arXiv subjects

D. della Volpe

Publications and source records attributed to D. della Volpe.

At least 55 records · Page 3Linked to original sources

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.

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arXiv2021

Probing Dark Matter and Fundamental Physics with the Cherenkov Telescope Array

Astrophysical observations provide strong evidence that more than 80% of all matter in the Universe is in the form of dark matter (DM). Two leading candidates of particles beyond the Standard Model that could constitute all or a fraction of the DM content are the so-called Weakly Interacting Massive Particles (WIMPs) and Axion-Like Particles (ALPs). The upcoming Cherenkov Telescope Array, which will observe gamma rays between 20 GeV and 300 TeV with unprecedented sensitivity, will have unique capabilities to search for these DM candidates. A particularly promising target for WIMP searches is the Galactic Center. WIMPs with annihilation cross sections correctly producing the DM relic density will be detectable with CTA, assuming an Einasto-like density profile and WIMP masses between 200 GeV and 10 TeV. Regarding new physics beyond DM, CTA observations will also enable tests of fundamental symmetries of nature such as Lorentz invariance.

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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.

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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.

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arXiv2021

Calibration of the Air Shower Energy Scale of the Water and Air Cherenkov Techniques in the LHAASO experiment

The Wide Field-of-View Cherenkov Telescope Array (WFCTA) and the Water Cherenkov Detector Arrays (WCDA) of LHAASO are designed to work in combination for measuring the energy spectra of various cosmic ray species over a very wide energy range from a few TeV to 10 PeV. The energy calibration of WCDA can be achieved with a proven technique of measuring the westward shift of the Moon shadow of galactic cosmic rays due to the geomagnetic field. This deflection angle $Δ$ is inversely proportional to the energy of the cosmic rays. The precise measurements of the shifts by WCDA allows us to calibrate its energy scale for energies as high as 35 TeV. The energy scale measured by WCDA can be used to cross calibrate the energy reconstructed by WFCTA, which spans the whole energy range up to 10 PeV. In this work, we will demonstrate the feasibility of the method using the data collected from April 2019 to January 2020 by the WFCTA array and WCDA-1 detector, the first of the three water Cherenkov ponds, already commissioned at LHAASO site.

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arXiv2020

The observation of the Crab Nebula with LHAASO-KM2A for the performance study

As a sub-array of the Large High Altitude Air Shower Observatory (LHAASO), KM2A is mainly designed to cover a large fraction of the northern sky to hunt for gamma-ray sources at energies above 10 TeV. Even though the detector construction is still underway, a half of the KM2A array has been operating stably since the end of 2019. In this paper, we present the pipeline of KM2A data analysis and the first observation on the Crab Nebula, a standard candle in very high energy gamma-ray astronomy. We detect gamma-ray signals from the Crab Nebula in both energy ranges of 10$-$100 TeV and $>$100 TeV with high significance, by analyzing the KM2A data of 136 live days between December 2019 and May 2020. With the observations, we test the detector performance including angular resolution, pointing accuracy and cosmic ray background rejection power. The energy spectrum of the Crab Nebula in the energy range 10-250 TeV fits well with a single power-law function dN/dE =(1.13$\pm$0.05$_{stat}$$\pm$0.08$_{sys}$)$\times$10$^{-14}$$\cdot$(E/20TeV)$^{-3.09\pm0.06_{stat}\pm0.02_{sys}}$ cm$^{-2}$ s$^{-1}$ TeV$^{-1}$. It is consistent with previous measurements by other experiments. This opens a new window of gamma-ray astronomy above 0.1 PeV through which ultrahigh-energy gamma-ray new phenomena, such as cosmic PeVatrons, might be discovered.

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arXiv2020

Characterisation of a large area silicon photomultiplier

This work illustrates and compares some methods to measure the most relevant parameters of silicon photo-multipliers (\sipm{}s), such as photon detection efficiency as a function of over-voltage and wavelength, dark count rate, optical cross-talk, afterpulse probability. For the measurement of the breakdown voltage, $V_{BD}$, several methods using the current-voltage $IV$ curve are compared, such as the "IV Model", the "relative logarithmic derivative", the "inverse logarithmic derivative", the "second logarithmic derivative", and the "third derivative" models. We also show how some of these characteristics can be quite well described by few parameters and allow, for example, to build a function of the wavelength and over-voltage describing the photodetection efficiency. This is fundamental to determine the working point of SiPMs in applications where external factors can affect it. These methods are applied to the large area monolithic hexagonal SiPM S10943-2832(X), developed in collaboration with Hamamatsu and adopted for a camera for a gamma-ray telescope, called the SST-1M. We describe the measurements of the performance at room temperature of this device. The methods used here can be applied to any other device and the physics background discussed here are quite general and valid for a large phase-space of the parameters.

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arXiv2019

A Mini-Imaging Air Cherenkov Telescope

In this paper we describe the different software and hardware elements of a mini-telescope for the detection of cosmic rays and gamma-rays using the Cherenkov light emitted by their induced particle showers in the atmosphere. We estimate the physics reach of the standalone mini-telescope and present some results of the measurements done at the Sauverny Observatory of the University of Geneva and at the Saint-Luc Observatory, which demonstrate the ability of the telescope to observe cosmic rays with energy above about 100 TeV. Such a mini-telescope can constitute a cost-effective out-trigger array that can surround other gamma-ray telescopes or extended air showers detector arrays. Its development was born out of the desire to illustrate to students and amateurs the cosmic ray and gamma-ray detection from ground, as an example of what is done in experiments using larger telescopes. As a matter of fact, a mini-telescope can be used in outreach night events. While outreach is becoming more and more important in the scientific community to raise interest in the general public, the realisation of the mini-telescope is also a powerful way to train students on instrumentation such as photosensors, their associated electronics, acquisition software and data taking. In particular, this mini-telescope uses silicon photomultipliers (SiPM) and the dedicated ASIC, CITIROC.

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arXiv2019

SiPM behaviour under continuous light

This paper reports on the behaviour of Silicon Photomultiplier (SiPM) detectors under continuous light. Usually, the bias circuit of a SiPM has a resistor connected in series to it, which protects the sensor from drawing too high current. This resistor introduces a voltage drop when a SiPM draws a steady current, when illuminated by constant light. This reduces the actual SiPM bias and then its sensitivity to light. As a matter of fact, this effect changes all relevant SiPM features, both electrical (i.e. breakdown voltage, gain, pulse amplitude, dark count rate and optical crosstalk) and optical (i.e. photon detection efficiency). To correctly operate such devices, it is then fundamental to calibrate them under various illumination levels. In this work, we focus on the large area ($\sim$1~cm$^{2}$) hexagonal SiPM S10943-2832(X) produced by Hamamatsu HPK for the camera of a gamma-ray telescope with 4 m-diameter mirror, called the SST-1M. We characterize this device under light rates raging from 3~MHz up to 5~GHz of photons per sensor at room temperature (T = 25 $^{\circ}$C). From these studies, a model is developed in order to derive the parameters needed to correct for the voltage drop effect. This model can be applied for instance in the analysis of the data acquired by the camera to correct for the effect. The experimental results are also compared with a toy Monte Carlo simulation and finally, a solution is proposed to compensate for the voltage drop.

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arXiv2019

SENSE: A comparison of photon detection efficiency and optical crosstalk of various SiPM devices

This paper describes a comparison of photon detection efficiency and optical crosstalk measurements performed by three partners: Geneva University, Catania Observatory and Nagoya University. The measurements were compared for three different SiPM devices with different active areas: from 9 $mm^2$ up to 93.6 $mm^2$ produced by Hamamatsu. The objective of this work is to establish the measurements and analysis procedures for calculating the main SiPM parameters and their precision. This work was done in the scope of SENSE project which aims to build roadmap for the last developments in field of sensors for low light level detection.

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arXiv2017

Control Software for the SST-1M Small-Size Telescope prototype for the Cherenkov Telescope Array

The SST-1M is a 4-m Davies--Cotton atmospheric Cherenkov telescope optimized to provide gamma-ray sensitivity above a few TeV. The SST-1M is proposed as part of the Small-Size Telescope array for the Cherenkov Telescope Array (CTA), the first prototype has already been deployed. The SST-1M control software of all subsystems (active mirror control, drive system, safety system, photo-detection plane, DigiCam, CCD cameras) and the whole telescope itself (master controller) uses the standard software design proposed for all CTA telescopes based on the ALMA Common Software (ACS) developed to control the Atacama Large Millimeter Array (ALMA). Each subsystem is represented by a separate ACS component, which handles the communication to and the operation of the subsystem. Interfacing with the actual hardware is performed via the OPC UA communication protocol, supported either natively by dedicated industrial standard servers (PLCs) or separate service applications developed to wrap lower level protocols (e.g. CAN bus, camera slow control) into OPC UA. Early operations of the telescope without the camera were already carried out. The camera is fully assembled and is capable to perform data acquisition using artificial light source.

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arXiv2017

Performance of a small size telescope (SST-1M) camera for gamma-ray astronomy with the Cherenkov Telescope Array

The foreseen implementations of the Small Size Telescopes (SST) in CTA will provide unique insights into the highest energy gamma rays offering fundamental means to discover and under- stand the sources populating the Galaxy and our local neighborhood. Aiming at such a goal, the SST-1M is one of the three different implementations that are being prototyped and tested for CTA. SST-1M is a Davies-Cotton single mirror telescope equipped with a unique camera technology based on SiPMs with demonstrated advantages over classical photomultipliers in terms of duty-cycle. In this contribution, we describe the telescope components, the camera, and the trigger and readout system. The results of the commissioning of the camera using a dedicated test setup are then presented. The performances of the camera first prototype in terms of expected trigger rates and trigger efficiencies for different night-sky background conditions are presented, and the camera response is compared to end-to-end simulations.

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arXiv2017

Development of a strategy for calibrating the novel SiPM camera of the SST-1M telescope proposed for the Cherenkov Telescope Array

CTA will comprise a sub-array of up to 70 small size telescopes (SSTs) at the southern array. The SST-1M project, a 4 m-diameter Davies Cotton telescope with 9 degrees FoV and a 1296 pixels SiPM camera, is designed to meet the requirements of the next generation ground based gamma-ray observatory CTA in the energy range above 3 TeV. Silicon photomultipliers (SiPM) cameras of gamma-ray telescopes can achieve good performance even during high night sky background conditions. Defining a fully automated calibration strategy of SiPM cameras is of great importance for large scale production validation and online calibration. The SST-1M sub-consortium developed a software compatible with CTA pipeline software (CTApipe). The calibration of the SST-1M camera is based on the Camera Test Setup (CTS), a set of LED boards mounted in front of the camera. The CTS LEDs are operated in pulsed or continuous mode to emulate signal and night sky background respectively. Continuous and pulsed light data analysis allows us to extract single pixel calibration parameters to be used during CTA operation.

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arXiv2017

Prospects for CTA observations of the young SNR RX J1713.7-3946

We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX~J1713.7$-$3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very-high-energy (VHE) gamma rays. Special attention is paid to explore possible spatial (anti-)correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H{\sc i} emission. We present a series of simulated images of RX J1713.7$-$3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the non-thermal X-ray emission observed by {\it XMM-Newton}, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H{\sc i} observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic vs leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.

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arXiv2016

The Single Mirror Small Sized Telescope For The Cherenkov Telescope Array

The Small Size Telescope with Single Mirror (SST-1M) is one of the proposed types of Small Size Telescopes (SST) for the Cherenkov Telescope Array (CTA). About 70 SST telescopes will be part the CTA southern array which will also include Medium Sized Telescopes (MST) in its threshold configuration. Optimized for the detection of gamma rays in the energy range from 5 TeV to 300 TeV, the SST-1M uses a Davies-Cotton optics with a 4 m dish diameter with a field of view of 9 degrees. The Cherenkov light resulting from the interaction of the gamma-rays in the atmosphere is focused onto a 88 cm side-to-side hexagonal photo-detection plane. The latter is composed of 1296 hollow light guides coupled to large area hexagonal silicon photomultipliers (SiPM). The SiPM readout is fully digital readout as for the trigger system. The compact and lightweight design of the SST-1M camera offers very high performance ideal for gamma-ray observation requirement. In this contribution, the concept, design, performance and status of the first telescope prototype are presented.

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arXiv2015

Prototype of the SST-1M Telescope Structure for the Cherenkov Telescope Array

A single-mirror small-size (SST-1M) Davies-Cotton telescope with a dish diameter of 4 m has been built by a consortium of Polish and Swiss institutions as a prototype for one of the proposed small-size telescopes for the southern observatory of the Cherenkov Telescope Array (CTA). The design represents a very simple, reliable, and cheap solution. The mechanical structure prototype with its drive system is now being tested at the Institute of Nuclear Physics PAS in Krakow. Here we present the design of the prototype and results of the performance tests of the structure and the drive and control system.

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arXiv2015

Using muon rings for the optical throughput calibration of the SST-1M prototype for the Cherenkov Telescope Array

Imaging Atmospheric Cherenkov Telescopes (IACTs) are ground-based instruments devoted to the study of very high energy gamma-rays coming from space. The detection technique consists of observing images created by the Cherenkov light emitted when gamma rays, or more generally cosmic rays, propagate through the atmosphere. While in the case of protons or gamma-rays the images present a filled and more or less elongated shape, energetic muons penetrating the atmosphere are visualised as characteristic circular rings or arcs. A relatively simple analysis of the ring images allows the reconstruction of all the relevant parameters of the detected muons, such as the energy, the impact parameter, and the incoming direction, with the final aim to use them to calibrate the total optical throughput of the given IACT telescope. We present the results of preliminary studies on the use of images created by muons as optical throughput calibrators of the single mirror small size telescope prototype SST-1M proposed for the Cherenkov Telescope Array.

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arXiv2015

Software design for the control system for Small-Size Telescopes with single-mirror of the Cherenkov Telescope Array

The Small-Size Telescope with single-mirror (SST-1M) is a 4 m Davies-Cotton telescope and is among the proposed telescope designs for the Cherenkov Telescope Array (CTA). It is conceived to provide the high-energy ($>$ few TeV) coverage. The SST-1M contains proven technology for the telescope structure and innovative electronics and photosensors for the camera. Its design is meant to be simple, low-budget and easy-to-build industrially. Each device subsystem of an SST-1M telescope is made visible to CTA through a dedicated industrial standard server. The software is being developed in collaboration with the CTA Medium-Size Telescopes to ensure compatibility and uniformity of the array control. Early operations of the SST-1M prototype will be performed with a subset of the CTA central array control system based on the Alma Common Software (ACS). The triggered event data are time stamped, formatted and finally transmitted to the CTA data acquisition. The software system developed to control the devices of an SST-1M telescope is described, as well as the interface between the telescope abstraction to the CTA central control and the data acquisition system.

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