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Millisecond Pulsars

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The data collected from the CYGNUS-I scintillator array and from the JASA water-Cerenkov array of the CYGNUS extensive air-shower experiment are searched for the emission of ultrahigh-energy gamma rays from the directions of the Crab, PSR 1937+21, PSR 1951+32, PSR 1953+29 and PSR 1957+20. For the unpulsed searches, the CYGNUS-I data spans the period from 1986 April 2 to 1994 March 7, and the JASA data covers the period from 1992 October 23 through 1993 October 23. For the pulsed searches, the CYGNUS-I data spans the period from 1991 February 27 to 1994 March 7, while the JASA data cover the same period of time as that for the unpulsed search. Each dataset is divided into two categories; one of them contains all events without any cuts and the other only contains events without observed muons. Both datasets are examined for long-term steady and pulsed emissions and single-day unpulsed and pulsed emissions. No evidence of statistically significant excesses above the expected cosmic-ray background for unpulsed emissions are found from any of the sources examined. Upper limits for the steady flux are quoted at the 90% confidence level above 100 TeV. The steady flux upper limits from the CYGNUS -I all-event (muon-poor) results are 3.0 (2.2), 2.6 (1.5), 1.3 (1.2), 1.4 (0.9), and 3.2 (2.4) times 10^{-14} photons cm^{-2} s^ {-1} for the Crab, PSR 1937+21, PSR 1951+32, PSR 1953+29, and PSR 1957+20, respectively. Also, no sporadic single-day emissions are found from any of the sources. The Z_sp{5}{2} test is used for the Crab to test the uniformity of the data against periodic signals, while the others are tested by the Z_sp{10}{2 } test. Long-term pulsed emissions are not seen in any of the data searched. Pulsed analysis on single source days with 2 sigma or more excess observed in the unpulsed daily search also shows no compelling results.

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