Interplanetary scintillation observations of eleven supernova remnants and the pulsar J1939+2134, around which the existence of a supernova remnant remains obscure, were carried out with the largest in the world decameter radio telescope UTR-2 at 20, 25 and 30 MHz to determine if any of them contain compact radio sources with the angular size θ<5″. The sample included the young Galactic remnants and the other powerful SNRs. The interplanetary scintillations of the compact radio source in the Crab Nebula associated with the well-known pulsar J0534+2200 and the pulsar J1939+2134 were observed. Apart from the Crab Nebula, we have not detected a compact radio source in supernova remnants with the angular size θ<5″ and the flux density more than 10 Jy. The observations do not confirm the existence of the low frequency compact source in Cassiopeia A that has remained controversial.

A search for compact decametric radio sources in supernova remnants using the interplanetary scintillation technique

The new Giant Ukrainian Radio Telescope (GURT) intended for operation in 8–80 MHz range is now under construction. It employs an active phased array antenna composed of many dipole subarrays, several of which have been implemented and now are used for radio astronomy observations. In this two-part paper, the electrical and noise parameters of the subarray are studied by numerical and experimental ways. In this part, a theoretical model of the subarray based on the wave theory of noisy multiport networks that takes into account the mutual coupling in the dipole array placed over imperfect ground and the correlation between all existing noise sources is proposed. It is assumed that the initial parameters for this model should be obtained using the correct electromagnetic and circuit simulation. A technique for using of this model to calculate the effective area, radiation efficiency, internal and external noise temperatures, as well as sensitivity of the subarray in terms of system equivalent flux density (SEFD) for all possible beam directions in the frequency band of the GURT radio telescope is described.

An Active Antenna Subarray for the Low-Frequency Radio Telescope GURT—Part I: Design and Theoretical Model

Hyperfine structure lines of highly-charged ions may open a new window in observations of hot rarefied astrophysical plasmas. In this paper we discuss spectral lines of isotopes and ions abundant at temperatures 10 − 10 K, characteristic for warm-hot intergalactic medium, hot interstellar medium, starburst galaxies, their superwinds and young supernova remnants. Observations of these lines will allow to study bulk and turbulent motions of the observed target and will broaden the information about the gas ionization state, chemical and isotopic composition. The most prospective is the line of the major nitrogen isotope having wavelength λ = 5.65 mm (Sunyaev & Churazov, 1984). Wavelength of this line is well-suited for observation of objects at z ≈ 0.15− 0.6 when it is redshifted to 6.5− 9 mm spectral band widely-used in ground-based radio observations, and, for example, for z ≥ 1.3, when the line can be observed in 1.3 cm band and at lower frequencies. Modern and future radio telescopes and interferometers are able to observe the absorption by N VII in the warmhot intergalactic medium at redshifts above z ≈ 0.15 in spectra of brightest mm-band sources. Sub-millimeter emission lines of several most abundant isotopes having hyperfine splitting might also be detected in spectra of young supernova remnants. PACS: 32.10.Fn, 98.62.Ra, 98.38.-j, 98.58.-w, 32.30.Bv

https://edoc.ub.uni-muenchen.de/8730/1/Docenko_Dmitrijs.pdf

Spectroscopy of high-Z ions as a way to understanding the nature of Cas A knots and intergalactic shocks

On presente les spectres de 114 radiosources. On donne egalement quelques parametres dans le domaine des frequences 12,6-1415 MHz

Decametric survey of discrete sources in the northern Sky: XII. Spectra of some Radio Sources in the Frequency range 12.6 to 1400 MHz for Declinations 41 to 52

/pdf/mapping-of-the-decameter-radio-sources-of-cassiopeia-a-using-2kngon483w.pdf

Mapping of the Decameter Radio Sources of Cassiopeia A Using a 100 km Range Long-Baseline Interferometer: Verification of a New Method of Phase Calibration of Interferometers

The observation results of the supernova remnant Cassiopeia A, obtained with the aid of two decameter radio interferometers at 20 and 25 MHz, are presented. The so obtained dependences of the visibility function modulus on the hour angle are compared with calculations based on the brightness distribution measurements of this source using the VLA at 1381 MHz. Discrepancies between the experimental data and the calculations considerably increase with the decrease in the frequency. It is suggested that interstellar medium absorption, causing a distortion in the source spectrum over the decameter range, may be responsible for changes in the Cas A brightness distribution at these frequencies as well.

An investigation of the Cassiopeia A radio-image in the decameter range

Rapid progress currently takes place in the field of low-frequency radio astronomy in the meter-decameter-hectometer range of wavelengths. It is caused by a radical modernization of the existing radio telescopes, creation of a new generation of instruments, space-borne observations, and by the development of research on all classes of astrophysical objects, including the Solar System. On the other hand, a range of difficulties specific to low-frequency radio astronomy is known, which are caused by technical, methodological, and physical limitations. An effective strategy for overcoming these difficulties is based on synchronous observations using several radio telescopes separated by distances from a few to several thousand kilometers. This provides an opportunity to reduce and identify radio interference and the influence of the propagation media, to increase the sensitivity and resolution, and to solve many problems with higher efficiency. In recent years such simultaneous observations were carried out for the Sun, Jupiter, Saturn, interplanetary medium, pulsars, exoplanets, and transients using the radio telescopes UTR-2, URAN, GURT, NDA, NenuFAR, LOFAR and other. Parallel observations with the space missions WIND, STEREO, Cassini and Juno also facilitate improvement of the quality and reliability of low-frequency radio astronomical experiments.

/pdf/multi-antenna-observations-in-the-low-frequency-radio-4isww26fto.pdf

Multi-antenna observations in the low-frequency radio astronomy of solar system objects and related topics studies

Investigation of the angular structure of the radio emitting quasar 3C196

Experimental investigation of angular structure in the radio emission from the quasar 3C196 at decameter wavelengths

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An investigation of the Cassiopeia A radio-image in the decameter range

Multi-antenna observations in the low-frequency radio astronomy of solar system objects and related topics studies

Investigation of the angular structure of the radio emitting quasar 3C196

Experimental investigation of angular structure in the radio emission from the quasar 3C196 at decameter wavelengths