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1.
New data for the energy and location of the hard-emission centers of a solar flare agree with an electrodynamic model of a solar flare based on the idea of the accumulation of free magnetic energy in the field of a current sheet. Three-dimensional MHD simulations are used to show that the energy stored in the preflare magnetic field of the current sheet is sufficient for the development of a flare and a coronal mass ejection. The flare and coronal mass ejection result from the explosive decay of the current sheet. The position of the brightness-temperature maximum of the radio emission during the flare coincides with the maximum of the current in the current sheet. The exponential spectrum of relativistic protons generated during the flare is consistent with acceleration by the electric field during the current-sheet decay.  相似文献   

2.
The initial fast decay phase of a stellar flare is shown to be caused by the rapid cooling of the flare plasma, which radiates as a perfect blackbody at the flare brightness maximum.  相似文献   

3.
The fine temporal structure of two flares observed on the red-dwarf flare star AD Leo on February 4, 2003 with the 1.25-m telescope of the Crimean Astrophysical Observatory in a rapidphotometry mode is studied. One flare lasted approximately 5 min and another was longer than 8 min. The amplitudes in the U band were 1.65 m and 1.76 m . A detailed color analysis shows that the flare parameters at the maximum brightnesses corresponded to blackbody radiation with temperatures of approximately 14 000 and 13 000 K, enabling the monitoring of temperature — the rapid cooling of flare plasma near the flare maxima—for the first time. During 1.5 and 3.5 min at the maxima, the flares radiated as blackbodies, but these behaved as optically thick plasmas in the Balmer continuum on the second half of the descending branches. At the end of the first flare, the plasma became optically thin in the Balmer continuum; the final stage of the second flare was not observed. The flare areas at the luminosity maxima were 2.1 × 1018 and 3.0×1018 cm2 in a blackbody approximation, or 0.07%and 0.11%of the visible stellar disk. The occurrence of quasi-periodic brightness pulsations during red-dwarf flares on time scales of approximately ten seconds is confirmed.  相似文献   

4.
Solar filtergrams obtained at the Crimean Astrophysical Observatory at the center and wings of the H?? line are used to study variations in filaments, in particular, in arch filament systems (AFSs). These are considered as an indicator of emerging new magnetic flux, providing information about the spatial locations of magnetic-field elements. Magnetic-field maps for the active region NOAA 10030 are analyzed as an example. A method developed earlier for detecting elements of emerging flux using SOHO/MDI magnetograms indicates a close link between the increase in flare activity in theNOAA 10030 group during July 14?C18, 2002 and variations in the topological disconnectedness of the magnetograms. Moreover, variations in the flare activity one day before a flare event are correlated with variations in the topological complexity of the field (the Euler characteristic) in regions with high field strengths (more than 700 G). Analysis of multi-wavelength polarization observations on the RATAN-600 radio telescope during July 13?C17, 2002 indicate dominance of the radio emission above the central spot associated with the increase in flare activity. In addition to the flare site near the large spot in the group, numerous weak flares developed along an extended local neutral line, far from the central line of the large-scale field. The statistical characteristics of the magnetic-field maps analyzed were determined, and show flare activity of both types, i.e., localized in spot penumbras and above the neutral line of the field.  相似文献   

5.
Observations of the total magnetic field in the active region NOAA 6757 have been used to study the turbulence regime from 2.5 h before the onset of a 2B/X1.5 flare until two minutes after its maximum. The curvature of the exponent ζ(q) for the structure functions of the B z field increases monotonically before the flare (i.e., the multifractal character of the B z field becomes more complex) but straightens at the flare maximum and coincides with a linear Kolmogorov dependence (implying a monofractal structure for the B z field). The observed deviations of ζ(q) from a Kolmogorov line can be used for short-term forecasting of strong flares. Analysis of the power spectra of the B z field and the dissipation of magnetic-energy fluctuations shows that the beginning of the flare is associated with the onset of a new turbulence regime, which is closer to a classical Kolmogorov regime. The scaling parameter (cancellation index) of the current helicity of the magnetic field, k h , remains at a high level right up until the last recording of the field just before the flare but decreases considerably at the flare maximum. The variations detected in the statistical characteristics of the turbulence can be explained by the formation and amplification of small-scale flux tubes with strong fields before the flare. The dissipation of magnetic energy before the flare is primarily due to reconnection at tangential discontinuities of the field, while the dissipation after the flare maximum is due to the anomalous plasma resistance. Thus, the flare represents an avalanche dissipation of tangential discontinuities.  相似文献   

6.
Using observational data obtained with the Yohkoh, SOHO, and TRACE satellites, it is shown that the three-dimensional structure of the large solar flare of July 14, 2000 was determined by the topology of the large-scale magnetic field of the active region giving rise to the flare. The locations and shapes of chromospheric ribbons and brightness centers on these ribbons are explained. The observed behavior of the flare is attributed to rapid magnetic reconnection in the corona. The electric field accelerating particles in the reconnecting current sheets is estimated.  相似文献   

7.
Flaring of associated gas from oil exploitation has several consequences on the environment. This study explores the spatial variability effects of gas flaring on the growth and development of cassava (Manihot esculenta), waterleaf (Talinum triangulare), and pepper (Piper spp.) crops commonly cultivated in the Niger Delta, Nigeria. Data was collected on soil and atmospheric temperature and moisture at a 20-m interval, starting at 40 m from the flare point to a distance of 140 m. Lengths and widths of crop leaves, height of crop plants and cassava yields were measured at the specified distances. The amino acid, ascorbic acid, starch, and sugar constituents of the cassava yields were determined. The results suggest that a spatial gradient exists in the effects of gas flares on crop development. Retardation in crop development manifests in decreased dimensions of leaf lengths and widths of cassava and pepper crops closer to the gas flare point. Statistical analysis also confirms that cassava yields are higher at locations further away from the flare point. In addition, the amount of starch and ascorbic acid in cassava decreased when the plant is grown closer to the gas flare. High temperatures around the gas flare appear to be the most likely cause of this retardation. The waterleaf crop, on the other hand, appears to thrive better around the gas flare point.  相似文献   

8.
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   

9.
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   

10.
Volvach  L. N.  Volvach  A. E.  Larionov  M. G.  Wolak  P.  Kramer  B.  Menten  K.  Kraus  A.  Brand  J.  Zanichelli  A.  Poppi  S.  Rigini  S.  Ipatov  A. V.  Ivanov  D. V.  Mikhailov  A. G.  Mel’nikov  A. 《Astronomy Reports》2019,63(8):652-665

The most powerful flare ever registered in the Galactic water-maser source W49N has been detected in long-term monitoring data in the 616–523 transition with line frequency f = 22.235 GHz carried out on the 22-m Simeiz, 32-m Toruń, 100-m Effelsberg, and 32-m Medicina radio telescopes, beginning in September 2017 and continuing in 2018. Some stages of the flare were monitored daily. Detailed variations of the source spectral flux density with time have been obtained. At the flare maximum, the flux exceeded P ≈ 8 × 104 Jy, and this was record highest flux registered over the entire history of observations of this source. Important conclusions related to details of the mechanism for the H2O line emission have been drawn. An exponential increase in the flare flux density was detected during both the rise and decline of the flare. The data obtained indicate that the maser is unsaturated, and remained in this state up to the maximum observed flux densities. Additional support for the idea that the maser is unsaturated is the shape of the dependence of the line width on the flux. The characteristics of the variations of the spectral flux density are probably associated with a sharp increase in the density of the medium and the photon flux that led to an increase in the temperature from an initial level of 10–40 K to hundreds of Kelvins. Interferometric maps of the object during the increase in the spectral flux density of the flare have been obtained. A possible mechanism for the primary energy release in W49N is considered.

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11.
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   

12.
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   

13.
Observations of the hard X-ray and radio event of October 27, 2002 are analyzed. This flare was observed from near-Martian orbit by the HEND instrument developed at the Space Research Institute of the Russian Academy of Sciences and installed on the Mars Odyssey satellite. Although this powerful flare was observed far over the eastern solar limb, the extended source associated with the flare was detected by RHESSI at energies up to about 60 keV. The eruptive event was observed in the radio at the Nobeyama Radio Observatory. The properties of the X-ray radiation are used to calculate the spectrum of the accelerated electrons responsible for the observed radiation, assuming that the target is thick for a Martian observer and thin for a terrestrial observer. The results are compared with the results of radio observations. The conditions for electron propagation in the corona are discussed.  相似文献   

14.
We present an analysis of data from multi-frequency monitoring of the blazar 3C 454.3 in 2010–2012, when the source experienced an unusually prolonged flare with a duration of about two years. This corresponds to the orbital period of the companion in a scenario in which two supermassive black holes are present in the nucleus of 3C 454.3. The flare’s shape, duration, and amplitude can be explained as a result of precession, if the plane of the accretion disk and the orbital plane of the binary are coincident. We detected small-scale structure of the flare, on time scales of no more than a month. These features probably correspond to inhomogeneities in the accretion disk and surrounding regions, with sizes of the order of 1015 cm. We estimated the size of the accretion disk based on the dynamical and geometrical parameters of this binary system: its diameter is comparable to the size of the orbit of the supermassive binary black hole, and its thickness does not exceed the gravitational radius of the central black hole. The presence of characteristic small-scale features during the flare makes it possible to estimate the relative time delays of variations in different spectral ranges: from gamma-ray to millimeter wavelengths.  相似文献   

15.

Results of a study of the influence of solar-type host stars superflares on the gas dynamics of the extended envelopes of giant exoplanets are presented. During flare events, the radiation intensity of the host star in the extreme ultraviolet and soft X-ray can increase by several orders of magnitude for a short time, leading to strong local heating of the exoplanet atmosphere on the side facing the star, with the formation of shocks in the atmosphere. Computations of the gas-dynamical response of the atmosphere of the hot Jupiter HD 209458b to characteristic superflares of solar-like stars were carried out earlier in [1] using a one-dimensional aeronomical model correctly taking into account heating and chemical processes in the atmosphere. To investigate the outflow of atmospheric gas, the results obtained with this onedimensional model were used as simple boundary conditions for computations of the three-dimensional flow structure after a flare. The results of these three-dimensional gas-dynamical computations show that the mass ejection of the flare increases the size of the envelope over several hours, which could be detected with existing observing facilities. It is shown that the mass-loss rates for the most powerful superflare considered could be enhanced by an order of magnitude over several tens of hours after the flare.

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16.
Semi-empirical models for three kernels emitting in the continuum during the pre-impulsive and impulsive phases of the white-light flare of August 9, 2011 have been calculated, based on observations of the continuum brightness near 6579 Å, Hα profiles, and photospheric iron lines. These computations show that, in order to achieve agreement between the computed and observed profiles and the contrast of the continuum emission of the impulsive kernels of the white-light flare, the temperature must be increased in both the lower chromosphere and the upper photosphere. The most efficient heating is located deeper in the photosphere in the pre-impulsive than in the impulsive phase, and chromospheric heating is negligible in the pre-impulsive phase. Spectral data and the results of model computations indicate that it is difficult to explain the emission of the white-light flare kernels as the effect of heating by energy transported from the corona into lower-lying, deep layers of the atmosphere by canonical transport mechanisms.  相似文献   

17.
A one-dimensional aeronomic model of the upper atmosphere of a giant planet is used to study the reaction of the atmosphere of the hot Jupiter HD 209458b to additional heating by a stellar flare. It is shown that the absorption of additional energy from the stellar flare in the extreme ultraviolet leads to local heating of the atmosphere, accompanied by the formation of two shocks propagating in the atmosphere. Possible observational manifestations of these shocks and the feasibility of their detection are discussed.  相似文献   

18.
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   

19.
Results on the spectral analysis using geomagnetic field at three low latitude stations and the planetary magnetic activity index have shown peaks in the power densities in a broad band centred around 146-day period. This periodic behaviour appears to be close to that shown by the solar flare activity index for the same interval. It is suggested that the geoeffectiveness of the flare activity signal in different phases of the solar cycle can be better worked out using long series of ground-based geomagnetic data.  相似文献   

20.
Data from the Nobeyama Radioheliograph at 17 GHz with high spatial and temporal resolution are used to detect quasi-periodic pulsations with periods from 55 to 250 s in the thermal component of the microwave emission of a solar flare loop observed on June 2, 2007. Observed pulsations with periods of about 110–120 s are co-phased along the entire loop axis. The observed periodicity is most likely due to modulation of the radio emission by slow magnetoacoustic waves trapped in the filamentary flare loop.  相似文献   

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