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Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity | | F. Yusef-Zadeh
; M. Wardle
; C. Heinke
; C. D. Dowell
; D. Roberts
; F. K. Baganoff
; G. C. Bower
; | | Date: |
18 Dec 2007 | | Abstract: | Sgr A*, the massive black hole at the center of the Galaxy, varies in radio
through X-ray emission on hourly time scales. The flare activity is thought to
arise from the innermost region of an accretion flow onto Sgr A*. We present
simultaneous light curves of Sgr A* in radio, sub-mm and X-rays that show a
possible time delay of 110$pm17$ minutes between X-ray and 850 $mu$m
suggesting that the sub-mm flare emission is optically thick. At radio
wavelengths, we detect time lags of of $20.4pm6.8, 30pm12$ and 20$pm6$
minutes between the flare peaks observed at 13 and 7 mm in three different
epochs using the VLA. Linear polarization of 1$pm0.2$% and 0.7$pm0.1$% is
detected at 7 and 13 mm, respectively, when averaged over the entire
observation on 2006 July 17. A simple picture of an expanding bubble of
synchrotron emitting hot plasma can explain the time delay between various
wavelengths, the asymmetric shape of the light curves, and the observed
polarization of the flare emission at 43 and 22 GHz. The derived physical
quantities that characterize the flare emission give the blob expansion speed
of v$_{exp} sim 0.003-0.1$c, magnetic field of B$sim$10-70 Gauss and particle
spectral index p$sim$1-2. These parameters suggest that the expanding gas can
not escape from Sgr A* unless it has a large bulk motion. | | Source: | arXiv, 0712.2882 | | Services: | Forum | Review | PDF | Favorites | |
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