Katherine S. Harris

A high resolution imaging detector for TeV gamma-ray astronomy

Details are presented of an atmospheric Cherenkov telescope for use in very high energy gamma-ray astronomy which consists of a cluster of 109 close-packed photomultiplier tubes at the focus of a 10 meter optical reflector. The images of the Cherenkov flashes generated both by gamma-ray and charged cosmic-ray events are digitized and recorded. Subsequent off-line analysis of the images improves the significance of the signal to noise ratio by a factor of 10 compared with non-imaging techniques.

The use of an ultra-violet camera in the atmospheric Cherenkov technique

Abstract The atmospheric Cherenkov technique for gamma ray astronomy is shown to be feasible using an ultraviolet (UV) camera on moon-lit-nights. The Whipple telescope has been used as the reflector and the Crab Nebula as the standard gamma ray beam. Our energy threshold is 1.2 TeV which is compared to 0.4 TeV in the visible.

A new optical filter for the ARTEMIS experiment

Abstract The properties of a new liquid filter for the ARTEMIS experiment are reported. ARTEMIS, which is run at the Whipple Gamma-Ray/Cosmic-Ray Telescope, aims to measure the negatively charged component of hadronic cosmic rays (presumably antiprotons) in the 1 TeV region. The Earth–Moon system is used as a spectrometer to perform a magnetic analysis of cosmic rays passing close to the Moon. The Moon acts as an aperture stop, resulting in a deficit of both protons and antiprotons. Air showers are detected using Cherenkov light emitted in the ultraviolet (UV) range in order to benefit from the large moonlight absorption through ozone in the upper atmosphere. The liquid UV filter needed to complement the ozone effect has been added to with a recently discovered dye. We report here on observations made using this dye. A background reduction to only 3% of its value without the dye has been achieved while maintaining the signal amplitude to at least 75% of its level. The reduced sensitivity to moonlight permits a lowering of the trigger threshold which, in turn, increases the air shower registration efficiency by a factor of three.