Upper limits to the SN1006 multi-TeV gamma-ray flux from HESS observations

Observations of the shell-type supernova remnant SN1006 have been carried out with the HESS system of Cherenkov telescopes during 2003 (18.2 h with two operating telescopes) and 2004 (6.3 h with all four telescopes). No evidence for TeV γ-ray emission from any compact or extended region associated with the remnant is seen and resulting upper limits at the 99.9% confidence level are up to a factor 10 lower than previously-published fluxes from CANGAROO. For SN1006 at its current epoch of evolution we define limits for a number of important global parameters. Upper limits on the γ-ray luminosity (for E = 0.26 to 10 TeV, distance d = 2 kpc) of L _γ < 1.7 × 10 ³³ erg s ^-1, and the total energy in corresponding accelerated protons, W _p < 1.6 × 10 ⁵⁰ erg are estimated (for proton energies E _p ∼ 1.5 to 60 TeV and assuming the lowest value n = 0.05 cm ^-3 of the ambient target density discussed in literature). Extending this estimate to cover the range of proton energies observed in the cosmic ray spectrum up to the knee (we take here E _p ∼ 1 GeV to 3 PeV, assuming a differential particle index -2) gives W _p < 6.3 × 10 ⁵⁰ erg. A lower limit on the post-shock magnetic field of B > 25 μG results when considering the synchrotron/inverse-Compton framework for the observed X-ray flux and γ-ray upper limits.