Please use this identifier to cite or link to this item: http://hdl.handle.net/2381/26640
 Title: Using close stars as probes of hot accretion flow in Sgr A* Authors: Nayakshin, S. First Published: Jan-2005 Publisher: EDP Sciences for European Southern Observatory (ESO) Citation: Astronomy & Astrophysics, 2005, 429 (2) Abstract: The extremely hot and tenuous accretion flow in the immediate vicinity of Sgr A * is believed to be invisible (too dim) in the X-ray band, except for short X-ray flares. Here we point out that during pericenter passages, close brightest stars irradiate the inner region of the accretion flow, providing a plenty of optical/UV photons. These seed photons are Compton up-scattered by the hot electrons of the accretion flow to higher frequencies, some into the X-ray band, potentially making the innermost accretion flow much brighter in X-rays than usual. We propose to use coordinated near infra-red and X-ray observations of close star passages to put constraints onto Sgr A * accretion theories. The absence of a noticeable change in the steady emission of Sgr A * as observed by Chandra in the year 2002, when the star named S2 passed through a pericenter of its orbit, already rules out the hotter of the "standard" Advection-Dominated Accretion Flows. The less dense accretion flows, in particular the model of Yuan et al. (2003), passes the test and is constrained to accretion rates no larger than ~ few $\times$ 10 $^{-7}~{\,M_\odot}$ year -1. DOI Link: 10.1051/0004-6361:200400101 ISSN: 0004-6361 Links: http://hdl.handle.net/2381/26640http://www.aanda.org/articles/aa/abs/2005/02/aagj201/aagj201.html Version: Publisher Version Status: Peer-reviewed Type: Journal Article Rights: Copyright © 2005 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO. Appears in Collections: Published Articles, Dept. of Physics and Astronomy

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