Lewis Ball

Australian SKA Pathfinder: A High-Dynamic Range Wide-Field of View Survey Telescope

The Australia SKA Pathfinder (ASKAP) is a new telescope under development as a world-class high-dynamic-range wide-field-of-view survey instrument. It will utilize focal plane phased array feeds on the 36 12-m antennas that will compose the array. The large amounts of data present a huge computing challenge, and ASKAP will store data products in an archive after near real-time pipeline processing. This powerful instrument will be deployed at a new radio-quiet observatory, the Murchison Radio-astronomy Observatory in the midwest region of Western Australia, to enable sensitive surveys of the entire sky to address some of the big questions in contemporary physics. As a pathfinder for the SKA, ASKAP will demonstrate field of view enhancement and computing/processing technology as well as the operation of a large-scale radio array in a remote and radio-quiet region of Australia.

Inverse Compton emission of TeV gamma-rays from PSR B1259-63

Abstract We derive light curves for the hard γ-ray emission, at energies up to several TeV, expected from the unique pulsar/Be-star binary system PSR B1259-63. This is the only known system in our galaxy in which a radio pulsar is orbiting a main sequence star. We show that inverse Compton emission from the electrons and positrons in the shocked pulsar wind, scattering target photons from the Be star, produces a flux of hard γ-rays that should be above the sensitivity threshold of present day atmospheric Cerenkov detectors. Furthermore, we predict that the flux of hard γ-rays produced via this mechanism has a characteristic variation with orbital phase that should be observable, and which is not expected from any other mechanism

Simulated Radio Images and Light Curves of Young Supernovae

We present calculations of the radio emission from supernovae based on high-resolution simulations of the hydrodynamics and radiation transfer, using simple energy density relations that link the properties of the radiating electrons and the magnetic field to the hydrodynamics. As a specific example we model the emission from SN 1993J, which cannot be adequately fitted with the often-used analytic minishell model, and present a good fit to the radio evolution at a single frequency. Both free-free absorption and synchrotron self-absorption are needed to fit the light curve at early times, and a circumstellar density profile of ρ ~ r-1.7 provides the best fit to the later data. We show that the interaction of density structures in the ejecta with the reverse supernova shock may produce features in the radio light curves such as have been observed. We discuss the use of high-resolution radio images of supernovae to distinguish between different absorption mechanisms and determine the origin of specific light curve features. Comparisons of VLBI images of SN 1993J with synthetic model images suggest that internal free-free absorption completely obscures emission at 8.4 GHz passing through the center of the supernova for the first few tens of years after explosion. We predict that at 8.4 GHz the internal free-free absorption is currently declining, and that over the next ~40 yr the surface brightness of the center of the source should increase relative to the bright ring of emission seen in VLBI images. Similar absorption in a nearby supernova would make the detection of a radio pulsar at 1 GHz impossible for ~150 yr after explosion.

Diffusive acceleration of electrons in SN 1987A

We suggest that synchrotron radiation emitted by electrons undergoing diffusive acceleration at the supernova blast wave is the cause of the reappearance of radio emission from SN 1987A in 1990 July. Making reasonable assumptions concerning adiabatic losses and the magnetic field in the preexplosion stellar wind, we find the light curve and spectrum which would be produced by a constant rate of particle injection occurring in a localized region of the shock front; i.e., in a clump or knot. Observations indicate that two such clumps have been encountered to date

RADIO SUPERNOVA 1987A AT 843 MHz

We report here the —ux densities of the evolving radio source SN 1987A at 843 MHz measured from observations made with the Molonglo Observatory Synthesis Telescope between 1994 September and 2000 May. The radio light curve shows that the rate of increase of the —ux density jumped markedly around days 2800¨3000 (i.e., in the —rst half of 1995) and that since then the radio evolution has been remarkably well —tted by a simple linear increase of 62.7 ^ 0.5 kJy day~1. We discuss in detail the relationship between the radio light curve and the recent brightening of the system at optical wavelengths.

A Model for the Radio Emission from SNR 1987A

The observations of radio emission from SNR~1987A can be accounted for on the basis of diffusive shock acceleration of electrons by the supernova blast wave. However, with this interpretation the observed spectral index implies that the compression ratio of the gas subshock is roughly

Origin of the Transient, Unpulsed Radio Emission from the PSR B1259–63 Binary System

2.7

Shock Geometry and Inverse Compton Emission from the Wind of a Binary Pulsar

rather than the value of

New radio observations of supernova remnant 1E 0102.2-7219 in the Small Magellanic Cloud

4

On 'high flyers' in Fermi acceleration

expected of a strong shock front. We propose that in SNR~1987A, ions also undergo diffusive acceleration at the shock, a process that is likely to be rapid. Unlike the electron population, the accelerated ions can have an important effect on the gas dynamics. We calculate this coupled gas and energetic particle dynamics on the basis of the two-fluid model, in which the accelerated ions provide an additional component to the total pressure acting on the fluid. By accelerating and possibly heating the upstream plasma, the initially strong shock is modified and a weaker subshock with an upstream precursor results. The electrons behave as test particles. They are accelerated at the evolving subshock, escape downstream, and emit synchrotron radiation in the swept up magnetic field. Two models are considered for the surroundings of the progenitor: that of a freely expanding wind of number density