The Cherenkov Telescope Array Observatory (CTAO) will include telescopes of three different sizes, the smallest of which are the Small-Sized Telescopes (SSTs). In particular, the SSTs will be installed at the southern site of CTAO, on the Chilean Andes, and will cover the highest energy range of CTAO (up to ~300 TeV). The SSTs are developed by an international consortium of institutes that will provide them as an in-kind contribution to CTAO. The optical design of the SSTs is based on a Schwarzschild-Couder-like dual-mirror polynomial configuration, with a primary aperture of 4.3m diameter. They are equipped with a focal plane camera based on SiPM detectors covering a field of view of ~9°. The preliminary design of the SST telescopes was evaluated and approved during the Product Review (PR) organised with CTAO in February 2023. The SST project is now going through a consolidation phase leading to the finalisation and submission of the final design to the Critical Design Review (CDR), expected to occur late 2024, after which the production and construction of the telescopes will begin leading to a delivery of the telescopes to CTAO southern site starting at the end of 2025-early 2026 onward. In this contribution we will present the progress of the SST programme, including the results of the PDR, the consolidation phase of the project and the plan up to the on-site integration of the telescopes.
The prototype of Gamma-ray Cherenkov Telescope (pGCT) is an Imaging Atmospheric Cherenkov Telescope (IACT) developed to detect Very High Energy (VHE) from various cosmic sources emitting gamma rays. It is based on a Schwarzschild-Couder (SC) dual-mirror configuration resulting in a compact telescope and an optimised PSF over a wide field of view. Moreover, some innovative features were implemented with the aim to ease and to fasten the assembly, integration, test (AIT) and maintenance activities. Both mirrors, the 4-meter tessellated primary mirror and the secondary mirror, are aspherical lightweight mirrors made by a subtractive manufacturing method. This process was improved several times leading to enhanced optical performance of the telescope in terms of Point Spread Function and improved signal to noise ratio. This paper deals with the optomechanical design of the pGCT and its latest measured performance. After a brief overview of the mechanical design of the telescope, the updated manufacturing process of the new generation mirrors and the optical performance of pGCT are given. Finally, recent operational performance of the telescope is given.
MOSAIC is the Multi-Object Spectrograph (MOS) for the 39m Extremely Large Telescope (ELT) of the European Southern Observatory (ESO), with unique capabilities in terms of multiplex, wavelength coverage and spectral resolution. It is a versatile multi-object spectrograph working in both the Visible and NIR domains, designed to cover the largest possible area (∼40 arcmin2) on the focal plane, and optimized to achieve the best possible signal-to-noise ratio on the faintest sources, from stars in our Galaxy to galaxies at the epoch of the reionization. In this paper we describe the main characteristics of the instrument, including its expected performance in the different observing modes. The status of the project will be briefly presented, together with the positioning of the instrument in the landscape of the ELT instrumentation. We also review the main expected scientific contributions of MOSAIC, focusing on the synergies between this instrument and other major ground-based and space facilities.
The Small Sized Telescope (SST) is one of the three types of telescopes that will constitute the Cherenkov Telescope Array (CTA). For the CTA Southern site, 37 SST will be realized for the first alpha CTA configuration. Their design is based on the ASTRI-Horn dual-mirror telescope. Some modifications of the design are currently under study searching for possible improvements of the behaviour of the telescope. Amongst them, there are studies on the primary mirror dish (M1 Dish) led by a team of the Observatoire de Paris. The main purpose of these studies is to optimize the mass stiffness ratio of this structure. It means reducing its total mass while keeping its performance, mainly its stiffness, and taking into account existing constraints related to dependent fixed subsystems (counterweight, secondary mirror...) or environment (gravity, wind). This problem can be described as a classical optimization problem in the way it aims at finding an optimal mass distribution by minimizing the compliance with a constraint of mass reduction and under given boundary conditions. This methodology, previously used by the Observatoire de Paris for the design of lightweight mirrors and of components of another Cherenkov telescope, is applied to propose an alternative option to the ASTRI-Horn baseline design of the M1 Dish. Its lays on the use of structural optimization tools, which can help to get more quickly an accurate mass distribution and to improve the design process by reducing the number of iterations between phases of design definition under computer-aided design (CAD) and phases of design validation under finite-element analysis. This methodology and the corresponding results are presented in this paper.
The Cherenkov Telescope Array Observatory (CTAO) consists of three types of telescopes: large-sized (LST), mediumsized (MST), and small-sized (SST), distributed in two observing sites (North and South). For the CTA South “Alpha Configuration” the construction and installation of 37 (+5) SST telescopes (a number that could increase up to 70 in future upgrades) are planned. The SSTs are developed by an international consortium of institutes that will provide them as an in-kind contribution to CTAO. The SSTs rely on a Schwarzschild-Couder-like dual-mirror polynomial optical design, with a primary mirror of 4 m diameter, and are equipped with a focal plane camera based on SiPM detectors covering a field of view of ~9°. The current SST concept was validated by developing the prototype dual-mirror ASTRI-Horn Cherenkov telescope and the CHEC-S SiPM focal plane camera. In this contribution, we will present an overview of the SST key technologies, the current status of the SST project, and the planned schedule.
Following a successful Phase A study, we introduce the delivered conceptual design of the MOSAIC1 multi-object spectrograph for the ESO Extremely Large Telescope (ELT). MOSAIC will provide R~5000 spectroscopy over the full 460-1800 nm range, with three additional high-resolution bands (R~15000) targeting features of particular interest. MOSAIC will combine three operational modes, enabling integrated-light observations of up to 200 sources on the sky (high-multiplex mode) or spectroscopy of 10 spatially-extended fields via deployable integral-field units: MOAO6 assisted high-definition (HDM) and Visible IFUs (VIFU). We will summarise key features of the sub-systems of the design, e.g. the smart tiled focal-plane for target selection and the multi-object adaptive optics used to correct for atmospheric turbulence, and present the next steps toward the construction phase.
Product Assurance is an essential activity to support the design and construction of complex instruments developed for major scientific programs. The international size of current consortia in astrophysics, the ambitious and challenging developments, make the product assurance issues very important. The objective of this paper is to focus in particular on the application of Product Assurance Activities to a project such as MOSAIC, within an international consortium. The paper will also give a general overview on main product assurance tasks to be implemented during the development from the design study to the validation of the manufacturing, assembly, integration and test (MAIT) process and the delivery of the instrument.
The Gamma-ray Cherenkov Telescope (GCT) is one of the telescopes proposed for the Small Sized Telescope (SST) section of CTA. Based on a dual-mirror Schwarzschild-Couder design, which allows for more compact telescopes and cameras than the usual single-mirror designs, it will be equipped with a Compact High-Energy Camera (CHEC) based on silicon photomultipliers (SiPM). In 2015, the GCT prototype was the first dual-mirror telescope constructed in the prospect of CTA to record Cherenkov light on the night sky. Further tests and observations have been performed since then. This report describes the current status of the GCT, the results of tests performed to demonstrate its compliance with CTA requirements, and the optimisation of the design for mass production. The GCT collaboration, including teams from Australia, France, Germany, Japan, the Netherlands and the United Kingdom, plans to install the first telescopes on site in Chile for 2019-2020 as part of the CTA pre-production phase.
When combined with the huge collecting area of the ELT, MOSAIC will be the most effective and flexible Multi-Object Spectrograph (MOS) facility in the world, having both a high multiplex and a multi-Integral Field Unit (Multi-IFU) capability. It will be the fastest way to spectroscopically follow-up the faintest sources, probing the reionisation epoch, as well as evaluating the evolution of the dwarf mass function over most of the age of the Universe. MOSAIC will be world-leading in generating an inventory of both the dark matter (from realistic rotation curves with MOAO fed NIR IFUs) and the cool to warm-hot gas phases in z=3.5 galactic haloes (with visible wavelenth IFUs). Galactic archaeology and the first massive black holes are additional targets for which MOSAIC will also be revolutionary. MOAO and accurate sky subtraction with fibres have now been demonstrated on sky, removing all low Technical Readiness Level (TRL) items from the instrument. A prompt implementation of MOSAIC is feasible, and indeed could increase the robustness and reduce risk on the ELT, since it does not require diffraction limited adaptive optics performance. Science programmes and survey strategies are currently being investigated by the Consortium, which is also hoping to welcome a few new partners in the next two years.
J. L. Dournaux, A. Abchiche, D. Allan, J. P. Amans, T. P. Armstrong, A. Balzer, D. Berge, C. Boisson, J.-J. Bousquet, A. Brown, M. Bryan, G. Buchholtz, P. Chadwick, H. Costantini, G. Cotter, L. Dangeon, M. Daniel, A. De Franco, F. De Frondat, D. Dumas, J. P. Ernenwein, G. Fasola, S. Funk, J. Gironnet, J. Graham, T. Greenshaw, B. Hameau, O. Hervet, N. Hidaka, J.A. Hinton, J.M. Huet, I. Jégouzo, T. Jogler, T. Kawashima, M. Kraush, J. Lapington, P. Laporte, J. Lefaucheur, S. Markoff, T. Melse, L. Mohrmann, P. Molyneux, S. Nolan, A. Okumura, J. Osborne, R. Parsons, S. Rosen, D. Ross, G. Rowell, C. Rulten, Y. Sato, F. Sayède, J. Schmoll, H. Schoorlemmer, M. Servillat, H. Sol, V. Stamatescu, M. Stephan, R. Stuik, J. Sykes, H. Tajima, J. Thornhill, L. Tibaldo, C. Trichard, J. Vink, J. Watson, R. White, N. Yamane, A. Zech, A. Zink
The GCT (Gamma-ray Cherenkov Telescope) is a dual-mirror prototype of Small-Sized-Telescopes proposed for the Cherenkov Telescope Array (CTA) and made by an Australian-Dutch-French-German-Indian-Japanese-UK-US consortium. The integration of this end-to-end telescope was achieved in 2015. On-site tests and measurements of the first Cherenkov images on the night sky began on November 2015. This contribution describes the telescope and plans for the pre-production and a large scale production within CTA.
A. Brown, A. Abchiche, D. Allan, J.-P. Amans, T. Armstrong, A. Balzer, D. Berge, C. Boisson, J.-J. Bousquet, M. Bryan, G. Buchholtz, P. Chadwick, H. Costantini, G. Cotter, M. Daniel, A. De Franco, F. de Frondat, J.-L. Dournaux, D. Dumas, G Fasola, S. Funk, J. Gironnet, J. Graham, T. Greenshaw, O. Hervet, N. Hidaka, J. Hinton, J.-M. Huet, I. Jégouzo, T. Jogler, M. Kraus, J. Lapington, P. Laporte, J. Lefaucheur, S. Markoff, T. Melse, L. Mohrmann, P. Molyneux, S. Nolan, A. Okumura, J. Osborne, R. Parsons, S. Rosen, D. Ross, G. Rowell, Y. Sato, F. Sayede, J. Schmoll, H. Schoorlemmer, M. Servillat, H. Sol, V. Stamatescu, M. Stephan, R. Stuik, J. Sykes, H. Tajima, J. Thornhill, L. Tibaldo, C. Trichard, J. Vink, J. Watson, R. White, N. Yamane, A. Zech, A. Zink, J. Zorn
The Gamma-ray Cherenkov Telescope (GCT) is proposed for the Small-Sized Telescope component of the Cherenkov Telescope Array (CTA). GCT's dual-mirror Schwarzschild-Couder (SC) optical system allows the use of a compact camera with small form-factor photosensors. The GCT camera is ~ 0:4 m in diameter and has 2048 pixels; each pixel has a ~ 0:2° angular size, resulting in a wide field-of-view. The design of the GCT camera is high performance at low cost, with the camera housing 32 front-end electronics modules providing full waveform information for all of the camera's 2048 pixels. The first GCT camera prototype, CHEC-M, was commissioned during 2015, culminating in the first Cherenkov images recorded by a SC telescope and the first light of a CTA prototype. In this contribution we give a detailed description of the GCT camera and present preliminary results from CHEC-M's commissioning.
The Cherenkov Telescope Array (CTA) is an international collaboration that aims to create the world's
largest (ever) Very High Energy gamma-ray telescope array, consisting of more than 100 telescopes
covering an area of several square kilometers to observe the electromagnetic showers generated by
incoming cosmic gamma-rays with very high energies (from a few tens of GeV up to over 100 TeV).
Observing such sources requires - amongst many other things - a large FoV (Field of View). In the
framework of CTA, SST-GATE (Small Size Telescope - GAmma-ray Telescope Elements) aims to
investigate and to build one of the two first CTA prototypes based on the Schwarzschild-Couder (SC)
optical design that delivers a FoV close to 10 degrees in diameter. To achieve the required
performance per unit cost, many improvements in mirror manufacturing and in other technologies are
required. We present in this paper the current status of our project. After a brief introduction of the
very high energy context, we present the opto-mechanical design, discuss the technological tradeoffs
and explain the electronics philosophy that will ensure the telescopes cost is minimised without
limiting its capabilities. We then describe the software nedeed to operate the telescope and conclude
by presenting the expected telescope performance and some management considerations.
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