Abstract
Observations indicate that fast electrons in solar flares, which cause the hard X-ray burst and the impulsive microwave burst, lose energy predominantly by collisional processes. This requires a thick-target theory of the emission, for which the electron spectrum inferred from the X-ray spectrum becomes 1.5 powers steeper than in the usual thin-target theory.
The low-energy end of this spectrum contains enough energy above about 5 keV to supply the white-light continuum emission occasionally observed in major flares. The penetration of the nonthermal electrons creates long-lived excess ionization which enhances the free-free and free-bound continuum in the heated medium. The emission will occur high above the photosphere at small optical depth in the visible continuum. Thus its spectrum will extend into the infrared and ultraviolet.
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References
Anderson, K. A. and Winckler, J. A.: 1962, J. Geophys. Res. 67, 4103.
Arnoldy, R. L., Kane, S. R., and Winckler, J. R.: 1968, Astrophys. J. 151, 711.
Athay, R. G., and Canfield, R. C.: 1970, NBS Special Publication 332, 65.
Brown, J. C.: 1971, Solar Phys. 18, 489.
Cox, D. and Tucker, W.: 1969, Astrophys. J. 157, 1157.
Croom, D. L.: 1970, Solar Phys. 15, 414.
De Mastus, H. and Stover, R. R.: 1967, Publ. Astron. Soc. Pacific 79, 615.
Dobbie, J, C., Moss, W., and Thackeray, A. D.: 1938, Monthly Notices Roy. Astron. Soc. 98, 606.
Donnelly, R.: 1970, ESSA Tech. Report ERL 169-SDL 14.
Evans, R. D.: 1955, The Atomic Nucleus, McGraw-Hill, New York.
ESSA 1969, Report UAG-5.
Friedman, M. and Hamberger, S. M.: 1969, Solar Phys. 8, 104.
Frost, K.: 1969, Astrophys. J. Letters 158, L159.
Gardner, J. B.: 1971, personal communication.
Holt, S. S. and Ramaty, R.: 1969, Solar Phys. 8, 119.
Hudson, H. S. and Ohki, K.: 1972, Solar Phys., to be published.
Hudson, H. S., Peterson, L. E., and Schwartz, D. A.: 1969, Astrophys. J. 157, 389.
Kahler, S. W. and Kreplin, R. W.: 1971, Astrophys. J. 168, 531.
Kane, S.: 1969, Astrophys. J. Letters 157, L39.
Kane, S. and Anderson, K. A.: 1970, Astrophys. J. 162, 1003.
Kane, S. and Donnelly, R. F.: 1971, Astrophys. J. 164, 151.
Kane, S. R. and Winckler, J. R.: 1968, Solar Phys. 6, 304.
Koch, H. M. and Motz, J. W.: 1959, Rev. Mod. Phys. 31, 920.
Korchak, A. A.: 1965, Geomagnetizm i Aeronomiya 5, 467.
Lin, R. P. and Hudson, H. S.: 1971, Solar Phys. 17, 412.
Maeda, K.: 1963, J. Geophys. Res. 68, 185.
McIntosh, P. S. and Donnelly, R. F.: 1972, Solar Phys. 23, 444.
Najita, K. and Orrall, F. W.: 1970, Solar Phys. 15, 176.
Spitzer, L.: 1967, The Physics of Fully Ionized Gases, 2nd ed., Interscience, New York.
Stein, W. A. and Ney, E. P.: 1963, J. Geophys. Res. 68, 65.
Švestka, Z.:1966, Space Sci. Rev. 5, 388.
Švestka, Z.. 1970, Solar Phys. 13, 471.
Takakura, T.: 1967, Solar Phys. 1, 304.
Takakura, T. and Kai, K.: 1966, Publ. Astron. Soc. Japan 18, 57.
Takakura, T. and Scalise, E. Jr.: 1970, Solar Phys. 11, 434.
Thomas, R. N. and Athay, R. G.: 1961, Physics of the Solar Chromosphere, Interscience, New York.
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Hudson, H.S. Thick-target processes and white-light flares. Sol Phys 24, 414–428 (1972). https://doi.org/10.1007/BF00153384
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DOI: https://doi.org/10.1007/BF00153384