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.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11584/32856
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