Zebras were observed not only in the solar radio emission but also in radio emissions of Jupiter and Crab Nebula pulsar. In their models, growth rates of the electrostatic waves play an important role. Considering the plasma composed from the thermal background plasma and hot and rare component with the Dory-Guest-Harris distribution, we compute the growth rates $\gamma$ and dispersion branches of the electrostatic waves in the $\omega - k_\perp$ domain. We show complexity of the electrostatic wave branches in the upper-hybrid band. In order to compare the results, which we obtained using the kinetic theory and Particle-in-cell (PIC) simulations, we define and compute the integrated growth rate $\Gamma$, where the "characteristic width" of dispersion branches was considered. We found a very good agreement between the integrated growth rates and those from PIC simulations. For maximal and minimal $\Gamma$ we showed locations of dispersion branches in the $\omega - k_\perp$ domain. We found that $\Gamma$ has a maximum when the dispersion branches not only cross the region with high growth rates $\gamma$, but when the dispersion branches in this region are sufficiently long and wide. We also mentioned the effects of changes in the background plasma and hot component temperatures.

Growth Rates of the Electrostatic Waves in Radio Zebra Models

Purpose: A historical review of the experimental baselopment of low-frequency radio astronomy in Ukraine, its foundation half a century ago by an outstanding scientist S.Ya. Braude to the current state. Design/methodology/approach: The constant progress of electronic, computer and digital technologies, information and telecommunication technologies, theory and practice of antenna and receiving systems design, which introduction enriched the hardware and methodological ideology of construction and usage of the UTR-2, URAN, and GURT radio telescopes, have been used. Findings: The worldwide most effective national experimental radio astronomy means, the UTR-2, URAN, and GURT decameter-meter wave radiotelescopes, have been created and improved. The best combination of the systems main parameters: sensitivity; frequency band; spatial, frequency and temporal resolutions; noise immunity; uniformity of amplitude-frequency and space-frequency characteristics and multifunctionality has been provided. Conclusions: For the half a century of radio astronomical scientific and technical at the Institute of Radio Astronomy of NAS of Ukraine, the high astrophysical informativeness of the low-frequency radio astronomy and the possibility of creating a highly efficient experimental base – giant radio telescopes of decameter-meter wavebands have been proved. Today, the Ukrainian radio telescopes are well known and recognized world-wide being indispensable and most in demand by the scientific community. The founder of the decameter radio astronomy in Ukraine, the eminent scientist Semen Yakovych Braude was not mistaken when he decided to start radio astronomical explorations. The memory of him will always remain in the minds and hearts of many generations. Key words: low-frequency radio astronomy; radio telescope; phase shifter; antenna amplifier; digital signal recorder; effective area; sensitivity; resolution; noise immunity

/pdf/the-founder-of-the-decameter-radio-astronomy-in-ukraine-42f2su8qqh.pdf

The Founder of the Decameter Radio Astronomy in Ukraine Academician of Nas of Ukraine Semen Yakovych Braude is 110 Years Old: History of Creation and Development of the National Experimental Base for the Last Half Century

Recently detected coherent low-frequency radio emission from M dwarf systems shares phenomenological similarities with emission produced by magnetospheric processes from the gas giant planets of our Solar System. Such beamed electron-cyclotron maser emission can be driven by a star-planet interaction or a breakdown in co-rotation between a rotating plasma disk and a stellar magnetosphere. Both models suggest that the radio emission could be periodic. Here we present the longest low-frequency interferometric monitoring campaign of an M dwarf system, composed of twenty-one $\approx$8 hour epochs taken in two series of observing blocks separated by a year. We achieved a total on-source time of 6.5 days. We show that the M dwarf binary CR Draconis has a low-frequency 3$\sigma$ detection rate of 90$^{+5}_{-8}$% when a noise floor of $\approx$0.1 mJy is reached, with a median flux density of 0.92 mJy, consistent circularly polarised handedness, and a median circularly polarised fraction of 66%. We resolve three bright radio bursts in dynamic spectra, revealing the brightest is elliptically polarised, confined to 4 MHz of bandwidth centred on 170 MHz, and reaches a flux density of 205 mJy. The burst structure is mottled, indicating it consists of unresolved sub-bursts. Such a structure shares a striking resemblance with the low-frequency emission from Jupiter. We suggest the near-constant detection of high brightness temperature, highly-circularly-polarised radiation that has a consistent circular polarisation handedness implies the emission is produced via the electron-cyclotron maser instability. Optical photometric data reveal the system has a rotation period of 1.984$\pm$0.003 days. We observe no periodicity in the radio data, but the sampling of our radio observations produces a window function that would hide the near two-day signal.

Low-frequency monitoring of flare star binary CR Draconis: Long-term electron-cyclotron maser emission

Context. We discuss the origin of quasi-harmonic emission bands that have been observed in the dynamic spectra of the Jovian decameter emission.Aims. We aim to show that the interpretation of the observed structure can be based on the effect of double plasma resonance (DPR) at ion cyclotron harmonics.Methods. According to the proposed model, in the extended source in the upper ionosphere of Jupiter, where the DPR condition is satisfied for one of the ion cyclotron frequency harmonics, the ion cyclotron waves are effectively excited at the frequency of the lower hybrid resonance. The observed electromagnetic radiation with a quasi-harmonic structure arises due to scattering of ion cyclotron waves by supra-thermal electrons.Results. Based on the VIP4 magnetic field model, we determine the longitudes at which the source of the considered radiation can be located. The obtained estimates of the plasma density and its height distribution in the source, as well as the energies of emitting ions and scattering electrons provide information about the plasma parameters in the upper ionosphere of Jupiter. Furthermore, these estimates are in good agreement with the observational data.

Origin of the zebra structure in the Jovian decameter radio emission

Growth rates of the electrostatic waves in radio zebra models

We report the systematic analysis of zebra-like fine spectral structures in decametric frequency range of Jovian radio emission. Observations were performed by the large ground-based radio telescope URAN-2 during three observation campaigns between, Sep., 2012, and May, 2015. In total, 51 zebra pattern (ZP) events were detected. These rare fine radio features are observed in frequency range from 12.5 to 29.7 MHz as quasi-harmonically related bands of enhanced brightness. ZPs are strongly polarized radio emission with a duration from 20 s to 290 s and flux densities similar to 10(5)-10(6) Jy (normalized to 1 AU), that is, 1-2 orders lower than for Io-decametric radio emission (DAM). Occurrence of the events does not depend on the position of Io satellite but is strongly controlled by the Jovian central meridian longitude (CML). ZPs are mainly detected in two active sectors of Jovian CMLs: 100 degrees to 160 degrees for Northern sources (right-handed polarized) and 300 degrees and 60 degrees (via 360 degrees) for the Southern sources (left-handed). The frequency interval between neighboring stripes is from 0.26 to 1.5 MHz and in most cases this interval increases with frequency. We discussed the double plasma resonance with electrons or ions as a possible source of the ZPs. The performed analysis of the observations allows us to conclude that the observed ZPs are a new type of narrow band spectral structures in the Jovian DAM.

Zebra pattern in decametric radio emission of Jupiter

We report the first systematic analysis of zebra–like fine spectral structures in the decametric frequency range of Jovian radio emission (DAM). These zebra patterns are observed in the frequency range from 12 to 30 MHz as a quasi-harmonically related bands (from 3 to 9) of enhanced brightness. The features have been observed by the ground-based radio telescope URAN-2 (Poltava, Ukraine). In total, 55 zebra pattern events have been detected during the period from September 2012 to March 2016. The minimum duration of one single zebra pattern was 20 s, and the maximum one was 4 min 50 s. The intensity of the zebra stripes is 1–2 magnitudes lower than the intensity of Io–controlled DAM. The numbers of stripes in one event may vary in time. The frequency interval between neighboring stripes is from 0.26 to 1.5 MHz. The zebra patterns are strongly polarized and have been observed as right-handed and left-handed polarized radio emission. The zebra patterns are mainly detected in two active sectors of Jovian CMLs: 100° to 160° for northern sources (righthanded polarized) and between 275° and 60° (via 360°) for the southern sources (left-handed). No correlation with the position of Io has been detected. We conclude that the observed zebra patterns are a new type of narrow band spectral structures in the Jovian decametric radio emission.

/pdf/zebra-like-fine-spectral-structures-in-jovian-decametric-5bg2f3tl9w.pdf

Zebra-like fine spectral structures in Jovian decametric radio emission

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Zebra pattern in decametric radio emission of Jupiter

Zebra-like fine spectral structures in Jovian decametric radio emission