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Antioch, United States

Hovey G.,National Research Council Canada | Baker L.,Cornell University | Cortes G.,Cornell University | Deboer D.,University of California at Berkeley | And 8 more authors.
2015 1st URSI Atlantic Radio Science Conference, URSI AT-RASC 2015 | Year: 2015

Radio telescopes striving for orders of magnitude more sensitivity in the cm-wave band require reflector antennas with high performance at low relative cost compared to conventional approaches. The Composite Applications for Radio Telescopes (CART) programme at the National Research Council's (NRC's) Dominion Radio Astrophysical Observatory, near Penticton Canada has been investigating ways to build such telescopes since 2005. In 2010 a collaboration between NRC and the US-Technology Development Project (US TDP) was formed to develop a prototype 15m Gregorian offset antenna for the Square Kilometre Array (SKA). The telescope uses NRC's composite carbon fibre reflector technology to implement the highly optimized shaped optics design and innovative mechanical concepts developed by the US TDP. The result is Dish Verification Antenna-1 (DVA1), a next generation antenna that has exceptional sensitivity (> 9 m2/K), with low monotonically decreasing far out sidelobes (< -50 dB), and high stability over environmental conditions. As well, it is modular, highly reliable, and can be produced at competitive cost using mass production techniques. © 2015 International Union of Radio Science (URSI). Source


Croft S.,University of California at Berkeley | Bower G.C.,University of California at Berkeley | Ackermann R.,Search for Extraterrestrial Intelligence Institute | Atkinson S.,Search for Extraterrestrial Intelligence Institute | And 47 more authors.
Astrophysical Journal | Year: 2010

We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch (12 visits), 690 deg2 radio image and catalog at 1.4 GHz. The survey is designed to detect rare, very bright transients as well as to verify the capabilities of the ATA to form large mosaics. The combined image using data from all 12 ATATS epochs has rms noise σ = 3.94 mJy beam -1 and dynamic range 180, with a circular beam of 150″ FWHM. It contains 4408 sources to a limiting sensitivity of 5σ = 20 mJy beam -1. We compare the catalog generated from this 12 epoch combined image to the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency, and find that we can measure source positions to better than ∼20″. For sources above the ATATS completeness limit, the median flux density is 97% of the median value for matched NVSS sources, indicative of an accurate overall flux calibration. We examine the effects of source confusion due to the effects of differing resolution between ATATS and NVSS on our ability to compare flux densities. We detect no transients at flux densities greater than 40 mJy in comparison with NVSS and place a 2σ upper limit of 0.004 deg-2 on the transient rate for such sources. These results suggest that the ≳1 Jy transients reported by Matsumara et al. may not be true transients, but rather variable sources at their flux density threshold. © 2010. The American Astronomical Society. All rights reserved. Source


Bower G.C.,University of California at Berkeley | Croft S.,University of California at Berkeley | Keating G.,University of California at Berkeley | Whysong D.,University of California at Berkeley | And 49 more authors.
Astrophysical Journal | Year: 2010

The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array. PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky with an emphasis on synoptic observations that measure the static and time-variable properties of the sky. During the 2.5 year campaign, PiGSS will twice observe ∼250,000 radio sources in the 10,000 deg2 region of the sky with b < 30° to an rms sensitivity of ∼1 mJy. Additionally, sub-regions of the sky will be observed multiple times to characterize variability on timescales of days to years. We present here observations of a 10 deg2 region in the Boötes constellation overlapping the NOAO Deep Wide Field Survey field. The PiGSS image was constructed from 75 daily observations distributed over a 4 month period and has an rms flux density between 200 and 250 μJy. This represents a deeper image by a factor of 4-8 than we will achieve over the entire 10,000 deg2. We provide flux densities, source sizes, and spectral indices for the 425 sources detected in the image. We identify ∼100 new flat-spectrum radio sources; we project that when completed PiGSS will identify 104 flat-spectrum sources. We identify one source that is a possible transient radio source. This survey provides new limits on faint radio transients and variables with characteristic durations of months. © 2010. The American Astronomical Society. All rights reserved. Source

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