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.
POMATA (Protective Oils for Mirrors Aging on Telescopes Alfresco) is a project funded by the Italian National Institute for Astrophysics (INAF) aimed at identifying an adequate protective overcoating layer for mirrors used on Cherenkov telescopes. Unlike traditional observatories with domes, Air-Cherenkov instruments lack protective enclosures, exposing their mirrors to a range of detrimental elements, including atmospheric agents, thermal shocks, chemical reactions, and abrasive particles. Usually, on top of the mirrors’ reflecting layer a protective nanometric coating transparent in the UV band (e.g., SiO2) is deposited under vacuum. However, an additional over-coating is desirable to prevent micro-damages. Moreover, mitigating the accumulation of dirt on the mirror surface would be beneficial, as it may reduce the effective area and degrade the telescope’s performance. For this reason, we are currently working on the POMATA project, whose main goal is to conduct a comparative study of various overcoating layers that can be applied without depositions under high vacuum conditions. Our study is focused on silicone oils, a class of synthetic polymers composed of siloxane units. Silicone oils are well known for their unique properties, such as low surface tension, even spreadability, and resilience to extreme temperatures and environmental stressors. We evaluated four commercial silicone oils during a preliminary phase, and we are now testing their effectiveness in preventing aging as an additional layer for the Cherenkov mirrors developed for the project ASTRI. This contribution will cover the project’s development program and the results achieved after a preliminary characterization campaign.
In the development of next generation telescopes, the quality of optical surfaces in terms of roughness is an important parameter for determining their performance and it is constantly monitored during the manufacturing process. While portable instruments are commonly employed for on-surface monitoring, their effectiveness diminishes in case of large optics with complex geometry and/or thin substrate. In such a scenario, the replica approach emerges as a highly efficient alternative, involving the acquisition of imprints on surfaces with silicone-based replication materials. This paper aims to systematically characterize the measurement process by comparing standard methods with the replica approach. Samples of diverse vinyl polysiloxane impression materials were cured and measured at various stages of the optical manufacturing. The goal is to optimize the process, providing a comprehensive evaluation of its advantages and effectiveness.
KEYWORDS: Software development, Telescopes, Data modeling, Computer architecture, Control systems, Atmospheric Cherenkov telescopes, Data acquisition, Data archive systems, Design, Cameras
The Astrophysics with Italian Replicating Technology Mirrors (ASTRI) Mini-Array is an international collaboration led by the Italian National Institute for Astrophysics (INAF) and devoted to imaging atmospheric Cherenkov light for very-high γ-ray astrophysics, detection of cosmic-rays, and stellar Hambury-Brown intensity interferometry. The project is deploying an array of nine dual-mirror aplanatic imaging atmospheric Cherenkov telescopes of 4-m class at the Teide Observatory on Tenerife in the Canary Islands. Based on SiPM sensors, the focal plane camera covers an unprecedented field of view of 10.5 deg in diameter. The array is most sensitive to γ-ray radiation above 1 up to 200 TeV, with an angular resolution of 3 arcmin, better than the current particle arrays, such as LHAASO and HAWC. We describe the overall software architecture of the ASTRI Mini-Array and the software engineering approach for its development. The software covers the entire life cycle of the Mini-Array, from scheduling to remote operations, data acquisition, and processing until data dissemination. The on-site control software allows remote array operations from different locations, including automated reactions to critical conditions. All data are collected every night, and the array trigger is managed post facto. The high-speed networking connection between the observatory site and the Data Center in Rome allows for ready data availability for stereoscopic event reconstruction, data processing, and almost real-time science products generation.
It has been known for some time that sputtered low-density coatings deposited under vacuum (e.g. carbon or B4C), applied on top of high-density metallic coatings, can enhance the reflectivity in the soft x-ray band (below ~5 keV). In the last years, we experimented with novel carbonated coatings obtained by dip-liquid deposition, in which a thin film is formed on the surface of a mirror by immersion in a suitable precursor solution. After several attempts with different chemical compounds, we found an optimal candidate both for the reflectivity performance and for the convenience of the deposition process, which is much simpler and inexpensive compared to conventional processes. In particular, such coatings can enhance the soft x-ray response at the reflection angles employed in future telescopes, like ATHENA (ESA), Lynx (NASA) and eXTP (CAS). In this paper we consider the application of dip-liquid overcoatings on conventional coatings (Au, Ir) or in combination with recently proposed chromium overcoatings and their possible uses to enhance the reflectivity of x-ray mirrors at low, medium or higher energies, presenting the first experimental results of x-ray tests on these coatings.
ASTRI-Horn is a 4-m class Cherenkov telescope located on Mt. Etna, Serra La Nave, Italy, operated at the Italian National Institute for Astrophysics (INAF) “M.G. Fracastoro” observing station. It is the end-to-end prototype for the nine telescopes of the ASTRI Mini-Array, a collaborative international effort led by INAF under construction at the Teide Observatory on Tenerife, in the Canary Islands. The ASTRI Mini-Array is based on nine Image Atmospheric Cherenkov Telescopes (IACTs) and it is devoted to perform astronomical observations in the high-energy gamma-ray band, above 1 TeV. ASTRI-Horn is characterized by a Schwarzschild-Couder dual-mirror optical design with a 4.3 m diameter primary mirror (M1), segmented in 18 hexagonal panels, and a monolithic 1.8 m diameter secondary mirror. The focal plane camera is based on arrays of Silicon Photo-Multiplier (SiPM) sensors, working in the wavelength band of 300-900 nm. The panels of the upgraded version of the telescope’s primary mirror are based on a multilayer dielectric coating instead of the classical Aluminium (with a thin SiO2 protection layer) coating. This multilayer coating has been designed to strongly reduce the reflectivity above 700 nm, where the diffuse night sky background dominates over the Cherenkov signal from showers and the SiPM sensors are still effective. In this work we present the computation of the average reflectivity of ASTRI-Horn primary mirror starting from reflectivity measurements performed on each panel over a wide wavelength range (200-1000 nm). This experimental average reflectivity curve will be adopted in the ASTRI-Horn simulation chain, which does not handle the reflectivity of the single panels.
The ASTRI Mini-Array is an international project led by the Italian National Institute for Astrophysics (INAF) that foresees the construction and operation of an array of nine Imaging Atmospheric Cherenkov Telescopes at the Observatorio del Teide in Tenerife (Spain). The main purpose of the project is to study gamma-ray astrophysical sources in the very high-energy range, particularly at the multi-TeV energy scale. The camera and electronics used for the detection of the Cherenkov light are designed to trigger on the very fast flashes from atmospheric particle showers. Although the variance method is implemented in ASTRI Mini-Array cameras, it is difficult to obtain an adequate pointing model using only Cherenkov cameras. In order to build the pointing model and to monitor and control the pointing accuracy during observations a Pointing Monitoring Camera will be installed on each telescope. The PMC systems will acquire images of the sky with a machine vision camera in the direction pointed by the telescopes and perform an astrometry check on a dedicated computer hosted in the telescope electronics cabinet. The astrometry results will be fed back to the main Telescope Control System. The PMC system will be controlled and it will exchange data through the OPC-UA protocol. During the Assembly Integration and Verification phase and for maintenance activities, a specifically developed Graphical User Interface will be used. The PMC hardware and software systems are described.
KEYWORDS: Atmospheric Cherenkov telescopes, Data acquisition, Cameras, Control systems, Telescopes, Interferometry, Data centers, Software development, Computer architecture, Quality systems
The ASTRI Mini-Array is an international collaboration led by the Italian National Institute for Astrophysics. This project aims to construct and operate an array of nine Imaging Atmospheric Cherenkov Telescopes to study gamma-ray sources at very high energy (TeV) and perform stellar intensity interferometry observations. We describe the software architecture and the technologies used to implement the Online Observation Quality System (OOQS) for the ASTRI Mini-Array project. The OOQS aims to execute data quality checks on the data acquired in real-time by the Cherenkov cameras and intensity interferometry instruments, and provides feedback to both the Central Control System and the Operator about abnormal conditions detected. The OOQS can notify other sub-systems, triggering their reaction to promptly correct anomalies. The results from the data quality analyses (e.g. camera plots, histograms, tables, and more) are stored in the Quality Archive for further investigation and they are summarised in reports available to the Operator. Once the OOQS results are stored, the operator can visualize them using the Human Machine Interface. The OOQS is designed to manage the high data rate generated by the instruments (up to 4.5 GB/s) and received from the Array Data Acquisition System through the Kafka service. The data are serialized and deserialized during the transmission using the Avro framework. The Slurm workload scheduler executes the analyses exploiting key features such as parallel analyses and scalability.
KEYWORDS: Atmospheric Cherenkov telescopes, Telescopes, Data archive systems, Calibration, Data centers, Data processing, Monte Carlo methods, Data storage, Device simulation, Data acquisition
The ASTRI Mini-Array is an international project led by the Italian National Institute for Astrophysics (INAF) to build and operate an array of nine 4-m class Imaging Atmospheric Cherenkov Telescopes (IACTs) at the Observatorio del Teide (Tenerife, Spain). The system is designed to perform deep observations of the galactic and extragalactic gamma-ray sky in the TeV and multi-TeV energy band, with important synergies with other ground-based gamma-ray facilities in the Northern Hemisphere and space-borne telescopes. As part of the overall software system, the ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) Team is developing dedicated systems for Data Processing, Simulation, and Archive to achieve effective handling, dissemination, and scientific exploitation of the ASTRI Mini-Array data. Thanks to the high-speed network connection available between Canary Islands and Italy, data acquired on-site will be delivered to the ASTRI Data Center in Rome immediately after acquisition. The raw data will be then reduced and analyzed by the Data Processing System up to the generation of the final scientific products. Detailed Monte Carlo simulated data will be produced by the Simulation System and exploited in several data processing steps in order to achieve precise reconstruction of the physical characteristics of the detected gamma rays and to reject the overwhelming background due to charged cosmic rays. The data access at different user levels and for different use cases, each one with a customized data organization, will be provided by the Archive System. In this contribution we present these three ASTRI Mini-Array software systems, focusing on their main functionalities, components, and interfaces.
KEYWORDS: Data modeling, Atmospheric Cherenkov telescopes, Control systems, Software development, Telescopes, Data processing, Data archive systems, Data acquisition, Calibration, Computer architecture
The ASTRI Mini-Array is an international collaboration led by the Italian National Institute for Astrophysics (INAF) and devoted to the imaging of atmospheric Cherenkov light for very-high gamma-ray astronomy. The project is deploying an array of 9 telescopes sensitive above 1 TeV. In this contribution, we present the architecture of the software that covers the entire life cycle of the observatory, from scheduling to remote operations and data dissemination. The high-speed networking connection available between the observatory site, at the Canary Islands, and the Data Center in Rome allows for ready data availability for stereo triggering and data processing.
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 pointing calibration of Imaging Atmospheric Cherenkov Telescopes (IACTs) is often a technological challenge: their cameras are not designed for imaging the stars in the Field of View (FoV) and this prevents from using the standard astrometry of the focal plane for monitoring the pointing of the instrument. A common solution is to adopt auxiliary optical devices aligned with the line-of-sight of the telescope but, in order to avoid systematic errors, a pointing strategy considering also the signal from the Cherenkov camera is desirable, especially when a dual-mirror optical configuration is adopted. In this contribution, we present a new custom astrometry technique that we developed for the Cherenkov camera of ASTRI telescopes, using the so-called Variance method: an ancillary output data-flow owning the possibility to image the stellar component of the Night Sky Background with relatively good sensitivity (limiting magnitude ∼7). Despite the large angular size of Cherenkov camera pixels (∼11 ′′) and their relatively small number (a few thousand), our automatic astrometric routine is able to identify the stars in the FoV with sub-pixel precision, giving the possibility of monitoring the pointing of the telescope in real-time, without any additional hardware. Our technique has been already tested on archive data taken with the ASTRI-Horn prototype telescope, located in Italy, and it will be implemented in the incoming ASTRI Mini-Array: a facility of 9 identical Cherenkov telescopes under construction in Tenerife (Canary Islands). In this contribution we discuss the features of this novel procedure, its potentialities, and how they will enhance the scientific accuracy of future ASTRI telescopes.
The Cherenkov Telescope Array (CTA) is the next ground-based gamma-ray observatory in the TeV γ-ray spectral region operating with the Imaging Atmospheric Cherenkov Technique. It is based on almost 70 telescopes of different class diameters—Large-Sized Telescope, Medium-Sized Telescope (MST), and Small-Sized Telescope (SST) of 23, 12, and 4 m, respectively—to be installed in two sites in the two hemispheres (at La Palma, Canary Islands, and near Paranal, Chile). Several thousands of reflecting mirror tiles larger than 1 m2 will be produced for realizing the segmented primary mirrors of a so large number of telescopes. Almost in parallel, the ASTRI mini-array (MA) is being implemented in Tenerife (Canary Islands), composed of nine 4-m diameter dual-mirror Cherenkov telescopes (very similar to the SSTs). We completed the mirror production for all nine telescopes of the ASTRI MA and two MSTs (400 segments in total) using the cold glass slumping replication technology. The results related to the quality achieved with a large-scale production are presented, also discussing the adopted testing methods and approaches. They will be very useful for the adoption and optimization of the quality assurance process for the huge production (almost 3000 m2 of reflecting surface) of the MST and SST CTA telescopes.
In this paper we discuss the latest developments of the STRIP instrument of the “Large Scale Polarization Explorer” (LSPE) experiment. LSPE is a novel project that combines ground-based (STRIP) and balloon-borne (SWIPE) polarization measurements of the microwave sky on large angular scales to attempt a detection of the “B-modes” of the Cosmic Microwave Background polarization. STRIP will observe approximately 25% of the Northern sky from the “Observatorio del Teide” in Tenerife, using an array of forty-nine coherent polarimeters at 43 GHz, coupled to a 1.5 m fully rotating crossed-Dragone telescope. A second frequency channel with six-elements at 95 GHz will be exploited as an atmospheric monitor. At present, most of the hardware of the STRIP instrument has been developed and tested at sub-system level. System-level characterization, starting in July 2018, will lead STRIP to be shipped and installed at the observation site within the end of the year. The on-site verification and calibration of the whole instrument will prepare STRIP for a 2-years campaign for the observation of the CMB polarization.
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