Are PSR 0656+14, PSR 0950+08, and PSR 1822-09 gamma ray pulsars?

The possible discovery of three new gamma-ray pulsars PSR 0656+14, PSR 0950+08, and PSR 1822-09 (Ma, Lu, Yu, and Young, 1993) in data obtained with the COS-B experiment is reinvestigated using a refined technique for pulsar light curve analysis. The results of this study do not confirm the previously claimed gamma-ray pulsar nature of any of these pulsars. Even when using the standard epoch folding technique in conjunction with energy-dependent acceptance cones, we do not detect pulsed gamma-ray emission from these sources. We suspect that insufficient position accuracy is the cause for the discrepancy between our results and those of Ma et al. (1993). We do not rule out that any one of the three candidates, or all of them, is in fact a gamma-ray pulsar, but their spin properties must differ from those derived by Ma et al. (1993). More work is needed to determine the correct high-energy properties of these three sources.