Constraints on the very high energy emission from BL Lacertae objects

We present results from observations of 29 BL Lacertae objects, taken with the Whipple Observatory 10m Gamma-Ray Telescope between 1995 and 2000. The observed objects are mostly at low redshift (z < 0.2) but observations of objects of z up to 0.444 are also reported. Five of the objects are EGRET sources and two are unconfirmed TeV sources. Three of the confirmed sources of extragalactic TeV gamma rays were originally observed as part of this survey and have been reported elsewhere. No significant excesses are detected from any of the other objects observed, on time scales of days, months or years. We report 99.9% confidence level flux upper limits for the objects for each observing season. The flux upper limits are typically 20% of the Crab flux although, for some sources, limits as sensitive as 6% of the Crab flux were derived. The results are consistent with the synchrotron-self-Compton (SSC) model predictions considered in this Fred Lawrence Whipple Observatory, Harvard-Smithsonian CfA, P.O. Box 97, Amado, AZ 85645-0097 Physics Department, Tanta University, Tanta, Egypt Department of Physics, University of Leeds, Leeds, LS2 9JT, Yorkshire, England, UK Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA Department of Physics, Washington University, St. Louis, MO 63130, USA Department of Physics and Astronomy, Iowa State University, Ames, IA 50011-3160, USA Department of Physics, University of California, Los Angeles, CA 90095-1562, USA Department of Physics, Purdue University, West Lafayette, IN 47907, USA Department of Physics, Grinnell College, Grinnell, IA 50112-1690, USA Experimental Physics Department, National University of Ireland, Belfield, Dublin 4, Ireland Department of Physics, National University of Ireland, Galway, Ireland High Energy Astrophysics Institute, University of Utah, Salt Lake City, UT 84112, USA Department of Physics and Astronomy, University of Arkansas at Little Rock, Little Rock, AR 722041099, USA Physics Department, McGill University, Montreál, QCH3A2T8, Canada Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA School of Science, Galway-Mayo Institute of Technology, Galway, Ireland University of Maryland, Baltimore County and NASA/GSFC, USA Department of Applied Physics and Instrumentation, Cork Institute of Technology, Cork, Ireland