Arguments against a dominantly hadronic origin of the VHE radiation from the supernova remnant RX J1713-3946

The flux of photons above 1 TeV from the direction of the centre and a cloud in the western part of the nearby southern supernova remnant (SNR) RX J1713.7-3946 is calculated in the hadronic scenario that aims to explain the intense VHE radiation from this remnant with the decay of pi(0) pions produced in nuclear collisions. The expected flux from its centre is found to fall short by about factor 40 from the one observed by the HESS collaboration. This discrepancy presents a serious obstacle to the hadronic scenario. The theoretically expected flux from the molecular cloud exceeds the one observed by HESS by at least a factor 3. While the size of this discrepancy might still seem acceptable in the face of various theoretical uncertainties, the result strongly suggests a strict spatial correlation of the cloud with an excess of TeV gamma-radiation. The observational lack of such correlations in the remnant reported by HESS is another counter argument against the hadronic scenario. In combination these arguments cannot be refuted by choosing certain parameters for the total energy or acceleration efficiency of the SNR. (C) 2007 Elsevier B.V. All rights reserved.