Ulyanov O.M., Zakharenko V.V., Alekseev E.A., Reznichenko O.M., Kulahin I.O., Budnikov V.V., Prisiazhnii V.I., Poikhalo A.V., Voytyuk V.V., Mamarev V.N., Ozhinskyi V.V., Vlasenko V.P., Chmil V.M., Sunduchkov I.K., Berdar M.M., Lebed V.I., Palamar M.I., Chaikovskii A.V., Pasternak Yu V., Strembitskii M.A., Natarov M.P., Steshenko S.O., Glamazdin V.V., Shubnyi O.I., Kyrylenko A.O., Kulyk D.Yu. «The RT-32 radio telescope construction based on the MARK-4b antenna system. 3. Local oscillators and self-noise of the receiving system» Радиофизика и радиоастрономия (Украина), 25, № 3, с. 175-192 (2020)

Предмет и цель работы: Исследование с высоким разрешением спектральных линий космических радиоисточников требует низких собственных шумов приемной системы радиотелескопа. Они обеспечиваются как входными криогенными усилителями, так и низкими фазовыми шумами гетеродинов. Для выполнения спектральных исследований необходимо иметь возможность перестроения частот гетеродинов с малым частотным шагом. В работе приведены результаты разработки синтезаторов частоты, которые одновременно обеспечивают как очень малый частотный шаг, так и низкий уровень фазовых шумов. Приведены также результаты измерений собственных шумов криогенных приемных систем радиотелескопа РТ-32. Методы и методология: Приемные системы РТ-32 созданы по схемам супергетеродинных приемников с двумя степенями преобразования частоты. Настройка приемной системы с частотным шагом 10 или 20 МГц обеспечивается гетеродина первого преобразования частоты, а точная настройка происходит благодаря сверхвысокой разрешающей способности (0.0001 МГц) гетеродинов второго преобразования частоты, созданные на основе синтезаторов прямого цифрового синтеза. Результаты: Показано, что применение синтезаторов прямого цифрового синтеза возможно только с низкими значениями коэффициентов умножения частоты, а также при тщательной фильтрации всех опорных сигналов. Измерение параметров гетеродинов проводилось с помощью спектра N9951A (Keysight Technologies), который имеет высокое разрешение и широкий динамический диапазон. Для измерений шумовых характеристик радиоприемной системы радиотелескопа была изготовлена специально согласованная нагрузка с возможностью охлаждения до температуры жидкого азота. Измерения шумовой температуры было проведено в различных разрезах приемного тракта РТ-32. Сопоставление таких измерений в различных конфигурациях дает возможность сделать предварительную оценку собственных шумов РТ-32 в С и K диапазонах. Вывод: Результаты измерений собственных шумов радиоприемных систем и фазовых шумов гетеродинов радиотелескопа РТ-32 показывают, что радиотелескоп в С-диапазоне способен выполнять высокочувствительные исследования как в широкой полосе частот, так и в узкой полосе частот с высокой спектральной разрешающей способностью. В K-диапазоне собственные шумы сопоставимы (≈60–80 К) с внешними шумами, что также дает возможность исследовать излучение мазерных источников.

Sobitnyak L.I., Ryabov M.I., Orlyuk M.I., Sukharev A.L., Romenents A.O., Sumaruk Yu.P., Pilipenko A.A. «Analysis of the magnetic storms catalog for monitoring radio source fluxe data with the URAN-4 radio telescope in the Odesa magnetic anomaly zone» Радиофизика и радиоастрономия (Украина), 25, № 4, с. 324-330 (2020)

Purpose: Compilation of a digital catalog of magnetic storms in the Odesa magnetic anomaly zone in order to find the reasons for possible changes in the radiation fluxes of cosmic radio sources, according to observations at the URAN-4 radio telescope. Design/methodology/approach: Since 1987 until now, the radio flux of powerful galactic and extragalactic radio sources has been monitored at the URAN-4 radio telescope of the Odesa Observatory of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine. The monitoring program includes radio galaxies 3C274, 3C405 and supernova remnants 3C144, 3C461. Changes in the radio source flux level are determined by the ionosphere state due to the changes in space weather. At the “Odesa” geomagnetic observatory of the Institute of Geophysics of the National Academy of Sciences of Ukraine, the geomagnetic field measurements have been made since 1948. Simultaneously, the measurements of three elements of the geomagnetic field: horizontal component (H), vertical component (Z) and inclination (D), have been recorded. Findings: Using the “Odesa” geomagnetic observatory data, the digital catalog of magnetic storms was compiled for the measuring period of the powerful space radio source fluxes obtained with the URAN-4 radio telescope. For the magnetic storms monitored during the periods of 1987–1995 and 2000–2009, the date and time are shown for the beginning and the end of the magnetic storm, the magnetic storm duration, the amplitude of the three magnetic field elements, being H, Z, and D, and the magnetic storm type characteristic.The “Odesa” geomagnetic observatory is located near the magnetic anomaly zone. To find the distinctions in manifestations of the geomagnetic activity arisen owing to the magnetic anomaly existence, the geomagnetic disturbances recorded at the “Odesa” and “Moscow” (IZMIRAN, Russia) observatories were compared. It was shown that the total annual duration of the magnetic storms was longer in Odesa than in Moscow. This demonstrates some special role of the magnetic anomaly in the development of geomagnetic disturbances. Conclusions: The digital catalog of magnetic storms in the Odesa magnetic anomaly zone was compiled for the 1987–1995 and 2000–2009 periods. It is also planned to terminate working over the complete catalog of magnetic storms recorded at the “Odesa” observatory for the entire continuous period of monitoring space radio sources at the URAN-4 radio telescope in order to find the manifestations of geomagnetic disturbances impact upon the ionosphere state and changes of intensity in cosmic radio source fluxes. These studies are supplemented by the comparative analysis of the “Odesa” observatory geomagnetic data and the data from some other geomagnetic observatories.

Gorbunov A.A., Ryabov M.I., Sukharev A.L., Bezrukovs V.V. «Periodic and sporadic variations in the spectral flux density of the Cas A supernova remnant» Радиофизика и радиоастрономия (Украина), 25, № 4, с. 268-275 (2020)

Purpose: Based on the long-term study data in all radio spectrum ranges, the nature of deviations of spectral flux density of the Cas A supernova remnant from the tendency of its secular decrease is considered. The aim of this work is determining the presence of quasiperiodic variations and sporadic changes in the Cas A spectral radiation flux density depending on frequency. Design/methodology/approach: The main database is using the published results obtained with the method of absolute measurements of the Cas A spectral radiation flux density in a wide range from millimeter to decimeter wavelengths, as well as the results obtained with the method of relative measurements of the ratio of the flux densities of the Cas A supernova remnant and radio galaxy Cyg A, this latter being used as a reference source in the meter wavelength range. For making comparison with the aforesaid data obtained with different methods, the results of a long-term monitoring (since 1987) of the variation of the ratio of the spectral flux densities of Cas A and Cyg A made with the URAN-4 radio telescope of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine at 25 MHz were used. Findings: As a result of the analysis of the observed data for the Cas A radiation flux density in the entire radio wavelength range, the existence of quasiperiodic variations in the range from millimeter to meter wavelengths within 2 to 9 years has been noted. The reason for the detected quasiperiodic variations can be the processes in the Cas A remnant itself. In the decameter wavelength range, according to monitoring data obtained with the URAN-4 radio telescope, the seasonal-diurnal and long-term variations are noted, being associated with changes in the ionosphere state in the solar activity cycle, with some weak appearance of the secular decrease of the Cas A radiation flux. The presence of sporadic variations in the ratio of the spectral flux densities of Cas A and Cyg A is associated with the effect of the increased solar activity. For explaining the lowering of the Cas A spectral flux density to the Cyg A level and maintaining the excess of the Cas A flux at decameter waves, the quasi-simultaneous observations made with radiotelescopes for different wavelength ranges will be required. Conclusions: The evolution of the Cas A supernova remnant remains the focus of interest of current research efforts. An intriguing moment was the discovery of a point X-ray source in the center of radio source Cas A as a possible supernova remnant. The role of this source in the Cas A radio flux secular decrease and in its variations needs to be clarified. A detailed analysis of the long-term data and making quasi-simultaneous observations will allow to reveal the processes occurring in the radio source itself and to determine the influence of the ionosphere state on the results of measurements. A joint program is suggested for observations of Cas A and Cyg A flux variations with the RT-32 and RT-16 radio telescopes, the LOFAR element of the Ventspils International Radio Astronomy Center (Latvia), and the URAN, UTR-2 and GURT radio telescopes of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine.

Sobitnyak L.I., Ryabov M.I., Orlyuk M.I., Sukharev A.L., Romenents A.O., Sumaruk Yu.P., Pilipenko A.A. «Analysis of the magnetic storms catalog for monitoring radio source fluxe data with the URAN-4 radio telescope in the Odesa magnetic anomaly zone» Радиофизика и радиоастрономия (Украина), 25, № 4, с. 324-330 (2020)

Purpose: Compilation of a digital catalog of magnetic storms in the Odesa magnetic anomaly zone in order to find the reasons for possible changes in the radiation fluxes of cosmic radio sources, according to observations at the URAN-4 radio telescope. Design/methodology/approach: Since 1987 until now, the radio flux of powerful galactic and extragalactic radio sources has been monitored at the URAN-4 radio telescope of the Odesa Observatory of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine. The monitoring program includes radio galaxies 3C274, 3C405 and supernova remnants 3C144, 3C461. Changes in the radio source flux level are determined by the ionosphere state due to the changes in space weather. At the “Odesa” geomagnetic observatory of the Institute of Geophysics of the National Academy of Sciences of Ukraine, the geomagnetic field measurements have been made since 1948. Simultaneously, the measurements of three elements of the geomagnetic field: horizontal component (H), vertical component (Z) and inclination (D), have been recorded. Findings: Using the “Odesa” geomagnetic observatory data, the digital catalog of magnetic storms was compiled for the measuring period of the powerful space radio source fluxes obtained with the URAN-4 radio telescope. For the magnetic storms monitored during the periods of 1987–1995 and 2000–2009, the date and time are shown for the beginning and the end of the magnetic storm, the magnetic storm duration, the amplitude of the three magnetic field elements, being H, Z, and D, and the magnetic storm type characteristic.The “Odesa” geomagnetic observatory is located near the magnetic anomaly zone. To find the distinctions in manifestations of the geomagnetic activity arisen owing to the magnetic anomaly existence, the geomagnetic disturbances recorded at the “Odesa” and “Moscow” (IZMIRAN, Russia) observatories were compared. It was shown that the total annual duration of the magnetic storms was longer in Odesa than in Moscow. This demonstrates some special role of the magnetic anomaly in the development of geomagnetic disturbances. Conclusions: The digital catalog of magnetic storms in the Odesa magnetic anomaly zone was compiled for the 1987–1995 and 2000–2009 periods. It is also planned to terminate working over the complete catalog of magnetic storms recorded at the “Odesa” observatory for the entire continuous period of monitoring space radio sources at the URAN-4 radio telescope in order to find the manifestations of geomagnetic disturbances impact upon the ionosphere state and changes of intensity in cosmic radio source fluxes. These studies are supplemented by the comparative analysis of the “Odesa” observatory geomagnetic data and the data from some other geomagnetic observatories.