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.

Further results from the timing of the millisecond pulsars in 47 Tucanae

Abstract: We have been observing the millisecond pulsars in the globular cluster 47 Tucanae (47 Tuc) at the Parkes radio telescope since 1999 August with threefold higher time-resolution than hitherto possible. We present the results in this paper, including: improved 1400-MHz pulse profiles; one new timing solution, for PSR J0024-72045, which imposes stringent constraints on the acceleration model for 47 Tucanae and implies a projected mass-to-light ratio > 1.4 M O . / L O . at the centre of the cluster; refined estimates for the five previously determined proper motions; and newly determined proper motions for six pulsars. We have detected, for the first time, relative motions between the pulsars. We have detected a second period derivative for the pulsar in the PSR J0024-7204H binary system, which could indicate the presence of a third nearby object, and improved measurement of the rate of advance of periastron of this pulsar, which yields a total system mass of 1.61 ′ 0.04 M O .. We also have determined upper limits for the masses of any hypothetical planets orbiting the pulsars in 47 Tuc. PSR J0023-7203J shows variations of dispersion measure (DM) as a function of orbital phase with a total column density at superior conjunction of about 1.7 x 10 1 6 cm - 2 , 10 times smaller than observed for a similar system in the Galaxy. We interpret the small value as being due to a smaller inclination of the orbit of PSR J0023-7203J. We find that the DM variation with orbital phase changes with time, and we detect material at more than 90° (in orbital phase) from the companion. PSR J0024-72040 also shows variations of DM with orbital phase, but these are restricted to phases near the eclipse. This binary system displays significant monotonic variation of its orbital period: P b = (9 ′ 1) x 10 - 1 2 . This is probably due to spin-orbit coupling; this effect seems to be significantly smaller for PSR J0023-7203J.

A large light-mass component of cosmic rays at 10 17 –10 17.5 electronvolts from radio observations

Abstract: Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 1017–1018 electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal1 comes from accelerators capable of producing cosmic rays of these energies2. Cosmic rays initiate air showers—cascades of secondary particles in the atmosphere—and their masses can be inferred from measurements of the atmospheric depth of the shower maximum3 (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground4. Current measurements5 have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays6, 7, 8 is a rapidly developing technique9 for determining Xmax (refs 10, 11) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front6, 12. Here we report radio measurements of Xmax with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 1017–1017.5 electronvolts. This high resolution in Xmax enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 1017.5 electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 1017–1017.5 electronvolt range.

The Detection of an Extremely Bright Fast Radio Burst in a Phased Array Feed Survey

Abstract: We report the detection of an ultra-bright fast radio burst (FRB) from a modest, 34-day pilot survey with the Australian Square Kilometre Array Pathfinder The survey was conducted in a wide-field fly's-eye configuration using the phased-array-feed technology deployed on the array to instantaneously observe an effective area of 160 deg^2, and achieve an exposure totaling 13200 deg^2 hr We constrain the position of FRB 170107 to a region 8^'x 8^' in size (90% containment) and its fluence to be 58 ± 6 Jy ms The spectrum of the burst shows a sharp cutoff above 1400 MHz, which could be due to either scintillation or an intrinsic feature of the burst This confirms the existence of an ultra-bright (> 20 Jy ms) population of FRBs

Bipolar outflows in OH/IR stars

Abstract: We investigate the development of bipolar outflows during the early post-AGB evolution. A sample of 10 OH/IR stars with irregular OH spectra and unusually large expansion velocities is observed at high angular resolution. The sample includes bipolar nebulae (e.g., OH231.8+4.2), bright post-AGB stars (HD 101584) and reflection nebulae (e.g., Roberts 22). The IRAS colour–colour diagram separates the sample into different types of objects. One group may contain the immediate progenitors to the (few) extreme bipolar planetary nebulae. Two objects show colours and chemistry very similar to the planetary nebulae with late IR-[WC] stars. One object is a confirmed close binary. A model is presented consisting of an outer AGB wind which is swept up by a faster post-AGB wind, with either the AGB or post-AGB wind being non-spherically symmetric. The interface of the two winds is shown to exhibit a linear relation between velocity and distance from the star, giving the impression of an accelerating outflow. The OH data confirm the predicted linear velocity gradients, and also reveal torus-like, uniformly expanding components. All sources are discussed in detail using optical/HST images where available. ISO data for Roberts 22 reveal a chemical dichotomy, with both crystalline silicates and PAH features being present. IRAS 16342-3814 shows a dense torus with mass 0.1 M⊙ and density of 108 cm−3; HST data show four point-like sources located symmetrically around the nebula, near the outer edge of the dense torus. Lifetimes for the bipolar OH/IR stars are shown to be in excess of 104 yr, longer than normal post-AGB time-scales. This suggests that the toruses or discs are near-stationary. We suggest that accretion from such a disc slows down the post-AGB evolution. Such a process could explain the link between the long-lived bipolar nebular geometry and the retarded star.

The Southern Galactic Plane Survey: The Test Region

Abstract: The Southern Galactic Plane Survey (SGPS) is a project to image the H I line emission and 1.4 GHz continuum in the fourth quadrant of the Milky Way at high resolution using the Australia Telescope Compact Array and the Parkes Radio Telescope. This paper describes the survey details and goals, presents 21 cm continuum data, and discusses H I absorption and emission characteristics of the SGPS test region (3255 ≤ l ≤ 3335; -05 ≤ b ≤ +35). We explore the effects of massive stars on the interstellar medium through a study of H I shells and the H I environments of H II regions and supernova remnants (SNRs). We find an H I shell surrounding the H II region RCW 94, which indicates that the region is embedded in a molecular cloud. We give lower limits for the kinematic distances to SNRs G327.4+0.4 and G330.2+1.0 of 4.3 and 4.9 kpc, respectively. We find evidence of interaction with the surrounding H I for both of these remnants. We also present images of a possible new SNR G328.6-0.0. Additionally, we have discovered two small H I shells with no counterparts in continuum emission.