Jamie Stevens

Publications (5)10.06 Total impact

• Article: Fast Holographic Deconvolution: a new technique for precision radio interferometry

  Ian Sullivan, Miguel Morales, Bryna Hazelton, Wayne Arcus, David Barnes, Gianni Bernardi, Frank Briggs, Judd D. Bowman, John Bunton, Roger Cappallo, [......], Jamie Stevens, Ravi Subrahmanyan, Steven Tingay, Randall Wayth, Mark Waterson, Rachel Webster, Alan Whitney, Andrew Williams, Chris Williams, Stuart Wyithe
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  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.
  09/2012;
• Source

  Available from: Robert John Sault

  Article: First Spectroscopic Imaging Observations of the Sun at Low Radio Frequencies with the Murchison Widefield Array Prototype

  Divya Oberoi, Lynn D. Matthews, Iver H. Cairns, David Emrich, Vasili Lobzin, Colin J. Lonsdale, Edward H. Morgan, T. Prabu, Harish Vedantham, Randall B. Wayth, [......], K. S. Srivani, Jamie Stevens, Ravi Subrahmanyan, D. Thakkar, Steven J. Tingay, J. Tuthill, Annino Vaccarella, Mark Waterson, Rachel L. Webster, Alan R. Whitney
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  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.
  01/2011;
• Source

  Available from: Robert John Sault

  Article: The Murchison Widefield Array: Design Overview

  Colin J. Lonsdale, Roger J. Cappallo, Miguel F. Morales, Frank H. Briggs, Leonid Benkevitch, Judd D. Bowman, John D. Bunton, Steven Burns, Brian E. Corey, Ludi deSouza, [......], K. S. Srivani, Jamie Stevens, Steven Tingay, Annino Vaccarella, Mark Waterson, Randall B. Wayth, Rachel L. Webster, Alan R. Whitney, Andrew Williams, Christopher Williams
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  ABSTRACT: The Murchison Widefield Array (MWA) is a dipole-based aperture array synthesis telescope designed to operate in the 80-300 MHz frequency range. It is capable of a wide range of science investigations, but is initially focused on three key science projects. These are detection and characterization of 3-dimensional brightness temperature fluctuations in the 21cm line of neutral hydrogen during the Epoch of Reionization (EoR) at redshifts from 6 to 10, solar imaging and remote sensing of the inner heliosphere via propagation effects on signals from distant background sources,and high-sensitivity exploration of the variable radio sky. The array design features 8192 dual-polarization broad-band active dipoles, arranged into 512 tiles comprising 16 dipoles each. The tiles are quasi-randomly distributed over an aperture 1.5km in diameter, with a small number of outliers extending to 3km. All tile-tile baselines are correlated in custom FPGA-based hardware, yielding a Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point spread function (PSF) quality. The correlated data are calibrated in real time using novel position-dependent self-calibration algorithms. The array is located in the Murchison region of outback Western Australia. This region is characterized by extremely low population density and a superbly radio-quiet environment,allowing full exploitation of the instrumental capabilities.
  04/2009;
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  Available from: ArXiv

  Article: Detection of Crab Giant Pulses Using the Mileura Widefield Array Low Frequency Demonstrator Field Prototype System

  N. D. Ramesh Bhat, Randall B. Wayth, Haydon S. Knight, Judd D. Bowman, Divya Oberoi, David G. Barnes, Frank H. Briggs, Roger J. Cappallo, David Herne, Jonathon Kocz, Colin J. Lonsdale, Mervyn J. Lynch, Bruce Stansby, Jamie Stevens, Glen Torr, Rachel L. Webster, and J. Stuart B. Wyithe
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  ABSTRACT: We report on the detection of giant pulses from the Crab Nebula pulsar at a frequency of 200 MHz using the field deployment system designed for the Mileura Widefield Array's Low Frequency Demonstrator (MWA-LFD). Our observations are among the first high-quality detections at such low frequencies. The measured pulse shapes are deconvolved for interstellar pulse broadening, yielding a pulse-broadening time of 670 ± 100 μs, and the implied strength of scattering (scattering measure) is the lowest that is estimated toward the Crab Nebula from observations made so far. The sensitivity of the system is largely dictated by the sky background, and our simple equipment is capable of detecting pulses that are brighter than ~9 kJy in amplitude. The brightest giant pulse detected in our data has a peak amplitude of ~50 kJy, and the implied brightness temperature is 1031.6 K. We discuss the giant pulse detection prospects with the full MWA-LFD system. With a sensitivity over 2 orders of magnitude larger than the prototype equipment, the full system will be capable of detecting such bright giant pulses out to a wide range of Galactic distances; from ~15 to ~30 kpc depending on the frequency. The MWA-LFD will thus be a highly promising instrument for the studies of giant pulses and other fast radio transients at low frequencies.
  The Astrophysical Journal 12/2008; 665(1):618. · 6.02 Impact Factor
• Source

  Available from: arxiv.org

  Article: Field Deployment of Prototype Antenna Tiles for the Mileura Widefield Array Low Frequency Demonstrator

  Judd D. Bowman, David G. Barnes, Frank H. Briggs, Brian E. Corey, Merv J. Lynch, N. D. Ramesh Bhat, Roger J. Cappallo, Sheperd S. Doeleman, Brian J. Fanous, David Herne, [......], Colin J. Lonsdale, Miguel F. Morales, Divya Oberoi, Joseph E. Salah, Bruce Stansby, Jamie Stevens, Glen Torr, Randall Wayth, Rachel L. Webster, and J. Stuart B. Wyithe
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  ABSTRACT: Experiments were performed with prototype antenna tiles for the Mileura Widefield Array Low Frequency Demonstrator (MWA LFD) to better understand the wide-field, wide-band properties of their design and to characterize the radio-frequency interference (RFI) between 80 and 300 MHz at the site in Western Australia. Observations acquired during the 6 month deployment confirmed the predicted sensitivity of the antennas, sky-noise-dominated system temperatures, and phase-coherent interferometric measurements. The radio spectrum is remarkably free of strong terrestrial signals, with the exception of two narrow frequency bands allocated to satellite downlinks, and rare bursts due to ground-based transmissions being scattered from aircraft and meteor trails. Results indicate the potential of the MWA LFD to make significant achievements in its three key science objectives: epoch of reionization science, heliospheric science, and radio transient detection.
  The Astronomical Journal 12/2007; 133(4):1505. · 4.03 Impact Factor