Properties and magnetic origins of solar S-bursts

Context. Solar activity is often accompanied by solar radio emission, consisting of numerous types of solar radio bursts. At low frequencies (<100 MHz) radio bursts with short durations of milliseconds, such as solar S-bursts, have been identified. To date, their origin and many of their characteristics remain unclear. Aims. We report observations from the Ukrainian T-shaped Radio telescope, (UTR-2), and the LOw Frequency ARray (LOFAR) which give us new insight into their nature. Methods. Over 3000 S-bursts were observed on 9 July 2013 at frequencies of 17.4-83.1MHz during a period of low solar activity. Leading models of S-burst generation were tested by analysing the spectral properties of S-bursts and estimating coronal magnetic field strengths. Results. S-bursts were found to have short durations of 0.5-0.9 s. Multiple instruments were used to measure the dependence of drift rate on frequency which is represented by a power law with an index of 1.57. For the first time, we show a linear relation between instantaneous bandwidth and frequency over a wide frequency band. The flux calibration and high sensitivity of UTR-2 enabled measurements of their fluxes, which yielded 11 +/- 3 solar flux units (1 SFU equivalent to 10(4) Jy). The source particle velocities of S-bursts were found to be similar to 0.07 c. S-burst source heights were found to range from 1.3 R-circle dot to 2 R-circle dot. Furthermore, a contemporary theoretical model of S-burst generation was used to conduct remote sensing of the coronal magnetic field at these heights which yielded values of 0.9-5.8 G. Within error, these values are comparable to those predicted by various relations between magnetic field strength and height in the corona.Peer reviewe

Using large radio telescopes at decametre wavelengths

International audienceWith the aim of evaluating the actual possibilities of doing, from the ground, sensitive radio astronomy at decametre wavelengths (particularly below &tilde;50MHz), an extensive program of radio observations was carried out, in 1999-2002, by using digital spectral and waveform analysers (DSP) of new generation, connected to several of the largest, decametre radio telescopes in the world (i.e., the UTR-2 and URANs arrays in Ukraine, and the Nançay Decametre Array in France). We report and briefly discuss some new findings, dealing with decametre radiation from Jupiter and the Solar Corona: namely the discovery of new kinds of hyper fine structures in spectrograms of the active Sun, and a new characterisation of Jupiter's "millisecond" radiation, whose waveform samples, with time resolution down to 40 ns, and correlated measurements, by using far distant antennas (3000 km), have been obtained. In addition, scattering effects, caused by the terrestrial ionosphere and the interplanetary medium, could be disentangled through high time resolution and wide-band analyses of solar, planetary and strong galactic radio sources. Consequences for decametre wavelength imaging at high spatial resolution (VLBI) are outlined. Furthermore, in spite of the very unfavourable electromagnetic environment in this frequency range, a substantial increase in the quality of the observations was shown to be provided by using new generation spectrometers, based on sophisticated digital techniques. Indeed, the available, high dynamic range of such devices greatly decreases the effects of artificial and natural radio interference. We give several examples of successful signal detection in the case of much weaker radio sources than Solar System ones, down to the &tilde;1Jy intensity level. In summary, we conclude that searching for sensitivity improvement at the decametre wavelength is scientifically quite justified, and is now technically feasible, in particular by building giant, phased antenna arrays of much larger collecting area (as in the LOFAR project). In this task, one must be careful of some specifics of this wavelength range - somewhat unusual in "classical" radio astronomy - i.e., very high level and density of radio interference (telecommunications) and the variable terrestrial ionosphere

An Active Ribbon Dipole as an Array Element Prototype for the Lunar Very Low Frequency Radio Telescope

This work is concerned with a detailed study of an active antenna, which can serve as a prototype of a phased array antenna element for a future lunar very-low-frequency (VLF) radio telescope operating in the frequency range of 1&#x2013;30 MHz. The antenna consisted of a ribbon symmetrical dipole and a low-noise preamplifier. A dipole 10 m long lay on a flat surface of lunar soil, consisting of a layer of regolith 10 m thick and solid bedrock. The dipole parameters were determined by full-wave simulation using the Altair Feko 2022 software. The preamplifier was a single-stage HEMT low-noise amplifier, whose parameters were determined using the Advanced Design System 2023 software. An active antenna was analyzed using a model created to calculate all electrical and noise parameters. Special attention was paid to the analysis of the antenna sensitivity in terms of the System Equivalent Flux Density (SEFD) and Sky Noise Dominance (SND), taking into account changes in the lunar ambient temperature from 100 K to 400 K. It was shown that the frequency dependences of many active antenna parameters, in particular, radiation efficiency, directivity, effective area, SND, and SEFD had noticeable oscillatory components. The radiation pattern of the antenna was also subject to cyclical changes that occur in sync with the changes in directivity. These properties of the active antenna, caused by the presence of two-layer soil, should be considered when developing future lunar VLF radio telescopes

Ground-based and Space-based Radio Observations of Planetary Lightning

International audienceWe review radio detection of planetary lightning performed by Voyager, Galileo (including in-situ probe measurements), Cassini, and other spacecraft, and compare the information on the underlying physics derived from these observations---especially the discharge duration, at Jupiter and Saturn---with our knowledge of terrestrial lightning. The controversial evidence at Venus is discussed, as well as the prospects for lightning-like discharges in Martian dust-storms (and studies on terrestrial analogues). In addition, lightning sources provide radio beacons that allow us to probe planetary ionospheres. Ground-based observations of Saturn's lightning have been attempted several times in the past and have been recently successful. They will be the subject of observations by the new generation of giant radio arrays. We review past results and future studies, focussing on the detection challenges and on the interest of ground-based radio monitoring, in conjunction with spacecraft observations or in standalone mode

Sporadic radio emission of the Sun in the decametre range

International audienceResults of the last observations of solar sporadic radio emission at the UTR-2 radio telescope (Kharkov, Ukraine) at the frequencies 10 - 30 MHz are presented. The use of new backend facilities, the DSP and 60-channel spectrometer, allows us to obtain data with time resolution up to 2 ms and frequency resolution of 12 kHz in the continuous frequency band 12 MHz. Usual Type III bursts, Type IIIb bursts, U- and J-bursts in the decameter range are discussed. Special attention is paid to detection and analysis of Type II bursts and their properties, newly discovered fine time structures of Type III bursts, Type III-like bursts, s-bursts, new observational features of drift pair bursts, and ‘absorption’ bursts

Sporadic Decameter Radio Emission of the Sun

International audienc

Sporadic Radio Emission of the Sun in the Decameter Range

International audienc

Sporadic Decameter Radio Emission of the Sun

International audienc