The current generation of ground-based imaging atmospheric Cherenkov telescopes (IACTs) operate in the very-high-energy (VHE) domain from ~100 GeV to ~100 TeV. They use electronic digital trigger ...systems to discern the Cherenkov light flashes emitted by extensive air showers (EASs), from the overwhelming light of the night sky (LoNS) background. Near the telescope energy threshold, the number of emitted Cherenkov photons by gamma-ray-induced EASs is comparable to the fluctuations of the LoNS and the photon distribution at the Cherenkov-imaging camera plane becomes patchy. This results in a severe loss of effectiveness of the digital triggers based on combinatorial logic of thresholded signals. A stereoscopic analog trigger system has been developed for improving the detection capabilities of the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes at the lowest energies. It is based on the analog sum of the photosensor electrical signals. In this article, the architectural design, technical performances, and configuration of this stereoscopic analog trigger, dubbed " Sum-Trigger-II ," are described.
This paper describes the concept of an FPGA-based digital camera trigger for imaging atmospheric Cherenkov telescopes, developed for the future Cherenkov Telescope Array (CTA). The proposed camera ...trigger is designed to select images initiated by the Cherenkov emission of extended air showers from very-high energy (VHE, E>20GeV) photons and charged particles while suppressing signatures from background light. The trigger comprises three stages. A first stage employs programmable discriminators to digitize the signals arriving from the camera channels (pixels). At the second stage, a grid of low-cost FPGAs is used to process the digitized signals for camera regions with 37 pixels. At the third stage, trigger conditions found independently in any of the overlapping 37-pixel regions are combined into a global camera trigger by few central FPGAs. Trigger prototype boards based on Xilinx FPGAs have been designed, built and tested and were shown to function properly. Using these components a full camera trigger with a power consumption and price per channel of about 0.5W and 19€, respectively, can be built. With the described design the camera trigger algorithm can take advantage of pixel information in both the space and the time domain allowing, for example, the creation of triggers sensitive to the time-gradient of a shower image; the time information could also be exploited to online adjust the time window of the acquisition system for pixel data. Combining the results of the parallel execution of different trigger algorithms (optimized, for example, for the lowest and highest energies, respectively) on each FPGA can result in a better response over all photons energies (as demonstrated by Monte Carlo simulation in this work).
We have designed and implemented a new trigger concept (hereafter called sumtrigger) for Cherenkov telescopes, which allowed us to lower the trigger threshold of the MAGIC telescope by a factor of ...two to 25 GeV. For the new trigger, we subdivided the camera in 24 overlapping patches, each patch consisting of 18 pixels. In each patch the clipped analog signals of all pixels are summed and the trigger decision is subsequently derived from the summed signal. The clipping of the individual analog signals before summing prevented accidental triggers from large afterpulses of the photomultipliers (PMT). Special emphasis were put in the design of the analog part of the electronics to preserve the fast characteristics of the PMT signals. The 2.6 ns FWHM of the analog signals results in an effective coincidence window of about 3 ns, thus strongly suppressing accidental triggers caused by fluctuations of the night sky background (NSB). In the sumtrigger all pixels of one patch contribute to the trigger decision. For 25 GeV gamma-ray showers, a patch size of 18 PMT maximizes the signal to noise ratio of the air shower signal over the fluctuations of the NSB. In combination with the clipping of the signals before forming the sum we achieved a factor of two lower trigger threshold of the sumtrigger compared to the standard MAGIC trigger. The sumtrigger was successfully used to detect pulsed gamma-ray emission from the Crab Pulsar with the MAGIC telescope.
A device for noninvasive measurement of the repetition frequency of single-motor-unit action potential is described. The device was built using virtual instruments in LabVIEW software. The ...mathematical foundations of the measurement method and results are presented.
The article presents a method for obtaining quantitative signs of pulmonary pathology, based on the analysis of medical imaging computed tomography. These signs may be suitable for the differential ...diagnosis of spherical lung formations. In particular, the possibility of diagnosing cancer and pulmonary tuberculosis was investigated by quantitative statistical characteristics of images of spherical lung formations. Two of these characteristics (the densitometric value and its standard deviation) can be called classical, since modern basic software of computer tomographs can easily calculate them. In addition, characteristics were considered, for which it is necessary to carry out additional calculations using fractal analysis. The article presents the results of a study of the relationship of statistical and fractal characteristics of a tomographic image with the type of pathology in the lungs. The results of a statistical analysis of the fractal dimension of the region of interest and its related parameters are presented, and signs are found suitable for the diagnosis of pulmonary pathologies.
Selection of photomultipliers for the Cherenkov Telescope Array facility Shayduk, M.; Mirzoyan, R.; Zimmer, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2010, Volume:
617, Issue:
1
Journal Article
Peer reviewed
The future ground-based gamma-ray facility—Cherenkov Telescope Array (CTA)—is aiming for a sensitivity of 1
mCrab at energies above 20
GeV. This goal in sensitivity is aiming for an order of ...magnitude increase compared to currently operating instruments H.E.S.S., MAGIC, CANGAROO III and VERITAS. In order to provide high sensitivity and low energy threshold the photosensors should have highest possible photon detection efficiency (PDE), low after-pulsing rate and good single photoelectron resolution. Photosensors of Cherenkov telescopes are permanently exposed to the background light of the night sky, therefore a long life time and low fatigue are also necessary conditions.
Various photomultipliers (PMT) of 1–2
in. size from PHOTONIS and HAMAMATSU were tested in MPI for Physics in Munich. Comparative measurements of quantum efficiency, timing, after-pulsing and single photoelectron resolution will be presented here. An evaluation of Electron Tubes photomultipliers is ongoing
Context. Very high-energy (VHE, E > 100 GeV) γ-ray data are a valuable input for multi-wavelength and multi-messenger (e.g. combination with neutrino data) studies. Aims. We aim at the conservation ...and homogenization of historical, current, and future VHE γ-ray-data on active galactic nuclei (AGN). Methods. We have collected lightcurve data taken by major VHE experiments since 1991 and combined them into long-term lightcurves for several AGN, and now provide our collected datasets for further use. Due to the lack of common data formats in VHE γ-ray astronomy, we have defined relevant datafields to be stored in standard data formats. The time variability of the combined VHE lightcurve data was investigated, and correlation with archival X-ray data collected by RXTE/ASM tested. Results. The combination of data on the prominent blazar Mrk 421 from different experiments yields a lightcurve spanning more than a decade. From this combined dataset we derive an integral baseline flux from Mrk 421 that must be lower than 33% of the Crab Nebula flux above 1 TeV. The analysis of the time variability yields log-normal flux variations in the VHE-data on Mrk 421. Conclusions. Existing VHE data contain valuable information concerning the variability of AGN and can be an important ingredient for multi-wavelength or multi-messenger studies. In the future, upcoming and planned experiments will provide more data from many transient objects, and the interaction of VHE astronomy with classical astronomy will intensify. In this context a unified and exchangeable data format will become increasingly important.
► Extensive simulations for the design and optimization of CTA were carried out. ► Different sets of simulation tools were checked against each other. ► Large-scale simulations with 275 telescopes ...for later layout selection.► Different analysis methods were applied and compared. ► Resulting sensitivity predictions confirmed the goals of CTA.
The Cherenkov Telescopes Array (CTA) is planned as the future instrument for very-high-energy (VHE) gamma-ray astronomy with a wide energy range of four orders of magnitude and an improvement in sensitivity compared to current instruments of about an order of magnitude. Monte Carlo simulations are a crucial tool in the design of CTA. The ultimate goal of these simulations is to find the most cost-effective solution for given physics goals and thus sensitivity goals or to find, for a given cost, the solution best suited for different types of targets with CTA. Apart from uncertain component cost estimates, the main problem in this procedure is the dependence on a huge number of configuration parameters, both in specifications of individual telescope types and in the array layout. This is addressed by simulation of a huge array intended as a superset of many different realistic array layouts, and also by simulation of array subsets for different telescope parameters. Different analysis methods – in use with current installations and extended (or developed specifically) for CTA – are applied to the simulated data sets for deriving the expected sensitivity of CTA. In this paper we describe the current status of this iterative approach to optimize the CTA design and layout.
MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma. Since autumn 2009 both telescopes have been working together in stereoscopic mode, ...providing a significant improvement with respect to the previous single-telescope observations. We use observations of the Crab Nebula taken at low zenith angles to assess the performance of the MAGIC stereo system. The trigger threshold of the MAGIC telescopes is 50−60GeV. Advanced stereo analysis techniques allow MAGIC to achieve a sensitivity as good as (0.76±0.03)% of the Crab Nebula flux in 50h of observations above 290GeV. The angular resolution at those energies is better than ∼0.07°. We also perform a detailed study of possible systematic effects which may influence the analysis of the data taken with the MAGIC telescopes.
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