http://arxiv.org/abs/1804.02860
The density distribution of the accretion flow around Sgr A* – the massive black hole at our Galactic Centre (GC) – is not very well known. The so-called S2 star will reach its closest approach to Sgr A* at around 1500 $R_\mathrm{s}$ in May 2018. It has been proposed that the interaction of its stellar wind with the accretion flow will lead to a detectable X-ray flare. Our goal is to verify whether the S2 star wind can be used as a diagnostic tool to infer the properties of the accretion flow towards Sgr A* at its peri centre, putting important constraints on black hole accretion flow models. We run a series of three-dimensional AMR simulations with the help of the RAMSES code which include the realistic treatment of the interaction of S2’s stellar wind with the accretion flow along its orbit and – apart from hydrodynamical and thermodynamical effects – include the tidal interaction with the massive black hole. The X-ray emission is calculated in the observable 2-10 keV window. No significant excess of X-ray emission is found for typical accretion flow models. A measurable excess is produced for a significantly increased density of the accretion flow. This can, however, be ruled out for standard power-law accretion flow models as in this case the thermal X-ray emission without the S2 wind interaction would already exceed the observed, quiescent luminosity. Alternatively, a change of the wind parameters within their uncertainties (increased mass loss rate and decreased wind velocity) might lead to a (marginally) observable X-ray flaring event. Even the detection of an X-ray flare during the upcoming peri centre passage of the S2 star would not allow to put strict constraints on the accretion flow around Sgr A* due to the degeneracy caused by the dependence on multiple parameters. A more accurate knowledge of the stellar wind parameters would be needed (abridged).
M. Schartmann, A. Burkert and A. Ballone
Tue, 10 Apr 18
6/79
Comments: submitted to A&A Letters, comments very welcome!