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1.
The impulsive phase of the powerful solar flare of September 13, 2005 (～23:18–23:21 UT) observed in hard X-rays (～25–300 keV) by the RHESSI spacecraft is analyzed. The spatial locations of numerous X-ray sources are compared with the locations of Transition Point (TP) singularities in the magnetic field calculated for flare regions. It is shown that the hard X-ray sources are related to TP singularities, i.e., to possible locations of primary flare energy release. Magnetic field lines expelled from the vicnity of these magnetic singularities end in the chromosphere, near hard X-ray sources. The question of how these multiple magnetic singularities are involved virtually simultaneously in the energy-release process requires further study.  相似文献   

2.
The flare source of thermal X-rays above a magnetic arch in the corona arises from the dissipation of the magnetic energy of the current sheet formed at the reconnection of magnetic-field lines. The sources of hard X-rays emitted from the footpoints of the magnetic arch are beams of electrons accelerated in field-aligned currents induced by the Hall electric field generated in the current sheet. Both the hard X-rays detected above the active region and the type III radio emission are radiated by electrons accelerated in the field-aligned currents induced by Alfven waves. The solar cosmic rays are emitted promptly at the instant of the flare. It is important that the Lorentz electric field accelerates protons along the singular magnetic X line. The relativistic protons propagate along the interplanetary magnetic field. These protons have exponential spectra, typical for acceleration occurring in current sheets. A mechanism that is relevant for the generation of delayed cosmic rays, which demonstrate significant anisotropy and a power-law spectrum with γ ∼5, is also discussed.  相似文献   

3.
Magnetic field singularities detected earlier as the self-intersection points of the F = 0 curves/surfaces are studied (where F is a certain differential factor calculated in the reference frame of the magnetic field at the given point); these singularities can be considered to be sources of the energy release in solar flares. Two types of such singularities, called transition points (TPs), have been found: the first type (TP1) corresponds to an intersection of the same type of components (terms) of the divergence of the magnetic field, and the second type (TP2) to the intersection of dissimilar components. There are some discontinuous spatial processes at these singularities, which produce jumps in the components of the divergence of the magnetic field (and their signs). TP2 singularities should result in much stronger effects than those resulting from TP1 singularities, which should give rise to the most powerful solar flares. The singularities studied are also compared with the null point of the magnetic field, when it exists. In particular, a model magnetic field containing a null point is considered. It is shown that the TP singularities do not coincide with the null point, but can be located in its vicinity; in the case considered, the TP1 singularity is located fairly close to the null point.  相似文献   

4.
An analysis is presented for the class-M9.3 solar flare of November 6, 2004, whose decay phase displayed weakly damped harmonic oscillations of the predominantly thermal X-ray flux detected by the RHESSI spacecraft (at energies ≲25 keV). The period of these oscillations was ≈78 s, and their characteristic decay time ≈100 min. Similar quasi-periodic pulsations were observed in the decimeter-centimeter radio flux (pulsations of a type-IV radio outburst), but were less pronounced in the non-thermal hard X-ray flux (≳25 keV). The area of the quasi-stationary X-ray source, which was located primarily at the apex of a set of flare loops (≲15 keV) that were cooled primarily via thermal conduction, was found to be in anti-phase with the oscillating X-ray flux it emitted. The observed oscillations are interpreted as harmonic modulations of the radiation flux emitted by the heated thermal flare-loop plasma, due to the global, standing, sausage mode of fast magnetoacoustic waves excited in the loop.  相似文献   

5.
We analyze the flare events of October 28 and May 27, 2003 to examine the possible connection of solar flares with singularities in the differential characteristics of solar magnetic fields. The relation between flares and the behavior of F indicators (which describe structural singularities of the magnetic fields) introduced earlier is analyzed. It is shown that the generation of flares can be associated with self-intersections (or reconnection) of the F = 0 curves, where magnetic reconnection can occur. Consequently, the current sheets generated in such regions can be sources of energy release.  相似文献   

6.
Powerful solar flares contain one or more impulsive events, plasma ejection, and the subsequent development of gigant post-eruptive loops. In the middle of the 1980s, Jakimiec proposed an analysis of the flare loops based on log T-1/2log EM diagrams constructed from the observed soft X-rays (the so-called Jakimiec model). We have used this method to construct and analyze these diagrams not for various arbitrary events, but instead for similar flares within a single center of activity; in other words, for homological flares (two-ribbon flares observed in November 2000, powerful prolonged events observed in October–November 2003, etc.). This eliminated the effect of differences in the magnetic configurations, enabling us to find a new relationship: the slope (tan α) of the logT-1/2log EM line during the flare decay depends on the maximum temperature T max at the source of the soft X-rays. The dependence of tan α on T max gradually evolves from a series of short flares to a series of powerful, prolonged, nonstationary processes. Our results support the idea that the development of post-eruptive loops depends on the energy of the impulsive events for the phenomenon as a whole. Explosive evaporation simultaneously increases both the temperature and the density of the plasma at the loop top. The subsequent evolution of the post-eruptive formations depends on the difference in the initial conditions and on the degree of opening of the magnetic configuration. The importance of our analysis for the duration of flares and differences between dimmings is briefly discussed.  相似文献   

7.
The results of monitoring the flaring activity of Mrk 421 with the XMM-Newton and RXTE orbiting observatories are presented. The ASM/RXTE data show that, during most of the observational period, 2002–2006, the source was in a very active state, with a mean 1.5–12 keV flux equals ∼17 mCrab. Analysis of daily and weekly averaged data shows strong X-ray variability of Mrk 421 on time scales from days to months. The long-term light curve demonstrates a rich variety of variability patterns and a complex hierarchical flare structure, in most cases superimposed on longer trends of rising and decreasing source activity. Quantitative estimates of the variability of Mrk 421 shows evidence of correlations between the source intensity in X-rays and the variability parameters, both for separate years and epochs and for most of the observational period. The soft and hard X-ray components (according to XMM-Newton data) are correlated with each other, and spectral changes (according to ASM/RXTE data) are characterized by increasing hardness with brightening of the object in X-rays. Moderate spectral variability at individual epochs and evidence for an energy dependence of the source variability are also observed. The 2–12 keV fluxes from Mrk 421 detected by XMM-Newton are consistent with the maximum 2–10 keV flux detected by ASCA ∼10 years ago. An analysis of simultaneous day-time-scale variability of Mrk 421 in X-rays (ASM/RXTE) and very-high-energy γ-rays (GT-48 Cherenkov telescope of the Crimean Astrophysical Observatory) in periods of increased activity of the source in December 2002 and April 2004 is also presented. Published in Russian in Astronomicheskiĭ Zhurnal, 2008, Vol. 85, No. 7, pp. 589–602. The article was translated by the authors.  相似文献   

8.
The acceleration of particles by solar flares with extremely large proton fluxes whose energies exceed 100 MeV is considered. Most importantly, the location of the source of such acceleration in the flare of July 14, 2000, is determined assuming that the acceleration time coincides with the observed burst of hard line and continuous gamma-ray emission. The onset of this event corresponds to 10:19 UT, when data taken by the TRACE space observatory show that one of the flare ribbons reached a large sunspot in a group. The time interval for the development of the flare, 10:20–10:28 UT, is associated with the beginning of an increasing proton flux at the Earth. The region of efficient acceleration is estimated to be approximately two to three times higher than the height where the hard X-ray pulse usually originates (about 7000 km). The results are generalized for 28 powerful flares with extremely efficient acceleration of relativistic particles—in particular, for the well-studied events of June 15, 1991, and May 24, 1990—and are compared with the results of a statistical analysis of over 1100 increasing-proton-flux events. Efficient particle acceleration seems to be associated with the powerful impulsive episodes of the large flares analyzed. The results suggest that, along with sources of local (as in impulsive flares) and post-eruptive acceleration, there is an additional, very efficient, moderate-scale “accelerator” in tenuous regions with fairly strong magnetic fields and magnetic-field gradients.  相似文献   

9.
Multi-wavelength observations and magnetic-field data for the solar flare of May 10, 2012 (04: 18 UT) are analyzed. A sign change in the line-of-sight magnetic field in the umbra of a small spot has been detected. This is at least partly associated with the emergence of a new magnetic field. A hard X-ray flare was recorded at almost the same time, and a “sunquake” was generated by the impact of the disturbance in the range of energy release on the photosphere. A sigmoid flare was recorded at the beginning of the event, but did not spread, as it usually does, along the polarity inversion (neutral) line. SDO/HMI full vectormagnetic-fieldmeasurements are used to extrapolate the magnetic field of AR 11476 into the corona, and to derive the distribution of vertical currents jz in the photosphere. The relationship between the distribution of currents in the active region and the occurrence of flares is quite complex. The expected “ideal” behavior of the current system before and after the flare (e.g., described by Sharykin and Kosovichev) is observed only in the sigmoid region. The results obtained are compared with observations of two other flares recorded in this active region on the same day, one similar to the discussed flare and the other different. The results confirm that the formation and eruption of large-scale magnetic flux ropes in sigmoid flares is associated with shear motions in the photosphere, the emergence of twisted magnetic tubes, and the subsequent development of the torus instability.  相似文献   

10.
Results of observations of the OH maser in W75N at 18 cm are reported. The observations were obtained on the radio telescope of the Nancay Radio Astronomy Observatory (France) from October 2007 to April 2009. The profiles of the Stokes parameters I, Q, U, and V in the 1665 and 1667 MHz OH lines have been measured. A technique taking into account instrumental polarization has been developed and applied. The emission in the OH lines is strongly polarized both linearly and circularly. The degree of polarization of some emission features reaches almost 100%. There were two flares of the maser emission in 2008–2009. During a flare at a radial velocity of +5.5 km/s, a Zeeman pattern was detected in the 1667 MHz line. The measured intensity of the line-of-sight component of the magnetic field was −1.1 mG, which corresponds to the field being directed away from the observer. The maser flares and the associated enhancement of the magnetic field could be associated with the compression of gas at a shock front.  相似文献   

11.
An analysis of the dynamics of the electron temperature of the solar atmosphere in regions where solar flares appear is presented. The temperatures are estimated from the emission in spectral lines of ions with various degrees of ionization. The emission of ionized helium and highly ionized iron was used. Images of preflare states and of flares from the archive of the American SDO spacecraft are analyzed. A solar flare is usually preceded by the registration of a bright glowing structure above the action region, with a temperature exceeding that of the corona. This preflare structure (~1010 cm) is identified with the development of a system of currents, which, according to numerical simulations, is responsible for the accumulation of energy above the active region before the flare. After several tens of hours of a slow increase in the brightness of the preflare glow in the 94 Å iron (FeXVIII) line, the emission in the 193 Å line of FeXXIV increases sharply, indicating a flare-like growth of the temperature up to at least 20 MK. This growth of the emission coincides with the onset of the solar flare. The observed dynamics of the emission in spectral lines of highly ionized ions is consistent with an electrodynamic model of a solar flare based on the accumulation of magnetic energy in a current sheet above the active region and the explosive release of the stored energy. Studies of mechanisms for solar flares are of special importance in connection with the discovery of solar cosmic rays. Information from the worldwide network of neutron monitors and from the GOES spacecraft has made it possible to firmly state that the source of solar rays is solar flares, not shocks generated by such flares. It cannot be ruled out that a similar mechanism, not shocks, is also responsible for the acceleration of cosmic rays in the Galaxy.  相似文献   

12.
Soft X-ray data for prolonged flares in subgiants in RS CVn binary systems and some other active late-type stars (AB Dor, Algol) are analyzed. During these nonstationary events, a large amount of hot plasma with temperatures exceeding 108 K exists for many hours. Numerical simulations of gas-dynamical processes in the X-ray source—giant loops—can yield reliable estimates of the plasma parameters and flare-source size. This confirms that such phenomena exist while considerable energy is supplied to the top part of a giant loop or system of loops. Refined estimates of the flare energy (up to 1037 erg) and scales contradict the widely accepted idea that prolonged X-ray flares are associated with the evolution of local magnetic fields. The energy of the current component of the large-scale magnetic field arising during the ejection of magnetic field by plasma jets or stellar wind is estimated. Two cases are considered: a global stellar field and fields connecting regions with oppositely directed unipolar magnetic fields. The inferred energy of the current component of the magnetic field associated with distortion of the initial MHD configuration is close to the total flare energy, suggesting that large-scale magnetic fields play an important role in prolonged flares. The flare process encompasses some portion of a streamer belt and may propagate along the entire magnetic equator of the star during the most powerful prolonged events.  相似文献   

13.
We have carried out 3D MHD modeling of the solar corona above the active region AR 0365 before a series of flares observed on May 26–27, 2003. Maps of the evolving photospheric magnetic fields preceding the flares were used as boundary conditions. An emergence of new flux equal to ～1.5 × 1022 Maxwell preceded the observed series of X-ray flares. Modeling a large region 4 × 1010 cm in size demonstrates the formation of several current sheets in the vicinities of coronal Xlines, both already existing in the initial potential field and arising due to the emergence of the new magnetic flux. Each current sheet could be responsible for an elementary flare.  相似文献   

14.
This work continues earlier statistical analyses of catalogued proton events in cosmic rays. The spectra of proton enhancements identified from the logarithm of the ratio of the proton fluxes with energies exceeding 100 and 10 MeV, δ = log(F 100/F 10), are studied focusing on 172 powerful events with favorable conditions for escaping from the corona and subsequent propagation in the interplanetary space. The δ distribution for the flares is Gaussian, with a comparatively weak spread in δ. The distribution maximum corresponds to an excess of the 10 MeV flux over the 100 MeV flux by a factor of 30. The fact such a frequent spectrum does exist supports the idea that both soft and hard protons are efficiently accelerated, probably by a single mechanism that operates during the explosive phases of the flares. The sizes of the loops of M2-X4 flares observed by the Yohkoh Hard X-Ray Telescope at energies exceeding 50 keV indicate low heights for the main acceleration regions. There is some excess over the Gaussian distribution for “softer” events. Some post-eruptive phenomena can be clearly distinguished in these events, and they display a correlation between δ and the total flare duration. Thus, there are two sources of the particle acceleration operating at low and high altitudes during the explosive and post-eruptive phases of the solar flares, respectively. The second source, which is manifested through some prolonged flares and filament-ejection phenomena, accelerates protons only to energies of 10–30 MeV.  相似文献   

15.
The correlation between the magnetic flux in an active solar region and associated powerful solar flares is studied. The behavior of the active regions AR 10486 and AR 10365 is considered. These regions produced a series of class X flares as they crossed the solar disk. The flares appeared when the magnetic flux exceeded 1022 Mx. The magnetic flux remained constant during all the flares except for one. During this flare, the flux decreased by about 10%; this impulsive decrease of the flux was also recorded in the absence of flares. No energy flux from the photosphere to the corona at the time of the flare was observed. The behavior of the photospheric field in AR 10486 and AR 10365 is consistent with a slow accumulation of energy in the corona and the explosive release of energy stored in the magnetic field of a current sheet above an active region during the flare.  相似文献   

16.
Interactions of particles accelerated in solar flares with matter in the solar atmosphere give rise to neutrons, which are efficiently captured on hydrogen nuclei as they are slowed to thermal velocities. This capture is accompanied by the emission of a gamma-ray with energy 2.223 MeV. Observational data for the temporal profiles of the gamma-ray fluxes in this line are used to study the plasma-density distribution in the solar atmosphere during the flares of December 16, 1988, March 22, 1991, and November 6, 1997. This analysis is based on comparisons between the observations and profiles computed taking into account a number of parameters describing the generation and transport of the flare neutrons in atmospheric layers of various densities. In three cases studied, the density of the material in the photosphere below the flare region is enhanced compared to the density in an unperturbed part of the solar atmosphere at the same height. In the case of the December 16, 1988 flare, we are able for the first time to relate the profile of the 2.223 MeV line with the shape of the accelerated particle (proton) spectrum. This opens new possibilities for studies of particle acceleration on the Sun based on observations of flare gamma-ray emission.  相似文献   

17.
A detailed study of two major solar flares that occurred in Group 10786 at the time of its disappearance behind the western limb is presented. The flares of July 14, 2005 were previously studied fairly poorly, as no RHESSI hard X-ray observations were available for themaxima of the twomost powerful of these flares. Observations carried out using the HEND equipment (on the Mars Odyssey spacecraft) developed at the Institute for Space Research in Moscow are used here to fill this gap. In the first flare, an intense, impulsive burst occurred at 07:23 UT, about 1.5 h after the onset of a weak, prolonged event. While processes in the neighborhood of the northern spot dominated in the flares of July 5–9, a powerful impulsive energy release on July 14 emerged when the flare process that originated in the North reached the southern spot. Our analysis of the flare activity of this medium-sized group reveals a gradual enhancement of the flare activity and a strong interaction between the acceleration above the magnetic-field neutral line and in the immediate vicinity of the spots. At the time of the culmination of the flare activity in the group on July 13 and 14, the pattern of nonstationary processes changes: fast coronal mass ejections form after a series of impulsive energy-release events. Spacecraft observations of the burst of July 14 after 11 UT at points separated in longitude (on RHESSI and Mars Odyssey) revealed clear anisotropy of the flare emission at energies exceeding 80 keV.  相似文献   

18.
Regularities have been searched for in the dynamics of characteristics of flare solar radiation during the development of the active region NOAA 0069 in the interval of August 14–24, 2002. The SONG (Solar Neutrons and Gamma rays) instrument onboard the Russian CORONAS-F Solar Observatory recorded hard X-ray and gamma-ray radiation in nine of the 30 flares of class above C5 in this active region within the indicated time interval. It was obtained that, in accordance with the development of the active region, the X- and gamma-ray flux tended to increase at the flare maxima while the hard X-ray spectral index tended to decrease; flares with a harder radiation spectrum occurred in the sunspot umbra, i.e., in the region with the strongest magnetic fields.  相似文献   

19.
We present the first results of data on solar flares detected by the HEND instrument onboard the 2001 Mars Odyssey interplanetary spacecraft during its flight to Mars and in orbit around Mars. The instruments carried by the spacecraft, which was developed at the Space Research Institute of the Russian Academy of Sciences, included a scintillation detector with two crystals, enabling the detection of photons with energies from tens of keV to 2.5 MeV with high time resolution. Several dozen flares were detected on both the sides visible from the Earth and back side of the Sun, supplementing other available data in a number of cases. A joint analysis of the HEND data together with data obtained in near-Earth orbits enabled the detection of variations in the integrated fluxes of photons with energies exceeding 80 keV during observations of flares near the limb from various directions. Two events were analyzed in great detail: the setting of a region displaying frequent very short flares on May 20, 2001, and the rising of the group 10486, which displayed numerous flare phenomena on the limb followed by extremely high activity in October–November 2003. These variations appear in simultaneous observations of limb M flares made at angles differing by only 8°–10°. Analyses of observations of rising sources obtained on two spacecraft lead to similar results. This indicates that the vast majority of emission at energies exceeding 80 keV arises at altitudes of no higher than seven to ten thousand kilometers. We briefly consider the powerful solar-disk gamma-ray flare of August 25, 2001. In this case, there are some differences in the behavior of the hard radiation in the decay phase for observations made at angles differing by 25°, which is most likely due to differences in the instrumental responses to radiation with this spectrum. The absence of hard radiation at great heights in the region of the “cusp” places some constraints on our picture of the physical processes occurring in powerful solar flares.  相似文献   

20.
The results of a study of H2O and OH maser emission in the complex region of active star formation W75 N are presented. Observations were obtained using the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) and the Nan3ay radio telescope (France). Flaring H2O maser features may be identified with maser spots associated with the sources VLA 1 and VLA 2. Themain H2O flares occurred in VLA 1. The flare emission was associated with either maser clusters having closely spaced radial velocities and sizes up to ~2 AU or individual features. The maser emission is generated in a medium where turbulence on various scales is present. Analysis of the line shapes during flare maxima does not indicate the presence of the simplest structures—homogeneous maser condensations. Strong variability of the OH maser emission was observed. Zeeman splitting of the 1665-MHz line was detected for several features of the same cluster at a radial velocity of +5.5 km/s. The mean line-of-sight magnetic field in this cluster is ~0.5 mG, directed away from the observer. Flares of the OH masers may be due to gas compression at a shock or MHD wave front.  相似文献   

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