scholarly journals Radio signatures of shock-accelerated electron beams in the solar corona

2018 ◽  
Vol 609 ◽  
pp. A41 ◽  
Author(s):  
G. Mann ◽  
V. N. Melnik ◽  
H. O. Rucker ◽  
A. A. Konovalenko ◽  
A. I. Brazhenko
Keyword(s):  
Solar Corona ◽  
Electron Beams ◽  
Radio Spectrum ◽  
Plasma Emission ◽  
Radio Bursts ◽  
Thermal Electron ◽  
Langmuir Waves ◽  
Energetic Electrons ◽  
Fine Structures ◽  
Theoretical Results

Context. The Sun’s activity can appear in terms of radio bursts. In the frequency range 8−33 MHz the radio telescope URAN-2 observed special fine structures appearing as a chain of stripes of enhanced radio emission in the dynamic radio spectrum. The chain drifts slowly from 26 to 23 MHz within 4 min. The individual structures consist of a “head” at the high-frequency edge and a “tail” rapidly drifting from the “head” to lower frequencies over an extent of ≈10 MHz within 8 s. Since they resemble the well-known “herring bones” in type II radio bursts, they are interpreted as shock accelerated electron beams. Aims. The electron beams generating these fine structures are considered to be produced by shock drift acceleration (SDA). The beam electrons excite Langmuir waves which are converted into radio waves by nonlinear wave-plasma processes. That is called plasma emission. The aim of this paper is to link the radio spectral data of these fine structures to the theoretical results in order to gain a better understanding of the generation of energetic electrons by shocks in the solar corona. Methods. Adopting SDA for generating energetic electrons, the accelerated electrons establish a beam-like velocity distribution. Plasma emission requires the excitation of Langmuir waves, which is efficient if the velocity of the beam electrons exceeds a few times thermal electron speed. That is the case if the angle between the shock normal and the upstream magnetic field is nearly perpendicular. Hence, the Rankine-Hugoniot relationships, which describe the shock transition in the framework of magnetohydrodynamics, are evaluated for the special case of nearly perpendicular shocks under coronal circumstances. Results. The radio data deduced from the dynamic radio spectrum can be related in the best way to the theoretical results, if the electron beams, which generate these fine structures, are generated via SDA at an almost perpendicular shock, which is traveling nearly horizontally to the surface of the Sun.

scholarly journals The effects of density inhomogeneities on the radio wave emission in electron beam plasmas

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
Xin Yao ◽  
Patricio A. Muñoz ◽  
Jörg Büchner ◽  
Xiaowei Zhou ◽  
Siming Liu
Keyword(s):  
Magnetic Reconnection ◽  
Radio Wave ◽  
Solar Flares ◽  
Electron Beams ◽  
Distribution Functions ◽  
Plasma Emission ◽  
Langmuir Waves ◽  
Radio Emissions ◽  
Density Inhomogeneities ◽  
Effects Of Density

Type III radio bursts are radio emissions associated with solar flares. They are considered to be caused by electron beams travelling from the solar corona to the solar wind. Magnetic reconnection is a possible accelerator of electron beams in the course of solar flares since it causes unstable distribution functions and density inhomogeneities (cavities). The properties of radio emission by electron beams in an inhomogeneous environment are still poorly understood. We capture the nonlinear kinetic plasma processes of the generation of beam-related radio emissions in inhomogeneous plasmas by utilizing fully kinetic particle-in-cell code numerical simulations. Our model takes into account initial electron velocity distribution functions (EVDFs) as they are supposed to be created by magnetic reconnection. We focus our analysis on low-density regions with strong magnetic fields. The assumed EVDFs allow two distinct mechanisms of radio wave emissions: plasma emission due to wave–wave interactions and so-called electron cyclotron maser emission (ECME) due to direct wave–particle interactions. We investigate the effects of density inhomogeneities on the conversion of free energy from the electron beams into the energy of electrostatic and electromagnetic waves via plasma emission and ECME, as well as the frequency shift of electron resonances caused by perpendicular gradients in the beam EVDFs. Our most important finding is that the number of harmonics of Langmuir waves increases due to the presence of density inhomogeneities. The additional harmonics of Langmuir waves are generated by a coalescence of beam-generated Langmuir waves and their harmonics.

scholarly journals Separation of solar radio bursts in a complex spectrum

2010 ◽  
Vol 6 (S274) ◽  
pp. 150-152
Author(s):  
Hana Mészárosová ◽  
Ján Rybák ◽  
Marian Karlický ◽  
Karel Jiřička
Keyword(s):  
Radio Emission ◽  
Current Sheet ◽  
Solar Flares ◽  
Solar Radio ◽  
Radio Spectrum ◽  
New Method ◽  
Complex Spectrum ◽  
Radio Bursts ◽  
Solar Radio Bursts ◽  
Fine Structures

AbstractRadio spectra, observed during solar flares, are usually very complex (many bursts and fine structures). We have developed a new method to separate them into individual bursts and analyze them separately. The method is used in the analysis of the 0.8–2.0 GHz radio spectrum of the April 11, 2001 event, which was rich in drifting pulsating structures (DPSs). Using this method we showed that the complex radio spectrum consists of at least four DPSs separated with respect to their different frequency drifts (−115, −36, −23, and −11 MHz s−1). These DPSs indicate a presence of at least four plasmoids expected to be formed in a flaring current sheet. These plasmoids produce the radio emission on close frequencies giving thus a mixture of superimposed DPSs observed in the radio spectrum.

Nonrelativistic electron beam expansion in the solar corona/wind  and their type III radio bursts observed with LOFAR

2021 ◽  
Author(s):  
Hamish Reid ◽  
Eduard Kontar
Keyword(s):  
Electron Beam ◽  
Energy Density ◽  
Solar Corona ◽  
Electron Beams ◽  
Low Frequency ◽  
High Energy ◽  
High Energy Density ◽  
Moderate Intensity ◽  
Radio Bursts ◽  
Type Iii

<div> <div><span>Solar type III radio bursts contain a wealth of information about the dynamics of near-relativistic electron beams in the solar corona and the inner heliosphere; this information is currently unobtainable through other means.  Whilst electron beams expand along their trajectory, the motion of different regions of an electron beam (front, middle, and back) had never been systematically analysed before.  Using LOw Frequency ARray (LOFAR) observations between 30-70 MHz of type III radio bursts, and kinetic simulations of electron beams producing derived type III radio brightness temperatures, we explored the expansion as electrons propagate away from the Sun.  From relatively moderate intensity type III bursts, we found mean electron beam speeds for the front, middle and back of 0.2, 0.17 and 0.15 c, respectively.  Simulations demonstrated that the electron beam energy density, controlled by the initial beam density and energy distribution have a significant effect on the beam speeds, with high energy density beams reaching front and back velocities of 0.7 and 0.35 c, respectively.  Both observations and simulations found that higher inferred velocities correlated with shorter FWHM durations of radio emission at individual frequencies.  Our radial predictions of electron beam speed and expansion can be tested by the upcoming in situ electron beam measurements made by Solar Orbiter and Parker Solar Probe.</span></div> </div>

Type III Radio Bursts and Langmuir Wave Excitation

2020 ◽  
Author(s):  
Gottfried Mann ◽  
Christian Vocks ◽  
Mario Bisi ◽  
Eoin Carley ◽  
Bartosz Dabrowski ◽  
...  
Keyword(s):  
Distribution Function ◽  
Interplanetary Space ◽  
Langmuir Wave ◽  
Velocity Distribution Function ◽  
Radio Bursts ◽  
Radio Waves ◽  
Langmuir Waves ◽  
Low Frequencies ◽  
Energetic Electrons ◽  
Type Iii

<p>Type III radio bursts are a common phenomenon the Sun’s nonthermal radio radiation. They appear as stripes of enhanced radio emission with a rapid drift from high to low frequencies in dynamic radio spectra. They are considered as the radio signatures of beams of energetic electrons travelling along magnetic field lines from the solar corona into the interplanetary space. With the ground based radio interferometer LOFAR and the instrument FIELDS onboard NASA’s “Parker Solar Probe” (PSP) , type III radio bursts can be observed simultaneously from high (10-240 MHz) to low frequencies (0.01-20 MHz) with LOFAR and PSP’s FIELDs, respectively. That allows to track these electron beams from the corona up to the interplanetary space. Assuming that a population of energetic electrons is initially injected, the velocity distribution function of these electrons evolves into a beam like one. Such distribution function leads to the excitation of Langmuir waves which convert into radio waves finally observed as type II radio bursts. Numerical calculations of the electron-beam-plasma interaction reveal that the Langmuir waves are excited by different parts of the energetic electrons at different distances in the corona and interplanetary space. This result is compared with special type III radio bursts observed with LOFAR and PSP’s FIELDS.</p>

scholarly journals Multiwavelength Observations of Fast Radio Bursts

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 76
Author(s):  
Luciano Nicastro ◽  
Cristiano Guidorzi ◽  
Eliana Palazzi ◽  
Luca Zampieri ◽  
Massimo Turatto ◽  
...  
Keyword(s):  
Radio Burst ◽  
High Energy ◽  
Medium Size ◽  
Radio Bursts ◽  
Starting Point ◽  
Key Points ◽  
Fast Radio Burst ◽  
Theoretical Results ◽  
Observational Strategy ◽  
Shed Light

The origin and phenomenology of the Fast Radio Burst (FRB) remains unknown despite more than a decade of efforts. Though several models have been proposed to explain the observed data, none is able to explain alone the variety of events so far recorded. The leading models consider magnetars as potential FRB sources. The recent detection of FRBs from the galactic magnetar SGR J1935+2154 seems to support them. Still, emission duration and energetic budget challenge all these models. Like for other classes of objects initially detected in a single band, it appeared clear that any solution to the FRB enigma could only come from a coordinated observational and theoretical effort in an as wide as possible energy band. In particular, the detection and localisation of optical/NIR or/and high-energy counterparts seemed an unavoidable starting point that could shed light on the FRB physics. Multiwavelength (MWL) search campaigns were conducted for several FRBs, in particular for repeaters. Here we summarize the observational and theoretical results and the perspectives in view of the several new sources accurately localised that will likely be identified by various radio facilities worldwide. We conclude that more dedicated MWL campaigns sensitive to the millisecond–minute timescale transients are needed to address the various aspects involved in the identification of FRB counterparts. Dedicated instrumentation could be one of the key points in this respect. In the optical/NIR band, fast photometry looks to be the only viable strategy. Additionally, small/medium size radiotelescopes co-pointing higher energies telescopes look a very interesting and cheap complementary observational strategy.

scholarly journals Electron beam relaxation in inhomogeneous plasmas

2013 ◽  
Vol 31 (8) ◽  
pp. 1379-1385 ◽  
Author(s):  
A. Voshchepynets ◽  
V. Krasnoselskikh
Keyword(s):  
Electron Beam ◽  
Beam Energy ◽  
Electron Beams ◽  
Inhomogeneous Plasma ◽  
Density Fluctuations ◽  
Langmuir Waves ◽  
Wave Trapping ◽  
Beam Plasma ◽  
Beam Plasma Instability ◽  
Accelerated Particles

Abstract. In this work, we studied the effects of background plasma density fluctuations on the relaxation of electron beams. For the study, we assumed that the level of fluctuations was so high that the majority of Langmuir waves generated as a result of beam-plasma instability were trapped inside density depletions. The system can be considered as a good model for describing beam-plasma interactions in the solar wind. Here we show that due to the effect of wave trapping, beam relaxation slows significantly. As a result, the length of relaxation for the electron beam in such an inhomogeneous plasma is much longer than in a homogeneous plasma. Additionally, for sufficiently narrow beams, the process of relaxation is accompanied by transformation of significant part of the beam kinetic energy to energy of accelerated particles. They form the tail of the distribution and can carry up to 50% of the initial beam energy flux.

scholarly journals Response of chromospheric lines to different periodic non-thermal electron beams

2015 ◽  
Vol 11 (S320) ◽  
pp. 239-242
Author(s):  
Jianxia Cheng ◽  
Mingde Ding
Keyword(s):  
Electron Beam ◽  
Solar Flares ◽  
Local Thermodynamic Equilibrium ◽  
Response Times ◽  
Electron Beams ◽  
Lower Atmosphere ◽  
Mass Motion ◽  
Thermal Electron ◽  
Hydrodynamic Simulations ◽  
Beam Injection

AbstractSolar flares produce radiations in very broad wavelengths. Spectra can supply us abundant information about the local plasma, such as temperature, density, mass motion and so on. Strong chromospheric lines, like the most studied Hα and Ca II 8542 Å lines are formed under conditions of departures from local thermodynamic equilibrium in the lower atmosphere subject to flare heating. Understanding how these lines are formed is very useful for us to correctly interpret the observations. In this paper, we try to figure out the response of chromospheric lines heated by different periodic non-thermal electron beams. Our results are based on radiative hydrodynamic simulations. We vary the periods of electron beam injection from 1.25 s to 20 s. We compare the response times to different heating parameters. Possible explanations are discussed.

Sign in / Sign up

Export Citation Format

Share Document