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1.
Simultaneous X-ray images in hard (20–40 keV) and softer (6.5–15 keV) energy ranges were obtained with the hard X-ray telescope aboard the Hinotori spacecraft of an impulsive solar X-ray burst associated with a flare near the solar west limb.The burst was composed of an impulsive component with a hard spectrum and a thermal component with a peak temperature of 2.8 × 107 K. For about one minute, the impulsive component was predominant even in the softer energy range.The hard X-ray image for the impulsive component is an extended single source elongated along the solar limb, rather steady and extends from the two-ribbon H flare up to 104 km above the limb. The centroid of this source image is located about 10 (7 × 103 km) ± 5 above the neutral line. The corresponding image observed at the softer X-rays is compact and located near the centroid of the hard X-ray image.The source for the thermal component observed in the later phase at the softer X-rays is a compact single source, and it shows a gradual rising motion towards the later phase.  相似文献   

2.
An impulsive flare October 24, 1969 produced two bursts with virtually identical time profiles of 8800 MHz emission and X-rays above 48 keV. The two spikes of hard X-rays correspond in time to the times of sharp brightening and expansion in the H flare. The first burst was not observed at frequencies below 3000 MHz. This cut off is ascribed to plasma cutoff above the low-lying flare.A model of the flare based on H observations at Big Bear shows that the density of electrons with energy above 10 keV is 5 × 107 if the field density is 1011. The observed radio flux would be produced by this electron distribution with the observed field of 200 G. The H emission accompanying the hard electron acceleration is presumed due to excitation of the field atoms by the hard electrons.  相似文献   

3.
Multiple energetic injections in a strong spike-like solar burst   总被引：1，自引：0，他引：1  
An intense and fast spike-like solar burst was observed with high sensitivity in microwaves and hard X-rays, on December 18,1980, at 19h21m20s UT. It is shown that the burst was built up of short time scale structures superimposed on an underlying gradual emission, the time evolution of which showed remarkable proportionality between hard X-ray and microwave fluxes. The finer time structures were best defined at mm-microwaves. At the peak of the event the finer structures repeat every 30–60 ms (displaying an equivalent repetition rate of 16–20 s-1). The more slowly varying component with a time scale of about 1 s was identified in microwaves and hard X-rays throughout the burst duration. Similarly to what has been found for mm-microwave burst emission, we suggest that X-ray fluxes might also be proportional to the repetition rate of basic units of energy injection (quasi-quantized). We estimate that one such injection produces a pulse of hard X-ray photons with about 4 × 1021 erg, for 25 keV. We use this figure to estimate the relevant parameters of one primary energy release site both in the case where hard X-rays are produced primarily by thick-target bremsstrahlung, and when they are purely thermal, and also discuss the relation of this figure to global energy considerations. We find, in particular, that a thick-target interpretation only becomes possible if individual pulses have durations larger than 0.2 s.  相似文献   

4.
The 2B/X2.8 double-ribbon flare of 30 March, 1982 is investigated using H, white light, X-rays, and microwaves. The X-ray burst seems to consist of two components, i.e., an impulsive component showing a long chain of peaks and a thermal component (T 2 × 107 K).In the early phase, the source images for the impulsive component were available simultaneously at soft (7–14 keV) and hard (20–40 keV) X-rays. Both sources are elongated along a neutral line. The core of the source for the hard X-rays is located at one end which seems to be a footpoint (or a leg) of a loop or arcade, while the core for the soft X-rays is located at the center of the elongated source which would be the center of the loop. The core for the hard X-rays shifted to this center in the main and later phase, accompanied by decrease in the source size in the later phase.A peak of one-directional intensity distribution at 35 GHz always lies on the core of the hard X-ray source, showing a shift of the position synchronous with the hard X-ray core. This may imply a common source for the radio waves and the hard X-rays.The source of the thermal component observed at the soft X-rays (7–14 keV) after the early phase covers a whole H patches. This may imply a physical relation between the thermal X-ray loops and the H brightening.  相似文献   

5.
The angular distribution of solar flare associated hard X-rays ( 10 keV) is calculated on the assumption that they originate as bremsstrahlung emission of energetic electrons with a power law spectrum. For the cross section the relativistic Sauter formula was used. Supposing the electrons to move in a fixed direction, the X-radiation is considerably anisotropic, especially at high photon energies. Taking into account a magnetic field, the anisotropy decreases with increasing pitch angles of the electrons. The anisotropic angular distribution of solar X-radiation seems to be connected with the centre-to-limb variation of hard X-ray bursts and with the correlation of shortwave fadeouts and geomagnetic crochets to H flares.  相似文献   

6.
The burst component of the solar X-ray flux in the soft wavelength range 2 < < 12 Å observed from Explorer 33 and Explorer 35 from July 1966 to September 1968 was analyzed. In this period 4028 burst peaks were identified.The differential distributions of the temporal and intensity parameters of the bursts revealed no separation into more than one class of bursts. The most frequently observed value for rise time was 4 min and for decay time was 12 min. The distribution of the ratio of rise to decay time can be represented by an exponential with exponent -2.31 from a ratio of 0.3 to 2.7; the maximum in this distribution occurred at a ratio of 0.3. The values of the total observed flux, divided by the background flux at burst maximum, can be represented by a power law with exponent -2.62 for ratios between 1.5 and 32. The distribution of peak burst fluxes can be represented by a power law with exponent - 1.75 over the range 1–100 milli-erg (cm2 sec)–1. The flux time integral values are given by a power law with exponent -1.44 over the range 1–50 erg cm–2.The distribution of peak burst flux as a function of H importance revealed a general tendency for larger peak X-ray fluxes to occur with both larger H flare areas and with brighter H flares. There is no significant dependence of X-ray burst occurrence on heliographic longitude; the emission thus lacks directivity.The theory of free-free emission by a thermal electron distribution was applied to a composite quantitative discussion of hard X-ray fluxes (data from Arnoldy et al., 1968; Kane and Winckler, 1969; and Hudson et al., 1969) and soft X-ray fluxes during solar X-ray bursts. Using bursts yielding measured X-ray intensities in three different energy intervals, covering a total range of 1–50 keV, temperatures and emission measures were derived. The emission measure was found to vary from event to event. The peak time of hard X-ray events was found to occur an average of 3 min before the peak time of the corresponding soft X-ray bursts. Thus a changing emission measure during the event is also required. A free-free emission process with temperatures of 12–39 × 106K and with an emission measure in the range 3.6 × 1047 to 2.1 × 1050 cm–3 which varies both from event to event and within an individual event is required by the data examined.Now at Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey.  相似文献   

7.
Taeil Bai 《Solar physics》1978,59(1):141-144
When emitted at the same time, solar hard X-rays reflected by the photosphere arrive at an observer at later times than primary hard X-rays coming directly from the source. This time lag of albedo photons, therefore, should be taken into account in interpreting fine-scale hard X-ray time profiles. If hard X-ray bursts consist of succession of short-lived elementary bursts, under favorable conditions reflected hard X-rays can be resolved from primary hard X-rays with good time resolution. If so, from the time lag and the ratio of the albedo flux to the primary flux, one can determine the source height and anisotropy of solar hard X-rays.  相似文献   

8.
Evidence for a delayed acceleration process in solar flares is presented in the form of an analysis of simultaneous observations in microwaves, decimetre and metrewaves, and hard X-rays of six delayed gradual bursts which appear 0.5–1 hr after the strong main bursts have faded. The observed characteristics of the delayed bursts are: (a) similarity of flux time profiles at all the wavelengths, (b) low turn-over frequency (4 GHz) of the microwave spectrum, (c) moderately strong circular polarization (30–40%) and low altitude of the microwave source (which is displaced toward the disk centre by a projected distance of 10–20 from that of the preceding main burst), and (d) low spectral index of the energy spectrum of hard X-rays.From these observations it is suggested that (i) electrons are accelerated up to MeV even some tens of minutes after the impulsive phase acceleration has almost ceased, (ii) the delayed acceleration occurs in a large magnetic structure extending to a height of at least 2 × 105 km, and (iii) the radio source has columnar structure with the microwave source predominantly near a leg or legs and the metrewave source near the top of the magnetic structure. The present observations of the delayed bursts do not seem to be consistent with the classical second-phase acceleration mechanism proposed in the past for normal hard X-ray gradual (extended) bursts.Minamimaki-mura, Minamisaku-gun, Nagano-ken 384-13, Japan.Greenbelt, MD 20771, U.S.A., NASA/NRC Research Associate, on leave from Tokyo Astronomical Observatory.P.O. Box 76, Epping, N.S.W. 2121, Australia.Berkeley, CA 94720, U.S.A.  相似文献   

9.
S. R. Kane 《Solar physics》1972,27(1):174-181
Observations of impulsive solar flare X-rays 10 keV made with the OGO-5 satellite are compared with ground based measurements of type III solar radio bursts in 10–580 MHz range. It is shown that the times of maxima of these two emissions, when detectable, agree within 18 s. This maximum time difference is comparable to that between the maxima of the impulsive X-ray and impulsive microwave bursts. In view of the various observational uncertainties, it is argued that the observations are consistent with the impulsive X-ray, impulsive microwave, and type III radio bursts being essentially simultaneous. The observations are also consistent with 10–100 keV electron streams being responsible for the type III emission. It is estimated that the total number of electrons 22 keV required to produce a type III burst is 1034. The observations indicate that the non-thermal electron groups responsible for the impulsive X-ray, impulsive microwave, and type III radio bursts are accelerated simultaneously in essentially the same region of the solar atmosphere.  相似文献   

10.
R. Snijders 《Solar physics》1969,6(2):290-293
According to Snijders (1968) the decay profile of an X-ray burst determines the effective temperature describing the distribution of fast electrons in the emitting source. In this paper it is concluded that the observations of the hard X-ray burst of 7 July, 1966; 0038 UT are not in disagreement with the concept of thermal bremsstrahlung from electrons with a Maxwellian distribution of about 108 K. Some physical parameters of the source are determined. The magnetic field strength is found to be about 1200 gauss. The initial temperature kT 0 is approximately 40 keV.  相似文献   

11.
We searched for a new phenomenon, called coronal explosions, in three solar flares, and found them in all three. A coronal explosion is the propagation of a density wave through the flaring area. The wave emerges from one or two small areas (the sources) which are close to, but not identical with the sources of hard X-ray burst emission. In all three cases the explosion starts at the end of the impulsive phase, during or after the last hard ( 20 keV) X-ray burst. The velocities of propagation range between 1800 and a few tens of km s-1, and tend to decrease with time. We suggest that the bursts are magneto-hydrodynamical (shock) waves moving downward into denser regions.  相似文献   

12.
During the GRIF experiment onboard the Mir orbiting station, the sky was monitored with a PX-2 wide-field (～1 sr) scintillation X-ray spectrometer to detect bursts in the photon energy range 10–300 keV. Because of the comprehensive instrumentation, which, apart from the X-ray and gamma-ray instruments, also included charged-particle detectors, the imitations of astrophysical bursts by magnetospheric electron precipitations and strongly ionizing nuclei were effectively filtered out. It was also possible to separate solar and atmospheric events. Several tens of bursts interpreted as being astrophysical were detected in the experiment at sensitivity levels S～10?7 erg cm?2 (for bursts whose spectra were characterized by effective temperatures kT～100 keV) and S～3×10?8 erg cm?2 (for bursts with kT～25 keV). Some of the soft gamma-ray or hard X-ray bursts with kT～10–50 keV were identified with the bursting pulsar GRO J1744-28. Our estimate of the detection rate for cosmological soft gamma-ray or hard X-ray bursts from the entire sky suggests that the distributions of long-duration (>1 s) gamma-ray bursts (GRBs) in characteristic energy kT and duration are inconsistent with the steady-state cosmological model in which the evolution of burst sources is disregarded. Based on GRIF and BATSE/CGRO data, we conclude that most of the GRB sources originate at redshifts 1<z<5.  相似文献   

13.
Pohjolainen  S.  Valtaoja  E.  Urpo  S.  Aurass  H. 《Solar physics》1997,173(1):131-149
Two small radio flares following the great gamma-ray burst on 11 June 1991 are studied. We analyse the different association of emission features at microwaves, decimeter waves, and soft and hard X-rays for the events. The first flare has well-defined emission features in microwaves and soft and hard X-rays, and a faint decimetric signature well after the hard X-ray burst. It is not certain if the decimetric event is connected to the burst features. The second event is characterized by an almost simultaneous appearance of hard X-ray burst maxima and decimetric narrowband drift bursts, but soft X-ray emission is missing from the event. With the exception of the possibility that the soft X-ray emission is absorbed along the way, the following models can explain the reported differences in the second event: (1) Microwave emission in the second event is produced by 150 keV electrons spiraling in the magnetic field relatively low in the corona, while the hard X-ray emission is produced at the beginning of the burst near the loop top as thick-target emission. If the bulk of electrons entered the loop, the low-energy electrons would not be effectively mirrored and would eventually hit the footpoints and cause soft X-ray emission by evaporation, which was not observed. The collisions at the loop top would not produce observable plasma heating. The observed decimetric type III bursts could be created by plasma oscillations caused by electron beams traveling along the magnetic field lines at low coronal heights. (2) Microwave emission is caused by electrons with MeV energies trapped in the large magnetic loops, and the electrons are effectively mirrored from the loop footpoints. The hard X-ray emission can come both from the loop top and the loop footpoints as the accelerated lower energy electrons are not mirrored. The low-energy electrons are not, however, sufficient to create observable soft X-ray emission. The type III emission in this case could be formed either at low coronal heights or in local thick regions in the large loops, high in the corona.  相似文献   

14.
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   

15.
We present two large flares which were exceptional in that each produced an extensive chain of H emission patches in remote quiet regions more than 105 km away from the main flare site. They were also unusual in that a large group of the rare type III reverse slope bursts accompanied each flare.The observations suggest that this is no coincidence, but that the two phenomena are directly connected. The onset of about half of the remote H emission patches were found to be nearly simultaneous with RS bursts. One of the flares (August 26, 1979) was also observed in hard X-rays; the RS bursts occurred during hard X-ray spikes. For the other flare (June 16, 1973), soft X-ray filtergrams show coronal loops connecting from the main flare site to the remote H brightenings. There were no other flares in progress during either flare; this, along with the X-ray observations, indicates that the RS burst electrons were generated in these flares and not elsewhere on the Sun. The remote H brightenings were apparently not produced by a blast wave from the main flare; no Moreton waves were observed, and the spatially disordered development of the remote H chains is further evidence against a blast wave. From geometry, time and energy considerations we propose: (1) That the remote H brightenings were initiated by direct heating of the chromosphere by RS burst electrons traveling in closed magnetic loops connecting the flare site to the remote patches; and (2) that after onset, the brightenings were heated by thermal conduction by slower thermal electrons (kT1 keV) which immediately follow the RS burst electrons along the same loops.  相似文献   

16.
We study the spatial and spectral characteristics of the 3.5 to 30.0 keV emission in a solar flare of 9 May, 1980. We find that: (a) A classical thick target interpretation of the hard X-ray burst at energies E 10 keV implies that approximately all the electrons contained within the flare loop(s) have to be accelerated per second. (b) A thermal model interpretation does not fit the data, unless its characteristics are such that it does not represent an efficient alternative to the acceleration model. We thus conclude that: (c) Acceleration does take place during the early phase of the impulsive hard X-ray event, but substantial amount of the emission at low (<20 keV) energies is of thermal origin. (d) We show the evolution of the energy content in the flare volume, and find that the energy input requirements are such that 102 erg cm-3 s-1 have to be released within the flare structure(s), for a period of time comparable to that of the hard X-ray burst emission. We also point out that although the main flare component ( 90% of the soft X-ray emission) was confined to a compact magnetic kernel, there are evidences of interaction of this structure with a larger field structure connecting towards the leading portion of the active region, where secondary H brightenings were observed.  相似文献   

17.
An impulsive burst of 100–400 keV solar X-rays associated with a small solar flare was observed on October 10, 1970 with a large area scintillator aboard a balloon floating at an altitude of 4.2 g cm-2 above the Earth's surface. The X-ray burst was also observed simultaneously in 10–80 keV range by the OGO-5 satellite and in 8–20 Å range by the SOLRAD-9 satellite. The impulsive X-ray emission reached its maximum at 1643 UT at which time the differential photon spectrum in 20–80 keV range was of the form 2.3 × 104 E -3.2 photons cm-2 s-1 keV-1 at 1 AU. The event is attributed to a H-subflare located approximately at S13, E88 on the solar disc. The spectral characteristics of this event are examined in the light of the earlier X-ray observations of small solar flares.  相似文献   

18.
The flare of 11 November, 1980, 1725 UT occurred in a magnetically complex region. It was preceded by some ten minutes by a gradual flare originating over the magnetic inversion line, close to a small sunspot. This seems to have triggered the main flare (at 70 000 km distance) which originated between a large sunspot and the inversion line. The main flare started at 172320 UT with a slight enhancement of hard X-rays (E > 30 keV) accompanied by the formation of a dark loop between two H bright ribbons. In 3–8 keV X-rays a southward expansion started at the same time, with - 500 km s –1. At the same time a surge-like expansion started. It was observable slightly later in H, with southward velocities of 200 km s–1. The dark H loop dissolved at 1724 UT at which time several impulsive phenomena started such as a complex of hard X-ray bursts localized in a small area. At the end of the impulsive phase at 172540 UT, a coronal explosion occurred directed southward with an initial expansion velocity of 1800 km s–1, decreasing in 40 s to 500 km s–1.Now at Fokker Aircraft Industries, Schiphol, The Netherlands.  相似文献   

19.
Using data from a proportional counter spectrometer, sensitive in the wavelength range 1–20 Å, on OSO-4, X-ray bursts in the energy band 3.0 to 4.5 keV have been studied. 150 events have been identified between October 27, 1967 and May 8, 1968, mostly of an impulsive nature. Some gradual rise and fall bursts occur, but there is a selection bias against such long-enduring events. A study of the profiles of these events reveals no basis for identifying different types of impulsive event.Single frequency radio bursts and H flares of class > 1F are almost always accompanied by X-ray enhancements. For the sample of X-ray events, only 25% are correlated with radio bursts and 46% with flares. Only 11% of the sample events are associated with type III radio bursts. Microwave burst peaks occur an average of two minutes earlier than the X-ray burst peak, but the first observation of X-ray activity is usually before the start of the corresponding microwave burst.Impulsive bursts, although differing widely in fall time, are due to the heating of a volume of plasma from a temperature of 10.0 to 30.0 × 106 K. Differences infall time probably indicate different electron densities in the source. Observation of an iron line at 1.9 Å suggests that a non-thermal mechanism may be operating during some of these events since the temperatures are too low to permit thermal excitation of the 1s 2-1s 2p transition in Fe+24. It is also possible that, in spite of the low temperature, most of the iron ions have been stripped to the Fe+24 stage. Collisional excitation and dielectronic recombination processes would then be able to provide the observed flux in the resonance line of Fe+24. A gradual rise and fall event and event precursors have also been studied.  相似文献   

20.
The Comptonization-softening of very hard X-ray photons withEm 0 c 2 in the cold electron gas is discussed. The frequency diffusion equation for Comptonization of hard X-rays has been derived to the zero-temperature approximation. By use of this equation, and under the assumption of pair-annihilation origin of hard X-rays, we calculated the energy spectrum withE>80 keV, for Cyg X-1, which is in good fit with the observation. The high-energy edge 400 keV of the observed spectrum and the small bump in the range 100–200 keV also can be explained by this way.  相似文献   

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