### The First Flare Observation with a New Solar Microwave Spectrometer Working in 35–40 GHz, By Yan et al.

2023-01-31

Microwave emission of solar flares can be excited by energetic electrons through the gyrosynchrotron (GS) radiation. Thus, the microwave spectra contain valuable/unique information not only about energetic electrons accelerated during solar flares, but also about the underlying magnetic field and energy release process. The typical microwave spectra peak below or around, say, ~10 GHz, at which the spectral slope turns over from positive  — the optically thick regime — to […]

### Radio Scintillation Observations of the Plasma Tail of Interstellar Comet 2I/Borisov, by P K Manoharan et al.*

2023-01-17

Comet 2I/Borisov was only the second interstellar object known to have entered the solar system. The highly eccentric, hyperbolic orbit of 2I/Borisov and its high inclination to the ecliptic plane demonstrated that the comet had an extrasolar system origin (e.g., Manzini et al. 2020). Polarimetric observations of this comet suggested a remarkably smooth, pristine coma with a high concentration of carbon monoxide, that had likely never interacted with the solar […]

### Microwave imaging of quasi-periodic pulsations at flare current sheet by Yuankun Kou et al.

2023-01-03

Quasi-periodic pulsations (QPPs; also known as quasi-periodic oscillations, i.e., QPOs) are phenomena that electromagnetic emissions vary quasi-periodically with time. They appear in celestial transient events with different temporal/spatial scales, such as stellar flares, gamma ray bursts and fast radio bursts, and etc. The Sun is a normal but the closest star from us, where flares with QPPs appear frequently (e.g. Zimovets et al. 2021 as a review). In the standard […]

### Zebra Stripes with High Gyro-Harmonic Numbers by Jan Benacek and Marian Karlicky

2022-12-20

The solar radio zebra patterns, or zebras, provide detailed diagnostics of plasma density and magnetic field in the corona. The zebras appear in radiograms during Type IV solar radio bursts as a series of parallel stripes that are narrow in frequency. The main emission model of radio zebras relies on a double plasma resonance, a resonance between the plasma frequency, gyro-harmonic of the cyclotron frequency, and the frequency of unstable upper-hybrid (UH) […]

### Flares detected in ALMA single-dish images by I. Skokic et al

2022-12-06

The (sub)millimeter radiation of solar flares, explosive events detected as brightenings across the electromagnetic spectrum, is poorly understood (Krucker et al. 2013). The major limit of the previous >100 GHz observations was spatial resolution, impeding the combination with observations at other wavelengths. The Atacama Large Millimeter-submillimeter Array (ALMA) offers sufficient resolution for the first time. Shimizu et al. (2021) reported a microflare observed in interferometric mode. However, used as an […]

### Third and fourth harmonics of electromagnetic emissions by a weak beam in a solar wind plasma with random density fluctuations by C. Krafft

2022-11-22

Electromagnetic emissions at the third harmonic of the plasma frequency $\omega _{p}$ have been reported during the occurrence of type II and type III solar radio bursts (e.g. Zlotnik 1978, Zlotnik et al. 1998, Cairns; 1986), even if rarely and sometimes controversially. Recently the Wind spacecraft detected several events exhibiting third harmonic emissions in interplanetary type III bursts observed locally near 1 AU (Reiner and MacDowald; 2019). For the first […]

### Characteristics of stripes-pattern radio-emission sources by Khaled Alielden

2022-10-18

Investigating the generation mechanism for the stripes-pattern radio spectra is important to understand the dynamics of non-thermal electrons in several astronomical objects, including the Sun, Jupiter, and the Crab Pulsar. A new analytical study is carried out to identify the plasma characteristics of fiber- and zebra-pattern emission sources without an underlying density or magnetic model. The study suggests that the plasma condition of the source region for zebra pattern emission […]

### Narrowband Spikes Observed During the 13 June 2012 Flare in the 800 – 2000 MHz Range by Marian Karlicky et al

2022-09-06

The solar radio spikes can provide detailed information about plasma processes in solar flares on kinetic scales. Among them, the decimetric spikes belong to the most interesting ones because they are recorded in some cases close to the starting frequency of Type-III bursts and in relation to hard X-ray emissions. Stepanov et al. (1999) and Bárta and Karlický (2001) presented models where spike frequencies correspond to those of the upper-hybrid […]

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