The Ooty Wide Field Array

We describe here an ongoing upgrade to the legacy Ooty Radio Telescope (ORT).The ORT is a cylindrical parabolic cylinder 530mx30m in size operating at a frequency of 326.5 (or z ~ 3.35 for the HI 21cm line). The telescope has been constructed on a north-south hill slope whose gradient is equal to the latitude of the hill, making it effectively equitorially mounted. The feed consists of an array of 1056 dipoles. The key feature of this upgrade is the digitisation and cross-correlation of the signals of every set of 4-dipoles. This converts the ORT into a 264 element interferometer with a field of view of 2 degrees x 27cos(delta) degrees . This upgraded instrument is called the Ooty Wide Field Array (OWFA). This paper briefly describes the salient features of the upgrade, as well as its main science drivers. There are three main science drivers viz. (1) Observations of the large scale distribution of HI in the post-reionisation era (2) studies of the propagation of plasma irregularities through the inner heliosphere and (3) blind surveys for transient sources. More details on the upgrade, as well as on the expected science uses can be found in other papers in this special issue.Comment: To appear in the special section of the JAA on the Ooty Wide Field Arra

Space Weather and Solar Wind Studies with OWFA

In this paper, we review the results of interplanetary scintillation (IPS) observations made with the legacy system of the Ooty Radio Telescope (ORT) and compare them with the possibilities opened by the upgraded ORT, the Ooty Wide Field Array (OWFA). The stability and the sensitivity of the legacy system of ORT allowed the regular monitoring of IPS on a grid of large number of radio sources and the results of these studies have been useful to understand the physical processes in the heliosphere and space weather events, such as coronal mass ejections, interaction regions and their propagation effects. In the case of OWFA, its wide bandwidth of 38 MHz, the large field of view of $\sim$27$^\circ$ and increased sensitivity provide a unique capability for the heliospheric science at 326.5 MHz. IPS observations with the OWFA would allow one to monitor more than 5000 sources per day. This, in turn, will lead to much improved studies of space weather events and solar wind plasma, overcoming the limitations faced with the legacy system. We also highlight some of the specific aspects of the OWFA, potentially relevant for the studies of coronal plasma and its turbulence characteristics.Comment: 15 pages, 2 figures (Accepted for Publication J. Astrophysics and Astronomy

High Performance Power Spectrum Analysis Using a FPGA Based Reconfigurable Computing Platform

Power-spectrum analysis is an important tool providing critical information about a signal. The range of applications includes communication-systems to DNA-sequencing. If there is interference present on a transmitted signal, it could be due to a natural cause or superimposed forcefully. In the latter case, its early detection and analysis becomes important. In such situations having a small observation window, a quick look at power-spectrum can reveal a great deal of information, including frequency and source of interference. In this paper, we present our design of a FPGA based reconfigurable platform for high performance power-spectrum analysis. This allows for the real-time data-acquisition and processing of samples of the incoming signal in a small time frame. The processing consists of computation of power, its average and peak, over a set of input values. This platform sustains simultaneous data streams on each of the four input channels.Comment: 5 pages, 3 figures. Published in the Proceedings of the IEEE International conference on Reconfigurable Computing and FPGAs (ReConFig 2006). Article also available at http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4100006&isnumber=409995

The Receiver System for the Ooty Wide Field Array

The legacy Ooty Radio Telescope (ORT) is being reconfigured as a 264-element synthesis telescope, called the Ooty Wide Field Array (OWFA). Its antenna elements are the contiguous 1.92 m sections of the parabolic cylinder. It will operate in a 38-MHz frequency band centred at 326.5 MHz and will be equipped with a digital receiver including a 264-element spectral correlator with a spectral resolution of 48 kHz. OWFA is designed to retain the benefits of equatorial mount, continuous 9-hour tracking ability and large collecting area of the legacy telescope and use modern digital techniques to enhance the instantaneous field of view by more than an order of magnitude. OWFA has unique advantages for contemporary investigations related to large scale structure, transient events and space weather watch. In this paper, we describe the RF subsystems, digitizers and fibre optic communication of OWFA and highlight some specific aspects of the system relevant for the observations planned during the initial operation.Comment: 10 pages, 5 figures, 1 table, (Accepted for publication in J. Astrophysics and Astronomy

The Molonglo Reference Catalog 1-Jy radio source survey IV. Optical spectroscopy of a complete quasar sample

Optical spectroscopic data are presented here for quasars from the Molonglo Quasar Sample (MQS), which forms part of a complete survey of 1-Jy radio sources from the Molonglo Reference Catalogue. The combination of low-frequency selection and complete identifications means that the MQS is relatively free from the orientation biases which affect most other quasar samples. To date, the sample includes 105 quasars and 6 BL Lac objects, 106 of which have now been confirmed spectroscopically. This paper presents a homogenous set of low-resolution optical spectra for 79 MQS quasars, the majority of which have been obtained at the Anglo-Australian Telescope. Full observational details are given and redshifts, continuum and emission-line data tabulated for all confirmed quasars.Comment: 40 pages, ApJS in pres

A new method of deconvolution and its application to lunar occultations

A new method of deconvolution is described which uses our prior knowledge about the solution to derive some of the information obscured in the data because of the smoothing nature of convolution and the presence of noise. It uses a regularized least-squares criterion of agreement with the data, according to which the computed solution will lead to a minimum variance of noise and also be smooth in the sense of minimum variance of its second-differences. In addition, the present optimum deconvolution method (ODM) also constrains this solution to satisfy our prior knowledge about it by using a combination of a new algorithm for incorporating bounds on the solution like positivity, and the Lagrange multiplier method for equality-constraints. The new algoritham is a rapidly converging sequence of iterations for minimizing a weighted sum of squares of the deviation of the solution from the specified bounds. For the sake of illustration, ODM is compare with the conventional method of Scheuer for deconvolving the lunar occultation data to derive the brightness distribution of a radio source. The required occultation data have been obtained both from computer stimulations and from the observations of occultation with the Ooty radio telescope. A comparison of the restorations using the two methods indicates that a) ODM can be effectively applied even in very noisy situations; b) it leads to superresolution, implying an improvement in resolution by about a factor of two over the conventional method; and c) ODM provides a "clean" output leaving all the effects of noise to the residuals. A practical procedure has also been discussed for obtaining the effective resolution and restoring errors from an analysis of the residuals, perticularly their variance and power spectrum

On the interpretation of the observed angular-size-flux-density relation for extragalactic radio sources

The interpretation of the observed relation between median angular sizes (θm) of extragalactic radio sources and flux density at 408 MHz has been examined. The predicted θm-S relations based on well-observed strong sources in parent samples selected at 178 and 1400 MHz, and existing models of the evolving radio luminosity function can be made to fit the observed relation only by invoking cosmological evolution in linear sizes even for the q0 = 0 universe. Predictions based on a parent sample at 2.7 GHz are shown to overestimate the contribution of steep-spectrum, compact (SSC) sources in low-frequency samples unless the downward curvature in the spectra of such sources is taken into account. When approximate corrections are made for this effect, predictions based on the 2.7 GHz parent sample cannot obviate the need for linear size evolution as claimed in the literature

MSH 05-22 - a giant radio source in the Southern sky

During a program of mapping a complete sample of extended radio sources with the Molonglo Observatory Synthesis Telescope (MOST), the source MSH 05-22 (0503-286) was discovered to be a giant radio source. Our map at 843 MHz clearly suggests the association of the observed radio emission, extending over 42 arcmin, with a 15.5 mag D-galaxy. The galaxy redshift of z = 0.0384 leads to a projected linear extent of 2.6 Mpc (H0 = 50 kms-1Mpc-1), making this the largest known radio source in the southern sky