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1.
We report the imaging observations of a slowly moving type IV burst associated with a filament eruption. This event was preceded by weak type III burst activity and was accompanied by a quasi-stationary continuum that persisted for several hours. The starting times and speeds of moving type IV burst and the erupting filament are nearly the same, implying a close physical relation between the two. The moving type IV burst is interpreted as gyrosynchrotron emission from a plasmoid containing a magnetic field of 1–2 G and nonthermal electrons of density 105–106 cm–3 with a relatively low average energy of 50 keV.  相似文献   

2.
We analyze hard and soft X-ray, microwave and meter wave radio, interplanetary particle, and optical data for the complex energetic solar event of 22 July 1972. The flare responsible for the observed phenomena most likely occurred 20° beyond the NW limb of the Sun, corresponding to an occultation height of 45 000 km. A group of type III radio bursts at meter wavelengths appeared to mark the impulsive phase of the flare, but no impulsive hard X-ray or microwave burst was observed. These impulsive-phase phenomena were apparently occulted by the solar disk as was the soft X-ray source that invariably accompanies an H flare. Nevertheless essentially all of the characteristic phenomena associated with second-stage acceleration in flares - type II radio burst, gradual second stage hard X-ray burst, meter wave flare continuum (FC II), extended microwave continuum, energetic electrons and ions in the interplanetary medium - were observed. The spectrum of the escaping electrons observed near Earth was approximately the same as that of the solar population and extended to well above 1 MeV.Our analysis of the data leads to the following results: (1) All characteristics are consistent with a hard X-ray source density n i 108 cm–3 and magnetic field strength 10 G. (2) The second-stage acceleration was a physically distinct phenomenon which occurred for tens of minutes following the impulsive phase. (3) The acceleration occurred continuously throughout the event and was spatially widespread. (4) The accelerating agent was very likely the shock wave associated with the type II burst. (5) The emission mechanism for the meter-wave flare continuum source may have been plasma-wave conversion, rather than gyrosynchrotron emission.  相似文献   

3.
We present observations of a UV event which occurred in a polar coronal hole. They were obtained by SUMER on SOHO in several chromospheric and transition region spectral lines. Its birth site was about 50 arc sec inside the limb and in a network lane showing a net outflow before its initiation. The event had an extension of about 5 arc sec along the slit, a duration of about 3 min and was characterized by a large increase of intensity together with a significant line broadening with, however, downflows of about 50 km s–1 being dominant. Proper motions with a velocity of about 10 km s–1 were also observed. The event appeared at middle transition (Ovi) temperatures and it simultaneously showed up in chromospheric (Oi, Ly ) and low transition region (Cii) temperatures. We discuss this event in view of different scenarios to account for it. Our event could be a part of the large family of quiet-Sun explosive events observed by Ryutova and Tarbell (2000) taking place in polar coronal holes that are triggered by magnetic reconnection in the low solar atmosphere.  相似文献   

4.
We discuss a solar flare microwave burst complex, which included a major structure consisting of some 13 spikes of 60 ms FWHM each, observed 21 May, 1984 at 90 GHz (3 mm). It was associated with a simultaneous very hard X-ray burst complex. We suggest that the individual spikes of both bursts were caused by the same electron population: the X-bursts by their bremsstrahlung, and the microwave bursts by their gyrosynchrotron emission. This latter conclusion is based on the evidence that the radio turnover frequency was 150 GHz. It follows that the emission sources were characterized by an electron density of about 1011 cm–3, a temperature of 5 × 108 K and a magnetic field of about 1400–2000 G. They had a size of about 350 km; if the energy release is caused by reconnection the sources of primary instability could have been smaller and in the form of thin sheets with reconnection speed at a fraction of the Alfvén velocity and burst-like energy injections of 1027 erg during about 50 ms each. The energized plasma knots lost their injection energy by saturated convective flux (collisionless conduction) in about 30 ms.  相似文献   

5.
Huang  G.L.  Wu  H.A.  Grechnev  V.V.  Sych  R.A.  Altyntsev  A.T. 《Solar physics》2003,213(2):341-358
A solar radio burst on 25 August 1999 with fine structures (FS) at 4.5–7.5 GHz is studied in this paper. The FS started about one minute prior to the main burst. The maximum emission took place at 4–5 GHz for the FS, and at 10–11 GHz for the main burst, respectively. The time profiles at 4.5–7.5 GHz coincide very well with those of hard X-rays (from 25 keV to >300 keV) in both the main burst and the FS, which shows that the same population of accelerated electrons is responsible for both the microwave and hard X-ray bursts. The source of FS is 20 arc sec away from the main source close to a compact dipolar magnetic field, which is confirmed by different time and polarization profiles in the FS and main sources. It is interesting that the FS at 4.5–7.5 GHz are associated with a series of twisted magnetic loops or ropes, which may be modulated by Alfvén waves with a period of 1 s and a spatial wavelength of 103 km in respect to the typical Alfvén velocity of 103 km s–1 in corona. These magnetic ropes may be rooted in the dipole site, which extended into the corona during the event and retracted after the event. Therefore, the FS in this event may show an important signature or precursor for energy release. The magnetic reconnection may be triggered by the interaction of the magnetic ropes at the height corresponding to 5–6 GHz, followed by cascaded energy release close to the foot-point of the magnetic ropes.  相似文献   

6.
In this paper the solar neutron and white-light flare is studied on the basis of radioastronomical observations. It is shown that the 3 June, 1982 flare had an impulsive character. A strong shock wave (M A 2.9) was observed unusually soon after the impulsive phase of the flare. The radio spectrum of this event shows that the primary acceleration process probably occurred in the region with an electron density of n e = 4.4 × 1015 m–3. The pulsations of the type IV radio burst, observed 15 min after the mass ejection process, manifest the reconnection process in the post-flare stage.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.  相似文献   

7.
Wang  M.  Duan  C.C.  Xie  R.X.  Yan  Y.H. 《Solar physics》2003,212(2):401-406
A group of type III bursts observed with the 2.6–3.8 GHz spectrometer of National Astronomical Observatory of China on 15 April 1998 is analyzed. They have the characteristics of broad bandwidth (>100 MHz), very short durations (<100 ms), high polarization degree (100%), high frequency drift rates (>1 GHz s–1), and fast pulsations (with a period of about 100–200 ms). Their time profiles are also analysed. According to these characteristics, we suggest that these microwave type III bursts may be due to the fundamental plasma emission.  相似文献   

8.
A detailed comparison is made between hard X-ray spikes and decimetric type III radio bursts for a relatively weak solar flare on 1981 August 6 at 10: 32 UT. The hard X-ray observations were made at energies above 30 keV with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and with a balloon-born coarse-imaging spectrometer from Frascati, Italy. The radio data were obtained in the frequency range from 100 to 1000 MHz with the analog and digital instruments from Zürich, Switzerland. All the data sets have a time resolution of 0.1 s or better. The dynamic radio spectrum shows many fast drift type III radio bursts with both normal and reverse slope, while the X-ray time profile contains many well resolved short spikes with durations of 1 s. Some of the X-ray spikes appear to be associated in time with reverse-slop bursts suggesting either that the electron beams producing the radio bursts contain two or three orders of magnitude more fast electrons than has previously been assumed or that the electron beams can trigger or occur in coincidence with the acceleration of additional electrons. One case is presented in which a normal slope radio burst at 600 MHz occurs in coincidence with the peak of an X-ray spike to within 0.1 s. If the coincidence is not merely accidental and if it is meaningful to compare peak times, then the short delay would indicate that the radio signal was at the harmonic and that the electrons producing the radio burst were accelerated at an altitude of 4 × 109 cm. Such a short delay is inconsistent with models invoking cross-field drifts to produce the electron beams that generate type III bursts but it supports the model incorporating a MASER proposed by Sprangle and Vlahos (1983).  相似文献   

9.
Radio emissions of electron beams in the solar corona and interplanetary space are tracers of the underlying magnetic configuration and of its evolution. We analyse radio observations from the Culgoora and WIND/WAVES spectrographs, in combination with SOHO/LASCO and SOHO/MDI data, to understand the origin of a type N burst originating from NOAA AR 10540 on January 20, 2004, and its relationship with type II and type III emissions. All bursts are related to the flares and the CME analysed in a previous paper (Goff et al., 2007). A very unusual feature of this event was a decametric type N burst, where a type III-like burst, drifting towards low frequencies (negative drift), changes drift first to positive, then again to negative. At metre wavelengths, i.e., heliocentric distances ≲1.5R ⊙, these bursts are ascribed to electron beams bouncing in a closed loop. Neither U nor N bursts are expected at decametric wavelengths because closed quasi-static loops are not thought to extend to distances ≫1.5R ⊙. We take the opportunity of the good multi-instrument coverage of this event to analyse the origin of type N bursts in the high corona. Reconnection of the expanding ejecta with the magnetic structure of a previous CME, launched about 8 hours earlier, injects electrons in the same manner as with type III bursts but into open field lines having a local dip and apex. The latter shape was created by magnetic reconnection between the expanding CME and neighbouring (open) streamer field lines. This particular flux tube shape in the high corona, between 5R ⊙ and 10R ⊙, explains the observed type N burst. Since the required magnetic configuration is only a transient phenomenon formed by reconnection, severe timing and topological constraints are present to form the observed decametric N burst. They are therefore expected to be rare features.  相似文献   

10.
Mukul R. Kundu 《Solar physics》1982,113(1-2):87-94
In this article, we review some of the recent results obtained with imaging observations of the Sun at meter-decameter wavelengths, using the Clark Lake multifrequency radioheliograph. We briefly discuss the use of imaging observations to study the large scale structure of the upper corona. We discuss non-flare associated type II/type IV bursts associated with a coronal streamer disruption event associated with a slow (100 Km/s) CME. We discuss meter-decameter microbursts, which occur at coronal heights, often without any surface activity. Finally, we discuss a correlated type III burst whose emission originates almost simultaneously from two widely separated ( 105 Km) locations.  相似文献   

11.
We present observations of the solar flare on 1980 June 27, 16:14–16:33 UT, which was observed by a balloon-borne 300 cm2 phoswich hard X-ray detector and by the IKARUS radio spectrometer. This flare shows intense hard X-ray (HXR) emission and an extreme productivity of (at least 754) type III bursts at 200–400 MHz. A linear correlation was found between the type III burst rate and the HXR fluence, with a coefficient of 7.6 × 1027 photons keV–1 per type III burst at 20 keV. The occurrence of 10 type III bursts per second, and also the even higher rate of millisecond spikes, suggests a high degree of fragmentation in the acceleration region. This high quantization of injected beams, assuming the thick-target model, shows up in a linear relationship between hard X-ray fluence and the type III rate, but not as fine structures in the HXR time profile.The generation of a superhot isothermal HXR component in the decay phase of the flare coincides with the fade-out of type III production.Universities Space Research Associates.ST Systems Corporation.  相似文献   

12.
A well-developed multiple impulsive microwave burst occurred on February 17, 1979 simultaneously with a hard X-ray burst and a large group of type III bursts at metric wavelengths. The whole event is composed of several subgroups of elementary spike bursts. Detailed comparisons between these three classes of emissions with high time resolution of 0.5 s reveal that individual type III bursts coincide in time with corresponding elementary X-ray and microwave spike bursts. It suggests that a non-thermal electron pulse generating a type III spike burst is produced simultaneously with those responsible for the corresponding hard X-ray and microwave spike bursts. The rise and decay characteristic time scales of the elementary spike burst are 1 s, 1 s and 3 s for type III, hard X-ray and microwave emissions respectively. Radio interferometric observations made at 17 GHz reveal that the spatial structure varies from one subgroup to others while it remains unchanged in a subgroup. Spectral evolution of the microwave burst seems to be closely related to the spatial evolution. The spatial evolution together with the spectral evolution suggests that the electron-accelerating region shifts to a different location after it stays at one location for several tens of seconds, duration of a subgroup of elementary spike bursts. We discuss several requirements for a model of the impulsive burst which come out from these observational results, and propose a migrating double-source model.  相似文献   

13.
High-resolution spectra near 4 m of the four red giants— Peg,o 1 Ori, 10 Dra, and HR 1105—have been analysed to obtain estimates of the28Si/29Si and28Si/30Si abundance ratios. For Peg and the S star HR 1105, the28Si/29Si ratio is close to the solar ratio (28Si/29Si=20).29Si appears to be underabundant in the MS staro 1 Ori (28Si/29Si=40) and the M star 10 Dra (28Si/29Si53). The30Si isotope appears to be underabundant by, perhaps, about a factor of 2 in all four stars.  相似文献   

14.
The radio-burst on August 7, 1972, is discussed. On 17 GHz the peak flux was about 25000 SFU. Considering the decreasing phase of the burst, it was found that an exponential decrease as well as a power-law decrease can be used. The magnetic field in the origin of the burst should be of the order of 1000 G, while the exponent g due to a power-law of the energy distribution is estimated to be about g 3. The degree of circular polarisation shows an increase to about 25% during the ascending phase of the burst, while in the phase of maximal radiation and during the decrease the polarisation degree was small.  相似文献   

15.
Storms of type III solar radio bursts observed from 5.4 ot 0.2 MHz consist of a quasi-continuous production of type III events observable for half a solar rotation but persisting in some cases for well over a complete rotation (Fainberg and Stone, 1970). The observed burst drift rates are a function of the heliographic longitude of the associated active region. This apparent drift rate dependence is a consequence of the radio emission propagation time from source to observer. Based on this dependence, a least squares analysis of 2500 drift rates between frequencies in the 2.8 to 0.7 MHz range yields an average exciter speed of 0.38 c for the height range from approximately 11 to 30 R . In conjunction with the available determinations of exciter speeds of 0.33 c close to the sun, i.e. less than 3 R , and with in situ measurements of 40 keV solar electrons by space probes, the present results suggest that the exciters are electron packets which propagate with little deceleration over distances of at least 1 AU.  相似文献   

16.
L. C. Lee  Y. Lin  G. S. Choe 《Solar physics》1996,163(2):335-359
Magnetic reconnection can take place between two plasma regions with antiparallel magnetic field components. In a time-dependent reconnection event, the plasma outflow region consists of a leading bulge region and a trailing reconnection layer. Magnetohydrodynamic (MHD) discontinuities, including rotational discontinuities, can be formed in both the bulge region and the trailing layer. In this paper, we suggest that the rotational discontinuities observed in the solar wind may be generated by magnetic reconnection associated with microflares in coronal holes. The structure of the reconnection layer is studied by solving the one-dimensional Riemann problem for the evolution of an initial current sheet after the onset of magnetic reconnection as well as carrying out two-dimensional MHD simulations. As the emerging magnetic flux reconnects with ambient open magnetic fields in the coronal hole, rotational discontinuities are generated in the region with open field lines. It is also found that in the solar corona with a low plasma beta ( 0.01), the magnetic energy is converted through magnetic reconnection mostly into the plasma bulk-flow energy. Since more microflares will generate more rotational discontinuities and also supply more energy to the solar wind, it is expected that the number of rotational discontinuities observed in the solar wind would be an increasing function of solar wind speed. The observation rate of rotational discontinuities generated by microflares is estimated to be dN RD/dt - f/63 000 s (f > 1) at 1 AU. The present mechanism favors the generation of rotational discontinuities with a large shock normal angle.  相似文献   

17.
An overview of particle beams in the solar atmosphere is separated into discussions of (i) current-carrying beams, (ii) current-neutralized electron beams, and (iii) ion beams. The Alfvén-Lawson limit on an electric current implies some severe limitations including the following: the current flowing into the corona cannot exceed about 1012 A; if the current density is near threshold for a current instability then the current must flow in thin layers; and, the primary electrons and ions cannot be accelerated simply by the particles falling down a parallel potential drop. Considerable progress has been made in understanding how electron beams in type III solar radio events propagate in a way that is consistent with the generation of Langmuir waves, but a completely consistent picture has not yet emerged. Such beams, and more importantly the electron beams that generate hard X-ray bursts require current neutralization; how the required return current is set up is still not entirely clear. There is direct evidence for ion beams with energies 10 MeV per nucleon from -ray line emission; there is no unambiguous evidence for ion beams of lower energy. A mechanism is suggested for bulk energization of electrons due to dissipation of a parallel current in solar flares. Some outstanding problems concerning particle beams are identified.  相似文献   

18.
The Main-Sequence positions as well as the evolutionary behavior of Population III stars up to an evolution age of 2×1010 yr, taking this time as the age of the Universe, have been investigated in the mass range 0.2 and 0.8M . While Population III stars with masses greater than 0.3M develop a radiative core during the approach to the Main Sequence, stars with masses smaller than 0.3M reach the Main Sequence as a wholly convective stars. Population III stars with masses greater than 0.5M show a brightening of at most 2.2 in bolometric magnitude when the evolution is terminated as compared to the value which corresponds to zero-age Main Sequence. The positions of stars with masses smaller than 0.5M remain almost the same in the H-R diagram.If Population III stars have formed over a range of redshifts, 6相似文献   

19.
D. L. Croom 《Solar physics》1970,15(2):414-423
The results of 2 1/2 years (July 1967 – December 1969) monitoring of solar radio bursts at 71 GHz ( = 4.2 mm) at the Radio and Space Research Station, Slough are presented. During this period only seven events were positively identified as 71 GHz bursts. One of these events (6 July, 1968) is among the largest solar bursts ever recorded anywhere in the microwave-millimetre wave band (47000 × 10–22Wm–2Hz–1), and the associated magnetic field may possibly have exceeded 7200 G. Another event (27 March, 1969) has demonstrated that bursts at 71 GHz can be both intense (4700 × 10–22Wm–2Hz–1) and complex. On other occasions, the absence of any detectable event at 71 GHz helps to define the high frequency spectrum of the burst, this being an important factor in determining the initial energy distribution of the electrons ejected by the associated flare. On one such occasion (21 March, 1969) the derived energy distribution index is 8, in contrast with the more usual values of 2–4.1969–1970 NCR-OAR Senior Post-Doctoral Research Associate at Air Force Cambridge Research Laboratories, L. G. Hanscom Field, Bedford, Mass., U.S.A.  相似文献   

20.
Type III radio bursts observed at kilometric wavelengths ( 0.35 MHz) by the OGO-5 spacecraft are compared with > 45 keV solar electron events observed near 1 AU by the IMP-5 and Explorer 35 spacecraft for the period March 1968–November 1969.Fifty-six distinct type III bursts extending to 0.35 MHz ( 50 R equivalent height above the photosphere) were observed above the threshold of the OGO-5 detector; all but two were associated with solar flares. Twenty-six of the bursts were followed 40 min later by > 45 keV solar electron events observed at 1 AU. All of these 26 bursts were identified with flares located west of W 09 solar longitude. Of the bursts not associated with electron events only three were identified with flares west of W 09, 18 were located east of W 09 and 7 occurred during times when electron events would be obscured by high background particle fluxes.Thus almost all type III bursts from the western half of the solar disk observed by OGO-5 above a detection flux density threshold of the order of 10–13 Wm–2 Hz–1 at 0.35 MHz are followed by > 45 keV electrons at 1 AU with a maximum flux of 10 cm–2 s–1 ster–1. If particle propagation effects are taken into account it is possible to account for lack of electron events with the type III bursts from flares east of the central meridian. We conclude that streams of 10–100 keV electrons are the exciting agent for type III bursts and that these same electrons escape into the interplanetary medium where they are observed at 1 AU. The total number of > 45 keV electrons emitted in association with a strong kilometer wavelength type III burst is estimated to be 5 × 1032.  相似文献   

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