Kravtsov I. Survey of the Northern sky in order to find sporadic radio emission sources in decameter wave range

The thesis is devoted to conducting a full survey of the Northern sky in order to find unknown sources of sporadic radio emission (hereinafter – the Survey). In present work a detailed review of known and hypothetical cosmic sources of periodic and sporadic radio emission is made, and the probability of their radiation presence in the low-frequency wave range is estimated. The advantages and disadvantages of the low-frequency observations are analyzed. A lot of surveys for searching of such sources, which were carried out at other radio telescopes and at higher frequencies of the radio frequency range were considered and analyzed. Various types of radio frequency interference which imitate the signals of cosmic origin were considered. It is shown that the best instrument for conducting the Survey is the world’s largest radio telescope of this range – UTR-2. The concept, purpose and objectives of the Survey are formulated. There was carried out a large number of UTR-2 observations. All observational data has been processed with the special routines. The first part of the processing pipeline – the "long pipeline" – is a fully automated stage and includes RFI mitigation, the dispersion delay compensation and the search for intensive individual pulses. After that, all data was visualized and visual checked for the purpose of searching for intensive signals that meet the established criteria of cosmic origin. The next stage of data processing is a semi-automatic pulses analysis using a new routines and algorithms – “short pipeline”. It was proved that the transient signals could not be generated by the flickering of continuum radio emission sources on the inhomogeneities of the ionosphere. It has been shown that random emission can’t generate noise signals with SNR more than 8. Therefore, a new threshold was introduced: pulses with SNR < 8 were removed from the candidates’ list. The number of signals that exceed this threshold is 380. After that, distributions of different parameters (SNR, time of appearance, dispersion measure and galactic latitude) of these pulses were built. The distribution of appearance times has shown that the signals are distributed approximately uniformly over the observation time. The signals’ SNRs distribution is very similar to the distribution of the probability of occurrence of anomalously intense pulsar’s pulses depending on the intensity. The DMs distribution of signals found in the Survey is quite similar to the simulated DMs distribution of known pulsars, which will be available for observing at the SKA radio telescope. In addition, a distribution of 380 pulses galactic latitudes was built, comparing it with a similar distribution for 98 known close pulsars (which have DM < 30 pc/cm3 and periods more than 0.2 s) showed their similarity. In the thesis the original results are obtained, which extend the frequency range of sporadic radio emission sources studies to decameter wave range. For the first time, a full survey of the entire available part of celestial sphere was conducted. The survey data was fully processed, individual pulse analysis routines were developed, and all identified «candidates» were analyzed. Due to the multi-parametric analysis, 380 signals were selected corresponding to the criteria of cosmic origin; the distributions of their parameters were built and analyzed. Comparison with similar distributions of known sources’ parameters showed that the detected signals are the pulses of cosmic origin and, thus, 380 new sources of transient radio emission in the decameter wave range were discovered in present work.