The S2 star as a probe of the accretion disk of Sgr A*. (arXiv:1303.2115v1 [astro-ph.HE])

The S2 star as a probe of the accretion disk of Sgr A*. (arXiv:1303.2115v1 [astro-ph.HE]):
How accretion proceeds around the massive black hole in the Galactic center
and other highly sub-Eddington accretors remains poorly understood. The orbit
of the S2 star in the Galactic center passes through the accretion disk of the
massive black hole and any observational signature from such interaction may be
used as an accretion probe. Because of its early stellar type, S2 is expected
to possess a fairly powerful wind. We show here that the ram pressure of the
accretion disk shocks the stellar wind fairly close to the star. The shocked
fluid reaches a temperature of ~ 1 keV and cools efficiently through optically
thin, thermal bremsstrahlung emission. The radiation from the shocked wind
peaks around the epoch of the pericenter passage of the star at a luminosity
potentially comparable to the quiescent emission detected from Sgr A*.
Detection of shocked wind radiation can constrain the density of the accretion
disk at a distance of several thousands of gravitational radii from the black
hole.