Nonthermal Electron Density Research Articles

Propagation of three-dimensional ion-acoustic solitary waves in magnetized negative ion plasmas with nonthermal electrons

Properties of small amplitude nonlinear ion-acoustic solitary waves in a warm magneto plasma with positive-negative ions and nonthermal electrons are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive the corresponding nonlinear evolution equation; Zkharov–Kuznetsov (ZK) equation, in the small amplitude regime. The ZK equation is analyzed to examine the existence regions of the solitary pulses. It is found that compressive and rarefactive ion-acoustic solitary waves strongly depend on the mass and density ratios of the positive and negative ions as well as the nonthermal electron parameter. Also, it is found that there are two critical values for the density ratio of the negative-to-positive ions (υ), the ratio between unperturbed electron-to-positive ion density (μ), and the nonthermal electron parameter (β), which decide the existence of positive and negative ion-acoustic solitary waves. The present study is applied to examine the small amplitude nonlinear ion-acoustic solitary excitations for the (H+, O2−) and (H+, H−) plasmas, where they are found in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in understanding the salient features of the nonlinear ion-acoustic solitary waves in space and in laboratory plasmas where two distinct groups of ions and non-Boltzmann distributed electrons are present.

Fully nonlinear ion-acoustic solitary waves in a plasma with positive-negative ions and nonthermal electrons

Properties of fully nonlinear ion-acoustic solitary waves in a plasma with positive-negative ions and nonthermal electrons are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive the energy integral equation with a new Sagdeev potential. The latter is analyzed to examine the existence regions of the solitary pulses. It is found that the solitary excitations strongly depend on the mass and density ratios of the positive and negative ions as well as the nonthermal electron parameter. Numerical solution of the energy integral equation clears that both positive and negative potentials exist together. It is found that faster solitary pulses are taller and narrower. Furthermore, increasing the electron nonthermality parameter (negative-to-positive ions density ratio) decreases (increases) the localized excitation amplitude but increases (decreases) the pulse width. The present model is used to investigate the solitary excitations in the (H+,O2−) and (H+,H−) plasmas, where they are presented in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in understanding the salient features of the fully nonlinear ion-acoustic solitary waves in space and in laboratory plasmas where two distinct groups of ions and non-Boltzmann distributed electrons are present.

The Radio Signature of Magnetic Reconnection for the M-Class Flare of 2004 November 1

In this Letter, we present radio diagnostics for the magnetic field and the density distribution of nonthermal electrons in the microwave source of the M1.1 flare of 2004 November 1. We calculate the nonthermal gyrosynchrotron radiation using observations made at the Nobeyama Radio Observatory to get the longitudinal magnetic field and the magnitude of the transverse magnetic field. The computed longitudinal magnetic field at two hard X-ray footpoints has opposite polarities, which basically agrees with SOHO MDI observations. The main finding is that the magnitude of the transverse magnetic field summed around the magnetic neutral line of the SOHO MDI magnetogram has a short-term impulsive increase during the rising phase of the flare. We propose that the increase of the transverse magnetic field may be considered evidence of the magnetic reconnection process in this flare. The computed mean angle between the magnetic field and line of sight decreases steadily during the flare, clearly indicating the reconfiguration of the magnetic field, presumably the relaxation of the sheared magnetic field. Moreover, the calculated density of nonthermal electrons increases from footpoints to looptop, while the spectral index calculated by the Nobeyama Radio Heliograph at 17 and 34 GHz decreases from footpoints ( soft) to looptop ( hard), which may confirm that the reconnection site is close to the looptop source.

On invisible plasma content in radio-loud AGNs: the case of TeV blazar Markarian 421

Invisible plasma content in blazar jets such as protons and/or thermal electron-positron (e ± ) pairs is explored through combined arguments of dynamical and radiative processes. By comparing physical quantities required by the internal shock model with those obtained through the observed broad-band spectra for Mrk 421, we obtain that the ratio of the Lorentz factors of a pair of cold shells resides in about 2 ∼ 20, which implies that the shocks are at most mildly relativistic. Using the obtained Lorentz factors, the total mass density p in the shocked shells is investigated. The upper limit of p is obtained from the condition that thermal bremsstrahlung emission should not exceed the observed γ-ray luminosity, whilst the lower limit is constrained from the condition that the energy density of non-thermal electrons is smaller than that of the total plasma. Then, we find p is 10 2 -10 3 times heavier than that of non-thermal electrons for pure e ± pairs, while 10 2 -10 6 times heavier for pure electron-proton (e/p) content, implying the existence of a large amount of invisible plasma. The origin of the continuous blazar sequence is briefly discussed and we speculate that the total mass density and/or the blending ratio of e ± pairs and e/p plasma could be new key quantities for the origin of the sequence.

Diagnosis of coronal magnetic field and nonthermal electrons from Nobeyama observations of a simple flare

Coronal magnetic field and nonthermal electrons are very important parameters for understanding of the global heliophysical processes. A flare on November 1, 2004 is selected for self-consistent calculations of coronal magnetic field parallel and perpendicular to the line-of-sight, and density of nonthermal electrons from Nobeyama observations. Both of the diagnosis methods and results are discussed in this paper.

The Radio Spectrum of TVLM 513‐46546: Constraints on the Coronal Properties of a Late M Dwarf

We explore the radio emission from the M9 dwarf TVLM 513-46546 at multiple radio frequencies, determining the flux spectrum of persistent radio emission, as well as constraining the levels of circular polarization. Detections at both 3.6 and 6 cm provide a spectral index measurement α (where Sν ∝ να) of -0.4 ± 0.1. A detection at 20 cm suggests that the spectral peak is between 1.4 and 5 GHz. The most stringent upper limits on circular polarization are at 3.6 and 6 cm, with V/I < 15%. These characteristics agree well with those of typical parameters for early- to mid-type M dwarfs, confirming that magnetic activity is present at levels comparable with those extrapolated from earlier M dwarfs. We apply analytic models to investigate the coronal properties under simple assumptions of dipole magnetic field geometry and radially varying nonthermal electron density distributions. Requiring the spectrum to be optically thin at frequencies higher than 5 GHz and reproducing the observed 3.6 cm fluxes constrains the magnetic field at the base to be less than about 500 G. There is no statistically significant periodicity in the 3.6 cm light curve, but it is consistent with low-level variability.

Constraining the Emission Properties of TeV Blazar H1426+428 by the Synchrotron Self‐Compton Model

H1426+428 is one of blazars that are observed by $\gamma$-rays in the TeV region. Because TeV $\gamma$-rays from distant sources are subject to attenuation by the extragalactic background light (EBL) via electron-positron pair production, the intrinsic spectrum of the TeV $\gamma$-rays should be inferred by using the models of radiation processes and EBL spectrum. We set constraints on the physical condition of H1426+428 with the synchrotron-self-Compton model applying several EBL models. We find that the emission region of H1426+428 is moving toward us with the bulk Lorentz factor of $\sim 20$ and that its magnetic field strength is $\sim 0.1$ G. These properties are similar to other TeV blazars such as Mrk 421 and Mrk 501. However, the ratio of the energy density of nonthermal electrons to that of the magnetic fields is about 190 and fairly larger than those of Mrk 421 and Mrk 501, which are about 5 -- 20. It is also found that the intensity of EBL in the middle and near infrared wavelengths should be low, i.e., the intensity at 10 $\mu$m is about 1 nW m$^{-2}$ sr$^{-1}$ to account for the observed TeV $\gamma$-ray flux. Because the spectral data of H1426+428 in X-rays and $\gamma$-rays used in our analysis were not obtained simultaneously, further observations of TeV blazars are necessary to make the constraints on EBL more stringent.

Very Large Array and SOHO Observations of Type I Noise Storms, Large-Scale Loops and Magnetic Restructuring in the Corona

Very Large Array (VLA) observations at 91-cm wavelength are combined with data from the SOHO EIT, MDI and LASCO and used to study the evolving coronal magnetic environment in which Type I noise storms and large-scale coronal loops occur. On one day, we have shown the early evolution of a coronal mass ejection (CME) in projection in the disk by tracing its decimetric continuum emission. The passage of the CME and an associated EUV ejection event coincided with an increase in the 91-cm brightness temperature of an extended coronal loop located a significant distance away and with the displacement of the 91-cm source during the early stage of the CME. We suggest that the energy deposited into the corona by the CME may have caused a local increase in the thermal or nonthermal electron density or in the electron temperature in the middle corona resulting in a transient increase in the brightness of the 91-cm loop. On a second observing day, we have consolidated the known association between magnetic changes in the photosphere and low corona with noise storm enhancements in an overlying radio source well in advance of a flare event in the same region. We find anti-correlated changes in the brightness of a bipolar 91-cm Type I noise storm that appear to be associated with the cancellation and emergence of magnetic flux in the underlying photosphere. In this case, the evolving fields may have led to magnetic instabilities and reconnection in the corona and the acceleration of nonthermal particles that initiated and sustained the Type I noise storm.

Electron acoustic solitary waves with non-thermal distribution of electrons

Abstract. Electron-acoustic solitary waves are studied in an unmagnetized plasma consisting of non-thermally distributed electrons, fluid cold electrons and ions. The Sagdeev pseudo-potential technique is used to carry out the analysis. The presence of non-thermal electrons modifies the parametric region where electron acoustic solitons can exist. For parameters representative of auroral zone field lines, the electron acoustic solitons do not exist when either α &gt; 0.225 or Tc/Th &gt; 0.142, where α is the fractional non-thermal electron density, and Tc (Th) represents the temperature of cold (hot) electrons. Further, for these parameters, the simple model predicts negatively charged potential structures. Inclusion of an electron beam in the model may provide the positive potential solitary structures.

Constraints on the energetics and plasma composition of relativistic jets in FR II sources

We explore the energetics and plasma composition in FR II sources using a new simple method of combining shock dynamics and radiation spectrum. The hot spots are identified with the reverse shocked region of jets. With the one-dimensional shock jump conditions taking account of the finite pressure of hot ICM, we estimate the rest mass and energy densities of the sum of thermal and non-thermal particles in hot spots. Independently, based on the Synchrotron Self-Compton (SSC) model, we estimate the number and energy densities of {\it non-thermal} electrons using the multi-frequency radiation spectrum of hot spots. We impose the condition that the obtained rest mass, internal energy, and number densities of non-thermal electrons should be lower than those of the total particles determined by shock dynamics. We apply this method to Cygnus A. We examine three extreme cases of pure electron-positron pair plasma (Case I), pure electron-proton plasma with separate thermalization (Case II), and pure electron-proton plasma in thermal-equilibrium (Case III). By detailed SSC analysis for Cygnus A and 3C123, we find that the energy density of non-thermal electrons is about 10 times larger than that of magnetic field. We find that the Case III is not acceptable because predicted photon spectra do not give a good fit to the observed one. We find that Case II can also be ruled out since the number density of non-thermal electrons exceeds that of the total number density. Hence, we find that only pure $e^{\pm}$ plasma (Case I) is acceptable among the three cases. Total kinetic power of jet and electron acceleration efficiency are also constrained by internal energy densities of non-thermal and total particles.

Temporal and spatial distribution of the magnetic field and density of nonthermal electrons in the source of solar microwave bursts

The temporal and spatial distribution of the magnetic field and density of non-thermal electrons in the source of solar microwave bursts are studied by the gyrosynchrotron model, using the observations of the high-resolution spectrometer at the Owens Valley solar interferometer. The general results are consistent with the previous knowledge about these parameters. For example, the magnetic field decreases with increasing radio flux, and the distribution gradually flattens, so that the non-uniformity of the magnetic field decreases gradually, meanwhile the density increases, and the nonthermal electrons propagate from lower to higher levels. It is interesting that the oscillation of the density is detected at lower frequencies, and there is a correlation between the density and the energy index. The main purpose of this paper is to develop a diagnostic method for the basic plasma parameters in solar flares.

Nonthermal electrons responsible for solar radio and X-ray emissions

The properties of nonthermal electrons are calculated from solar radio and X-ray bursts based on the intrinsic wave-particle interaction in an unstable radiation process excited by plasma instabilities. One example of multiwavelength observations shows that the density of nonthermal electrons decreases with increasing the energy of single electrons, which just corresponds to a power law distribution with the index of the energy spectrum about 3. The slope of the rising phase increases in the order from low energy to high energy for SXR, HXR, microwave and millimeter wave bands, which is interpreted by the increasing of the ratio between nonthermal and thermal radiation. Moreover, the evolution of nonthermal electrons is calculated from a typical event composed of several pulsations, at both microwave and HXR bursts, the electrons are accelerated in the rising phase and decelerated in the decay phase, while in the meantime the ratio between nonthermal and thermal radiation in the rising phase is larger than that in the decay phase. Hence, not only the acceleration processes but also the wave-particle interaction caused by plasma instabilities contribute to the evolution of the radiation spectrum.

SOURCE PARAMETERS FOR IMPULSIVE BURSTS OBSERVED IN THE RANGE 18–23 GHz

Here, we report on impulsive solar radio bursts observed for the first time with high time/spectral resolution in the range 18 to 23 GHz. Using observational parameters and assuming nonthermal gyrosynchrotron emission from energetic electrons in a loop structure, we have estimated the density of nonthermal electrons, magnetic field, and dimension of the source along the line of sight.

Nonlinear interaction of powerful radio waves with the plasma in the Earth's lower ionosphere

The nonlinear interaction of powerful radio waves with nonresonant density fluctuations in a nonuniform weakly ionized magnetoplasma is considered. It is shown that the interaction can generate a high‐frequency radio wave envelope, which generally is governed by a nonlinear Schrödinger equation. Accounting for the dependence of the attachment frequency on the radiation intensity, as well as the differential Joule heating nonlinearity, we derive the equations for the nonthermal electron density and temperature perturbations. The various nonlinear terms in the electron motion are compared. The implications of our investigation for the filamentation of radio waves in the lower part of the Earth's ionosphere are pointed out.

VLA observations of compact, variable sources on the sun

view Abstract Citations (11) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS VLA Observations of Compact, Variable Sources on the Sun Willson, R. F. ; Lang, K. R. Abstract Observations of solar active region AR 4508, obtained at 2.1 and 20.7 cm using the C configuration of the VLA on June 4, 1984, are reported. Compact (5-arcsec) sources with brightness temperature 50,000-300,000 K and circular polarization 80-90 percent are detected at 2.1 cm in regions with magnetic fields 80 G or less and found to vary on times scales of 10-20 s and 30-60 min. The emission of the sources is attributed to power-law-spectrum gyrosynchrotron radiation from mildly relativistic electrons, and its variability is related to variations in either the magnetic field or the nonthermal-electron density. Publication: The Astrophysical Journal Pub Date: September 1986 DOI: 10.1086/164514 Bibcode: 1986ApJ...308..443W Keywords: Solar Activity; Solar Magnetic Field; Solar Radio Emission; Circular Polarization; Interferometry; Relativistic Electron Beams; Synchrotron Radiation; Solar Physics; INTERFEROMETRY; POLARIZATION; RADIATION MECHANISMS; SUN: ACTIVITY; SUN: RADIO RADIATION full text sources ADS |

Search for nonthermal electron density fluctuations by light scattering

Enhancements above the predicted spectrum for a thermal plasma have been reported at various multiples of 1/4 the plasma frequency in an $\ensuremath{\alpha}\ensuremath{\lesssim}1$ plasma. We have investigated the spectrum of a $\ensuremath{\theta}$-pinch plasma over the range of parameters covering reported deviations. With a 2-\ensuremath{\gg} resolution we were able to fit thermal spectra to the observed spectra with a standard error of estimate, in most cases, of less than 2%. Using parameters very similar to those used in a recently published study where many deviations were reported, we were able to fit a thermal spectrum to our measured spectrum with a standard error of estimate of 4% and 0.66-\ensuremath{\gg} resolution.

Observation of nonthermal electron density fluctuations by light scattering

Deviations from the linear theory of light scattering for thermal plasmas observed by several authors have been studied in detail. In a laser scattering experiment on a magnetized arc plasma the spectral resolution was improved by means of a Fabry-Perot interferometer from typically 5-10 to 0.3 AA. The spectrum of the scattered light revealed a fine structure showing peaks several tenths of an Angstrom in width. Such narrow peaks could be 'smeared out' in most of the cases by a poorer spectral resolution. The feature of these spectra does, most likely not depend on how the fluctuations are oriented with respect to the magnetic field (or arc axis). By varying the scattering angle from 90 degrees ( alpha 1) the wavelength dependence of the fluctuation spectrum was determined. The nonthermal part of the spectrum is presented as a function of frequencies and wave numbers in a three dimensional array.

Free-Free Absorption of Gyrosynchrotron Radiation in Solar Microwave Bursts

Abstract : A model for solar microwave bursts is considered in which over a broad frequency band the flux density is a slowly varying function of frequency. It is proposed that such an essentially flat spectrum could result from free-free absorption of gyrosynchrotron emission of nonthermal electrons accelerated in solar flares. The theory of gyrosynchrotron radiation is reviewed, and simplified formulae for the Razin effect, selfabsorption and gyroresonance absorption are given and their range of validity is discussed. Using these results the thermal electron density, temperature, emission measure, magnetic fields and number of nonthermal electrons in the emitting region are evaluated for a flare with a flat microwave spectrum. (Author)

Radio emission from shock waves and type II solar outbursts

A model for Type II solar radio outbursts is discussed. The radiation is hypothesized to originate in the process of collective bremsstrahlung emitted by non-thermal electron and ion density fluctuations in a plasma containing a flux of energetic electrons. The source of radiation is assumed to be collisionless plasma shock wave rising through the solar corona. It is also suggested that non-thermal electrons in the ionospheres of the Earth and planets might be sources of the same type of radiation.