We report on the spectral analysis of Circinus X–1 observed by the ASCA satellite in March 1998 along one orbital period .
The luminosity of the source ( in the 0.1–100 keV band ) ranges from 2.5 \times 10 ^ { 38 } erg s ^ { -1 } at the periastron ( orbital phase 0.01 ) to 1.5 \times 10 ^ { 38 } erg s ^ { -1 } at orbital phase 0.3 .
From the spectral analysis and the lightcurve we argue that Cir X–1 shows three states along the orbital evolution .
The first state is at the orbital phase interval 0.97–0.3 : the luminosity becames super–Eddington and a strong flaring activity is present .
In this state a shock could form in the inner region of the system due to the super–Eddington accretion rate , producing an outflow of ionized matter whose observational signature could be the prominent absorption edge at \sim 8.7 keV observed in the energy spectrum at these phases .
In the second state , corresponding to the orbital phase interval between 0.3 and 0.7 , the accretion rate is sub–Eddington and we observe a weaker outflow , with smaller hydrogen column : the absorption edge is now at \sim 8.3 keV with an optical depth a factor of 2.5 to 6 smaller .
The third state corresponds to the orbital phase interval 0.78–0.97 .
In this state the best fit model to the spectrum requires the presence of a partial covering component , indicating that the emission from the compact object is partially absorbed by neutral matter , probably the atmosphere of the companion star and/or the accreting matter from the companion .