位于日冕微波区的微波Ⅲ型爆发界面频率的发现

在北京天台１．０－２．０ＧＨｚ射电频谱仪记录到的１９９４年１月５日爆发图上，首次发现一界面频率位于１２４０ＭＨｚ与１３４０ＭＨｚ之间的微波Ⅲ型爆发对，其频率漂率为－０．２２ＧＨｚ／ｓ和＋０．２３ＧＨｚ／ｓ由此推出电子加速区位于光球之上，３．７×１０＾４ｋｍ的高度，电子加速区及Ⅲ型爆发形成区的高度范围约为１０００公里，而电子束的速度相应为０．１０２ｃ及０．１０６ｃ。     

微波爆发区的日冕磁场研究

回顾了日冕磁的研究历史，介绍了我们首镒提出的日冕磁场的微波诊断方法及其应用的带来的启迪，提出进一步开展日冕磁场及其相关研究的建议。     

米波射电毫秒级SPIKE-Ⅲ型爆发与日冕电子加速过程的研究

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,和在处理资料时 一些共生毫秒级Ｓｐｉｋｅ的Ⅲ型爆发,它们的不同形态提示了Ⅲ型爆发和毫秒级Ｓｐｉｋｅ的发生关系。通过两个典型事件的分析,根据Ｓｐｉｋｅ和Ⅲ型爆发出现的 时序以及形态的连续和转换特性,证实了日冕电子加速区位于毫秒级Ｓｐｉｋｅ爆发和Ⅲ型爆发的源区之上,由观测指出Ⅲ型爆发对应的界面频率是位于２５０ＭＨｚ附近,并试图用等离子假设     

微波Ⅲ型爆发与日冕物质抛射的统计分析

对国家天文台2.6～3.8GHz频谱仪在第23太阳活动周上升段(1996～1998)记录到的Ⅲ型爆发,与日冕物质抛射(CME)作了统计分析。发现微波Ⅲ型爆发可能是CME的先兆现象,并讨论了它们的辐射机制。     

微波Ⅲ型爆发与日冕物质抛射的统计分析

对国家天文台2．6～3．8GHz频谱仪在第23太阳活动周上升段(1996～1998)记录到的Ⅲ型爆发，与日冕物质抛射(CME)作了统计分析。发现微波Ⅲ型爆发可能是CME的先兆现象，并讨论了它们的辐射机制。     

一个微波爆发的源区磁场和高能电子的能流估计

本文分析了１９９３年１０月２日０７：３９：４０－０７：４１：００ＵＴ时段太阳产生的一个多脉冲微波暴的观测，认为它是由多个脉冲爆发叠加在一个慢变爆发背景上组成的．根据谱分析和利用我们的日冕磁场诊断公式［１］，第一次获得了一个爆发源区的磁场强度和高能电子的信息，其主要结果是：（１）脉冲爆发分量在光薄部分的射电谱指数的平均值比慢变爆发背景的值小１，即前者的谱比后者的硬．在１９．６ＧＨｚ上的亮度温度前者比后者高６倍．（２）从脉冲爆发分量和慢变爆发背景分量推断的源区磁场平均值分别为１５８和５３１高斯，且发现在爆发期间，慢变暴源区磁场强度随时间圣马鞍形变化，在极大相的值比脉冲相和下降相低约５０％（３）产生脉冲暴分量的高能电子的柱密度ＮＬ和数密度Ｎ（＞Ｅ０）分别为慢变暴分量的４％和８％，但它们所携带的能流和发射系数要比慢变爆发分量的值高１倍和８倍！表明这两种爆发成份可能分别来自能谱不同的两群电子在不同爆发源区的辐射．     

微波Ⅲ型爆发的观测特征

统计分析了国家天文台2．6-3．8 GHz高时间分辨率射电动态频谱仪在23周峰年期间(1998．4—2003．1)观测到的266个III型爆发．对这些事件的频率漂移、持续时间、偏振、带宽、开始和结束频率做了详细分析．开始和结束频率的统计分析表明,开始频率在一个非常大的范围,从小于2．6 GHz到大于3．8 GHz,而结束频率的截止区相对集中,从2．82-3．76 G．Hz．这些现象说明,电子加速的高度相当分散,在观测频率范围内具有正、负漂移率的III型爆发数基本相等,这可能意味着被加速的向上和向下传播的电子束在2．6—3．8 GHz范围有相同的比例．统计结果表明,微波III型爆发的辐射机制主要是等离子体辐射和电子回旋脉泽辐射过程．     

关于日冕双向电子束的加速问题

介绍了云南天文台和北京天文台频谱仪所观测到具有正、负频漂的米波Ⅲ型爆发和微波尖峰辐射.对双向电子束源的频率和高度进行了估计.2个事件都表明在具有正、负频漂率的爆发之间有一分界频率(250和2900MHz),这说明爆发源是一个复杂加速源,电子束同时向上、下2个方向注入.由本文的2个事例可以说明1.双向电子束的转换(changeover)范围是在250～2900MHz的宽频带里,并且起源是在很小范围(4～70MHz)内.这些电子束从高层到低层日冕都有一个很窄的独立加速区,文中的Ⅲ型爆发对可能是它们的等离子体辐射现象.2.在低日冕分离开放磁场和闭合磁场的电流片,以及高日冕相反方向的开放磁力线的交叉区域可能都是双向电子加速区.从闭合磁场到开放磁场的磁拓扑范围将是很大的(大约在光球上2×104km到10.7×104km).     

由对偶的Ⅲ型射电爆发观测探讨日冕双向电子束的起源问题

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。     

Microwave Type III Burst Group in the 1993 October 2 Flare

Microwave Type III bursts with positive frequency drifting rate were found by Stahli and Benz (1987) for first time. Type III events are especially interesting because they are well-known to be signatures of electron beams in coronal plasma, and they are effective means for diagnosting of source plasma. A microwave burst consisting of some microwave type III burst groups was registered at Beijing Astronomical Observatory with the 2545–2645–2840 MHz synchronous observing system. The distributions of frequency drifting rate, half power duration, and intensity for each impulse in the groups have been statistically analysed. From this analysis, some important parameters for the dynamic process in the flare are deduced and discussed.     

A Type IV Radio Burst Associated with Type III Burst,Pulsation and Spike Emissions

A type IV radio burst accompanied by several normal- and reverse-drifting type III bursts, multiple long-term quasi-periodic pulsations and spikes was observed with the radio spectrometers (1.0–2.0 and 2.6–3.8 GHz) at National Astronomical Observatories of China (NAOC) on 23 September 1998. In combination with the images of Siberian Solar Radio Telescope (SSRT) of Russia, the complex and multiple magnetic structures inferred from the radio bursts reveal the existence of both large-scale and small-scale magnetic structures. This event suggests that the geometries of coronal magnetic fields contain multiple discrete electron acceleration/injection sites at different heights, and extended open and closed magnetic field lines. It can be shown that the energetic electrons gain access to open, diverging and closed field lines thus producing different types of radio bursts. From the characteristics of position, polarization, dispersion and displacement of the sources, the model of the type IV event is supported, which involves synchrotron emission from the electrons confined by the rapid scattering through the interaction of hydromagnetic wave with particles.     

太阳微波M型爆发

分析北京天文台１９９８年４月１５日观测到的一个太阳微波Ｍ型爆发事件．Ｍ型爆发实质上是Ⅲ型爆发的一个次型,它由两个连续的Ｕ型爆发所组成,即爆发源在同一个磁环中由于磁镜的作用而连续往返运动后的轨迹,但是在低时间分辨率（０．２ｓ）记录资料中却是 Ｕ型爆发的形态．因此高时间分辨率（８ ｍｓ）的记录资料能更准确地反映Ｍ型爆发源的真实运动情况．对比组成Ｍ型爆发的两个Ｕ型爆发,可以看到,该磁环很可能处在下降的演化阶段．最后讨论该磁环可能的空间分布．     

The Energetic Spectrum of Non-Thermal Electrons in an Acceleration Region Calculated From a Solar Microwave Type III Burst with both Positive and Negative Frequency Drifts

A typical event of solar microwave type III burst with both positive and negative frequency drifts was observed by the 1–2 GHz spectrograph at Beijing Observatory on January 5, 1994. The separatrix frequency (1.3 GHz) may correspond to an acceleration region. The energy of the electron beam responsible for the burst is calculated from the drift rate and the height of the source above the photosphere. Moreover, if the solar microwave type III burst is explained by the beam-plasma instability as suggested by Huang (1998), the energy density as well as the particle density of the electron beam may be estimated from the burst flux, the growth rates and the modularity (Huang et al., 1996). So that, a very good power- law distribution is simulated for the energetic spectrum of the electron beam in this event with a spectrum index 4.5. The electron beam may be accelerated by an electric field with a length of 10⁷ m and a strength of <10-4 V m- 1. These results are necessary for understanding the acceleration process in solar flares. This revised version was published online in July 2006 with corrections to the Cover Date.     

Densities Probed by Coronal Type III Radio Burst Imaging

We present coronal density profiles derived from low-frequency (80?–?240 MHz) imaging of three Type III solar radio bursts observed at the limb by the Murchison Widefield Array (MWA). Each event is associated with a white-light streamer at larger heights and is plausibly associated with thin extreme-ultraviolet rays at lower heights. Assuming harmonic plasma emission, we find average electron densities of 1.8\(\times10^{8}\) cm^?3 down to 0.20\(\times10^{8}\) cm^?3 at heights of 1.3 to 1.9 R_⊙. These values represent approximately 2.4?–?5.4× enhancements over canonical background levels and are comparable to the highest streamer densities obtained from data at other wavelengths. Assuming fundamental emission instead would increase the densities by a factor of four. High densities inferred from Type III source heights can be explained by assuming that the exciting electron beams travel along overdense fibers or by radio propagation effects that may cause a source to appear at a larger height than the true emission site. We review the arguments for both scenarios in light of recent results. We compare the extent of the quiescent corona to model predictions to estimate the impact of propagation effects, which we conclude can only partially explain the apparent density enhancements. Finally, we use the time- and frequency-varying source positions to estimate electron beam speeds of between 0.24 and 0.60 c.     

从一个微波C型爆推算到的高能电子数

本文分析了Sag。Hill天文台观测到的1989年3月6日在1353 UT左右发生的一个罕见的大C型爆,即延伸型耀斑大爆发。假设射电辐射来自处于磁环顶部的均匀源,采用合适的日冕磁场值(100高斯),可推算出射电源中的非热电子总数N_R(5.6×10~(37)),这与一个标准硬X射线发射(I_p=10~6ε~(-3.5))的薄靶模型所预计的非热电子总数N_X(2.8×10~(37))相近。由此表明这两类辐射可能有共同的或紧密相关的非热电子分布起源。文中还用统计规律估算该事件的硬X射线大于30keV以上各通道的总记数率,即HXRBS峰率F_X为1.1×10~5s~(-1)。 文中还分析了长期存有争论的N_R与N_X相差10~3—10~5的原因,可能主要是N_R估计不准。这种估计不准,除理论原因外,还有流量测量精度不够的原因。如流量测量误差在±30％时,就可使N_R的估计值相差10~2—10~3。     

一个太阳微波射电爆发中的快速脉动现象

１９９０年７月３０日观测到一个射电大爆发,其中在２８４０ＭＨｚ射电爆发的峰值附近,发现了周期约为３０ｍｓ的快速脉动现象,脉动是窄带的,调制度约为５０％。     

太阳微波低频段射电III型爆发的一些特性分析

本文介绍了云南天文台四波段（１．４２,２．１３,２．８４和４．２６ＧＨｚ）太阳射电高时间分辩率同步观测得到的五个微波ＩＩ型爆发事件,它们具有宽频带、长和短寿命、内向和外向快速频漂等特征．观测事例表明,非热电子束引起的等离子体辐射和电子回旋脉泽辐射两种机制都可能发生．这些观测特征既不完全同于米波—分米波ＩＩ型爆发,也不完全同于微波高频段ＩＩ型爆发,说明在微波低频段可能存在二重性或过渡现象     

Type III Bursts Associated with Millisecond Spikes Which Occurred Within the Frequency Range from 230 to 300 MHz

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.