XMM‐NewtonSpectra 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) observedwith XMM-Newton Observatory. These extra-nuclear X-ray sources in nearbylate-type galaxies have been considered as intermediate-mass black holecandidates. We have performed Monte-Carlo simulations of Comptonizedmulti-color black-body accretion disks. This unified and self-consistentspectral model assumes a spherically symmetric, thermal corona around each diskand accounts for the radiation transfer in the Comptonization. We find that themodel provides satisfactory fits to the XMM-Newton spectra of thesources. Thecharacteristic temperatures of the accretion disks (T_in), for example, are inthe range of ~ 0.05-0.3 keV, consistent with the intermediate-mass black holeinterpretation. We find that the black hole mass is typically about a few times10^3 M_\odot and has an accretion rate ~ 10^{-6} - 10^{-5} M_\odot yr^{-1}. Forthe spectra considered here, we find that the commonly used multi-colorblack-body accretion disk model with an additive power law component, thoughnot physical, provides a good mathematical approximation to the Monte-Carlosimulated model. However, the latter model provides additional constraints onthe properties of the accretion systems, such as the disk inclination anglesand corona optical depths.Comment: 23 pages, 4 figures, 5 tables. ApJ accepted, July 2004 issu