Pinelands, South Africa
Pinelands, South Africa

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Bhat N.D.R.,Curtin University Australia | Ord S.M.,Curtin University Australia | Tremblay S.E.,Curtin University Australia | Tingay S.J.,Curtin University Australia | And 45 more authors.
Astrophysical Journal Letters | Year: 2014

We report on the detection of the millisecond pulsar PSR J0437-4715 with the Murchison Wide-field Array (MWA) at a frequency of 192 MHz. Our observations show rapid modulations of pulse intensity in time and frequency that arise from diffractive scintillation effects in the interstellar medium (ISM), as well as prominent drifts of intensity maxima in the time-frequency plane that arise from refractive effects. Our analysis suggests that the scattering screen is located at a distance of ∼80-120 pc from the Sun, in disagreement with a recent claim that the screen is closer (∼10 pc). Comparisons with higher frequency data from Parkes reveal a dramatic evolution of the pulse profile with frequency, with the outer conal emission becoming comparable in strength to that from the core and inner conal regions. As well as demonstrating the high time resolution science capabilities currently possible with the MWA, our observations underscore the potential to conduct low-frequency investigations of timing-array millisecond pulsars, which may lead to increased sensitivity in the detection of nanoHertz gravitational waves via the accurate characterization of ISM effects. © 2014. The American Astronomical Society. All rights reserved.

Loi S.T.,University of Sydney | Murphy T.,University of Sydney | Cairns I.H.,University of Sydney | Menk F.W.,University of Newcastle | And 40 more authors.
Geophysical Research Letters | Year: 2015

Ionization of the Earth's atmosphere by sunlight forms a complex, multilayered plasma environment within the Earth's magnetosphere, the innermost layers being the ionosphere and plasmasphere. The plasmasphere is believed to be embedded with cylindrical density structures (ducts) aligned along the Earth's magnetic field, but direct evidence for these remains scarce. Here we report the first direct wide-angle observation of an extensive array of field-aligned ducts bridging the upper ionosphere and inner plasmasphere, using a novel ground-based imaging technique. We establish their heights and motions by feature tracking and parallax analysis. The structures are strikingly organized, appearing as regularly spaced, alternating tubes of overdensities and underdensities strongly aligned with the Earth's magnetic field. These findings represent the first direct visual evidence for the existence of such structures. ©2015. American Geophysical Union. All Rights Reserved.

Hess K.M.,University of Cape Town | Hess K.M.,University of Groningen | Hess K.M.,Netherlands Institute for Radio Astronomy | Jarrett T.H.,University of Cape Town | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

The Antlia Cluster is a nearby, dynamically young structure, and its proximity provides a valuable opportunity for detailed study of galaxy and group accretion on to clusters. We present a deep HI mosaic completed as part of spectral line commissioning of the Karoo Array Telescope (KAT-7), and identify infrared counterparts from the Widefield Infrared Survey Explorer extended source catalogue to study neutral atomic gas content and star formation within the cluster. We detect 37 cluster members out to a radius of ~0.9 Mpc with MHI > 5 × 107M⊙. Of these, 35 are new HI detections, 27 do not have previous spectroscopic redshift measurements, and one is the Compton thick Seyfert II, NGC 3281, which we detect in HI absorption. The HI galaxies lie beyond the X-ray-emitting region 200 kpc from the cluster centre and have experienced ram pressure stripping out to at least 600 kpc. At larger radii, they are distributed asymmetrically suggesting accretion from surrounding filaments. Combining HI with optical redshifts, we perform a detailed dynamical analysis of the internal substructure, identify large infalling groups, and present the first compilation of the largescale distribution of HI and star-forming galaxies within the cluster. We find that elliptical galaxy NGC 3268 is at the centre of the oldest substructure and argue that NGC 3258 and its companion population are more recent arrivals. Through the presence of HI and ongoing star formation, we rank substructures with respect to their relative time since accretion on to Antlia. © 2015 The Authors.

Kourouma H.,Nelson Mandela Metropolitan University | Rotich E.,Nelson Mandela Metropolitan University | Gamatham R.R.G.,Nelson Mandela Metropolitan University | Leitch A.W.R.,Nelson Mandela Metropolitan University | And 4 more authors.
IEEE AFRICON Conference | Year: 2013

We evaluate the effects of optical fibre bending on polarization mode dispersion (PMD) and states of polarization (SOP) for a KAT-7 dish antenna riser cable. The antenna riser cable is the optical cable extending from the pedestal to the focus of the antenna. The riser cable for each antenna is subjected to environmental variations and to any physical variation caused by the motion of the fibre while the antenna is being scanned. To emulate this, we have investigated the effects of optical fibre bending with a riser cable inserted in a bending jig built to simulate antenna scanning movements. Measurements have shown that Differential Group Delay (DGD) values remain below 10 fs in the loop back configuration and below 6fs in the straight through configuration of the optical fibre placement in the bending jig. For the purpose of this paper, PMD and SOP measurements were made with a single varying element being the amount of bending enforced onto the optical fibres under test. © 2013 IEEE.

Kipnoo E.K.R.,Nelson Mandela Metropolitan University | Kourouma H.Y.S.,Nelson Mandela Metropolitan University | Gamatham R.R.,Nelson Mandela Metropolitan University | Leitch A.W.R.,Nelson Mandela Metropolitan University | And 4 more authors.
IEEE AFRICON Conference | Year: 2013

We experimentally investigate the differential group delay (DGD) in KAT-7 optical fibre network using polametric measurement technique. Low PMD values in the femtosecond range are obtained over the 10 km single mode fibre. It is also established that deployment of the fibre alters the DGD of the network. This study is paramount in ensuring accurate and stable clock signal as well as error free transmission at very high bit rates in the optical network. © 2013 IEEE.

Ridolfi A.,Max Planck Institute for Radio Astronomy | Freire P.C.C.,Max Planck Institute for Radio Astronomy | Torne P.,Max Planck Institute for Radio Astronomy | Heinke C.O.,Max Planck Institute for Radio Astronomy | And 14 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

For the past couple of decades, the Parkes radio telescope has been regularly observing the millisecond pulsars in 47 Tucanae (47 Tuc). This long-term timing programme was designed to address a wide range of scientific issues related to these pulsars and the globular cluster where they are located. In this paper, the first of a series, we address one of these objectives: the characterization of four previously known binary pulsars for which no precise orbital parameters were known, namely 47 Tuc P, V, W and X (pulsars 47 Tuc R and Y are discussed elsewhere). We determined the previously unknown orbital parameters of 47 Tuc V and X and greatly improved those of 47 Tuc P and W. For pulsars W and X we obtained, for the first time, full coherent timing solutions across the whole data span, which allowed a much more detailed characterization of these systems. 47 Tuc W, a well-known tight eclipsing binary pulsar, exhibits a large orbital period variability, as expected for a system of its class. 47 Tuc X turns out to be in a wide, extremely circular, 10.9-d long binary orbit and its position is ~3.8 arcmin away from the cluster centre, more than three times the distance of any other pulsar in 47 Tuc. These characteristics make 47 Tuc X a very different object with respect to the other pulsars of the cluster. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Mao S.A.,U.S. National Radio Astronomy Observatory | Mao S.A.,University of Wisconsin - Madison | Mao S.A.,Harvard - Smithsonian Center for Astrophysics | Mao S.A.,CSIRO | And 10 more authors.
Astrophysical Journal | Year: 2012

We present a study of the magnetic field of the Large Magellanic Cloud (LMC), carried out using diffuse polarized synchrotron emission data at 1.4 GHz acquired at the Parkes Radio Telescope and the Australia Telescope Compact Array. The observed diffuse polarized emission is likely to originate above the LMC disk on the near side of the galaxy. Consistent negative rotation measures (RMs) derived from the diffuse emission indicate that the line-of-sight magnetic field in the LMC's near-side halo is directed coherently away from us. In combination with RMs of extragalactic sources that lie behind the galaxy, we show that the LMC's large-scale magnetic field is likely to be of quadrupolar geometry, consistent with the prediction of dynamo theory. On smaller scales, we identify two brightly polarized filaments southeast of the LMC, associated with neutral hydrogen arms. The filaments' magnetic field potentially aligns with the direction toward the Small Magellanic Cloud (SMC). We suggest that tidal interactions between the SMC and the LMC in the past 109 years are likely to have shaped the magnetic field in these filaments. © 2012 The American Astronomical Society. All rights reserved.

Van Der Byl A.,Square Kilometre Array South Africa | Inggs M.R.,University of Cape Town
Digital Signal Processing: A Review Journal | Year: 2016

The sliding discrete Fourier transform provides an alternative to the FFT, permitting a custom choice of frequency decomposition which outputs an update after each input sample. The technique relies on the application of the Fourier shift property, and is recursive by nature. This work investigates the error performance of alternative techniques (SDFT; gSDFT; mSDFT, rSDFT; and Douglas and Soh algorithms) under both floating point and fixed point arithmetic constraints. The results highlight that the sliding discrete Fourier transform with error correction provides consistent error performance over a range of test cases, and indicates the limitations applicable to all techniques. © 2016 Elsevier Inc. All rights reserved.

Somanah R.,University of Mauritius | Issur N.,University of Mauritius | Oozeer N.,Square Kilometre Array South Africa | Oozeer N.,African Institute for Mathematical Sciences
IOP Conference Series: Materials Science and Engineering | Year: 2012

One of the first scientific justifications of building the Mauritius Radio Telescope (hereafter referred to as MRT) was to complement the Cambridge 6C survey, which is a radio map of most of the northern sky at 150 MHz [1]; the MRT would then be the equivalent of the 6C survey for the southern sky and together we would obtain a whole sky radio map at 150 MHz. When the MRT was built, there were no radio surveys of the southern sky at frequencies less than 408 MHz; the frequency of 150 MHz was also chosen to complement the other radio surveys of the southern sky, which have been done at higher frequencies. Furthermore low radio frequencies like 150 MHz are bound to see new sources that would have been missed at higher frequencies due to the form of their spectra. Interesting features of resolved objects can also be studied in more details. In this paper, a brief description of the MRT will be made as well as the observations and imaging with the MRT data, and some astrophysical results obtained since its commissioning in 1992 (20 years of existence this year 2012).

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