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 Ultraviolet Transient Astronomy Satellite (ULTRASAT) is a space-borne near UV telescope with an unprecedented large field of view (200 deg2 ). The mission, led by the Weizmann Institute of Science and the Israel Space Agency in collaboration with DESY (Helmholtz association, Germany) and NASA (USA), is fully funded and expected to be launched to a geostationary transfer orbit in Q2/Q3 of 2025. With a grasp 300 times larger than GALEX, the most sensitive UV satellite to date, ULTRASAT will revolutionize our understanding of the hot transient universe, as well as of flaring galactic sources. We describe the mission payload, the optical design and the choice of materials allowing us to achieve a point spread function of ∼ 10 arcsec across the FoV, and the detector assembly. We detail the mitigation techniques implemented to suppress out-of-band flux and reduce stray light, detector properties including measured quantum efficiency of scout (prototype) detectors, and expected performance (limiting magnitude) for various objects.
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.
The Ultraviolet Transient Astronomical Satellite (ULTRASAT) is a scientific UV space telescope that will operate in geostationary orbit. The mission, targeted to launch in 2024, is led by the Weizmann Institute of Science (WIS) in Israel and the Israel Space Agency (ISA). Deutsches Elektronen Synchrotron (DESY) in Germany is tasked with the development of the UV-sensitive camera at the heart of the telescope. The camera's total sensitive area of ≈90mm x 90mm is built up by four back-side illuminated CMOS sensors, which image a field of view of ≈200 deg2. Each sensor has 22:4 megapixels. The Schmidt design of the telescope locates the detector inside the optical path, limiting the overall size of the assembly. As a result, the readout electronics is located in a remote unit outside the telescope. The short focal length of the telescope requires an accurate positioning of the sensors within ±50 μm along the optical axis, with a flatness of ±10 μm. While the telescope will be at around 295K during operations, the sensors are required to be cooled to 200K for dark current reduction. At the same time, the ability to heat the sensors to 343K is required for decontamination. In this paper, we present the preliminary design of the UV sensitive ULTRASAT camera.
The Ultraviolet Transient Astronomical Satellite (ULTRASAT) is a scientific space mission carrying an astronomical telescope. The mission is led by the Weizmann Institute of Science (WIS) in Israel and the Israel Space Agency (ISA), while the camera in the focal plane is designed and built by Deutsches Elektronen Synchrotron (DESY) in Germany. Two key science goals of the mission are the detection of counterparts to gravitational wave sources and supernovae.1 The launch to geostationary orbit is planned for 2024. The telescope with a field-of-view of ≈ 200 deg2, is optimized to work in the near-ultraviolet (NUV) band between 220 and 280 nm. The focal plane array is composed of four 22:4-megapixel, backside-illuminated (BSI) CMOS sensors with a total active area of 90 x 90mm2.2 Prior to sensor production, smaller test sensors have been tested to support critical design decisions for the final flight sensor. These test sensors share the design of epitaxial layer and antireflective coatings with the flight sensors. Here, we present a characterization of these test sensors. Dark current and read noise are characterized as a function of the device temperature. A temperature-independent noise level is attributed to on-die infrared emission and the read-out electronics' self-heating. We utilize a high-precision photometric calibration setup3 to obtain the test sensors' quantum efficiency relative to PTB/NIST-calibrated transfer standards (220-1100 nm), the quantum yield for λ >300 nm, the non-linearity of the system, and the conversion gain. The uncertainties are discussed in the context of the newest results on the setup's performance parameters. From the three ARC options Tstd, T1 and T2, the last assists the out-of-band rejection and peaks in the mid of the ULTRASAT operational waveband. We recommend ARC option T2 for the final ULTRASAT UV sensor.
Our contribution presents a high bandwidth platform that implements traffic aggregation and switching capabilities for the Cherenkov telescope array (CTA) cameras. Our proposed system integrates two different data flows: a unidirectional one from the cameras to an external server and a second one, fully configurable dedicated to configuration and control traffic for the camera management. The former requires high bandwidth mechanisms to be able to aggregate several 1 gigabit Ethernet links into one high speed 10 gigabit Ethernet port. The latter is responsible for providing routing components to allow a control and management path for all the elements of the cameras. Hence, a simple, efficient, and flexible routing mechanism has been implemented avoiding complex circuitry that impacts in the system performance. As a consequence, an asymmetric network topology allows high bandwidth communication and, at the same time, a flexible and cost-effective implementation. In our contribution, we analyze the camera requirements and present the proposed architecture. Moreover, we have designed several evaluation tests to demonstrate that our solution fulfills the CTA project needs. Finally, we illustrate the general possibilities of the proposed solution for other data acquisition applications and the most promising futures lines of research are discussed.
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.
Gianluca Giavitto, Terry Ashton, Arnim Balzer, David Berge, Francois Brun, Thomas Chaminade, Eric Delagnes, Gérard Fontaine, Matthias Füßling, Berrie Giebels, Jean-François Glicenstein, Tobias Gräber, James Hinton, Albert Jahnke, Stefan Klepser, Marko Kossatz, Axel Kretzschmann, Valentin Lefranc, Holger Leich, Hartmut Lüdecke, Iryna Lypova, Pascal Manigot, Vincent Marandon, Emmanuel Moulin, Mathieu de Naurois, Patrick Nayman, Marek Penno, Duncan Ross, David Salek, Markus Schade, Thomas Schwab, Rachel Simoni, Christian Stegmann, Constantin Steppa, Julian Thornhill, François Toussnel
KEYWORDS: Cameras, Imaging systems, Atmospheric Cherenkov telescopes, Electronics, Control systems, Data acquisition, Imaging systems, Control systems, Analog electronics, Telescopes, Field programmable gate arrays, Calibration
The High Energy Stereoscopic System (H.E.S.S.) is an array of five imaging atmospheric Cherenkov telescopes, sensitive to cosmic gamma rays of energies between ~30 GeV and several tens of TeV. Four of them started operations in 2003 and their photomultiplier tube (PMT) cameras are currently undergoing a major upgrade, with the goals of improving the overall performance of the array and reducing the failure rate of the ageing systems. With the exception of the 960 PMTs, all components inside the camera have been replaced: these include the readout and trigger electronics, the power, ventilation and pneumatic systems and the control and data acquisition software. New designs and technical solutions have been introduced: the readout makes use of the NECTAr analog memory chip, which samples and stores the PMT signals and was developed for the Cherenkov Telescope Array (CTA). The control of all hardware subsystems is carried out by an FPGA coupled to an embedded ARM computer, a modular design which has proven to be very fast and reliable. The new camera software is based on modern C++ libraries such as Apache Thrift, ØMQ and Protocol buffers, offering very good performance, robustness, flexibility and ease of development. The first camera was upgraded in 2015, the other three cameras are foreseen to follow in fall 2016. We describe the design, the performance, the results of the tests and the lessons learned from the first upgraded H.E.S.S. camera.
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