W. Cui

Recent Observations of IC443 with the Whipple 10m Telescope

We present here the results of recent observations made with the Whipple 10m imaging Cherenkov telescope of the region of the supernova remnant IC443. No evidence for gamma‐ray emission was found, and we obtain an upper limit above 500 GeV (99.9% confidence) of 0.6 × 10−7 ph m−2 s−1 (0.11 Crab) at the location of the recently identified X‐ray plerion nebula and 0.8 × 10−7 ph m−2 s−1 (0.14 Crab) at the site of the OH maser at the densest part of the molecular cloud.

The VERITAS Prototype and the Upcoming VERITAS Array

The prototype for the VERITAS imaging atmospheric Cherenkov telescope array was successfully operated in southern Arizona between September 2003 and April 2004. The prototype consisted of 86 mirror facets mounted centrally on a 12‐meter dish, which was built to accommodate up to 350 facets when converted to a complete VERITAS telescope. The camera consisted of half of the full 499 pixel camera. The signal and trigger electronics were nearly identical to those that will be used for the individual VERITAS array telescopes. By observing the Crab and Mrk421, as well as performing a variety of tests, the characteristics of the instrument were evaluated. The prototype met all performance expectations and served as a valuable test bed for the current design, as well as for the construction and operation of VERITAS. This prototype instrument is now being upgraded to a complete VERITAS telescope that will be operated during the construction of the full VERITAS array. The array is expected to be operational by Nove...

The very high energy gamma ray spectra of IES 1959+650 and Mrk 421 as measured with the Whipple 10 m telescope

In observations made with the Whipple 10 m telescope, 1ES 1959+650 (z = 0.048) was caught in a high flaring state in May 2002, concurrent with a high X‐ray state, and in June 2002, for which there was no corresponding X‐ray flare. The spectra for both of those occasions are well fitted by a power law of differential spectral index ∼ −2.8. The relative stability of the spectral index for those flares argues strongly in favour of a two‐component model as to the emission zones for the two radiation regimes.Markarian 421 (z = 0.031) was observed to be in a high flaring state, at levels of ⩾ 3 Crab, during March and April 2004. The average spectrum over this time period shows evidence for a cut‐off in the spectrum at ∼ 5 TeV, similar to a cut‐off seen during an equivalently strong episode of flaring activity in 2001. The continued appearance of this feature indicates a long term stability, either in the physical conditions at the source, or in the intervening medium (such as attenuation on the extra‐galactic i...

Very High Energy Observations of Gamma Ray Bursts with the Whipple/VERITAS Telescopes

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.