Further observations of Cygnus X-3 with the Uhuru satellite.

We present observations of the periodically varying X-ray source Cygnus X-3 made with the Uhuru satellite between 1970 December 27 and 1973 January 16. Our results are: 1. A value for the period. P = 0d.l9968l 1 + 0('.00000l6; the 2(7 upper limit to a continuous change in the period is P-1dPJdt < 2 x 10-12 1 2. No systematic change is observed in the effective low energy absorption across the 0d.2 cycle. 3. Cyg X-3 exhibits different average intensity levels which have been seen to persist for as long as 9 days at a time. The hardest spectra (in the 2-10 keV range) are derived from the times of lowest 2-6 keV intensity. 4. Cygnus X-3 was observed with Uhuru during the large radio outburst first noted on 1972 September 3. The spectral parameter kTfor thermal bremsstrahlung emission increased systematically from 2 keV to 3 keV from August 30 to September 3, and then decreased back to 2 keV by September 7. During this time, the 2-6 keV intensity of Cygnus X-3 fluctuated by a factor of 4 ranging from 150 cnt 1 to 600 ent -1 which is the highest intensity yet observed for this source. Subject headings: spectra, X-ray - X-ray sources