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On the Sources Above the Neutral Line of Radial Magnetic Fields in Solar Active Regions

On the Sources Above the Neutral Line of Radial Magnetic Fields in Solar Active Regions. A. G. Stupishin, L. V. Yasnov Radio Physics Research Institute, St. Petersburg University, Russia. V. M. Bogod St. Petersburg branch of Special Astrophysical Observatory, Russia.

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On the Sources Above the Neutral Line of Radial Magnetic Fields in Solar Active Regions

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  1. On the Sources Above the Neutral Line of Radial Magnetic Fieldsin Solar Active Regions A. G. Stupishin, L. V. Yasnov Radio Physics Research Institute,St. PetersburgUniversity, Russia V. M. Bogod St. Petersburg branch ofSpecial Astrophysical Observatory, Russia

  2. Neutral Line Sources (NLS) – stable, bright, compact sources in microwaves, placed over the neutral line of photosphere magnetic field of active region. Observations: WSRT, VLA, RATAN-600, NoRH Kundu, M. R. , Alissandrakis, C.E., Solar Phys., 1984, 94, 249 Alissandrakis, C. E., Gel'frejkh, G. B., Borovik, V. N., Korzhavin, A. N., Bogod, V. M., Nindos, A., Kundu, M. R., Astronomy and Astrophysics, 1993, 270, 509. Alissandrakis C. E.,Kundu, M. R. Astroph. J., 1982 , 253, L49 Akhmedov, Sh. B., Borovik, V.N., Gelfreikh, G.B., Bogod, V.M., Korzhavin, A.N., Petrov, Z.E., Dikij, V.N., Lang, K.R., and Willson, R.F., Astroph. J.,1986, 301, 460. Uralov A.M., Grechnev V.V., Rudenko G.V., Rudenko I.G., Nakajima H. Solar Phys. 2008, V. 249. P. 315. PS-type NLS peculiarities: Sizes – 10”… 30” Brightness Temperatures – up to 10 MK (at wavelengths 3…4 cm) High spectral indices at short wavelengths Low or medium polarization degree Halo-type NLS: Sizes – all active region RATAN-600 characteristics: frequency range: 0.75 … 18.2 GHz 112 frequencies in R and L polarization max. angular resolution: 2 arcsec brightness temperature limit: 5∙10-5 K

  3. 10956 A, D – low polarization, related to plages C, B – cyclotron sources, high polarization NLS – no polarization, above neutral line

  4. 10956 Size: 20”…30” in 6…14 GHz NLS between cyclotron sources, in the top of magnetic field lines δNLS=3 … 4

  5. 11358 B (NLS) – stable δNLS= 0.7

  6. 10486 Change sign of polarization at 5.7 GHz: ordinary mode emission

  7. 10486 Zheleznyakov, V. V., Zlotnik, E. Ya. 1980: Astronomical Journal (R), 57, 778: Emission of such narrow region because of hot loops or hot current sheets. Estimation of ordinary mode emission region size: - Magnetic field scale,

  8. 10904 Halo-type NLS

  9. 10904

  10. 10904

  11. 10904

  12. Low polarization, same size at different wavelengths, Flux decreases with frequency increases – mechanism of generation? Cyclotron mechanism in quasi-transversal field at the top of magnetic loop Fulfilled in the angle range 60o … 85o

  13. Tor model of magnetic field

  14. Conclusions Several NLSs was observed in wide range of wavelengths. It allowed to estimate spectral indices of such kind of sourcesδNLS =3 … 4and maybe lower in some cases. NLS placed at the top of magnetic loop. Low polarization can be explained by cyclotron mechanism (thermal electrons) in the regions with angle between magnetic field and line of sight 60o … 85o. Non-thermal electrons – possible not (sources are stable in few days, while thermalization of electron distribution – tens of minutes). Some spectral details (sudden change of polarization sign) can be explained by propagation through the hot areas (with typical sizes about 5∙107 cm).

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