aagj201.pdf (195.76 kB)

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

journal contribution
posted on 24.10.2012, 09:22 by S. Nayakshin
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.

## Citation

Astronomy & Astrophysics, 2005, 429 (2)

## Version

VoR (Version of Record)

## Published in

Astronomy & Astrophysics

## Publisher

EDP Sciences for European Southern Observatory (ESO)

0004-6361

2005

24/10/2012

## Publisher version

http://www.aanda.org/articles/aa/abs/2005/02/aagj201/aagj201.html

en