Abstract
Characteristic times for heating and cooling of the thermal X-ray plasma in solar flares are estimated from the time profile of the thermal X-ray burst and from the temperature, emission measure and over-all length scale of the flare-heated plasma at thermal X-ray maximum. The heating is assumed to be due to magnetic field reconnection, and the cooling is assumed to be due to heat conduction and radiation.
Temperatures and emission measures derived from UCSD OSO-7 X-ray flare observations are used, and length scales are obtained from Big Bear large-scale Hα filtergrams for 17 small (subflare to Class 1) flares. The empirical values obtained for the characteristic times imply (1) that flares are produced by magnetic field reconnection, (2) that conduction cooling of the thermal X-ray plasma dominates radiative cooling and (3) that reconnection heating and conduction cooling of the thermal X-ray plasma are approximately in balance at thermal X-ray maximum. This model in combination with the data gives estimates for the electron number density (1010–1011 cm−3) and the magnetic field strength (10–100 G) in the thermal X-ray plasma and for the total thermal energy generated in a subflare (≈ 1030 erg for an Hα area ≈ 1 square degree) which agree with previous observational and theoretical estimates obtained by others.
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References
Culhane, J. L. and Acton, L. W.: 1970, Monthly Notices Roy. Astron. Soc. 151, 141.
Culhane, J. L., Vesecky, J. F., and Phillips, K. J. H.: 1970, Solar Phys. 15, 394.
Datlowe, D. W., Hudson, H. S., and Peterson, L. E.: 1974, Solar Phys. 35, 193.
Delcroix, A. and Lemaire, A.: 1969, Astrophys. J. 156, 787.
Garriott, O. K., DaRosa, A. V., Davis, M. J., Wagner, L. S., and Thome, G. D.: 1969, Solar Phys. 8, 226.
Hudson, H. S. and Ohki, K.: 1972, Solar Phys. 23, 155.
Neupert, W. M.: 1969, Ann. Rev. Astron. Astrophys. 7. 121.
Parker, E. N.: 1973, Astrophys. J. 180, 247.
Petschek, H. E.: 1964, in W. N. Hess (ed.) AAS-NASA Symp. on the Physics of Solar Flares, Goddard Spaceflight Center, p. 425.
Roy, J.-R.: 1972, Solar Phys. 26, 418.
Roy, J.-R. and Datlowe, D. W.: 1974, preprint, Big Bear Solar Obs. Reft. No. 0143.
Schmidt, H. U.: 1969 in C. de Jager and Z. Švestka (eds.), COSPAR Symp. on Solar Flares and Space Research, North-Holland, Amsterdam, p. 331.
Sturrock, P. A.: 1973, in R. Ramaty and R. G. Stone (eds.), High Energy Phenomena on the Sun Symp. Proc., Goddard Space Flight Center, p. 3.
Sweet, P. A.: 1969, Ann. Rev. Astron. Astrophys. 7, 149.
Thomas, R. J. and Teske, R. G.: 1971, Solar Phys. 16, 431.
Tucker, W. H. and Koren, M.: 1971, Astrophys. J. 168, 283.
Vaiana, G. S. and Giacconi, R.: 1969, in D. A. Tidman and D. G. Wentzel (eds.), Plasma Instabilities in Astrophysics, Gordon and Breach, New York, p. 91.
Widing, K. G. and Cheng, C.-C.: 1974, Astrophys. J. 194, L111.
Zirin, H.: 1974, Vistas in Astron. 16, 1.
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Moore, R.L., Datlowe, D.W. Heating and cooling of the thermal X-ray plasma in solar flares. Sol Phys 43, 189–209 (1975). https://doi.org/10.1007/BF00155153
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DOI: https://doi.org/10.1007/BF00155153