XMM-Newton Spectra of Intermediate-Mass Black Hole Candidates:   Application of a Monte-Carlo Simulated Model
  We present a systematic spectral analysis of six ultraluminous X-ray sources (NGC1313 X-1/X-2, IC342 X-1, HoIX X-1, NGC5408 X-1 and NGC3628 X-1) observed with XMM-Newton Observatory. These extra-nuclear X-ray sources in nearby late-type galaxies have been considered as intermediate-mass black hole candidates. We have performed Monte-Carlo simulations of Comptonized multi-color black-body accretion disks. This unified and self-consistent spectral model assumes a spherically symmetric, thermal corona around each disk and accounts for the radiation transfer in the Comptonization. We find that the model provides satisfactory fits to the XMM-Newton spectra of thesources. The characteristic temperatures of the accretion disks (T_in), for example, are in the range of ~ 0.05-0.3 keV, consistent with the intermediate-mass black hole interpretation. We find that the black hole mass is typically about a few times 10^3 M_\odot and has an accretion rate ~ 10^{-6} - 10^{-5} M_\odot yr^{-1}. For the spectra considered here, we find that the commonly used multi-color black-body accretion disk model with an additive power law component, though not physical, provides a good mathematical approximation to the Monte-Carlo simulated model. However, the latter model provides additional constraints on the properties of the accretion systems, such as the disk inclination angles and corona optical depths. 
Q. Daniel Wang, Yangsen Yao, Wakako Fukui, ShuangNan Zhang, & Rosa   Williams