Other
Scientific paper
Jan 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt........75h&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF NOTTINGHAM (UNITED KINGDOM), 1990.Source: Dissertation Abstracts International, Volume: 52-05, Se
Other
1
Grex Array, Cygnus X-3
Scientific paper
Available from UMI in association with The British Library. Requires signed TDF. This thesis is concerned with analysis of data from the University of Nottingham's 40 m^2 muon detector which is triggered by the GREX extensive air shower array operated by the University of Leeds. The GREX array was built for high resolution (<1 ^circ) searches of PeV gamma-ray point sources. The muon content of showers detected between 1st October 1988 and 30th September 1989 from the direction of Cygnus X-3 was analysed with the hope that evidence for PeV gamma -ray emission would be found by the selection of muon poor showers. No evidence for emission was found by selecting muon poor showers, however weak evidence for emission pulsed with the 4.8 hr period of Cygnus X-3 was seen when muon rich showers were selected. The phase of emission (0.25 -0.30) and the muon rich nature of the showers is in agreement with previous observations by other groups. If the weak evidence for emission is accepted the muon rich nature of the showers is difficult to understand. The muon observations were also used to study the mass of the primary cosmic rays in the PeV region. Measurements of the elongation rate (the rate of increase in the depth of shower maximum with primary energy) in the 1-100 PeV region indicate a decrease in the average primary mass with energy, Linsley and Fichtel (1985). Such a decrease should be accompanied by a flattening of the relation between muon number and shower size (a reduced value of alpha in the relation N_μ ~ N _{rm e}^alpha). A reduction in alpha is not seen by most groups, contradicting the elongation rate measurements. This disparity was investigated experimentally. The elongation rate was determined indirectly through the variation with primary energy and atmospheric depth of the ratio of the densities in adjacent muon and unshielded deep water Cerenkov detectors (rho_mu/rho _{rm c}). An elongation rate of 122(+/-15) g/cm^2 per decade of energy was obtained for the region 0.5 to 4 PeV, in significant agreement with the results of other groups. The relation between the muon and electromagnetic components of detected showers was determined through the relation rho_mu~ rho_{rm c}^beta . Above 16 PeV beta has been measured at Haverah Park as 0.94. The present observations give beta = 0.82(+/- 0.01) in the energy range 0.5 to 4 PeV. This significant reduction in beta confirms the interpretation of the measured elongation rate, that the average mass of the primary cosmic rays is decreasing in the energy range 0.5 to 4 PeV.
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