Very high energy gamma rays from Markarian 501

Abstract

During remarkable flaring activity in 1997 Markarian 501 was the brightest source in the sky at TeV energies, outshining the Crab Nebula by a factor of up to 10. Periods of flaring activity each lasting a few days were observed simultaneously by several gamma ray telescopes. Contemporaneous multiwavelength observations in April 1997 show that a substantial fraction of the total AGN power is at TeV energies indicating that high energy processes dominate the energetics of this object. Rapid variability, on time scales of less than a day, and a flat spectrum extending up to at least 10 TeV characterize this object. Results of 1997 observations by 6 telescopes are summarized and some of the implications of these results are discussed.