Stanyslavskyi L. New astrophysical advances in radio astronomy of the longest waves

The purpose of the work is the studies of cosmic radiation of various natures at the longest radio waves using the latest approaches and radio telescopes to establish the astrophysical perspectives of such measurements. To achieve this goal, the following tasks were solved. First, to develop a technique for observing the radiation of space objects at the longest wavelengths, which is adversely affected by various types of natural and artificial radio interference, as well as the ionosphere. Secondly, to experimentally test the possibilities of radio astronomical measurements using a prototype ultra-low-frequency antenna. Thirdly, to conduct experimental studies of ionospheric cutoff of III-type solar bursts and compare their values with simultaneous measurements of critical frequencies of the ionosphere F2-layer with the help of ionosondes. Fourth, to perform experimental studies of the characteristics of a U-type solar burst at the beginning of a new cycle of solar activity using both ground- and space-based instruments. Fifth, to perform experimental studies of the continuous radio spectrum of Cassiopeia A using interferometric observations, in which the Cygnus A radio galaxy is a calibration source. Sixth, to conduct an astrophysical interpretation and establish the most appropriate model which describes the thermal absorption of radio emission inside and outside Cassiopeia A. The object of research is continuous and sporadic radio emission of space objects at the longest waves. Theoretical and practical results. The obtained methods of cosmic radiation research at the longest waves have practical value for observing various objects of the Universe, which include supernova remnants, radio galaxies, quasars, pulsars and others. From the point of view of practical applications, a technique has been developed to refine the parameters of the electron density of the solar corona over the active regions of the photosphere, the magnetic fields of which are bipolar and can generate bursts of types U and III. The practical value of the proposed approach using measurements on the radio telescopes URAN-2 (Ukraine) and NenuFAR (France) illustrates the synergy of different instruments for radio astronomical observations, when the results of measurements from one instrument significantly complement the results of measurements from another. With the help of URAN-2, it is possible to conduct observations in the frequency range of 8-40 MHz, and NenuFAR observes Cassiopeia A at frequencies of 20-66 MHz. Thus, by combining their spectra, it is possible to establish a more complete picture of the astrophysical processes studied. Novelty of scientific results. Techniques for broadband observations of ultra-low frequency radio emission from cosmic objects of various nature at the longest wavelengths with the simultaneous use of Ukrainian radio telescopes along with a prototype antenna for the future lunar observatory have been developed. Joint studies of variations in the critical frequency of the ionosphere F2-layer were carried out with the simultaneous use of radio observations of the ionospheric cutoff of type III solar bursts and measurements using ionosondes. The association of U+III solar bursts predicted in theoretical models was registered and investigated. Calibration of the corona model using radio observations of U-type solar flares is proposed. The values of thermal absorption parameters inside and outside the Cassiopeia A supernova remnant were determined using interferometric observations of ultralow-frequency broadband radio emission from this object. Research methods. The following methods of modern radio astronomy and astrophysics were used to solve the tasks: (I) experimental studies of radio emission from space objects in time and frequency at the longest waves; (II) processing the results of observations and cleaning them from radio frequency interference using the most modern methods of data processing; (III) theoretical models of generation of solar bursts, thermal absorption of radio emission in ionized gas, as well as methods of numerical analysis. Degree of implementation. The obtained results are of fundamental importance in understanding the Universe, and the developed means and tools make it possible to carry out astrophysically significant measurements of space objects of various nature in a wide frequency band. Scope of use. The developed methods of radio observations and data processing are effective and significantly minimize the influence of unwanted signals on the measurement results. This allows them to be used in the study of very weak cosmic signals, such as the signal in the 21 cm line of neutral hydrogen in the early Universe during the Dark Ages.