HEAO Observations of X-Ray Sources

N. E. White, S. S. Holt, E. A. Boldt and P. J. Serlemitsos, Goddard Space Flight Center, write that HEAO 1 and 2 observations in 1978 and 1979 have confirmed the x-ray fluxes of three x-ray sources to be modulated with periods as follows: 4U 1822-37: 5.57-hour period (cf. IAUC 3406). The light curve is to first order sinusoidal with a peak-to-mean amplitude of 25 percent and the minimum centered on photometric phase ~ 0.8. In addition, there is a sharp feature from phase 0.0 to 0.09 wherein the flux drops to 75 percent of the other minimum. 2A 0311-227: 81-min period (cf. IAUC 3324). The light curve is sinusoidal with a peak-to-mean amplitude of 40 percent and maximum centered on linear-polarization phase 0.5 (cf. IAUC 3327). In addition, there is an absorption dip from phase 0.40 to 0.47. 4U 2129+47: 5.3-hour period (cf. Ulmer et al. 1980, Ap.J. 235, L159). The light curve is basically the same as that reported by Ulmer with in addition a secondary minimum at phase ~ 0.6 about three times less deep than the primary minimum.