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Session 58 - Gamma Rays & Cosmic Rays.
Oral session, Tuesday, January 16
Salon del Rey South, Hilton
The detection of gamma-rays of energy > 300 GeV from the BL Lac object, Markarian 501, demonstrates that extragalactic TeV emission is not unique to Markarian 421, which was detected by the Whipple air Cherenkov telescope in 1992. During more than 60 hours of observations between March 1995 and July 1995 we measured an average flux of 8.1 +- 1.4 x 10-12 cm-2 s-1, above 300 GeV, a flux only about 1/5 that of Markarian 421. The new gamma-ray source which has not been reported as an emitter of gamma-rays at lower energies displays weak variability on time-scales of days. The two Markarian objects have, in addition to being at comparable distances, very similar characteristics across the wave- bands. This raises the question whether the TeV gamma-ray emission is an intrinsic feature of a sub-class of TeV-loud AGNs or whether the non-detection of TeV emission from other, more distant, AGNs is explained by intergalactic absorption.
