PoS(HEASA 2016)029 , c , , g b http://pos.sissa.it/ j , i , H. Falcke ‡ , f , G. MacLeod b , R. Evans -plane for these observations across e v − u , M. Klein Wolt c and H.J. van Langevelde h , R.P. Deane d PACS: 95.45.+i, 99.55.-n, 95.55.Jz, 98.35.Jk , Z.-Q. Shen b , T.P. Krichbaum b [email protected] , J.E. Conway , c , b . Although the Event Horizon Telescope utilises an extensive network of ∗ , C. Goddi , F. Roelofs b ,] b , C. Müller a , ∗ [email protected] Department of Physics and Astronomy, Botswana International University of Science & Department of Physics, University of Namibia, Private Bag 13301, Windhoek, Namibia Speaker. Africa. We discuss the benefits of adding the Africaand Millimetre present Telescope to Mt. the Gamsberg Event Horizon in Telescope Namibiain as Africa. the best site for this new and first mm-wave telescope It is believed thatMilky supermassive Way. black Still, holes only are indirectobjects found evidence that in has are the been predicted centres gathered bya for the of Very the general galaxies, Long theory existence including Baseline of of the relativity. Interferometry thesepossible With enigmatic network to the of directly Event millimetre-wave image Horizon (radio)the Telescope, the Milky telescopes, ‘shadow’ Way, it Sgr of A will thetelescopes, be event there horizon is of a the huge black gap hole in at the the coverage centre of of the ∗ Copyright owned by the author(s) under the terms of the Creative Commons c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). R. Fraga-Encinas now at Technology, Private Bag 16, Palapye, Botswana E-mail: 4th Annual Conference on High Energy25-27 Astrophysics August, in 2016 Southern Africa Cape Town, South Africa Onsala Space Observatory, Department of EarthTechnology, SE-43992 and Onsala, Space Sweden Sciences, Chalmers UniversityCentre of for Radio Astronomy Techniques & TechnologiesElectronics, (RATT), Rhodes Department University, of Grahamstown Physics 6140, and SouthSchool Africa of Physics & Astronomy, CardiffHartebeesthoek University, Cardiff Radio CF24 Astronomy 3AA, Observatory, United P.O. Box Kingdom 443,Shanghai Krugersdorp Astronomical 1740, Observatory, Chinese South Academy Africa ofShanghai Sciences, 200030, 80 P.R. Nandan China Road, Joint Institute for VLBI ERIC (JIVE),Sterrewacht Postbus Leiden, 2, Leiden NL-7990 University, AA, Postbus 9513, Dwingeloo, NL-2300 thenow RA Netherlands at Leiden, the Netherlands Department of Physics, University of Namibia,Department Private of Bag Astrophysics/IMAPP, Radboud 13301, University Windhoek, Nijmegen, Namibia PONijmegen, Box the 9010, Netherlands NL-6500 GL Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany V.A.R.M. Ribeiro M. Backes The Africa Millimetre Telescope i j ] f e c g h ‡ a b d PoS(HEASA 2016)029 . ∗ M. Backes ] are starting in Greenland. 6 ] and references 10 2 ]. 7 ) and the Submillimeter Ar- ∗ 3 ], and 230 GHz [ 5 . is a SMBH. However, by utilizing , ∗ ∗ and the SMBH at the centre of M87. 4 ∗ in Arizona, the Large Millimeter Tele- at the South Pole, and the IRAM 30 m 5 7 ]. For further details see [ projects are given in a recent and extensive 1 11 ], 86 GHz [ 3 1 arcsec and therefore have sufficient resolution to arcsec [ µ µ is an initiative to create a global mm-wave VLBI net- 1 . These indications and the aforementioned possibility to ∗ in France and the Greenland Telescope (GLT) at 43 GHz [ 9 ∗ ] and BlackHoleCam 6 have given rise to the Event Horizon Telescope project. ∗ arcsec ‘shadow’ of the event horizon of Sgr A in Chile, the James Clerk Maxwell telescope (JCMT) µ 2 in Mexico, the South Pole Telescope (SPT) 6 50 in Hawaii, the Submillimeter Telescope (SMT) in Spain. In the following years, observations are also planned with the NOrthern Ex- 4 ∼ 8 , which has an angular size of about 50 ∗ https://blackholecam.org The millimetre VLBI campaign, scheduled for April 2017, will be the first with the required Although the EHT already constitutes an impressive VLBI network of mm-wave radio tele- http://pole.uchicago.edu http://www.iram-institute.org/EN/30-meter-telescope.php?ContentID=2 http://www.iram-institute.org/EN/noema-project.php?ContentID=9 https://www.cfa.harvard.edu/greenland12m http://www.eventhorizontelescope.org https://www.eso.org/sci/facilities/alma.html http://www.eaobservatory.org/jcmt https://www.cfa.harvard.edu/sma http://aro.as.arizona.edu/smt_docs/smt_telescope_specs.htm http://www.lmtgtm.org Recent observations of Sgr A The general theory of relativity is still largely untested in the strong-field limit. Certainly, The Event Horizon Telescope (EHT) 7 8 9 1 2 3 4 5 6 11 10 scope (LMT) telescope tended Millimeter Array (NOEMA) More details about the EHT [ ray (SMA) resolution and sensitivity to image the event horizon of Sgr A scopes, their spacial distribution is clustered around the Americas, thus limiting its capabilities. &rub=2&srub=0&ssrub=0&sssrub=0 &rub=9&srub=0&ssrub=0&sssrub=0 The following telescopes will be part ofArray this (ALMA) network: the Atacama Large Millimeter/submillimeter overview, including their motivation and anticipated observational results [ therein. work that will achieveimage a the resolution of 12–20 directly image Sgr A the best objects to pursuewhich such is tests also are the supermassive largest black in holes apparent (SMBHs) diameter, and is the located nearest at one, the centre of the Milky Way, Sgr A 2. The Event Horizon Telescope The Africa Millimetre Telescope 1. Imaging the Black Hole at the centre of our Galaxy (Sgr A Currently, we can only infer fromVery indirect Long evidence Baseline that Interferometry Sgr (VLBI) A able techniques to at achieve millimetric sufficient wavelengths, angular one resolutionSgr to should A directly be image the ‘shadow’ of the event horizon of to resolve the source. Thein observation the of plasma non-zero emission closure around phases indicates Sgr possible A substructure PoS(HEASA 2016)029 -plane v − M. Backes u Plateau de Bure to the EHT (see ] presently under ∗ 8 -plane coverage of [ v − 13 u , a single mm-wave radio telescope on the ; included is the improvement in coverage by 12 . In particular, it will enable the ‘Eastern sub- 2 ∗ 2 , the AMT will have common baselines for observations of 1 denotes the IRAM 30 m telescope on Pico del Veleta, denotes the AMT. IRAM PV Gamsberg m RMS surface accuracy and with 4–5 arcsec pointing accuracy. The AMT will µ Baselines of the current EHT VLBI network (in yellow) and additional baselines provided by the ). This will greatly improve the imaging capabilities of the EHT and, hence, advance its 2 with all the high-sensitivity telescopes (the IRAM 30 m telescope on Pico Veleta, NOEMA, on the right). As shown in fig. ∗ http://www.ska.ac.za/science-engineering/avn It is proposed that the AMT consists of a commercially available 12–16 m diameter antenna http://www.ru.nl/amt Adding the Africa Millimetre Telescope (AMT) 1 13 12 ALMA, and the LMT) as well as with all the other EHT telescopes. The Sgr A with 40–50 denotes NOEMA, and the current EHT configuration is presentedadding in the figure AMT. support 1.3 mm / 230AMT GHz supports and centrimetric 0.8 radio mm receiverswould / in allow 345 the GHz the 6–2 band cm AMT / receivers. to 5–15 participate GHz It in bands. is the The African also latter VLBI suggested receivers Network that (AVN) the Figure 1: AMT (in red). Note:observations the in Combined 2015, Array for Research in Millimeter-wave Astronomy (CARMA) ceased African continent, to the EHT network will significantly increase the coverage in the fig. capabilities to directly image the ‘shadow’array’, of including Sgr the A IRAM 30 mobservations, telescope, NOEMA, thus SPT, adding ALMA, a and significant AMT amount to perform of imaging daily observing time of Sgr A The Africa Millimetre Telescope Significant improvement can be achievednominally by called adding the a Africa single Millimetre Telescope. mm-wave radio telescope in Africa, 3. The Africa Millimetre Telescope (see fig. PoS(HEASA 2016)029 ], 9 [ ∗ ], and for M. Backes 11 is proposed. 14 observations from different ∗ ]. Subsequently, it was chosen 12 4,300 m a.s.l.) in Tanzania and the can be observed at elevation angles ≥ ∗ 3,050 m a.s.l.). However, primarily because Elevation of Sgr A ≥ 3 with the mm-wave telescopes in the Americas, the Figure 3: observatories and possible locations in Africafor for UT the 2014/02/30. AMT Note the remarkablyfor symmetric ALMA/APEX curves and the Gamsberg (Namibia) assimilar for latitudes. their ∗ ]. 10 -plane coverage of the current v − -plane coverage limited case of long integration times, the AMT will prove invaluable v u 30 kW and an off-grid ‘green power’ solution like HIPERSENSE − and that are at sufficiently high altitude to ensure an average precipitable water vapour u ∼ ◦ https://hipersense.eu Besides these prospects for the use of the AMT within the EHT network, there is ample scope For decades Mt. Gamsberg (2,347 m a.s.l.) in the Khomas Highlands in Namibia has been Based on simulations of the reconstructed EHT image of the black hole ‘shadow’ of Sgr A Potential sites on the African continent where Sgr A 14 40 Figure 2: EHT configuration depicted in blue and theditional ad- coverage to be addeddicated by in the red. AMT in- simulations including the AMT at Mt.in Gamsberg the were conducted. These simulations indicate that, seeing conditions comparable to the ESO site at La Silla in Chile [ for further science applications, suchitoring as and single-dish studies mm-wave of observations molecular forAfrican emission flux and lines, European density VLBI and mon- Networks (cm-wave) (AVN and VLBI EVN). observations as part of the 4. Mt. Gamsberg as a site for the AMT known as an excellent site for astronomy, both for the number of photometric nights [ for reconstructing the imageforthcoming of article [ the ‘shadow’ of the black hole. Details will be published in a western-most site, Mt. Gamsberg (2,347 mfor a.s.l.) further investigations. in Additional Namibia supporting hasby arguments been the for chosen Max-Planck this Society, as site and the that are primarydevelopment. the that site government the of land Namibia is is owned very encouraging of astronomy column of less than 6 mm include sites on Mt. Kilimanjaro ( The Africa Millimetre Telescope construction and with the Europeanto VLBI be Network (EVN). The power consumption is estimated ≥ Sani Pass in the Drakensberg mountains inof Lesotho temporal ( overlap in visibility of Sgr A PoS(HEASA 2016)029 ◦ ]. 19 , 18 M. Backes ]. The av- at 200 mbar E, only 0.32 20 ◦ 1 and estimated − will be possible 1 ∗ − ], professional as- 0 m s 17 . 1 ± S and 16.23 3 ◦ . of area available for many as- 4 telescope at the site [ 2 . 4 / f ], showing that the site has the low 21 ] through to 1986 [ since 2004, about 30 km from Mt. Gams- 16 16 ]. 4 24 ]. Despite the quality of the site, none of these projects has ]. In addition, the precipitable water vapour has been interpo- 15 22 , Mt. Gamsberg has long been regarded as a world-class astronomical ]. The results indicate the exceptional capabilities for observations up 4 23 . ]. It was even proposed to establish an inter-African astronomical observatory 3 ]), and was ranked the best site for scientific potential during the bid to host the 14 [ at a height of 10 m above ground level [ ] and was later considered as a possible site for the Southern African Large Tele- 25 1 15 − 13 https://www.mpi-hd.mpg.de/hfm/HESS We have shown that the Africa Millimetre Telescope (AMT) will be a valuableAs addition outlined to in the Section http://www.salt.ac.za Some site characterization of Mt. Gamsberg has been undertaken previously. It was deter- Physically, the site itself is a flat tabletop mountain with 2.3 km The latter site investigation campaign by ESO and the MPI for Astronomy in 1994–1995 also 16 15 berg (see e.g. [ EHT and have presented arguments supporting locating the AMT on Mt. Gamsbergsite. in Namibia, Namibia. in general, hasHigh excellent Energy astronomical Stereoscopic sites: System (H.E.S.S.) the telescopes country has successfully hosted the 5. Conclusion and Outlook to 3 mm / 100 GHztions throughout at the 1.3 mm year. / In 230particularly GHz, addition, which around strong is the but the seasonal southern observational capabilities winter bandtedly, for months of for observa- the of simultaneous EHT, June co-observing and through with, atservations to 0.8 particularly, need mm the August / to northern are 345 be GHz, hemisphere indicated. scheduled instruments,absorption in Admit- by ob- fall water vapour or at spring, 1.3 mm. whichup Also, will to most 345 EHT still GHz sites allow under have for suitable normal weather winter observations for conditions with observations [ low tronomical observations were conducted usingassociation of a amateur 50 astronomers cm has cassegrain operated telescope a 28” and, (71 cm) since 2010, an (i.e. approximately 12 km a.s.l.), below the limits set for adaptive optics techniques [ lated from satellite observations for comparisonof purposes the at Mt. the Gamsberg altitude site and [ geographical location ultimately used Mt. Gamsberg. However, from 1972 [ mined that there is a relatively low annual average wind speed of 23 and science park on the mountain [ measured the yearly average precipitable water vapourwith column on the photometric maximum nights monthly to be average 5.2erage of mm, of 6.7 mm 2.5 mm in in December August 1994 1994 and [ the minimum monthly av- The Africa Millimetre Telescope as the planned siteAstronomy for [ the 2.2 m diameterscope (SALT) telescope of the southern observatory of the MPI for tronomical instruments. The geographic coordinates of the site are 23.34 erage wind speed, 2 m above ground level, waswind measured speeds to necessary be to as achieve lowtelescope. the as required 4 high m s pointing accuracy for a large mm-wave radio different in latitude to ALMA. Hence, similaras high elevation indicated observations in of Sgr fig. A to be 5.4 m s PoS(HEASA 2016)029 ]. The , Wisps in M. Backes ´ DOI: c ], [ at 43 GHz ∗ The Astrophysical , DOI: . This station, designed ]. Still, Namibia attracts ], [ 18 DOI: 27 ], [ arXiv:1311.1841 at 3.5 mm Wavelength ∗ DOI: 10.3847/0004-637X/824/1/40 ], [ 5 (2013) id.244003 [ arXiv:1512.07509 ]. arXiv:astro.ph/9912263 30/24 ]. ] but the bid was unsuccessful [ 26 [ Viewing the Shadow of the Black Hole at the Galactic Center (2016) A37 [ 17 ]. The University of Namibia and Radboud University recently 28 587 Toward the event horizon—the supermassive black hole in the Galactic (2000) L13 [ arXiv:1601.06571 528/1 ]. The Intrinsic Shape of Sagittarius A (2016) 40 [ 824 Classical and Quantum Gravity , Journal 10.1086/312423 10.1088/0264-9381/30/24/244003 the Galactic center: Near-infrared triggered observationsAstronomy of and the Astrophysics radio source Sgr A 10.1051/0004-6361/201527286 E. Castillo, A.A.Chael, A. Hernandez-Gómez, D.H.G. Hughes, Narayanan, J. K. León-Tavares, Rosenfeld, R.-S. D. Lu, Sánchez, A.L. F.P. Montana, Schloerb, Vertatschitsch, Z.-Q. Shen,H. Shiokawa, J. SooHoo, and Center Astrophysical Journal http://geodesy.hartrao.ac.za https://www.cta-observatory.org In the near future, a geodetic observing station will be installed on Mt. Gamsberg in collabora- The initial estimate of the capital investment needed to build the AMT, including the antenna, It is anticipated that the AMT will be fully operational within two years after funding and This work is supported by the ERC Synergy Grant “BlackHoleCam: Imaging the Event Hori- 18 17 [3] C. Rauch, E.Ros, T.P. Krichbaum, A. Eckart, J.A. Zensus, B. Shahzamanian, and K. Munži [4] G.N. Ortiz-León, M.D. Johnson, S.S. Doeleman, L. Blackburn, V.L. Fish, L. Loinard, M.J. Reid, [2] H. Falcke and S.B. Markoff, [1] H. Falcke, F. Melia, and E. Agol, tion with the Hartebeesthoek Radio Astronomy Observatory (HartRAO) various cm- and mm-wave receivers, VLBI equipment,lion infrastructure Euros. and Since software governmental is funding about schemes 10to at mil- this the level project, would introduce a aand/or fund-raising significant philanthropists, latency campaign is seeking underway. alternative sources of funding, e.g.permits are foundations secured. Acknowledgements zon of Black Holes” (Grant 610058). 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