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1.
We report detailed observations of the herringbone (HB) fine structure on type II solar radio bursts. Data from the Culgoora radiospectrograph, radiometer and radioheliograph are analyzed. We determine the characteristic spectral profiles, frequency drift rates and exciter velocities, fluxes, source sizes, brightness temperatures, and polarizations of individual HB bursts. Correlations between individual bursts within the characteristic groups of bursts and the properties of the associated type II bursts are examined. Our data are compatible with HB bursts being radiation at multiples of the plasma frequency generated by electron streams accelerated by the type II shock. We conclude that HB bursts are physically distinct phenomena from type II and type III bursts, differing significantly in emission processes and/or source conditions; this conclusion indicates that many of the presently available theoretical ideas for HB bursts are incorrect.Now at: Department of Physics and Astronomy, University of Iowa, U.S.A.Now at Anglo-Australian Observatory, Sydney, Australia. 相似文献
2.
介绍云南和北京天文台射电频谱仪观测到的3个对偶的米波－－微波Ⅲ型爆发，估计了双向电子束起源的频率和高度，3个事件分别揭示了在正向和反向漂移爆发之间的分界频率（约为250，1300和2900MHz),它们指出了一个致密的电子加速源，在这个源中产生了向上和向下两个方向注入的电子束，从这些事例可以表明不同事件的双向电子束的分界频率有一个相当大的范围（250－2900MHz)，而它们的起源范围却是在一个很小的（大约4－100MHz)和不同的频段范围内。最后讨论了日冕磁结构的拓扑范围、电子加速源构造的空间尺度、电子束运动速度和对偶Ⅲ型爆发的产生机制。 相似文献
3.
Electron beams in the low corona 总被引：3，自引：0，他引：3
Selected high-resolution spectrograms of solar fast-drift bursts in the 6.2–8.4 GHz range are presented. The bursts have similar characteristics as metric and decimetric type III bursts: rise and decay in a few thermal collision times, total bandwidth 3% of the center frequency, low polarization, drift rate of the order of the center frequency per second, and flare association. They appear in several groups per flare, each group consisting of some tens of single bursts. Fragmentation is also apparent in frequency; there are many narrowband bursts randomly scattered in the spectrum. The maximum frequency of the bursts is highly variable.The radiation is interpreted in terms of plasma emission of electron beams at plasma densities of more than 1011 cm–-3. At this extremely high frequency, emission from the plasma level even at the harmonic is only possible in a very anisotropic plasma. The scale lengths perpendicular and parallel to the magnetic field can be estimated. A model of the source region and its environment is presented.Paper presented at the 4th CESRA Workshop in Ouranopolis (Greece) 1991. 相似文献
4.
V. N. Mel’nik A. A. Konovalenko H. O. Rucker B. P. Rutkevych V. V. Dorovskyy E. P. Abranin A. I. Brazhenko A. A. Stanislavskii A. Lecacheux 《Solar physics》2008,250(1):133-145
We report the first observations of Type III-like bursts at frequencies 10 – 30 MHz. More than 1000 such bursts during 2002 – 2004
have been analyzed. The frequency drift of these bursts is several times that of decameter Type III bursts. A typical duration
of the Type III-like bursts is 1 – 2 s. These bursts are mainly observed when the source active region is located within a
few days from the central meridian. The drift rate of the Type III-like bursts can take a large value by considering the velocity
of Type III electrons and the group velocity of generated electromagnetic waves. 相似文献
5.
与太阳射电爆发相比,通常认为频率较低的行星际射电爆发产生于远离低日冕的行星际空间.地球电离层的截止导致地基设备无法对其进行观测.美国国家航空航天局(National Aeronautics and Space Administration, NASA)发射的帕克太阳探测器(Parker Solar Probe, PSP)是迄今为止距离太阳最近的空间探测器.其搭载的射电频谱仪能够对10 k Hz–19.17 MHz频段范围内的射电辐射进行观测. PSP能够靠近甚至可能穿越行星际III型射电爆发的辐射源区,因此使用PSP对行星际射电爆发进行观测具有前所未有的优势.简要介绍了目前为止使用PSP的射电观测数据对行星际III型射电爆发的多方面研究,包括爆发的发生率、偏振、散射、截止频率、可能的辐射机制和相关的辐射源区等方面的研究进展,并讨论了其未来的研究前景. 相似文献
6.
Ya. G. Tsybko 《Solar physics》1984,92(1-2):299-315
Type-IIIb, IIId, and III solar decametric radio bursts, being distinguished by the typical negative drift rate of their dynamic spectra, are compared. Observational data were obtained with a UTR-2 antenna during the period 1973–1982. During the analysis of the bursts of all these spectral varieties, the frequency drift time (drift delay) was measured in the ranges 25 to 12.5 MHz, 25 to 20 MHz, and 12.5 to 10 MHz. Durations of type-III bursts were determined at the harmonically-related frequencies of 25 and 12.5 MHz; radio source locations were also used.It is shown that these decametric bursts are distinctly divided into two groups: (1)type-IIIb chains of simple stria bursts and also normal type-III storm bursts observed at central regions constitute a group of events with a fast drifting spectrum; (2) type-III bursts from type-IIIb-III pairs and the limb variant of normal III bursts, as well as peculiar type-IIId chains of diffuse striae and related chains with an echo component, constitute a second group of events with comparatively slow drift rates.The first group of the phenomena is associated with the fundamental F frequency and the second one, with the harmonic H of the coronal plasma frequency. The results of the present investigation agree well with earlier conclusions on the harmonic origin of decametric chains and type-III bursts. Measurements of drift delays in narrow frequency ranges, an octave apart, as well as type-III burst durations at harmonically-related frequencies confirm the existence of both F and H components in the solar radiation. The essential result of 10 years of decametric observations is that the frequency drift rates and durations are rather stable parameters for the various type-III bursts and stria-burst chains. The stability characterizes some unspecified conditions of burst generation in the middle corona. 相似文献
7.
The change of source characteristics during the transition from the impulsive phase to the post-burst phase is investigated for cm bursts on a statistical basis. The results are the following: (1) The sudden decrease of the circular polarization degree is found almost invariably at the transition; typically from 20–30% down to a few percent. (2) Some bursts show remarkable source expansions in the post-burst phase. There are no cases in which impulsive bursts have larger source size than the associated post-burst increases. (3) Type III bursts which are indicative of non-thermal phenomena are associated with the impulsive phase but not with the post-burst phase. Implications of these observed results are discussed. 相似文献
8.
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
9.
Using the data from our experiments on the IMP-6 (Explorer 43) satellite, we have examined over 200 type III bursts at kilometric wavelengths, including 16 bursts which were accompanied by >18 keV electron events with sharp onsets, in a search for the electrostatic waves which, according to theory, should be the primary source of type III bursts. No electrostatic waves of sufficient intensity to generate the type III bursts by any of the wave-wave scattering theories which produce the second harmonic of the plasma frequency, have been found. 相似文献
10.
Tatsuo Takakura 《Solar physics》1972,26(1):151-175
The gyro-synchrotron emission from a model source with a non-uniform magnetic field is computed taking into account the self absorption. This model seems adequate not only to interpret the radio spectrum and its time variation of microwave impulsive bursts but also to solve the discrepancy between the numbers of non-thermal electrons emitting radio burst and those emitting hard X-ray burst.The decrease of flux of radio burst with decreasing frequency at low microwave frequencies is due to the self absorption and/or the thermal gyro-absorption. In this frequency range, the radio source is optically thick even at weak microwave bursts. The weakness of the bursts may be rather due to the small size of the radio source and/or the weakness of the magnetic field than the small number density of the non-thermal electrons.The time variation of the flux of radio burst may be mainly attributed to the variation of source size in a horizontal direction ( direction) instead of the variation of the number density of non-thermal electrons itself, implying that the acceleration region progressively moves in the horizontal direction leaving the non-thermal electrons behind during the increasing phase of the radio burst. 相似文献
11.
《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
12.
13.
Richard R. Weber 《Solar physics》1978,59(2):377-385
Flux density spectra have been determined for ninety-one simple type III solar bursts observed by the Goddard Space Flight Center radio astronomy experiment on the IMP-6 spacecraft during 1971 and 1972. Spectral peaks were found to occur at frequencies ranging from 44 kHz up to 2500 kHz. Half of the bursts peaked between 250 kHz and 900 kHz, corresponding to emission at solar distances of about 0.3 to 0.1 AU. Maximum burst flux density sometimes exceeds 10–14 W m–2 Hz–1. The primary factor controlling the spectral peak frequency of these bursts appears to be variation in intrinsic power radiated by the source as the exciter moves outward from the Sun, rather than radio propagation effects between the source and IMP-6. Thus, a burst spectrum strongly reflects the evolution of the properties of the exciting electron beam, and according to current theory, beam deceleration could help account for the observations. 相似文献
14.
Fiber – or intermediate drift – bursts are a continuum fine structure in some complex solar radio events. We present the analysis of such bursts in the X17 flare on 28 Oct. 2003. Based on the whistler wave model of fiber bursts we derive the 3D magnetic field structures that carry the radio sources in different stages of the event and obtain insight into the energy release evolution in the main flare phase, the related paths of nonthermal particle propagation in the corona, and the involved magnetic field structures. Additionally, we test the whistler wave model of fiber bursts for the meter and the decimeter wave range. Radio spectral data (Astrophysikalisches Institut Potsdam, Astronomical Observatory Ond?ejov) show a continuum with fibers for ≈?6 min during the main flare phase. Radio imaging data (Nançay Radio Heliograph) yield source centroid positions of the fibers at three frequencies in the spectrometer band. We compare the radio positions with the potential coronal magnetic field extrapolated from SOHO/MDI data. Given the detected source site configuration and evolution, and the change of the fiber burst frequency range with time, we can also extract those coronal flux tubes where the high-frequency fiber bursts are situated even without decimeter imaging data. To this aim we use a kinetic simulation of whistler wave growth in sample flux tubes modeled by selected potential field lines and a barometric density model. The whistler wave model of fiber bursts accurately explains the observations on 28 Oct. 2003. A laterally extended system of low coronal loops is found to guide the whistler waves. It connects several neighboring active regions including the flaring AR 10486. For varying source sites the fiber bursts are emitted at the fundamental mode of the plasma frequency over the whole range (1200?–?300 MHz). The present event can be understood without assuming two different generation mechanisms for meter and decimeter wave fiber bursts. It gives new insight into particle acceleration and propagation in the low flare and post-CME corona. 相似文献
15.
B. L. Gotwols 《Solar physics》1973,33(2):475-482
Several models for pulsating type IV radio bursts are presented based on the assumption that the pulsations are the result of fluctuations in the synchrotron emission due to small variations in the magnetic field of the source. It is shown that a source that is optically thick at low frequencies due to synchrotron self-absorption exhibits pulsations that occur in two bands situated on either side of the spectral peak. The pulsations in the two bands are 180° out of phase and the band of pulsations at the higher frequencies is the more intense. In contrast, a synchrotron source that is optically thin at all frequencies and whose low frequency emission is suppressed due to the Razin effect develops only a single band of pulsations around the frequency of maximum emission. However, the flux density associated with the later model would be too small to explain the more intense pulsations that have been observed unless the source area is considerably larger than presently seems reasonable. 相似文献
16.
We present observational imaging evidence for the existence of metric radio bursts closely associated with the front edge of coronal mass ejections (CMEs). These radio bursts drift in frequency similarly to type II bursts. They are weak and usually go undetected on spectrograph data. We find the same measured projected velocity for the displacement of, respectively, the radio source (when observed at two or more frequencies) and the CME leading edge. The position of the emitting source coincides with the CME leading edge. Among the events analyzed, the fastest of them, with a velocity over 1400 km s-1, was associated with interplanetary type II bursts. 相似文献
17.
A morphological study is made for the hard X-ray images (25–50 keV) of nine impulsive bursts observed by Hinotori. Most of them revealed single sources, either extended or compact, during the whole duration of the bursts. The sources of all of four spike bursts in the present sample are compact. After the main phase of the impulsive bursts, generally the source size becomes smaller accompanying a shift of position. The X-ray source size is much greater than that of the Hα kernel in two events out of three. Four possible explanations for the X-ray source to be single are suggested. One of these is the strong electric field along the magnetic field as demonstrated to be produced at the decay of force-free current. 相似文献
18.
The properties of powerful (flux >10−19 W m−2 Hz−1) type III bursts observed in July – August 2002 by the radio telescope UTR-2 at frequencies 10 – 30 MHz are analyzed. Most
bursts have been registered when the active regions associated to these bursts were located near the central meridian or at
40° – 60° to the East or West from it. All powerful type III bursts drift from high to low frequencies with frequency drift
rates 1 – 2.5 MHz s−1. It is important to emphasize that according to our observations the drift rate is linearly increasing with frequency. The
duration of the bursts changes mainly from 6 s at frequency 30 MHz up to 12 s at 10 MHz. The instantaneous frequency bandwidth
does not depend on the day of observations, i.e. on the disk location of the source active region, and is increasing with frequency. 相似文献
19.
We analyze the radioheliograph and SMM-C/P observations of 1986 November 3 mass ejection event. The metric radio emissions are the only detected activity associated with the mass ejection, but are adequate to study the evolution of the event. The start time of the ejection seems to precede a possible flare behind the limb indicated by the early type III bursts. We discuss the physical relation between various types of bursts and the CME. We interpret moving type IV bursts as a plasma emission process. It is also shown using white-light coronagraph data that the density in the source region of the moving type IV is sufficient to support second harmonic plasma emission at the observed frequency of 50 MHz. 相似文献
20.
Hans Rosenberg 《Solar physics》1975,42(1):247-257
The observational evidence is reviewed for the occurrence of type III solar radio bursts in pairs with frequency ratio two to one. We show that the observations can be explained under the hypothesis that there is a tendency for a type III burst to be followed by a second burst within approximately one second. This explanation leads to fewer difficulties than the hypothesis that type III bursts occur in pairs, one member being emitted at the fundamental of the local coronal plasma frequency, the other at its second harmonic. We conclude that in general, type III bursts are emitted at the second harmonic of the plasma frequency and that type III theories should account for this and only under very special circumstances (which are rare) for the emission at the fundamental and the second harmonic. 相似文献