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T. Montaruli

Publications and source records attributed to T. Montaruli.

At least 19 recordsLinked to original sources
arXiv2026

Molecular absorption of Cherenkov light at CTAO

The Cherenkov Telescope Array Observatory (CTAO) is the next-generation observatory for high energy \gamma-ray astronomy with unprecedented sensitivity and accuracy. Accurate estimation and mitigation of systematic uncertainties are crucial for its scientific performance. Atmospheric properties significantly influence both the generation and extinction of Cherenkov light generated by gamma and cosmic rays interacting in the atmosphere. This study provides a detailed analysis of molecular extinction processes, including Rayleigh scattering and molecular absorption, and their impact on the transmission of Cherenkov light. We examine typical summer and winter behaviour of Rayleigh scattering and seasonal and event-driven variations of the main absorbing molecules, such as ozone and nitrogen oxides, at the two CTAO array sites. Using simulations, we assess the effects of these variations on image intensity and trigger effective area, particularly during dynamic atmospheric events like stratosphere-to-troposphere transport. Based on our findings, we propose an atmospheric monitoring and calibration strategy to ensure that the CTAO meets its systematic uncertainty requirements, particularly for low-energy gamma-ray observations.

astro-ph.IM↗
arXiv2026

Prospects for the detection of gamma rays using Cherenkov telescopes enhanced by a ground array observatory

We study through detailed simulated data and their optimized analysis the expected performance of the Single-Mirror Small-Size imaging atmospheric Cherenkov Telescopes (SST-1M) potentially located inside a high-altitude array of Water-Cherenkov Detectors (WCDs) inspired by the current foreseen design of the Southern Wide-field Gamma-ray Observatory (SWGO). For such a hybrid setup, we show an improvement in the flux sensitivity above 10 TeV by about 60% for monocular and 30% for stereoscopic SST-1M observation, due to the improved gamma/hadron separation when additional parameters from the WCD array are used. We also discuss further benefits of the hybrid gamma observatory concept and its technical challenges.

astro-ph.IM↗
arXiv2025

The simulation chain for the Terzina Cherenkov telescope on board the NUSES space mission

The Terzina telescope is designed to detect ultra-high energy cosmic rays (UHECRs) and Earth-skimming neutrinos from a 550 km low-Earth orbit (LEO) by observing Cherenkov light emitted by Extensive Air Showers (EAS) in the Earth's atmosphere pointing towards the telescope and in the field of view. In this contribution, a simulation chain for the Terzina telescope on board the NUSES mission will be presented. The chain encompasses all stages of the detection process, from event generation and EAS modelling with CORSIKA and EASCherSim to Geant4-based simulations of the telescope's geometry and optics, followed by modelling of the trigger system and silicon photomultiplier (SiPM) response. The Geant4 module includes the real CAD model of the telescope structure and optical components, with aspherical lenses manually implemented to ensure accurate representation of the optical efficiency and point spread function in Geant4. This comprehensive pipeline, developed using modular C++ code and Python tools for event analysis and reconstruction, produces detailed performance assessments of a telescope operating in a LEO mission but can be adapted for any high altitude Cherenkov telescope, making it a versatile tool for future observatory designs. The possibility of modelling balloons in the atmosphere has also been developed.

astro-ph.IM↗
arXiv2025

The SST-1M stereoscopic system

The Single-Mirror Small-Size Telescope (SST-1M) is an Imaging Atmospheric Cherenkov Telescope designed for detecting very high-energy gamma rays. With a compact design achieved through the adoption of silicon-photomultiplier pixels and a lightweight structure, SST-1M offers a large field of view of about 9{\deg} and features a mirror system of 4 m diameter with an optical PSF (at 80% of photon inclusion) of 0.08{\deg} on axis and 0.21{\deg} at 4{\deg} off-axis, and a fully digitizing readout almost deadtime free up to few kHz. The SST-1M achieved a high-performance and cost-effective solution for implementing an array of small-sized telescopes. The stereoscopic system of two SST-1Ms is temporarily installed at the Ond\v{r}ejov Observatory in the Czech Republic. From an altitude of only about 510 m and in harsh meteorological conditions, the system is detecting galactic sources and flares of AGNs. The accurate calibration of the detector and the simulation benchmark are ongoing. The results of its performance are shown. A future final location is being considered and a future performance outlook is discussed.

astro-ph.IM↗
arXiv2025

Observation of the Crab Nebula with the Single-Mirror Small-Size Telescope stereoscopic system at low altitude

The Single-Mirror Small-Size Telescope (SST-1M) stereoscopic system is composed of two Imaging Atmospheric Cherenkov Telescopes (IACTs) designed for optimal performance for gamma-ray astronomy in the multi-TeV energy range. It features a 4-meter-diameter tessellated mirror dish and an innovative SiPM-based camera. Its optical system features a 4-m diameter spherical mirror dish based on the Davies-Cotton design, maintaining a good image quality over a large FoV while minimizing optical aberrations. In 2022, two SST-1M telescopes were installed at the Ond\v{r}ejov Observatory, Czech Republic, at an altitude of 510 meters above sea level, and have been collecting data for commissioning and astronomical observations since then. We present the first SST-1M observations of the Crab Nebula, conducted between September 2023 and March 2024 in both mono and stereoscopic modes. During this observation period, 46 hours for the SST-1M-1 and 52 hours for the SST-1M-2 were collected for which 33 hours are in stereoscopic mode. We use the Crab Nebula observation to validate the expected performance of the instrument, as evaluated by Monte Carlo simulations carefully tuned to account for instrumental and atmospheric effects. We determined that the energy threshold at the analysis level for the zenith angles below $30^\circ$ is 1 TeV for mono mode and 1.3 TeV for stereo mode. The energy and angular resolutions are approximately 20% and $0.18^\circ$ for mono mode and 10% and $0.10^\circ$ for stereo mode, respectively. We present the off-axis performance of the instrument and a detailed study of systematic uncertainties. The results of a full simulation of the telescope and its camera is compared to the data for the first time, allowing a deep understanding of the SST-1M array performance.

astro-ph.IM↗
arXiv2025

Performance and radiation damage mitigation strategy for silicon photomultipliers on LEO space missions

Space missions require lightweight, low-power consuming, radiation-tolerant components. Silicon photomultipliers are increasingly used for detecting near-UV, optical, and infrared light in space due to their compact design, low cost, low power consumption, robustness, and high photo-detection efficiency, which makes them sensitive to single photons. Although SiPMs outperform traditional photomultiplier tubes in many areas, concerns about their radiation tolerance and noise remain. In this study, we estimate the radiation effects on a satellite in sun-synchronous low Earth orbit (LEO) at an altitude of 550~km during the declining phase of solar cycle 25 (2026-2029). We evaluated silicon photomultipliers produced by the Foundation Bruno Kessler (FBK) using front-side illuminated technology with metal trenches (NUV-HD-MT), assessing their response to a 50~MeV proton beam and exposure to a $\beta$-radioactive source (strontium-90). Simulations with SPENVIS and Geant4 were used to validate the experimental results. Based on our findings, we propose a photosensor annealing strategy for space-based instruments.

hep-ex↗
arXiv2024

Analysis of commissioning data from SST-1M : A Prototype of Single-Mirror Small Size Telescope

SST-1M is a prototype of a single-mirror Small Size Telescope developed by a consortium of institutes from Poland, Switzerland and the Czech Republic. With a wide field of view of 9 degrees, SST-1Ms are designed to detect gamma-rays in the energy range between 1 and 300 TeV. The design of the SST-1M follows the Davies-Cotton concept, with a 9.42m2 multi-segment mirror. SST-1M is equipped with DigiCam camera, which features a fully digital readout and trigger system using 250 MHz ADC, and a compact Photo-Detector Plane (PDP) composed of 1296 pixels, each made of a hexagonal light guide coupled to silicone photomultipliers (SiPM). Two SST-1M telescopes are currently being commissioned at the Ondrejov Observatory in the Czech Republic, where they are successfully observing Cerenkov events in stereo. This contribution will present an overview of calibration strategies and performance evaluation based on data collected at the observatory.

astro-ph.IM↗
arXiv2024

The SST-1M imaging atmospheric Cherenkov telescope for gamma-ray astrophysics

The SST-1M is a Small-Sized Telescope (SST) designed to provide a cost-effective and high-performance solution for gamma-ray astrophysics, particularly for energies beyond a few TeV. The goal is to integrate this telescope into an array of similar instruments, leveraging its lightweight design, earthquake resistance, and established Davies-Cotton configuration. Additionally, its optical system is designed to function without a protective dome, allowing it to withstand the harsh atmospheric conditions typical of mountain environments above 2000 m. The SST-1M utilizes a fully digitizing camera system based on silicon photomultipliers (SiPMs). This camera is capable of digitizing all signals from the UV-optical light detectors, allowing for the implementation of various triggers and data analysis methods. We detail the process of designing, prototyping, and validating this system, ensuring that it meets the stringent requirements for gamma-ray detection and performance. An SST-1M stereo system is currently operational and collecting data at the Ond\v{r}ejov observatory in the Czech Republic, situated at 500 m. Preliminary results from this system are promising. A forthcoming paper will provide a comprehensive analysis of the performance of the telescopes in detecting gamma rays and operating under real-world conditions.

astro-ph.IM↗
arXiv2023

The Terzina instrument onboard the NUSES space mission

In this paper we will introduce the Terzina instrument, which is one of the two scientific payloads of the NUSES satellite mission. NUSES serves as a technological pathfinder, hosting a suite of innovative instruments designed for the in-orbit detection of cosmic rays, neutrinos, and gamma rays across various energy ranges. The Terzina instrument itself is a compact telescope equipped with Schmidt-Cassegrain optics. Its primary objective is to detect Cherenkov radiation emitted by Extensive Air Showers generated by the interaction of high-energy (> 100 PeV) cosmic rays with the Earth's atmosphere. Terzina represents a critical step forward in the development of future space-based instruments aimed at detecting upward-moving showers induced by tau-leptons and muons resulting from the interaction of high-energy astrophysical neutrinos with the Earth. In this paper, we will delve into the key technical aspects of the Terzina instrument, its capabilities, and its potential for detection.

astro-ph.IM↗
arXiv2023

Mono and stereo performance of the two SST-1M telescope prototypes

The Single-Mirror Small-Sized Telescope, or SST-1M, was originally developed as a prototype of a small-sized telescope for CTA, designed to form an array for observations of gamma-ray-induced atmospheric showers for energies above 3 TeV. A pair of SST-1M telescopes is currently being commissioned at the Ondrejov Observatory in the Czech Republic, and the telescope capabilities for mono and stereo observations are being tested in better astronomical conditions. The final location for the telescopes will be decided based on these tests. In this contribution, we present a data analysis pipeline called sst1mpipe, and the performance of the telescopes when working independently and in a stereo regime.

astro-ph.IM↗
arXiv2023

The High-Altitude Water Cherenkov (HAWC) Observatory in M\'exico: The Primary Detector

The High-Altitude Water Cherenkov (HAWC) observatory is a second-generation continuously operated, wide field-of-view, TeV gamma-ray observatory. The HAWC observatory and its analysis techniques build on experience of the Milagro experiment in using ground-based water Cherenkov detectors for gamma-ray astronomy. HAWC is located on the Sierra Negra volcano in M\'exico at an elevation of 4100 meters above sea level. The completed HAWC observatory principal detector (HAWC) consists of 300 closely spaced water Cherenkov detectors, each equipped with four photomultiplier tubes to provide timing and charge information to reconstruct the extensive air shower energy and arrival direction. The HAWC observatory has been optimized to observe transient and steady emission from sources of gamma rays within an energy range from several hundred GeV to several hundred TeV. However, most of the air showers detected are initiated by cosmic rays, allowing studies of cosmic rays also to be performed. This paper describes the characteristics of the HAWC main array and its hardware.

astro-ph.HE↗
arXiv2021

Development of an advanced SiPM camera for the Large Size Telescope of the Cherenkov Telescope Array

Silicon photomultipliers (SiPMs) have become the baseline choice for cameras of the small-sized telescopes (SSTs) of the Cherenkov Telescope Array (CTA). On the other hand, SiPMs are relatively new to the field and covering large surfaces and operating at high data rates still are challenges to outperform photomultipliers (PMTs). The higher sensitivity in the near infra-red and longer signals compared to PMTs result in higher night sky background rate for SiPMs. However, the robustness of the SiPMs represents a unique opportunity to ensure long-term operation with low maintenance and better duty cycle than PMTs. The proposed camera for large size telescopes will feature $0.05 degree pixels, low power and fast front-end electronics and a fully digital readout. In this work, we present the status of dedicated simulations and data analysis for the performance estimation. The design features and the different strategies identified, so far, to tackle the demanding requirements and the improved performance are described.

astro-ph.IM↗
arXiv2021

Monitoring the pointing of the prototype LST-1 using star reconstruction in the Cherenkov camera

The first Large-Sized Telescope (LST-1) proposed for the forthcoming Cherenkov Telescope Array (CTA) has started to operate in 2019 in La Palma. The large structure of LST-1 - with a 23 m mirror dish diameter - imposes a strict control of its deformations that could affect the pointing accuracy and its overall performance. According to CTA specifications that are conceived to resolve e.g. the fine structure of galactic sources, the LST post-calibration pointing accuracy should be better than 14 arcseconds. To fulfill this requirement, the telescope pointing precision is monitored with two dedicated CCD cameras located at the dish center. The analysis of their images allows us to disentangle different systematic deformations of the structure. In this work, we investigate a complementary approach that offers the possibility to monitor the pointing of the telescope during the acquisition of sky data. After properly cleaning the events from the Cherenkov showers, the reconstructed positions of the stars imaged in the camera field of view are compared to their nominal expected positions in catalogues. This provides a direct measurement of the telescope pointing, that can be used to cross-check the other methods and as a real-time monitoring of the optical properties of the telescope and of the pointing corrections applied by the bending models. Additionally, this method benefits from not relying on specific hardware or dedicated observations. In this contribution we will illustrate this analysis and show results based on simulations of LST-1.

astro-ph.IM↗
arXiv2021

Origin and role of relativistic cosmic particles

This white paper briefly summarizes the importance of the study of relativistic cosmic rays, both as a constituent of our Universe, and through their impact on stellar and galactic evolution. The focus is on what can be learned over the coming decade through ground-based gamma-ray observations over the 20 GeV to 300 TeV range. The majority of the material is drawn directly from "Science with the Cherenkov Telescope Array", which describes the overall science case for CTA. We request that authors wishing to cite results contained in this white paper cite the original work.

astro-ph.HE↗
arXiv2021

Multi-messenger and transient astrophysics with the Cherenkov Telescope Array

The discovery of gravitational waves, high-energy neutrinos or the very-high-energy counterpart of gamma-ray bursts has revolutionized the high-energy and transient astrophysics community. The development of new instruments and analysis techniques will allow the discovery and/or follow-up of new transient sources. We describe the prospects for the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory, for multi-messenger and transient astrophysics in the decade ahead. CTA will explore the most extreme environments via very-high-energy observations of compact objects, stellar collapse events, mergers and cosmic-ray accelerators.

astro-ph.HE↗
arXiv2021

Probing extreme environments with the Cherenkov Telescope Array

The physics of the non-thermal Universe provides information on the acceleration mechanisms in extreme environments, such as black holes and relativistic jets, neutron stars, supernovae or clusters of galaxies. In the presence of magnetic fields, particles can be accelerated towards relativistic energies. As a consequence, radiation along the entire electromagnetic spectrum can be observed, and extreme environments are also the most likely sources of multi-messenger emission. The most energetic part of the electromagnetic spectrum corresponds to the very-high-energy (VHE, E>100 GeV) gamma-ray regime, which can be extensively studied with ground based Imaging Atmospheric Cherenkov Telescopes (IACTs). The results obtained by the current generation of IACTs, such as H.E.S.S., MAGIC, and VERITAS, demonstrate the crucial importance of the VHE band in understanding the non-thermal emission of extreme environments in our Universe. In some objects, the energy output in gamma rays can even outshine the rest of the broadband spectrum. The Cherenkov Telescope Array (CTA) is the next generation of IACTs, which, with cutting edge technology and a strategic configuration of ~100 telescopes distributed in two observing sites, in the northern and southern hemispheres, will reach better sensitivity, angular and energy resolution, and broader energy coverage than currently operational IACTs. With CTA we can probe the most extreme environments and considerably boost our knowledge of the non-thermal Universe.

astro-ph.IM↗
arXiv2020

Large scale characterization and calibration strategy of a SiPM-based camera for gamma-ray astronomy

The SST-1M is a 4-m diameter mirror Davies-Cotton gamma-ray telescope. It has been designed to cover the energy range above 500 GeV and to be part of an array of telescopes separated by 150-200 m. Its innovative camera is featuring large area hexagonal silicon photo-multipliers as photon detectors and a fully digital trigger and readout system. Here, the strategy and the methods for its calibration are presented, together with the obtained results. In particular, the off and on-site calibration strategies are demonstrated on the first camera prototype. The performances of the camera in terms of charge and time resolution are described.

astro-ph.IM↗