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

(Astron. Astrophys., in press)

H. Muraishi, T. Tanimori, S. Yanagita, T. Yoshida, M. Moriya, T. Kifune, S.A. Dazeley, P.G. Edwards, S. Gunji, S. Hara, T. Hara, A. Kawachi, H. Kubo, Y. Matsubara, Y. Mizumoto, M. Mori, Y. Muraki, T.Naito, K. Nishijima, J.R. Patterson, G.P. Rowell, T. Sako, K. Sakurazawa, R. Susukita, T. Tamura and T. Yoshikoshi

We report the results of TeV gamma-ray observations of the shell type SNR RXJ1713.7-3946 (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 RXJ1713.7-3946 from May to August 1998 with the CANGAROO 3.8m atmospheric imaging Cerenkov telescope and obtained evidence for TeV gamma-ray emission from the NW rim of the remnant with the significance of 5.6 sigma. The observed TeV gamma-ray flux from the NW rim region was estimated 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 indicate 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 Compton scattering of the Cosmic Microwave Background Radiation by shock accelerated ultra-relativistic electrons. Under this assumption, a rather low magnetic field of 11 micro gauss is deduced for the remnant from our observation.