Markarian 421 was the first extragalactic source to be detected with high statistical certainty at TeV energies. The Whipple Observatory gamma-ray telescope has been used to observe the Active Galactic Nucleus, Markarian 421 in 1996 and 1997. The rapid variability observed in TeV gamma rays in previous years is confirmed. Doubling times as short as 15 minutes are reported with flux levels reach...

The CELESTE experiment uses the heliostats of an old solar farm in the French Pyrenees to detect gamma ray air showers by the atmospheric Cerenkov technique. Observations of the TeV blazar Markarian 421 have been made with the fully instrumented CELESTE experiment since December 1999. The detection of gamma ray emission from this source at energies greater than 50 GeV is presented here. A compa...

It is surprising to find a fact for migration in the peak positions of synchrotron spectra energy distribution component during activity epochs Mrk 421, accompanying with an orphan flaring at X-ray and GeV-TeV $\gamma$-ray bands. A geometric interpretation standard shock or stochastic acceleration models blazar emission have difficulty reproducing these observed behaviours. The present paper in...