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arXiv · astro-ph/0312118

XMM-Newton Observations of the Ultraluminous Nuclear X-ray Source in M33

L. Foschini·J. Rodriguez·Y. Fuchs·L. C. Ho·M. Dadina·G. Di Cocco·T. J. -L. Courvoisier·G. Malaguti
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Abstract

We present observations with XMM-Newton of M33 X-8, the ultraluminous X-ray source (L_{0.5-10 keV} ~ 2x10^39 erg/s) closest to the centre of the galaxy. The best-fit model is similar to the typical model of Galactic black holes in very high state. Comparison with previous observations indicates that the source is still in a very high state after about 20 years of observations. No state transition has been observed even during the present set of XMM-Newton observations. We estimate the lower limit of the mass of the black hole >6 M_sun, but with proper parameters taking into account different effects, the best estimate becomes 12 M_sun. Our analysis favours the hypothesis that M33 X-8 is a stellar mass black hole candidate, in agreement with the findings of other authors. In addition, we propose a different model where the high luminosity of the source is likely to be due to orientation effects of the accretion disc and anisotropies in the Comptonized emission.

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L. Foschini, J. Rodriguez, Y. Fuchs, L. C. Ho, M. Dadina, G. Di Cocco, T. J. -L. Courvoisier, G. Malaguti. 2003-12-05. XMM-Newton Observations of the Ultraluminous Nuclear X-ray Source in M33. https://doi.org/10.1051/0004-6361%3A20034303

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