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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
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国家天文台分米波太阳射电频谱仪用新的观测模式获得太阳射电频谱的一些新的观测现象。新的观测模式频率在1.1—1.34GHz范围,时间分辨率是1.25ms;正常的观测模式下频率在1.1—2.06GHz范围,时间分辨率是5ms。在两种模式下频率分辨率为4MHz。发现窄带Ⅲ型爆发(“blips”)斑马纹(Zebra)和纤维结构(Fiber)中的超精细结构和一些新的精细结构。这些新的结果有助于深入理解在太阳耀斑期间低日冕中能量的释放和转移,也为拟建中的太阳射电频谱日像仪提出了新的要求。 相似文献
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In our recent paper (Jakimiec and Tomczak, Solar Physics
261, 233, 2010) we investigated quasi-periodic oscillations of hard X-rays during the impulsive phase of solar flares. We have come to the
conclusion that they are caused by magnetosonic oscillations of magnetic traps within the volume of hard-X-ray (HXR) loop-top
sources. In the present paper we investigate four flares that show clear quasi-periodic sequences of the HXR pulses. We also
describe our phenomenological model of oscillating magnetic traps to show that it can explain the observed properties of the
HXR oscillations. The main results are the following: i) Low-amplitude quasi-periodic oscillations occur before the impulsive
phase of some flares. ii) The quasi-periodicity of the oscillations can change in some flares. We interpret this as being
due to changes of the length of oscillating magnetic traps. iii) During the impulsive phase a significant part of the energy
of accelerated (non-thermal) electrons is deposited within a HXR loop-top source. iv) The quick development of the impulsive
phase is due to feedback between the pressure pulses by accelerated electrons and the amplitude of the magnetic-trap oscillation.
v) The electron number density and magnetic field strength values obtained for the HXR loop-top sources in several flares
fall within the limits of N≈(2 – 15)×1010 cm−3, B≈(45 – 130) gauss. These results show that the HXR quasi-periodic oscillations contain important information about the energy
release in solar flares. 相似文献
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The aim of the present paper is to use quasi-periodic oscillations in hard X-rays (HXRs) of solar flares as a diagnostic tool
for the investigation of impulsive electron acceleration. We have selected a number of flares which showed quasi-periodic
oscillations in hard X-rays and their loop-top sources could be easily recognized in HXR images. We have considered MHD standing
waves to explain the observed HXR oscillations. We interpret these HXR oscillations as being due to oscillations of magnetic
traps within cusp-like magnetic structures. This is confirmed by the good correlation between periods of the oscillations
and the sizes of the loop-top sources. We argue that a model of oscillating magnetic traps is adequate to explain the observations.
During the compressions of a trap, particles are accelerated, but during its expansions plasma, coming from chromospheric
evaporation, fills the trap, which explains the large number of electrons being accelerated during a sequence of strong pulses.
The advantage of our model of oscillating magnetic traps is that it can explain both the pulses of electron acceleration and
quasi-periodicity of their distribution in time. 相似文献
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The radio emission during 201 selected X-ray solar flares was surveyed from 100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH Zürich. The selection includes all RHESSI flares larger than C5.0 jointly observed from launch until June 30, 2003. Detailed association rates of radio emission during X-ray flares are reported. In the decimeter wavelength range, type III bursts and the genuinely decimetric emissions (pulsations, continua, and narrowband spikes) were found equally frequently. Both occur predominantly in the peak phase of hard X-ray (HXR) emission, but are less in tune with HXRs than the high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron radiation. In 10% of the HXR flares, an intense radiation of the above genuine decimetric types followed in the decay phase or later. Classic meter-wave type III bursts are associated in 33% of all HXR flares, but only in 4% are they the exclusive radio emission. Noise storms were the only radio emission in 5% of the HXR flares, some of them with extended duration. Despite the spatial association (same active region), the noise storm variations are found to be only loosely correlated in time with the X-ray flux. In a surprising 17% of the HXR flares, no coherent radio emission was found in the extremely broad band surveyed. The association but loose correlation between HXR and coherent radio emission is interpreted by multiple reconnection sites connected by common field lines. 相似文献
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对于足点被日面边缘遮挡住的耀斑的观测研究是诊断日冕硬X射线辐射的一个重要方法.通过统计分析RHESSI (Reuven Ramaty High-Energy Solar Spectroscopic Imager)卫星观测到的71个此类耀斑硬X射线源发现,前人提出的两类源,即日冕X射线辐射中热辐射与非热辐射源区空间分离较小的源和分离较大的源,在能谱、成像、光变曲线以及GOES持续时间等方面都没有显著的区别,其中辐射区的面积、耀斑总热能以及GOES持续时间与分离距离之间有很好的相关性.这些结果支持近年来提出的一些耀斑统一模型.同时也表明Masuda耀斑只是一类非常特殊的事件,不具有日冕硬X射线辐射的一般特征. 相似文献
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The distribution of pauses between subsequent elements of a periodic process is symmetric, while a random process produces an asymmetric exponential distribution. The third moment of the pause distribution, which is sensitive to the asymmetry, can therefore be used to discriminate between perodic and random processes. With such a method we analyze the observations of 19 series of solar type III radio bursts and find with a confidence of 0.99 that, on average, the bursts are randomly distributed in time. Only one series can be considered to be periodic with a confidence 0.5. The bandwidth of the repetition frequency of most bursts corresponds to the quality of oscillations of Q¯ = 1.0±0.6 that does not indicates a resonance. Therefore, the modulation of particle beams and intensity of type III radio emission should be considered mainly as the result of random processes. Thus, these properties observed in the majority of radio type III bursts do not support the existence of any periodic or resonant oscillations in the solar corona during flares, although some periodic processes in active regions cannot entirely be ruled out. 相似文献
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We present results from a study of sunspots and faculae on continuum and Caii K images taken at the San Fernando Observatory (SFO) during 1989–1992; a total of approximately 800 images in each bandpass were used. About 18000 red sunspots, 147000 red faculae, and 800000 Caii K faculae were identified based on their contrasts. In addition, we computed the contrasts of pixels on the red images cospatial with Caii K faculae. Sunspot contrasts show a strong dependence on size but no dependence on heliocentric angle. There are continuous but systematic differences among facular regions. We find that the contrast of Caii K faculae is relatively insensitive to heliocentric angle, but is a strong function of facular size, in the sense that larger Caii K faculae are always brighter. The contrast of red faculae is a function of both heliocentric angle and size: the contrast functions show that larger regions contain larger flux tubes, contain deeper flux tubes, and have larger filling factors than small facular regions. Comparisons of cospatial pixels on red and Caii K images show a tight correlation between the average contrast of a region in the continuum and its size and heliocentric angle in the Caii K images. The average contrast of all facular regions is positive everywhere on the disk, even though the largest regions contain flux tubes which appear dark at disk center. 相似文献
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利用国家天文台(北京和昆明)的射电频谱仪(频段为0.65~7.6 GHz)和相关的NoRH/17GHz射电以及TRACE/171 EUV和Yohkoh/SXT的观测资料,分析了2001/04/10和10/19的2个共生精细时间结构的稀有事件,这2个事件的射电爆发时间轮廓和观测特征相似,通过这2个事件的微波(17GHz)偏振观测资料的比较,发现这2个射电爆发均由包含多重(4极)磁结构的复杂活动区引起,特别指出这2个耀斑最后都导致了耀斑后相的分米波射电爆发(第二次触发耀斑),这可能是后环引起的射电爆发。它们都分别对应于双极磁位形,表明这两次触发耀斑是由相似的耀斑模型产生。2个分米波爆发可能是相似(homologous)耀斑的射电表现,可以推测这两次耀斑的驱动器可能皆是磁流浮现或对消(因为源区有新的单或双极出现或消失),而它们的触发器皆是由双极反向Y型位形(具有一个双极拱的单磁流系统)的磁重联,耀斑后环的演化是导致耀斑后相分米波射电爆发的必要条件。我们认为,这双带耀斑对应的宽带射电爆发辐射机制是回旋同步加速辐射过程,而耀斑后相的窄带分米波爆发的辐射机制是等离子体辐射过程。 相似文献
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综述云南天文台在太阳活动22周峰年期间观测到的米波射电频谱资料,处理资料时发现230~300MHz频段有一些有趣的观测现象。如米波Ⅲ型爆发;“blips”;毫秒级Spike与Ⅲ型爆发共存事件;快速脉动等。根据这些事件的现象,讨论了它们的产生机制。 相似文献
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The impulsive phase of the 23 July 2002 2B/X4.8 proton flare with a classical two-ribbon structure was observed with the Irkutsk
Large Solar Vacuum Telescope (LSVT) in spectropolarimetric mode, with high spatial, spectral, and time resolution. On the
basis of 49 spectrograms and 1200 spectral cuts across the flare ribbons, evidence for Hα line impact polarization has been obtained. A systematic change of the Stokes Q and U parameters has been detected across the ribbons for different flare regions measured with a scanning step of 0.85″. In the
eastern side of the ribbons, the degree of polarization is 4 – 8%; its plane is oriented toward the solar disk center (radial
direction). In the western side, the polarization degree runs up to 25%, and its plane is perpendicular to the disk center
direction (tangential direction). A comparison of these results with hard X-ray data (RHESSI) allows us to conclude that high-energy
electron beams reached the chromosphere during this flare. The observed changes of the direction of polarization and the vanishing
polarization within the ribbons mean that, at the chromospheric level, the energy of electrons remaining in the beam is about
200 eV. A shift of the peak position of polarization relative to the intensity maximum in the ribbons may result from the
inclination of the electron beam axis with respect to the solar surface. 相似文献
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The GOES C7.5 flare on 20 February 2002 at 11:07 UT is one of the first solar flares observed by RHESSI at X-ray wavelengths. It was simultaneously observed at metric/decimetric wavelengths by the Nançay radioheliograph (NRH) which provided images of the flare between 450 and 150 MHz. We present a first comparison of the hard X-ray images observed with RHESSI and of the radio emission sites observed by the NRH. This first analysis shows that: (1) there is a close occurrence between the production of the HXR-radiating most energetic electrons and the injection of radio-emitting non-thermal electrons at all heights in the corona, (2) modifications with time in the pattern of the HXR sources above 25 keV and of the decimetric radio sources at 410 MHz are observed occurring on similar time periods, (3) in the late phase of the most energetic HXR peak, a weak radio source is observed at high frequencies, overlying the EUV magnetic loops seen in the vicinity of the X-ray flaring sites above 12 keV. These preliminary results illustrate the potential of combining RHESSI and NRH images for the study of electron acceleration and transport in flares. 相似文献
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通过1991年6月6日共生太阳白光耀斑(WLF)的射电运动IV型爆发及其伴随现象(包括耀斑后环、爆发衰减相的射电脉动、多波段射电辐射和太阳物质抛射等)观测资料的分析,定性地探讨了WLF的起源、加热机制和发射地点的问题.假设了WLF和射电运动IV型射电爆发可能有共同起源的低日冕电子加速区,讨论了WLF的能量传输可能是通过二步加速过程,即来自低日冕的非热电子沉降能量于色球层,产生色球层的压缩波或向下的辐射场进而使上光球层温度增加导致WLF此外,提出WLF可能会伴有耀斑后环和射电精细结构的对应物. 相似文献