Ограничения на модели ускорения электронов в солнечных вспышках Мельников В.Ф., Пятаков Н.П. (ГАО РАН, ФГНУ НИРФИ) ИКИ РАН, Конференция по физике плазмы в солнечной системе, 08 февраля 2010г )

2009 г.2 Particle Acceleration Processes There exists a wide variety of acceleration mechanisms: (1) electric DC-field acceleration (current sheets, twisted loops) (2) stochastic acceleration (wave turbulence, microflares) (3) shock acceleration (propagating MHD shocks; standing MHD shocks in reconnection outflows) (4) betatron acceleration (in collapsing magnetic traps) Their properties are not the same. They may act in different places inside a flaring loop, and they may produce electrons with different types of pitch-angle distribution, Possibly, all of them can operate in solar flares!

2009 г.3 Acceleration in a Current Sheet (X-type reconnection) Energy gained: W = E x L z Large-scale electric field in Sweet-Parker current sheet (e.g. Syrovatskii, 1976; Litvinenko & Somov, 1995; Somov & Kosugi, 1997; Shibata …) Injection Injection across the loop axes Loop top Zharkova & Gordovsky: injection along the MFL???

2009 г.4 Betatron Acceleration in a Collapsing Magnetic Trap across the loop axes (Bogachev and Somov, 2004; Karlicky, Kosugi, 2004)

2009 г.5 DC-Acceleration in Twisted Magnetic Loops (Zaitsev, Urpo, Stepanov 2000; Zaitsev & Stepanov 2008) Acceleration along the loop axes Acceleration can be in the loop top (due to prominence) or near a footpoint Footpoint Looptop E E

2009 г.6 Stochastic acceleration in micro- current sheets (L. Vlahos et al, 2004; J. Brown et al 2009; R. Turkmani et al 2009) Acceleration is isotropic or partly across the magnetic field lines. Acceleration sites are distributed along a whole loop(s)

2009 г.7 Are there any constraints from observations? The properties of the electron source in a flaring loop are not the same. They may act in different places inside a flaring loop, and they may produce electrons with different types of pitch-angle distribution, Possibly, all of them can operate in solar flares! Only observations can tell us which mechanism is dominant in a specific flare configuration. The purpose of this talk is to show that modern spatially resolved observations can provide us with data about the key questions: acceleration site and pitch-angle anisotropy and, therefore, give us valuable constraints on acceleration models.

2009 г.8 Transport effects It is clear from a simple collisionless consideration that electron distribution along a magnetic loop must depend on a specific position and pitch-angle distribution of the acceleration/ injection. The loss-cone condition:  < arcsin (B s /B m )

2009 г.9 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 ). Non-stationary Fokker-Plank equation ( Lu and Petrosian 1988 ): Kinetics of Nonthermal Electrons in Magnetic Loops

2009 г.10 Initial and boundary conditions Initial condition Boundary condition, s (precipitated electrons do not come back into the magnetic loop).(35) Injection function: (no electrons at moment t = 0) In the case of isotropic injection: ),()()()(),,,( 4321 tSsSSEStsES 

Different acceleration models give three basic predictions on the position of the acceleration site and pitch angle distribution homogeneousat the looptop near a footpoint isotropic longitudinal perpendicular

2009 г.12 For illustration, consider transport effects on the example of two simple models: Case 1: Isotropic injection in the center of a magnetic trap. Case 2: Isotropic injection near the footpoints of a magnetic trap.

2009 г.13 Dynamics of the high energy electron distribution along a flaring loop s=0 corresponds the loop center. Injection is isotropic. Mirror ratio к=5. Plasma density n 0 =5*10 10 cm -3 throughout the loop Case 1: Injection at the looptopCase 2: Injection near the right footpoint (Melnikov 2006; Gorbikov & Melnikov 2007)

2009 г.14 Dynamics of the pitch-angle distribution. Case 1: isotropic injection at the loop top Decreasing of the perpendicular anisotropy at the center of the loop, and increasing of it near a footpoint Mirror ratio к=2. Plasma density n0=5*10 10 cm -3 throughout the loop

2009 г.15 Evolution of the pitch-angle distribution Case 2: injection near a footpoint looptop Leg near a footpoint Formation of the oblique anisotropy at the center of the loop in the rise and maximum phase of injection, and formation of perpendicular anisotropy near a footpoint

Properties of Gyrosynchrotron Emission from a Realistic Radio Source Taking into account: 1)influence of the enhanced plasma density on the energy spectrum of trapped electrons and gyrosynchrotron emissivity, 2)influence of magnetic mirroring and change of the pitch-angle distribution along a loop, 3)influence of electron pitch-angle anisotropy on the parameters of GS emission, 4)influence of the magnetic loop curvature, 5)Influence of inhomogeneities of magnetic field and plasma density. (Fleishman, Melnikov 2003; Melnikov, Pyatakov, Gorbikov )

2009 г.17 GS emission and absorption coefficients, exact expressions Calculations are done using Fleishman’s code (Fleishman & Melnikov, ApJ 2003)

2009 г.18 Case 1 Case 2

2009 г.19 Radio brightness distribution Case 1: Injection at the loop top Case 2: Injection near a footpoint 17 GHz

2009 г.20 Distribution of the optical depth Case 1: Injection at the loop top Case 2: Injection near a footpoint Tau << 1

2009 г.21 Spatial profiles of brightness at 34 GHz at the burst maximum (Melnikov, Reznikova, Shibasaki, 2002, 2006)

2009 г.22 Brightness distribution dynamics, 24 August 2002 (main peak, 34 GHz) Reznikova et al. ApJ 2009 : Footpoint sources exist on the rise and peak phases, and even in the beginning of the decay phase.

2009 г.23 Distribution of the polarization degree Case 1: Injection at the loop top Case 2: Injection near a footpoint Ordinary mode circular polarization  Signature of the longitudinal anisotropy Increase in X-mode polarization degree  signature of the perpendicular anisotropy

2009 г.24 Distribution of the spectral index (Limb Loop) Case 1: Injection at the loop top Case 2: Injection near a footpoint Spectral steepening  signature of the longitudinal anisotropy Spectral flattening  Signature of the perpendicular anisotropy

2009 г.25 Distribution of the spectral index (solar disk, Theta = 45 deg) Case 1: Injection at the loop top Case 2: Injection near a footpoint Spectral steepening  Signature of the perpendicular anisotropy Spectral steepening  Signature of the longitudinal anisotropy

2009 г.26 High frequency spectral index variations along a loop. Yokoyama et al. 2002, ApJ, 576, L87. Microwave spectrum near footpoints is considerably softer (by ~ 0.5-1) than near the loop top during the main peak of bursts

2009 г.27 Радиопризнаки ускоренных электронов во вспышечной петле Радиопризнаки продольной питч- угловой анизотропии ускоренных электронов во вспышечной петле установлены недавно в работах: 1) Altyntsev A.T. et al. (Astrophys. J. 2008, ) 1) Altyntsev A.T. et al. (Astrophys. J. 2008, 677, p.1367) 2) Reznikova V.E. et al. (Astrophys. J. 2009, ) 2) Reznikova V.E. et al. (Astrophys. J. 2009, V.697, p.735)

2009 г.28 Новый взгляд на Солнце Фильмы, полученные с помощью радиоинтерферометров - Сибирского Солнечного Радиотелескопа (Иркутск) и радиогелиографа Нобеяма (Япония), а также с помощью приборов на космических аппаратах Yohkoh, HESSI (мягкий и жесткий рентген), SOHO (оптика), TRACE (ультрафиолет) поражают воображение и меняют наши представления о физике явлений в солнечной короне. Microwave diagnostics of the position of an acceleration site and pitch-angle anisotropy of energetic electrons in the flare 24 Aug 2002 Резникова В.Э. 1,2, Мельников В.Р. 2,3, Пятаков Н.П. 2 1 Nobeyama Solar Radio Observatory/NAOJ, Nagano , Japan 2 ФГНУ НИРФИ, Нижний Новгород, , Россия 3 ГАО РАН, Санкт-Петербург, , Россия

Influence of electron pitch-angle anisotropy on parameters of gyrosynchrotron emission

2009 г.30 Gyrosynchrotron emission directivity The angular width of the emission beam:  ~  -1 = mc 2 /E

2009 г.31 Influence of the electron distribution anisotropy on the frequency spectrum The angular width of the emission beam:  ~  -1 = mc 2 /E f max  f B (E/mc 2 ) 2 For solar flare conditions, the broad band microwave emission are mainly generated by mildly relativistic electrons At low frequencies the beam is wide, and at the high fs it is large.  the anisotropy does influence the emission spectrum

2009 г.32 Observational evidence for electron pitch-angle anisotropy in a microwave GS source Quasi-longitudinal propagation Quasi-transverse propagation Radio waves’ Quasi-longitudinal propagation Differences in: - intensity, - spectrum and - polarization

2009 г.33 f 2 (  ) ~ exp{-  2 /  0 2 }  = cos(  ),  =B^V.  considerable change of microwave parameters for the quasi-parallel propagation (  =0.8): -Decrease of intensity; -Increase of polarization degree -Increase of the spectral index (Fleishman & Melnikov 2003) Results of simulations: Electron pitch-angle distribution of the loss-cone type: Quasi-longitudinalQuasi-transverse

2009 г.34 f 2 (  ) ~ exp{-(  -  1 ) 2 /  0 2 }  = cos(  ),  =B^V.  considerable change of microwave parameters for the quasi- transverse propagation (  =0.2): -Decrease of intensity; -Change of polarization degree to O-mode -Increase of the spectral index (Fleishman & Melnikov, ApJ 2003) Results of simulations: Electron pitch-angle distribution of the beam type: Quasi-longitudinalQuasi-transverse

Заключение 1) Показано, что для разных характеристик источника электронов (положение области ускорения/инжекции в петле, тип анизотропии) можно получить сильно отличающиеся характеристики пространственного распределения интенсивности, поляризации и частотного спектра микроволнового излучения вспышечной петли. 2) Установлено, что эти отличия могут быть надежно зарегистрированы с помощью современных радиогелиографов сантиметрового-миллиметрового диапазонов и могут быть использованы для выбора наиболее подходящей модели ускорения, реализующейся в той или иной конкретной вспышечной петле. 3) Заложены основы нового метода диагностики положения области ускорения/инжекции в петле и типа анизотропии ускоренных электронов.

2009 г.36 Спасибо за внимание!

2009 г.37 References 1.Melnikov V.F., K. Shibasaki, V.E. Reznikova. "Loop-top nonthermal microwave source in extended flaring loops." - ApJ, 2002, V.580, pp.L185-L188 2.Fleishman G.D. & Melnikov V.F. Gyrosynchrotron Emission from Anisotropic Electron Distributions - ApJ, 2003, V. 587, PP. 823–835 3.Melnikov V.F. Electron Acceleration and Transport in Microwave Flaring Loops. In: "Solar Physics with the Nobeyama Radioheliograph", Proc. Nobeyama Symposium (Kiosato, October 2004), Ed. K.Shibasaki, NSRO Report No.1, p.9-20, Melnikov V.F., Gorbikov S.P., Reznikova V.E., Shibasaki K. Relativistic Electron Spatial Distribution in Microwave Flaring Loops. – Izv. RAN, ser.fiz., 2006, V.70, pp Gorbikov S.P., Melnikov V.F. Numerical solution of the Fokker-Plank equation for modeling of particle distribution in solar magnetic traps. - Mathematical Modeling, 2007, V.19, No.2, pp Reznikova V.E., Melnikov V.F., Shibasaki K., Gorbikov S.P., Pyatakov N.P., Myagkova I.N., Ji H August 24 limb flare loop: dynamics of microwave brightness distribution. – ApJ, 2009, V.697, pp.735–746.

Аннотация Различные теоретические модели ускорения частиц в солнечных вспышках предсказывают различия в положении области ускорения и в типах питч- углового распределения ускоренных электронов. В данной работе проведено решение нестационарного кинетического уравнения Фоккера-Планка при различных предположениях о характеристиках инжекции энергичных электронов в магнитную петлю с тем, чтобы определить их пространственное, энергетическое и питч-угловое распределения и рассчитать соответствующие характеристики гиросинхротронного излучения. Показано, что для разных характеристик источника электронов (положение области ускорения/инжекции в петле, тип анизотропии) можно получить сильно отличающиеся характеристики пространственного распределения интенсивности, поляризации и частотного спектра микроволнового излучения вспышечной петли. Установлено, что эти отличия могут быть надежно зарегистрированы с помощью современных радиогелиографов сантиметрового-миллиметрового диапазонов и могут быть использованы для выбора наиболее подходящей модели ускорения, реализующейся в той или иной конкретной вспышечной петле. Приведены результаты диагностики, полученные на основе данных наблюдений Радиогелиографа Нобеяма.