PoS(HEASA2015)001 http://pos.sissa.it/ ∗ [email protected] Speaker. The Cherenkov Telescope Arrayergy (VHE) (CTA) gamma-ray is astronomy. Being the successor to nextin the vastly , generation successful MAGIC instruments on instrument H.E.S.S. the Canary for Islandpected of very to La outperform high Palma, the and former en- VERITAS in byenergy Arizona, a range. USA, factor it of To is 10, achieve ex- both thesethus in goals, sensitivity a the as world-wide best well possible site as operational investigation incessfully conditions the campaign hosting must accessible was the be launched. H.E.S.S. met telescopes and BasedNamibia. since on 2002, Thorough the proposals investigations experience of were of the submittedto suc- atmospheric to estimate and host the climatic CTA average in conditions annualmeans were observation of carried time. Monte out Carlo simulations, The taking scientificaccount. both performance Eventually, the was the altitude estimated proposed and by site thein in local the Namibia geomagnetic world was field to singled into host outnegotiations the as with the CTA the and scientifically Republic in best of Namibia April site being and 2014, patron with to the the the decision European competitor was Southern sitestatus Observatory taken in will (ESO), . to be engage Details presented. of into the official bidding process as well as the current ∗ 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). 3rd Annual Conference on High Energy18-20 June in 2015 Southern Africa -HEASA2015, University of Johannesburg, Auckland Park, M. Backes Current Status of the Namibian bidCherenkov Telescope to Array host the University of Namibia, Department of Physics,E-mail: Private Bag 13301, Windhoek, Namibia PoS(HEASA2015)001 ], 7 M. Backes x [m] indicates the 1000 1 500 ] and 15 medium-sized 2 0 . The baseline array for the 2 500 − 1000 . − ]. 2 6 0

500 500 y [m] y 1000 − 1000 − 2 10 GeV) gamma-ray regime of the electromagnetic ], cf. Fig. ] is the next-generation imaging atmospheric Cherenkov > 1 10 and consists of 4 LSTs, 25 MSTs, and 70 small-sized x [m] 2 ]. 400 ], spread on an area of 1 km 32 3 ]. Additionally, several medium-sized Schwarzschild-Couder ] shall complement the Southern array. Figure 4 5 200 ] or [ 1 ] by a factor of 10 in sensitivity and an increased energy coverage 9 0 200 − 400 − ], and VERITAS [ 8 Reference layouts for the Northern (on the left) and Southern (on the right) CTA sites. Note the 0

200 400 400 200 y [m] y − − As CTA will be the world leading facility in VHE gamma-ray astronomy for an estimated life- The scientific contributions to construction and operations of CTA will come from the Particularly with the Southern array, CTA aims to outperform its predecessors H.E.S.S. [ The Cherenkov Telescope Array (CTA) [ time of several decades, the decisionas on the the quality where of to a placelifetime. the chosen two site arrays will is affect of the utmost data importance quality and sensitivity of CTA during its entire MAGIC [ 2. The CTA Site Search CTA Consortium, which is formedcountries can by be more obtained from than [ 1,200 scientists in 31 countries. A full list or Figure 1: difference in scales of the axes betweenmid-sized North telescopes; and green South. markers: Red small-sized circles: telescopes large-sized [ telescopes; black markers: from a few tens of GeV to beyond 100 TeV [ Southern hemisphere spreads over 10telescopes km (SSTs) of 6 m-diameter [ planed baseline layouts for the Northern and Southern site, respectively. telescope (IACT) system that is in processsist of of being two designed for separate being array, builtIACTs one operate as in of in the 2017. the very It high Northern energy will (VHE; and con- one in the Southern hemisphere, respectively. (SC) telescopes of 9.5 m-diameter [ Status of the Namibian bid to host the CTA 1. Introduction spectrum during clear and mostlyto moonless be nights. comprised of Thetelescopes 4 Northern (MSTs) hemisphere large-sized of array telescopes 12 m-diameter is (LSTs) [ supposed of 23 m-diameter [ PoS(HEASA2015)001 above h M. Backes North and ◦ 70% cloud free > , 3) were found. 2 3 3 km 500 m a.s.l., maximal slope of , 1 × ≥ h ]. 11 3 -ray source of the Northern and Southern CTA arrays (for γ 000 m a.s.l., 2) a flat area of 3 ]. , 4 12 ≤ the one at the current IACT sites, 6) latitude around 30 h × ≤ 5 . 1 < ]. By these criteria, the regions highlighted in Fig. 12 500 m a.s.l. , World map, showing (in green) areas fulfilling the criteria Differential sensitivity for a point-like In 2009, the initial requirements on the sites for the CTA were defined to be: 1) height nights, 4) good atmospheric conditionsspeed, in 5) terms light of pollution high transparency, lowSouth, respectively humidity, [ modest wind Figure 3: Figure 2: 50 h of observations) compared to current generation instruments [ 2.1 Initial Criteria and Call for Proposals , with 1 50 m on 1 km, and low light pollution [ Status of the Namibian bid to host the CTA PoS(HEASA2015)001 M. Backes . Against this 500 m a.s.l., flat 4 , 3 ≤ ]. Emphasizing the h 14 ≤ ]. Crime rates, especially 18 ]. 500 m a.s.l. ]. , 19 13 ]. ] in the Sutherland region in South Africa 17 16 4 ]. Among the investigated sites were a site close to 15 , low light pollution, and sufficiently low cloudiness [ 2 ]. 13 World map, showing (in green) areas fulfilling the criteria 1 Concerning socio-political risks in Namibia, one has to note that since independence in 1990, Following the call for proposals, two proposals were submitted from Southern Africa. The A refined analysis, limiting the maximum hight to 3,500 m a.s.l. and including information on in rural areas of Namibia arefor very Namiba, low, which as are indicated comparable by to the those 2013 of Numbeo the crime Netherlands and [ safety indexes long-known astronomical quality of the Gamsberg region, thisand proposal infrastructure focused as on well the as accessibility the politicalthe support North-West toward University the at project. Potchefstroom submitted At a the proposal, sameand investigating time, in-depth weather a cloudiness conditions group as from well asstability geographical of contours, and several geological, sites political, in and Southern economical Africa [ as well as sites inyears the of Kuibis region, investigations, Karas, updated Namibia,Namibian proposals including group, were a supported requested site by on and South theHESS a African farm and comprehensive scientists Aar. Aar proposal sites, was After by their submitted, two respectiveaccessing the focusing cloudiness, infrastructural on weather, conditions, both and construction geo-technical the conditions, and Aar risks, as operation and well local, costs, as national natural and as regional political well support as [ political Namibia runs a stable democracyalso without corroborated any conflicts by and the with “B1” free risk elections grade ever assigned since. by This Euler-Hermes is [ the South African Astronomical Observatory (SAAO) [ group at the University ofH.E.S.S. Namibia telescopes proposed in to the Khomas host Highland the region, CTA close close to to Mt. the Gamsberg [ well-known site of the Figure 4: area of 10 km 3. Southern African Proposals and the site Aar in Namibia the cloudiness narrowed down the possible regions to the ones highlighted in Fig. Status of the Namibian bid to host the CTA background, a call for proposalsthe was CTA [ issued, for CTA members to propose potential sites to host PoS(HEASA2015)001 ± 4 . 64 %, and ( ) 7 M. Backes . 0 ± % and 3 ) ]. . 0 . 15 13 1 ( ± 5 . 46 ( 5 1,800 m a.s.l. (black). The panel on the left, shows the ≥ ], the potential sites in the Kuibis region, Karas, Namibia, lie in the 15 1,500 m a.s.l. (white) – 1 km length that can be used by up to twin-engine small aircrafts. Furthermore, ≤ . 1 . . 5 × 6 % of clear night time, this region significantly outperforms the site of the South African ) 4 km Southern African regional average night-time cloud cover contours. The gray-scale overlay in- 7 . . 0 ± In addition, Southern Namibia is one of the darkest regions of the sub-continent, as can be Though the Kuibis region appears to be very remote, the region as well as the Aar site in As pointed out in [ 0 % of clear night time, respectively. The contour map of regional night-time cloud cover is . ) 4 . 73 seen from Fig. region of central and Southern Namibia enlarged, including the H.E.S.S. and Aar sites [ particular, have very good accessibility,about both 120 km for West personnel of andweek the for from Aar cargo: and site The to offersdriving Lüderitz a Windhoek. the airport, 1.8 km national By long tar car,cross tarred roads the of landing B1 1 Aar strip and site and B4. can four be flights The reached per close-by within (23 km) 7 h town Aus from offers Windhoek, a dirt airstrip Figure 5: dicates elevations of the Aus railway stationconnected offers to a the Lüderitz container harbor, the handling secondto facility, largest 150 harbor m whereas in length the Namibia, and capable handling railway of containers line hosting up ships is to up 40 directly ft and 36 t. Astronomical Observatory and even the current H.E.S.S. site, offering least cloudy part of the subcontinent: with an average cloud cover of only Status of the Namibian bid to host the CTA 3.1 Site Aar ( 1 depicted in Fig. PoS(HEASA2015)001 ]. M. Backes 21 ], the Aar site was singled out 15 6 Night-lights image of Southern Namibia. The coastal town Lüderitz as well Bottom: ]. 20 Artificial night sky brightness for Southern Africa in astronomical V band, at zenith, for a Top: In comparison to the other proposed sites in the Kuibis region [ Figure 6: as the regional capital Keetmanshoop cancentral easily in be identified. the picture Lights are from bare the town seen Aus and at the the Aar road site, crossing indicated by a red circle is completely dark [ clean atmosphere [ as being close to all needed infrastructure,away and from thus the must cost-effective: national The tar siteline road is as only B4, well about as and 4 of km the the national closesta optical 33 substation fiber kV feeder backbone of and is the an only optical national 20town fiber km power Aus connection to grid could is West-North-West, from easily 132 also where be kV only established. 23 Furthermore, km the away. railway Status of the Namibian bid to host the CTA PoS(HEASA2015)001 . 7 M. Backes ]. These numbers 25 ], atmospheric model- 70 GeV), see the bottom 22 < 7 ], where available, archival data measured by ground 23 ], except for the lowest energies ( ]. The ATMOSCOPE comprises a weather station, a cloud 26 24 ], testifying to the low cloudiness of the Namibian and Chilean sites, . Altogether, the site Aar in Namibia and the Armazones sites in Chile 9 23 ]. 25 . 8 The average annual observation time (AAOT) with less than 20% cloud cover, corrected for Monte Carlo simulations indicated that high altitude (3,700 m a.s.l.) sites are disfavored against In order to assess the submitted site proposals, the CTA Consortium investigated twofold the For estimating the AAOT, the atmospheric site characteristics were investigated: remote sens- left panel of Fig. lower altitude (2,000 m a.s.l.) sites [ Figure 7: losses due to high wind speedNorthern and sites high in green optical [ density. The Southern sites are indicated in blue, the ing was used to estimate long-term trends [ sensor a light of the nightera. sky (LoNS) The monitor thorough a analysis Unihedron of Sky allcloud Quality collected Meter coverage ATMOSCOPE and data of an essentially all-sky e.g. supported cam- [ the simulated offer the highest AAOT of morealready than account 1,200 h for with losses low due cloudiness to conditions high [ wind speeds and high aerosol optical density, see Fig. see the left panel of Fig. stations was analyzed and a dedicatedfor instrument, more the ATMOSCOPE, than was developed a and year operated at each site [ scientific quality of the proposed sites: Onwas the estimated one and hand on the the average annual other observation hand, timethe immense (AAOT) Monte performance Carlo per simulations unit were conducted time to (PPUT). estimate ing data of the MODIS, METEOSAT, and GOES satellites were analyzed [ Status of the Namibian bid to host the CTA 4. Site Investigations and Ranking by the CTA Consortium PoS(HEASA2015)001 (4.1) . The 2 10 sens M. Backes F D (3700 m, 50 h) D (3700 m, 50 D (2000 m, 50 h) I (3700 m, 50 h) I (2000 m, 50 h) ]. The lower left panel 26 100% Crab 100% Crab 1 10 10% Crab 10% Crab 1% Crab 1% Crab 0.1% Crab 0.1% Crab , zenith angle [ N ◦ / 1 ! and the achieved flux sensitivity sens 2 −2 −1 F sens, ref 10 10 10 8 F ]. The PPUT is calculated as the inverse geometric Energy [ TeV ] 6 sens, ref N ∏ F

= E (3700 m, 50 h) E (2000 m, 50 h) B (3700 m, 50 h) B (3700 m, 50 B (2000 m, 50 h) PPUT 100% Crab 100% Crab 1 10 10% Crab 10% Crab 1% Crab 1% Crab 0.1% Crab 0.1% Crab −1 shows the altitude dependence of the PPUT for Northern and Southern pointing ]. 9 27 Prod−1 DESY analysis Preliminary −2 10 10 −11 −11 −10 −12 −13 −14 −10 −12 −13 −14 10 10 10 10 10 10 10 10 10 10 Differential sensitivity for different layout candidates for CTA at 2,000 m a.s.l. (red, solid line)

bins in energy (from 30 GeV to 300 TeV for CTA South, and to 20 TeV for CTA North,

x Flux Sensitivity [ erg cm erg [ Sensitivity Flux x E s ]

−2 −1 2 N Together with the high AAOT, these results single out site Aar as the scientifically best possible Additional Monte Carlo studies concerning the PPUT of the different sites, taking into account Based on these findings, the CTA Consortium ranked the Aar site in Namibia the best site with respectively) of the reference flux sensitivity right panel of Fig. directions at the different sites,compared which to clearly all demonstrates other the potential superior CTA sites sensitivity in at the the Southern site hemisphere. Aar site to host the CTA. both, the different altitudes asperior well performance as of the the differences site in Aar in the Namibia geo-magnetig [ field underlined the su- regarding scientific potential, whereas the Armazones siteranked in second Chile [ and the H.E.S.S. site in Namibia Figure 8: and 3,700 m a.s.l. (black, dashedcorresponds line) to for the 50 CTA h South of reference observations layout at mentioned 20 in the text. mean of the differential sensitivity, normalized by a reference sensitivity in each energy band: Status of the Namibian bid to host the CTA PoS(HEASA2015)001 ]. ], 29 30 M. Backes 4000 ) as function 4.1 ]. 3500 ], see also [ 6 altitude [m] 28 SAC Leoncito Leoncito++ Armazones Aar Aar@500m 3000 2500 ], Hon. Mrs. G.M.N. Pandor, 2000 31 1500 1000 500 2

2.8 2.6 2.4 2.2 1.8 1.6 PPUT 9 Performance per unit time (PPUT, see Eq. Right: ]. 23 Simulated cloud cover distributions for Southern hemisphere sites. An estimation of each . Left: 10 both countries reaffirm their commitment towardsAstronomy strengthening and cooperation Space in Science; the fields of South Africa reaffirms its political, scientificthe and CTA; technical support for Namibia’s bid to host both countries commit themselves to enhancing thecompetitive capacity scientific for and developing a technical globally communityand in Space support Science in of Southern multi-wavelength Africa. Astronomy Particularly in the context of CTA, SKA, and AVN, a joint bilateral ministerial meeting be- The governing body of CTA, the CTA Resource Board, decided on April 10, 2014 to start nego- • • • tween Namibia and South AfricaAugust 12, on 2014 in Cooperation Windhoek, in Namibia. Astronomy In the and common statement Space [ Science was held on After a year of further investigations, thenegotiations CTA with Resource Board two decided countries on about March the 25, NorthernMexico 2015 hemisphere (San to sites, Pedro begin namely Mártir), Spain (La keeping Palma)see the and Fig. United States of America (Arizona) as back-up site [ 6. Recent Political Developments in Namibia Minister of Science and Technology ofMinister the of Republic Education of of South the Africa, Republic and of Hon. Namibia, Dr. communicate D. amongst Namwandi, others that tiations on the two sites inern the Observatory Southern hemisphere, (ESO) namely in Aar Chile, in Namibia keeping and Argentina European as South- possible back-up site [ value is provided everyof 3 hours altitude [ for the Southernpointing hemisphere in candidate Southern direction, sites. green-colored Red-colored markers for markers pointing indicate in results Northern for direction the [ 5. array Decisions by the CTA Resource Board Figure 9: Status of the Namibian bid to host the CTA PoS(HEASA2015)001 ], see 32 M. Backes ]. 30 10 The sites selected by the CTA Resource Board as of March 2015 [ Figure 10: ]. 33 After the conclusion of this conference, on July 16, 2015, the CTA Resource Board took the de- Altogether, the proposed Namibian site, Aar, shows world-leading scientific potential as South- Meanwhile, the Cabinet of the Republic of Namibia officially approved support for Namibia to also [ cision to enter into detailed contractin negotiations Chile for and hosting at the the CTA on Institutiotory the de in ESO Astrofisica La Paranal de Palma, grounds Spain. Canarias (IAC), The Roque Namibian de and los Mexican Muchachos sites Observa- are kept as viable alternatives [ 8. Post-Conference Developments ern site of the CTA.makes This, it together appear not with unlikely the thatCTA demonstrated Consortium, the national and CTA Resource select and Board Aar regional will as political follow Southern the site support recommendation for by the the CTA. 7. Conclusion host the CTA. This includes sufficientto funds for the power, edge data of transfer, water thethe and proposed CTA road by site infrastructure the within National Namibia,more, Commission as in-kind on well contributions Research, as concerning Science the customapproved. and purchase duties, It Technology of import was (NCRST). also the levies, Further- decided land andrelated that for VAT activities concessions the in hosting NCRST were Namibia shall as assume well the as leading leading the role negotiations in with coordinating the CTA CTA Resource Board. Status of the Namibian bid to host the CTA PoS(HEASA2015)001 . In: DOI: M. Backes . In: . In: . In: Proceedings of . In: CTA internal ]. ]. ]. ]. ]. . In: CTA internal note (2011). http://www.saao.ac.za ]. arXiv:1508.06042 http://www.mpi-hd.mpg.de/hfm/HESS arXiv:1508.06075 arXiv:1509.01361 arXiv:1508.06472 . In: CTA internal note (2011). http://www.cta-observatory.org . In: Astroparticle Physics 43 (2013) 3–18. [ 11 . In: Proceedings of Science PoS(ICRC2015)1029: arXiv:1508.06438 DOI: 10.7529/ICRC2011/V09/1257 ]. . In: Proceedings of the 32nd International Southern Africa CTA Site Proposal ]. Namibian Site Proposal Status of the Medium-Sized Telescope for the Cherenkov Telescope Array , Site Search for the Cherenkov Telescope Array (CTA) based on satellite data Introducing the CTA concept The small size telescope projects for the Cherenkov Telescope Array , , , ]. Candidate Sites for the Cherenkov Telescope Array in Namibia A Medium Sized Schwarzschild-Couder Cherenkov Telescope Mechanical Design et al. Second large-scale Monte Carlo study for the Cherenkov Telescope Array Status of the Cherenkov Telescope Array’s Large Size Telescopes , Monte Carlo Performance Studies of Candidate Sites for the Cherenkov Telescope , , , The CTA site search , arXiv:1509.03074 et al. et al. , et al. et al. et al. et al. et al. et al. et al. . 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Enke, [23] K. Louedec and M. Will, Status of the Namibian bid to host the CTA [18] A. Atkinson and Euler Hermes Economic Research Team, [24] C. Fruck [19] Numbeo, [20] P. Cinzano