Abstract
The Very Large Array (VLA) and the RATAN 600 were used to observe a solar active region on two consecutive days around the time of a partial solar eclipse in July 1990. VLA synthesis maps at 2.0, 3.5, and 6.2 cm wavelength reveal bright (T b = 0.2 − 2.2 × 106 K), compact (θ = 10″–40″) sources above the penumbra of the leading sunspot while maps at 20 cm wavelength reveal an extended (θ ≈ 4.5′) looplike structure (T b ≈ 106 K) between the dominant spots. Total flux and brightness temperature spectra of both components were obtained by the RATAN at nine wavelengths between 1.7 and 21 cm. The relatively-flat spectrum of the extended emission is attributed to the optically thin thermal brems Strahlung of electrons trapped in a magnetic loop at coronal temperatures. Step-spectrum sunspot-associated emission is attributed to thermal gyroresonance radiation at different heights along the leg of a loop joining regions of opposite magnetic polarity. Comparisons with predicted distributions of gyroresonance radiation indicate that the compact sunspot-associated sources lie at heights of h = 2500–17500 km above the photosphere. Although potential fields of sufficient strength appear to exist at coronal heights, differences n the observed and predicted brightness distributions suggest some role for non-potential fields or for an inhomogeneous distribution of electron density or temperature above the sunspot.
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References
Akhmedov, Sh. B. et al.: 1986, Astrophys. J. 301, 460.
Alissandrakis, C. E. and Kundu, M. R.: 1982, Astrophys. J. 253, L49.
Alissandrakis, C. E. Kundu, M. R., and Lantos, P.: 1980, Astron. Astrophys. 82, 30.
Brosius, J. W. and Holman, G. D. 1989, Astrophys. J. 342, 1172.
Brosius, J. W., Willson, R. F., Holman, G. D., and Schmelz, J. T.: 1992, Astrophys. J. (to appear).
Doyle, J. G., Raymond, J. C., Noyes, R. W., and Kingston, A. E.: 1985, Astrophys. J. 297, 816.
Dulk, G. A.: 1985, Ann. Rev. Astron. Astrophys. 23, 169.
Dulk, G. A. and Gary, D. E.: 1983, Astron. Astrophys. 124, 103.
Felli, M., Lang, K. R., and Willson, R. F.: 1981, Astrophys. J. 247, 325.
Gary, D. E. and Hurford, G. J.: 1987, Astrophys. J. 317, 527.
Gelfreikh, G. B. and Lubyshev, B. I. 1979, Soviet Astron. 23, 316.
Gelfreikh, G. B., Peterova, N. G., and Ryabov, B. I.: 1987, Solar Phys. 108, 89.
Khaikin, S. E., Kaidanovskii, N. L., Parijskij, Yu. N., and Esepkina, N. A.: 1972, Isvestia, Main Astronomical Obs. Pulkova, No. 188, 3.
Krüger, A. and Hildebrandt, J.: 1986, Astron. Nach., 306, 157.
Krüger, A., Hildebrandt, J., and Fürstenburg, F.: 1985, Astron. Astrophys. 143, 72.
Krüger, A., Hildebrandt, J., Bogod, V. M., Korzhavin, A. N., Akhmedov, Sh. B., and Gelfreikh, G. B.: 1986, Solar Phys. 105, 111.
Lang, K. R. and Willson, R. F.: 1982, Astrophys. J. 255, L111.
Lang, K. R. and Willson, R. F.: 1983, Astron. Astrophys. 127, 135.
Lang, K. R., Willson, R. F., and Gaizauskas, V.: 1983, Astrophys. J. 267, 455.
Lang, K. R., Willson, R. F., and Rayrole, J.: 1982, Astrophys. J. 258, 384.
Lang, K. R., Willson, R. F., Smith, K. L., and Strong, K. T.: 1987, Astrophys. J. 322, 1035.
Nicolas, K. R., Kjeldseth-Moe, O., Bartoe, J.-D. F., and Brueckner, G. E.: 1982, Solar Phys. 81, 253.
Nitta, N., White, S. M., Kundu, M. R., Gopalswamy, N., Holman, G. D., Brosius, J. W., Schmelz, J. T., Saba, J. L. R., and Strong, K. T.: 1991, Astrophys. J. 374, 374.
Parijskij, Yu. N. et al.: 1976, Soviet Astron. 20, 577.
Sakurai, T.: 1982, Solar Phys. 76, 301.
Shevgaonkar, R. K. and Kundu, M. R.: 1984, Astrophys. J. 283, 413.
Staude, J.: 1981, Astron. Astrophys. 100, 284.
Strong, K. T. Alissandrakis, C. E. and Kundu, M. R.: 1984, Astrophys. J. 277, 865.
Webb, D. F., Holman, G. D., Davis, J. M., Kundu, M. R., and Shevgaonkar, R. K.: 1987, Astrophys. J. 315, 716.
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Bogod, V.M., Gelfreikh, G.B., Willson, R.F. et al. Very Large Array-RATAN 600 observations of a solar active region. Sol Phys 141, 303–323 (1992). https://doi.org/10.1007/BF00155182
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DOI: https://doi.org/10.1007/BF00155182