7- я Ежегодная Конференция "Физика плазмы в солнечной системе" (6 - 10 февраля 2012 г., ИКИ РАН). МИКРОВОЛНОВОЕ И СУБ-ТГЦ ИЗЛУЧЕНИЕ ВСПЫШЕЧНОЙ ПЕТЛИ. В . Ф . Мельников , ГАО РАН , Санкт - Петербург , Россия J.E.R. Costa , INPE, S.J. Campos, Brazil
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
- routinely with SST at 212 and 405 GHz
- short observing campaigns with KOSMA and BEMRAK at 230, 345 and 210 GHz resp.
About 15 major flares (GOES M3.2 - > X28) have been detected.
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
Normal extention of microwave spectrum
With sub-THz component
Costa, Simões, Giménez de Castro
Microwave Spectrum+ Sub-THz- April 12, 2001 – 10:17UT (Adapted from Luthi etal, 2004 – A&A 415, 1123).
Microwave Spectrum+ Sub-THz- August 25, 2001 – 16:31UT (Adapted from Raulin etal, 2004 – S.Phys. 223, 181).
Types of Radio Spectra in microwave – sub-THz range
August 25, 2001
August 25, 2001
April 12, 2001
Costa, Simões, Giménez de Castro
Kaufmann et al 2001, 2002; Trottet et al. 2002;
Lüthi et al. 2004a; Raulin et al. 2003, 2004;
Cristiani et al. 2007a, 2010;
Giménez de Castro et al. 2009
Kaufmann et al. 2002, 2004; Lüthi et al. 2004b;
Silva et al. 2007; Cristiani et al. 2008
Trottet et al, 2011
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.
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):
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 ~ 104sfu.
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.
at the looptop
In this model a compact source of electrons is located at the loop top with the “beam-like” injection directed toward the left foot.
Pitch-angle distribution of injection function:
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
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)
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 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
n0min=5 x 1010 cm-3 , n0max=1013 cm-3
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.
e is the electron charge, and Ris the radius-vector of the electron moving with velocityvtaken at the retarded time t’= t-nR/c.
H(t) = rotA(t)
E(t) = -(1/c) ∂A/ ∂t - ∆φ
The potentials are closely connected with vectors of magnetic and electric fields:
In a plasma, a refraction index
n =1 - fp2/ f 2 < 1
the denominator can never be very close to 0, even ifv is close to c. So a relativistic electron has an emission efficiency comparable with a nonrelativisticone, i.e. much lower than in vacuo.
This causes a strong suppression of radiation in theplasma, especially at lower frequencies,
f < fR=20n0/B
(Razin, 1960; Ramaty 1969; Klein 1987, Fleishman & Melnikov, 2003).
Left hand spectra are from the middle part of the loop
Right hand spectra are generated from the lower parts of the loop
The frequency spectra of GS emission coefficients from lower parts of the loop have the maximum near 400 GHz due to the Razin effect .
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)
-- 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
-- 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
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
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.
Sub-THz gyrosynchrotron spectral peak has been disappeared!
Instead, we obtain a significant free-free emission spectral increase!
Plasma density distribution is the same, as for the previous case
Temperature distribution is homogeneous, T = 107 K
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.