Australian low-frequency precursor ready for SKA Phase 1 science
The Murchison Widefield Array (MWA) is an interferometric radio telescope operating at low radio frequencies (80-300 MHz), composed of 128 aperture arrays (‘tiles’) and located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia. The instrument qualified as the official SKA-low precursor because it serves as a technology demonstrator at the chosen Australian site of the Square Kilometre Array (SKA) where levels of human-made radio frequency interference are extremely low. Just as the other two SKA precursors, CSIRO’s Australian SKA Pathfinder (ASKAP) and the South African MeerKAT, the MWA has undergone a prototype test phase (32 tiles) which has recently been decommissioned and re-built as the full 128-tile array. Of the three SKA precursors, the MWA will be the first to commence operations, in 2013. Its modular layout, with a high tile density in a core region and spread-out tiles over several kilometres, was driven by the four main science goals for which the instrument was optimised. These goals are detection of the Epoch of Reionisation in the early Universe, galactic and extra-galactic processes, transient radio sources and solar science.
In their paper (accepted, Publications of the Astronomical Society of Australia), MWA Director and CAASTRO Chief Investigator at Curtin University Professor Steven Tingay and the international MWA consortium provide a full description of the telescope, including its final system architecture and sub-systems, signal processing and data handling strategies.
Data collection with the MWA starts with small, low-noise amplifying dual-polarisation dipole antennas, 16 to a tile, mounted on a 5m x 5m mesh ground plane. The radio frequency signals of all dipoles are fed into an analogue beamformer, where signal delays provide directionality and make up for the lack of movable parts to point the telescope in 256 possible directions. Filtering and digital conversion of the analogue signals takes place in 16 receiver elements, each processing data from eight tiles. The digital data are transmitted via fibre optic links to a CSIRO-owned Central Processing Facility on-site where data are processed, calibrated and imaged, prior to being transmitted to the Pawsey High Performance Computing Centre for SKA Science in Perth, a dedicated supercomputing facility currently under construction.
All components have been designed and laid out to be flexible, modifiable and upgradable in the future – a valuable lesson learnt from the prototype test phase. Systems also had to be constructed such that they would not introduce any radio frequency interference into the pristine environment and could operate in the open field. Users of the MWA telescope, however, will be able to stay in the comfort of their research institute by using a web-based interface for remote operations.
S. J. Tingay, R. Goeke, J. D. Bowman, D. Emrich, S. M. Ord, D. A. Mitchell, M. F. Morales, T. Booler, B. Crosse, D. Pallot, A. Wicenec, W. Arcus, D. Barnes, G. Bernardi, F. Briggs, S. Burns, J. D. Bunton, R. J. Cappallo, T. Colegate, B. E. Corey, A. Deshpande, L. deSouza, B. M. Gaensler, L. J. Greenhill, J. Hall, B. J. Hazelton, D. Herne, J. N. Hewitt, M. Johnston-Hollitt, D. L. Kaplan, J. C. Kasper, B. B. Kincaid, R. Koenig, E. Kratzenberg, C. J. Lonsdale, M. J. Lynch, B. McKinley, S. R. McWhirter, E. Morgan, D. Oberoi, J. Pathikulangara, T. Prabu, R. A. Remillard, A. E. E. Rogers, A. Roshi, J. E. Salah, R. J. Sault, N. Udaya-Shankar, F. Schlagenhaufer, K. S. Srivani, J. Stevens, R. Subrahmanyan, S. Tremblay, R. B. Wayth, M. Waterson, R. L. Webster, A. R. Whitney, A. Williams, C. L. Williams, J. S. B. Wyithe in PASA xxx 2013: