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X. Sun, S. N. Zhang (NASA MSFC/UAH), W. Cui (MIT), W. Chen (NASA GSFC/U. of Maryland)
We present our results on spectral modeling of the data for XTEJ1748-288 with a sequence of 24 RXTE observations during its outburst in 1998. Its spectral shape changed significantly during all observations, covering the initial rising phase, two flux peaks, and the final decay phase. The spectra can be represented consistently by a spectral model which includes a hard component, a soft component, and an iron line at 6.4 keV; the hard and soft components are fit by the thermal Comptonization and disk blackbody spectral models, respectively. The hard component dominated the emission until the second peak in its X-ray light curve, while the soft component dominated from this peak until this component became undetectable during the decay phase. During the final decay phase the hard Comptonization component remains as the only detectable continuum in the RXTE band. The radiation transfer correction developed by us is applied to calculate the inner disk radius. We find that the emission area for the disk blackbody component after this correction is consistent with being a constant throughout the rising, the peaks and the initial decay phases. The inferred inner disk radius is 22d(10kpc)/sqrt(cos(theta)) km. Without this correction, the apparent inner disk radius during the first peak appears systematically smaller than that during the rest of the observations, indicating the importance of the radiation transfer effect.
The author(s) of this abstract have provided an email address for comments about the abstract: xuejun.sun@msfc.nasa.gov