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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. 8, No. 11                                              Jun 12, 1998


Recently submitted papers:
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Email    : rohan@cfata1.harvard.edu
Title    : Explaining the spectrum from the Galactic Centre using a two 
           temperature plasma
Author(s): Rohan Mahadevan
Institute: Institute of Astronomy, University of Cambridge,   
           Madingley Road, Cambridge, CB3 0HA, England
Paper    : to appear in Nature
EPrint   : astro-ph/9806018

Abstract: 
The radio source Sagittarius A^* (Sgr A^*), is thought to be a
supermassive black hole located at the centre of our Galaxy, that is
accreting gas from the surrounding region.  Using the high inferred
accretion rates, however, standard accretion models are unable to
explain the low luminosity and observed spectrum from Sgr A*. A new
accretion model has been proposed - an advection dominated accretion
flow (ADAF), where most of the accretion energy is stored in the gas
and lost into the black hole.  The gas therefore has a two-temperature
structure, with the protons being much hotter than the electrons.  The
model explains the low luminosity from Sgr A* and most of the
millimeter to hard X-ray spectrum, but has had serious difficulty in
agreeing with the low energy radio observations. Here we report an
emission process associated with the protons that naturally resolves
the observed discrepancy.  This provides, for the first time,
observational evidence for a two-temperature plasma in hot accretion
flows, and gives strong support to the idea that an ADAF does accrete
onto a 2.5 * 10^6 solar mass black hole at the Galactic Centre.
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			       Edited by
Angela Cotera                                Heino Falcke
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