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1.
A time-dependent model for the energy of a flaring solar active region is presented based on an existing stochastic jump-transition
model (Wheatland and Glukhov in Astrophys. J.
494, 858, 1998; Wheatland in Astrophys. J.
679, 1621, 2008 and Solar Phys.
255, 211, 2009). The magnetic free energy of an active region is assumed to vary in time due to a prescribed (deterministic) rate of energy
input and prescribed (random) jumps downwards in energy due to flares. The existing model reproduces observed flare statistics,
in particular flare frequency – size and waiting-time distributions, but modeling presented to date has considered only the
time-independent choices of constant energy input and constant flare-transition rates with a power-law distribution in energy.
These choices may be appropriate for a solar active region producing a constant mean rate of flares. However, many solar active
regions exhibit time variation in their flare productivity, as exemplified by NOAA active region (AR) 11029, observed during
October – November 2009 (Wheatland in Astrophys. J.
710, 1324, 2010). Time variation is incorporated into the jump-transition model for two cases: (1) a step change in the rates of flare transitions,
and (2) a step change in the rate of energy supply to the system. Analytic arguments are presented describing the qualitative
behavior of the system in the two cases. In each case the system adjusts by shifting to a new stationary state over a relaxation
time which is estimated analytically. The model exhibits flare-like event statistics. In each case the frequency – energy
distribution is a power law for flare energies less than a time-dependent rollover set by the largest energy the system is
likely to attain at a given time. The rollover is not observed if the mean free energy of the system is sufficiently large.
For Case 1, the model exhibits a double exponential waiting-time distribution, corresponding to flaring at a constant mean
rate during two intervals (before and after the step change), if the average energy of the system is large. For Case 2 the
waiting-time distribution is a simple exponential, again provided the average energy of the system is large. Monte Carlo simulations
of Case 1 are presented which confirm the estimate for the relaxation time and the expected forms of the frequency – energy
and waiting-time distributions. The simulation results provide a qualitative model for observed flare statistics in AR 11029. 相似文献
2.
We present an analysis of hard X-ray imaging observations from one of the first solar flares observed with the Reuven Ramaty
High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft, launched on 5 February 2002. The data were obtained from the 22
February 2002, 11:06 UT flare, which occurred close to the northwest limb. Thanks to the high energy resolution of the germanium-cooled
hard X-ray detectors on RHESSI we can measure the flare source positions with a high accuracy as a function of energy. Using
a forward-fitting algorithm for image reconstruction, we find a systematic decrease in the altitudes of the source centroids
z(ε) as a function of increasing hard X-ray energy ε, as expected in the thick-target bremsstrahlung model of Brown. The altitude
of hard X-ray emission as a function of photon energy ε can be characterized by a power-law function in the ε=15–50 keV energy
range, viz., z(ε)≈2.3(ε/20 keV)−1.3 Mm. Based on a purely collisional 1-D thick-target model, this height dependence can be inverted into a chromospheric density
model n(z), as derived in Paper I, which follows the power-law function n
e(z)=1.25×1013(z/1 Mm)−2.5 cm−3. This density is comparable with models based on optical/UV spectrometry in the chromospheric height range of h≲1000 km, suggesting that the collisional thick-target model is a reasonable first approximation to hard X-ray footpoint sources.
At h≈1000–2500 km, the hard X-ray based density model, however, is more consistent with the `spicular extended-chromosphere model' inferred from radio sub-mm observations, than with standard models based on hydrostatic equilibrium. At coronal heights,
h≈2.5–12.4 Mm, the average flare loop density inferred from RHESSI is comparable with values from hydrodynamic simulations
of flare chromospheric evaporation, soft X-ray, and radio-based measurements, but below the upper limits set by filling-factor
insensitive iron line pairs. 相似文献
3.
We revisit the flare that occurred on 13 January 1992, which is now universally termed the “Masuda flare”. The new analysis
is motivated not just by its uniqueness despite the increasing number of coronal observations in hard X-rays, but also by
the improvement of Yohkoh hard X-ray image processing, which was achieved after the intensive investigations on this celebrated event. Using an uncertainty
analysis, we show that the hard X-ray coronal source is located closer to the soft X-ray loop by about 5000 km (or 7 arcsec)
in the re-calibrated Hard X-ray Telescope (HXT) images than in the original ones. Specifically, the centroid of the M1-band
(23 – 33 keV) coronal source is above the maximum brightness of the Soft X-ray Telescope (SXT) loop by 5000±1000 km (9600
km in the original data) and above the apex of the SXT loop represented by the 30% brightness contour by 2000±1000 km (∼ 7000 km
in the original data). The change is obviously significant, because most coronal sources are above the thermal loop by less
than 6 arcsec. We suggest that this change may account for the discrepancy in the literature, i.e., the spectrum of the coronal emission was reported to be extremely hard below ∼ 20 keV in the pre-calibration investigations,
whereas it was reported to be considerably softer in the literature after the re-calibration done by Sato, Kosugi, and Makishima
(Pub. Astron. Soc. Japan
51, 127, 1999). Still, the coronal spectrum is flatter at lower energies than at higher energies, due to the lack of a similar, co-spatial
source in the L-band (14 – 23 keV), for which a convincing explanation is absent. 相似文献
4.
Rajmal Jain Arun Kumar Awasthi Arvind Singh Rajpurohit Markus J. Aschwanden 《Solar physics》2011,270(1):137-149
We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent
timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the
“Solar X-ray Spectrometer” (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May
2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F(ε) from the flare by integrating a series of isothermal plasma flux. We find that the multi-temperature integrated flux F(ε) is a power-law function of ε with a spectral index (γ)≈−4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E=4 – 15 keV is dominated by temperatures of T=12 – 50 MK, while the multi-thermal power-law DEM index (δ) varies in the range of −4.4 and −5.7. The temporal evolution of the X-ray flux F(ε,t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling
time varies between 296 and 4640 s and the electron density (n
e) varies in the range of n
e=(1.77 – 29.3)×1010 cm−3. Employing temporal evolution technique in the current study as an alternative method for separating thermal from nonthermal
components in the energy spectra, we measure the break-energy point, ranging between 14 and 21±1.0 keV. 相似文献
5.
We explore the hard X-ray source distributions of an C1.1 flare occurred on 14 December 2007. Both Hinode/EIS and RHESSI observations are used. One of EIS rasters perfectly covers the double hard X-ray footpoints, where the EUV
emission appears strong from the cool line of He ii (log T=4.7) to the hot line of Fe xvi (log T=6.4). We analyze RHESSI X-ray images at different energies and different times before the hard X-ray maximum. The results
show a similar topology for the time-dependent source distribution (i.e. at 14:14:35 UT) as that for energy-dependent source distribution (i.e. at a given energy band of 6 – 9 keV) overlapped on EUV bright kernels, which seems to be consistent with the evaporation
model. 相似文献
6.
We performed a detailed analysis of 27 slow coronal mass ejections (CMEs) whose heights were measured in at least 30 coronagraphic
images and were characterized by a high quality index (≥4). Our primary aim was to study the radial evolution of these CMEs
and their properties in the range 2 – 30 solar radii. The instantaneous speeds of CMEs were calculated by using successive
height – time data pairs. The obtained speed – distance profiles [v(R)] are fitted by a power law v = a(R−b)
c
. The power-law indices are found to be in the ranges a=30 – 386, b=1.95 – 3.92, and c=0.03 – 0.79. The power-law exponent c is found to be larger for slower and narrower CMEs. With the exception of two events that had approximately constant velocity,
all events were accelerating. The majority of accelerating events shows a v(R) profile very similar to the solar-wind profile deduced by Sheeley et al. (Astrophys. J.
484, 472, 1997). This indicates that the dynamics of most slow CMEs are dominated by the solar wind drag. 相似文献
7.
Zongjun Ning 《Solar physics》2011,273(1):81-92
We explore the speed distributions of X-ray source motions after the start of chromospheric evaporation in two Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) flares. First, we make CLEAN images at 15 energy bands with a 12 second integration window; then, we outline a flaring
loop geometry to cover the looptop and footpoint sources as much as possible. Consistent with the previous steps, we find
converging motion of the double footpoint sources along the flaring loop in these two events. This motion is dependent on
the energy band and time and is typically seen at 3 – 25 keV, indicating a chromospheric evaporation origin. The speed distributions
at various energy bands are measured for the 10 September 2002 flare, which exhibits a separation-to-mergence motion pattern
well correlated with the rising-to-decay phases at 50 – 100 keV. 相似文献
8.
Jiangtao Su Yu Liu Jihong Liu Xinjie Mao Hongqi Zhang Hui Li Xiaofan Wang Wenbin Xie 《Solar physics》2008,252(1):55-71
Zhao and Kosovichev (Astrophys. J.
591, 446, 2003) found two opposite sub-photospheric vortical flows in the depth range of 0 – 12 Mm around a fast rotating sunspot. So far
there is no theoretical model explaining such flow motions. In this paper, we try to explain this phenomenon from the point
of view of magnetic flux tubes interacting with large-scale vortical motions of plasma. In the deeper zone under the photosphere,
the magnetic force may be less than the nonmagnetic force of plasma. The vortical flow located there twists the flux tube
and magnetic free energy is built up in the tube. In the shallower zone under the photosphere, the magnetic force may be greater
than the nonmagnetic force. Thus, part of the stored magnetic free energy is released to drive the plasma to rotate in two
opposite directions, e.g., in the depth ranges of 0 – 3(5) and 9 – 12 Mm. In addition, we also define a vector of nonpotential magnetic stress τ, which can be related to flare occurrence. It is calculated for the active region NOAA 10930 on 11 December 2006. We find
that: i) the integral of its line-of-sight (LOS) stress successively increases around the magnetic neutral line (MNL) prior to and
during the flare and decreases to a minimum after the flare; ii) the integral of its transverse stress exceeds the integral of its LOS component by one order of magnitude over the whole
field of view; iii) the transverse stress first points toward the MNL, then along it, and finally it points away from it. We need other data
to verify whether or not the magnetic energy is transported in the horizontal direction to the neutral line, and then partly
changes into the energy in LOS direction before and during the flare. 相似文献
9.
In an effort to examine the relationship between flare flux and corresponding CME mass, we temporally and spatially correlate
all X-ray flares and CMEs in the LASCO and GOES archives from 1996 to 2006. We cross-reference 6733 CMEs having well-measured
masses against 12 050 X-ray flares having position information as determined from their optical counterparts. For a given
flare, we search in time for CMEs which occur 10 – 80 minutes afterward, and we further require the flare and CME to occur
within ± 45° in position angle on the solar disk. There are 826 CME/flare pairs which fit these criteria. Comparing the flare
fluxes with CME masses of these paired events, we find CME mass increases with flare flux, following an approximately log-linear,
broken relationship: in the limit of lower flare fluxes, log (CME mass)∝0.68×log (flare flux), and in the limit of higher
flare fluxes, log (CME mass)∝0.33×log (flare flux). We show that this broken power-law, and in particular the flatter slope
at higher flare fluxes, may be due to an observational bias against CMEs associated with the most energetic flares: halo CMEs.
Correcting for this bias yields a single power-law relationship of the form log (CME mass)∝0.70×log (flare flux). This function
describes the relationship between CME mass and flare flux over at least 3 dex in flare flux, from ≈ 10−7 – 10−4 W m−2. 相似文献
10.
Using RHESSI and some auxiliary observations we examine possible connections between the spatial and temporal structure of
nonthermal hard X-ray (HXR) emission sources from the two-ribbon flares of 29 May 2003 and 19 January 2005. In each of these
events quasi-periodic pulsations (QPP) with time period of 1 – 3 minutes are evident in both hard X rays and microwaves. The
sources of nonthermal HXR emission are situated mainly at the footpoints of the flare arcade loops observed by TRACE and the
SOHO/EIT instrument in the EUV range. At least one of the sources moves systematically during and after the QPP phase in each
flare. The sources move predominantly parallel to the magnetic inversion line during the 29 May flare and along flare ribbons
during the QPP phase of both flares. By contrast, the sources start to show movement perpendicular to the flare ribbons with
velocity comparable to that along the ribbons’ movement after the QPP phase. The sources of each pulse are localized in distinct
parts of the ribbon during the QPP phase. The measured velocity of the sources and the estimated energy release rate do not
correlate well with the flux of the HXR emission calculated from these sources. The sources of microwaves and thermal HXRs
are situated near the apex of the flare loop arcade and are not stationary either. Almost all of the QPP as well as some pulses
of nonthermal HXR emission during the post-QPP phase reveal soft – hard – soft spectral behavior, indicating separate acts
of electron acceleration and injection. In our opinion at least two different flare scenarios based on the Nakariakov et al. (2006, Astron. Astrophys.
452, 343) model and on the idea of current-carrying loop coalescence are suitable for interpreting the observations. However,
it is currently not possible to choose between them owing to observational limitations. 相似文献
11.
H. Kiliç 《Solar physics》2009,255(1):155-162
The short-term periodicities in sunspot numbers, sunspot areas, and flare index data are investigated in detail using the
Date Compensated Discrete Fourier Transform (DCDFT) for the full disk of the Sun separately over the rising, the maximum,
and the declining portions of solar cycle 23 (1996 – 2006). While sunspot numbers and areas show several significant periodicities
in a wide range between 23.1 and 36.4 days, the flare index data do not exhibit any significant periodicity. The earlier conclusion
of Pap, Tobiska, and Bouwer (1990, Solar Phys.
129, 165) and Kane (2003, J. Atmos. Solar-Terr. Phys.
65, 1169), that the 27-day periodicity is more pronounced in the declining portion of a solar cycle than in the rising and maximum
ones, seems to be true for sunspot numbers and sunspot area data analyzed here during solar cycle 23. 相似文献
12.
The Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) X-ray data base (February 2002 – May 2006) has been searched to find solar flares with weak thermal components and
flat photon spectra. Using a regularized inversion technique, we determine the mean electron flux distribution from count
spectra for a selection of events with flat photon spectra in the 15 – 20 keV energy range. Such spectral behavior is expected
for photon spectra either affected by photospheric albedo or produced by electron spectra with an absence of electrons in
a given energy range (e.g., a low-energy cutoff in the mean electron spectra of nonthemal particles). We have found 18 cases that exhibit a statistically
significant local minimum (a dip) in the range of 13 – 19 keV. The positions and spectral indices of events with low-energy
cutoff indicate that such features are likely to be the result of photospheric albedo. It is shown that if the isotropic albedo
correction is applied, all low-energy cutoffs in the mean electron spectrum are removed, and hence the low-energy cutoffs
in the mean electron spectrum of solar flares above ∼ 12 keV cannot be viewed as real features. If low-energy cutoffs exist
in the mean electron spectra, their energies should be less than ∼ 12 keV. 相似文献
13.
Ulysses was launched in October 1990, and its Solar X-ray/Cosmic Gamma-Ray Burst Experiment (GRB) has provided more than 13 years
of uninterrupted observations of solar X-ray flare activity. Due to the large variation of the relative solar latitude and
longitude of the spacecraft orbit with respect to the Earth, the perspective of the GRB instrument often differed significantly
from that of X-ray instruments on Earth-orbiting satellites. During extended periods the GRB experiment made direct observations
of flares on the hidden face of the Sun, providing a unique record of events not visible to other instruments. The small detector
area of GRB and its optimization for very high counting rates minimized the effects of pulse pile-up. We interpret the spectra,
time histories, and occurrence distribution patterns of GRB data in terms of “thermal feed-through”, the confusion of thermal
soft X-rays and non-thermal hard X-rays. This effect is a systematic problem for scintillation-counter spectrometers observing
the solar hard X-ray spectrum. This paper provides a definitive catalog of the Ulysses X-ray flare observations and discusses various features of this unique database. For the equivalent GOES range X2 – X25,
we find a power-law fit for the (differential) occurrence frequency at >25 keV with slope −1.61±0.04, with no evidence for
a downturn at the highest event magnitudes (for the relatively small sample of such events available in this study). If the
nine most intense events are excluded because of concerns about the effects of pulse pile-up, the slope steepens to −1.75±0.08. 相似文献
14.
Based on the analysis of the microwave observations at the frequency range of 2.60 – 3.80 GHz in the solar X1.3 flare event
observed at the Solar Broadband RadioSpectrometer in Huairou (SBRS/Huairou) on 30 July 2005, an interesting reversed drifting quasi-periodic pulsating structure (R-DPS) is
confirmed. The R-DPS is mainly composed of two drifting pulsating components: one is a relatively slow very short-period pulsation
(VSP) with a period of about 130 – 170 ms, the other is a relatively fast VSP with a period of about 70 – 80 ms. The R-DPS
has a weak left-handed circular polarization. Based on the synthetic investigations of Reuven Ramaty High Energy Solar Spectroscopic Imaging (RHESSI) hard X-ray, Geostationary Operational Environmental Satellite (GOES) soft X-ray observations, and magnetic field extrapolation, we suggest that the R-DPS possibly reflects flaring dynamic
processes of the emission source regions. 相似文献
15.
Hard X-ray lightcurves, spectrograms, images, and spectra of three medium-sized flares observed by the Reuven Ramaty High-Energy
Solar Spectroscopic Imager (RHESSI) are presented. Imaging spectroscopy of the 20 February 2002, 11:06 UT flare at 10′′ spatial
resolution, comparable to the best previous hard X-ray imaging from Yohkoh, shows two footpoints with an ∼ 8 s delay of peak emission between footpoints. Subsequent imaging at le4′′ shows three sources consistent with two separate loops and simultaneous brightening in connected footpoints. Imaging for
the simple two footpoint flare of 2 June 2002 also shows simultaneous footpoint brightening. The more complex 17 March 2002
flare shows at least four different sources during the main peak of the event, and it is difficult to clearly demonstrate
simultaneous brightening of connected footpoints. Non-thermal power laws are observed down to ∼ 12–13 keV without flattening
in all these events, indicating the energy content in energetic electrons may be significantly greater than previously estimated
from assumed 25 keV low energy cutoff. Simultaneously brightening footpoints show similar spectra, at least in the three flares
investigated. Double-power-law spectra with a relatively sharp break are often observed.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022469902940 相似文献
16.
C. O. Lee J. G. Luhmann J. T. Hoeksema X. Sun C. N. Arge I. de Pater 《Solar physics》2011,269(2):367-388
The solar cycle 23 minimum period has been characterized by a weaker solar and interplanetary magnetic field. This provides
an ideal time to study how the strength of the photospheric field affects the interplanetary magnetic flux and, in particular,
how much the observed interplanetary fields of different cycle minima can be understood simply from differences in the areas
of the coronal holes, as opposed to differences in the surface fields within them. In this study, we invoke smaller source
surface radii in the potential-field source-surface (PFSS) model to construct a consistent picture of the observed coronal
holes and the near-Earth interplanetary field strength as well as polarity measurements for the cycles 23 and 22 minimum periods.
Although the source surface value of 2.5 R
⊙ is typically used in PFSS applications, earlier studies have shown that using smaller source surface heights generates results
that better match observations during low solar activity periods. We use photospheric field synoptic maps from Mount Wilson
Observatory (MWO) and find that the values of ≈ 1.9 R
⊙ and ≈ 1.8 R
⊙ for the cycles 22 and 23 minimum periods, respectively, produce the best results. The larger coronal holes obtained for the
smaller source surface radius of cycle 23 somewhat offsets the interplanetary consequences of the lower magnetic field at
their photospheric footpoints. For comparison, we also use observations from the Michelson Doppler Imager (MDI) and find that
the source surface radius of ≈ 1.5 R
⊙ produces better results for cycle 23, rather than ≈ 1.8 R
⊙ as suggested from MWO observations. Despite this difference, our results obtained from MWO and MDI observations show a qualitative
consistency regarding the origins of the interplanetary field and suggest that users of PFSS models may want to consider using
these smaller values for their source surface heights as long as the solar activity is low. 相似文献
17.
P. Rudawy K. J. H. Phillips A. Buczylko D. R. Williams F. P. Keenan 《Solar physics》2010,267(2):305-327
Some 8000 images obtained with the Solar Eclipse Coronal Imaging System (SECIS) fast-frame CCD camera instrument located at Lusaka, Zambia, during the total eclipse of 21 June 2001 have been analysed
to search for short-period oscillations in intensity that could be a signature of solar coronal heating mechanisms by MHD
wave dissipation. Images were taken in white-light and Fe xiv green-line (5303 ?) channels over 205 seconds (frame rate 39 s−1), approximately the length of eclipse totality at this location, with a pixel size of four arcseconds square. The data are
of considerably better quality than those that we obtained during the 11 August 1999 total eclipse (Rudawy et al.: Astron. Astrophys. 416, 1179, 2004), in that the images are much better exposed and enhancements in the drive system of the heliostat used gave a much improved
image stability. Classical Fourier and wavelet techniques have been used to analyse the emission at 29 518 locations, of which
10 714 had emission at reasonably high levels, searching for periodic fluctuations with periods in the range 0.1 – 17 seconds
(frequencies 0.06 – 10 Hz). While a number of possible periodicities were apparent in the wavelet analysis, none of the spatially
and time-limited periodicities in the local brightness curves was found to be physically important. This implies that the
pervasive Alfvén wave-like phenomena (Tomczyk et al.: Science
317, 1192, 2007) using polarimetric observations with the Coronal Multi-Channel Polarimeter (CoMP) instrument do not give rise to significant oscillatory intensity fluctuations. 相似文献
18.
19.
Individual tidal torque λ
2,E
2 and apsidal-motion k
2 constants were calculated for 112 close eclipsing binaries (CEBs) with Detached components belonging to the Main Sequence (DMS-type) from the catalogue by Svechnikov and Perevozkina (Catalogue of orbital elements, masses and luminosities of variable
stars of DMS-type and some results of its statistical treatment, Ural State University Press, Yekaterinburg, pp. 1–5, 1999) and for 95 detached binaries taken from the catalogue by Torres et al. (Astron. Astrophys. Rev. 18:67, 2010) on the base of theoretical evolutionary stellar models including tidal torque constants by Claret (Astron. Astrophys. 424:919,
2004). A method of the inversion of model track grid into isochrones was formulated as a complex interpolation procedure for DMS-binaries
data. Sets of isochrones were computed in k
2–M, k
2–R, λ
2–M, λ
2–R, E
2–M, and E
2–R planes. Calculated tidal torque constants allow to test stellar structure theory by comparing observed and estimated values
of apsidal motion period and analyzing the correlation between timescales of synchronization, circularization, magnetic braking,
as well as nuclear burning of DMS-components. 相似文献
20.
Details of the discovery (in February 2004) and results of subsequent (in 2004–2009) INTEGRAL observations of the transient
X-ray burster IGR J17380-3749 (IGR J17379-3747) are presented. Over the period of its observations, the INTEGRAL observatory
recorded two hard X-ray flares and one type I X-ray burst from the source, which allowed the nature of IGR J17380-3749 to
be determined. The burster radiation spectrum during the flares was hard—a power law with a photon index α = 1.8–2.0 or bremsstrahlung corresponding to a plasma with a temperature kT = 90–140 keV. The spectral shape at the flare peaks turned out to be the same, despite a more than twofold difference in
flux (the peak flux recorded in the energy range 18–100 keV reached ∼20 mCrab). The upper limit on the flux from the source
in its quiescent (off) state in the range of 18–40 keV was 0.15 mCrab (3σ). 相似文献