Odele Straub, Chris Done, Matthew J. Middleton
The transient, ultra-luminous X-ray source CXOM31 J004253.1+411422 in the Andromeda galaxy is most likely a 10 solar mass black hole, with super-Eddington luminosity at its peak. The XMM-Newton spectra taken during the decline then track luminosities of 0.86-0.27 L_Edd. These spectra are all dominated by a hot disc component, which roughly follows a constant inner radius track in luminosity and temperature as the source declines. However, at the highest luminosity the disc structure should change due to advection of radiation through the disc. This advected flux can be partly released in the plunging region, with the remainder being advected below the event horizon. We use a fully relativistic disc model, SLIMBH, that includes these effects, and uses full radiative transfer through the photosphere based on TLUSTY. It also incorporates full relativistic photon ray-tracing from the proper location of the disc photosphere rather than the mid-plane as the disc is no longer geometrically thin. However, we find that these new models differ only very slightly from the non-advective (standard) BHSPEC even at the highest luminosities considered here. While both discs can fit the highest luminosity data, neither is a good fit to the lower luminosities. We speculate that this could be due to a decreasing fraction of magnetic pressure support with increasing luminosity, such as seen in models where the magnetic pressure saturates to some fraction of the gas rather than total (gas plus radiation) pressure.
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http://arxiv.org/abs/1208.0160
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