IDENTIFICATION WITH H1705-25 (NOVA OPH-1977) AND THE SPECTRAL EVOLUTION OF THE PERIODIC 152-H SOURCE DETECTED IN THE PROGNOZ-9 X-RAY EXPERIMENT

Among the periodic processes with periods of the order of one day, obs erved in the Galactic-center region during an X-ray experiment on the Prognoz-9 satellite between November 1983 and January 1984, the 152-h periodicity with an extremely hard spectrum stands out as the most int ense process in the 50 to 200 keV energy band. Estimates for the angul ar position of the source with which the 152-h periodicity is associat ed and a combined analysis of the time properties of the light curves obtained in this experiment and from the HEAO-1 observations of the ha rd X-ray transient H1705-25 (Nova Ophiuchi 1977) show that this period icity can be identified with H1705-25. Evidence for the presence of a 167-h periodicity in the X-ray emission from H1705-25 during a transie nt flux increase in 1977 suggests a possible period drift of similar t o 2% per year. The spectral evolution of the periodic component is cha racterized (in power-law representation) by a change in the power-law index gamma along the phase curve from similar to 2.0 to similar to 1. 4.