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J. Lee, D.E. Gary, P.T. Gallagher (NJIT)
A powerful flare (GOES SX class of M9.8) occurred on 1999 August 20 at 23:06 UT near the eastern limb during a Max Millennium campaign. The Owens Valley Solar Array (OVSA) at the time was operating in a high time resolution (1 s) mode to observe an impulsive microwave burst rising very rapidly (within 3 s) at all observing frequencies in the range of 1.4 to 18 GHz. As a main characteristic of the burst, the microwave spectrum decays in a remarkably well-defined exponential profile with a timescale varying in the range of ~ 30 s to ~4 min, in proportion to the wavelength. The accompanying hard X ray emission from the BATSE DISCLA data is confined to a short time interval (~ 30 s), and its light curve is very similar to that of the high-frequency (15--18 GHz) microwaves. Our analysis is therefore focused on whether these observartions are consistent with theoretical predictions for the microwave emission from trapped electrons in the corona and thick target X-ray emission from the electrons precipitating into the chromosphere. In addition, we infer the magnetic reconnection geometry from EUV images obtained from SoHO/EIT which is used as another constraint to study the property of the acceleration.
The OVSA is supported by NSF grants ATM-9796213 and AST-9796238 and NASA grant NAG5-6381 to New Jersey Institute of Technology.
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