Search for pulsed VHE gamma-ray emission from young pulsars with HESS

¹ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany e-mail: stefan.schlenker@cern.ch
² Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
³ Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, 9 av. du Colonel Roche, BP 4346, 31029 Toulouse Cedex 4, France
⁴ Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
⁵ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
⁶ LUTH, UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, 92195 Meudon Cedex, France
⁷ DAPNIA/DSM/CEA, CE Saclay, 91191 Gif-sur-Yvette Cedex, France
⁸ University of Durham, Department of Physics, South Road, Durham DH1 3LE, UK
⁹ Unit for Space Physics, North-West University, Potchefstroom 2520, South Africa
¹⁰ Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
¹¹ Laboratoire Leprince-Ringuet, IN2P3/CNRS, École Polytechnique, 91128 Palaiseau, France
¹² Laboratoire d'Annecy-le-Vieux de Physique des Particules, IN2P3/CNRS, 9 Chemin de Bellevue – BP 110, 74941 Annecy-le-Vieux Cedex, France
¹³ European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
¹⁴ APC, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France (UMR 7164 (CNRS, Université Paris VII, CEA, Observatoire de Paris))
¹⁵ Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
¹⁶ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
¹⁷ Laboratoire de Physique Théorique et Astroparticules, IN2P3/CNRS, Université Montpellier II, CC 70, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
¹⁸ Universität Erlangen-Nürnberg, Physikalisches Institut, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
¹⁹ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
²⁰ Australia Telescope National Facility, CSIRO, PO Box 76, Epping NSW 1710, Australia
²¹ Laboratoire de Physique Nucléaire et de Hautes Énergies, IN2P3/CNRS, Universités Paris VI & VII, 4 place Jussieu, 75252 Paris Cedex 5, France
²² Institute of Particle and Nuclear Physics, Charles University, V Holesovickach 2, 180 00 Prague 8, Czech Republic
²³ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
²⁴ University of Namibia, Private Bag 13301, Windhoek, Namibia

Received: 11 November 2006
Accepted: 8 February 2007

Abstract

Aims.We present the results of a search for pulsed very-high-energy (VHE) γ-ray emission from young pulsars using data taken with the HESS imaging atmospheric Cherenkov telescope system.

Methods.Data on eleven pulsars, selected according to their spin-down luminosity relative to distance, are searched for γ-ray signals with periodicity at the respective pulsar spin period. Special analysis efforts were made to improve the sensitivity in the 100 GeV γ-ray energy domain in an attempt to reduce the gap between satellite and ground-based γ-ray instruments.

Results.No significant evidence for pulsed emission is found in any data set. Differential upper limits on pulsed energy flux are determined for all selected pulsars in the approximate γ-ray energy range between 100 GeV and 50 TeV, using different limit determination methods, testing a wide range of possible pulsar light curves and energy spectra.

Conclusions.The limits derived here imply that the magnetospheric VHE γ-ray production efficiency in young pulsars is less than 10^-4 of the pulsar spin-down luminosity, requiring spectral turnovers for the high-energy emission of four established γ-ray pulsars, and constrain the inverse Compton radiation component predicted by several outer gap models.