| |
 |
| Paper: |
Accretion and Ejection in Sgr A* |
| Volume: |
439, The Galactic Center: a Window to the Nuclear Environment of Disk Galaxies |
| Page: |
346 |
| Authors: |
Yuan, F. |
| Abstract: |
We review our current understanding to the accretion and ejection
processes in Sgr A*. Roughly speaking, they correspond to the
quiescent and flare states of the source respectively. The
high-resolution Chandra observations to the gas at the Bondi
radius combined with the Bondi accretion theory, the spectral energy
distribution from radio to X-ray, and the radio polarization provide
us strict constraints and abundant information to the theory of
accretion. We review these observational results and describe how
the advection-dominated accretion flow model explains these
observations. Recently more attentions have been paid to flares in
Sgr A*. Many simultaneous multi-wavelength campaigns have been
conducted, aiming at uncovering the nature of flares. The main
observational properties of flares are briefly reviewed. Especially,
the time lag between the peaks of flare at two radio frequencies
strongly indicates that the flare is associated with ejection of
radio-emitting blobs from the underlying accretion flow. Such kind
of episodic jets is distinctive from the continuous jets and are
quite common in black hole systems. We introduce the
magnetohydrodynamical model for the formation of episodic jets
recently proposed based on the analogy with the theory of coronal
mass ejection in the Sun. We point out that the various
observational appearances of flares should be explained in the
framework of this model, since ejection and flare originate from the
same physical process. |
|
|
|
|
|
