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Микроволновое и суб-тгц излучение вспышечной петли
Микроволновое и суб-тгц излучение вспышечной петли
Observations of flares in the 200-400 GHz domain
Observations of flares in the 200-400 GHz domain
Time profiles and intensities of sub-THz bursts
Time profiles and intensities of sub-THz bursts
Types of Radio Spectra in microwave – sub-THz range
Types of Radio Spectra in microwave – sub-THz range
Types of Radio Spectra in microwave – sub-THz range
Types of Radio Spectra in microwave – sub-THz range
So far: About 15 major flares (GOES M3
So far: About 15 major flares (GOES M3
Sub-THz spectral component enigma: emission mechanisms proposed
Sub-THz spectral component enigma: emission mechanisms proposed
GS-interpretation of the sub-THz spectral component
GS-interpretation of the sub-THz spectral component
Kinetics of Nonthermal Electrons in Magnetic Loops
Kinetics of Nonthermal Electrons in Magnetic Loops
Parameters for our model simulations
Parameters for our model simulations
Different acceleration models give three basic predictions on the
Different acceleration models give three basic predictions on the
Suitable model:
Suitable model:
Electron distribution over length of the model loop for electron
Electron distribution over length of the model loop for electron
Magnetic field distribution is assumed to be B(s)=Bmin exp(-s2/sB2)
Magnetic field distribution is assumed to be B(s)=Bmin exp(-s2/sB2)
n0min=5 x 1010 cm-3 , n0max=1013 cm-3
n0min=5 x 1010 cm-3 , n0max=1013 cm-3
Razin-effect
Razin-effect
In plasma:
In plasma:
Gyrosynchrotron frequency spectrum in different parts of a flaring
Gyrosynchrotron frequency spectrum in different parts of a flaring
Total gyrosynchrotron frequency spectrum of the flaring loop
Total gyrosynchrotron frequency spectrum of the flaring loop
Bmin=400 G,
Bmin=400 G,
Conclusions
Conclusions
Which observed properties of the sub-THz emission can be explained by
Which observed properties of the sub-THz emission can be explained by
What properties of the sub-THz emission we predict to be observed
What properties of the sub-THz emission we predict to be observed
Needs of observations at higher frequencies
Needs of observations at higher frequencies
Thank you for your attention
Thank you for your attention
Абстракт Предложен гиросинхротронный механизм одновременной генерации
Абстракт Предложен гиросинхротронный механизм одновременной генерации
Initial and boundary conditions
Initial and boundary conditions
Injection function:
Injection function:
Influence of the free-free absorption on the sub-THz emission spectrum
Influence of the free-free absorption on the sub-THz emission spectrum
As we can see, free-free emission itself can be very important for
As we can see, free-free emission itself can be very important for

Презентация на тему: «Микроволновое и суб-тгц излучение вспышечной петли». Автор: Victor Melnikov. Файл: «Микроволновое и суб-тгц излучение вспышечной петли.ppt». Размер zip-архива: 657 КБ.

Микроволновое и суб-тгц излучение вспышечной петли

содержание презентации «Микроволновое и суб-тгц излучение вспышечной петли.ppt»
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1 Микроволновое и суб-тгц излучение вспышечной петли

Микроволновое и суб-тгц излучение вспышечной петли

В.Ф. Мельников, ГАО РАН, Санкт-Петербург, Россия J.E.R. Costa, INPE, S.J. Campos, Brazil P.J.A. Simoes, CRAAM, Sao Paulo, Brazil

7-я Ежегодная Конференция "Физика плазмы в солнечной системе" (6 - 10 февраля 2012 г., ИКИ РАН)

2 Observations of flares in the 200-400 GHz domain

Observations of flares in the 200-400 GHz domain

200-400 GHz measurements of flares have been obtained since year 2000: - routinely with SST at 212 and 405 GHz - short observing campaigns with KOSMA and BEMRAK at 230, 345 and 210 GHz resp. Multi-beam observations at 210 GHz: estimate position and size of the radio emitting region. About 15 major flares (GOES M3.2 - > X28) have been detected.

2011

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3 Time profiles and intensities of sub-THz bursts

Time profiles and intensities of sub-THz bursts

Sub-THz events occur in strong X-class solar flares Their intensity in microwaves and sub-THz range reaches Ff = (1-10) 104 sfu They are long: several munutes The time profiles at sub-THz and microwaves are similar and some seconds delayed against hard X-ray time profiles

Kaufmann P. et al. Ap.J. (2004), v603 L121-L124

2011

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4 Types of Radio Spectra in microwave – sub-THz range

Types of Radio Spectra in microwave – sub-THz range

Normal extention of microwave spectrum

With sub-THz component

SST

OVSA

Costa, Sim?es, Gim?nez de Castro

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5 Types of Radio Spectra in microwave – sub-THz range

Types of Radio Spectra in microwave – sub-THz range

August 25, 2001

August 25, 2001

April 12, 2001

GOES X5.3

GOES X2.0

Costa, Sim?es, Gim?nez de Castro

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6 So far: About 15 major flares (GOES M3

So far: About 15 major flares (GOES M3

2 - > X28) have been detected at frequencies 200, 400 GHz 7 to 8 normal events reported Kaufmann et al 2001, 2002; Trottet et al. 2002; L?thi et al. 2004a; Raulin et al. 2003, 2004; Cristiani et al. 2007a, 2010; Gim?nez de Castro et al. 2009 5 THz events reported Kaufmann et al. 2002, 2004; L?thi et al. 2004b; Silva et al. 2007; Cristiani et al. 2008

Trottet et al, 2011

2011

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7 Sub-THz spectral component enigma: emission mechanisms proposed

Sub-THz spectral component enigma: emission mechanisms proposed

- synchrotron radiation from positrons emitted in pion or radioactive decay after nuclear interactions (Trottet et al., 2004) inverse Compton radiation (Kaufmann et al., 1986) - gyrosynchrotron emission from a compact source (Kaufmann and Raulin 2006, Silva et al. 2007) - free-free emission from an optically thick source (Silva et al. 2007, Fleishman and Kontar, 2010) - Cherenkov emission from chromospheric layers (Fleishman and Kontar, 2010) - synchrotron emission in stochastic medium (Fleishman and Kontar, 2010) However, none of them can explain the full set of known properties of sub-THz emission and its relations to other emissions like microwave, hard X-ray etc.

2011

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8 GS-interpretation of the sub-THz spectral component

GS-interpretation of the sub-THz spectral component

In this paper we propose an idea that can solve the above mentioned difficulties taking into account some recent findings concerning: the importance of Razin suppression on the formation of observed gyrosynchrotron spectra in microwave bursts; and the spatial distribution of gyrosynchrotron emission generated by anisotropic fluxes of accelerated electrons in inhomogeneous flaring loops

Silva etal (2007) have shown that strong and well separated microwave and sub-teraherz spectral peaks can be explained by the gyrosynchrotron emission of energetic electrons being injected, respectively, into two interacting magnetic loops, one large with relatively weak magnetic field (microwave source), another small with strong magnetic field (sub-THz source). However, the source of sub-THz component has to be extremely small (L<108 cm). It should also have very large magnetic field, B>2000 G, and very high number density of non-thermal electrons, n_e(E>50keV)>1012cm-3, in order to be optically thick up to about 300-400GHz, as well as to provide a sufficient instantaneous total number of electrons, N_t(E>50~keV)>5x1035, for fitting to very high observed flux density, F_f ~104sfu.

2011

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9 Kinetics of Nonthermal Electrons in Magnetic Loops

Kinetics of Nonthermal Electrons in Magnetic Loops

inetics of Nonthermal Electrons in Magnetic Loops

In a magnetic loop, a part of injected electrons are trapped due to magnetic mirroring and the other part directly precipitates into the loss-cone. The trapped electrons are scattered due to Coulomb collisions and loose their energy and precipitate into the loss-cone. A real distribution strongly depends on the injection position in the loop and on the pitch-angle dependence of the injection function S(E,?,s,t), and also on time (Melnikov et al. 2006; Gorbikov and Melnikov 2007, Reznikova etal, 2009). Non-stationary Fokker-Plank equation (Lu and Petrosian 1988):

2011

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10 Parameters for our model simulations

Parameters for our model simulations

For our simulations we take parameters in the sub-THz source derived from observations of the flare 2 November 2003 (Silva et al 2007) that presents a good example of the two simultaneously observed spectral peaks, microwave at f ~ 15 GHz, and sub-THz at f > 200 GHz, both with high intensity Ff ~ 104 sfu. We assume that the magnetic field is distributed exponentially along the loop: B(s)=Bmin exp(-s2/sB2) with the mirror ratio Bmax/Bmin=2. Plasma density distribution is chosen as: n0=n0min exp(s2/s12), where s12= b_s2/ln(104), n0min=5 1010 cm-3, b_s=3 109 cm is the distance from the center to the end of a loop.

2011

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11 Different acceleration models give three basic predictions on the

Different acceleration models give three basic predictions on the

position of the acceleration site and pitch angle distribution

12 Suitable model:

Suitable model:

Pitch-angle distribution of injection function:

In this model a compact source of electrons is located at the loop top with the “beam-like” injection directed toward the left foot.

Left FP

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13 Electron distribution over length of the model loop for electron

Electron distribution over length of the model loop for electron

energy E=405 keV and for two values of pitch-angles In the case of beamed injection of accelerated electrons from the loop top region, we can get a strong peak of the electron number density near the footpoints where the magnetic field is also strong. The upper plot shows the distribution for electrons rotating almost perpendicular to the magnetic field lines, with pitch-angle 89.36o. The lower plot is for electrons propagating along field lines with small pitch-angle 12.17o

2011

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14 Magnetic field distribution is assumed to be B(s)=Bmin exp(-s2/sB2)

Magnetic field distribution is assumed to be B(s)=Bmin exp(-s2/sB2)

with the mirror ratio Bmax/Bmin=2 The peak of non-thermal electrons near the footpoints can easily produce strong radio emission at frequencies up to THz range. However, even in this case, the spectral maximum is located at frequencies much less than 400 GHz under all reasonable parameters of non-thermal electrons and magnetic field!

Gyrosynchrotron brightness and frequency spectrum in different parts of a flaring loop (Case of small plasma density in the lower parts of the magnetic loop)

2011

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15 n0min=5 x 1010 cm-3 , n0max=1013 cm-3

n0min=5 x 1010 cm-3 , n0max=1013 cm-3

Gyrosynchrotron brightness and frequency spectrum in different parts of a flaring loop (Case of high plasma density in the lower parts of the magnetic loop – strong Razin effect)

Low plasma density

High plasma density

FP1 LT FP2

FP1 LT FP2

Due to the strong chromosphere heating during the flare energy release, the plasma density in the lower parts of the loop can be strongly enhanced.

2011

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16 Razin-effect

Razin-effect

H(t) = rot A(t) E(t) = -(1/c) ?A/ ?t - ??

Lienard-Wiechert potentials: In vacuo:

The potentials are closely connected with vectors of magnetic and electric fields:

e is the electron charge, and R is the radius-vector of the electron moving with velocity v taken at the retarded time t’ = t-nR/c.

2011

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17 In plasma:

In plasma:

In a plasma, a refraction index n =1 - fp2/ f 2 < 1 ? the denominator can never be very close to 0, even if v is close to c. So a relativistic electron has an emission efficiency comparable with a nonrelativistic one, i.e. much lower than in vacuo. ? This causes a strong suppression of radiation in the plasma, especially at lower frequencies, f < fR=20n0/B (Razin, 1960; Ramaty 1969; Klein 1987, Fleishman & Melnikov, 2003).

2011

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18 Gyrosynchrotron frequency spectrum in different parts of a flaring

Gyrosynchrotron frequency spectrum in different parts of a flaring

loop

Left hand spectra are from the middle part of the loop Right hand spectra are generated from the lower parts of the loop

17 GHz

400 GHz

The frequency spectra of GS emission coefficients from lower parts of the loop have the maximum near 400 GHz due to the Razin effect .

2011

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19 Total gyrosynchrotron frequency spectrum of the flaring loop

Total gyrosynchrotron frequency spectrum of the flaring loop

Frequency spectra obtained by integration over the whole flaring loop for two moments of time t1 and t2 on the rise phase of the burst. Two spectral components in the microwave and sub-THz regions are clearly seen.

The microwave component shows an increase of the peak frequency with time (due to the self-absorption effect) The peak frequency for sub-THz component remains constant (due to the Razin effect)

t2

t1

2011

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20 Bmin=400 G,

Bmin=400 G,

Bmin=100 G, n0max=1013 cm-3 ? n0max=1012 cm-3

2011

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21 Conclusions

Conclusions

The difficulties of gyrosynchrotron interpretation associated with the unrealistically small size, large non-thermal electrons number density ne, and large magnetic field can be overcome if the lower frequency turnover of the sub-THz spectral peak is caused by Razin suppression. In this case, the only requirement is a relatively high value of the Razin frequency: fR = 20 n0/B >= 200 GHz. Such the value normally can be realized in the lower parts of flaring loops. The large flux density of some sub-THz bursts, Ff ~ 104 sfu, associated with X-class solar flares, is reached not due to the large non-thermal electrons number density, but due to the large area occupied by arcades (a large number of corresponding flaring loops) usually present in such flares.

2011

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22 Which observed properties of the sub-THz emission can be explained by

Which observed properties of the sub-THz emission can be explained by

our model?

-- separate spectral peak at sub-THz; -- variability of the low frequency spectral index of sub-THz emission (alpha=1-6); -- presence and absence of the separate spectral peak at sub-THz; (depends on specific conditions in a flaring loop); -- fast temporal changes of the sub-THz intensity; -- time delays between microwave / sub-THz and hard X-ray time profiles

2011

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23 What properties of the sub-THz emission we predict to be observed

What properties of the sub-THz emission we predict to be observed

-- brightness spatial distribution with strong peaks near footpoints of flare loops; -- the size of sub-THz sources can be large enough (no need to be too small, like 0.5'', as for the simple GS mechanism); -- magnetic field strength can be not too strong (>2000G) and number density of nonthermal electrons should not to be too high (N(>50keV) ~ 1012cm-3 )!

Future observations in sub-THz to THz range are needed to check the validity of these predictions

2011

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24 Needs of observations at higher frequencies

Needs of observations at higher frequencies

ALMA? Space borne FIR experiments Solar T: P. Kaufmann (PI) Golay cells for photometry at 45 ?m and 100 ?m On NASA balloon with GRIPS (SSL Berkeley) Schedule: technical flight in 2012-2013; long duration flight in Antarctica in 2013-2014 DESIR: K.-L. Klein (PI) Arrays of microbolometers for photometry and source location at 35 ?m and 100 ?m Laboratory studies; technical balloon flight Mission concepts

2011

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25 Thank you for your attention

Thank you for your attention

2011

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26 Абстракт Предложен гиросинхротронный механизм одновременной генерации

Абстракт Предложен гиросинхротронный механизм одновременной генерации

двух спектральных пиков (микроволнового и суб-терагерцового) радиоизлучения солнечных вспышек в рамках модели одиночной тонкой вспышечной петли. Ключевым в модели является образование повышенной концентрации релятивистских электронов в нижней части петли, где соотношение плотности плазмы n0 к магнитному полю B достаточно велико, чтобы частота Разина fR=20 n0/B достигала значений fR ~ 200 ГГц. Установлено, что в этом случае суб-терагерцовая и микроволновая спектральные компоненты излучения генерируются в различных частях вспышечной петли - вблизи оснований и в ее вершине, соответственно. Низкочастотная часть суб-терагерцового спектрального пика синхротронного излучения формируется за счет эффекта Разина и ее источник является оптически тонким. Последнее позволяет получить суб-терагерцовый пик излучения как суммарное излучение от протяженной аркады вспышечных петель с общим размером до десятков угловых секунд.

2011

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27 Initial and boundary conditions

Initial and boundary conditions

. (35)

2011

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28 Injection function:

Injection function:

. (35)

2011

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29 Influence of the free-free absorption on the sub-THz emission spectrum

Influence of the free-free absorption on the sub-THz emission spectrum

Sub-THz gyrosynchrotron spectral peak has been disappeared! Instead, we obtain a significant free-free emission spectral increase!

17 GHz

400 GHz

Plasma density distribution is the same, as for the previous case Temperature distribution is homogeneous, T = 107 K

2011

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30 As we can see, free-free emission itself can be very important for

As we can see, free-free emission itself can be very important for

producing sub-THz spectral component. This can happen in the case of strong chromospheric evaporation in the lower part of flaring loops.

Note, however, that the influence of the free-free absorption on the gyrosynchrotron sub-THz spectral peak can be strongly decreased if we: make the temperature distribution more homogeneous along the loop decrease the plasma density and, in parallel, decrease the magnetic field strength in the loop The last two conditions make the Razin frequency almost unchanged: fR=20n0/B ~ const

2011

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