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Title: Upgrading and testing the 3D reconstruction of gamma-ray air showers as observed with an array of Cherenkov telescopes

Abstract

Stereoscopic arrays of Imaging Cherenkov Telescopes allow to reconstruct gamma-ray-induced showers in 3 dimensions. An analysis method based on a simple 3D-model of electromagnetic showers and implemented in the framework of the H.E.S.S. experiment was recently improved by an additional quality criterion which reduces the background contamination by a factor of about 2 in the case of extended sources, while hardly affecting gamma-ray selection efficiency. Moreover, the dramatic flares of PKS 2155-304 in July 2006, which provided H.E.S.S. data with an almost pure gamma-ray sample, offered the unique opportunity of a precision test of the 3D-reconstruction method as well as of the H.E.S.S. simulations used in its calibration. An agreement at a few percent level is found between data and simulations for the distributions of all 3D shower parameters.

Authors:
;  [1];  [2]
  1. Laboratoire Leprince-Ringuet, IN2P3/CNRS, Ecole Polytechnique, F 91128 Palaiseau Cedex (France)
  2. Centre d'Etudes Nucleaires de Bordeaux-Gradignan, Chemin du solarium, BP 120, F 33175 Gradignan Cedex (France)
Publication Date:
OSTI Identifier:
21255180
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1085; Journal Issue: 1; Conference: 4. international meeting on high energy gamma-ray astronomy, Heidelberg (Germany), 7-11 Jul 2008; Other Information: DOI: 10.1063/1.3076787; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; 99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; CALIBRATION; EXTENSIVE AIR SHOWERS; GAMMA ASTRONOMY; GAMMA RADIATION; IMAGE PROCESSING; PULSARS; SIMULATION; TELESCOPES

Citation Formats

Naumann-Godo, Melitta, Degrange, Bernard, and Lemoine-Goumard, Marianne. Upgrading and testing the 3D reconstruction of gamma-ray air showers as observed with an array of Cherenkov telescopes. United States: N. p., 2008. Web. doi:10.1063/1.3076787.
Naumann-Godo, Melitta, Degrange, Bernard, & Lemoine-Goumard, Marianne. Upgrading and testing the 3D reconstruction of gamma-ray air showers as observed with an array of Cherenkov telescopes. United States. doi:10.1063/1.3076787.
Naumann-Godo, Melitta, Degrange, Bernard, and Lemoine-Goumard, Marianne. Wed . "Upgrading and testing the 3D reconstruction of gamma-ray air showers as observed with an array of Cherenkov telescopes". United States. doi:10.1063/1.3076787.
@article{osti_21255180,
title = {Upgrading and testing the 3D reconstruction of gamma-ray air showers as observed with an array of Cherenkov telescopes},
author = {Naumann-Godo, Melitta and Degrange, Bernard and Lemoine-Goumard, Marianne},
abstractNote = {Stereoscopic arrays of Imaging Cherenkov Telescopes allow to reconstruct gamma-ray-induced showers in 3 dimensions. An analysis method based on a simple 3D-model of electromagnetic showers and implemented in the framework of the H.E.S.S. experiment was recently improved by an additional quality criterion which reduces the background contamination by a factor of about 2 in the case of extended sources, while hardly affecting gamma-ray selection efficiency. Moreover, the dramatic flares of PKS 2155-304 in July 2006, which provided H.E.S.S. data with an almost pure gamma-ray sample, offered the unique opportunity of a precision test of the 3D-reconstruction method as well as of the H.E.S.S. simulations used in its calibration. An agreement at a few percent level is found between data and simulations for the distributions of all 3D shower parameters.},
doi = {10.1063/1.3076787},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1085,
place = {United States},
year = {Wed Dec 24 00:00:00 EST 2008},
month = {Wed Dec 24 00:00:00 EST 2008}
}
  • H.E.S.S. (High Energy Stereoscopic System) is an array of four large imaging Cherenkov telescopes devoted to gamma-ray astronomy above 100 GeV. It has been fully operational since December 2003. Here, we report on a new analysis method based on a simple 3D-modeling of an electromagnetic air shower. This method allows to separate gamma-rays from background events in the field of view without any assumption on the morphology of the source or on the background distribution. This is a crucial point in the study of extended sources (e.g. Supernova Remnants) or in the search for unexpected sources in a sky survey.more » The performance and results of this method on galactic sources are presented.« less
  • We present a Monte-Carlo study of the phenomenology of Cherenkov light wavefronts from low energy gamma ray induced air showers. Experimentally the measurements of the spatially distributed arrival times of the wavefronts of the Cherenkov light of gamma ray air showers have been used to extract the directions of the showers. This has mainly been done for >500 GeV showers using a conical fit to the timing structure of the wavefront. This directionality is then used to contribute to the rejection of background showers (mainly hadron induced showers) which arrive isotropically. Investigation of the arrival times of simulated Cherenkov photonsmore » from gamma ray induced air showers of energies 100 GeV and below reveals that there is greater variation in the morphology of the wavefronts than at the higher energies and that the fitting of simple conical functions to determine arrival directions may no longer be appropriate. We demonstrate that the detailed structure of the wavefront of these low energy gamma ray showers is primarily determined by the height distribution of the emitting cascade particles. Preliminary work suggests a correlation between the shape of the wavefront and the height of shower-maximum.« less
  • The {gamma}-astronomy with Cherenkov telescope has recently made great progress coming to the 2nd generation of instruments. The higher sensitivity and lower energy threshold have brought to discover new sources. The determination of their spectra, necessary for developing models for acceleration, emission and absorption of the {gamma}-rays, will shed new light on the century-old problem of the origin of galactic cosmic rays.A short summary of the current physics objectives in the {gamma}-astronomy and a description of the Cherenkov telescopes technique is given. Some representative observations from the two operative telescopes, HESS and MAGIC are described.