Y. Kamata,K. Koyama, Y. Tawara, K. Makishima, T. Ohashi, N. Kawai, I. Hatsukade
Journal: Astronomical Society of Japan, Publications, vol. 42, no. 6, 1990, p.785-792.
A pulse timing analysis of X-ray pulsar OAO 1657-415 with the Tenma and Ginga satellites is presented. The long-term pulse period history shows a spin-up trend, with an average rate of -0.001/yr. An upper limit to a(x) sin i of 3 lt-s was obtained for the projected semimajor axis for a range of orbital periods of 1 to 6 d. The X-ray spectrum obtained with Ginga was found to be typical of those of other binary X-ray pulsars.