We have developed a non-sequential ray-tracing simulation library, ROOT-basedsimulatorforraytracing (ROBAST), which is aimed to be widely used in optical simulations of cosmic-ray (CR) and gamma-ray ...telescopes. The library is written in C++, and fully utilizes the geometry library of the ROOT framework. Despite the importance of optics simulations in CR experiments, no open-source software for ray-tracing simulations that can be widely used in the community has existed. To reduce the dispensable effort needed to develop multiple ray-tracing simulators by different research groups, we have successfully used ROBAST for many years to perform optics simulations for the Cherenkov Telescope Array (CTA). Among the six proposed telescope designs for CTA, ROBAST is currently used for three telescopes: a Schwarzschild–Couder (SC) medium-sized telescope, one of SC small-sized telescopes, and a large-sized telescope (LST). ROBAST is also used for the simulation and development of hexagonal light concentrators proposed for the LST focal plane. Making full use of the ROOT geometry library with additional ROBAST classes, we are able to build the complex optics geometries typically used in CR experiments and ground-based gamma-ray telescopes. We introduce ROBAST and its features developed for CR experiments, and show several successful applications for CTA.
The Cherenkov Telescope Array (CTA) is the next generation ground-based instrument for gamma-ray astronomy. It will consist of approximately 100 telescopes of three sizes, built on two sites: in the ...Northern Hemisphere, and in the Southern Hemisphere. FlashCam is a camera system proposed for the medium-sized telescopes of CTA; it is equipped with 1758 photo-multiplier tubes (PMTs). To reduce dead-space between pixels and to enlarge their effective sensitive area, hexagonal light concentrators will be used. We present a test setup for light concentrators as well as results for a specific light guide geometry and different reflective coatings. The wavelength-dependent angular efficiency of the light concentrators and the effectiveness of blocking stray light are discussed. A simple approach to fine-adjust cut-off angles with the given light concentrator geometry and PMT is shown. To cross-check measurements, a ray tracing simulation is performed taking into account the geometrical shape of the light concentrators and the anode sensitivity of the PMTs.
•A light concentrator test setup for spectral and angular measurements is presented.•Prototype coatings are characterised by effective reflectivity and acceptance angle.•Results are verified by ROBAST based ray-tracing simulations.•Larger distances between PMT and light concentrator can lower NSB background.•Degradation of characteristic values after climate chamber treatment is below 2%.
► We show the first physics results from the Middle Drum detector for Telescope Array. ► We quantify a spectral and energy scale comparison between Middle Drum and HiRes-1. ► We quantify a comparison ...between Middle Drum monocular and hybrid observation. ► We justify the transfer of the HiRes energy scale to all of Telescope Array.
The Telescope Array’s Middle Drum fluorescence detector was instrumented with telescopes refurbished from the High Resolution Fly’s Eye’s HiRes-1 site. The data observed by Middle Drum in monocular mode was analyzed via the HiRes-1 profile-constrained geometry reconstruction technique and utilized the same calibration techniques enabling a direct comparison of the energy spectra and energy scales between the two experiments. The spectrum measured using the Middle Drum telescopes is based on a three-year exposure collected between December 16, 2007 and December 16, 2010. The calculated difference between the spectrum of the Middle Drum observations and the published spectrum obtained by the data collected by the HiRes-1 site allows the HiRes-1 energy scale to be transferred to Middle Drum. The HiRes energy scale is applied to the entire Telescope Array by making a comparison between Middle Drum monocular events and hybrid events that triggered both Middle Drum and the Telescope Array’s scintillator ground array.
In the last few years a number of efforts have been undertaken to develop new technology related to Silicon Photomultipliers (SiPMs). These photosensors consist of an array of identical Avalanche ...Photodiodes operating in Geiger mode and connected in parallel to a single output. The Italian Institute of Nuclear Physics (INFN) is involved in the R&D program Progetto Premiale Telescopi CHErenkov made in Italy (TECHE.it) to develop photosensors for a SiPM based camera that will be part of the Cherenkov Telescope Array (CTA) observatory. In this framework tests are ongoing on innovative devices suitable to detect Cherenkov light in the blue and near-UV wavelength region, the so-called Near Ultra-Violet Silicon Photomultipliers (NUV SiPMs). The tests on photosensors produced by Fondazione Bruno Kessler (FBK) are revealing promising performance: low operating voltage, capability to detect very low intensity light down to a single photon and high Photo Detection Efficiency (PDE) in the range 390–410nm. In particular the developed device is a High Density NUV-SiPM (NUV-HD SiPM) based on a micro-cell of 30μm×30μm and 6mm×6mm area. Tests on this detector in single-cell configuration and in a matrix arrangement have been done. At the same time front-end electronics based on the waveform sampling technique optimized for the new NUV-HD SIPMs is under study and development.
The ASTRI Mini-Array is an Istituto Nazionale di Astrofisica (INAF) project to build and operate an array of nine Imaging Atmospheric Cherenkov Telescopes (IACTs) at the Teide Astronomical ...Observatory of the Instituto de Astrofisica de Canarias in Tenerife (Spain) based on a host agreement with INAF and, as such, it will be the largest IACT array until the Cherenkov Telescope Array Observatory starts operations. Implementing the ASTRI Mini-Array poses several challenges from technical, logistic, and management points of view. Starting from the description of the innovative technologies adopted to build the telescopes, we will discuss the solutions adopted to overcome these challenges, making the ASTRI Mini-Array a great instrument to perform deep observations of the galactic and extra-galactic sky at very high energies.
This book summarizes the science to be carried out by the upcoming Cherenkov Telescope Array, a major ground-based gamma-ray observatory that will be constructed over the next six to eight years. The ...major scientific themes, as well as core program of key science projects, have been developed by the CTA Consortium, a collaboration of scientists from many institutions worldwide.CTA will be the major facility in high-energy and very high-energy photon astronomy over the next decade and beyond. CTA will have capabilities well beyond past and present observatories. Thus, CTA's science program is expected to be rich and broad and will complement other major multiwavelength and multimessenger facilities. This book is intended to be the primary resource for the science case for CTA and it thus will be of great interest to the broader physics and astronomy communities. The electronic version (e-book) is available in open access.
The GCT camera for the Cherenkov Telescope Array Lapington, J.S.; Abchiche, A.; Allan, D. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
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The Gamma Cherenkov Telescope (GCT) is one of the designs proposed for the Small Sized Telescope (SST) section of the Cherenkov Telescope Array (CTA). The GCT uses dual-mirror optics, resulting in a ...compact telescope with good image quality and a large field of view with a smaller, more economical, camera than is achievable with conventional single mirror solutions. The photon counting GCT camera is designed to record the flashes of atmospheric Cherenkov light from gamma and cosmic ray initiated cascades, which last only a few tens of nanoseconds.
The GCT optics require that the camera detectors follow a convex surface with a radius of curvature of 1m and a diameter of ~35cm, which is approximated by tiling the focal plane with 32 modules. The first camera prototype is equipped with multi-anode photomultipliers, each comprising an 8×8 array of 6×6mm2 pixels to provide the required angular scale, adding up to 2048 pixels in total. Detector signals are shaped, amplified and digitised by electronics based on custom ASICs that provide digitisation at 1 GSample/s. The camera is self-triggering, retaining images where the focal plane light distribution matches predefined spatial and temporal criteria. The electronics are housed in the liquid-cooled, sealed camera enclosure. LED flashers at the corners of the focal plane provide a calibration source via reflection from the secondary mirror.
The first GCT camera prototype underwent preliminary laboratory tests last year. In November 2015, the camera was installed on a prototype GCT telescope (SST-GATE) in Paris and was used to successfully record the first Cherenkov light of any CTA prototype, and the first Cherenkov light seen with such a dual-mirror optical system. A second full-camera prototype based on Silicon Photomultipliers is under construction. Up to 35 GCTs are envisaged for CTA.
•Detailed simulations of a small-sized telescope with secondary optics for the Cherenkov Telescope Array, and for the first time, an attempt to show a comprehensive tolerance analysis of a ...Schwarzschild–Couder Cherenkov telescope.•The radius of the encircled point spread function (Θ80) for the ideal optical system is found to be approximately 1.3 arcmin for an on-axis observation and approximately 3.6 arcmin for an off-axis observation at the edge of the field of view.•Shadowing is found to be at a similar level (∼11%) to that seen with the current generation of conventional Davies–Cotton Cherenkov telescopes.•An extensive tolerance analysis highlights the importance of maintaining the correct separation distance between the secondary mirror and the focal plane in order to contain the Θ80 parameter within the size of a single pixel.•A small circular area (radius < 150 mm) at the center of the secondary mirror can be used for calibration and alignment instrumentation.
The Gamma-ray Cherenkov Telescope (GCT) is a small-sized telescope (SST) that represents one of three novel designs that are based on Schwarzschild–Couder optics and are proposed for use within the Cherenkov Telescope Array (CTA). The GAmma-ray Telescope Elements (GATE) program has led an effort to build a prototype of the GCT at the Paris Observatory in Meudon, France. The mechanical structure of the prototype, known as the SST-GATE prototype telescope, is now complete along with the successful installation of the camera. We present the results of extensive simulation work to determine the optical performance of the SST-GATE prototype telescope. Using the ROBAST software and assuming an ideal optical system, we find the radius of the encircled point spread function (θ80) of the SST-GATE to be ∼1.3 arcmin (∼0.02°) for an on-axis (θfield=0∘) observation and ∼3.6 arcmin (∼0.06°) for an observation at the edge of the field of view (θfield=4.4∘). In addition, this research highlights the shadowing that results from the stopping of light rays by various telescope components such as the support masts and trusses. It is shown that for on-axis observations the effective collection area decreases by approximately 1 m2 as a result of shadowing components other than the secondary mirror. This is a similar loss (∼11%) to that seen with the current generation of conventional Davies–Cotton (DC) Cherenkov telescopes. An extensive random tolerance analysis was also performed and it was found that certain parameters, especially the secondary mirror z-position and the tip and tilt rotations of the mirrors, are critical in order to contain θ80 within the pixel limit radius for all field angles. In addition, we have studied the impact upon the optical performance of introducing a hole in the center of the secondary mirror for use with pointing and alignment instruments. We find that a small circular area (radius < 150 mm) at the center of the secondary mirror can be used for instrumentation without any significant impact upon optical performance. Finally, we studied the impact of reducing the size of the primary mirror for the prototype telescope and found that this comes at the cost of poorer image quality and light collection efficiency for all field angles, but at a significant cost saving for a one-off prototype.
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