A major role of the 26m radio telescope at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) is to participate in global networks of radio telescopes in order to make images of astronomical radio sources with high angular resolution, through the technique of Very Long Baseline Interferometry (VLBI). This is normally done by recording the signal received at each telescope onto computer disks and then airfreighting these to the data processing system, known as a correlator, where the signals are combined to provide the data product from which the image is produced. The advent of wide bandwidth fibre-optic connections between continents has enabled this to move to the next level, e-VLBI, in which the telescopes are connected in real time through the internet to the correlator. The ability to transmit wide bandwidth data to the correlator is very important, as the sensitivity of the observations increases with increasing bandwidth.
e-VLBI with the HartRAO 26m telescope restarted after 2010 July following the return to service of the telescope after a main bearing that failed in 2008 October had been replaced.
HartRAO is an associate member of the European VLBI Network (EVN). On 2010 September 30, the first Target of Opportunity (ToO) e-VLBI was carried out with the HartRAO 26m telescope working with the other radio telescopes of the EVN. The data from all participating telescopes was transmitted to the correlator at the Joint Institute for VLBI in Europe (JIVE), at Dwingeloo in the Netherlands. HartRAO was able to transmit data at 896 Mbps. This may be contrasted with the maximum bandwidth of 64 Mbps achieved in the first demonstration e-VLBI's at HartRAO in 2008. In this experiment on September 30, radio emission was detected from a Black Hole candidate in the Milky Way named MAXI-J1659-152. The results were published in Astronomers Telegram 2906 by the experiment's Principal Investigator Zsolt Paragi and co-workers on October 5.
On 2010 November 05, courtesy of data rerouting by TENET, the maximum possible data capture rate from the current recording system of 1024 Mbps was achieved in another Target of Opportunity e-VLBI on the Crab pulsar - the rapidly spinning collapsed remnant of an exploded star.
The first ever e-VLBI between Africa and Australia was conducted on 2010 November 24 by the HartRAO 26m telescope working with the 64m Parkes radio telescope amongst others. This achieved a data transfer rate to the correlator in Australia of 512 Mbps, the rate being set to match the Australian processing capability. After successful initial test observations of bright quasar PKS1921-293 (a distant galaxy emitting radio waves from jets emerging from around a supermassive Black Hole) used to calibrate the system, the experiment was switched in real-time to investigate the sizes of various other southern quasars.
http://www.hartrao.ac.za/news/101124eVLBI/index.html
