Solar Eclipse of March 20, 2015 as observed by two radio telescopes RT-32 (Svetloe and Zelenchuksky): the frst results

I. Rahimov, A. Diakov, A. Ipatov, G. Ilin, A. N. Korzhavin, N. G. Peterova, N. A. Topchilo

Transactions of IAA RAS, issue 39, 81–90 (2016)

Keywords: radio telescope, solar eclipse, eclipse curve, radio image, active region, cyclotron radiation

Abstract

Investigations of Active Regions (ARs) on the Sun are able to meet the upto-date requirements if observations are made with a high spatial resolution. It is possible to achieve it in the radio range during observations of solar eclipses (where the theoretical resolution limit is ~ 3″). The best method for such observations is based on the use of quite large full-steering radio telescopes where the full-circle beam width is almost equal to the size of AR (2–4)'. RT-32 Radio telescopes of IAA "Quasar" network are among this kind of tools. They have been already used to observe five solar eclipses. A theoretical limit of spatial resolution was achieved when the Eclipse 2011 was observed. The first part of our new results received during the latest solar eclipse observations (March 20, 2015) is introduced. We used two radio telescopes RT-32 in the observatories “Svetloe” (near St. Petersburg) and “Zelenchukskaya” (North Caucasus) at the wavelengths of 3.5 cm, 6.2 cm and 13 cm, following with the circular polarization analysis. The observations had the goal to clarify some important AR features, such as a radio source size and its height above the photosphere, and also to explore the fine structure of the radiation brightness distribution on the solar limb. On the basis of these data parameters of coronal plasma are determined; models of its structure in the presence of a strong magnetic field above sunspots are being developed; and the concepts about the physics of internal AR processes are verified. The opportunities to achieve these goals during the March 20, 2015 Eclipse are illustrated on an example of observing a single sunspot in AR NOAA 12303. Due to the high precision coordinate measuring (1″), it was revealed that in the range (3.5 – 6.2 cm) the source of radiation associated with the sunspot lays very low – the height is less than 2000 km above the photosphere level; and its dimension are comparable to the size of the sunspot’s umbra. The validity of this conclusion is much higher than can be obtained with the help of modern radio telescopes, even the largest ones. The comparison with our previous observations of the January 04, 2011 Eclipse (also carried out on the radio telescopes RT-32 [1]) shows that the characteristic features of the fine image structure of the cyclotron microwave source above sunspots (the Gelfreich-Lubyshev effect [2]) are marked regardless of the power of the radiation source, in other words, for even a small area sunspots.

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