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Post Info TOPIC: CXOM31 J004253.1+411422
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RE: CXOM31 J004253.1+411422
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Title: The effect of advection at luminosities close to Eddington: The ULX in M31
Authors: 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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Title: CXOM31 J004253.1+411422: The first ultra-luminous X-ray transient in M 31
Authors: A. Kaur, M. Henze, F. Haberl, W. Pietsch, J. Greiner, A. Rau, D.H. Hartmann, G. Sala, M. Hernanz

We seek clarification of the nature of X-ray sources detected in M 31. Here we focus on CXOM31 J004253.1+411422, the brightness of which suggests that it belongs to the class of ultraluminous X-ray sources. We determine the X-ray properties of sources detected in the XMM-Newton Chandra monitoring program. We investigate spectral properties and search for periodic or quasi-periodic oscillations. A multi-component model is applied to the spectra obtained from XMM-Newton data to evaluate the relative contributions from thermal and non-thermal emission. The time dependence of this ratio is evaluated over a period of forty days. We simultaneously fit data from XMM-Newton EPIC-pn, MOS1 and MOS2 detectors with (non-thermal) powerlaw and (thermal) multicoloured blackbody. The X-ray spectrum is best fit by the combination of a thermal component with kT ~ 1 keV and a powerlaw component with photon index approximately 2.6. From combined analysis of Chandra, Swift and XMM-Newton data, the unabsorbed total luminosity of this source decreases from ~ 3.8 x 10^{39} erg s^{-1} in the first observation to ~ 0.5 x 10^{39} ergs s^{-1} over a period of three months. The decay closely follows an exponential decline with a time constant of 32 days. The source spectrum evolves significantly, exhibiting a faster decline of the thermal component. We do not find evidence of any significant temporal features in the power density spectrum. The presence of a thermal component at kT ~ 1 keV in conjunction with a non-thermal high energy tail, is also consistent with spectral properties of other ULXs in the "high state". Our analysis indicates that the underlying source of this first ULX in M 31 is a ~ 14 M_sun black hole, accreting near the Eddington limit, that underwent a transient outburst followed by an exponential decay reminiscent of transients associated with galactic X-ray novae.

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