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Session 19 - Solar Flares.
Oral session, Monday, June 10
Wisconsin Center,
We analyzed hard X-ray and microwave data for the solar flare BATSE #1791, which started at 1611UT and ended at 1656UT, on 2 November 1991. Data are available simultaneously from BATSE/LAD X-ray and OVRA microwave data base. This flare was particularly interesting, because of the deep cyclic intensity variation. We quantitatively compare the time variations in X-ray photon index and microwave spectral index (both high and low frequency), as well as microwave peak frequency at which the gyro-synchrotron radiation transits from optically-thin to optically thick. Using the time profile of the BASTE/LAD 25-50 KeV flux as a reference, the X-ray photon index profile is out of phase with it as expected; in addition, the microwave peak frequency profile and the low frequency slope profile are observed to be correlated with it. Interesting enough, the high frequency slope profile correlated with X-ray flux before the main peak and anti-correlated with it after the main peak. The relationship between X-ray photon peak counts and microwave peak fluxes is also studied. A plot of microwave peak flux versus X-ray photon peak count produces a curve tracing a tilted ellipse counter-clockwisely. This indicates that the X-ray peak counts arrive earlier than the corresponding microwave peak fluxes. Finally, we studied the time delays between X-ray and microwave flux peak as a function of frequency and found that delay increases as the frequency increases. The maximum delay time is found for the main peak, it is of about 72 seconds. Shorter delays are found for the other five sub-peaks.
