Pulsed X-ray observations of Cen X-3 from Ariel-5.

The 4.8-sec X-ray pulsations from Centaurus X-3 were monitored by a collimated proportional counter on board Ariel-5 between 1975 January 18-27. Analysis of the source Doppler effect shows that the pulsation period of Cen X-3 decreased by 3.70 + or - 0.04 msec during the preceding 2.3 yr. The Doppler analysis also yields updated values for the binary phase and period of Cen X-3. Phase zero occurred at JD 2442438.628 + or - 0.003 and the average heliocentric binary period between 1972 October and 1975 January was 2.087129 + or - 0.000007 days. Light curves of the 4.8-sec pulsations in the 3-9 keV band are characterized by two pronounced peaks, in contrast with the single peak profiles observed by Uhuru.