July 29, 2015 to August 6, 2015
World Forum
Europe/Amsterdam timezone

Studies towards an understanding of global array pointing for the Cherenkov Telescope Array

Aug 4, 2015, 4:00 PM
Mississippi Foyer (World Forum)

Mississippi Foyer

World Forum

Churchillplein 10 2517 JW Den Haag The Netherlands
Board: 120
Poster contribution GA-IN Poster 3 GA


Alexander Ziegler (ECAP, University of Erlangen-Nuremberg, Germany)


Current arrays of Imaging Atmospheric Cherenkov Telescopes (IACTs) routinely achieve an astrometric point-source location accuracy of 20-30 seconds of arc (given large photon statistics), which is well below the angular resolution obtained for individual photons. The location accuracy is mainly limited by systematic uncertainties due to possible deformations of the telescopes’ structures, causing a mis-orientation between the nominal optical axes of the telescopes and their actual pointing directions. Usually, only a subset of telescopes is triggered for a given gamma-ray event, and their mis-orientations enter the gamma-ray direction reconstruction in a combined manner. Hence, in general, the average location accuracy for a set of gamma-ray observations depends in a complex way on the individual telescope accuracy and the geometry of the array, but also on the observing conditions, the energy spectrum of the source and the chosen event selection cuts. For the proposed Cherenkov Telescope Array (CTA), a post-calibration point-source location accuracy of 3 seconds of arc is aimed for under favorable observing conditions and for gamma-ray energies exceeding 100 GeV. In this contribution, results of first studies on the location accuracy are presented. These studies are based on a toy Monte Carlo simulation of a typical CTA-South array layout, taking into account the expected trigger rates of the different CTA telescope types and the gamma-ray spectrum of the simulated source. With this simulation code it is possible to study the location accuracy as function of arbitrary telescope mis-orientations and for typical observing patterns on the sky. Results are presented for various scenarios, including one for which all individual telescopes are randomly mis-oriented within their specified limits. The study provides solid lower limits for the expected source location accuracy of CTA, and can be easily extended to include various other important effects like atmospheric refraction or partial cloud coverage.
Registration number following "ICRC2015-I/" 502
Collaboration CTA

Primary author

Stefan Eschbach (ECAP, University of Erlangen-Nuremberg, Germany)


Alexander Ziegler (ECAP, University of Erlangen-Nuremberg, Germany) Christopher van Eldik (ECAP, University of Erlangen-Nuremberg, Germany) David Berge (NIKHEF (NL)) Johannes Veh (ECAP, University of Erlangen-Nuremberg, Germany) Markus Gaug (Universitat Autònoma de Barcelona)

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