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1.
We analyze a special kind of temporal fine structure in microwave radio emission for the 25 August 1999 solar flare observed
by the PMO spectrometer over the range of 4.5 – 7.5 GHz. This flare displays continuum emission after a group of reverse-slope
type III bursts around 6 GHz. High-resolution dynamic spectra reveal three evolving emission lines (EELs) following the type
III group. They are characterized by isolated, narrow, and continuous emission strips, which display frequency fluctuations
with time. Their frequency-drift rates are between −2 and 3 GHz s−1. Distinct from the EELs at lower frequencies, three EELs have a very short duration of a few seconds. They show an average
bandwidth of Δf≈330 MHz and a relative bandwidth of Δf/f≈0.057. This is the first time that this kind of fine structure has been observed around 6 GHz. 相似文献
2.
Xu Fu-Ying Xu Zhi-Cai Huang Guang-Ii Yao Qi-Jun Meng Xuan Wu Hong-Ao 《Solar physics》2003,216(1-2):273-284
A broadband solar radio spectrometer with a bandwidth of about 7 GHz has been developed in China for solar maximum 23. This
work is a cooperative project of Beijing Astronomical Observatory (BAO), Purple Mountain Observatory (PMO), Yunnan Observatory
(YNO), and Nanjing University. The spectrometer of PMO worked in the waveband of 4.5–7.5 GHz, that of BAO in 1–2 GHz, 2.6–3.8 GHz,
and 5.2–7.6 GHz, and that of YNO in 0.7–1.5 GHz. The spectrometer of PMO is a multichannel and frequency-agile one with a
time resolution of 1–5 ms and a frequency resolution of 10 MHz. It started to operate in August 1999 and since then more than
300 spectral events have been observed, and some type III or type III-like structures have also been found. In this paper,
some selected typical events, for example, the events on 25 August 1999 and 27 October 1999, are presented, and some new observed
features are also described and discussed. 相似文献
3.
Magnetic reconnection is commonly accepted to play a key role in flare energy release, but only poor information about the
main characteristics of this process is available so far. An intrinsic feature of reconnection is plasma density enhancement
in current sheets. A unique method to detect this effect is provided by analysis of drifting bursts, whose emission frequency
is close to the local Langmuir frequency or its harmonics. With this purpose, we analyze a series of several tens of drifting
microwave bursts during the 30 March 2001 flare. The burst drift rates range from −10 to 20 GHz s−1. Using one-dimensional scans recorded with the SSRT interferometer at two different frequencies near 5.7 GHz, we have measured
relative positions of burst sources and their velocities along a flare loop revealed from soft X-ray and extreme-ultraviolet
images. It is argued that the contribution of the increasing density effect into the observed frequency drift rates is about
6 GHz s−1, which is shown to be consistent with theoretical models of magnetic reconnection with reasonable boundary conditions. 相似文献
4.
We analyze the pulses in high-frequency drift radio structures observed by the spectrometer at Purple Mountain Observatory
(PMO) over the frequency range of 4.5 – 7.5 GHz during the 18 March 2003 solar flare. A number of individual pulses are determined
from the drifting radio structures after the detected gradual component subtraction. The frequency distributions of microwave
pulse occurrence as functions of peak flux, duration, bandwidth, and time interval between two adjacent pulses exhibit a power-law
behavior, i.e.
. From regression fitting in log-log space, we obtain the power-law indexes, α
P=7.38±0.40 for the peak flux, α
D=5.39±0.86 for the duration, and α
B=6.35±0.56 for the bandwidth. We find that the frequency distribution for the time interval displays a broken power law. The
break occurs at about 500 ms, and their indexes are α
W1=1.56±0.08 and α
W2=3.19±0.12, respectively. Our results are consistent with the previous findings of hard X-ray pulses, type III bursts, and
decimetric millisecond spikes. 相似文献
5.
Wang Shujuan Yan Yihua Zhao Ruizhen Fu Qijun Tan Chengming Xu Long Wang Shijin Lin Huaan 《Solar physics》2001,204(1-2):153-164
25 MHz–7.6 GHz global and detailed (fine structure – FS) radio spectra are presented, which were observed in the NOAA 9077
active region for the Bastille Day (14 July 2000) flare at 10:10–11:00 UT. Besides broadband radio bursts, high-resolution
dynamic spectra reveal metric type II burst, decimetric type IV burst and various decimetric and microwave FSs, such as type III
bursts, type U bursts, reverse-slope (RS)-drifting burst, fiber bursts, patch and drifting pulsation structure (DPS). The
peak-flux-density spectrum of the radio bursts over the range 1.0–7.6 GHz globally appears as a U-shaped signature. Analyzing
the features of backbone and herringbones of the type II burst, the speeds of shock and relevant energetic electron beams
were estimated to be 1100 km s−1 and 58 500 km s−1, respectively. Also the time sequence of the radio emission is analyzed by comparing with the hard X-rays (HXRs) and the
soft X-rays (SXRs) in this flare. After the maxima of the X-rays, the radio emission in the range 1.0–7.6 GHz reached maxima
first at the higher frequency, then drifted to the lower frequency. This comparison suggested that the flare included three
successive processes: firstly the X-rays rose and reached maxima at 10:10–10:23 UT, accompanied by fine structures only in
the range 2.6–7.6 GHz; secondly the microwave radio emission reached maxima accompanied by many fine structures over the range
1.0–7.6 GHz at 10:23–10:34 UT; then a decimetric type IV burst and its associated FSs (fibers) in the range 1.0–2.0 GHz appeared
after 10:40 UT. 相似文献
6.
In the years 2002 – 2005, 38 groups of the reverse drift bursts (RDBs) were observed in the 0.8 – 4.5 GHz frequency range
by the Ondřejov radiospectrograph. In 21 cases, which were observed at the times of the RHESSI observations, spatial structure,
positional changes, and spectra of X-ray sources during RDB observations are studied in detail. First, based on the frequency
drift and the spatial structure of the associated X-ray source, the events are classified as: (a) fast drifting RDBs with
a compact X-ray source, (b) fast drifting RDBs with a multiple X-ray source (FM), and slowly drifting RDBs. Then, the spectra
of X-ray sources at the times of RDBs are analyzed. It is found that most fast drifting RDBs (16 of 17 cases) are associated
with the spectra having a distinct power-law (non-thermal) component. In contrast, the X-ray spectra associated with the slowly drifting RDBs are predominantly purely
thermal (in three out of four cases; in the 26 July 2004, case the X-ray spectrum is thermal and high temperature, with non-thermal
component). Two special cases of RDBs observed during the 28 October 2003, and 23 July 2004, flares are added for comparison.
The most frequent events are those with fast drifting RDBs, a compact short-lasting X-ray sources, and a power-law X-ray spectrum.
The individual reverse drift bursts (∼1 s duration) do not show a clear temporal association with individual peaks of hard
X-ray bursts. During slowly drifting RDBs the shape of the associated X-ray source changed or expanded. Among them the most
interesting one was observed in 26 July 2004, when the very slowly drifting RDBs (+40 MHz s−1) were associated with an X-ray loop-like source continuously elongating in the southwest direction. In the most cases the
model of RDBs with electron beams is compatible with the observations, but in flares on 26 July 2004, and 28 October 2003,
the RDBs are probably generated by some other type of an agent; we propose here a thermal conduction front. 相似文献
7.
In the paper by Kliem, Karlický, and Benz (Astron. Astrophys. 360, 715, 2000) it was suggested, that plasmoids formed during the bursty regime of solar flare reconnection can be “visualised” in the radio spectra as drifting pulsating structures via accelerated particles trapped inside the plasmoid. In the present paper we investigate this idea in detail. First, simple statistical analysis supporting this hypothesis is presented. Then, by using the 2.5-D MHD (including gravity) model solar flare reconnection in the inhomogeneous, stratified atmosphere is simulated and the formation and subsequent ejection of the plasmoid is demonstrated. The ejected plasmoid, which is considered to be a trap for accelerated electrons, is traced and its plasma parameters are computed. To estimate the associated plasma radio emission we need to know locations of accelerated electrons and corresponding plasma frequencies. General considerations predict that these electrons should be distributed mainly along the magnetic separatrix surfaces and this was confirmed by using a particle-in-cell simulation. Finally, under some simplifying assumptions the model dynamic radio spectrum is constructed. The relation between the global frequency drift and the plasmoid motion in the inhomogeneous ambient atmosphere is studied. The results are discussed with respect to the observed drifting pulsation structures and their possible utilisation for flare magnetic field diagnostics. 相似文献
8.
Min Wang Rui-Xiang Xie Chun Xu Shuo-Biao Shi Yi-Hua Yan National Astronomical Observatories Yunnan Observatory Chinese Academy of Sciences Kunming National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(5):508-518
We present a, large complex radio burst and its associated fast tune structures observed on 2001 April 10 in the frequency range of 0.65-7.6 GHz. The NoRH radio image observation shows very complex radio source structures which include preexisting, newly emerging, submerging/cancelling polarities and a bipolar, a tripolar (a 'bipolar + remote unipolar'), and a quadrupolar structure. This suggests that the radio burst is generated from a very complicated loop structure. According to the spectral and image observations, we assume that the beginning of this flare was caused by a single bipolar loop configuration with a 'Y-type' re-connection structure. A composite of radio continuum and fast time structures is contained in this flare. The various fast radio emission phenomena include normal and reverse drifting type III bursts, and slowly drifting and no-drift structures. The tripolar configurations may form a double-loop with a 'three-legged' structure, which is an important source of the various types of fast time structures. The two-loop reconnection model can lead simultaneously to electron acceleration and corona heating. We have also analyzed the behaviors of coronal magnetic polarities and the emission processes of different types radio emission qualitatively. Interactions of a bipolar or multi-polar loop are consistent with our observational results. Our observations favor the magnetic reconnection configurations of the 'inverted Y-type' (bipolar) and the 'three-legged' structures (tripolar or quadrupolar). 相似文献
9.
An analysis of new observations showing fine structures consisting of narrowband fiber bursts as substructures of large-scale
zebra-pattern stripes is carried out. We study four events using spectral observations taken with a newly built spectrometer
located at the Huairou station, China, in the frequency range of 1.1 – 2.0 GHz with extremely high frequency and time resolutions
(5 MHz and 1.25 ms). All the radio events were analyzed by using the available satellite data (SOHO LASCO, EIT, and MDI, TRACE,
and RHESSI). Small-scale fibers always drift to lower frequencies. They may belong to a family of ropelike fibers and can
also be regarded as fine structures of type III bursts and broadband pulsations. The radio emission was moderately or strongly
polarized in the ordinary wave mode. In three main events fiber structure appeared as a forerunner of the entire event. All
four events were small decimeter bursts. We assume that for small-scale fiber bursts the usual mechanism of coalescence of
whistler waves with plasma waves can be applied, and the large-scale zebra pattern can be explained in the conventional double
plasma resonance (DPR) model. The appearance of an uncommon fine structure is connected with the following special features
of the plasma wave excitation in the radio source: Both whistler and plasma wave instabilities are too weak at the very beginning
of the events (i.e., the continuum was absent), and the fine structure is almost invisible. Then, whistlers generated directly at DPR levels
“highlight” the radio emission only from these levels owing to their interaction with plasma waves. 相似文献
10.
Based on the analysis of the microwave observations at the frequency range of 2.60 – 3.80 GHz in the solar X1.3 flare event
observed at the Solar Broadband RadioSpectrometer in Huairou (SBRS/Huairou) on 30 July 2005, an interesting reversed drifting quasi-periodic pulsating structure (R-DPS) is
confirmed. The R-DPS is mainly composed of two drifting pulsating components: one is a relatively slow very short-period pulsation
(VSP) with a period of about 130 – 170 ms, the other is a relatively fast VSP with a period of about 70 – 80 ms. The R-DPS
has a weak left-handed circular polarization. Based on the synthetic investigations of Reuven Ramaty High Energy Solar Spectroscopic Imaging (RHESSI) hard X-ray, Geostationary Operational Environmental Satellite (GOES) soft X-ray observations, and magnetic field extrapolation, we suggest that the R-DPS possibly reflects flaring dynamic
processes of the emission source regions. 相似文献
11.
Zong-Jun Ning Yu-Ying Liu Qi-Jun Fu Fu-Ying Xu National Astronomical Observatories Chinese Academy of Sciences Beijing Purple Mountain Observatory Chinese Academy of Sciences Nanjing 《中国天文和天体物理学报》2003,3(4):381-390
We present a new sub-class of type Ⅲ solar radio burst at the high frequencies around 6.0 GHz. In addition to a descending and an ascending branch on the dynamic spectrum, it has an inverted morphology different from the simpletype U-burst. We call it “partial N-burst“ because it is interpreted as the known N-burst minus its first branch. The partial N-burst presented here was detected among a reverse slope type Ⅲ (RS-Ⅲ) burst group prior to the type V solar radio continuum and was simultaneously recorded by two spectrometers at the National Astronomical Observatories, Chinese Academy of Sciences (NAOC, 5.20-7.60 GHz) and at Purple Mountain Observatory (PMO, 4.50-7.50 GHz) on 1999 August 25.After the N-burst and M-burst, the partial N-burst is a third piece of evidence for a magnetic mirror effect in solar radio observation, when the same electron is reflected at a pinched foot of a flare loop. 相似文献
12.
N. S. Meshalkina A. T. Altyntsev D. A. Zhdanov S. V. Lesovoi A. A. Kochanov Y. H. Yan C. M. Tan 《Solar physics》2012,280(2):537-549
The analysis of narrowband drifting of type III-like structures in radio bursts dynamic spectra allows one to obtain unique information about the primary energy release mechanisms in solar flares. The SSRT (Siberian Solar Radio Telescope) spatially resolved images and its high spectral and temporal resolution allow for direct determination not only of the source positions but also of the exciter velocities along the flare loop. Practically, such measurements are possible during some special time intervals when SSRT is observing the flare region in two high-order fringes near 5.7?GHz; thus, two 1D brightness distributions are recorded simultaneously at two frequency bands. The analysis of type III-like bursts recorded during the flare 14?April 2002 is presented. Using multiwavelength radio observations recorded by the SSRT, the Huairou Solar Broadband Radio Spectrometer (SBRS), the Nobeyama Radio Polarimeters (NoRP), and the Radio Solar Telescope Network (RSTN), we study an event with series of several tens of drifting microwave pulses with drift rates in the range from ?7 to 13?GHz?s?1. The sources of the fast-drifting bursts were located near the top of a flare loop in a volume of a few Mm in size. The slow drift of the exciters along the flare loop suggests a high pitch anisotropy of the emitting electrons. 相似文献
13.
A specific combination of spectral fine structures in meter – decimeter dynamic spectra of solar radio burst emission is
reported in observations carried out at the Astrophysical Institute Potsdam. We describe and interpret the occurrence of zebra
patterns in fast drifting (type III burst-like) envelopes of absorbed continuum emission. A possible mechanism of the origin
of such an involved spectral pattern is put forward, leading to a necessarily multinonequlibrium component coronal plasma.
The suggested mechanism is based on the fact that during the passage of a fast electron beam through the corona the loss cone
instability (which is caused by electrons captured in a magnetic trap generating the continuum) is quenched. As result, a
fast drift burst appears in absorption, and the zebra pattern becomes visible on the low background emission. This zebra pattern
is generated by a group of electrons with a nonequilibrium distribution over transverse velocities. In the absence of the
beam the pattern is invisible against the background of the stronger continuum. It is shown that the mechanism is sensitive
to the distribution parameters of the different electron ensembles. Therefore the effect in dynamic radio spectra is comparatively
rare but its proper existence underlines that the simultaneous presence of different ensembles of electrons in the flaring
corona can be quite a frequent situation. This can explain some problems in deconvolving X-ray photon spectra to electron
energy spectra. 相似文献
14.
日球边界射电辐射是太阳系最强的射电辐射现象,辐射功率至少达1013 W,能够提供日球边界附近高能电子束和背景磁等离子体结构的重要物理信息.自1983年旅行者号卫星首次探测到日球边界射电辐射后,其便受到研究者们的广泛持续关注.日球边界射电辐射大致有两类:辐射频率相对较高的瞬时辐射或称漂移辐射以及辐射频率相对较低的持续辐射或称非漂移辐射.通常两类辐射都从大约2 kHz开始,漂移辐射具有向高频率漂移的特征,频漂率约为1–3 kHz/yr,频率范围1.8–3.6 kHz,持续时间较短大致100–300 d;非漂移辐射没有明显的频率漂移,频率范围1.8–2.6 kHz,持续时间较长大致3 yr.目前普遍认为日球边界射电辐射与激波有关.介绍了该射电辐射可能的辐射产生源区、辐射物理机制以及与辐射相关的激波来源,并且讨论了尚存在的科学问题以及展望了未来可以进一步开展的研究. 相似文献
15.
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
16.
一个太阳耀斑约含数千个微耀斑［１］，每个微耀斑以热的，低频波和加速粒子的形式释放能量。耀斑期间大部分能量的释放是通过电子加速转移的结果，然而电子加速是在耀斑前相开始，并在整个耀斑持续期间继续保持。在耀斑发展的不同相期间伴有各种各样的射电辐射现象（及其它波段共生现象），多波段射电观测和比较可以给出有关电子加速过程和耀斑自身发展的重要信息，尤其可检测加速开始的时间和频率部位（目前仍为太阳物理的前沿）。微耀斑能量的瞬时释放可能是引起不同类型快速精细结构的原因，射电毫秒级尖峰辐射是起因于连续能量释放的证据，其辐射源位于或靠近能量释放区［２］，公认射电辐射的快速结构是日冕电子束的特征信号［３，４］，所以今后使用高时间和高频率分辨率的宽带频谱仪同时观测可详细地探测加速过程，从而对预耀斑的加热和初始能量释放，耀斑的逐步建立和演化都具有重要意义。本文介绍几个典型事件，包括射电尖峰脉冲辐射，类尖峰辐射和短时标漂移结构 相似文献
17.
Anisotropic Beam Model for the Spectral Observations of Radio Burst Fine Structures on 1998 April 15
A fine structure consisting of three almost equidistant frequency bands was observed in the high frequency part of a solar burst on 1998 April 15 by the spectrometer of Beijing Astronomical Observatory in the range 2.6-3.8GHz. A model for this event based on beam-anisotropic instability in the solar corona is presented. Longitudinal plasma waves are excited at cyclotron resonance and then transformed into radio emission at their second harmonic.The model is in accordance with the observations if we suppose a magnetic field strength in the region of emission generation of about 200G. 相似文献
18.
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
19.
On April 21, 2002, a broadband solar radio burst was observed at about 01:00 – 03:00 UT with the digital spectrometers of
National Astronomical Observatories of China (NAOC). Also many fiber bursts superposed on the continuum bursts were detected
in the frequency range of 2.6 – 3.8 GHz during the time interval. After data processing, some parameters of the fibers such
as frequency drift rate, duration, bandwidth, and relative bandwidth were determined. The mean value of the frequency drift
was in the range of 42.3 – 87.4 MHz s−1 (negative). A theoretical interpretation for the fibers was presented based upon a model of the velocity of Alfvén solitons.
In this model, the source of the fiber emission was considered as the ducting of the solitons within the magnetic-mirror loop.
Then the magnetic field strength of the fiber source was estimated to be about 130 ≤ B0 ≤ 270 G. Also a comparison of the magnetic field estimation was made with another model of whistler group velocity. 相似文献
20.
The spatial and spectral behaviors of two solar flares observed by the Nobeyama Radioheliograph (NoRH) on 24 August 2002 and
22 August 2005 are explored. They were observed with a single loop-top source and double footpoint sources at the beginning,
then with looplike structures for the rest of the event. NoRH has high spatial and temporal resolution at the two frequencies
of 17 and 34 GHz where a nonthermal radio source is often optically thin. Such capabilities give us an opportunity to study
the spatial and spectral behaviors of different microwave sources. The 24 August 2002 flare displayed a soft – hard – soft
(SHS) spectral pattern in the rising – peak – decay phases at 34 GHz, which was also observed for the spectral behavior of
both loop-top and footpoint sources. In contrast, the 22 August 2005 flare showed a soft – hard – harder (SHH) spectral pattern
for its both loop-top and footpoint sources. It is interesting that this event showed a harder spectrum in the early rising
phase. We found a positive correlation between the spectral index and microwave flux in both the loop-top source and the footpoint
sources in both events. The conclusions drawn from the flux index could apply to the electron index as well, because of their
simple linear relationship under the assumption of nonthermal gyrosynchrotron mechanism. Such a property of spatial and spectral
behaviors of microwave sources gives an observational constraint on the electron acceleration mechanism and electron propagation. 相似文献