HESS upper limits for Kepler's supernova remnant

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 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 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 . © 2008 ESO.