STACEE Observations of Markarian 421 during an Extended Gamma-Ray Outburst

The active galaxy Markarian 421 underwent a substantial outburst in early 2001. Between January and May of that year, the STACEE detector was used to observe the source in γ-rays between the energies of 50 and 500 GeV. These observations represent the lowest energy γ-ray detection of this outburst by a ground-based experiment. Here we present results from these observations, which indicate an average integral γ-ray flux of (8.0 ± 0.7 ± 1.5) × 10 -10 cm -2 s -1 above 140 GeV. We also present a light curve for Markarian 421 as observed by STACEE from March to May and compare our temporal, as well as spectral, measurements with those of other experiments.