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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.64] On the Origin of Energy-dependent time Delays in Hard X-ray Emission from Impulsive Solar Flares

Recent studies of the timing of solar flare hard X-ray emission using cross-correlation techniques indicate that for the majority of impulsive flares there is a systematic time delay of a few tens of milliseconds between low (25- 50 keV) and higher energy emission (50-100 keV). Ashwanden and Schwartz (1995, ApJ, 455, 699) and Ashwanden et al (1996, ApJ, 464,985) have interpreted these delays as due to energy dependent time of flight differences for electron propagation from the corona to the chromosphere. We show here that the cross-correlation analysis is comprimised by spectral index variations within the flare. BATSE channel ratios indicate 50-100 5-10 seconds. Using simulated and actual data we show that cross-correlating energy channels with identical timing but with variations in the amplitude of a small number of emission spikes, produces asymmetric correlation functions that mimic a time delay of either sign. The time delays are, therefore, not uniquely due to time of flight differences.

Program listing for Friday