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Y. Yao, S. Zhang (U. Alabama in Huntsville), X. Wu (Beijing Astronomical Obs., Chinese Academy of Science, China. P. R.), X. Zhang (U. Alabama in Huntsville), W. Cui (Center for Space Research, MIT), W. Chen (U. Maryland), G. J. Sobczak (Harvard U.)
We report on the X-ray spectral behavior of the black hole candidate XTE J1550-564 during its 1998-1999 outburst. Our study is based on the 90 observations selected out of 306 pointed observations made with Rossi X-ray Timing Explorer (RXTE). The spectrum usually consists of one soft component and one hard component and an iron line around 6.4 keV. It is believed that the hard component is the output of the Comptonization between low-energy photons and hot electrons; those low-energy photons are emitted in the cold accretion disk and are originally a portion of the soft component. Therefore a correction should be made to transfer the photons of the hard component back to the soft component (i.e., radiation transfer correction) in order to get the correct parameters of the soft component which is usually used to calculate the inner disk radius. We therefore use the disk blackbody plus the thermal Comptonization model instead of the conventionally used disk blackbody plus power-law model in fitting the data for XTE J1550-564; a fairly constant inner disk radius was obtained after the radiation transfer correction.