PSR 1951+32

N. d'Amico, Universita di Palermo; K. Bennett and J. Clear ESA Space Science Department, Noordwijk; and R. Buccheri and B. Sacco, Laboratorio di Fisica Cosmica, Palermo, report: "Li, Li, Ma and Wu (IAUC 4492) have reported the detection of pulsed high- energy gamma-ray emission from PSR 1951+32. Their analysis was performed using observation No. 26 from the public COS-B database. During similar contemporaneous searches for pulsed emission, we found a 9.5-sigma effect for observation period 4, corresponding to a probability of less than 1 percent when the number of trials is taken into account. In this analysis we used the established event-selection criteria of Mayer-Hasselwander and an energy- dependent selection cone about the pulsar position that maximizes the signal-to-noise for the COS-B point-spread function (Buccheri et al.). Our analyis of observation period 26 does not show the signal of Li et al. at the quoted significance level. Furthermore, we were not able to reproduce the number of events (378) they quoted, and their period is not compatible with that found by us for observation period 4. We therefore urge that these discrepancies be investigated and resolved before making a firm statement on the existence of pulsed gamma-ray emission from PSR 1951+32."