Keith Bannister — Results of automatic, high time resolution GRB follow-up with the Parkes 12 m
Gamma ray bursts are the most powerful explosions in the universe. The properties of these explosions within seconds of the gamma-ray trigger are not well constrained at radio wavelengths. I present results of an automated, high-time resolution follow-up survey for prompt radio emission from GRBs at 1.4 GHz. Using the Parkes 12 m telescope with a single-pixel feed, we observed 9 GRBs, and were on source typically within 2 minutes. We detected two single pulse candidates in the high time resolution data. I will discuss the potential to expand this experiment with future instruments.
Cathryn Trott — Design and performance of fast transient detectors
Detection of fast radio transients relies on acquisition of a short duration signal pulse among static background signals and noise. Radio emission is affected by plasma along the line-of-sight to the observer, and in particular by a frequency-dependent time delay of pulse arrival due to dispersion by the interstellar medium. Correction for this dispersive effect is crucial for optimal signal detection, typically achieved by application of a matched filter detector on channelized time-series data. The classical matched filter, where the signal is known a priori, is used as the theoretical basis upon which fast transients detection experiments are designed. However, the matched filter is generally unachievable in practise, due to the lack of signal knowledge and computational constraints on real-time detection. I explore the performance of realistic detectors that are applied in real fast transients experiments, as well as a novel detector being explored for the CRAFT fast transients project for ASKAP.
James Miller-Jones — Resolving the jets of Circinus X-1 with Very Long Baseline Interferometry
Circinus X-1 is one of the few confirmed neutron star X-ray binaries with resolved relativistic jets, which have been studied from sub-arcsecond out to arcminute scales. I will present recent high-angular resolution observations of the jets made with the Australian Long Baseline Array, which have allowed us to resolve the jets on milliarcsecond scales for the first time. I will show how the most compact radio emission varies with orbital phase along the elliptical binary orbit, and will demonstrate that the morphology of the resolved emission at periastron passage suggests that the jets are not as ultra-relativistic as has previously been inferred. Finally, I will discuss how further VLBI observations could both rigorously constrain the jet speed and probe the origin of this intriguing system.
Hayley Bignall — Fast interstellar scintillation of quasars, and PKS 1257-326 revisited
The line-of-sight towards quasar PKS 1257-326 passes through a patch of ionised plasma in the local Galactic interstellar medium (~10 pc from the Sun) that causes large and rapid, intra-hour variations in the received flux density at centimetre wavelengths. This rapid interstellar scintillation (ISS) has been occurring for at least 15 years, implying the scattering \”screen\” is larger than 100 AU in physical extent. Recent analysis of VLA data on a sample of 128 quasars found that 6 sources scintillate with a characteristic timescale of <2 hours, implying that such nearby screens in the ISM are not uncommon. This is an important consideration for proposed surveys of the transient and variable radio sky. We have measured evolving micro-arcsecond scale \”core-shifts\” in PKS 1257-326, evidence of changing opacity during intrinsic outbursts, as well as evolving polarised structure. These observations allow detailed study of physical conditions in the inner jet at resolutions even VLBI cannot reach. Recent observations with the upgraded ATCA highlight the power of the instantaneous broad (2 GHz) bandwidth for detailed studies of the frequency dependence of ISS close to the transition between weak and strong scattering. PKS 1257-326 data also present an ideal test case for exploring algorithms to handle time variability in aperture synthesis data.
Balt Indermuehle — WVR\’s for the Australia Telescope Compact Array
In the millimetre wavelength regime of the electromagnetic spectrum used in radio astronomy, poorly mixed pockets of precipitable water vapour cause a change in the refractive index of the atmosphere, thereby inducing an excess path that the signal must travel through. This results in a phase delay for antennae receiving an astronomical signal. In an interferometer such as the Australia Telescope Compact Array (ATCA), variations in phase delay between the antennae thus lead to degradation in the image quality obtainable due to signal decorrelation. This phase fluctuation induced noise increases both with frequency and baseline length. It therefore also puts upper limits on the usable length of baselines without experiencing significant decorrelation, thus limiting the spatial resolution of the interferometer. By tracking the water vapour phase, WVR\’s also can increase the on source time between calibrator scans, thus increasing the probability of capturing transient events. We have developed Water Vapour Radiometers (WVRs) for the ATCA that are capable of determining excess path fluctuations by virtue of measuring small temperature fluctuations in the atmosphere using the 22.2 GHz water vapour line for each of the six antennae. By measuring the line of sight variations of the water vapour, the induced path excess and thus the phase delay can be estimated and corrections can then be applied during data reduction. This reduces decorrelation of the source signal. We demonstrate how this recovers the telescope\’s efficiency and image quality as well as how this improves the telescope\’s ability to use longer baselines at higher frequencies, thereby resulting in higher spatial resolution.
Ian Morrison — Advances in Wideband SETI and Implications for Radio Telescope Design
SETI has traditionally concentrated on detecting narrowband signals occupying a very small frequency range. Researchers are now using modern communications theory to extend the search scope to include wideband signals that may occupy a broad frequency spectrum. The emergence of wideband SETI and the construction of new generation radio telescopes is fuelling increased interest in \’next generation\’ SETI. The potential of instruments such as ASKAP and the SKA to conduct wideband SETI is being freshly evaluated in light of recent advances. This talk will briefly introduce the subject of wideband SETI and various detection methods under development, and highlight their requirements for data capture. It will conclude with some remarks concerning possible wideband SETI experiments for current ATNF telescopes, ASKAP and the SKA. Australia is taking a lead in high-resolution time-domain astronomy and hence is well placed to make central contributions to planning and implementing a SETI programme for the SKA.
Alina Donea — Transient emissions in solar flares
I will talk about the observed transient emissions in some solar flares that generated sunquakes. Transients in flares can have different flavours such as: radiative transients (radio, X ray), seismic transients (seismic sources and solar quakes) and magnetic and intensity transients. Mostly of these transients occur at approximately the same time during a flare. A delay in a transient appearance may tell us more about the local physics of the region where flares generated.
Giovanna Zanardo — 9000 Days of Supernova 1987A
Nearly 25 years after the explosion, the radio evolution of SN 1987A is receiving increasing attention over a wide range of wavelengths. As the supernova remnant (SNR) has been getting brighter over time, 20 cm high-resolution observations via Very Long Baseline Interferometry (VLBI) with the Australian Long Baseline Array (LBA) and 3 mm observations with the Australia Telescope Compact Array (ATCA), have been added to the already vast ATCA database, which covers monitoring and imaging observations over ~9000 days. At all wavelengths, a marked asymmetry in the SNR emission has emerged and the high-resolution images have identified an asymmetric distribution of small scale features in the equatorial plane. We present the results of recent observations and discuss the current stage of the remnant evolution.
Baerbel Koribalski — An update on SN1996cr in the Circinus Galaxy
(please consult)
Justin Bray — Searching for nanosecond-scale lunar pulses
The interaction of ultra-high energy particles with dense media is expected to produce nanosecond-scale radio pulses through the Askaryan effect. This provides a means to detect high-energy neutrinos – which have been predicted, but not yet seen – by monitoring the Moon for an Askaryan radio pulse. This is a form of time domain astronomy at the shortest possible timescales, which requires unconventional observing techniques.
Bill Coles — Time Domain Astronomy and Scintillation
For better or worse, scintillation is an integral part of time domain astronomy. It is easy to confuse scintillation with source time variation. Furthermore time variable sources are necessarily compact and thus are very likely to scintillate, so one often has to separate the two effects quite carefully. The good news is that we have made great progress in understanding scintillations in the IISM in the last decade. The bad news is that we now understand that it is more complex and less ideal than we had thought. Here we will discuss the new tools available for observing scintillation in the IISM and how they have altered our view of the mini- and micro-structure of the IISM. We will also discuss the various means by which one might separate scintillation from intrinsic variation of a radio source.
Ron Ekers — Review of Time Domain Astronomy (invited)
I will review the range of phenomena that have generated time variable signals at radio wavelengths and comment on the different instrumental requirements for signals with structure in time, space or frequency. The time scales involved range from decades to nanoseconds and require totally different observational techniques. I will look at the historical context and speculate about future oppurtunities.
Phil Edwards — Multi-epoch monitoring with the LBA and ATCA
EGRET and Fermi-LAT observations have revealed that gamma-ray–emitting AGN are very time variable, with outbursts and flares on a variety of timescales. The milli-arcsecond–scale angular resolution provided by the LBA, and the frequency agility of the ATCA enable complementary observations to be made of these sources, helping provide insight into the physical processes at work in these sources.
The HTRU survey is an ongoing project using the Parkes radio telescope. Combining a state-of-the-art digital backend with the highly successful 20 cm multibeam receiver, we have discovered more than 110 radio pulsars, including 20 millisecond pulsars and 15 RRATS. In this talk, I will focus on the transient and highly time-variable discoveries. Firstly, we will discuss the surprising discovery of a highly luminous radio pulsar discovered in a well surveyed patch of sky. Continued observation with Parkes and the ATCA has shown this highly variable source to be the first magnetar discovered through its radio emission. As well as the typical Fourier based searches for periodic signals from pulsars, the HTRU survey is aimed to detect short duration (less than 1 second) transient events. Although majority of these events are thought to arise from sparsely emitting pulsars (RRATS), there is great interest in other sources of fast transients such as the infamous “Lorimer burst” believed to be of extragalactic origin.
Ramesh Bhat — Searching for fast transients with interferometric arrays
Exploration of the transient Universe is a frontier research area within radio astronomy, and upcoming next-generation facilities will provide exciting avenues to explore this relatively uncharted territory. Searching for fast transients with such instruments however poses a number of challenges in terms of the signal processing and data management requirements as well as the planning of optimal survey strategies. With its moderate number of elements, high sensitivity and flexible design features, the GMRT makes a powerful test-bed for developing and demonstrating novel transient detection methodologies that will be applicable to next generation array instruments. I will describe ongoing efforts aimed at the development of a real-time transient detection pipeline for the GMRT and the pilot transient surveys undertaken. Such developments will provide valuable inputs as next-generation arrays such as ASKAP are designed and commissioned.
Kitty Lo — Radio emission from CU Virginis
CU Virginis is a magnetic Ap star with the unique property of emitting two 100% circularly polarised radio pulses every rotation period. The pulse arrival time of these radio pulses have shown remarkable stability over more than 10 years. In this presentation, I will show our radio observations of CU Virginis with the ATCA and describe how the frequency dependence of the pulse arrival times can give us insight into the geometry of the stellar magnetosphere.
George Hobbs — Pulsar timing experiments at Parkes
In this talk, I will discuss various pulsar timing projects that are currently being carried out at Parkes. These projects will include the Parkes Pulsar Timing Array project, the Fermi-timing programme and studies of relativistic binary systems. My talk will describe recent results and expectations for the near future.