Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity - AstrophysicsReportar como inadecuado

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Abstract: Sgr A*, the massive black hole at the center of the Galaxy, varies in radiothrough X-ray emission on hourly time scales. The flare activity is thought toarise from the innermost region of an accretion flow onto Sgr A*. We presentsimultaneous light curves of Sgr A* in radio, sub-mm and X-rays that show apossible time delay of 110$\pm17$ minutes between X-ray and 850 $\mu$msuggesting that the sub-mm flare emission is optically thick. At radiowavelengths, we detect time lags of of $20.4\pm6.8, 30\pm12$ and 20$\pm6$minutes between the flare peaks observed at 13 and 7 mm 22 and 43 GHz inthree different epochs using the VLA. Linear polarization of 1$\pm0.2$% and0.7$\pm0.1$% is detected at 7 and 13 mm, respectively, when averaged over theentire observation on 2006 July 17. A simple model of a bubble of synchrotronemitting electrons cooling via adiabatic expansion can explain the time delaybetween various wavelengths, the asymmetric shape of the light curves, and theobserved polarization of the flare emission at 43 and 22 GHz. The derivedphysical quantities that characterize the emission give an expansion speed ofv$ {exp} \sim 0.003-0.1$c, magnetic field of B$\sim$10-70 Gauss and particlespectral index p$\sim$1-2. These parameters suggest that the associated plasmacannot escape from Sgr A* unless it has a large bulk motion.

Autor: F. Yusef-Zadeh, M. Wardle, C. Heinke, C. D. Dowell, D. Roberts, F. K. Baganoff, W. D. Cotton



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