HESS upper limits for Kepler's supernova remnant

¹ Max-Planck-Institut für Kernphysik, Heidelberg, Germany e-mail: dominik.hauser@mpi-hd.mpg.de
² Dublin Institute for Advanced Studies, Dublin, Ireland
³ Yerevan Physics Institute, Armenia
⁴ University of Durham, Department of Physics, UK
⁵ Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, Toulouse, France
⁶ Landessternwarte, Universität Heidelberg, Königstuhl, Heidelberg, Germany
⁷ Universität Hamburg, Institut für Experimentalphysik, Germany
⁸ Institut für Physik, Humboldt-Universität zu Berlin, Germany
⁹ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, Meudon, France
¹⁰ IRFU/DSM/CEA, CE Saclay, Gif-sur-Yvette, France
¹¹ Universität Erlangen-Nürnberg, Physikalisches Institut, Erlangen, Germany
¹² Nicolaus Copernicus Astronomical Center, Warsaw, Poland
¹³ Unit for Space Physics, North-West University, Potchefstroom, South Africa
¹⁴ Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, France
¹⁵ Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, Palaiseau, France
¹⁶ Laboratoire d'Annecy-le-Vieux de Physique des Particules, CNRS/IN2P3, Annecy-le-Vieux, France
¹⁷ European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
¹⁸ Astroparticule et Cosmologie (APC), CNRS, Universite Paris 7 Denis Diderot, 10, Paris, France (UMR 7164 (CNRS, Université Paris VII, CEA, Observatoire de Paris))
¹⁹ Laboratoire de Physique Théorique et Astroparticules, CNRS/IN2P3, Université Montpellier II, France
²⁰ School of Physics & Astronomy, University of Leeds, UK
²¹ Institut für Astronomie und Astrophysik, Universität Tübingen, Germany
²² Toruń Centre for Astronomy, Nicolaus Copernicus University, Toruń, Poland
²³ LPNHE, Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, CNRS/IN2P3, Paris, France
²⁴ Institute of Particle and Nuclear Physics, Charles University, Prague, Czech Republic
²⁵ Obserwatorium Astronomiczne, Uniwersytet Jagielloński, Kraków, Poland
²⁶ School of Chemistry & Physics, University of Adelaide, Australia
²⁷ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, Germany
²⁸ University of Namibia, Windhoek, Namibia

Received: 15 January 2008
Accepted: 12 June 2008

Abstract

Aims. Observations of Kepler's supernova remnant (G4.5+6.8) with the HESS telescope array in 2004 and 2005 with a total live time of 13 h are presented.

Methods. Stereoscopic imaging of Cherenkov radiation from extensive air showers is used to reconstruct the energy and direction of the incident gamma rays.

Results. No evidence for a very high energy (VHE: >100 GeV) gamma-ray signal from the direction of the remnant is found. An upper limit (99% confidence level) on the energy flux in the range of 8.6  is obtained.

Conclusions. In the context of an existing theoretical model for the remnant, the lack of a detectable gamma-ray flux implies a distance of at least . A corresponding upper limit for the density of the ambient matter of is derived. With this distance limit, and assuming a spectral index , the total energy in accelerated protons is limited to   . In the synchrotron/inverse Compton framework, extrapolating the power law measured by RXTE between 10 and down in energy, the predicted gamma-ray flux from inverse Compton scattering is below the measured upper limit for magnetic field values greater than .