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Detection of TeV gamma-rays from the BL Lac 1ES 1959+650 in its low states and during a major outburst in 2002
Ist Teil von
Astronomy and astrophysics (Berlin), 2003-07, Vol.406 (1), p.L9-L13
Ort / Verlag
EDP Sciences
Erscheinungsjahr
2003
Link zum Volltext
Quelle
Electronic Journals Library
Beschreibungen/Notizen
TeV γ-rays from the BL Lac object 1ES 1959+650 have been measured during the years 2000 and 2001 with a significance of 5.2 σ at a value of 5.3% of the Crab flux and in May 2002 during strong outbursts with >$23\,\sigma$ at a flux level of up to 2.2 Crab, making 1ES 1959+650 the TeV Blazar with the third best event statistics. The deep observation of 197.4 h has been performed with the HEGRA stereoscopic system of 5 imaging atmospheric Cherenkov telescopes (IACT system). 1ES 1959+650 is located at a redshift of $z = 0.047$, providing an intermediate distance between the nearby Blazars Mkn 421 and Mkn 501, and the much more distant object H1426+428. This makes 1ES 1959+650 an important member of the class of TeV Blazars in view of the absorption of TeV photons by the diffuse extragalactic background radiation (DEBRA). The differential energy spectrum of 1ES 1959+650 during the flares can be fitted by a power law with a spectral index of $2.83 \pm 0.14_{\mbox{\tiny stat}} \pm 0.08_{\mbox{\tiny sys}}$ or by a power law with an exponential cut-off at $(4.2^{+0.8}_{-0.6~{\mbox{\tiny stat}}} \pm 0.9_{\mbox{\tiny sys}})$ TeV and a spectral index of $1.83 \pm 0.15_{\mbox{\tiny stat}} \pm 0.08_{\mbox{\tiny sys}}$. The low state differential energy spectrum obtained with lower statistics can be described by a pure power law with a spectral index of $3.18 \pm 0.17_{\mbox{\tiny stat}} \pm 0.08_{\mbox{\tiny sys}}$.