GENERALIZED SPECTRAL MODEL FOR 1-100 KEV X-RAY-EMISSION FROM CYGNUS-X-3 BASED ON EXOSAT DATA

The X-ray spectrum of the highly variable X-ray source, Cyg X-3, has s o far defied a consistent explanation based on simple emission models. We have extracted two of the best data sets from the EXOSAT archives and performed a detailed spectral analysis for its ''high'' and ''low' ' states. The analysis of the less frequently occurring ''low'' state is presented for the first time for the EXOSAT data. Combining data fr om the medium-energy argon and xenon detectors and the gas scintillati on proportional counter, with a better energy resolution, and carrying out a simultaneous fit, we find that the X-ray continuum in both the ''high'' and ''low'' state can be explained as a sum of a blackbody em ission and emission from a Comptonized plasma cloud with a common abso rption. The Comptonization model is sufficient as well as preferable t o many other models, in explaining the observed X-ray emission up to 1 00 keV. In addition, we find an emission-line feature due to ionized i ron (Fe XX-Fe XXVI) and absorption features due to cold iron (Fe I) as well as highly ionized iron (Fe XXV-Fe XXVI). The presence of absorpt ion due to Fe I has been shown for the first time here. This is the si mplest and the most generalized spectral model for the 1-100 keV X-ray emission from Cyg X-3, to date. We find that the blackbody temperatur e derived in the ''high'' state (1.47 keV) is much lower than that der ived for the ''low'' state (2.40 keV) and is associated with an increa se in the blackbody radius in the ''high'' state. The ratio of blackbo dy flux to the total flux is approximately 0.61 in the ''high'' state and approximately 0.44 in the ''low'' state. The Fe line energy is sig nificantly higher in the ''high'' state (approximately 6.95 keV) compa red to the ''low'' state (approximately 6.56 keV). The Comptonization parameter changes from 2 to approximately 15 in going from the ''high' ' to the ''low'' state implying a highly saturated Comptonization in t he ''low'' state. The Comptonized region has high electron temperature and low opacity in the ''high'' state and vice versa in the ''low'' s tate. The orbital light curve is mostly explained by variations in the intensities of the continuum components. We discuss the likely origin of different emission regions, continuum and line, and interpret them in terms of an accretion disk corona.