Spectral Study of GX339-4 in the Low Intensity State Observed with GINGA

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Session 55 -- Interacting Binaries: CVs and XRBs
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[55.16] Spectral Study of GX339-4 in the Low Intensity State Observed with GINGA

Ken Ebisawa (NASA/GSFC), Yoshihiro Ueda (ISAS, Japan), Chris Done (Leicester University)

Energy spectra of the black hole candidate GX339--4 in the low intensity state were observed on four occasions through 1989 to 1991 with the Large Area Counters onboard the GINGA satellite. The spectra showed significant deviations from a power-law function, with an iron K$_{\alpha}$ emission line at $\sim$ 6.4 keV and broad iron K-edge structure above $\sim$ 7 keV. The energy spectra above $\sim$ 4 keV were successfully explained with a reflection model, in which a part of the incident X-rays with a power-law spectrum is Compton reflected by optically thick matter, resulting in a harder continuum component with iron K-edge absorption and an iron fluorescent line. The line equivalent width with respect to the reflection component decreases as the source flux increases, consistent with an increase in the ionization state of the material so that resonant absorption followed by Auger ionization depletes the line. The photon-index of the power-law component was clearly variable, and it correlated with the relative amount of the reflection component. Such a correlation may be explained in the context of the anisotropic Comptonization models of Haardt et al.\ (1993), or by a variation of the relative geometry of the source and disk.

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