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1.
Zongjun Ning 《Solar physics》2008,248(1):99-111
Previous observations show that in many solar flares there is a causal correlation between the hard X-ray flux and the derivative
of the soft X-ray flux. This so-called Neupert effect is indicative of a strong link between the primary energy release to
accelerate particles and plasma heating. It suggests a flare model in which the hard X-rays are electron – ion bremsstrahlung
produced by energetic electrons as they lose their energy in the lower corona and chromosphere and the soft X-rays are thermal
bremsstrahlung from the “chromospheric evaporation” plasma heated by those same electrons. Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observes in a broad energy band and its high spectral resolution and coverage of the low-energy range allow us to
separate the thermal continuum from the nonthermal component, which gives us an opportunity to investigate the Neupert effect.
In this paper, we use the parameters derived from RHESSI observations to trace the primary energy release and the plasma response:
The hard X-ray flux or spectral hardness is compared with the derivative of plasma thermal energy in three impulsive flares
on 10 November 2002 and on 3 and 25 August 2005. High correlations show that the Neupert effect does hold for the two hard
X-ray peaks of the 10 November 2002 flare, for the first peaks of the 3 August 2005 flare, and for the beginning period of
the 25 August 2005 flare. 相似文献
2.
We present the results of the analysis of thirteen events consisting of dm-spikes observed in Toruń between 15 March 2000
and 30 October 2001. The events were obtained with a very high time resolution (80 microseconds) radio spectrograph in the
1352 – 1490 MHz range. These data were complemented with observations from the radio spectrograph at Ondřejov in the 0.8 – 2.0 GHz
band. We evaluated the basic characteristics of the individual spikes (duration, spectral width, and frequency drifts), as
well as their groups and chains, the location of their emission sources, and the temporal correlations of the emissions with
various phases of the associated solar flares. We found that the mean duration and spectral width of the radio spikes are
equal to 0.036 s and 9.96 MHz, respectively. Distributions of the duration and spectral widths of the spikes have positive
skewness for all investigated events. Each spike shows positive or negative frequency drift. The mean negative and positive
drifts of the investigated spikes are equal to −776 MHz s−1 and 1608 MHz s−1, respectively. The emission sources of the dm-spikes are located mainly at disk center. We have noticed two kinds of chains,
with and without frequency drifts. The mean durations of the chains vary between 0.067 s and 0.509 s, while their spectral
widths vary between 7.2 MHz and 17.25 MHz. The mean duration of an individual spike observed in a chain was equal to 0.03 s.
While we found some agreement between the global characteristics of the groups of spikes recorded with the two instruments
located in Toruń and Ondřejov, we did not find any one-to-one relation between individual spikes. 相似文献
3.
Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the
100 – 4000 MHz range (type I – V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them
occurred at a radial distance of more than 800″ from the disk center, indicating that radio waves from the limb may be completely
absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to
have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet above 100 MHz were accompanied
by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800″) without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5
generally emit coherent radio waves when observed radially above the source. 相似文献
4.
V. K. Verma 《Astrophysics and Space Science》2011,334(1):83-102
We present study of relationship of GSXR flares with Hα flares, hard X-ray (HXR) bursts, microwave (MW) bursts at 15.4 GHz, type II/IV radio bursts, coronal mass ejections (CMEs),
protons flares (>10 MeV) and ground level enhancement (GLE) events we find that about 85.7%, 93%, 97%, 69%, 60%, 11.1%, 79%,
46%, and 23%% GSXR flares are related/associated with observed Hα flares, HXR bursts, MW bursts at 15.4 GHz, type II radio bursts, type IV radio bursts, GLE events, CMEs, halo CMEs, and proton
flares (>10 MeV), respectively. In the paper we have studied the onset time delay of GSXR flares with Hα flares, HXR, and MW bursts which shows the during majority GSXR flares SXR emissions start before the Hα, HXR and MW emissions, respectively while during 15–20% of GSXR flares the SXR emissions start after the onset of Hα, HXT and MW emissions, respectively indicating two types of solar flares. The, onset time interval between SXR emissions
and type II radio bursts, type IV radio bursts, GLE events CMEs, halo CMEs, and protons flares are 1–15 min, 1–20 min, 21–30 min,
21–40 min, 21–40 min, and 1–4 hrs, respectively. Following the majority results we are of the view that the present investigations
support solar flares models which suggest flare triggering first in the corona and then move to chromospheres/ photosphere
to starts emissions in other wavelengths. The result of the present work is largely consistent with “big flare syndrome” proposed
by Kahler (1982). 相似文献
5.
C. Bouratzis P. Preka-Papadema A. Hillaris P. Tsitsipis A. Kontogeorgos V. G. Kurt X. Moussas 《Solar physics》2010,267(2):343-359
We present a multi-frequency and multi-instrument study of the 20 January 2005 event. We focus mainly on the complex radio
signatures and their association with the active phenomena taking place: flares, CMEs, particle acceleration, and magnetic
restructuring. As a variety of energetic-particle accelerators and sources of radio bursts are present, in the flare – ejecta
combination, we investigate their relative importance in the progress of this event. The dynamic spectra of ARTEMIS-IV – Wind/Waves – HiRAS, with 2000 MHz – 20 kHz frequency coverage, were used to track the evolution of the event from the low corona to
the interplanetary space; these were supplemented with SXR, HXR, and γ-ray recordings. The observations were compared with the expected radio signatures and energetic-particle populations envisaged
by the Standard Flare – CME model and the reconnection outflow termination shock model. A proper combination of these mechanisms seems to provide an adequate model for the interpretation of the observational
data. 相似文献
6.
We analyze a special kind of temporal fine structure in microwave radio emission for the 25 August 1999 solar flare observed
by the PMO spectrometer over the range of 4.5 – 7.5 GHz. This flare displays continuum emission after a group of reverse-slope
type III bursts around 6 GHz. High-resolution dynamic spectra reveal three evolving emission lines (EELs) following the type
III group. They are characterized by isolated, narrow, and continuous emission strips, which display frequency fluctuations
with time. Their frequency-drift rates are between −2 and 3 GHz s−1. Distinct from the EELs at lower frequencies, three EELs have a very short duration of a few seconds. They show an average
bandwidth of Δf≈330 MHz and a relative bandwidth of Δf/f≈0.057. This is the first time that this kind of fine structure has been observed around 6 GHz. 相似文献
7.
We compare the millimeter, microwave, and soft X-ray emission from a number of solar flares in order to determine the properties of the high-frequency radio emission of flares. The millimeter observations use a sensitive interferometer at 86 GHz which offers much better sensitivity and spatial resolution than most previous high-frequency observations. We find a number of important results for these flares: (i) the 86 GHz emission onset appears often to be delayed with respect to the microwave onset; (ii) even in large flares the millimeter-wavelength emission can arise in sources of only a few arc sec dimension; (iii) the millimeter emission in the impulsive phase does not correlate with the soft X-ray emission, and thus is unlikely to contain any significant thermal bremsstrahlung component; and (iv) the electron energy distributions implied by the millimeter observations are much flatter (spectral indices of 2.5 to 3.6) than is usual for microwave or hard X-ray observations. 相似文献
8.
The frequency dependence of the quasi-quantized energy release is reported for the first time in 14 bursts with pulsations
of seconds at 1.0, 2.0, 3.75, 9.4, 17, and 35 GHz, observed by the Nobeyama Radio Polarimeters (NoRP). There is a linear correlation
between the repetition rate of pulsations and the radio flux during the burst, the so-called R – S relation, at each burst frequency. The slope in the linear fitting, which is equivalent to the energy release in an individual
pulse, becomes maximum at a particular frequency around 10 GHz, which can be explained by electrons accelerated in solar flares
with maximum energy density around this frequency or coronal height. 相似文献
9.
Susan M. P. McKenna-Lawlor 《Solar physics》2011,272(2):257-299
During the International Geophysical Year (IGY, 1957/1958) Dunsink Observatory near Dublin in Ireland was a World Data Centre
for Solar Activity. In this circumstance, Hα Lyot Heliograph records secured on a daily basis between 07:00 – 14:00 UT at
the Cape of Good Hope (then an integral link in a network of similar instruments contributing during the IGY to global monitoring
of solar chromospheric activity) were routinely sent to Dunsink for analysis and dissemination. The investigations carried
out at Dunsink on these data resulted, inter alia, in the discovery of the Flare Nimbus phenomenon. The nimbus comprises a dark expanding halo seen in the plage regions around
major flares at, or within a few minutes of, the time of flare maximum intensity in Hα light. It reaches its greatest extent
about 30 minutes after flare maximum. Its maximum dimensions (estimated visually) lie in the range 2 – 4×105 km and its duration ranges from ∼ 1 – 2 hours. Within the nimbus the striation pattern is either completely destroyed or
loses its pre-flare configuration. An account of this phenomenon and its interpretation appeared primarily, although not exclusively,
in the locally produced Dunsink Observatory Publications which are not now easily accessible to the world community of solar researchers. Also, at around the time when the nimbus
was first identified and recorded in Lyot Heliograph data at several observatories, techniques in solar physics shifted towards
high resolution narrow field observations. Under these conditions no further examples of the nimbus were recorded and the
subject has remained dormant over several decades. The present paper again places the scientific results obtained with regard
to the nimbus in the public domain, together with an account of the evolution within the scientific community of an explanation
of this phenomenon. It is suggested here for the first time, in the light of present day data concerning coronal mass ejections
(CMEs) and coronal dimming, that the nimbus provides a signature of CME-related reorganization of the magnetic field in the
chromosphere (such that the transverse magnetic field component decreases and transforms into the line of sight component
as the vector field stretches out). Coronal dimming provides a complementary signature of CME-related mass depletion in the
corona. 相似文献
10.
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
11.
K. Ohki 《Solar physics》1975,45(2):435-452
Interferometric radio observations together with soft X-ray observations are presented here to show that during the growth phase of soft X-ray flares, a large mass increase occurs simultaneously with the creation of an X-ray hot region in the corona. The lack of an increase of radio flux from pre-flare active regions absolutely excludes the possibility of the coronal accumulation of low-temperature matter just prior to flare onset. Therefore we suggest a hypothesis that a large amount of hot matter, which contains almost the entire energy in the flare, is supplied from the chromosphere into the corona during each flare. Since even small flares produce coronal hot regions radiating thermal soft X-rays and microwaves, the formation of the hot region may be a basic process in most flares. Energy, created by some instability in the corona, travels by thermal conduction to the chromosphere where the dense matter is heated and subsequently expands into the corona, producing the observed hot region. Impulsive heating of the chromosphere by nonthermal electrons which simultaneously emit hard X-rays is not sufficient to be the energy source in our model. Slower heating, which supplies the flare more energy than that supplied in the impulsive phase, is required. If the temperature of the energy source in the corona exceeds 2 × 107 K, the conductive energy flux becomes sufficient to exceed the radiation loss from the chromosphere-corona transition region. This excess energy may cause the chromospheric gas expansion. 相似文献
12.
M. R. Kundu S. M. White V. I. Garaimov P. Subramanian S. Ananthakrishnan P. Janardhan 《Solar physics》2006,236(2):369-387
Observations of a solar flare at 617 MHz with the Giant Meter-wave Radio Telescope (GMRT) are used to study the morphology
of flare radio emission at decimetric wavelengths. There has been very little imaging in the 500 – 1000 MHz frequency range,
but it is of great interest, since it corresponds to densities at which energy is believed to be released in solar flares.
This event has a very distinctive morphology at 617 MHz: the radio emission is clearly resolved by the 30″ beam into arc-shaped
sources seeming to lie at the tops of long loops, anchored at one end in the active region in which the flare occurs, with
the other end lying some 200 000 km away in a region of quiet solar atmosphere. Microwave images show fairly conventional
behaviour for the flare in the active region: it consists of two compact sources overlying regions of opposite magnetic polarity
in the photosphere. The decimetric emission is confined to the period leading up to the impulsive phase of the flare, and
does not extend over a wide frequency range. This fact suggests a flare mechanism in which the magnetic field at considerable
height in the corona is destabilized a few minutes prior to the main energy release lower in the corona. The radio morphology
also suggests that the radiating electrons are trapped near the tops of magnetic loops, and therefore may have pitch angles
near 90˚. 相似文献
13.
High sensitivity observations of radio halos in galaxy clusters at frequencies ν ≤ 330 MHz are still relatively rare, and very little is known compared to the classical 1.4 GHz images. The few radio halos
imaged down to 150–240 MHz show a considerable spread in size, morphology and spectral properties. All clusters belonging
to the GMRT Radio Halo Survey with detected or candidate cluster-scale diffuse emission have been imaged at 325 MHz with the
GMRT. Few of them were also observed with the GMRT at 240 MHz and 150 MHz. For A 1682, imaging is particularly challenging
due to the presence of strong and extended radio galaxies at the center. Our data analysis suggests that thew radio galaxies
are superposed to very low surface brightness radio emission extended on the cluster scale, which we present here. 相似文献
14.
Evidence that Synchrotron Emission from Nonthermal Electrons Produces the Increasing Submillimeter Spectral Component in Solar Flares 总被引:1,自引:0,他引:1
Adriana V. R. Silva G. H. Share R. J. Murphy J. E. R. Costa C. G. Giménez de Castro J.-P. Raulin P. Kaufmann 《Solar physics》2007,245(2):311-326
We investigate the origin of the increasing spectra observed at submillimeter wavelengths detected in the flare on 2 November
2003 starting at 17:17 UT. This flare, classified as an X8.3 and 2B event, was simultaneously detected by RHESSI and the Solar
Submillimeter Telescope (SST) at 212 and 405 GHz. Comparison of the time profiles at various wavelengths shows that the submillimeter
emission resembles that of the high-energy X rays observed by RHESSI whereas the microwaves observed by the Owens Valley Solar
Array (OVSA) resemble that of ∼50 keV X rays. Moreover, the centroid position of the submillimeter radiation is seen to originate
within the same flaring loops of the ultraviolet and X-ray sources. Nevertheless, the submillimeter spectra are distinct from
the usual microwave spectra, appearing to be a distinct spectral component with peak frequency in the THz range. Three possibilities
to explain this increasing radio spectra are discussed: (1) gyrosynchrotron radiation from accelerated electrons, (2) bremsstrahlung
from thermal electrons, and (3) gyrosynchrotron emission from the positrons produced by pion or radioactive decay after nuclear
interactions. The latter possibility is ruled out on the grounds that to explain the submillimeter observations requires 3000
to 2×105 more positrons than what is inferred from X-ray and γ-ray observations. It is possible to model the emission as thermal; however, such sources would produce too much flux in the
ultraviolet and soft X-ray wavelengths. Nevertheless we are able to explain both spectral components at microwave and submillimeter
wavelengths by gyrosynchrotron emission from the same population of accelerated electrons that emit hard X rays and γ rays. We find that the same 5×1035 electrons inferred from RHESSI observations are responsible for the compact submillimeter source (0.5 arcsec in radius) in
a region of 4500 G low in the atmosphere, and for the traditional microwave spectral component by a more extended source (50
arcsec) in a 480 G magnetic field located higher up in the loops. The extreme values in magnetic field and source size required
to account for the submillimeter emission can be relaxed if anisotropy and transport of the electrons are taken into account. 相似文献
15.
The spatial and spectral behaviors of two solar flares observed by the Nobeyama Radioheliograph (NoRH) on 24 August 2002 and
22 August 2005 are explored. They were observed with a single loop-top source and double footpoint sources at the beginning,
then with looplike structures for the rest of the event. NoRH has high spatial and temporal resolution at the two frequencies
of 17 and 34 GHz where a nonthermal radio source is often optically thin. Such capabilities give us an opportunity to study
the spatial and spectral behaviors of different microwave sources. The 24 August 2002 flare displayed a soft – hard – soft
(SHS) spectral pattern in the rising – peak – decay phases at 34 GHz, which was also observed for the spectral behavior of
both loop-top and footpoint sources. In contrast, the 22 August 2005 flare showed a soft – hard – harder (SHH) spectral pattern
for its both loop-top and footpoint sources. It is interesting that this event showed a harder spectrum in the early rising
phase. We found a positive correlation between the spectral index and microwave flux in both the loop-top source and the footpoint
sources in both events. The conclusions drawn from the flux index could apply to the electron index as well, because of their
simple linear relationship under the assumption of nonthermal gyrosynchrotron mechanism. Such a property of spatial and spectral
behaviors of microwave sources gives an observational constraint on the electron acceleration mechanism and electron propagation. 相似文献
16.
We performed high resolution spectroscopy of the solar corona during the total solar eclipse of 22 July 2009 in two emission
lines: the green line at 5303 ? due to Fe xiv and the red line at 6374 ? due to Fe x, simultaneously from Anji (latitude 30°28.1′ N; longitude 119°35.4′ E; elevation 890 m), China. A two-mirror coelostat with
100 cm focal length lens produced a 9.2 mm image of the Sun. The spectrograph using 140 cm focal length lens in Littrow mode
and a grating with 600 lines per millimeter blazed at 2 μm provided a dispersion of 30 m? and 43 m? per pixel in the fourth
order around the green line and third order around the red line, respectively. Two Peltier cooled 1k × 1k CCD cameras, with
a pixel size of 13 μm square and 14-bit readout at 10 MHz operated in frame transfer mode, were used to obtain the time sequence
spectra in two emission lines simultaneously. The duration of totality was 341 s, but we could get spectra for 270 s after
a trial exposure at an interval of 5 s. We report here on the detection of intensity, velocity, and line width oscillations
with periodicity in the range of 25 – 50 s. These oscillations can be interpreted in terms of the presence of fast magnetoacoustic
waves or torsional Alfvén waves. The intensity ratios of green to red emission lines indicate the temperature of the corona
to be 1.65 MK in the equatorial region and 1.40 MK in the polar region, relatively higher than the expected temperature during
the low activity period. The width variation of the emission lines in different coronal structures suggests different physical
conditions in different structures. 相似文献
17.
We report very high temporal and spectral resolution interferometric observations of some unusual solar radio bursts near
1420 MHz. These bursts were observed on 13 September 2005, 22 minutes after the peak of a GOES class X flare from the NOAA
region 10808. Our observations show 11 episodes of narrow-band intermittent emission within a span of ≈ 8 s. Each episode
shows a heavily frequency-modulated band of emission with a spectral slope of about −245.5 MHz s−1, comprising up to 8 individual blobs of emission and lasts for 10 – 15 ms. The blobs themselves have a spectral slope of
≈ 0 MHz s−1, are ≈ 200 – 250 kHz wide, appear every ≈ 400 kHz and last for ≈ 4 – 5 ms. These bursts show brightness temperatures in the
range 1012 K, which suggests a coherent emission mechanism. We believe these are the first high temporal and spectral resolution interferometric
observations of such rapid and narrow-bandwidth solar bursts close to 1420 MHz and present an analysis of their temporal and
spectral characteristics. 相似文献
18.
R. E. Gershberg A. V. Terebizh A. A. Shlyapnikov 《Bulletin of the Crimean Astrophysical Observatory》2011,107(1):11-19
A catalogue of dwarf stars with different manifestations of Solar-type activity is compiled based on publications of the last
10–15 years. The catalogue includes objects with dark spots, hydrogen and calcium chromospheric emission, short-lived flares
in different wavelength ranges, and radio and X-ray emission of stellar corona. The resulting compiled list includes 5535
objects. 相似文献
19.
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
20.
Wang Shujuan Yan Yihua Zhao Ruizhen Fu Qijun Tan Chengming Xu Long Wang Shijin Lin Huaan 《Solar physics》2001,204(1-2):153-164
25 MHz–7.6 GHz global and detailed (fine structure – FS) radio spectra are presented, which were observed in the NOAA 9077
active region for the Bastille Day (14 July 2000) flare at 10:10–11:00 UT. Besides broadband radio bursts, high-resolution
dynamic spectra reveal metric type II burst, decimetric type IV burst and various decimetric and microwave FSs, such as type III
bursts, type U bursts, reverse-slope (RS)-drifting burst, fiber bursts, patch and drifting pulsation structure (DPS). The
peak-flux-density spectrum of the radio bursts over the range 1.0–7.6 GHz globally appears as a U-shaped signature. Analyzing
the features of backbone and herringbones of the type II burst, the speeds of shock and relevant energetic electron beams
were estimated to be 1100 km s−1 and 58 500 km s−1, respectively. Also the time sequence of the radio emission is analyzed by comparing with the hard X-rays (HXRs) and the
soft X-rays (SXRs) in this flare. After the maxima of the X-rays, the radio emission in the range 1.0–7.6 GHz reached maxima
first at the higher frequency, then drifted to the lower frequency. This comparison suggested that the flare included three
successive processes: firstly the X-rays rose and reached maxima at 10:10–10:23 UT, accompanied by fine structures only in
the range 2.6–7.6 GHz; secondly the microwave radio emission reached maxima accompanied by many fine structures over the range
1.0–7.6 GHz at 10:23–10:34 UT; then a decimetric type IV burst and its associated FSs (fibers) in the range 1.0–2.0 GHz appeared
after 10:40 UT. 相似文献