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 similar to6 x 10(3) s is present at the beginning of the observation. The luminosity during the persistent emission is 1 x 10(38) ergs s(-1), while during the flare it is 2 x 10(38) 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 similar to0.4 keV, by electrons at a temperature of similar to1 keV. After the flare, a power-law component with photon index similar to3 is dominant at energies higher than 10 keV. This component contributes similar to4% of the total luminosity. During the flare its addition is not statistically significant. An absorption edge at similar to8.4 keV, with optical depth similar to1, 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 similar to 10(24) 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 similar to 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.
A hard tail in the X-ray broadband spectrum of Circinus X-1 at the periastron: A peculiar Z source
BURDERI, LUCIANO;
2001-01-01
Abstract
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 similar to6 x 10(3) s is present at the beginning of the observation. The luminosity during the persistent emission is 1 x 10(38) ergs s(-1), while during the flare it is 2 x 10(38) 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 similar to0.4 keV, by electrons at a temperature of similar to1 keV. After the flare, a power-law component with photon index similar to3 is dominant at energies higher than 10 keV. This component contributes similar to4% of the total luminosity. During the flare its addition is not statistically significant. An absorption edge at similar to8.4 keV, with optical depth similar to1, 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 similar to 10(24) 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 similar to 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.