Solar Radio Bursts on 16 February 1999

The 2.60–3.80 GHz spectrometer at the Beijing Astronomical Observatory (BAO) recorded a ‘decimetric pulsation’ event (DCIM) around the time 1999 0216 0300. At the beginning and end of this DCIM, two groups of reverse slope type III bursts (RS-III) are also detected; meanwhile, metric type II bursts are recorded by CULG and HIRA during the same time. These solar radio bursts on that day might be caused by the same active region 8458 and a same flare. We present a plausible qualitative model for all of them. This revised version was published online in July 2006 with corrections to the Cover Date.     

Positively Drifting Structures During the 18 March 2003 Solar Flare

We analyze the 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. The drifting structures take place before the soft X-ray maximum, almost at the maximum of hard X-ray flux at 25 – 50 keV. For the first time, the positive drift in this kind of radio structures is detected in such a high frequency range. Their global drifting rate is roughly estimated as 3.6 GHz s⁻¹. They appear in four groups, lasting in total for less than 6 s, and have a broad bandwidth of more than 2 GHz but a smaller ratio of the bandwidth of the drifting structures to mean frequency than that of the lower frequency range. The lifetime of each individual burst in this event can be derived by using the high temporal resolution of the spectrometer at PMO and has an average value of 36.3 ms. Since the negative drifting structures observed in the 0.6 – 4.5 GHz frequency range were interpreted to be a radio signature of a plasmoid ejected upward (moving out of the Sun), the present observation may imply that it is possible for a plasmoid to move downward during a solar flare. However, for a confirmation of this suggestion direct radio imaging observation would be needed.     

High-Frequency Evolving Emission Lines for the 25 August 1999 Solar Flare

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.     

A broadband spectrometer for decimeter and microwave radio bursts

Observations of solar microwave bursts with high temporal and spectral resolution have shown interesting fine structures (FSs) of short duration and small bandwidth which are usually superimposed on the smooth continuum. These FSs are very intense (up to 10¹⁵ K) and show sometimes a high degree of circular polarization (up to 100%). They are believed to be generated by electron cyclotron maser emission (ECME) in magnetic loops. Another type are the microwave type III bursts, which are drifting microwave FSs, and are probably the signatures of travelling electron beams in the solar atmosphere. The exact emission mechanisms for these phenomena, in particular the source configuration, the plasma parameters and the distribution of radiating electrons are not clear. For a detailed study of these problems new observations of intensity and polarization with high resolution in time and in frequency in decimeter and microwave wavebands are essential. In order to investigate these features in greater detail, spectrometers with high temporal and spectral resolution are being developed by the solar radio astronomy community of China (Beijing Astronomical Observatory (BAO), Purple Mountain Observatory (PMO), Yunnan Astronomical Observatory (YAO), and Nanjing University (NJU)). The frequency range from 0.7 to about 12 GHz is covered by about five spectrometers in frequency ranges of 0.7–1.4 GHz, 1–2 GHz, 2.4–3.6 GHz, 4.9–7.3 GHz, and 8–12 GHz, respectively. The radiospectrometers will form a combined type of swept-frequency and multi-channel receivers. The main characteristics of the solar radio spectrometers are: frequency resolution: 1–10 MHz; temporal resolution: 1–10 ms; sensitivity: better than 2% of the quiet-Sun level. We pay special attention to the sensitivity and the accuracy of polarization. Now, the 1–2 GHz radiospectrometer is being set up. The full system will be set up in 3–4 years.Presented at the CESRA-Workshop on Coronal Magnetic Release at Caputh near Potsdam in May 1994.     

Solar Partial N－burst

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.     

1998年9月23 日复杂太阳爆发射电联合观测的初步分析

利用北京天文台1998.09.23日1-2GHz和2.6-3.8GHz频谱仪观测到的一个Ⅲ-Ⅳ型复杂大爆发，结合俄罗斯SSRT和德国分米-米波动态频谱仪的观测资料，进行了初步的比对分析，拓展了关于日冕电子加速和日冕磁结构方面的一些研究内容，简单地注释了一些可研究的现象和运动Ⅳ型爆发及多重脉动的辐射机制。     

Active regions losing their moorings by subsurface reconnection

Eleven microwave spike events observed with the 2.6–3.8 GHz spectrometer of Beijing Astronomical Observatory (BAO) are analysed. The polarization degrees of spikes are variable, some spikes have frequency drift with the drift rate of several GHz s^–1. In particular, the time delay (8 ms) between the two polarization modes of spike is detected, which is different from previous results. According to the leading spot rule, we conclude that the o-modes arrive first. Moreover, the reversal of polarization sense versus frequency is also found. A change of the emission mode may be the cause of the polarization reversal.     

Transition region and coronal plasmas: instrumentation and spectral analysis

The plasma conditions in the solar atmosphere and, in particular, in coronal holes are summarized, before space-borne instrumentation for observing these regions in vacuum-ultraviolet light is briefly introduced with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) as example. Spectroscopic measurements of small plasma jets are then analyzed in detail. Magnetic reconnection is thought to be responsible for heating the corona of the Sun as well as accelerating the solar wind by converting magnetic energy into thermal and kinetic energies. The continuous outflow of the fast solar wind from coronal holes on ‘open’ field lines, which reach out into interplanetary space, then requires many reconnection events of very small scale sizes – most of them probably below the resolution capabilities of present-day instruments. Our observations of such an event have been obtained with the Solar and Heliospheric Observatory (SOHO) providing both high-resolution imaging and spectral information for structural and dynamical studies. We find whirling or rotating motions as well as jets with acceleration along their propagation paths in close spatial and temporal vicinity to the coronal jet. This revised version was published online in July 2006 with corrections to the Cover Date.     

Observations of Microwave Type-U Bursts

Two microwave type-U bursts observed with the 2.6–3.8 GHz spectrometer of Beijing Astronomical Observatory (BAO) are described and analysed in this paper. The microwave type-U bursts have very short durations (about 200 ms), narrow bandwidth, high-frequency drift rates of the ascending and descending branches, and a high degree of circular polarization (80%). The sense of polarization remains the same from the ascending to the descending branch.     

Spikes in solar radio bursts at frequencies near 3 GHz

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.     

Spatial and Spectral Behaviors of Solar Flares Observed in Microwaves

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.     

Spectral and photometric study of compact groups of compact galaxies

Results are presented from a spectral, photometric, and morphological study of two compact groups of compact galaxies (CGCG) from Shahbazian’s list. The observations were made on the 1.5-m ESO telescope and the 2.6-m telescope at the Byurakan Astrophysical Observatory (BAO) during 1999–2000. These data are compared with data for the Shahbazian compact group 4. A high spatial density of galaxies, ranging from 10000 to 100000 galaxies per Mpc³, is observed in all the groups that were studied. The discovery of a Seyfert Sy1 galaxy in the Shahbazian 355 compact group is especially noteworthy. The direct photographs of the CGCGs that were studied contain no signs of merging or tidal interactions among the members of these groups. This suggests that the galaxies in these dense systems have a common origin. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 347–353 (August 2007).     

Type III burst pair

We present a special solar radio burst detected on 5 January 1994 using the multi-channel (50) spectrometer (1.0–2.0 GHz) of the Beijing Astronomical Observatory (BAO). Sadly, the whole event could not be recorded since it had a broader bandwidth than the limit range of the instrument. The important part was obtained, however. The event is composed of a normal drift type III burst on the lower frequency side and a reverse drift type III burst appearing almost simultaneously on the high side. We call the burst type III a burst pair. It is a typical characteristic of two type III bursts that they are morphologically symmetric about some frequency from 1.64 GHz to 1.78 GHz on the dynamic spectra records, which indicates that there are two different electron beams from the same acceleration region travelling simultaneously in opposite directions (upward and downward). A magnetic reconnection mode is a nice interpretation of type III burst pair since the plasma beta 0.01 is much less than 1 and the beams have velocity of about 1.07×10⁸ cm s^–1 after leaving the reconnection region if we assume that the ambient magnetic field strength is about 100 G.     

太阳微波尖峰辐射的高时间、高频率分辨率偏振观测

利用北京天文台 ２．６—３．８ ＧＨｚ频谱仪的观测资料,找到 １１个微波尖峰辐射事件．尖峰一般具有数十毫秒的寿命,数百个ｓｆｕ的流量密度和数十至数百ＭＨｚ的带宽,这与以前的报道类似．尖峰的偏振度各式各样,有的尖峰还有数千ＭＨｚ／ｓ的频率漂移．某些尖峰在二个偏振态之间有８毫秒的时间延迟（最大延迟可达１６毫秒）．另外,还发现了尖峰的偏振度随频率剧烈变化的偏振反转现象．     

Microwave Patch Structures on 12 June 1998

A microwave patch event observed with the 2.6–3.8 GHz spectrometer of Beijing Astronomical Observatory (BAO) on 12 June 1998 is described in detail in this paper. The patches show high flux densities, high polarization degree, extremely narrow bandwidth, and high spectral indexes. These observational characteristics may suggest that the favored emission mechanism is plasma or maser emission rather than gyrosynchrotron emission.     

Variations in the integral fluxes and structure of the radio source 3C120

The variability of the radio source 3C120 is studied using data from the international geodesic VLBI observation programs at 8.6 GHz and regular monitoring over frequencies of 4.8–36.8 GHz carried out at the Crimean Astrophysical Observatory (Ukraine) and the Radio Astronomy Observatory of the University of Michigan (USA). A combined analysis of the integral fluxes and structures on millisecond scales reveals the existence of flares at high frequencies accompanied by the appearance of new VLBI components at centimeter wavelengths. It is found that the variations in the fluxes for 3C120 at various radio frequencies have delayed maxima at low frequencies, and the flare of 1998 was accompanied by the birth of a new superluminal component. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 325–334 (August 2007).     

2.6--3.8 GHz太阳微波爆发中的精细结构

根据1994年lslike＆Benz给出的1－3GHz频带上的微波III型爆发和微波尖峰辐射的分类定义,分析北京天文台26－3．8GHz频带上观测到的微波爆发的精细结构．通过分析发现该定义有局限性．本文重新定义了该波段上的微波III型爆发和微波尖峰辐射,并讨论了这种分类定义与设备时间分辨率的关系     

Gauge-Invariant Helicity for Force-Free Magnetic Fields in a Rectangular Box

The Atacama Large Millimeter/sub-millimeter Array (ALMA) is a large interferometer that will consist up to 64 high-precision antennas operating in the 31.3 – 950 GHz frequency range. In this frequency range, which is largely unexplored, unique observations with a broad range of scientific objectives (cosmology, cold universe, galaxies, stars and their formation, planets and so on) are expected. Among these tasks there is a unique possibility to observe the Sun and to address several outstanding issues of solar physics. First, the ALMA is briefly described and then the new ESO-ALMA European node (ARC), built at Ondřejov Observatory, is presented. In Europe, this ARC is the only one oriented to solar physics. Consequently, the requirements and limitations for ALMA solar observations, as well as some examples of possible solar-oriented ALMA projects, are shown. A procedure of the preparation and submission of proposals for ALMA observations is mentioned.     

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.     

Frequency Distributions of Microwave Pulses for the 18 March 2003 Solar Flare

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.