Pinelands, South Africa
Pinelands, South Africa

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Hess K.M.,University of Groningen | Hess K.M.,Netherlands Institute for Radio Astronomy | Cluver M.E.,University of the Western Cape | Yahya S.,University of the Western Cape | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2017

Extending deep observations of the neutral atomic hydrogen (H I) to the environment around galaxy groups can reveal a complex history of group interactions which is invisible to studies that focus on the stellar component. Hickson Compact Group 44 (HCG 44) is a nearby example, and we have combined HI data from the Karoo Array Telescope,Westerbork Synthesis Radio Telescope, and Arecibo Legacy Fast ALFA survey, in order to achieve high column density sensitivity (NHI < 2 × 1018 cm-2) to the neutral gas over a large field of view beyond the compact group itself. We find that the giant HI tail north of HCG 44 contains 1.1 × 109 M⊙ of gas and extends 450 kpc from the compact group: twice as much mass and 33 per cent further than previously detected. However, the additional gas is still unable to account for the known HI deficiency of HCG 44. The tail likely formed through a strong tidal interaction and HI clouds in the tail have survived for 1 Gyr or more after being stripped. This has important implications for understanding the survival of neutral clouds in the intragroup and circumgroup medium, and we discuss their survival in the context of simulations of cold gas in hot haloes. HCG 44 is one of a growing number of galaxy groups found to have more extended HI in the intragroup and circumgroup medium than previously measured. Our results provide constraints for simulations on the properties of galaxy group haloes, and reveal a glimpse of what will be seen by future powerful HI telescopes and surveys. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Julie R.P.M.,Square Kilometre Array South Africa | Abbott T.,Square Kilometre Array South Africa
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2017

To synchronise the elements of a radio interferometer array, a phase stable reference frequency from a central clock is disseminated to the different elements of array. The reference frequency is modulated onto an optical carrier and transported over optical fibre over a distance of up to 12 km. For radio interferometric efficiency, the propagation delay of the transferred reference frequency is required to be stable to less than 3 picoseconds (ps) over 20 minutes. To enable this, the optical fibre transmission line is thermally shielded to minimise length changes due to thermal expansion and contraction on the optical fibre. A test setup and procedure, that measures propagation delay changes to the required accuracy and precision, is required to verify the efficiency of the thermal shielding on the installed optical fibre. This paper describes a method using photonic and radio frequency (RF) components together with an RF vector network analyser (VNA) and post-processing to measure changes in propagation delay on the optical fibre link to sub-picosecond levels. The measurement system has been tested to a stability of < 200 femtoseconds (fs) and a resolution of < 10 fs. © 2017 SPIE.

Rotich Kipnoo E.K.,Nelson Mandela Metropolitan University | Gamatham R.R.G.,Nelson Mandela Metropolitan University | Leitch A.W.R.,Nelson Mandela Metropolitan University | Gibbon T.B.,Nelson Mandela Metropolitan University | And 5 more authors.
Optik | Year: 2017

Polarization mode dispersion (PMD) is one of the key effects in optical fibre communication that distorts the transmitted signal. The effect of birefringence on the polarization states of an optical signal leads to broadening of the pulses in an optical fibre. The difference in propagation time of the orthogonal modes in a fibre results in differential group delay (DGD). For proper functioning of a telescope, accurate and stable clock signals will be distributed via an optical fibre network to each of the dishes. This paper presents field PMD measurement that is essential in estimating the expected phase change of the clock signal. The average DGD of a 10.2 km fibre link established to be about 62.1 fs. This study serves to address the applicability of optical fibre network transmission in the distribution of frequency and timing reference signals in the MeerKAT and later phases of the square kilometre array (SKA) telescope. © 2017

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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