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) γ-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 γ -ray/hadron separation and for flux comparison. The data analysis shows VHE γ-ray emission of 1ES 1959+650 with ~8 σ significance, at a time of low activity in both optical and X-ray wavelengths. An integral flux above ~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.