The ASTRI Mini-Array is a collaborative international effort led by the Italian National Institute for Astrophysics (INAF) to develop, build and operate a facility of nine Imaging Atmospheric Cherenkov Telescopes of the four meters class to study astronomical sources emitting very high energy gamma-rays in the TeV spectral band. The ASTRI Mini- Array is currently under construction on the island of Tenerife at the Observatorio del Teide based on a host agreement with the Instituto de Astrofísica de Canarias. The telescopes are alt-azimuthal with an innovative aplanatic dual mirror optical configuration. The first telescope of the ASTRI Mini-Array, named ASTRI-1, was installed at the end of summer 2022. In this paper we report on the results of the opto-mechanical characterization of the telescope. In particular, we analyzed the mechanical behavior of the telescope and we measured the pointing and tracking performance that resulted within the requirements. We tested the procedure to align and focus the panels of the primary mirror automatically. All the software procedures to run the telescope and perform these analyses were also tested.
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 ASTRI Stellar Intensity Interferometry Instrument (SI3) is a fast single photon counting instrument for performing intensity interferometry observations of bright stars with the ASTRI Mini-Array. SI3 is designed to perform accurate measurements of single photon arrival times (1ns) in a narrow optical bandwidth (1-8nm) centered at a wavelength in the range 420-500nm. The instrument will exploit the 36 simultaneous baselines over distances between 100m and 700m of the ASTRI Mini-Array to achieve angular resolutions below 100 microarcsec. At this level of resolution it turns out to be possible to reveal details on the surface and of the environment surrounding bright stars on the sky. During 2023 SI3 underwent a significant redesign, with an optical fiber positioned on the focal plane to feed the detectors and electronics. Here we present this new baseline design of SI3, and the motivations behind this choice, including the possibility of future upgrades of the instrument with dedicated front-end electronics and channel multiplexing. We will also show the first results of the target selection procedure based on simulations. Stars with angular diameters of less than 500- 600 microarcseconds up to about magnitude 4.5 will be observable. Thanks to the 36 simultaneous baselines, accurate (up to ∼1%) angular measurements can be obtained with 10-30 hours of observations. This accuracy can rival with that obtained with other arrays of Cherenkov telescopes, despite the smaller collecting area of a single ASTRI telescope.
Hard x-/soft gamma-ray astronomy (>100 keV) is a crucial field for the study of important astrophysical phenomena such as the 511 keV positron annihilation line in the galactic center region and its origin, gamma-ray bursts, soft gamma-ray repeaters, nuclear lines from SN explosions and more. However, several key questions in this field require sensitivity and angular resolution that are hardly achievable with present technology. A new generation of instruments suitable to focus hard x-/soft gamma-rays is necessary to overcome the technological limitations of current direct-viewing telescopes. One solution is using Laue lenses based on Bragg’s diffraction in a transmission configuration. To date, this technology is in an advanced stage of development and further efforts are being made in order to significantly increase its technology readiness level (TRL). To this end, massive production of suitable crystals is required, as well as an improvement of the capability of their alignment. Such a technological improvement could be exploited in stratospheric balloon experiments and, ultimately, in space missions with a telescope of about 20 m focal length, capable of focusing over a broad energy pass-band. We present the latest technological developments of the TRILL (technological readiness increase for Laue lenses) project, supported by ASI, devoted to the advancement of the technological readiness of Laue lenses. We show the method we developed for preparing suitable bent germanium and silicon crystals and the latest advancements in crystals alignment technology.
The ASTRI Mini-Array is an international project led by the Italian National Institute for Astrophysics (INAF) aiming at building and operating an array of nine Imaging Atmospheric Cherenkov Telescopes (IACTs) at the Observatorio del Teide in Tenerife (Canary Islands, Spain). UVSiPM, a calibrated small photon counter working in the 280-900 nm wavelength range, is one of the auxiliary instruments of the ASTRI Mini-Array.
UVSiPM is mainly devoted to measure the level of night sky background during the ASTRI Mini-Array observations in the same energy range of the ASTRI cameras. It is composed of one single multi-pixel SiPM sensor (the same model adopted in the ASTRI Mini-Array Cherenkov cameras) coupled to an electronic chain working in single photon counting mode. The design of the optical system foresees a pin-hole mask equipped with a collimator to regulate the UVSiPM field of view. UVSiPM will be mounted on the external structure of one of the ASTRI Mini-Array telescopes and co-aligned with its camera. In addition, it will be used as a support instrument for the absolute end-to-end calibration of the ASTRI Mini-Array telescopes performed with the illuminator, a further auxiliary device devoted to perform the optical throughput calibration of each telescope of the array. Last but not least, UVSiPM can be used as diagnostic tool for the camera functionalities. In this contribution we present the overall design of the UVSiPM instrument and some preliminary results of its performance based on simulations.
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.
ASTRI-Horn is an imaging atmospheric Cherenkov telescope developed by the Italian National Institute for Astrophysics (INAF), installed at the Serra La Nave Astronomical Station on Mount Etna (Italy). ASTRI-Horn detected the Crab proving the validity of its innovative camera and of the dual mirror configuration. Henceforth the telescope will play another important role. It will be the test bench for the upcoming cameras to be adopted for the ASTRI Mini-Array, a project led by INAF to build and operate an array of nine Cherenkov telescopes at the Observatorio del Teide (Tenerife, Spain). Moreover, the ASTRI-Horn camera will be used to test new technological solutions and explore innovative Cherenkov observation techniques. The Cherenkov camera uses Silicon-Photo Multiplier (SiPM) detectors. The fast front-end electronics implemented in the CITIROC ASIC is based on a custom peak-detector mode, which measures the electric pulses generated by the Cherenkov light flashes. The compact camera embeds all the components of a reliable thermal cooling system. This contribution gives a description of the upgrades of the ASTRI-Horn camera, which are the results of the lesson learnt during these years of sky observations. The improvements aim at correcting the drawbacks detected so far and at increasing the overall performance of the camera. The main ones are the increment of the power supplied to the photodetectors, the redesign of the Lids kinematic chain, a more efficient embedded calibration system, new control software routines and GUI.
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 ASTRI Mini-Array is an International collaboration, led by the Italian National Institute for Astrophysics, that is constructing and operating an array of nine Imaging Atmospheric Cherenkov Telescopes to study gamma-ray sources at very high energy and perform optical stellar intensity interferometry (SII) observations. Angular resolutions below 100 microarcsec are achievable with stellar intensity interferometry, using telescopes separated by hundreds to thousands of meters baselines. At this level of resolution it turns out to be possible to reveal details on the surface and of the environment surrounding bright stars on the sky. The ASTRI Mini-Array will provide a suitable infrastructure for performing these measurements thanks to the capabilities offered by its 9 telescopes, which provide 36 simultaneous baselines over distances between 100 m and 700 m. After providing an overview of the scientific context and motivations for performing SII science with the ASTRI Mini-Array telescopes, we present the baseline design for the ASTRI Stellar Intensity Interferometry Instrument, a fast single photon counting instrument that will be mounted on the ASTRI telescopes and dedicated to performing SII observations of bright stars.
The ASTRI Mini-Array is a gamma-ray experiment led by INAF with the partnership of the Instituto de Astrofisica de Canarias, Fundacion Galileo Galilei, University of Sao Paulo, North-West University S.A., and Observatoire de Geneve. It is being implemented at the Observatorio del Teide Tenerife. The nine (9) Cherenkov dual-mirror aplanatic telescopes of 4 m diameter are positioned at an average distance from each other of 160 m. Thanks to the unprecedented field-of-view (10.5 deg) of the ASTRI telescopes, the MA will allow us to observe the gamma-ray sky from a few up to a few hundred TeVs with competitive flux sensitivity and enhanced angular resolution. The curved focal plane of the camera is covered with SiPM sensors and is equipped with fast front-end electronics. The control SW will allow us to operate the Mini-array remotely, while a dedicated off-site Data Center in Italy will process the scientific products every night. The ASTRI Mini-Array represents a pivotal instrument to perform groundbreaking measurements very soon. In this paper, we will review the implementation plan of the ASTRI Mini-Array and report on the ongoing construction.
ASTRI-Horn is a prototypal telescope of an imaging atmospheric Cherenkov telescope developed by the Italian National Institute of Astrophysics (INAF), proposed for the Cherenkov Telescope Array (CTA) Observatory. The CTA Observatory represents the next generation of imaging atmospheric Cherenkov telescopes and will explore the very highenergy domain from a few tens of GeV up to few hundreds of TeV. It will be composed of large-, medium-, and small sized telescopes; ASTRI-Horn is an end-to-end prototype proposed for the Small Sized array.
The main scientific instrument of the ASTRI-Horn telescope is an innovative and compact Camera with Silicon- Photomultiplier based detectors and a specifically designed fast read-out electronics based on a custom peak-detector mode. The thermo-mechanical assembly is designed to host both the entire electronics chain, from the sensors to the raw data transmission system and the calibration system, and the complete thermoregulation system.
This contribution gives a high level description of the T/M and electrical design of the Cherenkov Camera, it describes the assembling procedure of its different subsystems and their integration into the complete camera system. A discussion about possible design improvements coming from the problems/difficulties encountered during assembly is also presented. Finally, results from engineering tests conducted in-field are also presented.
The Cherenkov Telescope Array (CTA) foresees, in its southern site (Chile), the implementation of up to 70 small-sized telescopes (SSTs), which will extend the energy coverage up to hundreds of TeV. It has been proposed that one of the first set of CTA SSTs will be represented by the ASTRI mini-array, which includes (at least) nine ASTRI telescopes. The endto-end prototype of such telescopes, named the ASTRI SST-2M, is installed in Italy and it is now completing the overall commissioning and entering the science verification phase. ASTRI telescopes are characterized by an optical system based on a dual-mirror Schwarzschild-Couder design and a camera at the focal plane composed of silicon photomultiplier sensors managed by a fast read-out electronics specifically designed. Based on a custom peak-detector mode, the ASTRI camera electronics is designed to perform Cherenkov signal detection, trigger generation, digital conversion of the signals and data transmission to the camera server. In this contribution we will describe the main features of the ASTRI camera, its performance and results obtained during the commissioning phase of the ASTRI SST-2M prototype in view of the ASTRI mini-array implementation.
ASTRI SST-2M is an imaging atmospheric Cherenkov telescope developed by the Italian National Institute of Astrophysics (INAF) in the framework of the Cherenkov Telescope Array (CTA) project as an end-to-end prototype for the Small Size array. Large-, medium-, and small-sized telescopes will compose the CTA observatory that represents the next generation of imaging atmospheric Cherenkov telescopes and will explore the very high-energy domain from a few tens of GeV up to few hundreds of TeV. The ASTRI SST-2M telescope has been installed at the INAF-Catania observing station at Serra La Nave, on Mt. Etna (Sicily, Italy) in September 2014. In these 3 years of open-air operations the telescope has been commissioned and its opto-mechanical performance is now well understood. The apparatus was made ready to host its main scientific instrument, the camera with Silicon-Photomultiplier based detectors. This contribution is a status report on the complete ASTRI SST-2M telescope assembly including the electro-mechanical structure and the optical system.
ASTRI SST-2M is an Imaging Atmospheric Cherenkov Telescope (IACT) developed by the Italian National Institute of Astrophysics, INAF. It is the prototype of the ASTRI telescopes proposed to be installed at the southern site of the Cherenkov Telescope Array, CTA. The optical system of the ASTRI telescopes is based on a dual mirror configuration, an innovative solution for IACTs, and the focal plane of the camera is composed of silicon photo-multipliers (SiPM), a recently developed technology for light detection, that exhibit very fast response and an excellent single photoelectron resolution. The ASTRI camera electronics is specifically designed to directly interface the SiPM sensors, detecting the fast pulses produced by the Cherenkov flashes, managing the trigger generation, the digital conversion of the signals and the transmission of the data to an external camera server connected through a LAN. In this contribution we present the general architecture of the camera electronics developed for the ASTRI SST-2M prototype, with special emphasis to some innovative solutions.
The Cherenkov Imaging Telescope Integrated Read Out Chip, CITIROC, is the front-end chip of the camera for the ASTRI SST-2M, one of the prototypes for the small sized telescopes of the Cherenkov Telescope Array, CTA. The telescope, operating in the energy range from a few TeV to beyond 300 TeV, is characterized by innovative technological solutions. The optical system is arranged in a dual-mirror configuration and the focal plane camera consists of a matrix of multi-pixel Silicon Photo-Multipliers. Among others, one of the most important project issue consists in the thermal characterization of the camera that, in the ASTRI SST-2M prototype, is thermo-controlled in a narrow temperature range. A set of at least nine similar telescopes will form the ASTRI mini-array proposed to be installed at the CTA southern site. In the cameras of the ASTRI mini-array telescopes the thermal control could be relaxed with a considerable gain in terms of power consumption, cost and simplicity. So, a study of the temperature dependence of the camera components is needed. The present work addresses this issue showing the results of the measurements carried out on CITIROC as a function of the temperature. We focused our investigation on the pedestal stability, linearity of the charge output signal, preamplifier gain and trigger uniformity in the temperature range 15-30°C. Our results show, for each of the above-mentioned measurable quantities, that temperature dependency is at the level of a few percent.
ASTRI is the end-to-end prototype for the CTA small-size class of telescopes in a dual-mirror configuration (SST-2M) proposed by the Italian National Institute of Astrophysics (INAF) in the framework of the Cherenkov Telescope Array. ASTRI SST-2M has been installed at the Serra La Nave Astrophysical Observatory on Mount Etna (Sicily) and its Performance Verification Phase will start in autumn 2016. For the relative pixel calibration and gain monitoring, the ASTRI SST-2M camera is equipped with an internal illumination device, while an external, portable, illumination system, placed at a few km distance from the telescope, will be used for the absolute end-to-end calibration of the telescope spectral response. Moreover analysis of signals induced in the camera pixels by the night sky background (diffuse emission and reference stars) will be used to monitor the long term evolution of the telescope calibration. We present an overview of the ASTRI SST-2M absolute calibration strategy and the external illuminating device that will be used for its spectral calibration
ASTRI SST-2M is the end-to-end prototype telescope under development by the Italian National Institute of Astrophysics, INAF, proposed for the investigation of the highest-energy gamma-ray band in the framework of the Cherenkov Telescope Array, CTA. The ASTRI SST-2M prototype will be installed in Italy at the INAF station located at Serra La Nave on Mount Etna during Fall 2014. The calibration and scientific validation phase will start soon after. The calibration of a Cherenkov telescope includes several items and tools. The ASTRI SST- 2M camera is equipped with an internal fiber illumination system that allows to perform the relative calibration through monitoring of gain and efficiency variations of each pixel. The absolute calibration of the overall system, including optics, will take advantage from auxiliary instrumentation, namely UVscope and UVSiPM, two small-aperture multi-pixels photon detectors NIST calibrated in lab. During commissioning phase, to measure the main features of ASTRI SST-2M, as its overall spectral response, the main telescope and the auxiliary UVscope-UVSiPM will be illuminated simultaneously by a spatially uniform flux generated by a ground-based light source, named Illuminator, placed at a distance of few hundreds meters. Periodically, during clear nights, the flux profiles of a reference star tracked simultaneously by ASTRI SST-2M and UVscope-UVSiPM will allow to evaluate the total atmospheric attenuation and the absolute calibration constant of the ASTRI SST-2M prototype. In this contribution we describe the auxiliary UVscope-UVSiPM and Illuminator sub-system together with an overview of the end-to-end calibration procedure foreseen for the ASTRI SST-2M telescope prototype.
The Cherenkov Telescope Array (CTA) is a worldwide new generation project aimed at realizing an array of a hundred ground based gamma-ray telescopes. ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) is the Italian project whose primary target is the development of an end-to-end prototype, named ASTRI SST-2M, of the CTA small size class of telescopes devoted to investigation of the highest energy region, from 1 to 100 TeV. Next target is the implementation of an ASTRI/CTA mini-array based on seven identical telescopes. Silicon Photo-Multipliers (SiPMs) are the semiconductor photosensor devices designated to constitute the camera detection system at the focal plane of the ASTRI telescopes. SiPM photosensors are suitable for the detection of the Cherenkov flashes, since they are very fast and sensitive to the light in the 300-700nm wavelength spectrum. Their drawbacks compared to the traditional photomultiplier tubes are high dark count rates, after-pulsing and optical cross-talk contributions, and intrinsic gains strongly dependent on temperature. Nonetheless, for a single pixel, the dark count rate is well below the Night Sky Background, the effects of cross-talk and afterpulses are typically lower than 20%, and the gain can be kept stable against temperature variations by means of adequate bias voltage compensation strategies. This work presents and discusses some experimental results from a large set of measurements performed on the SiPM sensors to be used for the ASTRI SST-2M prototype camera and on recently developed detectors demonstrating outstanding performance for the future evolution of the project in the ASTRI/CTA mini-array.
In the context of the Cherenkov Telescope Array observatory project, the ASTRI SST-2M end-to-end prototype
telescope, entirely supported by the Italian National Institute of Astrophysics, is designed to detect cosmic primary
gamma ray energies from few TeV up to hundreds of TeV. The ASTRI SST-2M prototype camera is part of the
challenging synergy of novel optical design, camera sensors, front-end electronics and telescope structure design. The
camera is devoted to imaging and recording the Cherenkov images of air showers induced by primary particles into the
Earth’s atmosphere. In order to match the energy range mentioned above, the camera must be able to trigger events
within a few tens of nanoseconds with high detection efficiency. This is obtained by combining silicon photo-multiplier
sensors and suitable front-end electronics. Due to the characteristic imprint of the Cherenkov image that is a function of
the shower core distance, the signal dynamic range of the pixels and consequently of the front-end electronics must span
three orders of magnitude (1:1000 photo-electrons). These and many other features of the ASTRI SST-2M prototype
camera will be reported in this contribution together with a complete overview of the mechanical and thermodynamic
camera system.
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