EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 429/2 Article
Free access article

Issue A&A
Volume 429, Number 2, January II 2005
Page(s) L33 - L36
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200400101



A&A 429, L33-L36 (2005)
DOI: 10.1051/0004-6361:200400101

Letter

Using close stars as probes of hot accretion flow in Sgr A *

S. Nayakshin

Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str.1, 85741 Garching, Germany
    e-mail: serg@mpa-garching.mpg.de

(Received 20 October 2004 / Accepted 6 November 2004 )

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.


Key words: accretion, accretion disks -- black hole physics -- Galaxy: center -- radiation mechanisms: general

SIMBAD Objects



© ESO 2004


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.