2001ApJ...547..412I

We report on the spectral analysis of the peculiar source Cir X-1 observed by the BeppoSAX satellite when the X-ray source was near the periastron. A flare lasting ∼6x10³ s is present at the beginning of the observation. The luminosity during the persistent emission is 1x10³⁸ ergs.s^–1, while during the flare it is 2x10³⁸ ergs.s^–1. We produced broadband (0.1-100 keV) energy spectra during the flare and the persistent emission. At low energies the continuum is well fitted by a model consisting of Comptonization of soft photons, with a temperature of ∼0.4 keV, by electrons at a temperature of ∼1 keV. After the flare, a power-law component with photon index ∼3 is dominant at energies higher than 10 keV. This component contributes ∼4% of the total luminosity. During the flare its addition is not statistically significant. An absorption edge at ∼8.4 keV, with optical depth ∼1, corresponding to the K edge of Fe XXIII-Fe XXV, and an iron emission line at 6.7 keV are also present. The iron-line energy is in agreement with the ionization level inferred from the absorption edge. The hydrogen column deduced from the absorption edge is ∼10²⁴ cm^–2, 2 orders of magnitude larger than the low-energy absorption measured in this source. We calculated the radius of the region originating the Comptonized seed photons, R_W∼150 km. We propose a scenario where R_W (the Wien radius) is the inner disk radius, a highly ionized torus surrounds the accretion disk, and a magnetosphere is present up to R_W. The absorption edge and the emission line could originate in the photoionized torus, while the Comptonized component originates in an inner region of the disk.