Observations of blazars with the Whipple Observatory gamma-ray telescope

The detection of the AGN Markarian 421 by the Whipple Observatory gamma-ray telescope and subsequent discovery of a TeV flare from this same source initiated the new field of extragalactic "TeV astronomy". The Whipple telescope has now observed gamma-ray emission at E >300 GeV from the BL Lac objects Mrk 421, Mrk 501 and 1ES2344+514 Here we give a review of the status of Whipple observations including measurements of rapid (sub hour-scale) gamma-ray variability at very high energies; observations of correlated variability in gamma-ray, X-ray, UV and optical wavebands; and measurements of the gamma-ray spectra of AGNs. These results are used to derive constraints on the physical conditions in the blazar jets, the emission mechanism and the level of the diffuse extragalactic IR radiation. (C) 1999 Elsevier Science B.V. All rights reserved.