Detection of absorption in the decimeter radio emission of solar corona

The results of new observations of the radio emission of the solar corona in the range of 1– 3 GHz with the RATAN-600 are presented. Observations in this range are characterized by a presence of strong industrial interference from mobile communications, GPS, microwave ovens, aircraft radars, etc. At the same time, problems related to the conversion of magnetic energy into flare energy, coronal heating, the role of narrow-band phenomena, and quasi-periodic pulsations in the solar corona remain topical. Change in the concept of receiving spectral equipment for the RATAN-600 radio telescope has become an urgency. Thus, work is now underway on the creation of a series of new generation spectral complexes covering the entire operating range of RATAN-600 from 1 GHz to 40 GHz. In this article, we present the results of the first series of observations with the Panoramic Analyzer of Spectrum in the range of 1–3 GHz (PAS 1–3 GHz) for studies of low-contrast coronal structures. This equipment has fine spectral resolution (more than 8000 channels/GHz), a wide frequency range (more than an octave), high time resolution (up to 8 ms/spectrum), and a wide dynamic range (about 90 dB). A multi-object observation mode becomes available for various objects, from powerful flare phenomena to faint structures down to the radio granulation level. A high-speed pipeline for receiving, digitizing, and processing information has been developed and implemented in order to separate useful signals and interference in real time. These features, together with the capabilities of the RATAN-600 in terms of effective area and wide frequency coverage, made it possible to observe weak coronal structures in the 1–3 GHz range. As a result, new properties of the coronal plasma were discovered. One of the first results of these observations was the registration of narrow-band absorption in the frequency band 1520–1630 MHz, near the OH absorption line (1612–1720 MHz). Possible ways of explaining the nature of such absorption in the solar corona are discussed.