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Combrinck L.,Hartebeesthoek Radio Astronomy Observatory
62nd International Astronautical Congress 2011, IAC 2011 | Year: 2011

The international network of Satellite Laser Ranging (SLR) stations is under represented in the Southern Hemisphere. Currently there are only three Lunar Laser Ranger (LLR) stations globally, all located in the Northern Hemisphere. We are in the process of developing a combined satellite and lunar capable laser ranger utilising a one metre optical telescope. A complete description of the link budget to the Moon, required electronic hardware, optics, laser system and integrated software for this new LLR is presented. Research work undertaken utilising data from the global network is described. Future work, which will include data from the newly developed Lunar Laser Ranger, is discussed. In particular the application of SLR and LLR to evaluate General Relativity Theory (GRT) is discussed. Results obtained evaluating post-Newtonian parameters γ and β through the precise orbit determination of the LAGEOS satellites are presented. These results are brought into context with other published work utilising different instrumentation and techniques. Limitations in testing GRT are described. These limitations result from modelling deficiencies, satellite and lunar laser ranging inaccuracies and imperfect analysis strategies. Copyright ©2011 by the International Astronautical Federation. All rights reserved. Source

Brook P.R.,University of Oxford | Brook P.R.,CSIRO | Karastergiou A.,University of Oxford | Buchner S.,Hartebeesthoek Radio Astronomy Observatory | And 6 more authors.
Astrophysical Journal Letters | Year: 2014

Debris disks and asteroid belts are expected to form around young pulsars due to fallback material from their original supernova explosions. Disk material may migrate inward and interact with a pulsar's magnetosphere, causing changes in torque and emission. Long-term monitoring of PSR J0738-4042 reveals both effects. The pulse shape changes multiple times between 1988 and 2012. The torque, inferred via the derivative of the rotational period, changes abruptly from 2005 September. This change is accompanied by an emergent radio component that drifts with respect to the rest of the pulse. No known intrinsic pulsar processes can explain these timing and radio emission signatures. The data lead us to postulate that we are witnessing an encounter with an asteroid or in-falling debris from a disk. © 2014. The American Astronomical Society. All rights reserved. Source

Miller-Jones J.C.A.,Curtin University Australia | Moin A.,Curtin University Australia | Tingay S.J.,Curtin University Australia | Reynolds C.,Curtin University Australia | And 6 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

We present the first resolved imaging of the milliarcsecond-scale jets in the neutron star X-ray binary Circinus X-1, made using the Australian Long Baseline Array. The angular extent of the resolved jets is ∼20mas, corresponding to a physical scale of ∼150au at the assumed distance of 7.8kpc. The jet position angle is relatively consistent with previous arcsecond-scale imaging with the Australia Telescope Compact Array. The radio emission is symmetric about the peak, and is unresolved along the minor axis, constraining the opening angle to be <20°. We observe evidence for outward motion of the components between the two halves of the observation. Constraints on the proper motion of the radio-emitting components suggest that they are only mildly relativistic, although we cannot definitively rule out the presence of the unseen, ultrarelativistic (Γ > 15) flow previously inferred to exist in this system. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

Bietenholz M.F.,Hartebeesthoek Radio Astronomy Observatory | Bietenholz M.F.,York University
Publications of the Astronomical Society of Australia | Year: 2013

Very long baseline interferometry observations of supernovae and gamma-ray bursts provide almost the only way of obtaining spatially resolved information about the sources. In particular, a determination of the expansion velocity of the forward shock, as well as the geometry of the fireball and its evolution with time are possible for relatively nearby events, provided they are radio bright. Monitoring the expansion of the shock front can provide information on the density profiles of both the circumstellar material and on the ejecta. Very long baseline interferometry observations can also potentially resolve gamma-ray burst jets which are not directed along the line of sight, providing crucial confirmation of relativistic expansion in such objects. This review gives an overview of recent results from supernovae, including the Type I b/c SNe 2011dh, 2009bb, and 2007gr, and discusses the prospects for future observations. © 2014 Astronomical Society of Australia. Source

Moin A.,Curtin University Australia | Moin A.,CSIRO | Reynolds C.,Curtin University Australia | Miller-Jones J.C.A.,Curtin University Australia | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

A recent detection of the peculiar neutron star X-ray binary Circinus X-1 with electronic very long baseline interferometry (e-VLBI) prompted the suggestion that compact, non-variable radio emission persists through the entire 16.6-d orbit of the binary system. We present the results of a high angular resolution monitoring campaign conducted with the Australian Long Baseline Array in real-time e-VLBI mode. e-VLBI observations of Circinus X-1 were made on alternate days over a period of 20 d covering the full binary orbit. A compact radio source associated with Circinus X-1 was clearly detected at orbital phases following periastron passage, but no compact radio emission was detected at any other orbital phase, ruling out the presence of a persistent, compact emitting region at our sensitivity levels. The jet was not resolved at any epoch of our 1.4-GHz monitoring campaign, suggesting that the ultrarelativistic flow previously inferred to exist in this source is likely to be dark. We discuss these findings within the context of previous radio monitoring of Circinus X-1. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

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