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1.
Several substorms were observed at Explorer 45 in November and December 1971, and January and February 1972, while the satellite was in the evening quadrant near L = 5. These same substorms were identified in ground level magnetograms from auroral zone and low latitude stations. The satellite vector magnetic field records and rapid run ground magnetograms were examined for evidence of simultaneous occurrence of Pi2 magnetic pulsations. Pulsations which began abruptly were observed at the satellite during 7 of the 13 substorms studied and the pulsations occurred near the estimated time of substorm onset. These 7 pulsation events were also observed on the ground and 6 were identified in station comments as Pi2. All of the events observed were principally compressional waves, that is, pulsations in field magnitude. There were also transverse components elliptically polarized counter-clockwise looking along the field line. Periods observed ranged from 40 to 200 sec with 80 sec often the dominant period.  相似文献   

2.
Electron-dominated episodes or events during solar flares are characterized by a flattening of the electron bremsstrahlung continuum above about 1 MeV. This flattening leads to a dominance of the continuum at MeV energies over nuclear emissions. We analyzed events recorded by the gamma-ray spectrometer on SMM with the aim to determine the nuclear contribution in the energy range between 4 and 8 MeV. We find that for comparable continuum fluences it is less by about an order of magnitude than for other flares. The spectral index of the best-fit power law of the > 1 MeV continuum with a median at –1.84 turns out to be independent of the heliocentric angle of the events, implying that the degree of anisotropy of the radiating particles was low. It is of interest to note that a value of –1.5 seems to be a limit. The spectral index of the continuum between 0.3 and 1 MeV does not differ significantly from that of other flares. Only measurements with detectors sensitive up to at least 10 MeV can, therefore, sort out electron dominated episodes during solar flares.  相似文献   

3.
Belinda Lipa 《Solar physics》1978,57(1):191-204
We have analyzed the hard X-ray emission from 28 large solar events, searching for pulsations in intensity profiles. Periodicity occurred in 26 events, usually soon after the onset, with periods in the range 10–100 s. Pulsations occurring at common frequencies in different energy bands are observed to be closely in phase. Periodic behavior in hard X-ray emission is related to that at microwave and decametric wavelength. We discuss our observations briefly in terms of two models: that of McClean et al. (1971), applied to X-ray emission, and that of Brown and Hoyng (1975). As periodicity is normal in extended hard X-ray bursts and occurs through a broad energy band, it is probably directly related to a principal flare acceleration mechanism. Our observations constrain possible mechanisms of flare acceleration and physical properties of the acceleration region.This work began when the author was at the Institute for Plasma Research, Stanford University.  相似文献   

4.
We present the results of our comparative timing and spectral analysis of the high and low (off) states in the X-ray pulsar Her X-1 based on data from the ART-P telescope onboard the Granat observatory. A statistically significant (several mCrab) persistent flux with a simple power-law spectrum was detected during the low state. The spectral slope changed from observation to observation by almost a factor of 2. Pulsations were detected only during the high state of the source, when its flux was a factor of ～25 larger than the low-state flux. The spectral shape of Her X-1 in its high state was complex, with the parameters depending on pulse phase.  相似文献   

5.
Pulsations of mm-wave emission with a period of about 5 s, which occurred during the impulsive phase of the flare of June 22, 1989, are investigated. It has been shown that these pulsations can be driven by Alfvénic oscillations of a flare loop excited due to upward motion of the chromospheric evaporated plasma. A method is proposed to determine the density and temperature of the evaporated plasma as well as the flare loop magnetic field and loop length in terms of Alfvénic oscillations of the loop and bremsstrahlung mechanism of mm-wave emission. The estimation of evaporated plasma energy has shown that for the flare of June 22, 1989 the energy content in electron beams is insufficient for chromospheric plasma evaporation. It is not excluded that the main energy release process occurs in the chromosphere.  相似文献   

6.
An investigation is made to determine the relationship between a coronal mass ejection (CME) and the characteristics of associated metre-wave activity. It is found that (1) the CME width and leading edge velocity can be highly influential in determining the intensity, spectral complexity and frequency coverage of both type II and continuum bursts; (2) the presence of a CME is possibly a necessary condition for the production of a metric continuum event and (3) metric continuum bursts as well as intense, complex type II events are preferentially associated with strong, long lasting soft X-ray events.  相似文献   

7.
Ramesh  R.  Sundaram  G.A. Shanmugha 《Solar physics》2001,202(2):355-361
We performed a statistical study of the metric noise-storm continuum sources (located close to/off the solar limb, and whose start time are precisely known) observed during the period January 1997 – June 1998. The main results are: (i) a majority of the events considered were temporally followed by a coronal mass ejection off the solar limb, and (ii) the noise-storm sources were located within the angular span of the latter.  相似文献   

8.
Cosmic gamma-ray burst spectroscopy   总被引：1，自引：0，他引：1  
A review is given of the gamma-ray burst energy spectrum measurements on Venera 11 and Venera 12 space probes. The gamma burst continuum approximates in shape thermal brems-strahlung emission of a hot plasma. The radiation temperature varies over a broad range, 50–1000 keV, for different events. Spectra of many bursts contain cyclotron absorption and/or redshifted annihilation lines. Strong variability is typically observed in both continuum and line spectra. These spectral data provide convincing evidence for the gamma-ray bursts being generated by neutron stars with superstrong magnetic fields 1012–1013 G.  相似文献   

9.
The current status of the morphological properties of the variation of the earth's magnetic field known as Intervals of Pulsations with Rising Periods (IPRP) observed at the polar cusp stations Casey, Mirny and Heiss throughout 1978 is presented. They have the characteristic of a “whistle” with steadily falling tone. Comprehensive observational and dynamical morphological accounts of the IPRP phenomenon are presented including new analyses of polarisation, power spectra and digital sonograms. Simultaneously occurring IPRP at the two widely spaced stations Casey and Mirny are examined. In an accompanying paper (Cole et al., 1982) a theory which accounts for the properties of the phenomenon is presented.  相似文献   

10.
Energetic electron injection events result in the arrival of loss-cone distributions of electrons at energies of a few keV close to the plasmapause at local midnight. These distributions favour the growth of strong electrostatic waves with some conversion to electromagnetic nonthermal continuum emissions near to the geomagnetic equator.GEOS2 located at the geostationary orbit (L = 6.6, 3.3° South) has observed these continuum emissions for a number of electron injection events. Their unique frequency structure provides a measurement of the geomagnetic field strength at the source and hence its radial position, while direction finding measurements at GEOS2 complete the source location determination.Measurements of source locations as a function of time after the start of an electron injection event, yield typical inwards motions of 1REh?1. In this way the emissions provide a remote sensing of the plasmapause location from the geostationary orbit.  相似文献   

11.
W.M. GrundyM.W. Buie 《Icarus》2002,157(1):128-138
We present four new near-infrared spectra of Pluto, measured separately from its satellite Charon during four HST/NICMOS observations in 1998, timed to sample four evenly spaced longitudes on Pluto. Being free of contamination by telluric absorptions or by Charon light, the new data are particularly valuable for studies of Pluto's continuum absorption. Previous studies of the major volatile species indicate the existence of at least three distinct terrains on Pluto's surface: N2-rich, CH4-rich, and volatile-depleted. The new data provide evidence that each of these three terrains has distinct near-infrared continuum absorption features. CH4-rich regions appear to show reddish continuum absorption through the near-infrared spectral range. N2-rich regions have very little continuum absorption. Visually dark, volatile-depleted regions exhibit intermediate continuum albedos with a bluish continuum slope. By analogy with Triton, we expected that careful spectral modeling would reveal strong evidence for the existence of H2O ice on Pluto's surface, but we found only very weak evidence for its existence in the volatile-depleted regions. These data require H2O ice to play a much less prominent role on Pluto's surface than it does on Triton's.  相似文献   

12.
White-light flares are considered to be the most energetic flaring events that are observable in the optical broad-band continuum of the solar spectrum. They have not been commonly observed. Observations of white-light flares with sub-arcsecond resolution have been very rare. The continuous high resolution observations of Hinode provide a unique opportunity to systematically study the white-light flares with a spatial resolution around 0.2 arcsec. We surveyed all the flares above GOES magnitude C5.0 since the launch of Hinode in 2006 October. 13 of these kinds of flares were covered by the Hinode G-band observations. We analyzed the peak contrasts and equivalent areas (calculated via integrated excess emission contrast) of these flares as a function of the GOES X-ray flux, and found that the cut-off visibility is likely around M1 flares under the observing limit of Hinode. Many other observational and physical factors should affect the visibility of white-light flares; as the observing conditions are improved, smaller flares are likely to have detectable white-light emissions. We are cautious that this limiting visibility is an overestimate, because G-band observations contain emissions from the upper atmosphere.Among the 13 events analyzed, only the M8.7 flare of 2007 June 4 had near-simultaneous observations in both the G-band and the blue continuum. The blue continuum had a peak contrast of 94% vs. 175% in G-band for this event. The equivalent area in the blue continuum is an order of magnitude lower than that in the G-band. Very recently, Jess et al.studied a C2.0 flare with a peak contrast of 300% in the blue continuum. Compared to the events presented in this letter, that event is probably an unusual white-light flare: a very small kernel with a large contrast that can be detected in high resolution observations.  相似文献   

13.
We report on the time-dependent behaviour of ultraviolet spectral lines in Hubble Space Telescope Goddard High-Resolution Spectrograph data of the classical nova V603 Aql. In particular, episodic blueshifted absorption (extending to ∼−2500 km s−1) is present, with a variability time-scale down to ∼1 min. The data provide a rare opportunity to study the rapid evolution of absorption structures that may be associated with accretion-disc winds in cataclysmic variables. At least three absorption events are recorded (at blueward velocities only) over ∼5 h, each lasting ∼10–15 min. The derived velocity, acceleration and optical depth properties provide an empirical picture of stochastically variable structures in the outflow, with no evidence for short-term (less than ∼1 h) cyclic or modulated behaviour in the overall absorption properties. In contrast, the emission components of the ultraviolet resonance lines are very stable in velocity and strength in this low-inclination system. On at least two occasions there is an intriguing short-term 'flare' in the ultraviolet continuum flux (of up to ∼40 per cent). Though there is no clear one-to-one relation in these data between the continuum fluctuations and the occurrence of the absorption events, the time-scales for the two variable phenomena are essentially the same. The irregular absorption episodes in the ultraviolet data of V603 Aql presently defy a clear physical interpretation. Their overall characteristics are discussed in the context of instabilities in radiation-pressure-driven disc winds.  相似文献   

14.
We report results from analysis performed on an eclipsing supergiant high mass X-ray binary pulsar XTE J1855-026 observed with the X-ray Imaging Spectrometer (XIS) on-board Suzaku Observatory in April 2015. Suzaku observed this source for a total effective exposure of \(\sim \)87 ks just before an eclipse. Pulsations are clearly observed and the pulse profiles of XTE J1855-026 did not show significant energy dependence during this observation consistent with previous reports. The time averaged energy spectrum of XTE J1855-026 in the 1.0–10.5 keV energy range can be well fitted with a partial covering power law model modified with interstellar absorption along with a black-body component for soft excess and a gaussian for iron fluorescence line emision. The hardness ratio evolution during this observation indicated significant absorption of soft X-rays in some segments of the observation. For better understanding of the reason behind this, we performed time-resolved spectroscopy in the 2.5–10.5 keV energy band which revealed significant variations in the spectral parameters, especially the hydrogen column density and iron line equivalent width with flux. The correlated variations in the spectral parameters indicate towards the presence of clumps in the stellar wind of the companion star accounting for the absorption of low energy X-rays in some time segments.  相似文献   

15.
The white light during M dwarf flares has long been known to exhibit the broadband shape of a T≈10 000 K blackbody, and the white light in solar-flares is thought to arise primarily from hydrogen recombination. Yet, a current lack of broad-wavelength coverage solar flare spectra in the optical/near-UV region prohibits a direct comparison of the continuum properties to determine if they are indeed so different. New spectroscopic observations of a secondary flare during the decay of a megaflare on the dM4.5e star YZ CMi have revealed multiple components in the white-light continuum of stellar flares, including both a blackbody-like spectrum and a hydrogen-recombination spectrum. One of the most surprising findings is that these two components are anti-correlated in their temporal evolution. We combine initial phenomenological modeling of the continuum components with spectra from radiative hydrodynamic models to show that continuum veiling causes the measured anti-correlation. This modeling allows us to use the components’ inferred properties to predict how a similar spatially resolved, multiple-component, white-light continuum might appear using analogies to several solar-flare phenomena. We also compare the properties of the optical stellar flare white light to Ellerman bombs on the Sun.  相似文献   

16.
We performed an analysis of the polarization of 60 pulsating radio events identified in type IV bursts recorded in the m-dm band during the Solar Cycle XXI at the Trieste Astronomical Observatory.Two major points summarize the results of such an analysis: (i) the emission is totally polarized at the source and the source itself is unique; (ii) the emission occurs in the ordinary magneto-ionic mode for most of the samples, if one accepts the leading-spot hypothesis.The first point confirms what was derived by other authors who anyhow considered a more limited set of samples: highly-polarized events are the most frequent, intense and long-lasting. The intermediate and low polarization observed in other cases are to be attributed to propagation effects, which are effective along the path after the emission, and this interpretation is supported by different observed features such as shorter duration and lower intensity of the events.Our second point differs from a previous work which claims the extraordinary mode, but this discrepancy can be justified by: (a) the small number of events analyzed in that work, which gives poorer statistics; (b) a quite different observing frequency range; (c) the different selection criterion. However, in spite of the relative richness of our data set we cannot give a final answer to the emission mode problem as the leading-spot hypothesis is questionable and we report critical arguments against it based on experimental results.The polarization degree of pulsations looks generally constant during the whole lifetime. As a general trend the selected events show the same polarization features both for the pulsations and the background. A different polarization degree of the continuum is probably the signature of the contemporaneous presence of more than one source.  相似文献   

17.
Solar X-ray observations from balloons and from the SMM and HINOTORI spacecraft have revealed evidence for a super-hot thermal component with a temperature of 3 × 107 K in many solar flares, in addition to the usual 10–20 × 106 K soft X-ray flare plasma. We have systematically studied the decay phase of 35 solar flare X-ray events observed by ISEE-3 during 1980. Based on fits to the continuum X-ray spectrum in the 4.8–14 keV range and to the intensity of the 1.9 Å feature of iron lines, we find that 15 (about 43%) of the analyzed events have a super-hot thermal component in the decay phase of the flare. In this paper the important properties of the super-hot thermal component in the decay phase are summarized. It is found that an additional input of energy is required to maintain the super-hot thermal components. Finally, it is suggested that the super-hot thermal component in the decay phase is created through the reconnection of the magnetic field during the decay phase of solar flares.  相似文献   

18.
We consider temporal, spectral, and polarization parameters of the hard X-ray and gamma-ray radiation observed during the solar flare of May 20, 2002, in the course of experiments with the SONG and SPR-N instruments onboard the Coronas-F spacecraft. This flare is one of the most intense gamma-ray events among all of the bursts of solar hard electromagnetic radiation detected since the beginning of the Coronas-F operation (since July 31, 2001) and one of the few gamma-ray events observed during solar cycle 23. A simultaneous analysis of the Coronas-F and GOES data on solar thermal X-ray radiation suggests that, apart from heating due to currents of matter in the the flare region, impulsive heating due to the injection of energetic electrons took place during the near-limb flare S21E65 of May 20, 2002. These electrons produced intense hard X-ray and gamma-ray radiation. The spectrum of this radiation extends up to energies ≥7 MeV. Intense gamma-ray lines are virtually unobservable against the background of the nonthermal continuum. The polarization of the hard X-ray (20–100 keV) radiation was estimated to be ≤15–20%. No significant increase in the flux of energetic protons from the flare under consideration was found. At the same time, according to ACE data, the fluxes of energetic electrons in interplanetary space increased shortly (～25 min) after the flare.  相似文献   

19.
We examine empirical atmospheric structures that are consistent with enhanced white-light continuum emission in solar flares. This continuum can be produced either by hydrogen bound-free emission in an enhanced region in the upper chromosphere, or by H- emission in an enhanced region around the temperature minimum. In the former case, weak Paschen jumps in the spectrum will be present, with the spectrum being dominated by a strong Balmer continuum, while in the latter case the spectrum exhibits a weaker, flat enhancement over the entire visible spectrum.We find that when proper account is taken of radiative backwarming processes, the two enhanced atmospheric regions above are not independent, in that irradiation by Balmer continuum photons from the upper chromosphere creates sufficient heating around the temperature minimum to account for the temperature enhancements there. Thus the problem of main phase white-light flare production reduces to one of creating temperature enhancements of order 104 K in the upper chromosphere; radiative backwarming then naturally accounts for the enhancements of order 100 K around the temperature minimum.Heating by electron and proton bombardment, and by XUV irradiation from above, are then considered as candidates for creating the necessary enhancements in the upper chromosphere. We find that electron bombardment can be ruled out, whereas bombardment by protons in the few-MeV energy range is a viable candidate, but one without strong observational support. The XUV irradiation hypothesis is examined by incorporating it self-consistently into the PANDORA radiative transfer algorithm used to construct the empirical model atmospheres; we find that the introduction of XUV radiation, with flux and spectrum appropriate to white-light flare events, does indeed produce sufficient radiative heating in the upper chromosphere to balance the radiative losses associated with the required temperature enhancements.In summary, we find that the radiative coupling of (i) the upper chromosphere and temperature minimum regions (through Balmer continuum photons) and (ii) the transition region and upper chromosphere (through XUV photons) can account for white-light emission in solar flares.Presidential Young Investigator.  相似文献   

20.
We present high-speed spectrophotometric observations of the Hα emission in the exotic cataclysmic variable AE Aqr. Over 10 000 spectra with a sampling rate of ∼ 6 s were obtained. The well-known 16.5- and 33-s oscillations were not detected in either the continuum or the line, nor were any quasi-periodic oscillations detected. The Hα line shows remarkably complex behaviour, with changes in flux of up to a factor of 3 in a few hours. The line does not act as a single entity — the instantaneous line profile is highly asymmetric and consists of a superposition of emission components that are localized in velocity. We find that during flares the Hα emission is delayed and decays more slowly than the continuum. The Hα variations are not linearly correlated with the continuum variations. Examination of the trailed spectrograms and Doppler tomograms reveals no signatures of an accretion disc, but rather supports the idea that mass is being ejected by a propeller mechanism.  相似文献   

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