Thermal to Nonthermal Energy Partition at the Early Rise Phase of Solar Flares

In some flares the thermal component appears much earlier than the nonthermal component in X-ray range. Using sensitive microwave observations we revisit this finding made by Battaglia et al. (2009) based on RHESSI data analysis. We have found that nonthermal microwave emission produced by accelerated electrons with energy of at least several hundred keV, appears as early as the thermal soft X-ray emission indicative that the electron acceleration takes place at the very early flare phase. The non-detection of the hard X-rays at that early stage of the flares is, thus, an artifact of a limited RHESSI sensitivity. In all considered events, the microwave emission intensity increases at the early flare phase. We found that either thermal or nonthermal gyrosynchrotron emission can dominate the low-frequency part of the microwave spectrum below the spectral peak occurring at 3-10 GHz. In contrast, the high-frequency optically thin part of the spectrum is always formed by the nonthermal, accelerated electron component, whose power-law energy spectrum can extend up to a few MeV at this early flare stage. This means that even though the total number of accelerated electrons is small at this stage, their nonthermal spectrum is fully developed. This implies that an acceleration process of available seed particles is fully operational. While, creation of this seed population (the process commonly called `injection' of the particles from the thermal pool into acceleration) has a rather low efficiency at this stage, although, the plasma heating efficiency is high. This imbalance between the heating and acceleration (in favor of the heating) is difficult to reconcile within most of available flare energization models. Being reminiscent of the tradeoff between the Joule heating and runaway electron acceleration, it puts additional constraints on the electron injection into the acceleration process.Comment: 11 pages, 12 figures, accepted for Ap

Study of flare energy release using events with numerous type III-like bursts in microwaves

The analysis of narrowband drifting of type III-like structures in radio bursts dynamic spectra allows to obtain unique information about primary energy release mechanisms in solar flares. The SSRT spatially resolved images and a high spectral and temporal resolution allow direct determination not only the positions of its sources but also the exciter velocities along the flare loop. Practically, such measurements are possible during some special time intervals when the SSRT (about 5.7 GHz) is observing the flare region in two high-order fringes; thus, two 1D scans are recorded simultaneously at two frequency bands. The analysis of type III-like bursts recorded during the flare 14 Apr 2002 is presented. Using-muliwavelength radio observations recorded by SSRT, SBRS, NoRP, RSTN we study an event with series of several tens of drifting microwave pulses with drift rates in the range from -7 to 13 GHz/s. The sources of the fast-drifting bursts were located near the top of the flare loop in a volume of a few Mm in size. The slow drift of the exciters along the flare loop suggests a high pitch-anisotropy of the emitting electrons.Comment: 16 pages, 6 figures, Solar Physics, in press, 201

Cold Solar Flares I. Microwave Domain

We identify a set of ~100 "cold" solar flares and perform a statistical analysis of them in the microwave range. Cold flares are characterized by a weak thermal response relative to nonthermal emission. This work is a follow up of a previous statistical study of cold flares, which focused on hard X-ray emission to quantify the flare nonthermal component. Here we focus on the microwave emission. The thermal response is represented by the soft X-ray emission measured by the GOES X-ray sensors. We obtain spectral parameters of the flare gyrosynchrotron emission and investigate patterns of the temporal evolution. The main results of the previous statistical study are confirmed: as compared to a "mean" flare, the cold flares have shorter durations, higher spectral peak frequencies, and harder spectral indices above the spectral peak. Nonetheless, there are some cold flares with moderate and low peak frequencies. In a majority of cold flares, we find evidence suggesting the presence of the Razin effect in the microwave spectra, indicative of rather dense flaring loops. We discuss the results in the context of electron acceleration efficiency

Zebrafish models in neuropsychopharmacology and CNS drug discovery

Despite the high prevalence of neuropsychiatric disorders, their aetiology and molecular mechanisms remain poorly understood. The zebrafish (Danio rerio) is increasingly utilized as a powerful animal model in neuropharmacology research and in vivo drug screening. Collectively, this makes zebrafish a useful tool for drug discovery and the identification of disordered molecular pathways. Here, we discuss zebrafish models of selected human neuropsychiatric disorders and drug-induced phenotypes. As well as covering a broad range of brain disorders (from anxiety and psychoses to neurodegeneration), we also summarize recent developments in zebrafish genetics and small molecule screening, which markedly enhance the disease modelling and the discovery of novel drug targets. © 2017 The British Pharmacological SocietyThe study was coordinated through the International Zebrafish Neuroscience Research Consortium (ZNRC), and this collaboration was funded by St. Petersburg State University, Ural Federal University and Guangdong Ocean University. A.V.K. is the Chair of ZNRC, and his research is supported by the Russian Foundation for Basic Research (RFBR) grant 16-04-00851

Zebrafish Models in NeuroPsychopharmacology and CNS Drug Discovery

Despite the high prevalence of neuropsychiatric disorders, their aetiology and molecular mechanisms remain poorly understood. The zebrafish (Danio rerio) is increasingly utilized as a powerful animal model in neuropharmacology research and in vivo drug screening. Collectively, this makes zebrafish a useful tool for drug discovery and the identification of disordered molecular pathways. Here, we discuss zebrafish models of selected human neuropsychiatric disorders and drug-induced phenotypes. As well as covering a broad range of brain disorders (from anxiety and psychoses to neurodegeneration), we also summarize recent developments in zebrafish genetics and small molecule screening, which markedly enhance the disease modelling and the discovery of novel drug targets

Comparative Analyses of Zebrafish Anxiety-Like Behavior Using Conflict-Based Novelty Tests

Modeling of stress and anxiety in adult zebrafish (Danio rerio) is increasingly utilized in neuroscience research and central nervous system (CNS) drug discovery. Representing the most commonly used zebrafish anxiety models, the novel tank test (NTT) focuses on zebrafish diving in response to potentially threatening stimuli, whereas the light-dark test (LDT) is based on fish scototaxis (innate preference for dark vs. bright areas). Here, we systematically evaluate the utility of these two tests, combining meta-analyses of published literature with comparative in vivo behavioral and whole-body endocrine (cortisol) testing. Overall, the NTT and LDT behaviors demonstrate a generally good cross-test correlation in vivo, whereas meta-analyses of published literature show that both tests have similar sensitivity to zebrafish anxiety-like states. Finally, NTT evokes higher levels of cortisol, likely representing a more stressful procedure than LDT. Collectively, our study reappraises NTT and LDT for studying anxiety-like states in zebrafish, and emphasizes their developing utility for neurobehavioral research. These findings can help optimize drug screening procedures by choosing more appropriate models for testing anxiolytic or anxiogenic drugs. © 2017, Mary Ann Liebert, Inc.The study was coordinated through the International Zebrafish Neuroscience Research Consortium (ZNRC), and this collaboration was supported by St. Petersburg State University Intramural Research program (DMM, EVK, AVK), Ural Federal University (AVK), Guangdong Ocean University (CS, AVK), the University of Passo Fundo (LJGB), CNPq grant 470260/2013 (LJGB) and CNPq research fellowships 301992/2014-2 (LJGB) and 307595/2015-3 (DBR). The funders had no involvement in the study design, data collection or analysis, and manuscript preparation. AVK is the Chair of ZNRC, and his research is supported by the Russian Foundation for Basic Research (RFBR) grant 16-04-00851. The authors thank Mr Rodrigo Zanandrea (University of Passo Fundo, Brazil) for his assistance with zebrafish cortisol analyses

Double peak quasi-periodic pulsations in a circular-ribbon flare

We study quasi-periodic pulsations (QPPs) during the impulsive phase of the C8.3 flare SOL2002-08-06T01:43. The shape of an extended 5.7 GHz source is similar to a tadpole with the head located above the region of a negative magnetic polarity, surrounded by positive polarity patches and with a remote tail source. The flare configuration includes bright extreme ultraviolet (EUV) ropes with footpoints near the boundary of the negative magnetic field region and it can be identified as a circular ribbon flare. We use simultaneous observations carried out by the Siberian Solar Radio Telescope at 5.7 GHz, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)/HXR, and the Transition Region and Coronal Explorer (TRACE) imaging in the extreme ultraviolet. The flare HXR emission is produced by a compact source located at the south periphery of the Negative Magnetic field Region (NMR). The QPPs are observed during a one-minute interval after the start of the impulsive phase, when this HXR source appeared. The remote source is detected on the variation maps of the of the brightness temperature at 17 GHz and is located at the end of tadpole tail about 60 arcsec eastward. More than a dozen cotemporal HXR and microwave pulses with timescales from 1.5 s up to about 8 s were observed in the flare kernel. At 5.7 GHz, the pulses are more prominent near the remote source where they are highly polarized and generated by the electron beams propagating from the flare kernel. The main tone of the QPP periodicity corresponds to the oscillations with a period of 8 s and is accompanied by the variations in the hardness of nonthermal electrons, that is, in the efficiency of the acceleration mechanism. The second intensity harmonic (about a 3-s period) appears due to a double peak structure of the QPP event. Such pulse shapes suggest oscillations of the current sheet during the loop coalescence as a modulation mechanism of the flare energy release

Temporal and spatial association between microwaves and type III bursts in the upper corona

One of the most important tasks in solar physics is the study of particles and energy transfer from the lower corona to the outer layers of the solar atmosphere. The most sensitive methods for detecting fluxes of non-thermal electrons in the solar atmosphere is observing their radio emission using modern large radioheliographs. We analyzed joint observations from the 13 April 2019 event observed by LOw-Frequency ARray (LOFAR) at meter wavelengths, and the Siberian Radio Heliograph (SRH) and the Badary Broadband Microwave Spectropolarimeter (BBMS) spectropolarimeter in microwaves performed at the time of the second PSP perihelion. During a period without signatures of non-thermal energy release in X-ray emission, numerous type III and/or type J bursts were observed. During the same two hours we observed soft X-ray brightenings and the appearance of weak microwave emission in an abnormally narrow band around 6 GHz. At these frequencies the increasing flux is well above the noise level, reaching 9 sfu. In the LOFAR dynamic spectrum of 53−80 MHz a region is found that lasts about an hour whose emission is highly correlated with 6 GHz temporal profile. The flux peaks in the meter waves are well correlated with extreme UV (EUV) emission variations caused by repeated surges from the bright X-point. We argue that there is a common source of non-thermal electrons located in the tail of the active region, where two loop systems of very different sizes interacted. The frequencies of type III and/or type J bursts are in accordance with large loop heights around 400 Mm, obtained by the magnetic field reconstruction. The microwave coherent emission was generated in the low loops identified as bright X-ray points seen in soft X-ray and EUV images, produced by electrons with energies several tens of keV at about twice the plasma frequency