Australia Telescope National Facility

About: Australia Telescope National Facility is a facility organization based out in Sydney, New South Wales, Australia. It is known for research contribution in the topics: Galaxy & Pulsar. The organization has 699 authors who have published 2774 publications receiving 151507 citations. The organization is also known as: ATNF.

Mapping on the HEALPix grid

Abstract: The natural spherical projection associated with the Hierarchical Equal-Area and Isolatitude Pixelization (HEALPix) is described and shown to be one of a hybrid class that combines the cylindrical equal-area and Collignon projections, not previously documented in the cartographic literature. Projection equations are derived for the class in general and are used to investigate its properties. It is shown that the HEALPix projection suggests a simple method of (i) storing and (ii) visualizing data sampled on the grid of the HEALPix pixelization, and also suggests an extension of the pixelization that is better suited for these purposes. Potentially useful properties of other members of the class are described, and new triangular and hexagonal pixelizations are constructed from them. Finally, the standard formalism is defined for representing the celestial coordinate system for any member of the class in the FITS data format.

The large-scale jet-powered radio nebula of Circinus X-1

Abstract: We present multi-epoch observations of the radio nebula around the neutron star X-ray binary Circinus X-1 made at 1.4 and 2.5 GHz with the Australia Telescope Compact Array between 2000 October and 2004 September. The nebula can be seen as a result of the interaction between the jet from the system and the interstellar medium and it is likely that we are actually looking toward the central X-ray binary system through the jet-powered radio lobe. The study of the nebula thus offers a unique opportunity to estimate for the first time using calorimetry the energetics of a jet from an object clearly identified as a neutron star. An extensive discussion on the energetics of the complex is presented: a first approach is based on the minimum energy estimation, while a second one employs a self-similar model of the interaction between the jets and the surrounding medium. The results suggest an age for the nebula of ≤ 10 5 yr and a corresponding time-averaged jet power ≥ 10 35 erg s -1 . During periodic flaring episodes, the instantaneous jet power may reach values of similar magnitude to the X-ray luminosity.

High-frequency observations of southern pulsars

Abstract: We present polarization data for 32 mainly southern pulsars at 8.4 GHz. The observations show that the polarization fraction is low in most pulsars at this frequency except for the young, energetic pulsars which continue to show polarization fractions in excess of 60 per cent. All the pulsars in the sample show evidence for conal emission with only one-third also showing core emission. Many profiles are asymmetric, with either the leading or the trailing part of the cone not detectable. Somewhat surprisingly, the asymmetric profiles tend to be more polarized than the symmetrical profiles. Little or no pulse narrowing is seen between 1 and 8.4 GHz. The spectral behaviour of the orthogonal polarization modes and radius to frequency mapping can likely account for much of the observational phenomenology. Highly polarized components may originate from higher in the magnetosphere than unpolarized components.

Dual-frequency VLBI study of Centaurus A on sub-parsec scales. The highest-resolution view of an extragalactic jet

Abstract: Centaurus A is the closest active galactic nucleus High resolution imaging using Very Long Baseline Interferometry (VLBI) enables us to study the spectral and kinematic behavior of the radio jet-<:ounterjet system on sub-parsec scales, providing essential information for jet emission and formation models Aims Our aim is to study the structure and spectral shape of the emission from the central-parsec region of Cen A Methods As a target of the Southern Hemisphere VLBI monitoring program TANAMI (Tracking Active Galactic Nuclei with Millliarcsecond Interferometry), VLBI observations of Cen A are made regularly at 84 and 223 GHz with the Australian Long Baseline Array (LBA) and associated telescopes in Antarctica, Chile, and South Africa Results The first dual-frequency images of this source are presented along with the resulting spectral index map An angular resolution of 04 mas x 07 mas is achieved at 84 GHz, corresponding to a linear scale of less than 0013 pc Hence, we obtain the highest resolution VLBI image of Cen A, comparable to previous space-VLBI observations By combining with the 223 GHz image, we present the corresponding dual-frequency spectral index distribution along the sub-parsec scale jet revealing the putative emission regions for recently detected y-rays from the core region by Fermi/LAT Conclusions We resolve the innermost structure of the milliarcsecond scale jet and counter jet system of Cen A into discrete components The simultaneous observations at two frequencies provide the highest resolved spectral index map of an AGN jet allowing us to identify up to four possible sites as the origin of the high energy emission Key words galaxies: active galaxies: individual (Centaurus A, NGC 5128) - galaxies: jets - techniques: high angular resolution