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1.
Properties of electron acceleration in flares, especially the density structure in the acceleration region, are deduced from a correlation study between decimetric type III, spike, and hard X-ray (HXR) bursts. The high association rate found (71%) strongly suggests that spikes also originate from energetic electrons. Spikes and type III bursts have been found to be easily identified by their different polarizations. The two types of emission generally do not overlap in frequency. A reliable lower limit to the density is derived from the starting frequency of type III and U bursts. The spike emission very likely yields an upper limit. The density inhomogeneity in the acceleration region spans more than one order of magnitude and is more than one order of magnitude larger in the associated type U sources. A peak-to-peak correlation does not always exist between type III, spike and HXR bursts. This discrepancy can be interpreted in terms of the different source conditions and propagation properties. Whereas spikes need special conditions to become visible, type III and peaks of HXR may be the product of many elementary accelerations.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
2.
Some fast bursts occurring at 237 MHz during type IV events in association with sawtooth pulsations have been studied. These bursts, when occurring sufficiently isolated from the adjacent pulsating activity, appear to have an exponential decay phase similar to that of fast type III bursts.A computational procedure, based on Fourier transform techniques, has been applied; it allows the computation, for every observed point in the time profile, of the corresponding value for the logarithmic derivative and for the exciter function. The results so far obtained show that the time decay value is of the same order observed for normal type III's. As the bursts studied appear clearly not to be type III's (mainly for their total polarization), but isolated components of pulsation groups, this result may be an interesting indicator of the emission mechanism (plasma waves excitation and its abrupt stop) involved in type IV decimetric pulsations.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
3.
Millisecond radio spikes 总被引：9，自引：0，他引：9
A. O. Benz 《Solar physics》1986,104(1):99-110
Millisecond spikes of the solar radio emission are known for more than two decades. They have recently seen a surge in interest of theoreticians who are fascinated by their high brightness temperature of up to 1015 K, their association with hard X-ray bursts, and a possibly very intimate relation to electron acceleration. This review is intended to bridge the gap that presently seems to separate theory and observations. The wide range of spike observations is summarized and brought into the perspective of recent models. It is concluded that spikes yield a considerable potential for the diagnostics of energetic particles, their origin, and history in astrophysical plasmas.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
4.
We studied the properties of fine structures in 23 type II bursts recorded at the Trieste Astronomical Observatory at frequencies above 200 MHz.The lifetime of a single fine structure is a fraction of a second. The ratio of fine structures intensity vs bulk flux density is different in different type II bursts and it changes during the evolution of a single event; the reported maximum ratio is 3. The polarization of fine structures is nearly the same during the lifetime of an event. There is also no essential difference in polarization between fine structures and bulk emission; this holds also for an example of high-polarization (about 80%) event.At frequencies lower than 200 MHz the analogy between herringbone structure and type III bursts is frequently mentioned in the literature. From the observations we studied, it results, however, that the time profile of single fine-structure elements and their polarization are substantially different from the morphology of type III bursts.The observed fine structures and their characteristics are discussed in the framework of the model by Holman and Pesses (1983).Paper presented at the 4th CESRA Workshop in Ouranopolis (Greece) 1991. 相似文献
5.
《天文和天体物理学研究(英文版)》2021,(6)
Solar radio spikes are one of the most intriguing spectral types of radio bursts. Their very short lifetimes, small source size and super-high brightness temperature indicate that they should be involved in some strong energy release, particle acceleration and coherent emission processes closely related to solar flares. In particular, for the microwave spike bursts, their source regions are much close to the related flaring source region which may provide the fundamental information of the flaring process. In this work,we identify more than 600 millisecond microwave spikes which recorded by the Solar Broadband Radio Spectrometer in Huairou(SBRS/Huairou) during an X3.4 solar flare on 2006 December 13 and present a statistical analysis about their parametric evolution characteristic. We find that the spikes have nearly the same probability of positive and negative frequency drifting rates not only in the flare rising phase, but also in the peak and decay phases. So we suppose that the microwave spike bursts should be generated by shockaccelerated energetic electrons, just like the terminational shock(TS) wave produced by the reconnection outflows near the loop top. The spike bursts occurred around the peak phase have the highest central frequency and obviously weak emission intensity, which imply that their source region should have the lowest position with higher plasma density due to the weakened magnetic reconnection and the relaxation of TS during the peak phase. The right-handed polarization of the most spike bursts may be due to the TS lying on the top region of some very asymmetrical flare loops. 相似文献
6.
Properties, including the time duration, polarization, quasi-periodical oscillations and so on, of the microwave spike emissions observed at 2.5 GHz and 2.6 GHz during the solar flare of 1991 May 16 are analyzed statistically. The left-handed and right-handed circular polarizations of the spike emissions at 2.5, 2.6 and 3.1 GHz are reported in detail. At these 3 frequencies, most of the spikes are superposed on both the rising (and maximum) and the descending phase of the burst. It is noteworthy that spikes also appeared superposed on the small bursts that appeared after the main burst. The spike emission lasted 17 minutes. Polarization reversals on different timescales appearing in the spike emissions at 2.5 and 2.6 GHZ are described. Our statistical analysis indicates that the polarization reversals at 2.5 and 2.6 GHz differ in characters on average, the polarization reversal at 2.5 GHz is earlier than that of 2.6 GHz by about 1.5 minutes, and polarization reversal of the spike emission is more frequent at 2.5 GHZ. 相似文献
7.
To obtain constraints for models of fiber bursts, high-resolution time (0.01 s) profiles of the fiber bursts recorded at 1420 and 2695 MHz by the Trieste radiometers are studied in detail. The fiber bursts were identified using Ond?ejov radio spectra. During the years 2000?–?2005, 18 intervals with fiber bursts were selected; 26 groups were defined and about 700 fibers were analyzed in detail. More than 300 pulsations, present almost simultaneously with the fibers, were also selected and studied in order to find similarities or differences between these two types of fine structures. It was found that the polarization of the associated continuum, both for fiber bursts and pulsations, is practically the same. Evaluating the ratio between absorption over emission of many single fibers we found that this parameter is very different even for nearby bursts; however, we realized that this ratio shows a tendency to decrease with time. Finally, the time profile of one selected fiber burst was fitted using a recent model based on the modulation of the broadband radio emission by fast magnetoacoustic waves. The results are discussed. 相似文献
8.
The microwave spectrum of solar millisecond spikes 总被引：5，自引：0，他引：5
The microwave radiation from solar flares sometimes shows short and intensive spikes which are superimposed on the burst continuum. In order to determine the upper frequency limit of their occurrence and the circular polarization, a statistical analysis has been performed on our digital microwave observations from 3.2 to 92.5 GHz. Additionally, fine structures have been investigated with a fast (5 ms) 32-channel spectrometer at 3.47 GHz. We found that 10% of the bursts show fine structures at 3.2 and 5.2 GHz, whereas none occurred above 8.4 GHz. Most of the observed spikes were very short ( 10 ms) and their bandwidth varied from below 0.5 MHz to more than 200 MHz. Simultaneous observations at two further frequencies showed no coincident spikes at the second and third harmonic. The observations can be explained by the theory of electron cyclotron masering if the observed bandwidths are determined by magnetic field inhomogeneities or if the rise times are independent of the source diameters. The latter would imply source sizes between 50 and 100 km.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
9.
The metric spectral data obtained at the Yunnan Observatory from July 1990 to December 1991 are analysed and some type III bursts associated with millisecond spikes are found. Their different morphologies reveal the relation between the type III bursts and the millisecond spikes. Based on the occurrence time and the characteristics of continuity and changes of the morphologies in the spikes and the type III bursts of two typical events, we verify that the acceleration region of the coronal electrons is located above the emitting region of the millisecond spikes and the type III bursts. The observations show that the interface frequency of a pair of type III bursts lies near 250 MHz. Finally the authors attempt to explain qualitatively the generating mechanism of the metric millisecond spike-type III bursts by means of the plasma hypothesis. 相似文献
10.
Many solar microwave bursts presenting fine structures were recorded at high temporal resolution (8 ms) by the 2.6–3.8 GHz
spectrometer of National Astronomical Observatories of China (NAOC). Here we present data that were recorded on 15 April 1998.
After data processing, more than one hundred spikes were detected in the interval 07:59:29.622–07:59:50.362 UT. Some of the
spikes were single, while others were grouped in clusters. We report the observational characteristics including lifetime,
frequency bandwidth, drift rate and polarization degree, as well as duration of spike clusters. Afterwards we discuss the
difference between the lifetime of the spikes presented here (near 3 GHz) and those reported formerly at frequency up to 1 GHz,
the probable source density and dimension, the brightness temperature and some other characteristics. 相似文献
11.
An analysis of solar radio bursts with temporal fine structure (TFS) at 5730 MHz in relation to the magnetic configuration
of the corresponding active regions (AR) is presented. We found that the occurrence of TFS bursts increases with increasing
complexity of the AR's magnetic configuration. The degree of polarization of TFS bursts varies over a wide range. Most of
these fast bursts with a high degree of polarization were observed in active regions with a simple magnetic configuration β.
Most of the unpolarized fast bursts were observed in active regions with the most complicated configuration βγδ. Because bursts
that are polarized in different modes have different displacements of position with respect to that of associated microwave
bursts, we conclude that there are at least two types of TFS bursts at 5730 MHz. We think that fast bursts that are polarized
in the ordinary mode are due to microwave type III bursts. 相似文献
12.
M. J. Aschwanden 《Solar physics》1986,104(1):57-65
A sample of 10 decimetric broadband pulsations were observed in 1980–1983 and analyzed in polarization. Half of the data set was 85–100% circularly polarized, the other half showed a mild polarization of 15–55%. The polarization is constant in time and frequency for the strongly polarized group. All the mildly polarized bursts originate from near the limb; the lower degree of circular polarization is likely to be caused by depolarization due to propagation effects. The degree of polarization is constant throughout the event, but varies in frequency for the mild polarized group. Following the leading spot hypothesis, the magneto-ionic mode of the emission was found to be extraordinary. The high circular polarization of the pulsations was interpreted to be determined by the emission mechanism itself, not by propagation effects or cut-offs (contrary to the metric type I noise storms). Implications for pulsation models are discussed.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
13.
The Source Regions of Impulsive Solar Electron Events 总被引：1，自引：0，他引：1
Benz Arnold O. Lin Robert P. Sheiner Olga A. Krucker Säm Fainberg Joe 《Solar physics》2001,203(1):131-144
Low-energy (2–19 keV) impulsive electron events observed in interplanetary space have been traced back to the Sun, using their interplanetary type III radiation and metric/decimetric radio-spectrograms. For the first time we are able to study the highest frequencies and thus the radio signatures closest to the source region. All the selected impulsive solar electron events have been found to be associated with an interplanetary type III burst. This allows to time the particle events at the 2 MHz plasma level and identify the associated coronal radio emissions. Except for 5 out of 27 cases, the electron events were found to be associated with a coronal type III burst in the metric wavelength range. The start frequency yields a lower limit to the density in the acceleration region. We also search for narrow-band spikes at the start of the type III bursts. In about half of the observed cases we find metric spikes or enhancements of type I bursts associated with the start of the electron event. If interpreted as the plasma emission of the acceleration process, the observed average frequency of spikes suggests a source density of the order of 3×108 cm–3 consistent with the energy cut-off observed. 相似文献
14.
We report the results of 1966, 1968, and 1969 polarization measurements of solar type III radio noise bursts made by recording the output of two orthogonally polarized receiving channels and subsequent digital processing of selected data. The processed data yield total intensity, degree of polarization, ellipticity, and polarization ellipse orientation at 1 second intervals. The measurements are made in a 100 Hz bandwith to minimize the influence of the propagating medium on the measurements. The mean degree of polarization was found to be about 65% in contrast to previous studies which indicated that type III events were more weakly polarized. By assuming that type III bursts are flare related we study the polarization characteristics of type III bursts as a function of the solar longitude of the related flares. The relation between type III event polarization characteristics and flare importance is also investigated. The significance of polarization measurements in studies of solar radio events is pointed out and suggestions for further theoretical research are given. 相似文献
15.
A new model for solar spike bursts is considered based on the interaction of Langmuir waves with ion-sound waves: l+st. Such a mechanism can operate in shock fronts, propagating from a magnetic reconnection region. New observations of microwave millisecond spikes are discussed. They have been observed in two events: 4 November 1997 between 05:52–06:10 UT and 28 November 1997 between 05:00–05:10 UT using the multichannel spectrograph in the range 2.6–3.8 GHz of Beijing AO. Yohkoh/SXT images in the AR and SOHO EIT images testify to a reconstruction of bright loops after the escape of a CME. A fast shock front might be manifested as a very bright line in T
e SXT maps (up to 20 MK) above dense structures in emission measure (EM) maps. Moreover one can see at the moment of spike emission (for the 28 November 1997 event) an additional maximum at the loop top on the HXR map in the AR as principal evidence of fast shock propagation. The model gives the ordinary mode of spike emission. Sometimes we observed a different polarization of microwave spikes that might be connected with the depolarization of the emission in the transverse magnetic field and rather in the vanishing magnetic field in the middle of the QT region. Duration and frequency band of isolated spikes are connected with parameters of fast particle beams and shock front. Millisecond microwave spikes are probably a unique manifestation of flare fast shocks in the radio emission. 相似文献
16.
Eleven microwave spike events observed with the 2.6–3.8 GHz spectrometer of Beijing Astronomical Observatory (BAO) are analysed. The polarization degrees of spikes are variable, some spikes have frequency drift with the drift rate of several GHz s–1. In particular, the time delay (8 ms) between the two polarization modes of spike is detected, which is different from previous results. According to the leading spot rule, we conclude that the o-modes arrive first. Moreover, the reversal of polarization sense versus frequency is also found. A change of the emission mode may be the cause of the polarization reversal. 相似文献
17.
We performed a statistical analysis of the dm-spikes that were present for an exceptionally long period (more than 10 min) during the 15 June 1991 flare. We realized that the polarization degree, the duration and the mutual delay of the R- and L-components were nearly the same for both CW and ACW cases. CW (ACW) means the clockwise (anti-clockwise) sense of the loop in the R–L versus L+R plots, when the data of a single spike are considered according to the time sequence. The presence of such a loop is determined by the delay of the weaker (stronger) polarimetric component in respect to the other one. The increase of the polarization percentage started first at 610, then at 408 and afterwards at 327 MHz. It was found that the duration of spikes was almost completely independent from the polarization degree. The mean duration of spikes at different frequencies corresponds to that computed using the formula of Güdel and Benz. Like the mean duration, also the mean delay decreased with increasing frequency. The CW/ACW ratio varied simultaneously for the frequencies we recorded during an interval of about three minutes. Spikes were considered as the radio manifestation of superthermal electrons accelerated in the MHD cascading waves. The evolution of spikes and their parameters were qualitatively interpreted within the flare reconnection model with turbulent plasma outflows. 相似文献
18.
Takeo Kosugi 《Solar physics》1981,71(1):91-105
A well-developed multiple impulsive microwave burst occurred on February 17, 1979 simultaneously with a hard X-ray burst and a large group of type III bursts at metric wavelengths. The whole event is composed of several subgroups of elementary spike bursts. Detailed comparisons between these three classes of emissions with high time resolution of 0.5 s reveal that individual type III bursts coincide in time with corresponding elementary X-ray and microwave spike bursts. It suggests that a non-thermal electron pulse generating a type III spike burst is produced simultaneously with those responsible for the corresponding hard X-ray and microwave spike bursts. The rise and decay characteristic time scales of the elementary spike burst are 1 s, 1 s and 3 s for type III, hard X-ray and microwave emissions respectively. Radio interferometric observations made at 17 GHz reveal that the spatial structure varies from one subgroup to others while it remains unchanged in a subgroup. Spectral evolution of the microwave burst seems to be closely related to the spatial evolution. The spatial evolution together with the spectral evolution suggests that the electron-accelerating region shifts to a different location after it stays at one location for several tens of seconds, duration of a subgroup of elementary spike bursts. We discuss several requirements for a model of the impulsive burst which come out from these observational results, and propose a migrating double-source model. 相似文献
19.
We performed an analysis of the polarization of 60 pulsating radio events identified in type IV bursts recorded in the m-dm band during the Solar Cycle XXI at the Trieste Astronomical Observatory.Two major points summarize the results of such an analysis: (i) the emission is totally polarized at the source and the source itself is unique; (ii) the emission occurs in the ordinary magneto-ionic mode for most of the samples, if one accepts the leading-spot hypothesis.The first point confirms what was derived by other authors who anyhow considered a more limited set of samples: highly-polarized events are the most frequent, intense and long-lasting. The intermediate and low polarization observed in other cases are to be attributed to propagation effects, which are effective along the path after the emission, and this interpretation is supported by different observed features such as shorter duration and lower intensity of the events.Our second point differs from a previous work which claims the extraordinary mode, but this discrepancy can be justified by: (a) the small number of events analyzed in that work, which gives poorer statistics; (b) a quite different observing frequency range; (c) the different selection criterion. However, in spite of the relative richness of our data set we cannot give a final answer to the emission mode problem as the leading-spot hypothesis is questionable and we report critical arguments against it based on experimental results.The polarization degree of pulsations looks generally constant during the whole lifetime. As a general trend the selected events show the same polarization features both for the pulsations and the background. A different polarization degree of the continuum is probably the signature of the contemporaneous presence of more than one source. 相似文献
20.
利用北京天文台 ２．６—３．８ ＧＨｚ频谱仪的观测资料,找到 １１个微波尖峰辐射事件．尖峰一般具有数十毫秒的寿命,数百个ｓｆｕ的流量密度和数十至数百ＭＨｚ的带宽,这与以前的报道类似．尖峰的偏振度各式各样,有的尖峰还有数千ＭＨｚ／ｓ的频率漂移．某些尖峰在二个偏振态之间有８毫秒的时间延迟（最大延迟可达１６毫秒）．另外,还发现了尖峰的偏振度随频率剧烈变化的偏振反转现象． 相似文献