OAO 1653-40

N. E. White, S. H. Pravdo and J. H. Swank, Goddard Space Flight Center, write: "An 8-hr HEAO-A2 pointed observation of OAO 1653-40 on 1978 Sept. 4 revealed the x-ray source to be modulated with a period of 38.22 +/- 0.01 s. The peak-to-mean amplitude ranged from 10 percent in the 2-10-keV band to 30 percent in the 8-25 keV." M. Johnston, T. Armstrong and the HEAO-1 Scanning Modulation Collimator Team at the Massachusetts Institute of Technology and the Center for Astrophysics report that their analysis of the above pointed observation of the OAO 1653-40 region confirms the presence of the pulsing x-ray source. Pulsations are detected only in the 5.5-13.5-keV energy band. Multiple lines of position are obtained for the source, but none of them is consistent with the position of V861 Sco, the suggested counterpart of OAO 1653-40 (IAUC 3234; Polidan et al. 1978, Nature 275, 296). An upper limit of < 1.0 uJy is placed on the 1.5-13.5-keV flux density of V861 Sco during the pointed observation.