TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 53 (No. 6), pp. 581-583, 2001

Hard X-rays from Slow Flares

H. S. Hudson1 and D. E. McKenzie2

1SPRC/ISAS, 3-1-1 Yoshinodai, Sagamihara-shi, Kanagawa 229, Japan
2Montana State University, Bozeman, MT 59717, U.S.A.

(Received June 14, 2000; Revised October 20, 2000; Accepted January 11, 2001)

Abstract: "Slow LDEs" are those for which the rise phase is slow, as well as the decay phase. Such flares follow the Neupert effect, which implies that the non-thermal energy release has a similar relationship to heating as in a normal impulsive flare. Based on a sample of 53 slow LDEs during the first nine years of Yohkoh observations, we find 19 for which substantial overlap occurs with BATSE hard X-ray observations. These events tend strongly to have extended hard X-ray emission even though their hard X-ray emission does not tend to be "impulsive" in the sense of rapid variation. The hard X-ray fluences for these 19 events correlate with the soft X-ray peak fluxes, implying strong non-thermal particle acceleration even for these relatively slow energy-release rates. These events often correspond to the occurrence of "supra-arcade downflows," a phenomenon consistent with the classical reconnection model for gradual-phase flare energy release. This correspondence suggests a close relationship, not depending strongly upon time scale, between large-scale reconnection and the acceleration of non-thermal electrons.

Corresponding author E-mail: hudson@isass1.solar.isas.ac.jp

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