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Pinelands, South Africa

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

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. Source

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

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). Source

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

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. Source

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

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. Source

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

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. Source

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