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Astron. Astrophys. 353, 847-852 (2000)

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2. Data

The HEGRA experiment, located on the Canary Island La Palma at the Observatorio del Roque de los Muchachos (2200 m a.s.l., 28.75oN, 17.89oW), consists of several arrays of particle and Cherenkov-detectors dedicated to cosmic ray research (Lindner 1997; Barrio et al. 1998).

Before September 1998, the CT-System consisted of four, (now it consists of five) telescopes with 8.5 m2 mirror area each. Each telescope is equipped with a 271 pixel camera with a pixel size of 0.25o, covering a field of view of 4.3o. The cameras are read out by 8 bit 120 Mhz Flash-ADC systems. Details about the CT-system and the performance of the stereoscopic air shower observation method are given by (Daum et al. 1997) and (Aharonian et al. 1999a).

Table 1 summarizes the observations and redshifts of the nine BL Lac objects considered in this work. The first 7 objects with right ascension [FORMULA] 9 h have been observed during October and November 1997. The data have been taken with only 3 telescopes in the system because the telescope CT4 was not operational from October 16 to November 15 1997. The last two sources have been observed with the 4-CT system, BL Lacertae in July/August 1997 and May/June 1998 and 1ES 2344+51.4 in December 1997.


Table 1. Summary of the data samples for the 9 BL Lac objects. [FORMULA] denotes the mean zenith angle of the observations and [FORMULA] the number of telescopes in the stereoscopic system.

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© European Southern Observatory (ESO) 2000

Online publication: January 18, 2000