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Register a new userA possible use for polarizers in imaging atmospheric Cherenkov telescopes
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Added by
Jose Luis Contreras
Publication date
2001
fields
Physics
and research's language is
English
Authors
I. de la Calle
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No Arabic abstract
Cherenkov radiation produced in Extensive Air Showers shows a net polarization. This article discusses its properties and physical origin, and proposes an arrangement of polarizers potentially useful for Imaging Atmospheric Cherenkov Telescopes.
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A fast trigger system is being designed as a potential upgrade to VERITAS, or as the basis for a future array of imaging atmospheric-Cherenkov telescopes such as AGIS. The scientific goal is a reduction of the energy threshold by a factor of 2 over the current threshold of VERITAS of around 130 GeV. The trigger is being designed to suppress both accidentals from the night-sky background and cosmic rays. The trigger uses field-programmable gate arrays (FPGAs) so that it is adaptable to different observing modes and special physics triggers, e.g. pulsars. The trigger consists of three levels: The level 1 (L1.5) trigger operating on each telescope camera samples the discriminated pixels at a rate of 400 MHz and searches for nearest-neighbor coincidences. In L1.5, the received discriminated signals are delay-compensated with an accuracy of 0.078 ns, facilitating a short coincidence time-window between any nearest neighbor of 5 ns. The hit pixels are then sent to a second trigger level (L2) that parameterizes the image shape and transmits this information along with a GPS time stamp to the array-level trigger (L3) at a rate of 10 MHz via a fiber optic link. The FPGA-based event analysis on L3 searches for coincident time-stamps from multiple telescopes and carries out a comparison of the image parameters against a look-up table at a rate of 10 kHz. A test of the single-telescope trigger was carried out in spring 2009 on one VERITAS telescope.
Ground-based gamma-ray astronomy experienced a major boost with the advent of the present generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) in the past decade. Photons of energies >~ 0.1 TeV are a very useful tool in the study of several fundamental physics topics, which have become an important part of the research program of all major IACTs. A review of some recent results in the field is presented.
The annihilations of WIMPs produce high energy gamma-rays in the final state. These high energy gamma-rays may be detected by imaging atmospheric Cherenkov telescopes (IACTs). Amongst the plausible targets are the Galactic Center, the centre of galaxy clusters, dwarf Sphreroidal galaxies and substructures in Galactic haloes. I will review on the recent results from observations of ongoing IACTs.
By means of third-order optical theory as well as ray-tracing simulations we have investigated the feasibility of wide-field imaging atmospheric Cherenkov telescopes with a reflective prime-focus design. For a range of desired optical resolutions, we have determined the largest available field-of-view of single-piece spherical, single-piece parabolic, tessellated spherical, tessellated parabolic and Davies-Cotton designs, always considering a wide range of design parameters. The Davies-Cotton design exhibits a surprising similarity to the tessellated parabolic design in its qualitative behaviour. Also, elliptic telescope designs with better off-axis imaging properties than Davies-Cotton are presented. We show that by using f/2 optics it is possible to build prime-focus telescopes with a full field-of-view of 10 degree at 0.1 degree resolution.
We estimate the limiting angular resolution and detection area for an array of 3 large-aperture Imaging Atmospheric Cherenkov Telescopes. We consider an idealized IACT system in order to understand the limitations imposed by the intrinsic nature of the atmospheric showers and geometry of the detector configuration. The idealization includes the assumptions of a perfect optical system and the absence of the night sky background with the goal of finding the optimum camera geometry and array configuration independent of detailed assumptions about the telescope design. The showers are simulated using the ALTAI code for the altitude of 2700 m corresponding to one of possible future sites for a new northern-hemisphere array. The optimal design depends on the target energy range; for each energy we vary both the cell length (telescope spacing) and the image processing parameters in order to maximize the signal-to-noise ratio. We then present the resulting values of the detection area and the angular resolution for this energy dependent optimization. We discuss the dependence of these quantities on the field of view of the telescopes and pixel size of the camera.
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