HESS observations of γ-ray bursts in 2003–2007

¹ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany e-mail: phtam@lsw.uni-heidelberg.de
² Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
³ Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
⁴ University of Durham, Department of Physics, South Road, Durham DH1 3LE, UK
⁵ Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, 9 Av. du Colonel Roche, BP 4346, 31029 Toulouse Cedex 4, France
⁶ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
⁷ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
⁸ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
⁹ IRFU/DSM/CEA, CE Saclay, 91191 Gif-sur-Yvette Cedex, France
¹⁰ Universität Erlangen-Nürnberg, Physikalisches Institut, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
¹¹ Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
¹² Unit for Space Physics, North-West University, Potchefstroom 2520, South Africa
¹³ Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
¹⁴ LPNHE, Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, CNRS/IN2P3, 4 place Jussieu, 75252 Paris Cedex 5, France
¹⁵ Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/ IN2P3, 91128 Palaiseau, France
¹⁶ Laboratoire d'Annecy-le-Vieux de Physique des Particules,CNRS/IN2P3, 9 chemin de Bellevue, BP 110, 74941 Annecy-le-Vieux Cedex, France
¹⁷ Astroparticule et Cosmologie (APC), CNRS, Université Paris 7 Denis Diderot, 10, rue Alice Domon et Leonie Duquet, 75205 Paris Cedex 13, France (UMR 7164, CNRS, Université Paris VII, CEA, Observatoire de Paris)
¹⁸ Instytut Fizyki Jądrowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
¹⁹ Laboratoire de Physique Théorique et Astroparticules, CNRS/IN2P3, Université Montpellier II, CC 70, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
²⁰ Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
²¹ School of Physics & Astronomy, University of Leeds, Leeds LS2 9JT, UK
²² Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
²³ Toruń Centre for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, 87-100 Toruń, Poland
²⁴ Institute of Particle and Nuclear Physics, Charles University, V Holesovickach 2, 180 00 Prague 8, Czech Republic
²⁵ European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
²⁶ Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland
²⁷ School of Chemistry & Physics, University of Adelaide, Adelaide 5005, Australia
²⁸ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
²⁹ University of Namibia, Private Bag 13301, Windhoek, Namibia

Received: 2 October 2008
Accepted: 22 December 2008

Abstract

Aims. Very-high-energy (VHE; 100 GeV) γ-rays are expected from γ-ray bursts (GRBs) in some scenarios. Exploring this photon energy regime is necessary for understanding the energetics and properties of GRBs.

Methods. GRBs have been one of the prime targets for the HESS experiment, which makes use of four Imaging Atmospheric Cherenkov Telescopes (IACTs) to detect VHE γ-rays. Dedicated observations of 32 GRB positions were made in the years 2003–2007 and a search for VHE γ-ray counterparts of these GRBs was made. Depending on the visibility and observing conditions, the observations mostly start minutes to hours after the burst and typically last two hours.

Results. Results from observations of 22 GRB positions are presented. Evidence of a VHE signal was found neither in observations of any individual GRBs nor from stacking data from subsets of GRBs with higher expected VHE flux according to a model-independent ranking scheme. Upper limits for the VHE γ-ray flux from the GRB positions were derived. For those GRBs with measured redshifts, differential upper limits at the energy threshold after correcting for absorption due to extra-galactic background light are also presented.