We present the calculation of X -ray spectra produced through Compton scattering of soft X-rays by hot electrons in the spherical shell geometry, using fully relativistic Monte Carlo simulation. With this model, we show that the power-law component, which has been observed in the low luminosity state of low-mass X-ray binaries (LMXBs), is explained physically. From a spectral. analysis, we find that spectral hardness is mainly due to the relative contribution of scattered component. In addition, we see that Wi en spectral features appear when the plasma is optically thick, especially in the high energy range, E≳100keV. We suggest that after a number of scattering the escape probability approaches an asymptotic form depending on the geometry of the scattering medium rather than on the initial photon spectrum.

• SEON KWANG IL(Department of Physics, Korea Advanced Institute of Science and Technology)
• MIN KYOUNG WOOK(Department of Physics, Korea Advanced Institute of Science and Technology)
• CHOI CHUL SUNG(Korea Astronomy Observatory)
• NAM UK WON(Korea Astronomy Observatory)