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The gamma ray content of ultrahigh energy cosmic radiation

Thesis/Dissertation ·
OSTI ID:5261024
Data from the Utah-Michigan (UM) extensive air shower (EAS) array at Dugway, Utah are examined for evidence of a gamma ray component in the UHE cosmic rays. The UM array consist of a 3 {times} 10{sup 4} sq m surface array with 40 sq m of charged particle detectors, and a 1200 sq m buried array for detecting muons. Data from the large muon array are used to search for a gamma ray signature, since gamma rays are expected to produce far fewer muons in EAS than hadronic cosmic ray primaries. When no evidence for gamma rays is found, limits are set based on expected gamma ray behavior. For a photon energy threshold of 200 TeV, results include: a limit on the omnidirectional gamma ray fraction of cosmic rays at 0.2 pct; a limit on the galactic gamma ray fraction of cosmic rays at 7 {times} 10{sup {minus}5}; no strong evidence for enduring gamma ray point sources at fluxes approx. = 4 {times} 10{sup {minus}14}/sq cm/s; and no strong evidence for bursts on a one day time scale at a flux sensitivity {approx} 2 {times} 10{sup {minus}12}/sq cm/s. These limits and measurements are based on muon poor data. While no strong signal of UHE gamma rays is found, future application to the large Chicago Air Shower Array-Michigan Array (CASA-MIA) is possible.
Research Organization:
Michigan Univ., Ann Arbor, MI (United States)
OSTI ID:
5261024
Country of Publication:
United States
Language:
English