2005/04/23 by F. Aharonian, The H. E. S. S. Collaboration, : +99
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #BL Lac object #Blazar #Cherenkov radiation #Crab Nebula #Dark Matter and Cosmic Phenomena #Flux (metallurgy) #Gamma ray #Neutrino Physics Research #Optics #Photon #Physics #astro-ph
paper · pdf · doi:10.1051/0004-6361:200500113
published as Astron.Astrophys. 436 (2005) L17-L20 · 5 pages, 2 figures, Accepted (April 20, 2005) for Publication in A&A Letters
arxiv created 2005/04/23 · openalex publication_date 2005/05/30 · arxiv updated 2012/08/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The high-frequency peaked BL Lac PKS 2005-489 () 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 σ level in the 2004 observations (24.2 h live time), but not in the 2003 data set (27.3 h live time). PKS 2005-489 is the first blazar independently discovered by HESS to be an emitter of VHE photons, and only the second such blazar in the Southern Hemisphere. The integral flux above 200 GeV observed in 2004 is ( cm -2 s -1 , corresponding to ~2.5% of the flux observed from the Crab Nebula. The 99% upper limit on the flux in 2003, I (>200 GeV 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 ).