Non-Thermal processes and Superhot Plasma Creation in Solar Flares
We review new aspects of solar flare energy release and related non-thermal/thermal processes revealed by the Hard X-ray Telescope (HXT) aboard Yohkoh. Hard X-ray imagery of impulsive solar flares with HXT has shown that the bulk of hard X-rays above 30 keV is emitted near the footpoints of a flaring magnetic loop by electrons accelerated near the top of the loop, manifesting itself most frequently as “double sources” located on both sides of a magnetic neutral line. Besides these “double footpoint sources”, a third hard X-ray source, located above the top of the flaring loop visible in soft X-rays, was discovered in some impulsive flares near the solar limb. This discovery provides us with clear evidence that solar flare energy release takes place outside the closed loop, most likely via mignetic reconnection in an open magnetic field configuration. Observations of superhot plasma creation with HXT are also briefly reviewed and their implication in the energy release and transfer in solar flares is discussed.
KeywordsSolar Flare Magnetic Reconnection Magnetic Neutral Line Double Source Impulsive Flare
Unable to display preview. Download preview PDF.
- Hoyng, P., Machado, M.E., Duijveman, A., Boelee, A., de Jager, C., Fryer, R., Galama, M., Hoekstra, R., Imhof, J., Lafleur, H., Maseland, H.V.A.M., Mels, W.A., Schadee, A., Schrijver, J., Simnett, G.M., Svestka, Z., van Beek, H.F., van Tend, W., van der Laan, J.J.M., van Rens, P., Werkhoven, F., Willmore, A.P., Wilson, J.W.G., and Zandee, W. (1981) Hard X-ray imaging of two flares in active region 2372, Astrophys. J. Lett, 244, pp. L153-L156.ADSCrossRefGoogle Scholar
- Kosugi, T., Sakao, T., Masuda, S., Hara, H., Shimizu, T., and Hudson, H.S. (1994) Hard and soft X-ray observations of a super-hot thermal flare of 6 February, 1992, in “Proc. of Kofu Symposium”, eds. Enome, S. and Hirayama, T., NRO Report No.360, pp. 127–129.Google Scholar
- Kosugi, T., Sawa, M., Sakao, T., Masuda, S., Inda-Koide, M., Yaji, K., and Sato, J. “The Yohkoh HXT Databook” (National Astronomical Observatory, Japan; available upon request from the authors).Google Scholar
- Masuda, S. (1994) Hard X-ray sources and the primary energy release site in solar flares, Ph.D. thesis (University of Tokyo).Google Scholar
- Sakao, T. (1994) Characteristics of solar flare hard X-ray sources as revealed with the hard X-ray telescope aboard the Yohkoh satellite, Ph.D. thesis (University of Tokyo).Google Scholar
- Sakao, T., Kosugi, T., and Makishima, K. (1996) Double footpoint hard X-ray sources in solar flares: II — Statistical approach —, Publ. Astron. Soc. Japan submitted.Google Scholar
- Wu, S.T., de Jager, C., Dennis, B.R., Hudson, H.S., Simnett, G.M., Strong, K.T., Bentley, R.D., and Bornmann, P.L. (1986) Flare energetics, in “Energetic Phenomena on the Sun”, eds. Kundu, M.R., and Woodgate, B.E., SMM Flare Workshop Proceedings, NASA CP-2376, (Greenbelt, Maryland)Google Scholar