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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]

The Short GAmma Ray Front Air-Cherenkov Experiment (SGARFACE) uses the Whipple 10 m telescope to search for bursts of gamma rays. Bursts can be detected on time scales from a few ns to 20 !s and with gamma-ray energy above 100 MeV. SGARFACE began operating in March 2003 and has acquired 2.2 million events since. A search for explosions of primordial black holes (PBH) was carried out using the recorded time-resolved images. No unambiguous burst detection could be made due to background events produced by cosmic rays. Upper limits on the PBH explosion rare are presented and compared to other experiments. [ABSTRACT FROM AUTHOR]

The Advanced Gamma-Ray Imaging System (AGIS) is a concept for the next generation observatory in ground-based very high energy gamma-ray astronomy. Design goals are ten times better sensitivity, higher angular resolution, and a lower energy threshold than existing Cherenkov telescopes. Simulations show that a substantial improvement in angular resolution may be achieved if the pixel diameter is reduced to the order of 0.05 deg, i.e. two to three times smaller than the pixel diameter of current Cherenkov telescope cameras. At these dimensions, photon detectors with smaller physical dimensions can be attractive alternatives to the classical photomultiplier tube (PMT). Furthermore, the operation of an experiment with the size of AGIS requires photon detectors that are among other things more reliable, more durable, and possibly higher efficiency photon detectors. Alternative photon detectors we are considering for AGIS include both silicon photomultipliers (SiPMs) and multi-anode photomultipliers (MAPMTs). Here we present results from laboratory testing of MAPMTs and SiPMs along with results from the first incorporation of these devices into cameras on test bed Cherenkov telescopes. [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]

We report on a periodicity analysis of γ-ray observations of very high energy (VHE, E>250 GeV) γ-rays from Markarian 501 (Mrk 501) taken with the Whipple telescope between March and July of 1997. The data correspond to a period of bright flaring of the source, quasi-periodic signals were detected by the Telescope Array Project (TAP) and HEGRA collaboration. Periodic analysis of these data is complicated because the source observations are not continuous and the reported period (approx. 24 days) is very close to the sampling period. We use the Lomb method, a technique for extracting spectral information from unevenly sampled data, in an attempt to overcome this difficulty. Similar results are shown to exist in data from the strongly correlated X-ray band sampled by the RXTE ASM instrument. No periodicity in the data could be identified with a source frequency. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Whipple Collaboration has been carrying out an upgrade program, GRANITE III, on the 10m telescope atop Mt. Hopkins. The 3 year program, 1996 through 1999, has involved a large field-of-view camera, a hardware pattern recognition trigger, and finally a small pixel camera. Results of the first and second stage of the program indicate that a large field-of-view yield an increased collection area for cosmic-ray triggers and the hardware pattern trigger reduces the energy threshold of the telescope by greatly suppressing night sky accidental triggers over a simple multiplicity coincidence trigger. The final phase of the program, being completed during the summer and fall of 1999, will be the installation of a small pixel camera. The pixel size of ∼0°.12 will yield the lowest threshold energy at which the 10 m Whipple telescope has ever operated. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A ToO observation of the TeV-emitting blazar Mrk 421 with INTEGRAL was triggered in June 2006 by an increase of the RXTE count rate to more than 30 mCrab. The source was then observed with all INTEGRAL instruments with the exception of the spectrometer SPI for a total exposure of 829 ks. During this time several outbursts were observed by IBIS and JEM-X. Multiwavelength observations were immediately triggered and the source was observed at radio, optical and X-ray wavelengths up to TeV energies. The data obtained during these observations are analysed with respect to spectral evolution and correlated variability. Preliminary results of the analysis are presented in this poster. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]