1991年6月6日与白光耀斑共生的微波大爆发

本文简要地介绍了发生于２５４５ＭＨｚ和２６４５ＭＨｚ频率上的一次与白光耀斑共生的微波射电大爆发。该爆发有很高的峰值流量，很高的偏振度和很复杂的偏振状态的变化．同时该爆发的第一主峰期间同时观测到色球层白光耀斑连续辐射。本文还简要地讨论了这次射电爆发与色球白光耀斑的时间演化关系及射电爆发在主峰期间偏振状态急剧变化的原因。     

The unusual X-ray light curve of GRB 080307: the onset of the afterglow?

Swift -detected GRB 080307 showed an unusual smooth rise in its X-ray light curve around 100 s after the burst, at the start of which the emission briefly softened. This 'hump' has a longer duration than is normal for a flare at early times and does not demonstrate a typical flare profile. Using a two-component power-law-to-exponential model, the rising emission can be modelled as the onset of the afterglow, something which is very rarely seen in Swift -X-ray light curves. We cannot, however, rule out that the hump is a particularly slow early-time flare, or that it is caused by upscattered reverse shock electrons.     

The flares of July 6 and 8, 1968

From our analysis of the flares of July 6, 1968 and July 8, 1968 the following points emerge: 1) The limb flare of July 6 has been observed in white light for approximately ten minutes during the maximum emission of the electromagnetic radiations. This observation fits the preceding observations of white light flares. The radio flux and radio spectrum hint to the nature of a PF. Corpuscular radiation up to more than 190 MeV has been detected from the spacecraft, Pioneer 6 and Pioneer 7. 2) The region of the proton flare has been characterized by the presence of a Delta magnetic configuration very probably due to the interaction of two different solar centers. This circumstance is quite common in the elaboration of the most active regions. 3) The flare of July 6 has been followed on July 8 by a similar event both for the optical appearance and for the associated electromagnetic radiation. 4) The flare of July 8 has shown the characteristics of the proton flares: coverage of the spots, scission in two ribbons, outstanding radio microwave emission, type IV burst, U radio spectrum etc..., however it has not been followed by a particle flux at the Earth (PCA) or measured in space by the satellites.     

太阳射电IV型爆发及伴随现象与白光耀斑的关系

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．     

High resolution observations of white‐light emissions from the opacity minimum during an X‐class flare

Using high cadence, high resolution near infrared (NIR) observations of the X10 white‐light flare (WLF) on 2003 October 29, we investigated the evolution of the core‐halo structure of white‐light emission during the two‐second period flare peak. We found that size and intensity of the halo remained almost constant in the range of 10 Mm². However, the core area was very compact and expanded rapidly from about 1 Mm² to 4 Mm². At the same time, the total emission of the core increased nearly twenty times. This distinct behavior indicates that different heating mechanisms might be responsible for core and halo emissions. In addition to the temporal analysis, we compared the intensity enhancements of the flare core and halo. The result shows that the halo contrast increased by about 8% compared to the flare‐quiet region, which could be explained by a combination of direct‐heating and backwarming models (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Visual and photographic white light flare observations of 4 July 1974

Visual impressions and a photograph of an intense white light flare are presented. A densitometer trace across the 4 July 1974 flare showing relative intensity of the white light flare, photosphere and umbra is also shown. A second white light flare is suspected on a photograph taken 43/4 hrs later. Both flares coincide in time with major H-flare activity.     

The GLE-associated flare of 21 August, 1979

We use a variety of ground-based and satellite measurements to identify the source of the ground level event (GLE) beginning near 06∶30 UT on 21 August, 1979 as the 2B flare with maximum at ～06∶15 UT in McMath region 16218. This flare differed from previous GLE-associated flares in that it lacked a prominent impulsive phase, having a peak ～9 GHz burst flux density of only 27 sfu and a ?20 keV peak hard X-ray flux of ?3 × 10^-6 ergs cm^-2s^-1. Also, McMath 16218 was magnetically less complex than the active regions in which previous cosmic-ray flares have occurred, containing essentially only a single sunspot with a rudimentary penumbra. The flare was associated with a high speed (?700 km s^-1) mass ejection observed by the NRL white light coronagraph aboard P78-1 and a shock accelerated (SA) event observed by the low frequency radio astronomy experiment on ISEE-3.     

Analysis of spike emission data at 2545/2645 MHz in the peak year of the 22nd solar cycle

We briefly discuss the observed features including the high flux density, short duration, narrow emission band, fast frequency drift, quasi-periodic oscillation and fast variation of polarized components, of 51 spike emission events observed at 2545/2645 MHz in the solar activity peak year, 1991 January–December, and carry out correlation analysis between these events and optical flares, magnetic field intensity and configuration of flare regions, and sunspot evolution types of active regions. In view of the fact that the observed and statistical characteristics of the spike emissions are very different from those of known types of solar radio burst and known solar radio components, we think that the spike emission in the peak years is probably a new type of radio burst excited by electron cyclotron maser instability under wave-particle resonance, or a new solar radio component.     

A brief description of observational results from the supersoft X-ray detector aboard Shenzhou-2

Observational results from the supersoft X-ray detector (SD) aboard the spacecraft Shenzhou-2 are briefly described. The resultspertain to cosmic γ-ray bursts solar x-ray bursts, high-energy charged particles and soft X-ray background radiation. The detector is a proportional counter with a polypropylene thin-film window of 50 mm diameter, it operates in the energy range 0.23–3.0keV covered by six energy channels. Two grades of time resolution are used: 40 ms for recording burst events and 520 ms when there is no triggering signal resulted from a burst event. Figures 1 and 2 show the light curves and energy spectra of two cosmic γ-ray bursts (starting time 2001 Jan 17, 09:37:25.21 UT and 2001 Mar 9, 12:33:55.692 UT), and Figures 3 and 4, the results on two solar X-ray burst (2001 Apr 6, 19:14:09.11 UT, and 2001 May 20, 06:02:12.58 UT). The detector records the ambient high-energy charged particles when there is no burst event and the shutter of the window is closed. 110 data sets of high-energy charged particles along the spacecraft orbit have been collected. As examples, the variations of the particle counting rate along the orbit are shown in Figs. 6a, 6b, 8e, 8f and 7. More than 10 events of particle precipitation induced by solar proton events have also been recorded, some of which are displayed in Figs.6c–6f and 7. Some of the data of soft X-ray background radiation shown in Fig. 8 were obtained when the shutter was open, and they are important for the data processing of the burst events.     

Measurement of linear polarization in the Hα line in solar flares

Large solar telescopes built at places with a quite excellent seeing, equipped with a sophisticated optics and control system are too expensive and unique to be used currently in hunting of sudden and short‐lasting activity events, e.g. flares and eruptive prominences. For a systematic observation of selected kinds of active phenomena it is still necessary to use smaller or medium‐sized telescopes equipped with a special setup of devices. Detection of linear polarization in the Hα line emitted in a flare seems to be just a right task and delicate matter for such a systematic observation. This kind of polarization is supposed to be generated by particle beams accelerated in thke corona and directed towards denser chromospheric layers where the particle beams deposit their kinetic energy. As the accelerated particle beams possess a preferred direction of velocity they can produce a linearly polarized light. However, the occurrence of the accelerated particle beams and the related linear polarization in the Hα line may have a tendency to appear: 1) at the early beginning of a flare 2) in pulses lasting just a few seconds or even less. To measure the linear polarization in flares regularly we have built an additional branch in the Ondřejov multichannel flare spectrograph. In this paper we describe the optical system, the detectors, the method used for data recording and reduction and we also briefly discuss the first results.     

恒星射电耀发6cm波段偏振观测试验

利用新疆天文台南山基地25m射电望远镜在6cm波段对恒星V772 Her和βPer进行了偏振观测试验.通过数据处理和校准得到恒星的射电光变曲线.探测到V772 Her的射电耀发现象,耀发时的线偏振度约达30%,偏振位置角约4°;探测到βPer的缓变成份及叠加其上的快速耀发,βPer耀发时线偏振很弱.     

Flare SOL2012-07-06: On the Origin of the Circular Polarization Reversal Between 17 GHz and 34 GHz

The new generation of multiwavelength radioheliographs with high spatial resolution will employ microwave imaging spectropolarimetry to recover flare topology and plasma parameters in the flare sources and along the wave propagation paths. The recorded polarization depends on the emission mechanism and emission regime (optically thick or thin), the emitting particle properties, and propagation effects. Here, we report an unusual flare, SOL2012-07-06T01:37, whose optically thin gyrosynchrotron emission of the main source displays an apparently ordinary mode sense of polarization in contrast to the classical theory that favors the extraordinary mode. This flare produced copious nonthermal emission in hard X-rays and in high-frequency microwaves up to 80 GHz. It is found that the main flare source corresponds to an interaction site of two loops with greatly different sizes. The flare occurred in the central part of the solar disk, which allows reconstructing the magnetic field in the flare region using vector magnetogram data. We have investigated the three possible known reasons of the circular polarization sense reversal – mode coupling, positron contribution, and the effect of beamed angular distribution. We excluded polarization reversal due to contribution of positrons because there was no relevant response in the X-ray emission. We find that a beam-like electron distribution can produce the observed polarization behavior, but the source thermal density must be much higher than the estimate from to the X-ray data. We conclude that the apparent ordinary wave emission in the optically thin mode is due to radio wave propagation across the quasi-transverse (QT) layer. The abnormally high transition frequency (above 35 GHz) can be achieved reasonably low in the corona where the magnetic field value is high and transverse to the line of sight. This places the microwave source below this QT layer, i.e. very low in the corona.     

Polarization structure of a solar flare region at 9.5 mm wavelength

Polarization structure of an active region that produced a minor flare around 1900 UT on September 28, 1971 was measured at 9.5 mm wavelength using the 85-ft telescope of the Naval Research Laboratory Maryland Point Observatory. The angular resolution of the telescope at this wavelength is 1.6. The flare region underwent changes both in the degree of polarization as well as in its polarization structure before and after the start of the flare. These changes in the degree of polarization correspond to a decrease of longitudinal magnetic field of about 200 G at the chromospheric levels where the 9.5 mm radiation originates. Observations on the polarization structure of active regions for several days before and after September, 1971 are also presented.     

Analysis of the August 7, 1972 white light flare: Light curves and correlation with hard X-rays

Cinematic, photometric observations of the 3B flare of August 7, 1972 are described in detail. The time resolution was 2 s; the spatial resolution was 1–2″. Flare continuum emissivity at 4950 Å and at 5900 Å correlated closely in time with the 60–100 keV non-thermal X-ray burst intensity. The observed peak emissivity was 1.5 × 10¹⁰ erg cm^?2 s^?1 and the total flare energy in the 3900–6900 Å range was ～10³⁰ erg. From the close temporal correspondence and from the small distance (3″) separating the layers where the visible emission and the X-rays arose, it is argued that the hard X-ray source must have had the same silhouette as the white light flare and that the emission patches had cross-sections of 3–5″. There was also a correlation between the location of the most intense visible emissions near sunspots and the intensity and polarization of the 9.4 GHz radio emission. The flare appeared to show at least three distinct particle acceleration phases: one, occurring at a stationary source and associated with proton acceleration gave a very bluish continuum and reached peak intensity at ～ 1522 UT. At 1523 UT, a faint wave spread out at 40 km s^?1 from flare center. The spectrum of the wave was nearly flat in the range 4950–5900 Å. Association of the wave with a slow drift of the microwave emission peak to lower frequencies and with a softening of the X-ray spectrum is interpreted to mean that the particle acceleration process weakened while the region of acceleration expanded. The observations are interpreted with the aid of the flare models of Brown to mean that the same beam of non-thermal electrons that was responsible for the hard X-ray bremsstrahlung also caused the heating of the lower chromosphere that produced the white light flare.     

A flare-associated thermal burst in the mm-wave region

A mm-wave thermal burst has been observed at 73 GHz. The simultaneous observation at 17 GHz revealed that this mm-wave burst was quite a different component from the non-thermal burst co-existing at a cm-wavelength range. Since the source of this burst seemed to be opaque or nearly opaque, the temperature became several tens of thousands degrees. Considering also the similarity between time profiles of the 73 GHz intensity and the H light curve, it is concluded that this mm-wave burst is situated very close to the H flare region.     

Timing analysis of hard X-ray emission and 22 GHz flux and polarization in a solar burst

A solar flare occurring on 26 February, 1981 at 19:32 UT was observed simultaneously in hard X-rays and microwaves with a time resolution of a fraction of a second. The X-ray observations were made with the Hard X-ray Monitor on Hinotori, and the microwave observations were made at 22 GHz with the 13.7 m Itapetinga mm-wave antenna. Timing accuracy was restricted to 62.5 ms, the best time resolution obtained in hard X-rays for this burst. We find that: (a) all 22 GHz flux structures were delayed by 0.2–0.9 s relative to similar structures in hard X-rays throughout the burst duration; (b) different burst structures showed different delays, suggesting that they are independent of each other; (c) the time structures of the degree of polarization at 22 GHz precede the total microwave flux time structures by 0.1–0.5 s; (d) The time evolutions of time delays of microwaves with respect to hard X-rays and also the degree of microwave polarization show fluctuations with are not clearly related to any other time structures. If we take mean values for the 32 s burst duration, we find that hard X-ray emission precedes the degree of microwave polarization by 450 ms, which in turn precedes the total microwave flux by 110 ms.     

White light flares: Protons or electrons?

The estimated values of the energy transported by flare accelerated protons and electrons, based on gamma-ray and hard X-ray measurements in space, are compared with the energy emitted in white light from the 1972, August 7, white light event. The aim is to evaluate the relative contribution of protons and electrons in producing the white light enhancement.     

Ferroelectric Liquid Crystal Polarimeter for High-cadence Hα Imaging Polarimetry

We developed a polarimeter with ferroelectric liquid crystals (FLCs) to observe polarization of flare kernels in the H line. Polarization is one of the important diagnostics of the high-energy particles in solar flares, and high-cadence imaging polarimetry with the precision of the order of 0.1% is required to observe the polarization of flare kernels. However, to achieve such high precision is difficult mainly due to the seeing-induced polarization error, which particularly appears around the flare kernels, because the brightness gradient is steep there. To reduce the seeing-induced error, a high modulation frequency is required, and our new polarimeter based on the combination of a high-speed CCD camera and FLCs realized high-frequency polarization modulation nearly 250 Hz. We evaluated the polarization error, and confirmed that the error was significantly reduced with the new polarimeter. We concluded that the polarimeter with FLCs meets the requirement of solar flare polarimetry.     

A long-enduring multi-source burst at 17 GHz and its relation to a type IVm-dm burst with spectral fine features

A proton-event-associated microwave burst occurred on November 10, 1978 and was observed with the 17 GHz interferometer at Nobeyama. The burst had a very broad extent of about 4.5 arc and consisted of at least four separate sources. The time evolutions of the individual sources were almost independent of each other. We suggest that the sources are fallen into two distinct types as follows: (i) The two-ribbon-associated sources are characterized by the source expansion in size and the relatively flat microwave spectrum, both of which can be explained by thermal emission from hot condensed plasma in the magnetic arcades whose legs are seen as the two-ribbon H flare, and (ii) the spot-related sources are characterized by the high polarization degree with a compact unipolar structure, the rapid time variation, and the inverted-U shape microwave spectrum. The intimate relation of the latter sources to the evolution of the associated type IV_m-dm burst with spectral fine features is also discussed.