pose some of the most challenging questions surrounding the pulsar emission mechanism, but typically have relatively minimal low-frequency (≲300 MHz) coverage. We present the first low-frequency detection of the intermittent pulsar J1107–5907 with the Murchison Widefield Array (MWA) at 154 MHz and the simultaneous detection from the recently upgraded Molonglo Observatory Synthesis Telescope (UTMOST) at 835 MHz, as part of an ongoing observing campaign. During a 30 minute simultaneous observation, we detected the pulsar in its bright emission state for approximately 15 minutes, where 86 and 283 pulses were detected above a signal-to-noise threshold of 6 with the MWA and UTMOST, respectively. Of the detected pulses, 51 had counterparts at both frequencies and exhibited steep spectral indices for both the bright main pulse component and the precursor component. We find that the bright state pulse energy distribution is best parameterized by a log-normal distribution at both frequencies, contrary to previous results that suggested a power law distribution. Further low-frequency observations are required in order to explore in detail aspects such as pulse-to-pulse variability and intensity modulations, as well as to better constrain the signal propagation effects due to the interstellar medium and intermittency characteristics at these frequencies. The spectral index, extended profile emission covering a large fraction of pulse longitude, and the broadband intermittency of PSR J1107–5907 suggest that future low-frequency pulsar searches—for instance, those planned with SKA-Low—will be in an excellent position to find and investigate new pulsars of this type.

Spectral index

10.3847/1538-4357/aaee7b

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Citations (8)