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Register a new userSouthern Africa CTA Site Proposal
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Added by
Paulus Kr\\\"uger Dr.
Publication date
2012
fields
Physics
and research's language is
English
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Southern Africa has some of the worlds best sites for air Cherenkov telescopes. South Africa has only one viable site, which is south of Sutherland and also close to the Southern African Large Telescope (SALT). This site has very good infrastructure and is easy to access, but only 47% of the night-time has a cloudless sky usable for observations. Namibia, which already hosts the H.E.S.S telescope, has a number of potential sites with much less cloud coverage. The H.E.S.S. site is one of the highest of these sites at 1840 m a.s.l. with about 64% of the night-time cloudless. It also has very low night sky background levels and is relatively close (about 100 km) to Windhoek. Moving further away from Windhoek to the south, the cloud coverage and artificial night sky brightness becomes even less, with the site at Kuibis (between Keetmanshoop and Luderitz) at 1640 m a.s.l. having clear night skies 73% of the time. Even though this site seems remote (being 660 km from Windhoek by road), it is close to the national B4 highway, a railway line, a power line and an optical fiber line. It is also less than two hours drive away from a harbour and national airports. The Namibian sites also receive very little snow, if any, and the wind speeds are less than 50 km/h for more than 90% of the time with maximum wind speeds of around 100 km/h. Seismically the whole Southern African region is very stable.
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Many atmospheric and climatic criteria have to be taken into account for the selection of a suitable site for the next generation of imaging air-shower Cherenkov telescopes, the Cherenkov Telescope Array CTA. Such data are not available with sufficient precision, thus a comparison of the proposed sites and final decision based on a comprehensive characterization is impossible. Identical cross-calibrated instruments have been developed which allow for precise comparison between sites, the cross-validation of existing data, and the ground-validation of satellite data. The site characterization work package of the CTA consortium opted to construct and deploy 9 copies of an autonomous multi-purpose weather sensor, incorporating an infrared cloud sensor, a newly developed sensor for measuring the light of the night sky, and an All-Sky-Camera, the whole referred to as Autonomous Tool for Measuring Observatory Site COnditions PrEcisely (ATMOSCOPE). We present here the hardware that was combined into the ATMOSCOPE and characterize its performance.
The history of southern Africa involved interactions between indigenous hunter-gatherers and a range of populations that moved into the region. Here we use genome-wide genetic data to show that there are at least two admixture events in the history of Khoisan populations (southern African hunter-gatherers and pastoralists who speak non-Bantu languages with click consonants). One involved populations related to Niger-Congo-speaking African populations, and the other introduced ancestry most closely related to west Eurasian (European or Middle Eastern) populations. We date this latter admixture event to approximately 900-1,800 years ago, and show that it had the largest demographic impact in Khoisan populations that speak Khoe-Kwadi languages. A similar signal of west Eurasian ancestry is present throughout eastern Africa. In particular, we also find evidence for two admixture events in the history of Kenyan, Tanzanian, and Ethiopian populations, the earlier of which involved populations related to west Eurasians and which we date to approximately 2,700 - 3,300 years ago. We reconstruct the allele frequencies of the putative west Eurasian population in eastern Africa, and show that this population is a good proxy for the west Eurasian ancestry in southern Africa. The most parsimonious explanation for these findings is that west Eurasian ancestry entered southern Africa indirectly through eastern Africa.
In the last two decades, very-high-energy gamma-ray astronomy has reached maturity: over 200 sources have been detected, both Galactic and extragalactic, by ground-based experiments. At present, Active Galactic Nuclei (AGN) make up about 40% of the more than 200 sources detected at very high energies with ground-based telescopes, the majority of which are blazars, i.e. their jets are closely aligned with the line of sight to Earth and three quarters of which are classified as high-frequency peaked BL Lac objects. One challenge to studies of the cosmological evolution of BL Lacs is the difficulty of obtaining redshifts from their nearly featureless, continuum- dominated spectra. It is expected that a significant fraction of the AGN to be detected with the future Cherenkov Telescope Array (CTA) observatory will have no spectroscopic redshifts, compromising the reliability of BL Lac population studies, particularly of their cosmic evolution. We started an effort in 2019 to measure the redshifts of a large fraction of the AGN that are likely to be detected with CTA, using the Southern African Large Telescope (SALT). In this contribution, we present two results from an on-going SALT program focused on the determination of BL Lac object redshifts that will be relevant for the CTA observatory.
Very Long Baseline Interferometry (VLBI) offers unrivalled resolution in studies of celestial radio sources. The subjects of interest of the IAU Symposium No. 356, the Active Galactic Nuclei (AGN) of all types, constitute the major observing sample of modern VLBI networks. At present, the largest in the world in terms of the number of telescopes and geographical coverage is the European VLBI Network (EVN), which operates under the open sky policy via peer-reviewed observing proposals. Recent EVN observations cover a broad range of science themes from high-sensitivity monitoring of structural changes in inner AGN areas to observations of tidal eruptions in AGN cores and investigation of redshift-dependent properties of parsec-scale radio structures of AGN. All the topics above should be considered as potentially rewarding scientific activities of the prospective African VLBI Network (AVN), a natural scientific ally of EVN. This contribution briefly describes the status and near-term strategy for the AVN development as a southern extension of the EVN-AVN alliance and as an eventual bridge to the Square Kilometre Array (SKA) with its mid-frequency core in South Africa.
The development of astronomy and space science in Africa has grown significantly over the past few years. These advancements make the United Nations Sustainable Development Goals more achievable, and open up the possibility of new beneficial collaborations.
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