A supercomputer-based software correlator at the Swinburne University of Technology

1. A supercomputer-based software correlator at the Swinburne University of Technology Tingay, S.J. and Deller, A. stingay@astro.swin.edu.au;adeller@astro.swin.edu.au Background: The Centre for Astrophysics and Supercomputing at the Swinburne University of Technology has been funded under the Major National Research Facilities (MNRF) program to investigate applications of baseband processing in radio astronomy, as a demonstration of techniques for the Square Kilometre Array (SKA). Baseband data are the sampled, digitised output of radio telescopes that are auto-correlated to form single dish spectra or cross-correlated for interferometry. Traditionally these data have been processed using application-specific integrated circuits (ASIC). We have departed from tradition and have developed parallelised software to correlate baseband data using supercomputers and/or commodity clusters to correlate baseband data. Computing resources: The main computing resources at our disposal are: a 300 node Beowulf cluster (Fig 1a) at Swinburne’s main campus; a 32 node cluster (Fig 1b) at the Parkes radio telescope; a Cray XD-1 at the University of Western Australia (Fig 1c); and a 16 node cluster (Fig 1d) at the Australia Telescope National Facility (ATCA). Extensive development and testing of these facilities has taken place over the last 3 years. A major milestone of the project was the successful correlation of a VLBI experiment that involved 9 different radio telescopes across 4 different continents (Australia, Africa, Asia, and North America). These telescopes recorded data in 3 different disk-based formats (LBADR in Australia [see Chris Phillips poster at this meeting]; Mark5 in South Africa and in the USA; K5 in Japan). The data were correlated together at the Swinburne University of Technology supercomputer and reduced/imaged using standard techniques in existing software packages such as AIPS, AIPS++, DIFMAP, and MIRIAD (Fig 3a; Horiuchi et al. 2006a, 2006b, in preparation). Since this milestone, spectral line data at 22 GHz have been correlated (Fig 3b: Horiuchi et al. 2006c, in preparation) and pulsar data for scintillation studies (Fig 3c: Brisken et al. 2006, in preparation). In May 2006, the first true PI-based projects from the ATNF time assignment process were correlated at Swinburne and delivered to the PIs (projects V193a: Norris et al. 2006, in preparation; v195a: Bains et al.; v190a,b,c: Deller et al.; v188a: Lenc et al.). This signals the start of a transition period that will see all Australian VLBI observations correlated in software at Swinburne within the next 12 months. The MNRF-funded program at Swinburne has therefore fulfilled all of its goals and has provided (within the 5 year MNRF timeframe and budget) a very significant enhancement of Australian VLBI facilities, that is now open for all ATNF users. Further, the MNRF project has been a stepping off point for a number of Australian Research Council projects at the Discovery, LIEF, and SRS level in 2005/2006. Other projects have now been proposed to the ARC on the basis of the continued success of the MNRF project. Funding has also been secured through the Australian National Collaborative Research Initiative Scheme (NCRIS) to adapt the software correlator for geodetic VLBI work, to support a new Australian 3-station geodesy network that will participate in IVS activities. Fig 1: (left to right) a) 300 node cluster; b) 32 node cluster; c) Cray XD-1; d) 16 node cluster. Interferometry The software correlator developed at the Swinburne University of Technology is now operated as part of the Australian VLBI array. This constitutes a major upgrade for this instrument, increasing the maximum recorded bandwidth to 1 Gbps, from 128 Mbps. These facilities are now available to all VLBI users: http://www.atnf.csiro.au/vlbi Fig 3: (left to right) a) First VLBI image from correlator J0003-066 b) High spectral resolution water maser data c) Complex secondary spectrum (FFT of dynamic spectrum) for pulsar.