Notes
Outline
Future plans and technical developments for the RATAN-600 radiotelescope
V.M.Bogod
SAO RAN
I. Introduction
The radiotelescope RATAN-600 already more than two tens years is used  for solar investigations. In the last several years ago the radiotelescope RATAN-600 (Fig.1) is used for regular solar study in monitoring mode (Korolkov&Parijskij,1979; Parijskij, 1993, Bogod &Gel'freikh, 1998, .Bogod et al., 1999). The solar observations is breaking only one month in a year. The radio instrument covers the range of 5,5 octave  from 0.5 GHz to 18 GHz and it is unique in practice. On the Table 1, the to-day and future parameters of the RATAN-600 for solar observations are presented.  The most effective regime is a mode of usage 1/4 parts (Southern sector) of Main circular mirror together with a Flat periscope mirror, consisting on 124 flat reflecting elements (8,5 m per 3 m) (see Fig.2). This antenna system forms the diagram pattern in the form of a vertical knife. Inside Southern sector there are circular rail-way tracts for moving of "Receive Mirror" (third mirror together with a receive cabin) in multi azimuth regime and tracking. The radiation from the Sun struck to the Flat mirror and is reflected as a plane wave to a Main circular mirror of Southern sector. The range of azimuth angles is about $\pm 30 degree$, that it is enough for realization of azimuth observations in a time interval $\pm 3 hours$ from a central meridian. Mean time of the culmination is about 9-00 UT. The receive horns are in focus of "Receive Mirror". The"Receive Mirror" and room for the receivers are located on a uniform platform, which can move in any azimuth with high accuracy.  For solar study the Panoramic Analyzer of Spectrum (PAS) is used (Bogod et al., 1999).
II. Parameters of RATAN-600 for solar study
The PAS ideology  consists in use of a parallel spectrum analysis in all frequency range. For this purpose all frequency range parted to the set subranges (receivers). The amplification part of each receiver is made in the scheme of direct amplification with output  frequency filters. The input amplifiers are executed on low noise microwave transistors. On the input of the PAS the special combined horn for all wavelengths is used. Such combined horn has one phase center for all frequencies with precision 1-2 angular seconds. It is provided the reception of the right and left-hand polarization in a modulation mode. Now the all frequency range (from 0.9 GHz to 18 GHz) covered by 7 receivers with next bands: 1) 12 - 18 GHz, 2) 8 - 12 GHz, 3) 5.5- 8 GHz, 4) 3.5 - 5.5 GHz, 5) 2.5 3.5 GHz, 6) 1.5 - 2.5 GHz, 7) 0.9 - 1.1 GHz. Each frequency band is divided for 6-8 channels. So, the receiver complex PAS consists of 48 channels with registration both intensity and circular polarization with about 5 % frequency resolution. As follows from the Table 1 the main positive parameters of RATAN-600 for solar study are:
- The High Flux sensitivity <0.001 s.f.u.
- The Wide range frequency coverage 0.92 GHz - 17.2 GHz with combined input horn.
- The Multy frequency instant spectral analysis with 5% frequency resolution.
- The High sensitivity of polarization degree  measurements <0.02 %.
- The High dynamic range >
            But RATAN-600 has the big difficulty  with two-dimensional mapping and
Sun tracking, which we try to overcome with development of Radioheliograph regime
(Bogod et al., 1998) and multi-wave multi-azimuth mapping. During 2001-2002 the
multiple azimuth regime is realized. Now we have about 60 multiwave scans during
4 hours (7:00 -11:00 UT) with 4 minute cadence.
Total view
RATAN-600 solar observations
with South sector + Periscope
Fig.2  Scheme of antenna system consisting on the Periscope, the circular South sector and the third collecting mirror with receive cabin, which can move along circular railway track for doing azimuth observations.
III. The spectral and polarization features of solar plasma in a wide frequency range according RATAN-600 data.
The aim of the reports is to show the different spectral and polarization features of  radio emission in active and stable  solar structures, The structures were observed with moderate spatial and frequency resolution at RATAN-600. The future progress in the study with the help of FASR can be expected.
At Fig.3 the example of one-dimensional scan with RATAN-600 observation both at one wavelength and many wavelength in the range from 1.8 cm to 17.1 cm is superimposed on the solar disk.
At the Fig.4 and 5 we demonstrate the spectral behaviour of different polarization details in wide wavelength range.
The importance of high flux sensitivity is needed for study of weak polarization signal. This is demonstrated at the Fig. 6, 8 and 9. The high dynamic range using in RATAN observations is shown at Fig. 7.
The Fig. 10, 11, 12 and 13 are devoted to different spectral-polarization features of preflare plasma, which appear in flare-productive active regions before powerful flares.
The interesting effect connected with radioemission depression before flare is demonstrated at Fig 14 (microwave «darkening») and Fig.15 (associated polarization inversion).
Table 1.
Fig.3 On the upper picture an example of one-dimensional  multiwave solar scan with knife diagram pattern at wavelength 3.21 cm is presented. Intensity scan I=I(L)+I(R) in red line, and circular polarization scan V=I(L)-I(R) in blue line are shown. The estimation of magnetic field on the base of cyclotron mechanism for each big source are written nearly (according method in Akhmedov et al., 1982). Below the multiwave scans in the range from 1.8 cm to 17.1 cm in Intensity (left) and circular polarization (right) are presented. The regular RATAN-600 data one can find at www.ratan.sao.ru\~sun
Multicomponent structure of prominence on the W-limb
Fig.4. An wide range observation of prominence on W-limb October 4, 1996  (Bogod et al., 1998) . The spectrum allowed us to separate the emissions associate to prominence (source A- green), arcade (source B- red) and strimmer (Source C- blue) due to different frequency dependance.
Example of prominence spectrum
Fig.5 The brightness temperature spectra of the sources shown in Fig.4. All sources have thermal spectra with different optical thickness. Source A’’ is a new type source on the boundary between of the  cool prominence and corona.
Example of high polarization sensitivity
Fig.6 An example of record of weak polarization sygnal from prominence on the W-limb (channel V-dotted line). The intensity channel I (solid line) is presented with the subracted quiet Sun level. The flux sensitivity in polarization channel is determined only by receive noise due to weak instrumental polarization.The  polarization degree sensitivity is about 0.02% at wavelength 2.11 cm.
High dynamic range
Fig.7 An example of observations with high dynamic range in RATAN-600 observations.
The weak details ( about several degrees of Kelvin) and strong bursts  with high temperature
(about           ) are recorded in one scale.
Fig.8   An example of polarization microburst emission at several  decimeter waves, which manifestates the energy release processes in a cusp of active region. High temporal resolution needs for adequate study of such structure.
Fig. 9  An example of decimeter microburst emission after the flare  X1.7 at 10h 15m UT in AR 9393     with 8 minute cadence. The microbursts were appeared 1.5 hour before and disappeared 0.5 hours after the flare
To study of preflare plasma.
Short-wave polarization inversion
Fig.10   A study of preflare plasma in flare-productive active region (FPAR) using spectral and polarization data.  One dimensional scans of AR 9393 (located near the meridian) at several wavelength is presented. The short-wave polarization inversion is observed one day before power flare occured at 10h 15m UT in AR 9393.
To study of preflare plasma.
Short-wave increasing of polarization flux spectrum
Fig. 11 Another example of preflare plasma manifestation in the form short-wave increasing of the spectra for AR 9415 in April 8, 2001 before powerfull flare X2.3 occured at 5h42m UT in April 10. Both effects (short-wave polarization inversion and increasing flux) are interpretated as manifestation of new magnetic flux rising with opposite and concide polarities with old magnetic field
To study of preflare plasma.
Formation frequency domain with weak polarization.
Fig. 12   Another example of preflare plasma at microwaves. On the multiwaves scans two AR’s are presented. Near the solar meridian the stable AR and near the West-limb the FPAR  9393 are located. The microwave emission of FPAR demonstrates the frequency domain (the wavelengths from 2.47 cm to 3.21 cm) with low polarization degree, which shown on the right in big scale also. The sharp structural changes one can see in narrow frequency band. The powewrful flare X 14.0 occured at April 15, 2001 in  13h50m UT.
To study of preflare plasma.
Multiple polarization inversions.
Fig. 13 Another example of circular polarization inversion in FPAR 9415 during  about 2, 5 hour at wavelength 2.9 cm. The polarization source located in E-part of the active region undergoes multiple structural changes and inversionsin time.
To study of preflare plasma.
 Microwave «darkening» effect in FPAR before flare
To study of preflare plasma.
 Polarization inversion accompany microwave «darkening» effect in FPAR before flare
Example of multi-azimuth mapping
Fig.16 An example of multiwave mapping using azimuth observation with the antenna system of South sector RATAN-600 and Periscope reflector.
Future aims for RATAN-600
To improve spectral resolution up to 1 % at all frequency range of the instrument.
To increase temporal cadence in azimuth observations up to 1 min.
To extend the coverage to high frequency part up to 40 GHz and to low frequency part down to 0.5 GHz.
To improve the azimuth two-dimensional mapping.
References
Sh.B.Akhmedov, V.Bogod, G.B.Gelfreikh, A.N.Korzhavin Measurements of Magnetic Field in the Solar Atmosphere above Sunspots Using Gyroresonance Emission,1982, Solar Physics, v.79, 41-58.
 Bogod V., Garaimov V., Grebinskij: The study of prominence fine structure during RATAN-600 - SOHO support program in September-October 1996., Solar Physics, 1998, vol.182, p.139-143.
Bogod V., Grebinskij A., Opeikina L., Gelfreikh G., 1998. The  Radio Heliograph of RATAN 600, in: C. Alissandrakis (ed.),  PASP Conf., vol.155, 279-283.
 Bogod V.M., Gel'freikh G.B.:  Study of the solar atmosphere based on  spectral and polarization observations on the RATAN-600.  Achievements and Perspectives. Bull.Spec. Astrophys. Obs. 1998, N 45, 5-16.
V.M.Bogod, V.I.Garaimov, N.P.Komar, A.N.Korzhavin: RATAN-600. Upgrade and Development of Software for Presentation of the Data, Proceedings of 9-th European Meeting on Solar Physics, 1999, (ESA SP-448, December 1999), p.1253-1258.
V.M. Bogod, C. Mercier, L. V. Yasnov: About the nature of long-term microflare energy release in the solar active regions, Journal of Geophysical Research, Vol. 106, NO. A11, 25.353-25.360, 2001.
Parijskij Yu.N., IEEEAnt. And Propag. Mag. 1993, v.35,4, 7-12.
Korol’kov & Parijskij Yu.N. 1979, Sky and telescope, 57,4.
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