Showing papers by "Richard Dodson published in 2007"
Australia Telescope National Facility1, Swinburne University of Technology2, York University3, Durham University4, University of Calgary5, University of Sydney6, University of Colorado Boulder7, University of Tasmania8, University of California, Berkeley9, University of Adelaide10, Laval University11, McGill University12, Herzberg Institute of Astrophysics13, California Institute of Technology14, La Trobe University15, University of Toronto16, Australian National University17, University of British Columbia18, University of Western Australia19, Curtin University20
TL;DR: The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflectors as mentioned in this paper.
Abstract: The future of centimetre and metre-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries that will be 50 times more sensitive than any existing radio facility. Most of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from a few hundred MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflectors. The large field-of-view makes ASKAP an unprecedented synoptic telescope that will make substantial advances in SKA key science. ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of two sites selected by the international community as a potential location for the SKA. In this paper, we outline an ambitious science program for ASKAP, examining key science such as understanding the evolution, formation and population of galaxies including our own, understanding the magnetic Universe, revealing the transient radio sky and searching for gravitational waves.
298 citations
TL;DR: In this paper, the authors report the glitch parameters of the 2004 event, along with reconfirmation that the spin up for the Vela pulsar occurs instantaneously to the accuracy of the data.
Abstract: Pulsar timing at the Mt Pleasant observatory has focused on Vela, which can be tracked for 18 hours of the day. These nearly continuous timing records extend over 24 years allowing a greater insight into details of timing noise, micro glitches and other more exotic effects. In particular we report the glitch parameters of the 2004 event, along with the reconfirmation that the spin up for the Vela pulsar occurs instantaneously to the accuracy of the data. This places a lower limit of about 30 seconds for the acceleration of the pulsar to the new rotational frequency. We also confirm of the low braking index for Vela, and the continued fall in the DM for this pulsar.
76 citations
TL;DR: In this article, phase referencing with the next-generation space VLBI mission, VSOP-2, is examined in detail based on a simulation tool called ARIS, and the criterion for successful phase referencing was set to keep the phase errors below one radian.
Abstract: The next-generation space VLBI mission, VSOP-2, is expected to provide unprecedented spatial resolution at 8.4, 22, and 43 GHz. In this report, phase referencing with VSOP-2 is examined in detail based on a simulation tool called ARIS. The criterion for successful phase referencing was set to keep the phase errors below one radian. Simulations with ARIS reveal that phase referencing achieves good performance at 8.4 GHz, even under poor tropospheric conditions. At 22 and 43 GHz, it is recommended to conduct phase referencing observations under good or typical tropospheric conditions. The satellite is required to have an attitude-switching capability with a one-minute or shorter cycle, and an orbit determination accuracy higher than 10 cm at apogee; the phase referencing calibrators are required to have a signal-to-noise ratio larger than four for a single scan. The probability to find a suitable phase referencing calibrator was estimated by using VLBI surveys. From the viewpoint of calibrator availability, VSOP-2 phase referencing at 8.4 GHz is promising. However, the chance of finding suitable calibrators at 22 and 43 GHz is significantly reduced; it is important to conduct specific investigations for each target at those frequencies.
60 citations
TL;DR: In this article, the authors reported the results of simultaneous observations of the Vela pulsar in X-rays and radio from the RXTE satellite and the Mount Pleasant Radio Observatory in Tasmania.
Abstract: We report the results of simultaneous observations of the Vela pulsar in X-rays and radio from the RXTE satellite
and the Mount Pleasant Radio Observatory in Tasmania.We sought correlations between Vela’s X-ray emission and
radio arrival times on a pulse-by-pulse basis. At a confidence level of 99.8% we have found significantly higher flux
density in Vela’s main X-ray peak during radio pulses that arrived early. This excess flux shifts to the ‘‘trough’’ following
the second X-ray peak during radio pulses that arrive later. Our results suggest that the mechanism producing
the radio pulses is intimately connected to the mechanism producing X-rays. Current models using resonant absorption
of radio emission in the outer magnetosphere as a cause of the X-ray emission are explored as a possible explanation
for the correlation.
17 citations
TL;DR: In this article, phase referencing with the next-generation space VLBI mission, VSOP-2, is examined in detail based on a simulation tool called ARIS, which reveals that phase referencing achieves good performance at 8.4GHz, even under poor tropospheric conditions.
Abstract: The next-generation space VLBI mission, VSOP-2, is expected to provide unprecedented spatial resolutions at 8.4, 22, and 43GHz. In this report, phase referencing with VSOP-2 is examined in detail based on a simulation tool called ARIS. The criterion for successful phase referencing was to keep the phase errors below one radian. Simulations with ARIS reveal that phase referencing achieves good performance at 8.4GHz, even under poor tropospheric conditions. At 22 and 43GHz, it is recommended to conduct phase referencing observations under good or typical tropospheric conditions. The satellite is required to have an attitude-switching capability with a one-minute or shorter cycle, and an orbit determination accuracy higher than about 10cm at apogee; the phase referencing calibrators are required to have a signal-to-noise ratio larger than four for a single scan. The probability to find a suitable phase referencing calibrator was estimated by using VLBI surveys. From the viewpoint of calibrator availability, VSOP-2 phase referencing at 8.4GHz is promising. However, the change of finding suitable calibrators at 22 and 43GHz is significantly reduced; it is important to conduct specific investigations for each target at those frequencies.
2 citations
Japan Aerospace Exploration Agency1, National Radio Astronomy Observatory2, University of Turku3, Graduate University for Advanced Studies4, Australia Telescope National Facility5, University of Calgary6, Joint Institute for VLBI in Europe7, Chinese Academy of Sciences8, University of Tasmania9, Curtin University10, Swinburne University of Technology11, Jet Propulsion Laboratory12, Whittier College13, Purdue University14, Konkoly Thege Miklós Astronomical Institute15, National University of Cordoba16
TL;DR: In this article, the authors presented images and models for the remaining 140 sources not included in Paper III, which contained 102 sources, and the brightness temperature distributions for all of the sources in the VSOP AGN survey were discussed.
Abstract: In February 1997, the Japanese radio astronomy satellite HALCA was launched to provide the space-bourne element for the VLBI Space Observatory Programme (VSOP) mission. Approximately twenty-five percent of the mission time was dedicated to the VSOP Survey of bright compact Active Galactic Nuclei (AGN) at 5 GHz. This paper, the fifth in the series, presents images and models for the remaining 140 sources not included in Paper III, which contained 102 sources. For most sources, the plots of the uv-coverage, the visibility amplitude versus uv-distance, and the high resolution image are presented. Model fit parameters to the major radio components are determined, and the brightness temperature of the core component for each source is calculated. The brightness temperature distributions for all of the sources in the VSOP AGN survey are discussed.
2 citations
22 Nov 2007
TL;DR: The Japanese radio astronomy satellite HALCA was launched to provide the space-borne element for the VSOP survey in 1997 as discussed by the authors, which was devoted to the survey of bright, compact, extra-galactic radio sources at 5 GHz.
Abstract: In February 1997 the Japanese radio astronomy satellite HALCA was launched to provide the space-borne element for the VSOP mission. HALCA provided linear baselines three-times greater than that of ground arrays, thus providing higher resolution and higher AGN brightness temperature measurements and limits. Twenty-five percent of the scientific time of the mission was devoted to the “VSOP survey” of bright, compact, extra-galactic radio sources at 5 GHz. A complete list of 294 survey targets were selected from pre-launch surveys, 91% of which were observed during the satellite’s lifetime. The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure, to provide a source list for use with future space VLBI missions, and to compare radio properties with other data throughout the electro-magnetic spectrum. All the data collected have now been analysed and is being prepared for the final image Survey paper. In this paper we present details of the mission, and some statistics of the images and brightness temperatures.