M. Pech

Status of the technologies for the production of the Cherenkov telescope array (CTA) mirrors

The Cherenkov Telescope Array (CTA) is the next generation very high-energy gamma-ray observatory, with at least 10 times higher sensitivity than current instruments. CTA will comprise several tens of Imaging Atmospheric Cherenkov Telescopes (IACTs) operated in array-mode and divided into three size classes: large, medium and small telescopes. The total reflective surface could be up to 10,000 m2 requiring unprecedented technological efforts. The properties of the reflector directly influence the telescope performance and thus constitute a fundamental ingredient to improve and maintain the sensitivity. The R&D status of lightweight, reliable and cost-effective mirror facets for the CTA telescope reflectors for the different classes of telescopes is reviewed in this paper.

Prototype of the SST-1M Telescope Structure for the Cherenkov Telescope Array

A single-mirror small-size (SST-1M) Davies-Cotton telescope with a dish diameter of 4 m has been built by a consortium of Polish and Swiss institutions as a prototype for one of the proposed small-size telescopes for the southern observatory of the Cherenkov Telescope Array (CTA). The design represents a very simple, reliable, and cheap solution. The mechanical structure prototype with its drive system is now being tested at the Institute of Nuclear Physics PAS in Krakow. Here we present the design of the prototype and results of the performance tests of the structure and the drive and control system.

Using muon rings for the optical throughput calibration of the SST-1M prototype for the Cherenkov Telescope Array

S. Toscano∗ a,n, E. Prandinia E-mail: simona.toscano@vub.ac.be W. Bilnikk, J. Blockic, L. .Bogaczm, T .Bulikd , F. Cadouxb, A. Christovb, M. Curyloc, D. della Volpeb, M. Dyrdac, Y. Favreb, A. Frankowskig, Ł. Grudnikic, M. Grudzinskad , M. Hellerb, B. Idźkowskie, M. Jamrozye, M. Janiakg, J. Kasperekk, K. Lalikk, E. Lyarda, E. Machc, D. Mandatl , A. Marszalekc,e, J. Michalowskic, R. Moderskig, T. Montarulib, A. Neronova, J. Niemiecc, M. Ostrowskie, P. Paśko f , M. Pechl , A. Porcellib, P. Rajdak, M. Rameezb, E. Jr. Schioppab, P. Schovanekl , K. Seweryn f , K. Skowronc, V. Sliusar j, M. Sowinskic, Ł. Stawarze, M. Stodulskae, M. Stodulskic, I. Troyano Pujadasb, R. Waltera, M. Wiȩcekk, A. Zagdanskie, K. Ziȩtarae, P. Żychowskic for the CTA Consortium† a. ISDC, Observatoire de Geneve, Universite de Geneve, 1290 Versoix, Switzerland. b. Department de physique nucleaire et corpusculaire, Universite de Geneve, CH-1205 Switzerland. c. Instytut Fizyki Jadrowej im. H. Niewodniczanskiego Polskiej Akademii Nauk, 31-342 Krakow, Poland. d. Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland e. Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244, Krakow, Poland. f. Centrum Badan Kosmicznych Polskiej Akademii Nauk, 18a Bartycka str., 00-716 Warsaw, Poland. g. Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw, Poland. j. Astronomical Observatory, Taras Shevchenko Nat. University of Kyiv, Observatorna str., 3, Kyiv, Ukraine. k. AGH University of Science and Technology, al.Mickiewicza 30, Krakow, Poland, l. Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic. m. Department of Information Technologies, Jagiellonian University, 30-348 Krakow, Poland. n. Vrije Universiteit Brussels, Pleinlaan 2 1050 Brussels, Belgium.

Development of an optical system for the SST-1M telescope of the Cherenkov Telescope Array observatory

The prototype of a Davies-Cotton small size telescope (SST-1M) has been designed and developed by a consortium of Polish and Swiss institutions and proposed for the Cherenkov Telescope Array (CTA) observatory. The main purpose of the optical system is to focus the Cherenkov light emitted by extensive air showers in the atmosphere onto the focal plane detectors. The main component of the system is a dish consisting of 18 hexagonal mirrors with a total effective collection area of 6.47 m 2 (including the shadowing and estimated mirror reflectivity). Such a solution was chosen taking into account the analysis of the Cherenkov light propagation and based on optical simulations. The proper curvature and stability of the dish is ensured by the mirror alignment system and the isostatic interface to the telescope structure. Here we present the design of the optical subsystem together with the performance measurements of its components.

Development of a strategy for calibrating the novel SiPM camera of the SST-1M telescope proposed for the Cherenkov Telescope Array

CTA will comprise a sub-array of up to 70 small size telescopes (SSTs) at the southern array. The SST-1M project, a 4 m-diameter Davies Cotton telescope with 9 degrees FoV and a 1296 pixels SiPM camera, is designed to meet the requirements of the next generation ground based gammaray observatory CTA in the energy range above 3 TeV. Silicon photomultipliers (SiPM) cameras of gamma-ray telescopes can achieve good performance even during high night sky background conditions. Defining a fully automated calibration strategy of SiPM cameras is of great importance for large scale production validation and online calibration. The SST-1M sub-consortium developed a software compatible with CTA pipeline software (CTApipe). The calibration of the SST-1M camera is based on the Camera Test Setup (CTS), a set of LED boards mounted in front of the camera. The CTS LEDs are operated in pulsed or continuous mode to emulate signal and night sky background respectively. Continuous and pulsed light data analysis allows us to extract single pixel calibration parameters to be used during CTA operation.

Performance of the SST-1M telescope of the Cherenkov Telescope Array observatory

R. Moderskic,W. Bilnikk, J. Blockig, L. Bogacze, T. Bulikd , F. Cadouxa, A. Christova, M. Chruślinskad , M. Curylog, D. della Volpea, M. Dyrdag, Y. Favrea, A. Frankowskic, Ł. Grudnikg, M. Grudzinskad , M. Hellera, B. Idźkowskib, M. Jamrozyb, M. Janiakc, J. Kasperekk, K. Lalikk, E. Lyard f , E. Machg, D. Mandatm, A. Marszalekh,b, J. Michalowskig, T. Montarulia, A. Neronov f , J. Niemiecg, M. Ostrowskib, P. Paśkoh, M. Pechm, A. Porcelli∗a, E. Prandini f , E. Puescheln, P. Rajdak, M. Rameeza, P. Rozwadowskid , E. jr Schioppaa, P. Schovanekm, K. Sewerynh, K. Skowrong, V. Sliusari, M. Sowinskig, Ł. Stawarzb, M. Stodulskab, M. Stodulskig, S. Toscano f ,l, I. Troyano Pujadasa, R. Walter f , M. Wiȩcekk, A. Zagdanskib, K. Ziȩtarab, P. Żychowskig for the CTA Consortium† aDPNC – Universite de Geneve, Geneve, Switzerland bAstronomical Observatory, Jagiellonian University, Krakow, Poland cNicolaus Copernicus Astronomical Centre, Polish Academy of Sciences, Warsaw, Poland dAstronomical Observatory, University of Warsaw, Warsaw,Poland eDepartment of Information Technologies, Jagiellonian University, Krakow, Poland f ISDC, Observatoire de Geneve, Universite de Geneve, Versoix, Switzerland gInstytut Fizyki Jadrowej im. H. Niewodniczanskiego Polskiej Akademii Nauk, Krakow, Poland hCentrum Badan Kosmicznych Polskiej Akademii Nauk, Warsaw, Poland iAstronomical Observatory, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine kAGH University of Science and Technology, Krakow, Poland lVrije Universiteit Brussels, Brussels, Belgium mInstitute of Physics of the Czech Academy of Sciences, Prague, Czech Republic nUniversity College Dublin, Ireland

Front-end and slow control electronics for large area SiPMs used for the single mirror Small Size Telescope (SST-1M) of the Cherenkov Telescope Array (CTA)

The single mirror Small Size Telescope (SST-1M) project proposes a design among others for the smallest type of telescopes (SST), that will compose the south observatory of the Cherenkov Telescope Array (CTA). The SST camera collecting the Cherenkov light resulting from very high energy gamma-ray interactions in the atmosphere proposes to use Silicon PhotoMultipliers (SiPM). The SST-1M design has led to the use of unique pixel shape and size that required a dedicated development by the University of Geneva and Hamamatsu. An active surface of ~94 mm2 and a resulting total capacitance of ~3.4 nF combined with the stringent requirements of the CTA project on timing and charge resolution have led the University of Geneva to develop a custom preamplifier stage and slow-control system. The design and performance of the tailor made preamplifier stage and of the slow control electronics will be briefly described. The bias circuit of the sensor contains a resistor meant to prevent the sensor from drawing high current. However this resistor also introduces a voltage drop at the sensor input impacting the stability of its operation. A model has been developed in order to derive the parameters needed to account for it at the data analysis level. A solution based on the SST-1M front-end and digital readout is proposed to compensate for the voltage drop at the sensor cathode.

Aspherical mirrors for the Gamma-ray Cherenkov Telescope, a Schwarschild-Couder prototype proposed for the future Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) project, led by an international collaboration of institutes, aims to create the worlds largest next generation Very High-Energy (VHE) gamma-ray telescope array, devoted to observations in a wide band of energy, from a few tens of GeV to more than 100 TeV. The Small-Sized Telescopes (SSTs) are dedicated to the highest energy range. Seventy SSTs are planned in the baseline array design with a required lifetime of about 30 years. The GCT (Gamma-ray Cherenkov Telescope) is one of the prototypes proposed for CTAs SST sub-array. It is based on a Schwarzschild-Couder dual-mirror optical design. This configuration has the benefit of increasing the field-of-view and decreasing the masses of the telescope and of the camera. But, in spite of these many advantages, it was never implemented before in ground-based Cherenkov astronomy because of the aspherical and highly curved shape required for the mirrors. The optical design of the GCT consists of a primary 4 meter diameter mirror, segmented in six aspherical petals, a secondary monolithic 2-meter mirror and a light camera. The reduced number of segments simplifies the alignment of the telescope but complicates the shape of the petals. This, combined with the strong curvature of the secondary mirror, strongly constrains the manufacturing process. The Observatoire de Paris implemented metallic lightweight mirrors for the primary and the secondary mirrors of GCT. This choice was made possible because of the relaxed requirements of optical Cherenkov telescopes compared to optical ones. Measurements on produced mirrors show that these ones can fulfill requirements in shape, PSF and reflectivity, with a clear competition between manufacturing cost and final performance. This paper describes the design of these mirrors in the context of their characteristics and how design optimization was used to produce a lightweight design. The manufacturing process used for the prototype and planned for the large scale production is presented as well as the performance, in terms of geometric and optical properties, of the produced mirrors. The alignment procedure of the mirrors is also detailed. This technique is finally compared to other manufacturing techniques based on composite glass mirrors within the framework of GCT mirrors specificities.

Status of the technologies for the production of the Cherenkov Telescope Array (CTA) mirrors

The Cherenkov Telescope Array (CTA) is the next generation very high-energy gamma-ray observatory, with at least 10 times higher sensitivity than current instruments. CTA will comprise several tens of Imaging Atmospheric Cherenkov Telescopes (IACTs) operated in array-mode and divided into three size classes: large, medium and small telescopes. The total reflective surface could be up to 10,000 m2 requiring unprecedented technological efforts. The properties of the reflector directly influence the telescope performance and thus constitute a fundamental ingredient to improve and maintain the sensitivity. The R&D status of lightweight, reliable and cost-effective mirror facets for the CTA telescope reflectors for the different classes of telescopes is reviewed in this paper.