Cutoff in the tev energy spectrum of markarian 421 during strong flares in 2001

Exceptionally strong and long-lasting flaring activity of the blazar Mrk 421 occurred between 2001 January and March. Based on the excellent signal-to-noise ratio of the data, we derive the energy spectrum between 260 GeV and 17 TeV with unprecedented statistical precision. The spectrum is not well described by a simple power law even with a curvature term. Instead, the data can be described by a power law with exponential cutoff: DN/dE ∝ E-2.14±0.03statℓ-E/E0m-2S-2 TeV-1 with E0=4.3±0.3statTeV.Mrk 421 is the second -ray blazar that 0 stat unambiguously exhibits an absorption-like feature in its spectral energy distribution at 3-6 TeV. © 2001. The American Astronomical Society.