by Staff Writers
Johannesburg, South Africa (SPX) Jul 06, 2017
The Ministries of Ghana and South Africa have announced the combination of 'first light' science observations which confirms the conversion of the Ghana communications antenna from a redundant telecoms instrument into a fully functioning Very Long Baseline Interferometry (VLBI) radio telescope.
Ghana is the first partner country of the African Very Large Baseline Interferometer (VLBI) Network (AVN) to complete the conversion of a communications antenna into a functioning radio telescope. The 32-metre converted telecommunications antenna at the Ghana Intelsat Satellite Earth Station at Kutunse will be integrated into the African VLBI Network (AVN) in preparation for the second phase construction of the Square Kilometre Array (SKA) across the African continent. The combination 'first light' science observations included methanol maser detections, VLBI fringe testing and pulsar observations.
Reaching these three objectives confirm that the instrument can operate as a single dish radio telescope and also as part of global VLBI network observations, such as the European VLBI network. Following the initial 'first light' observations, the research teams from Ghana and South Africa together with other international research partners, continue to do more observations and are analysing the data generated with the aim to characterise the system and improve its accuracy for future experiments.
"The Ghanaian government warmly embraces the prospect of radio astronomy in the country and our radio astronomy development plan forms part of the broader Ghana Science, Technology and Innovation Development Plan," says Professor Kwabena Frimpong-Boateng, the Ghana Minister of Environment, Science, Technology and Innovation (MESTI).
As an SKA Africa partner country, Ghana welcomed and collaborated with the SKA South Africa (SKA SA)/HartRAO (Hartebeesthoek Radio Astronomical Observatory) group to harness the radio astronomy potential of the redundant satellite communication antenna at Kutunse. A team of scientists and engineers from SKA SA/HartRAO and the Ghana Space Science and Technology Institute (GSSTI) which is under MESTI, has been working since 2011 on the astronomy instrument upgrade to make it radio-astronomy ready. In 2012, Ghana launched the GSSTI as the vehicle through which to grow its astrophysics programme.
The South African Department of International Relations and Cooperation (DIRCO) has been funding a large part of the conversion project through the African Renaissance and International Cooperation Fund (ARF). The South African Minister of DIRCO, Ms. Maite Nkoana-Mashabane says, "The African Renaissance Fund is aimed at strengthening cooperation between South Africa and other African countries and to support the development of skills and build institutional capacity on the continent." Nine African partner countries are members of the SKA AVN, including Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia, South Africa, and Zambia.
"A vital part of the effort towards building SKA on the African Continent over the next decade is to develop the skills, regulations and institutional capacity needed in SKA partner countries to optimise African participation in the SKA," says the South African Minister of Science and Technology, Mrs. Naledi Pandor.
The AVN programme is aimed at transferring skills and knowledge in African partner countries to build, maintain, operate and use radio telescopes. Minister Pandor continued by saying: "It will bring new science opportunities to Africa on a relatively short time scale and develop radio astronomy science communities in SKA partner countries."
The Leverhulme-Royal Society Trust and Newton Fund in the UK are co-funding extensive human capital development programmes in the SKA AVN partner countries. A seven-member Ghanaian team has undergone training in South Africa and have been trained in all aspects of the project including the operation of the telescope.
Several PhD students and one MSc student from Ghana have received SKA SA bursaries to pursue further education in various fields of astronomy and engineering while the Royal Society has awarded funding in collaboration with Leeds University to train two PhDs and 60 young aspiring scientists in the field of astrophysics.
Based on the success of the Leverhulme-Royal Society programme, a joint UK-South Africa Newton Fund intervention (the Development in Africa with Radio Astronomy (DARA)) has since been initiated in other partner countries to grow high technology skills that could lead to broader economic development in Africa. This Newton Fund programme is providing a pool of talented young people who have been inspired by astronomy ultimately play a leading role in the emergence of new economies.
A Ministerial Forum comprising Ministers from the nine SKA AVN partner countries convenes on an annual basis to provide strategic and political leadership on the cooperation with the SKA and AVN projects, and on other relevant radio astronomy programmes and initiatives. The next SKA AVN Ministerial Forum will be held in Accra, Ghana in August when the Kutunse radio telescope will officially be launched.
Ghana Intelsat Satellite Earth Station
The SKA SA/HartRAO team assessed the suitability of the 32-metre Beam Waveguide antenna and the Kutunse control station for radio astronomy through two successive working visits in March and May 2011. The conversion work started when the station was handed over from Vodafone to the Ghanaian state under the management of GSSTI.
Once the refurbishment and conversion was completed, a commissioning team looked at how the telescope performed during the process of blind tracking and how it is affected by factors such as gravity as the antenna rotates. The team checked the effect of Radio Frequency Interference (RFI) and how well the antenna does a full rotation. For Phase 1, the existing telecommunication feed horn was used in the frequency range 3.8 - 6.4 GHz (C-band). For the actual science observations (Phase 2), an uncooled 5 GHz and 6.7 GHz (C-band) receivers were fitted.
Future receiver developments may include replacing the original C-band feed horn with a wider band design covering more VLBI bands and introducing cryogenic receivers for improved sensitivity and adding more frequency bands. Future changes could be according to the science programme of the GSSTI, in collaboration with global partners.
The Science Requirements
For the single-dish component, the uncooled C-band receivers have been fitted. This allows the antenna to do: radio continuum flux measurements (with a wideband multi-channel radiometer); pulsar observations (with a wideband multi-channel pulsar timer); and emission lines spectroscopy (with a narrowband multi-channel spectrometer).
For the VLBI component, the station requires capacity for: mapping interstellar masers in star-forming regions in the Milky Way; determining the distances to star-forming regions in the Milky Way through methanol maser parallax measurements; using trigonometric parallax measurements to determine accurate pulsar distances as well as pulsar proper motions; imaging active galactic nuclei (AGN); and other important functionalities. The longitude and latitude geographic location of the station is significant for astrophysics research.
'First Light' Observations: Methanol Maser Detection
The first observations aimed at the detection of a maser (G9.621+0.196E) were carried out on 21 November 2016. Since the initial detection other masers have been detected routinely.
Off line, the data are correlated to remove the arrival time delays of the signal and derive a band of contrasting brightness produced by the interference of the signals from antenna pairs (fringes). The resolution achievable using interferometry is also proportional to the observing frequency.
The VLBI technique enables the distance between telescopes to be much greater than that possible with conventional interferometry, which requires antennas to be physically connected by coaxial cable, waveguide, optical fibre, or other types of transmission lines.
VLBI is most well-known for imaging distant cosmic radio sources, spacecraft tracking, and for applications in astrometry. However, since the VLBI technique measures the time differences between the arrival of radio waves at separate antennas, it can also be used "in reverse" to perform Earth rotation studies, map movements of tectonic plates very precisely, and perform other types of geodesy. Using VLBI in this manner requires large numbers of time difference measurements from distant sources (such as quasars) observed with a global network of antennas over a period of time.
The Kutunse telescope 'gate-crashed' one of the C-band VLBI test observations that was carried out on 28 February 2017. The European VLBI Network supported the observation from Kutunse with great enthusiasm and assisted in the data analysis and correlation through experts from the Joint Institute for VLBI (JIVE) European Infrastructure Research Consortium (ERIC) in the Netherlands.
Collaborators and Acknowledgments
The following groups of individuals and institutions are recognised for the participation, collaboration and support in realising this momentous milestone.
The telescopes involved in the successful detection of fringes during a VLBI test experiment were part of the European VLBI Network (EVN) and included: Badary Radio Astronomical Observatory (Institute of Applied Astronomy, Russia), Effelsberg Radio Telescope (Max-Planck Institute for Radio Astronomy, Germany), Hartebeesthoek Radio Astronomy Observatory (National Research Foundation, South Africa), Jodrell Bank Observatory (University of Manchester, UK), Medicina Radio Observatory (National Institute for Astrophysics, Italy), Onsala Space Observatory (Chalmers University of Technology, Sweden), Svetloe Radio Astronomical Observatory (Institute of Applied Astronomy, Russia), Torun; Centre for Astronomy (Nicolaus Copernicus University, Poland), Urumqi Astronomical Observatory (Chinese Academy of Sciences, China), Ventspils International Radio Astronomy Centre (Latvian Academy of Sciences, Latvia), Westerbork Synthesis Radio Telescope (ASTRON, the Netherlands), Yebes Observatory (National Geographic Institute, Spain), and Zelenchukskaya Observatory (Institute of Applied Astronomy, Russia).
The scientists at the JIVE ERIC in the Netherlands and the broader European network added tremendous value through Dr. Jay Blanchard, Support Scientist for the JUMPING JIVE project.
For the pulsar timer, Professor Ben Stappers, University of Manchester and his student Mr. Tom Scragg, University of Manchester, were key contributors, also providing equipment funded through the Leverhulme-Royal Society intervention.
Professor Melvin Hoare, Leeds University was responsible for the Leverhulme-Royal Society program.
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