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Gamma-ray Burst (GRB) observations at Very High Energies (VHE, E > 100 GeV) can impose tight constraints on some GRB emission models. Many GRB after-glow models predict a VHE component similar to that seen in blazars and supernova remnants, in which the GRB spectral energy distribution has a double-peaked shape extending into the VHE regime. Consistent with this afterglow scenario, EGRET detected delayed high energy emission from all five bright BATSE GRBs that occurred within its field of view. GRB observations have had high priority in the observing program at the Whipple 10m Telescope and will continue to be high priority targets when the next generation observatory VERITAS comes online. Upper limits on the VHE emission from ten GRBs observed with the Whipple Telescope are reported here. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

TeV gamma-ray observations are reported of 1H1426+428 (1H1426), an X-ray selected BL Lacertae object at a redshift of 0.129. The X-ray spectrum appears to peak near 100 keV; if this is the peak of the synchrotron emission, then this AGN is a prime candidate for TeV gamma-ray emission assuming a Compton-synchrotron model. During the 1999, 2000 and 2001 observing seasons, the source has been intensively studied with the Whipple 10m imaging atmospheric Čerenkov telescope; these observations, together with the indications from earlier observations confirm this hypothesis. The average signal was at the 4.2σ level during the 2000 observing season, while the average signal recorded during 2001 was at the 4.9σ level. [ABSTRACT FROM AUTHOR]

This is a short report on the preliminary findings of the gamma ray burst (GRB) working group for the white paper on the status and future of very high energy (VHE;>50 GeV) gamma-ray astronomy. The white paper discusses the status of past and current attempts to observe GRBs at GeV-TeV energies, including a handful of low-significance, possible detections. The white paper concentrates on the potential of future ground-based gamma-ray experiments to observe the highest energy emission ever recorded for GRBs, particularly for those that are nearby and have high Lorentz factors in the GRB jet. It is clear that the detection of VHE emission would have strong implications for GRB models, as well as cosmic ray origin. In particular, the extended emission phase (including both afterglow emission and possible flaring) of nearby long GRBs could provide the best possibility for detection. The difficult-to-obtain observations during the prompt phase of nearby long GRBs and short GRBs could also provide particularly strong constraints on the opacity and bulk Lorentz factors surrounding the acceleration site. The synergy with upcoming and existing observatories will, of course, be critical for both identification of GRBs and for multiwavelength/multimessenger studies. [ABSTRACT FROM AUTHOR]