Discovery of a new TeV gamma-ray source BL Lac object 1ES 1959+650

西山 孝文


   BL Lac object 1ES 1959+650 with a redshift of z=0.048 has been observed by using the Utah Seven Telescope Array detector at Dugway, Utah, for 56.7 hours from May, 1998 to August, 1998.
   Event excesses with significances of 5.3 σ and 5.0 σ were obtained for the data from MJD 50956 to MJD 50965 and from MJD 50996 to MJD 51023, respectively from the direction of the object, which shows the evidence of VHE gamma-ray emission from 1ES 1959+650.
   Excess of 3.9 σ was obtained from the analysis of all data taken in 1998. Variability of the VHE gamma-ray emission was seen from the light curve.
   We have discovered the BL Lac 1ES 1959+650 as the source emitting TeV gamma rays.