Russian Foundation for Basic Research

SSRT - Siberian Solar Radio Telescope

The influence of solar activity processes upon geophysical phenomena is a matter of common knowledge. These processes are triggered by emergence of deep-seated magnetic fields and evolve in the solar corona. Radio observations provide a powerful tool for studying the corona at the background of the solar disk and are an important adjunct to hard and soft X-ray measurements. They are sensitive to both the thermal and nonthermal plasma components under quiet as well as disturbed conditions in the corona, including coronal mass ejections. Radio astronomical observations provide the only way of measuring coronal magnetic fields, as related calculations from photospheric data under disturbed conditions yield unreliable results; they furnish an opportunity to diagnote the energetic electron temperature and parameters, the most sensitive technique for over 100 keV energies; and this is the onloy method to study particle acceleration and energy release processes in the outer corona.

The Siberian Solar Radio Telescope (SSRT) is among the largest astronomical instruments. It is located in a wooded picturesque valley separating two mountain ridges of the Eastern Sayan Mountains, 220 km from Irkutsk. It is a crossed interferometer, consisting of two arrays of 128x128 parabolic antennas 2.5 meters in diameter each, spaced equidistantly at 4.9 meters and oriented in the E-W and N-S directions. The main maxima of the radio telescope's multidirectional beam are arranged at intervals in some excess of the Sun's apparent size at the instrument's working wavelengths l = 5,2 sm. The length of each linear baselines of the interferometer is 622.3 meters.

The SSRT is a special-purpose solar radio telescope designed for studying solar activity in the microwave range (5.7 GHz) where the processes occuring in the solar corona are accessible to observation over the entire solar disk. The SSRT sensitivity is such that it is possible to observe active regions at all stages of their development, at the background of the emission of an undisturbed solar atmosphere. Signal accumulation in the radio telescope's full reception band is used to obtain radio images of faint features in the solar atmosphere. Fast varying emission of flares is recorded at additive linear interferometers comprising the SSRT.

Step-by-step commissioning of the radio telescope was begun in the spring of 1981 and completed in 1984. With completion of adjustments of the N-S line in 1985, the SSRT initiated an all-weather monitoring of solar activity in the one-dimensional mode with an angular resolution as high as 15" using both linear interferometers. The team of authors was awarded a RF Government Premium in the field of science and technology for the year 1996.

The SSRT was put on the list of Russia's unique facilities.

Since 1992, the SSRT has been involved in regular investigations of fine-structure active phenomena, such as spikes. Sine 1993, the time resolution has been 15 ms.

During 1995-1996, the SSRT incorporated two two-dimemsional modes: the projected correlation mode, and the combined additive-correlation mode. Two-dimensional mapping is done concurrently with one-dimensional images obtained in the additive mode. The correaltion mode with high sensitivity permits low-constrast features on the Sun to be investigated. The additive-correlation mode ensures, at a sacrifice in sensitivity, a siomultaneous construction of radio maps with a fast rcording in the one-dimensional mode at the time resolution of 56 ms, which is important in observations of active processes when a reduction in sensitivity is not critical and the active region image can be obtained every minute.