| Issue |
A&A
Volume 406, Number 1, July IV 2003
|
|
|---|---|---|
| Page(s) | L9 - L13 | |
| Section | Letters | |
| DOI | https://doi.org/10.1051/0004-6361:20030838 | |
| Published online | 17 November 2003 | |
Letter to the Editor
Detection of TeV gamma-rays from the BL Lac 1ES 1959+650 in its low states and during a major outburst in 2002 *
1
Max-Planck-Institut für Kernphysik, Postfach 103980, 69029 Heidelberg, Germany
2
Yerevan Physics Institute, Alikhanian Br. 2, 375036 Yerevan, Armenia
3
Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
4
Universität Kiel, Institut für Experimentelle und Angewandte Physik, Leibnizstraße 15-19, 24118 Kiel, Germany
5
Universität Wuppertal, Fachbereich Physik, Gaußstr. 20, 42097 Wuppertal, Germany
6
Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München, Germany
7
Universidad Complutense, Facultad de Ciencias Físicas, Ciudad Universitaria, 28040 Madrid, Spain
8
Now at Institut de Física d'Altes Energies, UAB, Edifici Cn, 08193, Bellaterra (Barcelona), Spain
9
On leave from Altai State University, Dimitrov Street 66, 656099 Barnaul, Russia
10
Home institute: University Lodz, Poland
Corresponding author: N. Götting, Niels.Goetting@desy.de
Received:
16
May
2003
Accepted:
4
June
2003
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 >
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 
, 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 
or by a power law with an exponential cut-off at
TeV
and a spectral index of
.
The low state differential energy spectrum obtained with lower statistics
can be described by a pure power law with a
spectral index of 
.
Key words: γ-rays: observations / BL Lacertae objects: individual: 1ES 1959+650
© ESO, 2003
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