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HartRAO Home > news > First Wide-band e-VLBI's linking Africa with Europe and with Australia 2010/11/05 - 2010/11/24

First Wide-band e-VLBI's linking Africa with Europe and with Australia 2010/11/05 - 2010/11/24

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.

Major impacts of these technical breakthroughs include:

At HartRAO, VLBI Operations Manager Jonathan Quick has been instrumental in setting up the radio telescope systems to successfully carry out these e-VLBI's.

The capability for transmitting wide bandwidth data to other continents is a result of the actions by the Department of Science and Technology (DST), through the CSIR's Meraka Institute, in providing the high-speed South African Research Network (SANReN) infrastructure within the country. The Tertiary Education Network (TENET) is the operator of SANReN that provides national and international connectivity to all universities and research councils via the SEACOM undersea cable and also provides comprehensive interconnections in London to other research and education networks and the Internet generally worldwide. At TENET, Duncan Martin and Andrew Alston have been key facilitators of this process. This worldwide connectivity is provided through the UbuntuNet Alliance, which is the regional research and education network for eastern and southern Africa, of which TENET is a founding member.

International partners were the European VLBI Network (EVN), the Joint Institute for VLBI in Europe (JIVE), and the Australian CSIRO's Astronomy and Space Science Division.

Left click on image for large version.
Data rates into the JIVE correlator in Dwingeloo, Holland during the first maximum rate (1024 Mbps) e-VLBI with Europe, 2010 November 05. Data received from HartRAO is represented by the dark green band at the top. Total maximum incoming data rate to JIVE was 7.77 Gbps.

Left click on image for large version.
Jonathan Quick monitors progress in the HartRAO control room during the first e-VLBI with Australia, 2010 November 24. The graphs on the screen in front of him show the excellent signal correlation between the 26m HartRAO telescope in South Africa and the 64m Parkes telescope in Australia.

Left click on image for large version.
The HartRAO 26m telescope, pointing low in the south east, as seen through the control room windows during the first e-VLBI with Australia on 2010 November 24.

Left click on image for large version.
Astronomer's Telegram 2906 reports the success of the e-VLBI of 2010 September 30 in detecting the radio emission from Black Hole candidate MAXI J1659-152.