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1. 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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2. 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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3. 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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4. 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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5. 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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6. Demonstration of a broadband-RF VLBI system at 16 Gbps data rate per station

Author: Whitney, Alan R., Beaudoin, Christopher J., Cappallo, Roger J., Corey, Brian E., Crew, Geoffrey B., Doeleman, Shepherd S., Lapsley, David E., Hinton, Alan A., McWhirter, Stephen R., Niell, Arthur E., Rogers, Alan E. E., Ruszczyk, Chester A., Smythe, Daniel L., SooHoo, Jason, and Titus, Michael A.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: The recent development of a relatively inexpensive 16-Gbps data-recording system based on commercial off-the-shelf technology and open-source software, along with parallel development in broadband Very Long Baseline Interferometry (VLBI) techniques, is enabling dramatically improved sensitivity for both astronomical and geodetic VLBI. The system is described, including the results of a demonstration VLBI experiment that illustrates a number of cutting-edge technologies that can be deployed in the near future to significantly enhance the power of the VLBI technique., Comment: Submitted to PASP
Published: 2012

7. 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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8. 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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9. The Murchison Widefield Array: Design Overview

Author: Lonsdale, Colin J., Cappallo, Roger J., Morales, Miguel F., Briggs, Frank H., Benkevitch, Leonid, Bowman, Judd D., Bunton, John D., Burns, Steven, Corey, Brian E., deSouza, Ludi, Doeleman, Sheperd S., Derome, Mark, Deshpande, Avinash, Gopalakrishna, M. R., Greenhill, Lincoln J., Herne, David, Hewitt, Jacqueline N., Kamini, P. A., Kasper, Justin C., Kincaid, Barton B., Kocz, Jonathan, Kowald, Errol, Kratzenberg, Eric, Kumar, Deepak, Lynch, Mervyn J., Madhavi, S., Matejek, Michael, Mitchell, Daniel, Morgan, Edward, Oberoi, Divya, Ord, Steven, Pathikulangara, Joseph, Prabu, T., Rogers, Alan E. E., Roshi, Anish, Salah, Joseph E., Sault, Robert J., Shankar, N. Udaya, Srivani, K. S., Stevens, Jamie, Tingay, Steven, Vaccarella, Annino, Waterson, Mark, Wayth, Randall B., Webster, Rachel L., Whitney, Alan R., Williams, Andrew, and Williams, Christopher
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Solar and Stellar Astrophysics
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., Comment: 9 pages, 5 figures, 1 table. Accepted for publication in Proceedings of the IEEE
Published: 2009
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10. Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre

Author: Doeleman, Sheperd, Weintroub, Jonathan, Rogers, Alan E. E., Plambeck, Richard, Freund, Robert, Tilanus, Remo P. J., Friberg, Per, Ziurys, Lucy M., Moran, James M., Corey, Brian, Young, Ken H., Smythe, Daniel L., Titus, Michael, Marrone, Daniel P., Cappallo, Roger J., Bock, Douglas C. J., Bower, Geoffrey C., Chamberlin, Richard, Davis, Gary R., Krichbaum, Thomas P., Lamb, James, Maness, Holly, Niell, Arthur E., Roy, Alan, Strittmatter, Peter, Werthimer, Daniel, Whitney, Alan R., and Woody, David
Subjects: Astrophysics
Abstract: The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation (ref 1). Sagittarius A*, the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4 million times that of the Sun (refs. 2,3). A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A* where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering (refs. 4-7). Here we report observations at a wavelength of 1.3 mm that set a size of 37 (+16, -10; 3-sigma) microarcseconds on the intrinsic diameter of Sgr A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of SgrA* emission may not be not centred on the black hole, but arises in the surrounding accretion flow., Comment: 12 pages including 2 figures
Published: 2008
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11. Rapid Turnaround EOP Measurements by VLBI over the Internet

Author: Koyama, Yasuhiro, Kondo, Tetsuro, Osaki, Hiro, Whitney, Alan R., Dudevoir, Kevin A., and Sansò, Fernando, editor
Published: 2005
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12. Demonstration of a 16 Gbps Station -1 Broadband-RF VLBI System

Author: Whitney, Alan R., Beaudoin, Christopher J., Cappallo, Roger J., Corey, Brian E., Crew, Geoffrey B., Doeleman, Shepherd S., Lapsley, David E., Hinton, Alan A., McWhirter, Stephen R., Niell, Arthur E., Rogers, Alan E. E., Ruszczyk, Chester A., Smythe, Daniel L., SooHoo, Jason, and Titus, Michael A.
Published: 2013
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13. The Mark IV VLBI Data-Acquisition and Correlation System

Author: Whitney, Alan R., Mueller, Ivan I., editor, and Kołaczek, Barbara, editor
Published: 1993
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14. Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis

Author: Cappallo, Roger J., Hinteregger, Hans F., Levine, James I., Nesman, Edwin F., Webber, John C., Whitney, Alan R., Clark, Thomas A., Ma, Chopo, Ryan, James, Corey, Brian E., Counselman, Charles C., Herring, Tomas A., Shapiro, Irwin I., Knight, Curtis A., Shaffer, David B., Vandenberg, Nancy R., Lacasse, Richard, Mauzy, Robert, Rayhrer, Benno, Schupler, Bruce R., and Pigg, J. C.
Published: 1983

15. Quasars Revisited: Rapid Time Variations Observed Via Very-Long-Baseline Interferometry

Author: Whitney, Alan R., Shapiro, Irwin I., Robertson, Douglas S., Knight, Curtis A., Clark, Thomas A., Goldstein, Richard M., Marandino, Gerard E., and Vandenberg, Nancy R.
Published: 1971

16. Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

Author: Kim, Jae-Young, Krichbaum, Thomas P., Broderick, Avery E., Wielgus, Maciek, Blackburn, Lindy, Gomez, Jose L., Johnson, Michael D., Bouman, Katherine L., Chael, Andrew, Akiyama, Kazunori, Jorstad, Svetlana, Marscher, Alan P., Issaoun, Sara, Janssen, Michael, Chan, Chi-kwan, Savolainen, Tuomas, Pesce, Dominic W., Ozel, Feryal, Alberdi, Antxon, Alef, Walter, Asada, Keiichi, Azulay, Rebecca, Baczko, Anne-Kathrin, Ball, David, Balokovic, Mislav, Barrett, John, Bintley, Dan, Boland, Wilfred, Bower, Geoffrey C., Bremer, Michael, Brinkerink, Christiaan D., Brissenden, Roger, Britzen, Silke, Broguiere, Dominique, Bronzwaer, Thomas, Byun, Do-Young, Carlstrom, John E., Chatterjee, Shami, Chatterjee, Koushik, Chen, Ming-Tang, Chen, Yongjun, Cho, Ilje, Christian, Pierre, Conway, John E., Cordes, James M., Crew, Geoffrey B., Cui, Yuzhu, Davelaar, Jordy, De Laurentis, Mariafelicia, Deane, Roger, Dempsey, Jessica, Desvignes, Gregory, Dexter, Jason, Doeleman, Sheperd S., Eatough, Ralph P., Falcke, Heino, Fish, Vincent L., Fomalont, Ed, Fraga-Encinas, Raquel, Friberg, Per, Fromm, Christian M., Galison, Peter, Gammie, Charles F., Garcia, Roberto, Gentaz, Olivier, Georgiev, Boris, Goddi, Ciriaco, Gold, Roman, Gu, Minfeng, Gurwell, Mark, Hada, Kazuhiro, Hecht, Michael H., Hesper, Ronald, Ho, Luis C., Ho, Paul, Honma, Mareki, Huang, Chih-Wei L., Huang, Lei, Hughes, David H., Ikeda, Shiro, Inoue, Makoto, James, David J., Jannuzi, Buell T., Jeter, Britton, Jiang, Wu, Jimenez-Rosales, Alejandra, Jung, Taehyun, Karami, Mansour, Karuppusamy, Ramesh, Kawashima, Tomohisa, Keating, Garrett K., Kettenis, Mark, Kim, Junhan, Kim, Jongsoo, Kino, Motoki, Koay, Jun Yi, Koch, Patrick M., Koyama, Shoko, Kramer, Michael, Kramer, Carsten, Kuo, Cheng-Yu, Lauer, Tod R., Lee, Sang-Sung, Li, Yan-Rong, Li, Zhiyuan, Lindqvist, Michael, Lico, Rocco, Liu, Kuo, Liuzzo, Elisabetta, Lo, Wen-Ping, Lobanov, Andrei P., Loinard, Laurent, Lonsdale, Colin, Lu, Ru-Sen, MacDonald, Nicholas R., Mao, Jirong, Markoff, Sera, Marrone, Daniel P., Marti-Vidal, Ivan, Matsushita, Satoki, Matthews, Lynn D., Medeiros, Lia, Menten, Karl M., Mizuno, Yosuke, Mizuno, Izumi, Moran, James M., Moriyama, Kotaro, Moscibrodzka, Monika, Mueller, Cornelia, Nagai, Hiroshi, Nagar, Neil M., Nakamura, Masanori, Narayan, Ramesh, Narayanan, Gopal, Natarajan, Iniyan, Neri, Roberto, Ni, Chunchong, Noutsos, Aristeidis, Okino, Hiroki, Olivares, Hector, Ortiz-Leon, Gisela N., Oyama, Tomoaki, Palumbo, Daniel C. M., Park, Jongho, Patel, Nimesh, Pen, Ue-Li, Pietu, Vincent, Plambeck, Richard, PopStefanija, Aleksandar, Porth, Oliver, Prather, Ben, Preciado-Lopez, Jorge A., Psaltis, Dimitrios, Pu, Hung-Yi, Ramakrishnan, Venkatessh, Rao, Ramprasad, Rawlings, Mark G., Raymond, Alexander W., Rezzolla, Luciano, Ripperda, Bart, Roelofs, Freek, Rogers, Alan, Ros, Eduardo, Rose, Mel, Roshanineshat, Arash, Rottmann, Helge, Roy, Alan L., Ruszczyk, Chet, Ryan, Benjamin R., Rygl, Kazi L. J., Sanchez, Salvador, Sanchez-Arguelles, David, Sasada, Mahito, Schloerb, F. Peter, Schuster, Karl-Friedrich, Shao, Lijing, Shen, Zhiqiang, Small, Des, Sohn, Bong Won, SooHoo, Jason, Tazaki, Fumie, Tiede, Paul, Tilanus, Remo P. J., Titus, Michael, Toma, Kenji, Torne, Pablo, Trent, Tyler, Traianou, Efthalia, Trippe, Sascha, Tsuda, Shuichiro, van Bemmel, Ilse, van Langevelde, Huib Jan, van Rossum, Daniel R., Wagner, Jan, Wardle, John, Ward-Thompson, Derek, Weintroub, Jonathan, Wex, Norbert, Wharton, Robert, Wong, George N., Wu, Qingwen, Yoon, Doosoo, Young, Andre, Young, Ken, Younsi, Ziri, Yuan, Feng, Yuan, Ye-Fei, Zensus, J. Anton, Zhao, Guangyao, Zhao, Shan-Shan, Zhu, Ziyan, Algaba, Juan-Carlos, Allardi, Alexander, Amestica, Rodrigo, Anczarski, Jadyn, Bach, Uwe, Baganoff, Frederick K., Beaudoin, Christopher, Benson, Bradford A., Berthold, Ryan, Blanchard, Jay M., Blundell, Ray, Bustamente, Sandra, Cappallo, Roger, Castillo-Dominguez, Edgar, Chang, Chih-Cheng, Chang, Shu-Hao, Chang, Song-Chu, Chen, Chung-Chen, Chilson, Ryan, Chuter, Tim C., Rosado, Rodrigo Cordova, Coulson, Iain M., Crowley, Joseph, Derome, Mark, Dexter, Matthew, Dornbusch, Sven, Dudevoir, Kevin A., Dzib, Sergio A., Eckart, Andreas, Eckert, Chris, Erickson, Neal R., Everett, Wendeline B., Faber, Aaron, Farah, Joseph R., Fath, Vernon, Folkers, Thomas W., Forbes, David C., Freund, Robert, Gomez-Ruiz, Arturo, I, Gale, David M., Gao, Feng, Geertsema, Gertie, Graham, David A., Greer, Christopher H., Grosslein, Ronald, Gueth, Frederic, Haggard, Daryl, Halverson, Nils W., Han, Chih-Chiang, Han, Kuo-Chang, Hao, Jinchi, Hasegawa, Yutaka, Henning, Jason W., Hernandez-Gomez, Antonio, Herrero-Illana, Ruben, Heyminck, Stefan, Hirota, Akihiko, Hoge, James, Huang, Yau-De, Impellizzeri, C. M. Violette, Jiang, Homin, John, David, Kamble, Atish, Keisler, Ryan, Kimura, Kimihiro, Kono, Yusuke, Kubo, Derek, Kuroda, John, Lacasse, Richard, Laing, Robert A., Leitch, Erik M., Li, Chao-Te, Lin, Lupin C-C, Liu, Ching-Tang, Liu, Kuan-Yu, Lu, Li-Ming, Marson, Ralph G., Martin-Cocher, Pierre L., Massingill, Kyle D., Matulonis, Callie, McColl, Martin P., McWhirter, Stephen R., Messias, Hugo, Meyer-Zhao, Zheng, Michalik, Daniel, Montana, Alfredo, Montgomerie, William, Mora-Klein, Matias, Muders, Dirk, Nadolski, Andrew, Navarro, Santiago, Neilsen, Joseph, Nguyen, Chi H., Nishioka, Hiroaki, Norton, Timothy, Nowak, Michael A., Nystrom, George, Ogawa, Hideo, Oshiro, Peter, Parsons, Harriet, Penalver, Juan, Phillips, Neil M., Poirier, Michael, Pradel, Nicolas, Primiani, Rurik A., Raffin, Philippe A., Rahlin, Alexandra S., Reiland, George, Risacher, Christopher, Ruiz, Ignacio, Saez-Madain, Alejandro F., Sassella, Remi, Schellart, Pim, Shaw, Paul, Silva, Kevin M., Shiokawa, Hotaka, Smith, David R., Snow, William, Souccar, Kamal, Sousa, Don, Sridharan, T. K., Srinivasan, Ranjani, Stahm, William, Stark, Antony A., Story, Kyle, Timmer, Sjoerd T., Vertatschitsch, Laura, Walther, Craig, Wei, Ta-Shun, Whitehorn, Nathan, Whitney, Alan R., Woody, David P., Wouterloot, Jan G. A., Wright, Melvin, Yamaguchi, Paul, Yu, Chen-Yu, Zeballos, Milagros, Zhang, Shuo, Ziurys, Lucy, Kim, Jae-Young, Krichbaum, Thomas P., Broderick, Avery E., Wielgus, Maciek, Blackburn, Lindy, Gomez, Jose L., Johnson, Michael D., Bouman, Katherine L., Chael, Andrew, Akiyama, Kazunori, Jorstad, Svetlana, Marscher, Alan P., Issaoun, Sara, Janssen, Michael, Chan, Chi-kwan, Savolainen, Tuomas, Pesce, Dominic W., Ozel, Feryal, Alberdi, Antxon, Alef, Walter, Asada, Keiichi, Azulay, Rebecca, Baczko, Anne-Kathrin, Ball, David, Balokovic, Mislav, Barrett, John, Bintley, Dan, Boland, Wilfred, Bower, Geoffrey C., Bremer, Michael, Brinkerink, Christiaan D., Brissenden, Roger, Britzen, Silke, Broguiere, Dominique, Bronzwaer, Thomas, Byun, Do-Young, Carlstrom, John E., Chatterjee, Shami, Chatterjee, Koushik, Chen, Ming-Tang, Chen, Yongjun, Cho, Ilje, Christian, Pierre, Conway, John E., Cordes, James M., Crew, Geoffrey B., Cui, Yuzhu, Davelaar, Jordy, De Laurentis, Mariafelicia, Deane, Roger, Dempsey, Jessica, Desvignes, Gregory, Dexter, Jason, Doeleman, Sheperd S., Eatough, Ralph P., Falcke, Heino, Fish, Vincent L., Fomalont, Ed, Fraga-Encinas, Raquel, Friberg, Per, Fromm, Christian M., Galison, Peter, Gammie, Charles F., Garcia, Roberto, Gentaz, Olivier, Georgiev, Boris, Goddi, Ciriaco, Gold, Roman, Gu, Minfeng, Gurwell, Mark, Hada, Kazuhiro, Hecht, Michael H., Hesper, Ronald, Ho, Luis C., Ho, Paul, Honma, Mareki, Huang, Chih-Wei L., Huang, Lei, Hughes, David H., Ikeda, Shiro, Inoue, Makoto, James, David J., Jannuzi, Buell T., Jeter, Britton, Jiang, Wu, Jimenez-Rosales, Alejandra, Jung, Taehyun, Karami, Mansour, Karuppusamy, Ramesh, Kawashima, Tomohisa, Keating, Garrett K., Kettenis, Mark, Kim, Junhan, Kim, Jongsoo, Kino, Motoki, Koay, Jun Yi, Koch, Patrick M., Koyama, Shoko, Kramer, Michael, Kramer, Carsten, Kuo, Cheng-Yu, Lauer, Tod R., Lee, Sang-Sung, Li, Yan-Rong, Li, Zhiyuan, Lindqvist, Michael, Lico, Rocco, Liu, Kuo, Liuzzo, Elisabetta, Lo, Wen-Ping, Lobanov, Andrei P., Loinard, Laurent, Lonsdale, Colin, Lu, Ru-Sen, MacDonald, Nicholas R., Mao, Jirong, Markoff, Sera, Marrone, Daniel P., Marti-Vidal, Ivan, Matsushita, Satoki, Matthews, Lynn D., Medeiros, Lia, Menten, Karl M., Mizuno, Yosuke, Mizuno, Izumi, Moran, James M., Moriyama, Kotaro, Moscibrodzka, Monika, Mueller, Cornelia, Nagai, Hiroshi, Nagar, Neil M., Nakamura, Masanori, Narayan, Ramesh, Narayanan, Gopal, Natarajan, Iniyan, Neri, Roberto, Ni, Chunchong, Noutsos, Aristeidis, Okino, Hiroki, Olivares, Hector, Ortiz-Leon, Gisela N., Oyama, Tomoaki, Palumbo, Daniel C. M., Park, Jongho, Patel, Nimesh, Pen, Ue-Li, Pietu, Vincent, Plambeck, Richard, PopStefanija, Aleksandar, Porth, Oliver, Prather, Ben, Preciado-Lopez, Jorge A., Psaltis, Dimitrios, Pu, Hung-Yi, Ramakrishnan, Venkatessh, Rao, Ramprasad, Rawlings, Mark G., Raymond, Alexander W., Rezzolla, Luciano, Ripperda, Bart, Roelofs, Freek, Rogers, Alan, Ros, Eduardo, Rose, Mel, Roshanineshat, Arash, Rottmann, Helge, Roy, Alan L., Ruszczyk, Chet, Ryan, Benjamin R., Rygl, Kazi L. J., Sanchez, Salvador, Sanchez-Arguelles, David, Sasada, Mahito, Schloerb, F. Peter, Schuster, Karl-Friedrich, Shao, Lijing, Shen, Zhiqiang, Small, Des, Sohn, Bong Won, SooHoo, Jason, Tazaki, Fumie, Tiede, Paul, Tilanus, Remo P. J., Titus, Michael, Toma, Kenji, Torne, Pablo, Trent, Tyler, Traianou, Efthalia, Trippe, Sascha, Tsuda, Shuichiro, van Bemmel, Ilse, van Langevelde, Huib Jan, van Rossum, Daniel R., Wagner, Jan, Wardle, John, Ward-Thompson, Derek, Weintroub, Jonathan, Wex, Norbert, Wharton, Robert, Wong, George N., Wu, Qingwen, Yoon, Doosoo, Young, Andre, Young, Ken, Younsi, Ziri, Yuan, Feng, Yuan, Ye-Fei, Zensus, J. Anton, Zhao, Guangyao, Zhao, Shan-Shan, Zhu, Ziyan, Algaba, Juan-Carlos, Allardi, Alexander, Amestica, Rodrigo, Anczarski, Jadyn, Bach, Uwe, Baganoff, Frederick K., Beaudoin, Christopher, Benson, Bradford A., Berthold, Ryan, Blanchard, Jay M., Blundell, Ray, Bustamente, Sandra, Cappallo, Roger, Castillo-Dominguez, Edgar, Chang, Chih-Cheng, Chang, Shu-Hao, Chang, Song-Chu, Chen, Chung-Chen, Chilson, Ryan, Chuter, Tim C., Rosado, Rodrigo Cordova, Coulson, Iain M., Crowley, Joseph, Derome, Mark, Dexter, Matthew, Dornbusch, Sven, Dudevoir, Kevin A., Dzib, Sergio A., Eckart, Andreas, Eckert, Chris, Erickson, Neal R., Everett, Wendeline B., Faber, Aaron, Farah, Joseph R., Fath, Vernon, Folkers, Thomas W., Forbes, David C., Freund, Robert, Gomez-Ruiz, Arturo, I, Gale, David M., Gao, Feng, Geertsema, Gertie, Graham, David A., Greer, Christopher H., Grosslein, Ronald, Gueth, Frederic, Haggard, Daryl, Halverson, Nils W., Han, Chih-Chiang, Han, Kuo-Chang, Hao, Jinchi, Hasegawa, Yutaka, Henning, Jason W., Hernandez-Gomez, Antonio, Herrero-Illana, Ruben, Heyminck, Stefan, Hirota, Akihiko, Hoge, James, Huang, Yau-De, Impellizzeri, C. M. Violette, Jiang, Homin, John, David, Kamble, Atish, Keisler, Ryan, Kimura, Kimihiro, Kono, Yusuke, Kubo, Derek, Kuroda, John, Lacasse, Richard, Laing, Robert A., Leitch, Erik M., Li, Chao-Te, Lin, Lupin C-C, Liu, Ching-Tang, Liu, Kuan-Yu, Lu, Li-Ming, Marson, Ralph G., Martin-Cocher, Pierre L., Massingill, Kyle D., Matulonis, Callie, McColl, Martin P., McWhirter, Stephen R., Messias, Hugo, Meyer-Zhao, Zheng, Michalik, Daniel, Montana, Alfredo, Montgomerie, William, Mora-Klein, Matias, Muders, Dirk, Nadolski, Andrew, Navarro, Santiago, Neilsen, Joseph, Nguyen, Chi H., Nishioka, Hiroaki, Norton, Timothy, Nowak, Michael A., Nystrom, George, Ogawa, Hideo, Oshiro, Peter, Parsons, Harriet, Penalver, Juan, Phillips, Neil M., Poirier, Michael, Pradel, Nicolas, Primiani, Rurik A., Raffin, Philippe A., Rahlin, Alexandra S., Reiland, George, Risacher, Christopher, Ruiz, Ignacio, Saez-Madain, Alejandro F., Sassella, Remi, Schellart, Pim, Shaw, Paul, Silva, Kevin M., Shiokawa, Hotaka, Smith, David R., Snow, William, Souccar, Kamal, Sousa, Don, Sridharan, T. K., Srinivasan, Ranjani, Stahm, William, Stark, Antony A., Story, Kyle, Timmer, Sjoerd T., Vertatschitsch, Laura, Walther, Craig, Wei, Ta-Shun, Whitehorn, Nathan, Whitney, Alan R., Woody, David P., Wouterloot, Jan G. A., Wright, Melvin, Yamaguchi, Paul, Yu, Chen-Yu, Zeballos, Milagros, Zhang, Shuo, and Ziurys, Lucy
Abstract: 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique - global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) - to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable gamma -ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of similar to 20 mu as (at a redshift of z=0.536 this corresponds to similar to 0.13 pc similar to 1700 Schwarzschild radii with a black hole mass M-BH=8x10(8) M-circle dot). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across different imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI core. This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet. We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of similar to 15 c and similar to 20 c (similar to 1.3 and similar to 1.7 mu as day(-1), respectively), which more strongly supports the scenario of traveling shocks or instabilities in a be
Published: 2020

17. A new layout optimization technique for interferometric arrays and the final MWA antenna layout

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Beardsley, A. P., Hazelton, B. J., Morales, M. F., Capallo, R.J., Goeke, Robert F, Emrich, D., Lonsdale, Colin John, Arcus, W., Barnes, D., Bernardi, G., Bowman, J. D., Bunton, J. D., Corey, Brian E, Deshpande, A., deSouza, L., Gaensler, B. M., Greenhill, L. J., Herne, D., Hewitt, Jacqueline N, Kaplan, D. L., Kasper, J. C., Kincaid, Barton B., Koenig, R., Kratzenberg, Eric W, Lynch, M. J., McWhirter, S. R., Mitchell, D. A., Morgan, Edward H, Oberoi, Divya, Ord, S. M., Pathikulangara, J., Prabu, T., Rogers, Alan E E, Roshi, A., Salah, Joseph E., Sault, R. J., Shankar, N. Udaya, Srivani, K. S., Stevens, J., Subrahmanyan, R., Tingay, S. J., Wayth, R. B., Waterson, M., Webster, R. L., Whitney, Alan R, Williams, A., Williams, C. L., Wyithe, J. S. B., Remillard, Ronald A, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Beardsley, A. P., Hazelton, B. J., Morales, M. F., Capallo, R.J., Goeke, Robert F, Emrich, D., Lonsdale, Colin John, Arcus, W., Barnes, D., Bernardi, G., Bowman, J. D., Bunton, J. D., Corey, Brian E, Deshpande, A., deSouza, L., Gaensler, B. M., Greenhill, L. J., Herne, D., Hewitt, Jacqueline N, Kaplan, D. L., Kasper, J. C., Kincaid, Barton B., Koenig, R., Kratzenberg, Eric W, Lynch, M. J., McWhirter, S. R., Mitchell, D. A., Morgan, Edward H, Oberoi, Divya, Ord, S. M., Pathikulangara, J., Prabu, T., Rogers, Alan E E, Roshi, A., Salah, Joseph E., Sault, R. J., Shankar, N. Udaya, Srivani, K. S., Stevens, J., Subrahmanyan, R., Tingay, S. J., Wayth, R. B., Waterson, M., Webster, R. L., Whitney, Alan R, Williams, A., Williams, C. L., Wyithe, J. S. B., and Remillard, Ronald A
Abstract: Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21-cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed - even at the remote Australian location of the Murchison Widefield Array (MWA) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhances the PSF sidelobes and reduces the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution and snapshot PSF for this array choice., U.S. National Science Foundation (grants AST CAREER-0847753, AST-0457585, AST-0908884 and PHY-0835713), Australian Research Council (grants LE0775621 and LE0882938), U.S. Air Force Office of Scientific Research (grant FA9550-0510247)
Published: 2020

18. Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre

Author: Doeleman, Sheperd S., Weintroub, Jonathan, Rogers, Alan E. E., Plambeck, Richard, Freund, Robert, Tilanus, Remo P. J., Friberg, Per, Ziurys, Lucy M., Moran, James M., Corey, Brian, Young, Ken H., Smythe, Daniel L., Titus, Michael, Marrone, Daniel P., Cappallo, Roger J., Bock, Douglas C.-J., Bower, Geoffrey C., Chamberlin, Richard, Davis, Gary R., Krichbaum, Thomas P., Lamb, James, Maness, Holly, Niell, Arthur E., Roy, Alan, Strittmatter, Peter, Werthimer, Daniel, Whitney, Alan R., and Woody, David
Published: 2008
Full Text: View/download PDF

19. First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole

Author: Akiyama, Kazunori, Alberdi, Antxon, Alef, Walter, Asada, Keiichi, Azulay, Rebecca, Baczko, Anne-Kathrin, Ball, David, Balokovic, Mislav, Barrett, John, Bintley, Dan, Blackburn, Lindy, Boland, Wilfred, Bouman, Katherine L., Bower, Geoffrey C., Bremer, Michael, Brinkerink, Christiaan D., Brissenden, Roger, Britzen, Silke, Broderick, Avery E., Broguiere, Dominique, Bronzwaer, Thomas, Byun, Do-Young, Carlstrom, John E., Chael, Andrew, Chan, Chi-kwan, Chatterjee, Shami, Chatterjee, Koushik, Chen, Ming-Tang, Chen, Yongjun, Cho, Ilje, Christian, Pierre, Conway, John E., Cordes, James M., Crew, Geoffrey B., Cui, Yuzhu, Davelaar, Jordy, De Laurentis, Mariafelicia, Deane, Roger, Dempsey, Jessica, Desvignes, Gregory, Dexter, Jason, Doeleman, Sheperd S., Eatough, Ralph P., Falcke, Heino, Fish, Vincent L., Fomalont, Ed, Fraga-Encinas, Raquel, Freeman, William T., Friberg, Per, Fromm, Christian M., Gomez, Jose L., Galison, Peter, Gammie, Charles F., Garcia, Roberto, Gentaz, Olivier, Georgiev, Boris, Goddi, Ciriaco, Gold, Roman, Gu, Minfeng, Gurwell, Mark, Hada, Kazuhiro, Hecht, Michael H., Hesper, Ronald, Ho, Luis C., Ho, Paul, Honma, Mareki, Huang, Chih-Wei L., Huang, Lei, Hughes, David H., Ikeda, Shiro, Inoue, Makoto, Issaoun, Sara, James, David J., Jannuzi, Buell T., Janssen, Michael, Jeter, Britton, Jiang, Wu, Johnson, Michael D., Jorstad, Svetlana, Jung, Taehyun, Karami, Mansour, Karuppusamy, Ramesh, Kawashima, Tomohisa, Keating, Garrett K., Kettenis, Mark, Kim, Jae-Young, Kim, Junhan, Kim, Jongsoo, Kino, Motoki, Koay, Jun Yi, Koch, Patrick M., Koyama, Shoko, Kramer, Michael, Kramer, Carsten, Krichbaum, Thomas P., Kuo, Cheng-Yu, Lauer, Tod R., Lee, Sang-Sung, Li, Yan-Rong, Li, Zhiyuan, Lindqvist, Michael, Liu, Kuo, Liuzzo, Elisabetta, Lo, Wen-Ping, Lobanov, Andrei P., Loinard, Laurent, Lonsdale, Colin, Lu, Ru-Sen, MacDonald, Nicholas R., Mao, Jirong, Markoff, Sera, Marrone, Daniel P., Marscher, Alan P., Marti-Vidal, Ivan, Matsushita, Satoki, Matthews, Lynn D., Medeiros, Lia, Menten, Karl M., Mizuno, Yosuke, Mizuno, Izumi, Moran, James M., Moriyama, Kotaro, Moscibrodzka, Monika, Mueller, Cornelia, Nagai, Hiroshi, Nagar, Neil M., Nakamura, Masanori, Narayan, Ramesh, Narayanan, Gopal, Natarajan, Iniyan, Neri, Roberto, Ni, Chunchong, Noutsos, Aristeidis, Okino, Hiroki, Olivares, Hector, Ortiz-Leon, Gisela N., Oyama, Tomoaki, Ozel, Feryal, Palumbo, Daniel C. M., Patel, Nimesh, Pen, Ue-Li, Pesce, Dominic W., Pietu, Vincent, Plambeck, Richard, PopStefanija, Aleksandar, Porth, Oliver, Prather, Ben, Preciado-Lopez, Jorge A., Psaltis, Dimitrios, Pu, Hung-Yi, Ramakrishnan, Venkatessh, Rao, Ramprasad, Rawlings, Mark G., Raymond, Alexander W., Rezzolla, Luciano, Ripperda, Bart, Roelofs, Freek, Rogers, Alan, Ros, Eduardo, Rose, Mel, Roshanineshat, Arash, Rottmann, Helge, Roy, Alan L., Ruszczyk, Chet, Ryan, Benjamin R., Rygl, Kazi L. J., Sanchez, Salvador, Sanchez-Arguelles, David, Sasada, Mahito, Savolainen, Tuomas, Schloerb, F. Peter, Schuster, Karl-Friedrich, Shao, Lijing, Shen, Zhiqiang, Small, Des, Sohn, Bong Won, SooHoo, Jason, Tazaki, Fumie, Tiede, Paul, Tilanus, Remo P. J., Titus, Michael, Toma, Kenji, Torne, Pablo, Trent, Tyler, Trippe, Sascha, Tsuda, Shuichiro, van Bemmel, Ilse, van Langevelde, Huib Jan, van Rossum, Daniel R., Wagner, Jan, Wardle, John, Weintroub, Jonathan, Wex, Norbert, Wharton, Robert, Wielgus, Maciek, Wong, George N., Wu, Qingwen, Young, Ken, Young, Andre, Younsi, Ziri, Yuan, Feng, Yuan, Ye-Fei, Zensus, J. Anton, Zhao, Guangyao, Zhao, Shan-Shan, Zhu, Ziyan, Algaba, Juan-Carlos, Allardi, Alexander, Amestica, Rodrigo, Anczarski, Jadyn, Bach, Uwe, Baganoff, Frederick K., Beaudoin, Christopher, Benson, Bradford A., Berthold, Ryan, Blanchard, Jay M., Blundell, Ray, Bustamente, Sandra, Cappallo, Roger, Castillo-Dominguez, Edgar, Chang, Chih-Cheng, Chang, Shu-Hao, Chang, Song-Chu, Chen, Chung-Chen, Chilson, Ryan, Chuter, Tim C., Rosado, Rodrigo Cordova, Coulson, Iain M., Crawford, Thomas M., Crowley, Joseph, David, John, Derome, Mark, Dexter, Matthew, Dornbusch, Sven, Dudevoir, Kevin A., Dzib, Sergio A., Eckart, Andreas, Eckert, Chris, Erickson, Neal R., Everett, Wendeline B., Faber, Aaron, Farah, Joseph R., Fath, Vernon, Folkers, Thomas W., Forbes, David C., Freund, Robert, Gomez-Ruiz, Arturo I., Gale, David M., Gao, Feng, Geertsema, Gertie, Graham, David A., Greer, Christopher H., Grosslein, Ronald, Gueth, Frederic, Haggard, Daryl, Halverson, Nils W., Han, Chih-Chiang, Han, Kuo-Chang, Hao, Jinchi, Hasegawa, Yutaka, Henning, Jason W., Hernandez-Gomez, Antonio, Herrero-Illana, Ruben, Heyminck, Stefan, Hirota, Akihiko, Hoge, James, Huang, Yau-De, Impellizzeri, C. M. Violette, Jiang, Homin, Kamble, Atish, Keisler, Ryan, Kimura, Kimihiro, Kono, Yusuke, Kubo, Derek, Kuroda, John, Lacasse, Richard, Laing, Robert A., Leitch, Erik M., Li, Chao-Te, Lin, Lupin C. -C., Liu, Ching-Tang, Liu, Kuan-Yu, Lu, Li-Ming, Marson, Ralph G., Martin-Cocher, Pierre L., Massingill, Kyle D., Matulonis, Callie, McColl, Martin P., McWhirter, Stephen R., Messias, Hugo, Meyer-Zhao, Zheng, Michalik, Daniel, Montana, Alfredo, Montgomerie, William, Mora-Klein, Matias, Muders, Dirk, Nadolski, Andrew, Navarro, Santiago, Neilsen, Joseph, Nguyen, Chi H., Nishioka, Hiroaki, Norton, Timothy, Nowak, Michael A., Nystrom, George, Ogawa, Hideo, Oshiro, Peter, Parsons, Harriet, Paine, Scott N., Penalver, Juan, Phillips, Neil M., Poirier, Michael, Pradel, Nicolas, Primiani, Rurik A., Raffin, Philippe A., Rahlin, Alexandra S., Reiland, George, Risacher, Christopher, Ruiz, Ignacio, Saez-Madain, Alejandro F., Sassella, Remi, Schellart, Pim, Shaw, Paul, Silva, Kevin M., Shiokawa, Hotaka, Smith, David R., Snow, William, Souccar, Kamal, Sousa, Don, Sridharan, T. K., Srinivasan, Ranjani, Stahm, William, Stark, Anthony A., Story, Kyle, Timmer, Sjoerd T., Vertatschitsch, Laura, Walther, Craig, Wei, Ta-Shun, Whitehorn, Nathan, Whitney, Alan R., Woody, David P., Wouterloot, Jan G. A., Wright, Melvin, Yamaguchi, Paul, Yu, Chen-Yu, Zeballos, Milagros, Zhang, Shuo, Ziurys, Lucy, Akiyama, Kazunori, Alberdi, Antxon, Alef, Walter, Asada, Keiichi, Azulay, Rebecca, Baczko, Anne-Kathrin, Ball, David, Balokovic, Mislav, Barrett, John, Bintley, Dan, Blackburn, Lindy, Boland, Wilfred, Bouman, Katherine L., Bower, Geoffrey C., Bremer, Michael, Brinkerink, Christiaan D., Brissenden, Roger, Britzen, Silke, Broderick, Avery E., Broguiere, Dominique, Bronzwaer, Thomas, Byun, Do-Young, Carlstrom, John E., Chael, Andrew, Chan, Chi-kwan, Chatterjee, Shami, Chatterjee, Koushik, Chen, Ming-Tang, Chen, Yongjun, Cho, Ilje, Christian, Pierre, Conway, John E., Cordes, James M., Crew, Geoffrey B., Cui, Yuzhu, Davelaar, Jordy, De Laurentis, Mariafelicia, Deane, Roger, Dempsey, Jessica, Desvignes, Gregory, Dexter, Jason, Doeleman, Sheperd S., Eatough, Ralph P., Falcke, Heino, Fish, Vincent L., Fomalont, Ed, Fraga-Encinas, Raquel, Freeman, William T., Friberg, Per, Fromm, Christian M., Gomez, Jose L., Galison, Peter, Gammie, Charles F., Garcia, Roberto, Gentaz, Olivier, Georgiev, Boris, Goddi, Ciriaco, Gold, Roman, Gu, Minfeng, Gurwell, Mark, Hada, Kazuhiro, Hecht, Michael H., Hesper, Ronald, Ho, Luis C., Ho, Paul, Honma, Mareki, Huang, Chih-Wei L., Huang, Lei, Hughes, David H., Ikeda, Shiro, Inoue, Makoto, Issaoun, Sara, James, David J., Jannuzi, Buell T., Janssen, Michael, Jeter, Britton, Jiang, Wu, Johnson, Michael D., Jorstad, Svetlana, Jung, Taehyun, Karami, Mansour, Karuppusamy, Ramesh, Kawashima, Tomohisa, Keating, Garrett K., Kettenis, Mark, Kim, Jae-Young, Kim, Junhan, Kim, Jongsoo, Kino, Motoki, Koay, Jun Yi, Koch, Patrick M., Koyama, Shoko, Kramer, Michael, Kramer, Carsten, Krichbaum, Thomas P., Kuo, Cheng-Yu, Lauer, Tod R., Lee, Sang-Sung, Li, Yan-Rong, Li, Zhiyuan, Lindqvist, Michael, Liu, Kuo, Liuzzo, Elisabetta, Lo, Wen-Ping, Lobanov, Andrei P., Loinard, Laurent, Lonsdale, Colin, Lu, Ru-Sen, MacDonald, Nicholas R., Mao, Jirong, Markoff, Sera, Marrone, Daniel P., Marscher, Alan P., Marti-Vidal, Ivan, Matsushita, Satoki, Matthews, Lynn D., Medeiros, Lia, Menten, Karl M., Mizuno, Yosuke, Mizuno, Izumi, Moran, James M., Moriyama, Kotaro, Moscibrodzka, Monika, Mueller, Cornelia, Nagai, Hiroshi, Nagar, Neil M., Nakamura, Masanori, Narayan, Ramesh, Narayanan, Gopal, Natarajan, Iniyan, Neri, Roberto, Ni, Chunchong, Noutsos, Aristeidis, Okino, Hiroki, Olivares, Hector, Ortiz-Leon, Gisela N., Oyama, Tomoaki, Ozel, Feryal, Palumbo, Daniel C. M., Patel, Nimesh, Pen, Ue-Li, Pesce, Dominic W., Pietu, Vincent, Plambeck, Richard, PopStefanija, Aleksandar, Porth, Oliver, Prather, Ben, Preciado-Lopez, Jorge A., Psaltis, Dimitrios, Pu, Hung-Yi, Ramakrishnan, Venkatessh, Rao, Ramprasad, Rawlings, Mark G., Raymond, Alexander W., Rezzolla, Luciano, Ripperda, Bart, Roelofs, Freek, Rogers, Alan, Ros, Eduardo, Rose, Mel, Roshanineshat, Arash, Rottmann, Helge, Roy, Alan L., Ruszczyk, Chet, Ryan, Benjamin R., Rygl, Kazi L. J., Sanchez, Salvador, Sanchez-Arguelles, David, Sasada, Mahito, Savolainen, Tuomas, Schloerb, F. Peter, Schuster, Karl-Friedrich, Shao, Lijing, Shen, Zhiqiang, Small, Des, Sohn, Bong Won, SooHoo, Jason, Tazaki, Fumie, Tiede, Paul, Tilanus, Remo P. J., Titus, Michael, Toma, Kenji, Torne, Pablo, Trent, Tyler, Trippe, Sascha, Tsuda, Shuichiro, van Bemmel, Ilse, van Langevelde, Huib Jan, van Rossum, Daniel R., Wagner, Jan, Wardle, John, Weintroub, Jonathan, Wex, Norbert, Wharton, Robert, Wielgus, Maciek, Wong, George N., Wu, Qingwen, Young, Ken, Young, Andre, Younsi, Ziri, Yuan, Feng, Yuan, Ye-Fei, Zensus, J. Anton, Zhao, Guangyao, Zhao, Shan-Shan, Zhu, Ziyan, Algaba, Juan-Carlos, Allardi, Alexander, Amestica, Rodrigo, Anczarski, Jadyn, Bach, Uwe, Baganoff, Frederick K., Beaudoin, Christopher, Benson, Bradford A., Berthold, Ryan, Blanchard, Jay M., Blundell, Ray, Bustamente, Sandra, Cappallo, Roger, Castillo-Dominguez, Edgar, Chang, Chih-Cheng, Chang, Shu-Hao, Chang, Song-Chu, Chen, Chung-Chen, Chilson, Ryan, Chuter, Tim C., Rosado, Rodrigo Cordova, Coulson, Iain M., Crawford, Thomas M., Crowley, Joseph, David, John, Derome, Mark, Dexter, Matthew, Dornbusch, Sven, Dudevoir, Kevin A., Dzib, Sergio A., Eckart, Andreas, Eckert, Chris, Erickson, Neal R., Everett, Wendeline B., Faber, Aaron, Farah, Joseph R., Fath, Vernon, Folkers, Thomas W., Forbes, David C., Freund, Robert, Gomez-Ruiz, Arturo I., Gale, David M., Gao, Feng, Geertsema, Gertie, Graham, David A., Greer, Christopher H., Grosslein, Ronald, Gueth, Frederic, Haggard, Daryl, Halverson, Nils W., Han, Chih-Chiang, Han, Kuo-Chang, Hao, Jinchi, Hasegawa, Yutaka, Henning, Jason W., Hernandez-Gomez, Antonio, Herrero-Illana, Ruben, Heyminck, Stefan, Hirota, Akihiko, Hoge, James, Huang, Yau-De, Impellizzeri, C. M. Violette, Jiang, Homin, Kamble, Atish, Keisler, Ryan, Kimura, Kimihiro, Kono, Yusuke, Kubo, Derek, Kuroda, John, Lacasse, Richard, Laing, Robert A., Leitch, Erik M., Li, Chao-Te, Lin, Lupin C. -C., Liu, Ching-Tang, Liu, Kuan-Yu, Lu, Li-Ming, Marson, Ralph G., Martin-Cocher, Pierre L., Massingill, Kyle D., Matulonis, Callie, McColl, Martin P., McWhirter, Stephen R., Messias, Hugo, Meyer-Zhao, Zheng, Michalik, Daniel, Montana, Alfredo, Montgomerie, William, Mora-Klein, Matias, Muders, Dirk, Nadolski, Andrew, Navarro, Santiago, Neilsen, Joseph, Nguyen, Chi H., Nishioka, Hiroaki, Norton, Timothy, Nowak, Michael A., Nystrom, George, Ogawa, Hideo, Oshiro, Peter, Parsons, Harriet, Paine, Scott N., Penalver, Juan, Phillips, Neil M., Poirier, Michael, Pradel, Nicolas, Primiani, Rurik A., Raffin, Philippe A., Rahlin, Alexandra S., Reiland, George, Risacher, Christopher, Ruiz, Ignacio, Saez-Madain, Alejandro F., Sassella, Remi, Schellart, Pim, Shaw, Paul, Silva, Kevin M., Shiokawa, Hotaka, Smith, David R., Snow, William, Souccar, Kamal, Sousa, Don, Sridharan, T. K., Srinivasan, Ranjani, Stahm, William, Stark, Anthony A., Story, Kyle, Timmer, Sjoerd T., Vertatschitsch, Laura, Walther, Craig, Wei, Ta-Shun, Whitehorn, Nathan, Whitney, Alan R., Woody, David P., Wouterloot, Jan G. A., Wright, Melvin, Yamaguchi, Paul, Yu, Chen-Yu, Zeballos, Milagros, Zhang, Shuo, and Ziurys, Lucy
Abstract: When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 +/- 3 mu as, which is circular and encompasses a central depression in brightness with a flux ratio greater than or similar to 10: 1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5 +/- 0.7) x 10(9) M-circle dot. Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.
Published: 2019

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

Author: Haystack Observatory, Cappallo, Roger J, Corey, Brian E, Kincaid, Barton B., Kratzenberg, Eric W, Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E E, Salah, Joseph E, Whitney, Alan R, Haystack Observatory, Cappallo, Roger J, Corey, Brian E, Kincaid, Barton B., Kratzenberg, Eric W, Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E E, Salah, Joseph E, and Whitney, Alan R
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: 2019

21. Quasars: Millisecond-of-Arc Structure Revealed by Very-Long-Baseline Interferometry

Author: Knight, Curtis A., Robertson, Douglas S., Shapiro, Irwin I., Whitney, Alan R., Clark, Thomas A., Goldstein, Richard M., Marandino, Gerard E., and Vandenberg, Nancy R.
Published: 1971

22. A digital-receiver for the Murchison Widefield Array

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Goeke, Robert F., Morgan, Edward H., Williams, Christopher Leigh, Hewitt, Jacqueline N., Remillard, Ronald Alan, Kratzenberg, Eric W., McWhirter, Stephen R., Cappallo, Roger J., Corey, Brian E., Kincaid, Barton B., Lonsdale, Colin John, Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Morgan, Edward H, Hewitt, Jacqueline N, Kratzenberg, Eric W, Cappallo, Roger J, Goeke, Robert F, Remillard, Ronald A, Corey, Brian E, Rogers, Alan E E, Whitney, Alan R, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Goeke, Robert F., Morgan, Edward H., Williams, Christopher Leigh, Hewitt, Jacqueline N., Remillard, Ronald Alan, Kratzenberg, Eric W., McWhirter, Stephen R., Cappallo, Roger J., Corey, Brian E., Kincaid, Barton B., Lonsdale, Colin John, Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Morgan, Edward H, Hewitt, Jacqueline N, Kratzenberg, Eric W, Cappallo, Roger J, Goeke, Robert F, Remillard, Ronald A, Corey, Brian E, Rogers, Alan E E, and Whitney, Alan R
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

23. FIRST SEASON MWA EOR POWER SPECTRUM RESULTS AT REDSHIFT 7

Author: Haystack Observatory, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J, Corey, Brian E, de Oliveira Costa, Angelica, Dillon, Joshua Shane, Ewall-Wice, Aaron Michael, Feng, Lu, Goeke, Robert F, Hewitt, Jacqueline N, Morgan, Edward H, Tegmark, Max Erik, Whitney, Alan R, Kratzenberg, Eric W, Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E E, Neben, Abraham Richard, Williams, Christopher Leigh, Haystack Observatory, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J, Corey, Brian E, de Oliveira Costa, Angelica, Dillon, Joshua Shane, Ewall-Wice, Aaron Michael, Feng, Lu, Goeke, Robert F, Hewitt, Jacqueline N, Morgan, Edward H, Tegmark, Max Erik, Whitney, Alan R, Kratzenberg, Eric W, Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E E, Neben, Abraham Richard, and Williams, Christopher Leigh
Abstract: The Murchison Widefield Array (MWA) has collected hundreds of hours of Epoch of Reionization (EoR) data and now faces the challenge of overcoming foreground and systematic contamination to reduce the data to a cosmological measurement. We introduce several novel analysis techniques, such as cable reflection calibration, hyper-resolution gridding kernels, diffuse foreground model subtraction, and quality control methods. Each change to the analysis pipeline is tested against a two-dimensional power spectrum figure of merit to demonstrate improvement. We incorporate the new techniques into a deep integration of 32 hours of MWA data. This data set is used to place a systematic-limited upper limit on the cosmological power spectrum of ∆² ≥ 2.7 x 10⁴ mK² at k = 0.27 h Mpc⁻¹ and z = 7.1, consistent with other published limits, and a modest improvement (factor of 1.4) over previous MWA results. From this deep analysis, we have identified a list of improvements to be made to our EoR data analysis strategies. These improvements will be implemented in the future and detailed in upcoming publications., National Science Foundation (U.S.) (Grants AST-1410484 and AST-1206552)
Published: 2017

24. THE IMPORTANCE OF WIDE-FIELD FOREGROUND REMOVAL FOR 21 cm COSMOLOGY: A DEMONSTRATION WITH EARLY MWA EPOCH OF REIONIZATION OBSERVATIONS

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J, Corey, Brian E, de Oliveira Costa, Angelica, Feng, Lu, Goeke, Robert F, Hewitt, Jacqueline N, Kratzenberg, Eric W, Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H, Rogers, Alan E E, Whitney, Alan R, Pober, J. C., Hazelton, B. J., Beardsley, A. P., Barry, N. A., Martinot, Z. E., Sullivan, I. S., Morales, M. F., Bell, M. E., Bernardi, G., Bhat, N. D. R., Bowman, J. D., Briggs, F., Carroll, P., Deshpande, A. A., Dillon, Joshua S., Emrich, D., Ewall-Wice, A. M., Greenhill, L. J., Hindson, L., Hurley-Walker, N., Jacobs, D. C., Johnston-Hollitt, M., Kaplan, D. L., Kasper, J. C., Kim, Han-Seek, Kittiwisit, P., Kudryavtseva, N., Lenc, E., Line, J., Loeb, A., Lynch, M. J., McKinley, B., Mitchell, D. A., Neben, A. R., Oberoi, D., Offringa, A. R., Ord, S. M., Paul, Sourabh, Pindor, B., Prabu, T., Procopio, P., Riding, J., Roshi, A., Sethi, Shiv K., Shankar, N. Udaya, Srivani, K. S., Subrahmanyan, R., Tegmark, M., Thyagarajan, Nithyanandan, Tingay, S. J., Trott, C. M., Waterson, M., Wayth, R. B., Webster, R. L., Williams, A., Williams, C. L., Wyithe, J. S. B., Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J, Corey, Brian E, de Oliveira Costa, Angelica, Feng, Lu, Goeke, Robert F, Hewitt, Jacqueline N, Kratzenberg, Eric W, Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H, Rogers, Alan E E, Whitney, Alan R, Pober, J. C., Hazelton, B. J., Beardsley, A. P., Barry, N. A., Martinot, Z. E., Sullivan, I. S., Morales, M. F., Bell, M. E., Bernardi, G., Bhat, N. D. R., Bowman, J. D., Briggs, F., Carroll, P., Deshpande, A. A., Dillon, Joshua S., Emrich, D., Ewall-Wice, A. M., Greenhill, L. J., Hindson, L., Hurley-Walker, N., Jacobs, D. C., Johnston-Hollitt, M., Kaplan, D. L., Kasper, J. C., Kim, Han-Seek, Kittiwisit, P., Kudryavtseva, N., Lenc, E., Line, J., Loeb, A., Lynch, M. J., McKinley, B., Mitchell, D. A., Neben, A. R., Oberoi, D., Offringa, A. R., Ord, S. M., Paul, Sourabh, Pindor, B., Prabu, T., Procopio, P., Riding, J., Roshi, A., Sethi, Shiv K., Shankar, N. Udaya, Srivani, K. S., Subrahmanyan, R., Tegmark, M., Thyagarajan, Nithyanandan, Tingay, S. J., Trott, C. M., Waterson, M., Wayth, R. B., Webster, R. L., Williams, A., Williams, C. L., and Wyithe, J. S. B.
Abstract: In this paper we present observations, simulations, and analysis demonstrating the direct connection between the location of foreground emission on the sky and its location in cosmological power spectra from interferometric redshifted 21 cm experiments. We begin with a heuristic formalism for understanding the mapping of sky coordinates into the cylindrically averaged power spectra measurements used by 21 cm experiments, with a focus on the effects of the instrument beam response and the associated sidelobes. We then demonstrate this mapping by analyzing power spectra with both simulated and observed data from the Murchison Widefield Array. We find that removing a foreground model that includes sources in both the main field of view and the first sidelobes reduces the contamination in high k[subscript ∥] modes by several per cent relative to a model that only includes sources in the main field of view, with the completeness of the foreground model setting the principal limitation on the amount of power removed. While small, a percent-level amount of foreground power is in itself more than enough to prevent recovery of any Epoch of Reionization signal from these modes. This result demonstrates that foreground subtraction for redshifted 21 cm experiments is truly a wide-field problem, and algorithms and simulations must extend beyond the instrument's main field of view to potentially recover the full 21 cm power spectrum.
Published: 2017

25. LOW-FREQUENCY OBSERVATIONS OF LINEARLY POLARIZED STRUCTURES IN THE INTERSTELLAR MEDIUM NEAR THE SOUTH GALACTIC POLE

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J, Corey, Brian E, de Oliveira Costa, Angelica, Dillon, Joshua Shane, Ewall-Wice, Aaron Michael, Feng, Lu, Goeke, Robert F, Hewitt, Jacqueline N, Morgan, Edward H, Neben, Abraham Richard, Rogers, Alan E E, Tegmark, Max Erik, Whitney, Alan R, Williams, Christopher Leigh, Lenc, E., Gaensler, B. M., Sun, X. H., Sadler, E. M., Willis, A. G., Barry, N., Beardsley, A. P., Bell, M. E., Bernardi, G., Bowman, J. D., Briggs, F., Callingham, J. R., Carroll, P., Deshpande, A. A., Dwarkanath, K. S., Emrich, D., For, B.-Q., Greenhill, L. J., Hancock, P., Hazelton, B. J., Hindson, L., Hurley-Walker, N., Johnston-Hollitt, M., Jacobs, D. C., Kapińska, A. D., Kaplan, D. L., Kasper, J. C., Kim, H.-S., Kratzenberg, E., Line, J., Loeb, A., Lonsdale, C. J., Lynch, M. J., McKinley, B., McWhirter, S. R., Mitchell, D. A., Morales, M. F., Morgan, J., Murphy, T., Oberoi, D., Offringa, A. R., Ord, S. M., Paul, S., Pindor, B., Pober, J. C., Prabu, T., Procopio, P., Riding, J., Roshi, A., Shankar, N. Udaya, Sethi, S. K., Srivani, K. S., Staveley-Smith, L., Subrahmanyan, R., Sullivan, I. S., Thyagarajan, Nithyanandan, Tingay, S. J., Trott, C., Waterson, M., Wayth, R. B., Webster, R. L., Williams, A., Wu, C., Wyithe, J. S. B., Zheng, Q., Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J, Corey, Brian E, de Oliveira Costa, Angelica, Dillon, Joshua Shane, Ewall-Wice, Aaron Michael, Feng, Lu, Goeke, Robert F, Hewitt, Jacqueline N, Morgan, Edward H, Neben, Abraham Richard, Rogers, Alan E E, Tegmark, Max Erik, Whitney, Alan R, Williams, Christopher Leigh, Lenc, E., Gaensler, B. M., Sun, X. H., Sadler, E. M., Willis, A. G., Barry, N., Beardsley, A. P., Bell, M. E., Bernardi, G., Bowman, J. D., Briggs, F., Callingham, J. R., Carroll, P., Deshpande, A. A., Dwarkanath, K. S., Emrich, D., For, B.-Q., Greenhill, L. J., Hancock, P., Hazelton, B. J., Hindson, L., Hurley-Walker, N., Johnston-Hollitt, M., Jacobs, D. C., Kapińska, A. D., Kaplan, D. L., Kasper, J. C., Kim, H.-S., Kratzenberg, E., Line, J., Loeb, A., Lonsdale, C. J., Lynch, M. J., McKinley, B., McWhirter, S. R., Mitchell, D. A., Morales, M. F., Morgan, J., Murphy, T., Oberoi, D., Offringa, A. R., Ord, S. M., Paul, S., Pindor, B., Pober, J. C., Prabu, T., Procopio, P., Riding, J., Roshi, A., Shankar, N. Udaya, Sethi, S. K., Srivani, K. S., Staveley-Smith, L., Subrahmanyan, R., Sullivan, I. S., Thyagarajan, Nithyanandan, Tingay, S. J., Trott, C., Waterson, M., Wayth, R. B., Webster, R. L., Williams, A., Wu, C., Wyithe, J. S. B., and Zheng, Q.
Published: 2017

26. A high reliability survey of discrete Epoch of Reionization foreground sources in the MWA EoR0 field

Author: Haystack Observatory, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J, Corey, Brian E, de Oliveira Costa, Angelica, Dillon, Joshua Shane, Ewall-Wice, Aaron Michael, Feng, Lu, Goeke, Robert F, Hewitt, Jacqueline N, Kratzenberg, Eric W, Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H, Neben, Abraham Richard, Rogers, Alan E E, Tegmark, Max Erik, Whitney, Alan R, Williams, Christopher Leigh, Carroll, P. A., Line, J., Morales, M. F., Barry, N., Beardsley, A. P., Hazelton, B. J., Jacobs, D. C., Pober, J. C., Sullivan, I. S., Webster, R. L., Bernardi, G., Bowman, J. D., Briggs, F., Emrich, D., Gaensler, B. M., Greenhill, L. J., Hurley-Walker, N., Johnston-Hollitt, M., Kaplan, D. L., Kasper, J. C., Kim, HS., Lenc, E., Loeb, A., Lynch, M. J., McKinley, B., Mitchell, D. A., Oberoi, D., Offringa, A. R., Ord, S. M., Paul, S., Pindor, B., Prabu, T., Procopio, P., Riding, J., Roshi, A., Shankar, N. Udaya, Sethi, S. K., Srivani, K. S., Subrahmanyan, R., Thyagarajan, Nithyanandan, Tingay, S. J., Waterson, M., Wayth, R. B., Williams, A., Wu, C., Wyithe, J. S. B., Haystack Observatory, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J, Corey, Brian E, de Oliveira Costa, Angelica, Dillon, Joshua Shane, Ewall-Wice, Aaron Michael, Feng, Lu, Goeke, Robert F, Hewitt, Jacqueline N, Kratzenberg, Eric W, Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H, Neben, Abraham Richard, Rogers, Alan E E, Tegmark, Max Erik, Whitney, Alan R, Williams, Christopher Leigh, Carroll, P. A., Line, J., Morales, M. F., Barry, N., Beardsley, A. P., Hazelton, B. J., Jacobs, D. C., Pober, J. C., Sullivan, I. S., Webster, R. L., Bernardi, G., Bowman, J. D., Briggs, F., Emrich, D., Gaensler, B. M., Greenhill, L. J., Hurley-Walker, N., Johnston-Hollitt, M., Kaplan, D. L., Kasper, J. C., Kim, HS., Lenc, E., Loeb, A., Lynch, M. J., McKinley, B., Mitchell, D. A., Oberoi, D., Offringa, A. R., Ord, S. M., Paul, S., Pindor, B., Prabu, T., Procopio, P., Riding, J., Roshi, A., Shankar, N. Udaya, Sethi, S. K., Srivani, K. S., Subrahmanyan, R., Thyagarajan, Nithyanandan, Tingay, S. J., Waterson, M., Wayth, R. B., Williams, A., Wu, C., and Wyithe, J. S. B.
Abstract: Detection of the epoch of reionization H i signal requires a precise understanding of the intervening galaxies and AGN, both for instrumental calibration and foreground removal. We present a catalogue of 7394 extragalactic sources at 182 MHz detected in the RA = 0 field of the Murchison Widefield Array Epoch of Reionization observation programme. Motivated by unprecedented requirements for precision and reliability we develop new methods for source finding and selection. We apply machine learning methods to self-consistently classify the relative reliability of 9490 source candidates. A subset of 7466 are selected based on reliability class and signal-to-noise ratio criteria. These are statistically cross-matched to four other radio surveys using both position and flux density information. We find 7369 sources to have confident matches, including 90 partially resolved sources that split into a total of 192 sub-components. An additional 25 unmatched sources are included as new radio detections. The catalogue sources have a median spectral index of −0.85. Spectral flattening is seen towards lower frequencies with a median of −0.71 predicted at 182 MHz. The astrometric error is 7 arcsec compared to a 2.3 arcmin beam FWHM. The resulting catalogue covers ∼1400 deg² and is complete to approximately 80 mJy within half beam power. This provides the most reliable discrete source sky model available to date in the MWA EoR0 field for precision foreground subtraction., National Science Foundation (U.S.) (AST-0847753), National Science Foundation (U.S.) (AST-1410484), National Science Foundation (U.S.) (AST-1506024)
Published: 2017

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

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Oberoi, Divya, Matthews, Lynn D., Lonsdale, Colin John, Benkevitch, Leonid, Cappallo, Roger J., Corey, Brian E., Derome, Mark F., Kennedy, Rachel, Kincaid, Barton B., McWhirter, Stephen R., Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Morgan, Edward H., Williams, Christopher, Goeke, Robert F., Hewitt, Jacqueline N., Rogers, Alan E E, Whitney, Alan R, Morgan, Edward H, Williams, Christopher Leigh, Goeke, Robert F, Hewitt, Jacqueline N, Cappallo, Roger J, Corey, Brian E, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Oberoi, Divya, Matthews, Lynn D., Lonsdale, Colin John, Benkevitch, Leonid, Cappallo, Roger J., Corey, Brian E., Derome, Mark F., Kennedy, Rachel, Kincaid, Barton B., McWhirter, Stephen R., Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Morgan, Edward H., Williams, Christopher, Goeke, Robert F., Hewitt, Jacqueline N., Rogers, Alan E E, Whitney, Alan R, Morgan, Edward H, Williams, Christopher Leigh, Goeke, Robert F, Hewitt, Jacqueline N, Cappallo, Roger J, and Corey, Brian E
Abstract: We present the first spectroscopic images of solar radio transients from the prototype for the Murchison Widefield Array, 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 online over the next few years.
Published: 2013

28. A new layout optimization technique for interferometric arrays and the final MWA antenna layout

Author: Capallo, R.J., Lonsdale, Colin John, Corey, Brian E., Kratzenberg, Eric W., McWhirter, Stephen R., Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Goeke, Robert F., Hewitt, Jacqueline N., Morgan, Edward H., Remillard, Ronald Alan, Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Capallo, R.J., Lonsdale, Colin John, Corey, Brian E., Kratzenberg, Eric W., McWhirter, Stephen R., Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Goeke, Robert F., Hewitt, Jacqueline N., Morgan, Edward H., Remillard, Ronald Alan, and Williams, Christopher Leigh
Abstract: Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21-cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed – even at the remote Australian location of the Murchison Widefield Array (MWA) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhances the PSF sidelobes and reduces the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution and snapshot PSF for this array choice., National Science Foundation (U.S.) (Grant AST CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), Australian Research Council (Grant LE0775621), Australian Research Council (Grant LE0882938), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), MIT School of Science
Published: 2012

29. The Murchison Widefield Array Correlator

Author: Haystack Observatory, Cappallo, Roger J., Corey, Brian E., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Ewall-Wice, Aaron Michael, Feng, Lu, Goeke, Robert F., Hewitt, Jacqueline N., Morgan, Edward H., Remillard, Ronald Alan, Williams, Christopher Leigh, Haystack Observatory, Cappallo, Roger J., Corey, Brian E., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Ewall-Wice, Aaron Michael, Feng, Lu, Goeke, Robert F., Hewitt, Jacqueline N., Morgan, Edward H., Remillard, Ronald Alan, and Williams, Christopher Leigh
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[superscript −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

30. THE SPECTRAL VARIABILITY OF THE GHZ-PEAKED SPECTRUM RADIO SOURCE PKS 1718-649 AND A COMPARISON OF ABSORPTION MODELS

Author: Haystack Observatory, Cappallo, Roger J., Corey, Brian E., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E. E., Whitney, Alan R., Haystack Observatory, Cappallo, Roger J., Corey, Brian E., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E. E., and Whitney, Alan R.
Abstract: Using the new wideband capabilities of the ATCA, we obtain spectra for PKS 1718-649, a well-known gigahertz-peaked 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

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

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E. E., Whitney, Alan R., Hewitt, Jacqueline N., Morgan, Edward H., Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E. E., Whitney, Alan R., Hewitt, Jacqueline N., Morgan, Edward H., and Williams, Christopher Leigh
Abstract: 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 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, which has a wide primary beam. We estimate the EoR power based on a cross-correlation of visibilities over time and show that the drift scan strategy is capable of detecting the EoR signal with a signal to noise that is comparable/better 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: 2015

32. FOREGROUNDS IN WIDE-FIELD REDSHIFTED 21 cm POWER SPECTRA

Author: Haystack Observatory, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., de Oliveira-Costa, Angelica, Dillon, Joshua Shane, Ewall-Wice, Aaron Michael, Feng, L., Goeke, Robert F., Hewitt, Jacqueline N., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Neben, Abraham Richard, Rogers, Alan E. E., Tegmark, Max Erik, Whitney, Alan R., Williams, Christopher Leigh, Haystack Observatory, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., de Oliveira-Costa, Angelica, Dillon, Joshua Shane, Ewall-Wice, Aaron Michael, Feng, L., Goeke, Robert F., Hewitt, Jacqueline N., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Neben, Abraham Richard, Rogers, Alan E. E., Tegmark, Max Erik, Whitney, Alan R., and Williams, Christopher Leigh
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., National Science Foundation (U.S.) (Award AST-1109257)
Published: 2015

33. On the detection and tracking of space debris using the murchison widefield array I. Simulations and test observations demonstrate feasibility

Author: Haystack Observatory, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Ewall-Wice, Aaron Michael, Feng, L., Goeke, Robert F., Morgan, Edward H., Remillard, Ronald Alan, Williams, Christopher Leigh, Cappallo, Roger J., Corey, Brian E., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., Haystack Observatory, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Ewall-Wice, Aaron Michael, Feng, L., Goeke, Robert F., Morgan, Edward H., Remillard, Ronald Alan, Williams, Christopher Leigh, Cappallo, Roger J., Corey, Brian E., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E. E., Salah, J. E., and Whitney, Alan R.
Abstract: The Murchison Widefield Array (MWA) is a new low-frequency interferometric radio telescope, operating in the benign radio frequency environment of remote Western Australia. The MWA is the low-frequency precursor to the Square Kilometre Array (SKA) and is the first of three SKA precursors to be operational, supporting a varied science mission ranging from the attempted detection of the Epoch of Reionization to the monitoring of solar flares and space weather. In this paper we explore the possibility that the MWA can be used for the purposes of Space Situational Awareness (SSA). In particular we propose that the MWA can be used as an element of a passive radar facility operating in the frequency range 87.5-108 MHz (the commercial FM broadcast band). In this scenario the MWA can be considered the receiving element in a bi-static radar configuration, with FM broadcast stations serving as non-cooperative transmitters. The FM broadcasts propagate into space, are reflected off debris in Earth orbit, and are received at the MWA. The imaging capabilities of the MWA can be used to simultaneously detect multiple pieces of space debris, image their positions on the sky as a function of time, and provide tracking data that can be used to determine orbital parameters. Such a capability would be a valuable addition to Australian and global SSA assets, in terms of southern and eastern hemispheric coverage. We provide a feasibility assessment of this proposal, based on simple calculations and electromagnetic simulations, that shows that the detection of sub-meter size debris should be possible (debris radius of >0.5 m to ~1000 km altitude). We also present a proof-of-concept set of observations that demonstrate the feasibility of the proposal, based on the detection and tracking of the International Space Station via reflected FM broadcast signals originating in southwest Western Australia. These observations broadly validate our calculations and simulations. We discuss some signifi, National Science Foundation (U.S.) (Grant AST CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant AST-0908884), National Science Foundation (U.S.) (Grant AST-1008353), National Science Foundation (U.S.) (Grant PHY-0835713), United States. Air Force Office of Scientific Research (Grant FA9550-0510247)
Published: 2015

34. A new layout optimization technique for interferometric arrays, applied to the Murchison Widefield Array

Author: Beardsley, A. P., Hazelton, B. J., Morales, M. F., Capallo, R.J., Goeke, Robert F, Emrich, D., Lonsdale, Colin John, Arcus, W., Barnes, D., Bernardi, G., Bowman, J. D., Bunton, J. D., Corey, Brian E, Deshpande, A., deSouza, L., Gaensler, B. M., Greenhill, L. J., Herne, D., Hewitt, Jacqueline N, Kaplan, D. L., Kasper, J. C., Kincaid, Barton B., Koenig, R., Kratzenberg, Eric W, Lynch, M. J., McWhirter, S. R., Mitchell, D. A., Morgan, Edward H, Oberoi, Divya, Ord, S. M., Pathikulangara, J., Prabu, T., Rogers, Alan E E, Roshi, A., Salah, Joseph E., Sault, R. J., Shankar, N. Udaya, Srivani, K. S., Stevens, J., Subrahmanyan, R., Tingay, S. J., Wayth, R. B., Waterson, M., Webster, R. L., Whitney, Alan R, Williams, A., Williams, C. L., Wyithe, J. S. B., Remillard, Ronald A, Haystack Observatory, and MIT Kavli Institute for Astrophysics and Space Research
Abstract: Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21-cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed - even at the remote Australian location of the Murchison Widefield Array (MWA) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhances the PSF sidelobes and reduces the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution and snapshot PSF for this array choice., U.S. National Science Foundation (grants AST CAREER-0847753, AST-0457585, AST-0908884 and PHY-0835713), Australian Research Council (grants LE0775621 and LE0882938), U.S. Air Force Office of Scientific Research (grant FA9550-0510247)
Published: 2012

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

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Goeke, Robert F., Lonsdale, Colin John, Cappallo, Roger J., Corey, Brian E., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Goeke, Robert F., Lonsdale, Colin John, Cappallo, Roger J., Corey, Brian E., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., and Williams, Christopher Leigh
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., National Science Foundation (U.S.) (Grant AST CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant AST-0908884), National Science Foundation (U.S.) (Grant PHY-0835713), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science
Published: 2014

37. LOW-FREQUENCY OBSERVATIONS OF THE MOON WITH THE MURCHISON WIDEFIELD ARRAY

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., and Williams, Christopher Leigh
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., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant AST-0908884), National Science Foundation (U.S.) (Grant PHY-0835713), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science
Published: 2014

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

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., and Williams, Christopher Leigh
Abstract: We present new wide-field observations of Centaurus A (Cen A) and the surrounding region at 118 MHz 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 118 MHz 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., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), National Science Foundation (U.S.) (Grant CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0908884), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science
Published: 2014

39. Science with the Murchison Widefield Array

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Coster, Anthea J., Erickson, Philip J., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, Matthews, Lynn D., McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Coster, Anthea J., Erickson, Philip J., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, Matthews, Lynn D., McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., and Williams, Christopher Leigh
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., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), National Science Foundation (U.S.) (Grant CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0908884), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science
Published: 2014

40. A STUDY OF FUNDAMENTAL LIMITATIONS TO STATISTICAL DETECTION OF REDSHIFTED H I FROM THE EPOCH OF REIONIZATION

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., and Williams, Christopher Leigh
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 [< over ~] 0.8 Mpc[superscript –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., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), National Science Foundation (U.S.) (Grant CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0908884), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science
Published: 2014

41. The Murchison Widefield Array: solar science with the low frequency SKA Precursor

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Tingay, S. J., Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Tingay, S. J., Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Remillard, Ronald Alan, Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., and Williams, Christopher Leigh
Abstract: The Murchison Widefield Array is a low frequency (80 – 300 MHz) SKA Precursor, comprising 128 aperture array elements (known as tiles) 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 concentrates on the capabilities of the MWA for solar science and summarises some of the solar science results to date, in advance of the initial operation of the final instrument in 2013., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant CAREER-0847753), National Science Foundation (U.S.) (Grant PHY-0835713), National Science Foundation (U.S.) (Grant AST-0908884), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science
Published: 2014

42. TYPO — a word processing program

Author: Whitney, Alan R., primary
Published: 1981
Full Text: View/download PDF

43. The Mark IIIA Correlator System

Author: Whitney, Alan R., primary
Published: 1988
Full Text: View/download PDF

44. DVBOO — a general-purpose driver for the 12966A ASCII interface card

Author: Whitney, Alan R., primary
Published: 1981
Full Text: View/download PDF

45. Rapid Turnaround EOP Measurements by VLBI over the Internet

Author: Koyama, Yasuhiro, primary, Kondo, Tetsuro, additional, Osaki, Hiro, additional, Whitney, Alan R., additional, and Dudevoir, Kevin A., additional
Full Text: View/download PDF

46. 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
Full Text: View/download PDF

47. Very-long-baseline radio interferometry: the Mark III system for geodesy, astrometry, and aperture synthesis

Author: Rogers, Alan E.E., Cappallo, Roger J., Levine, James I., Nesman, Edwin F., Webber, John C., Whitney, Alan R., Clark, Thomas A., Ryan, James (Irish novelist), Ma, Chopo, Corey, Brian E., Counselman, Charles C., Herring, Tomas A., Shapiro, Irwin I., Knight, Curtis A., Shaffer, David B., Vanderberg, Nancy R., Lacasse, Richard, Mauzy, Robert, Rayhrer, Benno, Schupler, Bruce R., and Pigg, J.C.
Subjects: Radio interferometers -- Innovations
Published: 1983

48. Interferometric Imaging with the 32 Element Murchison Wide-Field Array

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Benkevitch, Leonid, Cappallo, Roger J., Corey, Brian E., Doeleman, Sheperd Samuel, Derome, Mark F., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Hewitt, Jacqueline N., Matejek, Michael Scott, Morgan, Edward H., Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Benkevitch, Leonid, Cappallo, Roger J., Corey, Brian E., Doeleman, Sheperd Samuel, Derome, Mark F., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Hewitt, Jacqueline N., Matejek, Michael Scott, Morgan, Edward H., and Williams, Christopher Leigh
Abstract: The Murchison Wide-Field Array (MWA) is a low-frequency radio telescope, currently under construction, intended to search for the spectral signature of the epoch of reionization (EOR) and to probe the structure of the solar corona. Sited in western Australia, the full MWA will comprise 8192 dipoles grouped into 512 tiles and will be capable of imaging the sky south of 40° declination, from 80 MHz to 300 MHz with an instantaneous field of view that is tens of degrees wide and a resolution of a few arcminutes. A 32 station prototype of the MWA has been recently commissioned and a set of observations has been taken that exercise the whole acquisition and processing pipeline. We present Stokes I, Q, and U images from two ~4 hr integrations of a field 20° wide centered on Pictoris A. These images demonstrate the capacity and stability of a real-time calibration and imaging technique employing the weighted addition of warped snapshots to counter extreme wide-field imaging distortions., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), Australian Research Council (Grant LE0775621), Australian Research Council (Grant LE0882938), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), MIT School of Science
Published: 2013

49. A new layout optimization technique for interferometric arrays and the final MWA antenna layout

Author: Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Capallo, R.J., Lonsdale, Colin John, Corey, Brian E., Kratzenberg, Eric W., McWhirter, Stephen R., Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Goeke, Robert F., Hewitt, Jacqueline N., Morgan, Edward H., Remillard, Ronald Alan, Williams, Christopher Leigh, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Capallo, R.J., Lonsdale, Colin John, Corey, Brian E., Kratzenberg, Eric W., McWhirter, Stephen R., Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Goeke, Robert F., Hewitt, Jacqueline N., Morgan, Edward H., Remillard, Ronald Alan, and Williams, Christopher Leigh
Abstract: Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21-cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed – even at the remote Australian location of the Murchison Widefield Array (MWA) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhances the PSF sidelobes and reduces the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution and snapshot PSF for this array choice., National Science Foundation (U.S.) (Grant AST CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), Australian Research Council (Grant LE0775621), Australian Research Council (Grant LE0882938), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), MIT School of Science
Published: 2013

50. The Murchison Widefield Array: Design Overview

Author: Haystack Observatory, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology. Department of Physics, Hewitt, Jacqueline N., Lonsdale, Colin John, Cappallo, Roger J., Morales, Miguel F., Benkevitch, Leonid, Bowman, Judd D., Corey, Brian E., Doeleman, Sheperd Samuel, Derome, Mark F., Kincaid, Barton B., Kratzenberg, Eric W., Matejek, Michael Scott, Morgan, Edward H., Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., Williams, Christopher Leigh, Haystack Observatory, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology. Department of Physics, Hewitt, Jacqueline N., Lonsdale, Colin John, Cappallo, Roger J., Morales, Miguel F., Benkevitch, Leonid, Bowman, Judd D., Corey, Brian E., Doeleman, Sheperd Samuel, Derome, Mark F., Kincaid, Barton B., Kratzenberg, Eric W., Matejek, Michael Scott, Morgan, Edward H., Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., Whitney, Alan R., and Williams, Christopher Leigh
Abstract: The Murchison Widefield Array 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: detection and characterization of three-dimensional brightness temperature fluctuations in the 21 cm line of neutral hydrogen during the epoch of reionization (EoR) at redshifts from six to ten; 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 broadband active dipoles, arranged into 512 ldquotilesrdquo comprising 16 dipoles each. The tiles are quasi-randomly distributed over an aperture 1.5 km in diameter, with a small number of outliers extending to 3 km. All tile-tile baselines are correlated in custom field-programmable gate array based hardware, yielding a Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point spread function 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., U.S. Air Force Office of Scientific Research (Grant FA9550-0510247), Australian Research Council (Grants LE775621, LE882938, and DP345001), National Science Foundation (Grant AST-0457585)
Published: 2010

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