GCN Circular 1049
D. W. Fox and D. L. Kaplan (Caltech) report: "Analysis of data from the 22 April 2001 Chandra observation (GCN 1046, 1047), barycenter-corrected with the preliminary CXC ephemeris, reveals that the source emission is pulsed at a period of P = 5.17288(5) s with a pulse strength of 14.3(2)% RMS that remains constant (within errors) throughout the observation. Separation of the source photons into "on-pulse" and "off-pulse" components of 1/3 cycle each reveals that the off-pulse spatial distribution is significantly broader than the on-pulse distribution. Since the observation is taken in continuous-clocking mode, we can only make this determination in one dimension. Nonetheless, the sigma-widths of the one-dimensional Gaussian PSFs are 0.98(1) arcsec for on-pulse photons and 1.08(2) arcsec for off-pulse photons, different at >5-sigma level. We attribute this difference in widths to the presence of an underlying X-ray nebula."