On the correlation of microwave bursts with the Hα flares

High correlation between microwave bursts and H_α flares has already been reported. However, Solar Maximum Year cooperation made it possible to do simultaneous observations of selected active regions with good spatial resolution. In this paper the results of the direct comparison of solar microwave recordings at the Metsähovi Radio Research Station and H_α films at the Hvar Observatory are reported. This comparison reveals that the correlation of microwave gradual rise and fall (GRF) events (time scale tens of minutes) with H_α flares is practically 100 percent. On the other hand the correlation of the impulsive microwave bursts (time scale tens of seconds) with H_α flares is low. From this it can be concluded that the main contribution to the microwave GRF bursts comes from thermal radiation.     

CME影响下L1点附近等离子体及共生微波爆发的射电辐射机制研究

CME在产生和发展过程中与日冕和行星际介质相互作用并发出不同波长的射电辐射．在研究了无CME时空间等离子体的各种辐射机制基础上,统计分析了1999年2月至1999年8月期间有较大的CME发生情况下,在CME影响下L1拉格朗日点附近等离子体参数发生变化后的射电辐射机制．分析结果表明,其射电辐射机制主要是轫致辐射、微量的回旋辐射和更加微弱的复合辐射．此外,分析讨论了1999年2月至1999年8月期间与CME共生的太阳微波爆发．分析结果表明,与CME共生的是微波逐渐型爆发、尖峰爆发,其辐射机制主要是轫致辐射、回旋共振辐射、等离子体辐射及电子回旋脉泽辐射．     

太阳射电微波爆发的频谱分析

1981年4月1日太阳发生一个4N级Hα耀斑并伴随出现强烈的IV型射电爆发.本文对北京天文台,西澳大利亚站等射电资料进行分析.分析表明:(1)该事件的微波源状态相对稳定,米波源位置存在移动,因此产生微波辐射与米波辐射是两组不同的电子群体,在爆发频谱指数的时变曲线上表现出明显的形态差异.还由于两者辐射源的位置不同,微波与米波的爆发在峰值时刻上也不完全符合.(2)4月1日微波大爆发是由三个主爆发组成的,它们的峰值时刻分别为0135.1,0146.1,0153.6UT.由射电高频端谱指数算出的非热电子能谱指数表明,在射电爆发的三个峰值时刻电子能谱都变硬.本文还得出该活动区的非热电子平均速度(以光速c为单位)β为0.9左右,磁场强度B为430G.并由回旋同步辐射阻尼算得,非热电子的寿命为829秒,这个数值与三个主峰的持续时间相吻合.     

Radio emissions from Uranus

The Voyager Planetary Radio Astronomy Experiment detected strong 40 kHz to 850 kHz radio emissions from Uranus after closest approach and somewhat weaker emissions, but none above 100 kHz before closest approach, on the dayside of Uranus. The time variations of these emissions closely match Uranus' rotation, in a period of 17.24 h, and are evidently controlled by the strength and shape of its magnetic field. Throughout the entire encounter the polarization of the emission was approximately lefthand, corresponding to extraordinary mode. The emission associated with the nightside pole was a relatively smooth continuum (free of bursts) with a Gaussian-shaped rise and fall at low frequencies, 200 kHz for example, but a Gaussian with a central dip nearly to zero lasting a little less than two hours at frequencies above 400 kHz. Half a rotation later, when Voyager was near the magnetic equator of Uranus and farthest from the nightside dipole tip, the continuum emission was absent, but very strong, narrowband impulsive bursts appeared. Voyager successfully acquired one brief (24 seconds long) record of high time resolution radio observations in the range 500 to 700 kHz. This record, which was made near closest approach, shows a hierarchy of fast variations. Several days after closest approach, at the times of bowshock crossings outbound, the continuum emissions were modulated strongly in a manner suggestive of the presence of waves in the bowshock regions.

The instrument also recorded possible Uranian electrostatic discharges, vertex early arcs occurring in sequences of more than a dozen events with approximately ten-minute period, and, as early as several days before closest approach in the frequency range below 100 kHz, very intense isolated bursts lasting tens of minutes.     

On the effects of electron-cyclotron masers during flares

First recognized by Wu and Lee (Ap. J. 230, 621, 1979), electron-cyclotron masers can be activated under very mild conditions. Large growth rates can occur even for relatively mild anisotropies in the electron velocity distribution, e.g., the one-sided loss cones that commonly occur when electrons with small pitch angles precipitate into high density regions at the footpoints of flaring loops while others are reflected in the converging field in the corona. Maser action can plausibly occur at the second harmonic of the local gyrofrequency and so explain certain very bright (? 10¹⁰ K) microwave bursts from the sun and other stars. However, the preponderance of the energy is at the first harmonic.We suggest that masers operating at the local gyrofrequency in a flaring loop generate radiation at decimeter wavelengths that is a significant fraction of the total energy of the flare, in fact (and not coincidentally) comparable with the energy in electrons associated with hard X-ray bursts. Essentially all of the radio energy is trapped in the corona and serves to produce localized heating in a volume large compared with the energy release region. Thus it can transfer energy by radiation from one magnetic loop to another, possibly inducing further instabilities, and spreading the course of the flare. Eventually the energy probably escapes the corona as soft X-rays. The electron-cyclotron maser saturates by extracting the perpendicular energy of the electrons, thereby diffusing them into the loss cone at the maximum possible rate; the enhanced precipitation into the footpoints can produce bright emission in hard X-rays, EUV and Hα and remove any necessity for directive acceleration in the energy release region.Details of the proposed mechanism and effects are contained in two papers by Melrose and Dulk (Ap. J. 259, 1982).This work was sponsored by NASA under grants NAGW-91 and NSG-7287 to the University of Colorado.     

Observations of solar radio bursts from meter to kilometer wavelengths

Using the Clark Lake Radioheliograph data we present direct evidence that type III electron streams propagate in dense coronal streamers. We also present imaging observations of meter-decameter microbursts, which appear to be similar to those observed in hard X-rays. At meter-decameter wavelengths, these microbursts appear to be due to plasma radiation. From observations made with ISSE-3, we discuss the characteristics of hectometer and kilometer wavelength radio bursts. In particular, we show that from studies of type III storms that the exciter electrons propagate along spiral structures, where the density is enhanced and that there is an acceleration of the solar wind. We discuss type II bursts at kilometer wavelengths, compare them with meter type II bursts and discuss their association with interplanetary shocks. We show that the interaction between type III electron streams and shocks at kilometer wavelengths can provide information on the interplanetary shock geometry. Finally, we discuss the possibility that some shock associated (SA) events may be emissions caused by electrons accelerated lower in the atmosphere rather than high in the corona in type II shocks.Recent advances in solar research have resulted from new work on plasma radiation theory, new observations of active regions and flares across the electromagnetic spectrum and the availability of spacecraft in situ measurements of solar ejecta. In this paper, we review some results obtained with the Clark Lake multifrequency radioheliograph at meter-decameter wavelengths and from satellite multifrequency directive observations at hectometer and kilometer wavelengths. We present evidence that type III electrons propagate in dense coronal streamers, and that frequently observed microbursts (presumably of type III) at meter-decameter wavelengths are due to plasma radiation. We discuss observations of hectometer and kilometer type III radio storms which reveal information about active region structures, interplanetary magnetic field configuration, and solar wind acceleration. We also discuss kilometer type II bursts, interactions between type III electrons and interplanetary shocks, and present some new results on shock associated (SA) events.     

同无黑子耀斑相协的微波爆发机制的探讨

1980—1984年期间,我们在云南天文台9375MHz,3653MHz和2902 HHz三个波段的射电观测资料中,查到11组微波爆发与无黑子耀斑相伴随。本文研究了这些爆发与耀斑的大气层高度,射电爆发类型以及通过落进峰值流量-时间图的位置,确认出爆发机制是活动区中作麦克斯韦分布电子的热轫致辐射。     

从射电频谱指数的变化推求非热粒子能谱指数的变化

本文提出了一种由射电爆发的频谱指数α去推求电子能谱指数δ的方法;并对质子事件能谱指数和爆发峰值时的射电频谱指数之间作了相关统计,得到相关系数为0.70.以1972年8月7日15h22mUT的大爆发为例,在不同频率上进行了计算.由不同时刻的α所算得的δ值表明,在爆发峰值之前,电子能谱近似地可用幂律分布来表示;而在峰值之后,则与幂律分布有所偏离.在爆发脉冲相的20分钟时间内,δ值的变动范围约为0.4—3.6.      

太阳微波爆发精细结构与硬X射线耀斑的相关

北京天文台在２．８４ＧＨｚ频率上观测到的带短时标精细结构的微波爆发与日本ＹＯＨＫＯＨ卫星上ＨＸＴ在１９９１年１０月－１９９２年１２月观测到的硬Ｘ射线爆发（ＨＸＢ）事件作了比较，发现在２０个微波精细结构爆发事件只有１２个与ＹＯＨＫＯＨ卫星记录的ＨＸＢ有对应关系．本文对１９９２年６月７日典型事件中２．８４ＧＨｚ与ＨＸＢ共同存在的百秒量级的准周期振荡作了分析及源区参数的计算，并作了简要的讨论．     

HALE 17590 活动区的爆发辐射

本文根据1981年HALE 17590 太阳活动区的观测资料,着重分析了它的射电辐射特性后发现:(1)在光学活动区发展的上升阶段,每串射电爆发的强度也有由弱到强的变化,其频谱由单调谱变成不规则谱和U型谱;(2)对大的耀斑爆发而言,射电爆发的先兆相比X射线爆早。在射电先兆相期间常伴有谱斑增亮和暗条激活等现象;(3)大耀斑爆发的脉冲极大时刻在射电8毫米波段到来最早。      

Relative positions of microwave and hard X-ray burst sources

Simultaneous microwave and hard X-ray imaging observations of 12 bursts show that it is difficult to discern a general pattern between microwave and hard X-ray burst locations. In general, the microwave source is displaced from the hard X-ray source. The commonly believed behavior of the microwave source being located near the top and hard X-ray source near the footpoints of a loop appears to be true in some cases but not all. If the burst source is simple, both may be located near loop tops. Sometimes when the hard X-ray source has two components, one weak and one strong, the microwave source is not located over a neutral line (loop top) but close to a sunspot where the magnetic field is strongest. It appears that more than one loop or arcade may sometimes be involved in the microwave and hard X-ray emission. This is particularly true when several interacting loops trigger the onset of a flare.     

A homologous microwave flare on May 29, 1980

Two homologous solar bursts were recorded on May 29, 1980 at 1028 UT and at 1147 UT from the Hale region 16864. The measurements were done at 8 mm wavelength at the Metsähovi Radio Research Station using a 14 meter radio telescope. The time series of the bursts were similar even in the small details. The rise time of both bursts was about 10 seconds and the peak flux density was 3.3 sfu at 1028 UT and 1.2 sfu at 1147 UT. Both bursts were composed of several elementary spikes which were typically 3 seconds apart from each other. The maximum of the gyro-synchrotron type spectrum was close to 15 GHz. The time profile of the bursts, elementary spikes and the frequency spectrum indicated that the origin of these homologous microwave bursts was in a magnetic structure with several loops and that the same complex loop structure was producing energy during both bursts.     

Length scales for September 14, 2005 solar noise storm

Source length scales are estimated for the September 14, 2005 solar noise storm from the spectral and temporal observed characteristics of the background continuum fluctuations and clusters of Type I bursts. The characteristic height of the magnetic structure where the noise storm source is located and the size of the source where Type I bursts clustering takes place were calculated. A lower limit for the height of the magnetic structure supporting the noise storm at 237 MHz was estimated too.     

Microwave Type U and RS Bursts in the X2.2 Solar Flare on 15 February 2011

Two groups of microwave type U and Reverse-Slope (RS) bursts after the Soft X-Ray (SXR) maximum were observed with the 2.6～3.8GHz spectrometer of Chinese Solar Broadband Radio Spectrometers (SBRS/Huairou) on 15 February 2011, when an X2.2 solar flare occurred in the Active Region (AR) NOAA11158. A Shear-driven Quadrupolar Reconnection (SQR) model was utilized to analyze these bursts and the two loops involved were found to be basically in the same spatial scale and have a height difference of about 1300km. These bursts were interpreted to be a result of a new reconnection process between the two similar-scaled loops.     

Effects of the photo-ionized absorber on the continuum spectra of EXO 0748–676

We report on the analysis of XMM-Newton archival data of EXO 0748–676. We studied changes of the continuum spectra due to the presence of photo-ionized plasma on the line of sight. We show that the ionization degree of the plasma could change largely during the X-ray bursts and the dips. These changes can significantly modify the soft-band spectrum, which was in fact observed from EXO 0748–676. We discuss the effect of the photo-ionized plasma on the continuum spectra in comparison with a frequently used model such as partial covering absorption.     

Stellar absorption lines in the spectra of Seyfert galaxies

We have measured the strengths of Ca II triplet and Mgb stellar absorption lines in the nuclear and off-nuclear spectra of Seyfert galaxies. These features are diluted to varying degrees by continuum emission from the active nucleus and from young stars. Ca II triplet strengths can be enhanced if late-type supergiant stars dominate the near-IR light. Thus, objects with strong Ca II triplet and weak Mgb lines may be objects with strong bursts of star formation. We find that for most of our sample the line strengths are at least consistent with dilution of a normal galaxy spectrum by a power law continuum, in accord with the standard model for AGN. However, for several Seyferts in our sample, it appears that dilution by a power law continuum cannot simultaneously explain strong Ca II triplet and relatively weak Mgb. Also, these objects occupy the region of the IRAS color-color diagram characteristic of starburst galaxies. In these objects it appears that the optical to near-IR emission is dominated by late-type supergiants produced in a circumnuclear burst of star formation.     

Gamma-ray burst detection capabilities of comptel

The imaging gamma-ray telescope COMPTEL, capable of detecting gamma rays in the 1 to 30 MeV range, is one of four experiments onboard NASA's Gamma-Ray Observatory GRO. Besides its primary objectives COMPTEL will contribute to the understanding of cosmic gamma-ray bursts. Summarising, COMPTEL localises bursts (S (E > 1 MeV) ≥ 2.10⁻⁶ erg/cm²) within 1 sr FOV to better than 1° at medium gamma-ray energies, measures continuum energy spectra in the range 0.1 MeV to 20 MeV with fluence S ≥ 6.9 10⁻⁷ erg/cm² (5σ, E≥100 keV), measures gamma-ray lines with detector resolution 9.6% (at 0.5 MeV) and 7.0% (at 1.5 MeV) and determines time histories of both gamma-ray line and continuum emission with t ≥ 0.1 sec resolution.     

射电爆发显著事件与Ⅱ型爆发

本文分析了北京天文台2840MHz射电望远镜,1989年1月-1993年12月期间观测到的太阳射电爆发的显着事件与米波Ⅱ型、Ⅳ型爆发的对应关系,从相关结果来看,爆发的峰值流量越高△T越短,这说明当太阳流量越大,高达500s.f.u.以上时,Ⅱ型爆发会在爆发的峰值前后很短时间内发生,可能与粒子的加速有关。      

Radio observations of total solar eclipse of November 3, 1994 at Chapecó (Brzil)

Radio observations of the eclipse on November 3, 1994, were carried out at Chapecó, Brazil by using a decimetric spectrograph having high spectral and time resolution. The light curve shows that: (1) Time variation of the radio flux before the totality was more compared to that after. (2) During the totality radio emission at 1.5 GHz was observed. Advantage of high spatial resolution ( 3.2 arc sec) possible during solar eclipse enabled us to determine the height of radio emission at 1.5 GHz. (3) Microwave bursts were observed associated with metric Type III-RS bursts. The source size of one of the microwave bursts was 7 arc sec and its physical parameters have been estimated. (4) The time difference between radio and optical contacts suggested for the first time asymmetrical limb brightening at 1.5 GHz.     

Preliminary observing achievements of supersoft X-ray detector and γ-ray detector onboard Shenzhou2

Preliminary observing achievements by the Super Soft X-ray Detector and the γ-ray Detector in the fields of cosmic gamma-ray bursts, solar X-ray, bursts and cosmic X-ray/γ-ray background radiation are summarized. The detectors are aboard the spacecraft Shenzhou-2 that was launched on 2001 January 10. The scientific mission and general situation of the instruments are briefly described.