共查询到20条相似文献,搜索用时 31 毫秒
1.
Howe R Christensen-Dalsgaard J Hill F Komm RW Larsen RM Schou J Thompson MJ Toomre J 《The Astrophysical journal》2000,534(2):L163-L166
We discuss the spectrum arising from synchrotron emission by fast cooling (FC) electrons, when fresh electrons are continually accelerated by a strong blast wave, into a power-law distribution of energies. The FC spectrum has so far been described by four power-law segments divided by three break frequencies nusa相似文献
2.
The loss-cone instability of energetic electrons at double plasma resonance is considered. Conditions required for the formation
of a zebra pattern in type IV solar radio bursts are determined. It is shown that electrons with a power-law energetic spectrum
can effectively excite upper-hybrid waves at double plasma resonance. Stripes of a zebra pattern become more pronounced with
an increase of the loss-cone opening angle and the power-law spectral index. The growth rate at the resonance frequencies
decreases with an increase of the cyclotron harmonic number. Interpretation of observations and diagnostics of plasma for
the April 21, 2002, event are performed. Conclusions about the impulsive mode of injection of energetic electrons into a coronal
arc are made. 相似文献
3.
Hai-Ning LiNational Astronomical Observatories Chinese Academy of Sciences Beijing lhnDepartment of Astronomy Beijing Normal University Beijing 《中国天文和天体物理学报》2003,3(5)
We present a quantitative estimate of the relativistic corrections to the thermal SZ power spectrum produced by the energetic electrons in massive clusters. The corrections are well within 10% for current experiments with working frequencies below v < 100 GHz, but become non-negligible at high frequencies v > 350 GHz. Moreover, the corrections appear to be slightly smaller at higher l or smaller angular scales. We conclude that there is no need to include the relativistic corrections in the theoretical study of the SZ power spectrum especially at low frequencies unless the SZ power spectrum is used for precision cosmology. 相似文献
4.
Electrostatic solitary structures are studied in uniform and nonuniform magnetoplasmas with superthermal electrons. In the linear analysis, the differences in the acoustic frequencies for Maxwellian, Cairns, and Kappa distributed electrons for both homogeneous and inhomogeneous plasmas are highlighted and discussed. It is shown that using the linear dispersion relation, nonlinear Zakharov-Kuznetsov (ZK) equation can be derived both for the homogeneous and inhomogeneous magnetoplasmas. The solution of the ZK equation is presented using the tangent hyperbolic method. It is found that the increasing magnetic field and the angle of propagation enhances the amplitude whereas the increasing number density mitigates the amplitude of the acoustic drift solitary wave. Furthermore, it is observed that the amplitude of the solitary structure is maximum for Cairns, intermediate for Maxwellian, and minimum for the Kappa distributed electrons. The results presented in this paper may be beneficial to understand the formation of electrostatic drift solitary waves in planetary environments where the nonthermal population of electrons are observed by various satellite missions. 相似文献
5.
Kunitomo Sakurai 《Planetary and Space Science》1973,21(1):17-22
In association with solar flares accompanying type IV radio bursts of U-shaped spectrum, solar cosmic rays (MeV) and energetic electrons (keV) were generated. After acceleration, they were first stored in or near the flare regions and then gradually emitted into outer space. It seems that the streams of keV electrons generated the continuum radio emissions from metric to hectometric frequencies while passing through the outer coronal regions. 相似文献
6.
IMP-6 spacecraft observations of low frequency radio emission, fast electrons, and solar wind plasma are used to examine the dynamics of the fast electron streams which generate solar type-III radio bursts. Of twenty solar electron events observed between April, 1971 and August, 1972, four were found to be amenable to detailed analysis. Observations of the direction of arrival of the radio emission at different frequencies were combined with the solar wind density and velocity measurements at 1 AU to define an Archimedean spiral trajectory for the radio burst exciter. The propagation characteristics of the exciter and of the fast electrons observed at 1 AU were then conpared. We find that: (1) the fast electrons excite the radio emission at the second harmonic; (2) the total distance travelled by the electrons was between 30 and 70% longer than the length of the smooth spiral defined by the radio observations; (3) this additional distance travelled is the result of scattering of the electrons in the interplanetary medium; (4) the observations are consistent with negligible true energy loss by the fast electrons. 相似文献
7.
K.-H. Mack M. A. Prieto G. Brunetti M. Orienti 《Monthly notices of the Royal Astronomical Society》2009,392(2):705-717
We present new high spatial resolution Very Large Telescope (VLT) and Very Large Array (VLA) observations of a sample of nine low-power ( P 1.4 GHz ≤ 1025 W Hz−1 ) radio hotspots. Infrared/optical emission is definitely detected in four of the nine observed objects, resulting in a detection rate of at least 45 per cent. This emission is interpreted as synchrotron radiation from the electrons accelerated in the hotspots. The integrated spectra of these hotspots reveal typical break frequencies between 105 and 106 GHz, two orders of magnitude higher than typically found in high-power hotspots. This supports the idea that in low-power hotspots with their relatively low magnetic field strengths, electrons emit most of their energy at higher frequencies. A simple spectral ageing analysis would imply that the emitting electrons have been injected into the hotspot volume less than ∼103 years ago. We discuss possible scenarios to explain the lack of older electrons in the hotspot region. In particular, the extended morphology of the near-infrared/optical emission would suggest that efficient re-acceleration mechanisms rejuvenate the electron populations. 相似文献
8.
Until recently, most of the information on particle acceleration processes in solar flares has been obtained from hard X-ray and cm-microwave observations. As a rule they provide information on electrons with energies below 300 keV. During recent years it became possible to measure the gamma-ray and millimeter radio emission with improved sensitivities. These spectral ranges carry information on much higher energy electrons. We studied the temporal and spectral behaviour of the radio burst emission at centimeter-millimeter wavelengths (8–50 GHz) by using the data from the patrol instruments of IAP (Bern University). We have analyzed more than 20 impulsive and long duration radio bursts (of 10 s to several 100 s duration).The main finding of the data analysis is the presence of spectral flattening throughout the bursts, which occurs always during the decay phase of flux peaks, at frequencies well above the spectral peak frequency and independently of burst duration. Furthermore, for some of the bursts, the flux maxima at higher frequencies are delayed. These findings can serve as evidence of the hardening of the electron spectrum at energies above some hundreds of keV during the decay phase of cm–mm flux peaks. As a most likely reason for such a hardening we consider Coulomb collisions of energetic electrons continuously injected and trapped in a flaring loop. 相似文献
9.
Kunitomo Sakurai 《Planetary and Space Science》1976,24(7):657-659
The modulations of the non-Io-related radio emissions in hectometric and decametric wave frequencies are examined, and compared with the observed variation of the MeV electron fluxes in the morning sector of the Jovian magnetosphere. It is suggested that these radio emissions are controlled by the behaviour of these electrons in this sector. 相似文献
10.
Kunitomo Sakurai 《Astrophysics and Space Science》1976,42(2):349-368
Radio noise continuum emissions observed in metric and deca-metric wave frequencies are, in general, associated with actively varying sunspot groups accompanied by the S-component of microwave radio emissions. It is known that these continuum emission sources, often called type I storm sources, are often associated with type III burst storm activity from metric to hectometric wave frequencies. This storm activity is, therefore, closely connected with the development of these continuum emission sources.It is shown that the S-component emission in microwave frequencies generally precedes by several days the emission of these noise continuum storms of lower frequencies. In order for these storms to develop, the growth of sunspot groups into complex types is very important with the increase of the average magnetic field intensity and area of these groups. In particular, the types of these groups such as and are very important on the generation of noise continuum storm sources and sharp increase of the flux of these continuum emissions. This fact suggests that sunspot magnetic configuration and its variation, both space and time, are very effective on the growth of the sources for these noise continuum emissions.Although we have not known yet the true mechanism of these emissions, it is very likely that energetic electrons, 10 to 100 keV, accelerated in association with the variation of sunspot magnetic fields, are responsible as the sources of those radio emissions. Furthermore it seems that these electrons are contributing to the emission of type III burst storms, which are associated with the noise continuum storm sources. In explaining the origin of these storms, some plasma processes must be taken into consideration. Furthermore, it should be remarked that the storage mechanism of the electrons mentioned above plays an important role in generating both the noise continuum emissions and type III burst storms, because on-fringe type III bursts are all generated above these noise continuum storms sources. After reviewing the theories of these noise continuum storm emissions, a model is briefly considered to explain the relation between these continuums and type III bursts, and a discussion is given on the role of energetic electrons on these two emissions. It is pointed out that instabilities associated with these electrons and their relation to their own stabilizing effects are important in interpreting both of these storm emissions.Astrophysics and Space Science Review Paper. 相似文献
11.
C.A. Olano 《Astrophysics and Space Science》1999,266(3):347-369
From July 13 to August 21, 1994, we observed Jupiter at 1420 MHz using one of the 30-m single dishes of the Instituto Argentino
de Radioastronomía. After the impact of fragment G, we detected a rapid increase of the 21cm-continuum flux, which reached
the maximum (≈ 20% of Jupiter's flux) at the end of the impact period. The nature of this radiation is clearly synchrotron.
We interpret it in terms of a new population of relativistic electrons (≈ 2 × 1029) injected into the Jovian magnetosphere as a consequence of the impact explosions. The proposed mechanism is that the relativistic
plasma was blown as magnetic clouds that flowed along the magnetic lines of force towards the jovimagnetic equator. We constructed
a model in which the energies of the fresh electrons, generated within the magnetized clouds with a power law energy spectrum,
were highly degraded by the comet dust grains attached to the magnetized plasma. The model can account for the spectral shape
based on observations at several frequencies (de Pater et al., 1995, Science 268, 1879; Venturi et al., 1996, Astron. Astrophys. 316, 243). The energy released by the explosions under the form of relativistic electrons is of ≈ 2 × 1025 erg, which represents a fraction of about 1–3 per cent of the explosion energy. The efficiency in converting the explosion
energy into the relativistic electron energy is, therefore, of the same order of magnitude as that of supernova explosions.
An alternative model is considered. This gives figures for the total energy and number of relativistic electrons that are
similar to the corresponding ones of the favoured model. Finally, we suggest that the behavior of the flux decay in the various
observed frequencies is the result of the diffusion of electrons into the loss-cone due to the resonant scattering of the
electrons by Alfven waves.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
M. R. Kundu N. Gopalswamy J. L. R. Saba J. T. Schmelz K. T. Strong 《Solar physics》1987,114(2):273-288
We present a study of type III activity at meter- decameter wavelengths in the preflare phase of the 1986 February 3 flare using data obtained with the Clark Lake Multifrequency Radioheliograph. We compare this activity with similar type III burst activity during the impulsive phase and find that there is a displacement of burst sources between the onset and end times of the activity. A comparison of this displacement at three frequencies suggests that the type III emitting electrons gain access progressively to diverging and different field lines relative to the initial field lines. The energetics of the type III emitting electrons are inferred from observations and compared with those of the associated hard X-ray emitting electrons. The soft X-ray data from SMM-XRP shows enhanced emission measure, density and temperature in the region associated with the preflare type III activity.On leave from Indian Institute of Astrophysics, Kodaikanal, Tamil Nadu, India. 相似文献
13.
Marco Regis 《Astroparticle Physics》2011,35(4):170-176
Fluctuations in the Galactic synchrotron emission can be traced by the angular power spectrum of radio maps at low multipoles. At frequencies below few GHz, large-scale anisotropies are mainly induced by magnetic field turbulence, since non-thermal electrons radiating at these frequencies are uniformly distributed over the scales of magnetic field inhomogeneities. By performing an analysis of five radio maps, we extract constraints on turbulence spectral index and halo scale. Results favour a power spectrum significantly flatter than for 3D Kolmogorov-like turbulence, and a thin halo. This can be interpreted as an indication supporting non-conventional models of propagation of cosmic-ray particles in the Galaxy, or as a suggestion of a spectral-index break in the observed magnetic turbulence power spectrum. 相似文献
14.
S. K. Zaghbeer H. H. Salah N. H. Sheta E. K. El-Shewy A. Elgarayh 《Astrophysics and Space Science》2014,353(2):493-500
Propagation of nonlinear dust-acoustic waves in a magnetized collisionless plasma having positively, negatively charged dust grains and nonextensive distributed electrons and ions has been investigated. A reductive perturbation method is used to obtain a nonlinear Korteweg-de Vries (KdV) equation describing the model. The dynamics of the modulational instability gives rise to the formation of rogue waves that is described by a nonlinear Schrödinger equation. The dependence of rogue waves profiles on positive and negative charged dust cyclotron frequencies, nonextensive parameters of electrons and ions is investigated numerically. The result of the present investigation may be applicable to some plasma environments, such as cometary tails and upper mesosphere. 相似文献
15.
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. 相似文献
16.
《Chinese Astronomy and Astrophysics》2006,30(3):303-310
The 266 type III bursts, observed with the 2.6–3.8 GHz high temporal resolution dynamic spectrometer of NAO during the 23rd solar cycle (from April 1998 to January 2003), are statistically analyzed. The parameters of these events, including the frequency drift, duration, polarization, bandwidth, starting and ending frequencies, are analyzed in details. The statistics on the starting and ending frequencies indicate that the starting frequency varies in a very large range from less than 2.6 GHz to greater than 3.8 GHz, while the ending frequency varies in a relatively narrow range from 2.82 GHz to 3.76 GHz. These phenomena imply that the heights where the electrons are accelerated are quite scattered, while the cutoff regions of the type III bursts are relatively restricted. The numbers of the bursts with the positive and negative drift rates are nearly equal, this may suggest that the accelerated electrons propagating upward and those propagating downward are equally proportioned in the observing frequency range. And the statistical results demonstrate that the microwave type III bursts are mainly caused by the plasma radiation and electron gyro-maser radiation. 相似文献
17.
Correlated sixteen-second periodic bursts were observed during the flash phase of a class 2b solar flare in energetic X-rays, microwaves, and EUV ionizing radiation. The observations of the periodic structures in the various X-ray energy channels indicate that the structures are predominantly a phenomenon of high energy electrons, E>80 keV. In view of the fact that the periodic X-ray structures were correlated extensively in microwave and EUV frequencies, a plausible conclusion is that these three types of radiation have a common energy source. The acceleration of the energetic electrons must occur deep in the chromosphere where there are sufficient solar constituents that can be ionized to produce the correlated periodic EUV radiation. 相似文献
18.
The series of nine impulsive, highly collimated beams of near-relativistic electrons seen by ACE/EPAM on 26 and 27 June 2004
occurred at a quiet time with respect to solar flare and CME production. However, they were accompanied by decametric type
III radio bursts observed by WIND/WAVES, which had progressively higher starting frequencies, suggestive of coronal acceleration.
There were no CMEs seen by SOHO/LASCO in association with any of the type III bursts except possibly the first. The energy
spectrum of the electrons was soft, typically E−4.5 but extended up to at least ∼200 keV. We suggest that the source region for these events is in the high corona. We discuss
this result in the context of solar electron acceleration at other times. 相似文献
19.
This paper presents general relations for the intensity of the resonant transition radiation (RTR) and their detailed analysis.
This analysis shows that the spectrum amplitude of the x-mode at some frequencies for high-energy electrons can grow with
the magnetic field increase in some interval from zero value; it can even dominate over that for the o-mode. With further
magnetic field increase, the intensity of the RTR x-mode decreases in comparison with the intensity of the o-mode and this
decrease is higher for higher velocities of energetic electrons. The polarization of the RTR depends on the velocity of energetic
electrons, too. For velocities lower than some velocity limit v<v
i
the RTR emission is unpolarized in a broad interval of magnetic field intensities in the radio source. For reasonable values
of indices of the power-law distribution functions of energetic electrons, the RTR is broadband in frequencies (df/f≈0.2−0.4). Furthermore, we show various dependencies of the RTR and its spectral characteristics. Assuming the same radio
flux of the transition radiation and the gyro-synchrotron one at the Razin frequency, we estimate the limit magnetic field
in the radio source of the transition radiation. Then, we analyze possible sources of small-scale inhomogeneities (thermal
density fluctuations, Langmuir and ion-sound waves), which are necessary for the transition radiation. Although the small-scale
inhomogeneities connected with the Langmuir waves lead to the plasma radiation, which is essentially stronger than RTR, the
inhomogeneities of the ion-sound waves are suitable for the RTR without any other radiation.
We present the relations describing the RTR for anisotropic distribution functions of fast electrons. We consider the distribution
functions of fast electrons in the form of the Legendre polynomials which depend on the pitch-angle. We analyze the influence
of the degree of the anisotropy (an increase of the number of terms in the Legendre polynomial) on spectral characteristics
of the RTR. A comparison with previous studies is made. As an example of the use of the derived formulas for the RTR, the
24 December 1991 event is studied. It is shown that the observed decimetric burst can be generated by the RTR in the plasma
with the density inhomogeneities at the level 〈ΔN
2〉/N
2=2.5⋅10−5. 相似文献
20.
Bhimsen K. Shivamoggi 《Astrophysics and Space Science》1982,83(1-2):177-180
The instability of a linearly-polarised electromagnetic ordinary mode in counterrotating plasmas and propagating perpendicular to a uniform magnetic field caused by a counterstreaming of electrons along the latter is studied using a cold-plasma model. It is found that: (i) In the presence of either a streaming or a rotation or both, the ordinary-wave propagation is possible even for frequencies less than the plasma frequency; (ii) the Coriolis forces like the applied magnetic field stabilise the ordinary modes. 相似文献