MAGIC Observations of the Unidentified γ-Ray Source TeV J2032+4130

We observed the first known very high energy (VHE) γ-ray-emitting unidentified source, TeV J2032+4130, for 94 hr with the MAGIC telescope. The source was detected with a significance of 5.6 σ. The flux, position, and angular extension are compatible with the previous ones measured by the HEGRA telescope system 5 years ago. The integral flux amounts to (4.5 ± 0.3_stat ± 0.35_sys) × 10^-13 photons cm^-2 s^-1 above 1 TeV. The source energy spectrum, obtained with the lowest energy threshold to date, is compatible with a single power law with a hard photon index of Γ = -2.0 ± 0.3_stat ± 0.2_sys.