A1540-53

P. J. N. Davison, University College, London, writes that news of his discovery of an x-ray pulsator near 3U 1538-52 (cf. IAUC 3039) was contained in a preprint issued in Nov. 1976 (Monthly Notices Roy. Astron. Soc. in press). The observation was made on l976 Sept. 6-7, and the period was determined to be 528s.7 +/- 0s.4. The best estimate of the source's position, R.A. = 15h41m.2, Decl. = -53o.4 (equinox 1950.0), is > 1o from 3U 1538-52, which appeared to be at an intensity well below that given in the Uhuru catalogue. The 90-percent-confidence box for A1540-53 is a 0o.5 x 0o.2 ellipse, the major axis being approximately in the direction of 3U 1538-52.