We report the results of a spectral analysis over the range 0.1-200 keV performed on the dipping source X1822-371 observed by BeppoSAX. We find the best fit to the continuum using a partially covered Comptonization model, representing scattering of soft seed photons by electrons at a temperature of similar to4.8 keV, without the presence of any soft blackbody emission. The equivalent hydrogen column obtained for the absorbed component is similar to4.5 x 10(22) cm(-2), an order of magnitude larger than the Galactic absorption for this source, and the covering fraction is similar to 71%. Because the inclination angle of X1822-371 to the line of sight is similar to 85 degrees, this model gives a reasonable scenario for the source: the Comptonized spectrum could come from an extended accretion disk corona (ADC), probably the only region that can be directly observed as a result of the high inclination. The excess matter producing the partial covering could be close to the equatorial plane of the system, above the outer disk, occulting the emission from the inner disk and the inner part of the ADC. An iron emission line is also present at similar to6.5 keV with an equivalent width of similar to 150 eV. We argue that this strong iron line cannot be explained as reflection of the Comptonized spectrum by the accretion disk. It is probably produced in the ADC. An emission line at similar to1.9 keV (with an equivalent width of similar to 54 eV) and an absorption edge at similar to8.7 keV (with an optical depth of similar to0.1) are also required to fit this spectrum. These features are probably produced by highly ionized iron (Fe XXIV) present in the outer part of the ADC, where the plasma density is similar to 10(11)-10(12) cm(-3) and ionized plasma is present.
Partially absorbed comptonization spectrum from the nearly edge-on source X1822-371
BURDERI, LUCIANO;
2001-01-01
Abstract
We report the results of a spectral analysis over the range 0.1-200 keV performed on the dipping source X1822-371 observed by BeppoSAX. We find the best fit to the continuum using a partially covered Comptonization model, representing scattering of soft seed photons by electrons at a temperature of similar to4.8 keV, without the presence of any soft blackbody emission. The equivalent hydrogen column obtained for the absorbed component is similar to4.5 x 10(22) cm(-2), an order of magnitude larger than the Galactic absorption for this source, and the covering fraction is similar to 71%. Because the inclination angle of X1822-371 to the line of sight is similar to 85 degrees, this model gives a reasonable scenario for the source: the Comptonized spectrum could come from an extended accretion disk corona (ADC), probably the only region that can be directly observed as a result of the high inclination. The excess matter producing the partial covering could be close to the equatorial plane of the system, above the outer disk, occulting the emission from the inner disk and the inner part of the ADC. An iron emission line is also present at similar to6.5 keV with an equivalent width of similar to 150 eV. We argue that this strong iron line cannot be explained as reflection of the Comptonized spectrum by the accretion disk. It is probably produced in the ADC. An emission line at similar to1.9 keV (with an equivalent width of similar to 54 eV) and an absorption edge at similar to8.7 keV (with an optical depth of similar to0.1) are also required to fit this spectrum. These features are probably produced by highly ionized iron (Fe XXIV) present in the outer part of the ADC, where the plasma density is similar to 10(11)-10(12) cm(-3) and ionized plasma is present.
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