6 research outputs found
Free-free absorption parameters of Cassiopeia A from low-frequency interferometric observations
Context. Cassiopeia A is one of the most extensively studied supernova
remnants (SNRs) in our Galaxy. The analysis of its spectral features with the
help of low frequency observations plays an important role for understanding
the evolution of the radio source through the propagation of synchrotron
emission to observers through the SNR environment and the interstellar medium.
Aims. In this paper we present measurements of the integrated spectrum of Cas A
to characterize the properties of free-free absorption towards this SNR. We
also add new measurements to track its slowly evolving and decreasing
integrated flux density. Methods. We use the Giant Ukrainian radio telescope
(GURT) for measuring the continuum spectrum of Cassiopeia A within the
frequency range of 16-72 MHz. The radio flux density of Cassiopeia A relative
to the reference source of the radio galaxy Cygnus A has been measured on
May-October, 2019 with two subarrays of the GURT, used as a two-element
correlation interferometer. Results. We determine magnitudes of emission
measure, electron temperature and an average number of charges of the ions for
both internal and external absorbing ionized gas towards in Cassiopeia A.
Generally, their values are close to the ones suggested by Arias et al. (2018),
although for some there are slight differences. In the absence of clumping we
find the unshocked ejecta of M = 2.61 solar mass at the electron density of
15.3 cm^-3 has a gas temperature of T=100 K. If the clumping factor is 0.67,
then the unshocked ejecta of 0.96 solar mass the electron density of 18.7
cm^-3. Conclusions. The integrated flux density spectrum of Cassiopeia A
obtained with the GURT interferometric observations is consistent with the
theoretical model within measurement errors and also reasonably consistent with
other recent results in the literature.Comment: 9 pages, 9 figures, 2 table
Effect of the ground screen on sensitivity of low-frequency radio telescope array element
The Giant Ukrainian Radio Telescope (GURT) is a new generation radio telescope with active phased antenna array intended to operate within 10–80 MHz range. The radio telescope is being constructed now in Ukraine. The array elements are active antennas in form of flat wire dipoles integrated with low-noise preamplifiers. In the paper we present a comparative analysis of two GURT array element versions that differ in presence or absence of wire grid ground screen under the dipole. The analysis results are given and discussed
Parker Solar Probe detects solar radio bursts related with a behind–the–limb active region
Context. The interpretation of solar radio bursts observed by Parker Solar Probe (PSP) in the encounter phase plays a key role in understanding intrinsic properties of the emission mechanism in the solar corona. Lower time–frequency resolution of the PSP receiver can be overcome by simultaneous ground–based observations using more advanced antennas and receivers.
Aims. In this paper we present such observations for which the active active region 12 765, begetter of type III, J, and U solar bursts, was within sight of ground–based instruments and behind the solar limb of the PSP spacecraft.
Methods. We used a subarray of the Giant Ukrainian Radio Telescope to get the spectral properties of radio bursts at the frequency range of 8–80 MHz, as well as the PSP radio instruments with a bandwidth of 10.5 kHz–19.2 MHz, during solar observations on June 5, 2020.
Results. We directly detected the radio events initiated by the active region behind the solar limb of the PSP spacecraft, using special conditions in the solar corona, due to the absence of active regions from the PSP side. Following the generation mechanism of solar radio emission, we refined the density model for the solar corona above the active region 12765 responsible for the radio bursts. Based on the PSP spacecraft position near the Sun and delays of radio waves between space– and ground–based records, we found the corresponding radio responses on the PSP spectrogram.
Conclusions. The absence of sunspots from the PSP side contributes to the propagation of radio waves from a dense loop of the Sun to quiet regions with low densities, through which PSP instruments can detect the radiation
Signal delivery system in a subarray of Giant Ukrainian Radio Telescope
Radio astronomy deals with the weakest signals received by a radio electronic device, and, as a result, it is very complicated problem to maintain appropriate SNR while transferring signal from the antenna output to receiver's input. In this paper, a system for delivering the radio astronomical signals from dipole terminals to ADC input of Giant Ukrainian Radio Telescope (GURT) is described. Examples of the received signal spectra in wide frequency range are shown
New technique of testing and calibration of the UTR-2 radio telescope
The purpose of the work is to develop testing and calibration technique of large phased antenna arrays using reference noise generator as a standard signal source. This technique is developed for calibration of the phased antenna array of the unique decameter wave radio telescope UTR-2, but they could be easy adapted for similar large arrays with analog and digital beam forming