Papers from Scientific Meetings

Meeting of the American Astronomical Society – June 2009

The ATA was well represented at the meeting with eight papers demonstrating the broad capability of the array.  One paper reports on the SETI Galactic Center Survey and two describe radio astronomy survey projects.  Three papers describe studies of transient radio sources.  One of those studies is done commensally with the SETI survey.  One paper reports on observations of hydrogen (HI) in groups of galaxies.  The final paper describes a new data processing system that allows radio images to be made during observations.

Here are the abstracts of the papers.  Click on the title to see the full poster (PDF).

Results from the Allen Telescope Array: SETI Survey of the Galactic Center Region
Samantha K. Blair, ATA Team
SETI Institute.

We report initial results and status of a SETI Survey of the Galactic Center region. The survey spans longitude 357° to 7° and latitude -1° to + 1°, and covers the radio spectrum from 1410 MHz to 1730 MHz with a resolution of 0.7 Hz. The search system is sensitive to continuous and pulsed signals with frequency drift rates of up to ±1 Hz/sec and bandwidths less than ~ 10 Hz. In its current stage, the Allen Telescope Array (ATA-42) is an array of 42 six-meter dishes with two dual-polarization beamformers. The beams observe two independent positions within the field of view at the same frequency allowing each to serve as an “off” positions for the other beam. This is a new approach to RFI mitigation. While SETI observations proceed, two independently tunable correlators are used to image the field for other radio astronomy projects. This demonstrates the Radio Sky Survey capability of the ATA.

Results from the Allen Telescope Array: The ATA Twenty-centimeter Survey
Steve Croft, G. C. Bower, ATA Team
UC Berkeley.

We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a recently completed multi-epoch survey of 800 square degrees of sky. We are able to construct light curves to look for changes from epoch to epoch (including transient sources appearing in a single epoch) as well as a deep, multi-epoch image and associated catalog of the sky, which we compare to previous surveys such as the NRAO VLA Sky Survey (NVSS). We also describe the pipeline which allows us to reduce and analyze the data with a minimum of human interaction.

Results from the Allen Telescope Array: Launch of the Pi GHz Sky Survey (PiGSS)
Geoffrey C. Bower, S. Croft, D. Whysong, ATA Team
UC, Berkeley.

PiGGs, the Pi GHz Sky Survey, is a key project of the Allen Telescope Array. The principle goal is exploration of the static and transient radio sky at 3.1 GHz at flux densities an order of magnitude fainter than the best existing survey and matching FIRST and NVSS sensitivies, covering a large fraction of the northern sky, and exploring transient time scales from days to months through a ttiered approach. Specific results of the survey will be detection of 250,000 radio sources in a 10,000 degree region of the North Galactic Cap; daily monitoring of the 10 square degree region; automated identification and notification of transient sources in real time; and, multi-wavelength identification of sources overlapping with SDSS, FERMI, and other large surveys. PiGSS builds on the tools developed for ATATS (Croft et al.) and has been launched in Spring 2009. We present initial images and results from the survey.

A Note from Dr. Jill Tarter regarding the conversion of FiGGS to PiGGS.
The primary scientific goal was to conduct a transient survey at a frequency >>1.42 GHz, so that the spectral indices of the discovered sources could be determined.  Geoff Bower at UCB, the PI, originally picked 5 GHz as an arbitrary frequency that satisfied the requirement.  As we began commissioning the ATA and measuring its Tsys in detail, we found that a combination of RFI and the specific details of one of the standoffs that hold the feed arm to the pyramid structure added more noise to the system at exactly 5 GHz - View table (we've since redesigned the standoffs, but RFI is out of our control) so Geoff searched around for another frequency for his survey. Pi GHz raised its head - some poetry, some good Tsys values, and that is where the survey was conducted.

Results from the Allen Telescope Array: Imaging Sub-second Transients
Casey J. Law, ATA Team
UC Berkeley

Changes in computation are opening new domains of study with radio interferometers. I will describe how these capabilities are being used in the study of sub-second radio transients by the Allen Telescope Array (ATA). High-cadence imaging of the radio sky can be more efficient than existing radio surveys, improving odds of finding rare phenomena. More importantly, imaging at time scales shorter than a second gives radio interferometers new access to exciting physical processes. Potential science applications and initial fast-imaging results will be presented.

Results from the Allen Telescope Array: Launching the ATA Galactic Center Transient Survey
Peter K. G. Williams, G. C. Bower, C. J. Law, ATA Team
UC Berkeley.
 
The galactic center teems with transient phenomena at all wavelengths. The ATA Galactic Center Transient Survey (AGCTS) started in May 2009 and is currently observing 20 square degrees of sky for ~6 hours every night commensally with SETI observations. The AGCTS will collect 6 months of data operating simultaneously at two frequencies, generating a powerful dataset with spectral index information and uniform temporal coverage and observational parameters. We expect to attain a sensitivity of ~1 mJy/bm per hour-long integration and either detect significant numbers of transient events or establish robust upper limits on event rates. We present our observing and analysis techniques as well as preliminary results.

Results from the Allen Telescope Array: The ATA Fly's Eye Transient Search
Andrew Siemion1, G. Bower1, J. Cordes2, G. Foster1, W. Mallard1, P. McMahon3, J. van Leeuwen4, M. Wagner1, D. Werthimer1, Allen Telescope Array Team
1University of California, Berkeley, 2Cornell University, 3Stanford University, 4Netherlands Institute for Radio Astronomy, Netherlands.

We present results from the Fly's Eye Transient Search, a 500-hour wide-field survey for powerful millisecond time-scale dispersed radio transients using the Allen Telescope Array (ATA). In this effort, we pointed each of the extant 42 ATA dishes at a unique position on the sky to attain a maximal field-of-view of approximately 198 square degrees (at L-band). The Fly's Eye field programmable gate array-based fast readout spectrometer processes 44 independent signal paths, each with a bandwidth of 209 MHz, and produces 128-channel spectra, accumulated for 0.6ms.

Results from the Allen Telescope Array: HI in Galaxy Groups
Amber Bauermeister, G. Keating, L. Blitz, Allen Telescope Array Team
UC Berkeley.

With only the current reservoir of molecular gas, galactic star formation will cease much sooner than the decline of the observed star formation rate suggests. This is the molecular gas depletion problem. One aspect of the solution to this problem is including atomic hydrogen in the reservoir of gas for star formation. However, to form stars, the gas must be transported to the inner regions of galaxy disks: through inflow of HI from the outer disk or infall of intergalactic HI. We propose a mechanism for this is angular momentum loss through weak tidal interactions between galaxy group members. To constrain the contribution from this effect, we are imaging galaxy groups in the Local Volume (within 10 Mpc) in the 21 cm line with the ATA. This survey will look for extensions of the HI disks as well as intergalactic HI. The combination of the ATA's sensitivity and large beam make this instrument ideally suited for this project: we can easily image the whole group of galaxies in a small mosaic, with the potential of finding HI between group members that would be missed by other observations, which may be limited to mapping just the member galaxies and their immediate vicinity. Three groups of galaxies have been mapped so far, with good detections of HI in the member galaxies. No previously unknown intergalactic HI has been detected yet, but we expect that as our understanding of the instrument and data reduction processes improve, we will be able to get down to the expected column density limit of intergalactic HI and our observations will yield constraints on the amount of gas in the groups.

Results from the Allen Telescope Array: Real-Time Imaging
Garrett Keating1, J. Barott2, Allen Telescope Array Team
1University of California, Berkeley, 2Embry-Riddle Aeronautical University.

We present current results from the Automated Real-Time Imaging System (ARTIS), a software system that allows for rapid reduction of interferometer data at the Allen Telescope Array (ATA). ARTIS supports automated processing for both continuum and spectral line observations, and is capable of supporting wide-field surveys. Motivation for this system arises from both the volume of data produced at the ATA and the need for timely results from observations. The ATA is capable of producing hundreds of gigabytes of data, and covering thousands of square degrees of the sky in a single day. The ATA has also embarked upon several surveys searching for transient events, making quick and reliable automated analysis essential for scientific work. ARTIS (and its affiliated software) has been used for a number of large-scale observations, including transient, HI and maser surveys. ARTIS is also producing real-time data quality measurements for observations, allowing for more robust observing.

Meeting of the American Astronomical Society – January 2009

SETI Surveys on the Allen Telescope Array
Peter R. Backus, T. N. Kilsdonk, ATA Team
SETI Institute

The Allen Telescope Array (ATA-42) is a centimeter-wave array of 42 six-meter dishes that allows simultaneous SETI and other radio astronomy projects. In this paper we report on initial SETI observations using several observation and RFI mitigation strategies. We conducted both “targeted” observations of selected stars and “sky survey” observations of areas of the sky. Some observations were done with the SETI project directing the pointing of the array and others were “commensal,” in a direction selected by another project. In both modes, SETI observations used an independent RF tuning and two synthesized beams pointing at stars or positions in the field of view and tuned to the same frequency band. Results of the two SETI observations were compared and used to excise interference. In some observations, each beam had a null positioned at the center of the other beam. In the long term, we plan to observe one million target stars and survey large sections of the galactic plane over the frequency range from 1 GHz to 10 GHz. Much of this work may be done in parallel with other large-scale surveys.

Exploring the FIR-Radio Correlation with Continuous Spectra from the ATA
Peter K. G. Williams, G.C. Bower
University of California, Berkeley

Continuous frequency coverage is an important scientific and technical goal of the Square Kilometer Array (SKA). We investigate one avenue of reaching this goal with data taken from the high-resolution, broadband correlator of the Allen Telescope Array (ATA). With a total frequency coverage of 0.5 to 11.2 GHz and 1024 channels in a spectral window 100 MHz wide, the ATA is an ideal exploratory instrument for this kind of science. We present observations of calibrators taken over a broad swath of the ATA's frequency range and show how the well-known spectral indices of these sources can be recovered. With this consistency check in hand, a few sample broadband spectra and images of more scientifically interesting targets are presented. Our experiments explore the continuous frequency performance of the ATA antennas, feeds, and receivers and also identify the limitations that radio frequency interference place on our ability to make images. Further observations of this kind at the ATA will yield not only intriguing standalone science results but also valuable knowledge about the developments needed to endow the SKA with a robust continuous frequency capability.

Oral Presentations in Session #339: Facilities for the Next Decade

The Transient Radio Sky as Viewed from the Allen Telescope Array
Steve Croft, G.C. Bower, Allen Telescope Array Team
University of California, Berkeley

The Allen Telescope Array (ATA), dedicated on October 11, 2007 at Hat Creek, California, is currently, among other projects, undertaking transient surveys of the radio sky at 1.4 GHz. With its wide field of view (about 5 square degrees at 1.4 GHz), the ATA is one of the most powerful radio survey telescopes in the world. We will discuss the basic architecture of the ATA, and introduce ATATS (the ATA Twenty-cm Survey), an 800 square degree field which we have mapped repeatedly (19 times, as of September 2008) in a search for transient sources. As well as searching for changes from epoch to epoch, we are also able to build up a deep, multi-epoch image and associated catalog of the sky, which we can compare to previous surveys such as the NRAO VLA Sky Survey (NVSS).

The Dynamic Radio Sky: Future Directions at cm/m-Wavelengths
Geoffrey C. Bower1, J. Cordes2, S. Croft1, J. Lazio3, D. Lorimer4, M. McLaughlin4
1UC, Berkeley, 2Cornell, 3NRL, 4WVU

The time domain of the radio wavelength sky has been only sparsely explored. Nevertheless, recent discoveries from limited surveys and serendipitous discoveries indicate that there is much to be found on timescales from nanoseconds to years and at wavelengths from meters to millimeters. These observations have revealed unexpected phenomena such as rotating radio transients and coherent pulses from brown dwarfs. Additionally, archival studies have revealed an unknown class of radio transients without radio, optical, or high-energy hosts. The current generation of new meter- and centimeter-wave radio telescopes such as the MWA, LWA, PAPER, and ATA will exploit wide fields of view and flexible digital signal processing to systematically explore radio transient parameter space, as well as lay the scientific and technical foundation for the SKA. Known unknowns that will be the target of future transient surveys include orphan gamma-ray burst afterglows, radio supernovae, tidally-disrupted stars, flare stars, and magnetars.

Meeting of the American Astronomical Society – January 2008

Poster Presentations

The Search for Extrterrestrial Intelligence on the Allen Telescope Array: Implications for the Square Kilometer Array
Peter R. Backus, G.R. Harp, ATA Team
SETI Institute

The Allen Telescope Array (ATA) is a large N small D array that will inform the design, development and operations of the Square Kilometer Array (SKA). Search for extraterrestrial intelligence (SETI) observations will be a major component of ATA operations. The multi-beam capability of the array and the ability to form and position nulls will be prominent features in an observing strategy and RFI mitigation for SETI. Using software and commercial-off-the-shelf technology wherever possible creates a new data distribution and processing architecture that will allow new search techniques and increased capability to be added over time. This paper discusses plans for SETI on the ATA and the implications for SETI on the SKA.

The Allen Telescope Array as Square Kilometer Array Pathfinder
Geoffrey C. Bower
University of California, Berkeley

The Allen Telescope Array (ATA) is a new radio interferometer that has begun scientific operations in 2007. Many of the technologies, techniques, and observing modes developed for the ATA are directly applicable to the Square Kilometer Array (SKA). The ATA is a pioneer of the LNSD, which refers to a large number (LN) of small diameter (SD) dishes to create the array. This concept underlies nearly all SKA designs. Other relevant technologies are the offset Gregorian ATA antenna, the ATA wideband log periodic feed, transport of broadband data over fiber optic cables, and flexible digital signal processing electronics. The small dishes of the ATA gives it extraordinary wide-field imaging and survey capability but also require new solutions for calibration and imaging. Real time imaging, rapid response to transients, and thinking telescope technology are also under development. Finally, the ATA is developing commensal observing modes, which enable multiple simultaneous science programs, such as SETI, transient surveys, and HI surveys. Opportunities exist for community members to perform scientific investigations as well as develop techniques and technology for the SKA through use of the ATA.

Wide-Field Extragalactic Radio Astronomy with the Allen Telescope Array
Steve Croft, G. C. Bower
University of California, Berkeley

On October 11, 2007, the 42-element Allen Telescope Array was dedicated at Hat Creek in California, and is now undertaking routine science operations. With its wide field of view (about 5 square degrees at 1.4 GHz), the ATA is one of the most powerful radio survey telescopes in the world.

We describe initial results from ATA observations of a 100 square degree field centered on the NOAO Deep Wide Field Survey, and plans for the first year of operation, including the Five GHz Sky Survey (FiGSS), which will reach a detection threshold of 3 mJy over 10,000 square degrees, and greater depth in two smaller fields. FiGGS will be the highest frequency deep, large radio survey in existence, and will also be useful for transient detection and Galactic science.
Plans call for additional ATA antennas to be added in stages (for a total of 350) providing increased angular resolution and sensitivity. Our observing methods and results lay the groundwork for the Square Kilometer Array.

Broadband Spectra with the Allen Telescope Array
Peter K.G. Williams, G. C. Bower
UC Berkeley
 
Continuous frequency coverage is an important scientific and technical goal of the Square Kilometer Array (SKA). We investigate one avenue of reaching this goal with data taken from the high-resolution, broadband correlator of the Allen Telescope Array (ATA). With a total frequency coverage of 0.5 to 11.2 GHz and 1024 channels in a spectral window 100 MHz wide, the ATA is an ideal exploratory instrument for this kind of science. We present observations of calibrators taken over a broad swath of the ATA's frequency range and show how the well-known spectral indices of these sources can be recovered. With this consistency check in hand, a few sample broadband spectra and images of more scientifically interesting targets are presented. Our experiments explore the continuous frequency performance of the ATA antennas, feeds, and receivers and also identify the limitations that radio frequency interference place on our ability to make images. Further observations of this kind at the ATA will yield not only intriguing standalone science results but also valuable knowledge about the developments needed to endow the SKA with a robust continuous frequency capability.