R. M. Baltrusaitis

The Utah Fly's Eye detector

Abstract We report the details of the design, operation and performance of the University of Utah Flys Eye detector which was built to record the passage of ultra-high energy cosmic rays through the atmosphere via atmospheric fluorescence. Emphasized in the presentation are (1) light production by charged particles in the atmosphere, (2) kinematics of an EAS as seen by the Flys Eye, (3) signal to noise considerations and its impact on detector design, (4) details of detector hardware and software, (5) detector calibration, (6) techniques employed in measurement of shower longitudinal development profiles and primary particle energy, and (7) assessment of detector performance by a comparison of Monte Carlo and real data distributions.

The Fly's Eye detector: Present and future

Abstract The operation and recent results of the Flys Eye cosmic ray observatory are described. This detector observes ⩾ 10 17 eV cosmic ray extensive air showers via air fluorescence. Results on the cosmic ray spectrum, composition and the ultrahigh energy neutrino flux, are presented. Plans for a next generation high resolution eye are described.

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.

Limits on astrophysical. nu. /sub e/ flux at E/sub. nu. />10/sup 19/ eV

We report on a search for upward-going extensive air showers using the University of Utah Flys Eye detector. No eVents hae been found in 3.9 x 10/sup 6/ s of running time. The resultant ..nu.. flux limit at 10/sup 20/ eV varies from 5.8 x 10/sup -16/ ..nu.. cm/sup -2/ s/sup -1/-sr/sup -1/ to 3.0 x 10/sup -14/ ..nu.. cm/sup -2/ s/sup -1/ sr/sup -1/ for sigma/sub ..nu../ between 10/sup -33/ cm/sup 2/ and 10/sup -3/ cm/sup 2/. We also present flux limits for large sigma/sub ..nu../ using near-horizontal events originating in the atmosphere. The implications of the flux limit at E/sub ..nu../>10/sup 20/ ev are discussed.

Upper limits for northern hemisphere 10 V eV gamma-ray sources

Flux limits in the range 10 T to 10 S cm S s have been obtained by observing Cerenkov flashes from small air showers. Simultaneous drift scans by the 67 mirror units of the Utah Flys Eye gave nearly full coverage of the Northern Hemisphere. During 1983, a 3.5 sigma excess of showers was observed during the phase interval 0.2--0.3 of the 4.8 hr period of Cygnus X--3, but no excess was found in 1984 observations.

Sporadic and periodic 10-1000 TeV gamma rays from Cygnus X-3

During 1985 June, July, August, and October, small air showers from the direction of Cygnus X-3 were observed using the University of Utah Flys Eye. Useful spectral information was obtained from these showers. The combined data from 1985 June, July, and August show a 3.9 ó excess at 4.8 hr phase 0.65-0.70 for showers with energies above 100 TeV. The excess flux, averaged over all phases, is 4.5 ± 1.2 x 10 cms. During a short run in 1985 October, following a Cyg X-3 radio outburst, only upper limits for the fluxes were obtained. Evidence was obtained for a sporadic outburst in 1985 June 17 UT. The outburst occurred at various phases of the 4.8 hr Cygnus X-3 period. Part of the signal above 250 TeV was near phase 0, when the companion star eclipses the neutron star in some models of Cygnus X-3. The energy flux during the outburst was about 10 ergs cms, which is quite large compared with long-term periodic fluxes. Averaged over all the observing time, however, the sporadic flux is roughly comparable to the periodic flux. Subject headings: gamma rays: general stars: individual (Cyg X-3) X-rays: binaries

Limits on the ≳1017 eV cosmic ray νe flux

We report on a search for upward‐going extensive aire showers using the University of Utah Fly’s Eye detector. No event have been found in 6×106s of running time. The resultant νe flux limit for σν=10−33 cm2 varies from 7.2×10−14 to 5.0×10−17 ν/cm2‐sec‐ster for Eν between 1018 and 1021 eV. We also present limits for larger σν using near‐horizontal events originating in the atmosphere.

Measurement of the angular distribution of Cerenkov light in ultra-high-energy extensive air showers

The authors report on a direct measurement of the angular distribution of Cerenkov light in extensive air showers with energies greater than 1017 eV. The measurement is performed by viewing sections of showers simultaneously at different emission angles with two Flys Eye detectors. The data imply a value of the multiple scattering parameter theta 0=4.0+or-1.2 degrees for threshold energies between 20 and 60 MeV.