Evidence for TeV gamma-ray emission from the shell type SNR RXJ1713.7-3946

We report the results of TeV gamma-ray observa- tions of the shell type SNR RX J1713.7 3946 (G347.3 0.5). The discovery of strong non-thermal X-ray emission from the northwest part of the remnant strongly suggests the existence of electrons with energies up to 100 TeV in the remnant, making the SNR a good candidate TeV gamma-ray source. We observed RX J1713.7 3946 from May to August 1998 with the CANGAROO 3.8m atmospheric imaging ˇ Cerenkov telescope and obtained evidence for TeV gamma-ray emission from the NW rim of the remnant with the significance of 5:6. The observed TeV gamma-ray flux from the NW rim region was es- timated to be (5.3 0.9(statistical) 1.6(systematic)) 10 12 photons cm 2 s 1 at energies 1.8 0.9 TeV. The data in- dicate that the emitting region is much broader than the point spread function of our telescope. The extent of the emission is consistent with that of hard X-rays observed by ASCA. This TeV gamma-ray emission can be attributed to the Inverse Comp- ton scattering of the Cosmic Microwave Background Radiation by shock accelerated ultra-relativistic electrons. Under this as- sumption, a rather low magnetic field of 11G is deduced for the remnant from our observation.