We measure the spectrum of cosmic rays with energies greater than 1018.2eV with the fluorescence detectors (FDs) and the surface detectors (SDs) of the Telescope Array Experiment using the data taken ...in our first 2.3-year observation from May 27, 2008 to September 7, 2010. A hybrid air shower reconstruction technique is employed to improve accuracies in determination of arrival directions and primary energies of cosmic rays using both FD and SD data. The energy spectrum presented here is in agreement with our previously published spectra and the HiRes results.
Cosmic rays in the energy range 1018.0–1018.5 eV are thought to have a light, probably protonic, composition. To study their origin one can search for anisotropy in their arrival directions. ...Extragalactic cosmic rays should be isotropic, but galactic cosmic rays of this type should be seen mostly along the galactic plane, and there should be a shortage of events coming from directions near the galactic anticenter. This is due to the fact that, under the influence of the galactic magnetic field, the transition from ballistic to diffusive behavior is well advanced, and this qualitative picture persists over the whole energy range. Guided by models of the galactic magnetic field that indicate that the enhancement along the galactic plane should have a standard deviation of about 20° in galactic latitude, and the deficit in the galactic anticenter direction should have a standard deviation of about 50° in galactic longitude, we use the data of the Telescope Array surface detector in 1018.0 to 1018.5 eV energy range to search for these effects. The data are isotropic. Neither an enhancement along the galactic plane nor a deficit in the galactic anticenter direction is found. Using these data we place an upper limit on the fraction of EeV cosmic rays of galactic origin at 1.3% at 95% confidence level.
In this paper the technological aspects of the FAZIA array will be explored. After a productive commissioning phase, FAZIA blocks started to measure and give very useful data to explore the physics ...of Fermi energy heavy-ion reactions. This was possible thanks to many technical measures and innovations developed in the commissioning phase and tuned during the first experimental campaigns. This paper gives a detailed description of the present status of the FAZIA setup from the electronic and mechanical point of view, trying also to trace a path for new improvements and refinements of the apparatus.
The Large Size Telescopes (LSTs) are the largest telescopes of the Cherenkov Telescope Array (CTA). Their cameras are equipped with 1855 photomultiplier tube (PMT) pixels with GHz readout, to image ...the flashes of Cherenkov light emitted from atmospheric air-showers initiated by cosmic gamma rays. Silicon photomultipliers (SiPMs) are becoming valid alternatives for PMTs, and in fact many of the smaller telescopes in the array will feature a SiPM camera. To evaluate the performance of an LST SiPM-based camera we are building one of the LST camera elements (a cluster of 7 pixels with the readout electronics), replacing the PMTs with SiPM pixels. Most of the hardware of the baseline design is maintained, to keep the evaluation process simple and to use the existing calibration facilities. We discuss the design and construction of the demonstrator unit and some preliminary characterizations.
Optical feasibility of an upgrade of the CTA LST camera to SiPM Perennes, C.; Doro, M.; Corti, D. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2020, Letnik:
984
Journal Article
Recenzirano
The Large Size Telescope (LST) is the largest telescope of the Cherenkov Telescope Array project, with a diameter of 23 m and a focal plane instrumentation of 4 square metres. In the current design, ...it comprises cameras equipped with arrays of 1855 photomultiplier tubes (PMTs). Each PMT has a light concentrator in front to reduce the stray light as well as reduce the dead space between PMTs. These cameras are built to detect the nanoseconds flash of Cherenkov light emitted from atmospheric air-showers generated by a cosmic gamma ray entering the atmosphere. Thanks to a rapid development, silicon photomultipliers (SiPMs) are becoming valid alternatives for PMTs in several fields, due to their lower operating voltage, larger photon efficiency, reduced ageing, insensitivity to magnetic fields, and possibly lower costs. These properties make SiPMs suitable for gamma-ray astronomy and future development for imaging atmospheric Cherenkov telescopes. Here we discuss a minimal-effort scenario for an upgrade of an LST PMT-based camera to a SiPM-based camera, in which most of the hardware is maintained. Thanks to a ray-tracing software, we show that the minimal valid solution consists only in replacing each PMT by several SiPMs. In particular, the current PMT-tailored lightguides in front of each pixel do not have to be exchanged considering the angular distribution of light at the SiPM surface and its angular response. We briefly discuss the effect on the sensitivity of the instrument equipped with SiPM.
Abstract
Spaceborne nulling interferometry in the mid-infrared waveband is one of the most promising techniques for characterizing the atmospheres of extra-solar planets orbiting in the habitable ...zone of their parent star and possibly discovering life markers. One of the most difficult challenges is the control of a free-flying telescope spacecraft moving around a central combiner to modulate the planet signal. Moreover, the entire array must be reconfigured regularly to observe different celestial targets, thus increasing the risk of losing one or more spacecraft and aborting the mission before its normal end. This paper describes a simplified optical configuration in which the telescopes do not need to be rotated and the number of necessary array reconfigurations is minimized. It allows efficient modulation of the planet signal, using only making use of rotating prisms or mirrors located in the central combiner. The general principle of a Nulling interferometer with a fixed telescope array is explained. Mathematical relationships were established to determine the planet modulation signal. Numerical simulations were performed for three different arrangements of collecting telescopes. They confirmed that nulling interferometry in space did not require a rotating telescope array.
A ground-based electro-optical (EO) array, deployed at the Jilin Space Tracking Base of Changchun Observatory, China, has been in operation since April 2017. The array has 8 small telescopes, each ...has an aperture of 15 cm and a field of view of 14° × 14°. On average, the array can collect angles data over 3–4 thousand Very Short Arcs (VSAs) of Low Earth Orbit (LEO) space objects each night. Correlation of the VSA angles data with the NORAD catalogue objects results in about 85% of all the VSAs being correlated to NORAD objects. The remaining 15% VSAs angles data could be supposed from uncatalogued objects. The Initial Orbit Determination (IOD) solutions of the VSAs with the range-search method and the association results of the IODs with the geometrical method are presented. The mean IOD success rate is about 91% and the True Positive (TP) rate is more than 86%. In addition, the classical Gauss, Laplace, Gooding and Double-r angles-only IOD methods are applied to process VSA angles data and their performance is assessed. The CBTA method is used to associate the IOD tracks and compared with the geometrical method. A set of procedures for identifying the uncatalogued objects based on the VSA angles data is designed. Processing of the VSA angles data from Aug 4 to Sep 30, 2017 reveals there are possibly 415 uncatalogued LEO objects.
Recently, the Istituto Nazionale di Astrofisica (INAF) has placed a contract with Hamamatsu Photonics to acquire hundreds of Silicon Photomultipliers (SiPM) tiles to build 10 cameras with 37 tiles ...each for the ASTRI Mini-Array (MA) project. Each tile is made up of 8 × 8 pixels of 7 × 7 mm2 with micro-cells of 75μm. To check the quality of the delivered tiles a complex and accurate test plan has been studied. The possibility to simultaneously analyse as many pixels as possible becomes of crucial importance.
Dark Count Rate (DCR) versus over-voltage and versus temperature and Optical Cross Talk (OCT) versus over-voltage can be easily measured simultaneously for all pixels because they are carried out in dark conditions. On the contrary, simultaneous Photon Detection Efficiency (PDE) measurement of all pixels of a tile is not easily achievable and needs an appropriate optical set-up. Simultaneous measurements have the advantage of speeding up the entire procedure and enabling quick PDE comparison of all the tile pixels.
The paper describes the preliminary steps to guarantee an accurate absolute PDE measurement and the investigation the capability of the electronics to obtain simultaneous PDE measurements. It also demonstrates the possibility of using a calibrated SiPM as reference detector instead of a calibrated photodiode. The method to achieve accurate absolute PDE of four central pixels of a tile is also described.
In this paper some of the brightest GeV sources observed by the Fermi-LAT were analysed, focusing on their spectral cut-off region. The sources chosen for this investigation were the brightest blazar ...flares of 3C 454.3 and 3C 279 and the Vela pulsar with a reanalysis with the latest Fermi-LAT software. For the study of the spectral cut-off we first explored the Vela pulsar spectrum, whose statistics in the time interval of the 3FGL catalog allowed strong constraints to be obtained on the parameters. We subsequently performed a new analysis of the flaring blazar SEDs. For these sources we obtained constraints on the cut-off parameters under the assumption that their underlying spectral distribution is described by a power-law with a stretched exponential cut-off. We then highlighted the significant potential improvements on such constraints by observations with next generation ground based Cherenkov telescopes, represented in our study by the Cherenkov Telescope Array (CTA). Adopting currently available simulations for this future observatory, we demonstrate the considerable improvement in cut-off constraints achievable by observations with this new instrument when compared with that achievable by satellite observations.
The Italian Institute of Nuclear Physics (INFN) is involved in the development of a prototype for a SiPM-based camera for the Cherenkov Telescope Array (CTA), a new generation of telescopes for ...ground - based gamma ray astronomy. In this framework, an R&D program for the development of SiPMs suitable for Cherenkov light detection (Near-Ultraviolet SiPMs) has been carried out. The developed device is a High Density NUV-SiPM based on a micro cell of 30 μm × 30 μm and 6 mm × 6 mm area produced by Fondazione Bruno Kessler (FBK). A full characterisation of the single SiPM will be presented and compared with the old technology (NUV-SiPM) and with other SiPMs commercially available. The NUV-HD SiPM will be tested in the pSCT (Schwarzschild-Couder Telescope prototype) for CTA which is leading to a camera concept based on 8 × 8 NUV-HD SiPM module as detection unit. An update on recent tests on the detectors arranged in this matrix configuration and on the front-end electronics will be given.
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