Discovery of TeV Gamma Rays from SN 1006: Further Evidence for the Supernova Remnant Origin of Cosmic Rays

In this Letter we report the discovery of TeV gamma-ray emission from a supernova remnant made with the CANGAROO 3.8 m telescope. TeV gamma rays were detected at the sky position and extension coincident with the northeast rim of shell-type supernova remnant (SNR) SN 1006 (Type Ia). SN 1006 has been a most likely candidate for an extended TeV gamma-ray source, since the clear synchrotron X-ray emission from the rims was recently observed by ASCA (Koyama et al.), which is strong evidence for the existence of very high energy (up to hundreds of TeV) electrons in the SNR. The observed TeV gamma-ray flux was (2.4±0.5 [statistical]±0.7 [systematic])×10−12 cm-2 s-1 (≥3.0±0.9 TeV) and (4.6±0.6±1.4)×10−12 cm-2 s-1 (≥1.7±0.5 TeV) from the 1996 and 1997 observations, respectively. Also, we set an upper limit on the TeV gamma-ray emission from the southwest rim, which is estimated to be 1.1×10−12 cm-2 s-1 (≥1.7±0.5 TeV, 95% confidence level) in the 1997 data. The TeV gamma rays can be attributed to the 2.7 K cosmic background photons upscattered by electrons of energies up to about 1014 eV by the inverse Compton process. The observed flux of the TeV gamma rays, together with that of the nonthermal X-rays, gives firm constraints on the acceleration process in the SNR shell; a magnetic field of 6.5±2 μG is inferred from both the synchrotron X-rays and the inverse Compton TeV gamma rays, which provides entirely consistent evidence that electrons of energies up to 1014 eV are produced via shock acceleration in SN 1006.