A SEARCH FOR FAST GAMMA-RAY PULSARS WITH OSSE

Pulsar mode data from the Oriented Scintillation Spectrometer Experiment (OSSE) onboard the Compton Gamma Ray Observatory, with time resolution between 125 mu s and 8 ms, have been analyzed for the presence of short-period gamma-ray pulsations. Observations of known point sources (including SN 1987A, SN 1993J, GRO J0422+32, and several pulsars) and of regions where higher densities of pulsars are expected (including the Galactic center, the Galactic plane and arms, and the Large Magellanic Cloud) are included in the study. Both isolated pulsars and pulsars in close binary systems are searched for; in the latter case, the quadratic coherence recovery technique is used to correct for broadening of the pulsar signal from orbital motion. No new gamma-ray pulsars have been detected. Upper limits on the pulsed gamma-ray flux from isolated pulsars in the 50-210 keV energy range of OSSE are between 0.2 x 10(-3) and 2.0 x 10(-3) photons s(-1) cm(-2) for pulse periods between 250 mu s and 0.5 s. Upper limits on the pulsed flux from binary pulsars are between 1.5 x 10(-3) and 6.4 x 10(-3) photons s(-1) cm(-2) for the same energy band and pulse period range. We estimate that, in the Galaxy, there are fewer than similar to 125 isolated pulsars similar to PSR B1509-58 with radiation peaks in the OSSE band but undetected in the radio and X-ray bands.