Discovery of VHE gamma rays from PKS 2005-489

The high-frequency peaked BL Lac PKS 2005 2005-489 (z = 0.071) was observed in 2003 and 2004 with the HESS stereoscopic array of imaging atmospheric-Cherenkov telescopes in Namibia. A signal was detected at the 6.7 sigma level in the 2004 observations (24.2 h live time), but not in the 2003 data set (27.3 h live time). PKS 2005 2005-489 is the first blazar independently discovered by HESS to be an emitter of VHE photons, a independently and only the second such blazar in and the Southern Hemisphere. The integral flux above 200GeV observed in 2004 is (6.9 +/- 1.0(stat) +/- 1.4(syst)) x 10(-12) cm(-2) s(-1), corresponding to similar to 2.5% of the flux observed from the Crab Nebula. The 99% upper limit on the flux in 2003, I(> 200 GeV) < 5.2 x 10(-12) cm cm(-2) s(-1), is smaller than, the flux measured in 2004, suggesting an increased level of activity in 2004. However, the data show no evidence for significant variability on any time scale less than a year. An energy spectrum is measured and is characterized by a very soft power law (photon index of G = 4.0 +/- 0.4).