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 gamma-rays between the energies of 50 and 500 GeV. These observations represent the lowest energy gamma-ray detection of this outburst by a ground-based experiment. Here we present results from these observations, which indicate an average integral gamma-ray flux of (8.0 +/- 0.7 +/- 1.5)x10^-10 1/cm^2/s. 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 to those of other experiments. 
STACEE Collaboration: L. M. Boone, J. A. Hinton, D. Bramel, E. Chae,   C. E. Covault, P. Fortin, D. M. Gingrich, D. S. Hanna...