Eugene C. Loh

Evidence for 500 TeV gamma-ray emission from Hercules X-1

A signal (chance probability = 2 x 10/sup -4/) with a 1.24 s period has been observed from the direction of Hercules H-1. The signals relatively long period and high shower energy conflict with some popular models of particle acceleration by pulsars. Optical and X-ray data support our picture in which energetic particles produce multi--TeV ..gamma..-rays by collisions with Hercules X-1s accretion disk.

Steerable laser system for UV atmospheric monitoring at the High-Resolution Fly's Eye

Monitoring the aerosol component of the lowest 10 km of the atmosphere at UV wavelengths (300 - 400 nm) is an important part of the High Resolution Flys Eye astrophysics experiment. Our method of atmospheric monitoring uses a frequency tripled YAG laser and a steering system that can point the beam anywhere in the sky. The same detector that measures scintillation light from high energy cosmic rays also measures light scattered from this laser system over a range of laser energies, geometries, and polarizations. This paper describes the technique, the laser system, and some recent measurements.

Atmospheric studies using the high-resolution fly's eye xenon flasher array

The High Resolution Flys Eye (HiRes) cosmic ray detector at Dugway Utah, measures UV scintillation light from extensive air showers. The detection technique is calorimetric in that the amount of light produced is proportional to the energy of the primary particle. Primary particle energies range from 1017 to more than 1020 electron volts. The detector can measure air showers more than 30 km away, a distance of several atmospheric extinction lengths. Variations in the atmosphere can cause significant variations in the amount of light reaching the detector. Atmospheric monitoring is extremely important. This paper discusses a method, under development, that uses the HiRes detector to measure light scattered from pulsed collimated xenon flashbulb sources (Flashers). Discussion includes a description of the light sources and a preliminary data analysis to extract a measurement of atmospheric extinction length and scale height.

Maximum-energy Auger-shower satellite (MASS/AIRWATCH)

A concept for observation from space of the highest energy cosmic rays above 1020 eV with a satellite-borne observatory has been considered. A maximum-energy auger (air)-shower satellite (MASS) would use segmented lenses (and/or mirrors) and an array of imaging devices (about 106 pixels) to detect and record fluorescent light profiles of cosmic ray cascades in the atmosphere. The field-of-view of MASS could be extended to about (1000 km)2 so that more than 103 events per year could be observed above 1020 eV. From far above the atmosphere, MASS would be capable of observing events at all angles including near horizontal tracks, and would have considerable aperture for high energy photon and neutrino observation. With a large aperture and the spatial and temporal resolution, MASS could determine the energy spectrum, the mass composition, and arrival anisotropy of cosmic rays from 1020 eV to 1022 eV, a region hitherto not explored by ground-based detectors such as the flys eye and air-shower arrays. MASSs ability to identify comic neutrinos and gamma rays may help providing evidence for the theory which attributes the above cut-off cosmic ray flux to the decay of topological defects.