Issue |
A&A
Volume 410, Number 2, November I 2003
|
|
---|---|---|
Page(s) | 519 - 522 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20031264 | |
Published online | 17 November 2003 |
Radio variability of Sagittarius A* due to an orbiting star
1
Korea Institute for Advanced Study, 207-43 Cheongryangri-dong Dongdaemun-gu, Seoul 130-012, Korea
2
Korea Astronomy Observatory, 36-1 Hwaam-dong, Yusong-gu, Taejon 305-348, Korea e-mail: cschoi@kao.re.kr
Corresponding author: Heon-Young Chang, hyc@ns.kias.re.kr
Received:
5
June
2003
Accepted:
23
July
2003
Recently, unprecedentedly accurate data on the orbital motion of stars
in the vicinity of Sgr have become available.
Such information can be used not only to constrain the mass of the supermassive
black hole (SMBH) in the Galactic center but also to study the source
of the radio emission. Two major competing explanations
of the radio spectrum of Sgr
are based on
two different models, that is, hot accretion disk and jet.
Hence, independent observational constraints
are required to resolve related issues.
It has been suggested that a star passing by a hot accretion disk
may cool the hot accretion disk by Comptonization
and consequently cause the radio flux variation.
We explore the possibility of using the observational data of the star S2, currently closest to the Galactic center, to distinguish
physical models for the radio emission of Sgr
, by
applying the stellar cooling model to Sgr
with the orbital parameters derived from the observation. The
relative difference in the electron temperature due to stellar cooling by S2 is a few parts of a thousand
and the consequent relative radio luminosity
difference is of the order of 10-4. Therefore, one might expect to observe
the radio flux variation with a periodic or quasi-periodic
modulation in the frequency range
if radiatively inefficient hot accretion flows
are indeed responsible for the
radio emission, contrary to the case of a jet.
According to our findings, even though no periodic radio flux variations
have been reported up to date a radiatively inefficient hot
accretion disk model cannot be conclusively ruled out. This is because
the current available sensitivity is insufficient and because
the energy bands that have been studied are too high
to observe the effect of the star S2 even if
it indeed interacts with the hot disk.
Key words: accretion, accretion disks / Galaxy: center / galaxies: active / black hole physics
© ESO, 2003
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