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                              G C N E W S
                             * Newsflash *

            - The Newsletter for Galactic Center Research -

gcnews@mpifr-bonn.mpg.de             http://www.mpifr-bonn.mpg.de/gcnews
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Vol. 11, No. 13                                              May 4, 2000

Dear subscriber,

this is probably the last abstract for Vol. 11 of the newsletter which
will be distributed in a few days. So, if you have any announcements
to the GC community that should be included in the next issue please
send them to us as soon as possible.


Recently submitted papers:
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1) Sgr A* Polarization: No ADAF, Low Accretion Rate, and Non-Thermal 
   Synchrotron Emission (Agol, ApJL)

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Email    : agol@pha.jhu.edu
Title    : Sgr A* Polarization: No ADAF, Low Accretion Rate, and 
           Non-Thermal Synchrotron Emission
Author(s): Eric Agol
Institute: Physics and Astronomy Department, Johns Hopkins 
           University, Baltimore, MD 21218; agol@pha.jhu.edu
Paper    : ApJ Letters, submitted
EPrint   : astro-ph/0005051

Abstract:
The recent detection of polarized radiation from Sgr A* requires a 
non-thermal electron distribution for the emitting plasma. The Faraday 
rotation measure must be small, placing strong limits on the density 
and magnetic field strength. We show that these constraints rule out 
advection-dominated accretion flow models. We construct a simple 
two-component model which can reproduce both the radio to mm spectrum 
and the polarization. This model predicts that the polarization should 
rise to nearly 100% at shorter wavelengths. The first component, 
possibly a black-hole powered jet, is compact, low density, and 
self-absorbed near 1 mm with ordered magnetic field, relativistic 
Alfven speed, and a non-thermal electron distribution. The second 
component is poorly constrained, but may be a convection-dominated 
accretion flow with \dot M 10^-9M_o/yr, in which feedback from 
accretion onto the black hole suppresses the accretion rate at large 
radii. The black hole shadow should be detectable with sub-mm VLBI.
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(Older versions of the Newsflash can be found at the gcnews web-page)
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			       Edited by
Angela Cotera                                Heino Falcke
(cotera@ipac.caltech.edu)                    (hfalcke@mpifr-bonn.mpg.de)
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