Abstract
The Large-Sized Telescopes (LSTs) of the Cherenkov Telescope Array (CTA) are designed for gamma-ray studies focusing on low energy threshold, high flux sensitivity and rapid telescope ...repositioning. The LST has a tessellated parabolic mirror of 23 m diameter and a weight of about 100 tons, with the capability of pointing to any position in the sky in 20 seconds or less to catch transients. A 2 ton 3x3 m camera, placed in the focus of the mirror, is equipped with 1855 high QE PMTs corresponding to a FoV of about 4.5 degrees. LSTs will dominate the CTA performance between 20 GeV and approximately 200 GeV. The first LST (LST-1) was inaugurated in La Palma (Spain) in October 2018 and since then it is in the commissioning phase. The current status and performance of the LST-1 are discussed. The telescope behavior is well understood and the performance has reached the design level in terms of sensitivity, angular and energy resolutions. Still some work is needed to achieve the duty cycle goal. We briefly present here some of the first physics results. Finally the outlooks of the project are presented.
ABSTRACT
The X-ray and γ-ray emission of globular clusters (GCs) is attributed to their large fraction of compact binary systems, especially those with millisecond pulsars (MSPs). We analyse a ...population of 124 Galactic GCs to investigate how their dynamical properties affect the formation and evolution of compact binary systems and how this can be translated into the clusters’ observed X-ray and γ-ray emission. We use mainly Chandra X-ray Observatory and Fermi Large Area Telescope observations to achieve our goals and start by detecting 39 GCs in γ rays, seven of which are not listed in previous Fermi-LAT catalogs. Additionally, we find that the total number of X-ray sources within a GC and its γ-ray luminosity are linearly correlated with the stellar encounter rate, indicating that compact binary systems are mainly formed via close stellar encounters. We also find an unexpected rise in the number of X-ray sources for GCs with low rates of stellar encounters, suggesting that there is a dynamical threshold where the formation of X-ray sources is dominated by stellar encounters. Furthermore, we use the Heggie-Hills law to find that subsequent stellar encounters in these compact binaries will, on average, make the binaries even harder, with basically no possibility of binary ionization. Finally, we find that all GCs are point-like sources in γ rays, indicating that the MSPs are concentrated in the clusters’ cores, likely due to dynamical friction.
ASTRI ("Astronomia a Specchi con Tecnologia Replicante Italiana") is a flagship project of the Italian Ministry of Research (MIUR), devoted to the realization, operation and scientific validation of ...an end-to-end prototype for the Small Size Telescope (SST) envisaged to become part of the Cherenkov Telescope Array (CTA). The ASTRI SST-2M telescope prototype is characterized by a dual mirror, Schwarzschild-Couder optical design and a compact camera based on silicon photo-multipliers. It will be sensitive to multi-TeV very high energy (VHE) gamma rays up to 100 TeV, with a PSF ~ 6' and a wide (9.6°) unaberrated optical field of view. Right after validation of the design in single-dish observations at the Serra La Nave site (Sicily, Italy) during 2015, the ASTRI collaboration will be able to start deployment, at the final CTA southern site, of the ASTRI mini-array, proposed to constitute the very first CTA precursor. Counting 9 ASTRI SST-2M telescopes, the ASTRI mini-array will overtake current IACT systems in differential sensitivity above 5 TeV, thus allowing unprecedented observations of known and predicted bright TeV emitters in this band, including some extragalactic sources such as extreme high-peaked BL Lacs with hard spectra. We exploited the ASTRI scientific simulator ASTRIsim in order to understand the feasibility of observations tackling blazar and cosmic ray physics, including discrimination of hadronic and leptonic scenarios for the VHE emission from BL Lac relativistic jets and indirect measurements of the intergalactic magnetic field and of the extragalactic background light. We selected favorable targets, outlining observation modes, exposure times, multi-wavelength coverage needed and the results expected. Moreover, the perspectives for observation of effects due to the existence of axion-like particles or to Lorentz invariance violations have been investigated.
The prototype Schwarzschild-Couder Telescope (pSCT) is a candidate for a medium-sized telescope in the Cherenkov Telescope Array. The pSCT is based on a novel dual mirror optics design which reduces ...the plate scale and allows for the use of silicon photomultipliers as photodetectors. The prototype pSCT camera currently has only the central sector instrumented with 25 camera modules (1600 pixels), providing a 2.68\(^{\circ}\) field of view (FoV). The camera electronics are based on custom TARGET (TeV array readout with GSa/s sampling and event trigger) application specific integrated circuits. Field programmable gate arrays sample incoming signals at a gigasample per second. A single backplane provides camera-wide triggers. An upgrade of the pSCT camera is in progress, which will fully populate the focal plane. This will increase the number of pixels to 11,328, the number of backplanes to 9, and the FoV to 8.04\(^{\circ}\). Here we give a detailed description of the pSCT camera, including the basic concept, mechanical design, detectors, electronics, current status and first light.
The X-ray and $\gamma$-ray emission of globular clusters (GCs) is attributed
to their large fraction of compact binary systems, especially those with
millisecond pulsars (MSPs). We analyze a ...population of 124 Galactic GCs to
investigate how their dynamical properties affect the formation and evolution
of compact binary systems and how this can be translated into the clusters'
observed X-ray and $\gamma$-ray emission. We use mainly Chandra X-ray
Observatory and Fermi Large Area Telescope observations to achieve our goals
and start by detecting 39 GCs in $\gamma$ rays, seven of which are not listed
in previous Fermi-LAT catalogs. Additionally, we find that the total number of
X-ray sources within a GC and its $\gamma$-ray luminosity are linearly
correlated with the stellar encounter rate, indicating that compact binary
systems are mainly formed via close stellar encounters. We also find an
unexpected rise in the number of X-ray sources for GCs with low rates of
stellar encounters, suggesting that there is a dynamical threshold where the
formation of X-ray sources is dominated by stellar encounters. Furthermore, we
use the Heggie-Hills law to find that subsequent stellar encounters in these
compact binaries will, on average, make the binaries even harder, with
basically no possibility of binary ionization. Finally, we find that all GCs
are point-like sources in $\gamma$ rays, indicating that the MSPs are
concentrated in the clusters' cores, likely due to dynamical friction.
Advanced knowledge of the detailed atmospheric properties of both the future sites of the Cherenkov Telescope Array is essential in preparation of the arrival of the first scientific data. ...Meteorological variables are studied using a dedicated characterization station installed at the southern site in Chile and a wealth of data from existing observatories around the northern site on the La Palma island. Campaigns using radiosondes launched on balloons are foreseen to complement these data in the near future. Cloudiness during the night has been continuously monitored at both sites for several years using All-sky Cameras which assess the presence of clouds based on detection of stars. The integrated aerosol optical depth over the southern site has been measured using a Sun/Moon Photometer since 2016 and the small robotic FRAM telescope since 2017; identical instruments have been deployed at the northern site in autumn 2018. Also in October 2018, the ARCADE Raman lidar (RL) has started to take measurements on routine basis at the northern site, providing data on the vertical profile of the aerosol optical properties (i.e., extinction and scattering) and of the water vapour mixing ratio. We present the data currently available from these instruments from both sites with emphasis on characteristics important for the (future) operation of Imaging Atmospheric Cherenkov Telescopes.
A Central Laser Facility is a system often used in astroparticle experiments based on arrays of fluorescence or Cherenkov light detectors. The instrument is based on a laser source positioned at a ...certain distance from the array, emitting fast light pulses in the vertical direction with the aim of calibrating the array and/or measuring the atmospheric transmission. In view of the future Cherenkov Telescope Array (CTA), a similar device could provide a calibration of the whole installation, both relative, i.e. each individual telescope with respect to the rest of the array, and absolute, with a precision better than 10%, if certain design requirements are met. Additionally, a precise monitoring of the sensitivity of each telescope can be made on time-scales of days to years. During calibration runs of the central laser facility, all detectors will be pointed towards the same portion of the laser beam at a given altitude. Simulations of the possible configurations of a Central Laser Facility for CTA (varying laser energy, pointing height and distance from the telescopes) have been performed
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