Structure of a solar active region from RATAN 600 and very large array observations

Akhmedov, Sh. B.; Borovik, V. N.; Gelfreikh, G. B.; Bogod, V. M.; Коржавин, А. Н.; Петров, З. Е.; Dikij, V. N.; Lang, Kenneth R.; Willson, R. F.

doi:10.1086/163914

Cited by 69 publications

(25 citation statements)

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“…The strongest source of the active region, B, with a peak observed brightness temperature of 7.5 x 105 K, is not associated with any particular spot; instead, it is located above the principal neutral line of the magnetic field and the active region filament. Similar high brightness sources have been observed above neutral lines by Alissandrakis and Kundu (1982) in WSRT observations at 6 cm and by Pulkovo group (Akhmedov et aL, 1986) in RATAN-600 observation in the range of 2 to 4 cm.…”

Section: Active Region 5036supporting

confidence: 83%

Two-dimensional solar mapping at 5.2 cm with the Siberian Solar Radio Telescope

et al. 1992

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We present two-dimensional solar maps at 5.2 cm computed from one-dimensinal observations with the Siberian Solar Radio Telescope (SSRT), using Earth rotation aperture synthesis techniques. The resolution attained with the E-W branch of the instrument is 15 by 45" for a solar declination of about 23 ~ Maps during the period of June 8 to 13, 1988 clearly show the quiet-Sun background, sunspot and plage associated emission as well as compact sources above the neutral line in some active regions. We found that the latter disappear as the gradient of the longitudinal magnetic field decreases. We also detected emission associated with active regions behind the limb, apparently from unresolved loops, extending up to ~40". The prospects of the SSRT, as a dedicated solar instrument, are discussed.

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Section: Active Region 5036supporting

confidence: 83%

Two-dimensional solar mapping at 5.2 cm with the Siberian Solar Radio Telescope

et al. 1992

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“…It contains contributions from free-free and gyroresonant processes, and perhaps some non-thermal emission (Webb et al, 1983;Akhmedov et al, 1986;Gaizauskas and Tapping, 1988). There is considerable uncertainty about the relative importance of these processes, which probably varies from region to region, and with time.…”

Section: Introductionmentioning

confidence: 99%

“…The spatial distributions of the two thermal processes are different; the gyroresonant emission originates chiefly in the vicinity of sunspots, where the magnetic fields are strong enough, while the free-free emission is more widely-distributed over the host region or complex (Akhmedov et al, 1986;Gary and Hurford, 1987). A model for the widely-distributed emission at 10.7 cm is discussed by Tapping (1987b).…”

Section: Introductionmentioning

confidence: 99%

The origin of the 10.7 cm flux

Tapping

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Sol Phys

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We propose that when all sources on the solar disc are taken into account, the S component at 10.7 cm wavelength is dominated by thermal free-free (bremsstrahlung) emission. It is not produced only in the vicinity of sunspots; more than 60~ of the total flux may be due to a widely-distributed emission associated with the hot complexes of activity. Using a model for the solar atmosphere based upon an assumption of weak (or vertical) magnetic fields, the spectrum of the S-component is calculated and its sensitivity to changes in the model parameters investigated. Variation of the thicknesses of the chromosphere, transition region and mixed zone cause only small changes in the S-component spectrum; there is a much stronger dependence upon the plasma density, particularly at the base of the corona. The behaviour of the S-component at 10.7 cm wavelength is examined in more detail. We find that the largest contribution to the 10.7 cm flux originates in the low corona, that structural changes affect it only slightly, but that it is strongly density-related. This dependence upon few quantities, together with its relative localization in the low corona, contributes to the usefulness of the 10.7 cm flux as an index of solar activity.

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“…This mechanism is due to thermal gyroresonance absorption which was first suggested by Zheleznyakov (1962) and Kakinuma & Swarup (1962). Based on this mechanism, models have been put forward interpreting observations of high angular resolution and providing a tool for plasma diagnostics of coronal magnetic fields and other physical parameters (Zlotnik 1968a, b;Lantos 1968;Gelfreikh & Lubyshev 1979;Alissandrakis et al 1980;Kruger et al 1985;Lee et al 1995;Gopalswamy et al 1996). Some observations, however, have shown high brightness temperatures (Tb >> lo6 K) of S-component sources not associated with large sunspots or with enhanced soft X-rays (Webb et al 1983;Shibasaki et al 1983) thus requiring a nonthermal origin of the emission (Chiuderi Drago & Melozzi 1984;Akhmedov et al 1986;Chiuderi Drago et al 1987;Bogod et al 1992;Sych et al 1993).…”

Section: Introductionmentioning

confidence: 97%

Are short‐time variations of the solar S‐component emission identical with microwave bursts?

et al. 1997

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Extended time series (time resolution about 2-3 min) of spatially resolved observations (2 17 arcsec) in one dimension of solar S-component sources obtained at the Siberian Solar Radio Telescope (SSRT) at 5.2 cm wavelength allow the detection of evolutional features of the growth and decay of active regions in the solar corona. Characteristic slow flux variations with timescales of about 1-2 hours occurring during the decay phase of the radio emission in the low corona above plages and sunspots are compared with recently detected step-like flux increases on timescales of about 10-20 min followed by quasi-constant periods appearing in the initial phase of the development of active regions. Superimposed on this basic behaviour, also fluctuations at shorter timescales (or even periodic oscillations) have been observed. As it is well known from emission-model calculations, the variations of the S-component radiation can be due to variations of the magnetic field and/or changes of the energy of the radiating particles, which is basically the same emission mechanism as for microwave bursts. Since the "S-component" is originally defined by its long timescale behaviour derived from whole-Sun flux density measurements, the presently detected small-timescale features in S-component sources require either a revised definition of S-component emission or must be considered as "burst-like" .

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Structure of a solar active region from RATAN 600 and very large array observations

Cited by 69 publications

References 0 publications

Two-dimensional solar mapping at 5.2 cm with the Siberian Solar Radio Telescope

Two-dimensional solar mapping at 5.2 cm with the Siberian Solar Radio Telescope

The origin of the 10.7 cm flux

Are short‐time variations of the solar S‐component emission identical with microwave bursts?

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