On the Structure of Magnetic Field and Radioemission of Sunspot-related Source in

Solar Active Region

T. I. Kaltman, V. M. Bogod

St. Petersburg branch of Special Astrophysical Observatory, Russia

A. G. Stupishin, L. V. Yasnov Radio Physics Research Institute, St. Petersburg University, Russia

Goal:

To develop methods of physical condition diagnostics in the transition region and the lower corona on the base of reconstructed magnetic field and observations of radio emission on RATAN-600 radiotelescope.

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

To estimate physical conditions in particular active regions with simple configuration AR 10933, AR 10935.

AR 10933

RATAN-600 scans

MDI

Source separation

6 GHz

12 GHz

14 GHz

16 GHz

-282" 19"-207" -131" -56"

sun: 2007/01/05: 5.02[cm]Ta,L

2000 AR 10933:

RATAN scans compare with:

UV 195Å (EIT)

Photosphere Magnetic Field (MDI)

Lines of reconstructed Magnetic Field

Magnetic field reconstruction:

1. Source data of 3D photospheric magnetic field – Hinode/SOT instrumentHinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in co-operation with ESA and NSC (Norway).

2. 180-degree ambigity was resolved using minimal temperature method (Metcalf, T.R.: 1994, Solar Phys. 155, 235) with optimization suggested at (Leka, K.D., Barnes, G., Crouch, A.D., Metcalf, T.R., Gary, G. A.,

Jing, J., Liu, Y.: 2009, Solar Phys. 260, 83) (inhomogeneous initial temperature).

3. Potential magnetic field was reconstructed according (Nakagawa, Y., Raadu, M.A.: 1972, Solar Phys. 25, 127; Allissandrakis, C.E.: 1981, Astron. Astrophys.

100, 197) (concerning Bz component is not perpendicular to photosphere).

4. On the base of reconstructed potential field (as initial condition) and full 3D magnetic field on photosphere (as boundary condition) non-linear force-free field (NLFFF) was calculated by Landweber iteration algorithm (Wiegelmann, T.: 2004, Solar Phys. 219, 87).

Gyroresonance levels at 3 cm (10 GHz), 3rd harmonic:

at 1.25 Mm

at 1.75 MmReconstructed magnetic field – 3D view

3D view

AR 10933

dTTbTb ii 1

dheTdT kin

dh

)5()4()3()2()1()( s

Emission transition equation solution:

Optical thickness depends on: • emission mode (o-, x-mode), • wavelength, • angle, • magnetic field, • electron density, • electron temperature.

ffs )(

Calculated maps of brightness temperature

Effective heights of optical thickness = 1

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4

0,0

5,0x105

1,0x106

1,5x106

2,0x106

h, 104 km

Tkin, K

Observations vs. model

Temperature distribution:

Obtain calculated scans by convolutionwith the telescope beam

Modify distribution

Model parameters adaptation procedure

0.0 0.2 0.4

0.0

0.5

1.0

1.5

2.0

2.5

Tki

n, 10

6 K

0.0 0.2 0.41

10

h, 109 cmh, 109 cm

N, 10

9 c

m-3

Model electron temperature and density

AR 10933

6 8 10 12 14 16 18

0.1

1

10

6 8 10 12 14 16 185

10

15

20

25

30

35

40

45si

ze, a

rcse

c

6 8 10 12 14 16 18

104

105

106

Flu

x, s

fu

Tb, K

, GHz, GHz

, GHz

, GHz6 8 10 12 14 16 18

0.1

1

10

Flu

x (R

-L),

sfu

, GHz , GHz

Flu

x (R

-L),

sfu

6 8 10 12 14 16 180.1

1

10P

ola

riza

tion d

egre

e, %

6 8 10 12 14 16 180

20

40

60

80

100

Left polarization

Right polarization

Observation

Model

Spectra: observations vs. model

Observations vs. model: scansAR 10933

Left

Right

ObservationModel

Difference

6 8 10 12 14 16 18

0

1

2

3

4

5

Flu

x, s

fu

f, GHz

I=(R+L)/2

RATAN-600

gr

ff

Effective heights of the free-free emission

Spectrum by RATAN-600,

gyroresonance (gr) and

free-free (ff) emission mechanisms

AR 10935

ConclusionsMethod of active region physical condition diagnostic, based on

– multiwave observation of polarized emission in centimetric waverange on RATAN-600, – Magnetic field extrapolation,– Calculation of radioemission

allows– To estimate the electron density distribution at different height in different parts of active

region, – To estimate the relative contribution of cyclotron and free-free emission at different

wavelengths,– To estimate the contribution of various cyclotron emission harmonics,– To correct active region structural component sizes estimations.

Analyses based on AR 10933 and 10935 shows that reconstructed magnetic field corresponds to observed sizes of radiosources at high frequencies, but at low frequencies observed sizes is smaller that modeled ones. It can be solved by introduction of different density and temperature distribution over and outside the spot. Another possible reason is not full adequacy of magnetic field reconstruction.

Reconstructed magnetic field of simple one-spot active region can be used to modeling of active region structure and matches well with microwave observations in general.

Comparison of observed and calculated radioemission give us the follow estimation of physical condition in analyzed active regions:

– Low corona begins at the heights 2.0 … 2.3 Mm, – Corona temperature is 2.5 MK at low heights and, possibly, rises to 3.0 MK higher,– Electron density in low corona is about 1.5 … 1.8∙109 cm-3.