1. St. Petersburg branch of Special Astrophysical Observatory, Russia
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

2. Observations: WSRT, VLA, RATAN-600, NoRH
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 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 sources δNLS = 3 … 4 and 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).