Observation of very high energy gamma-ray emission from the active galactic nucleus 1ES 1959+650 using the MAGIC telescope

The MAGIC Cerenkov telescope has observed very high energy (VHE) gamma-ray emission from the active galactic nucleus 1ES 1959+650 during 6 hr in 2004 September and October. The observations were carried out alternating with observations of the Crab Nebula, whose data were used as a reference source for optimizing gamma -ray/hadron separation and for flux comparison. The data analysis shows VHE gamma-ray emission of 1ES 1959+650 with similar to 8 sigma significance, at a time of low activity in both optical and X-ray wavelengths. An integral flux above similar to 180 GeV of about 20% that of the Crab Nebula was obtained. The light curve, sampled over 7 days, shows no significant variations. The differential energy spectrum between 180 GeV and 2 TeV can be fitted with a power-law of index -2.72 +/- 0.14. The spectrum is consistent with the slightly steeper spectrum seen by HEGRA at higher energies, also during periods of low X-ray activity.