Particle Acceleration and Kinematics in Solar FlaresOver the last decade we entered a new exploration phase of solar flare physics, equipped with powerful spacecraft such as Yohkoh, SoHO, and TRACE that pro vide us detail-rich and high-resolution images of solar flares in soft X-rays, hard X -rays, and extreme-ultraviolet wavelengths. Moreover, the large-area and high sensitivity detectors on the Compton GRO spacecraft recorded an unprecedented number of high-energy photons from solar flares that surpasses all detected high energy sources taken together from the rest of the universe, for which CGRO was mainly designed to explore. However, morphological descriptions of these beau tiful pictures and statistical catalogs of these huge archives of solar data would not convey us much understanding of the underlying physics, if we would not set out to quantify physical parameters from these data and would not subject these measurements to theoretical models. Historically, there has always been an unsatisfactory gap between traditional astronomy that dutifully describes the mor phology of observations, and the newer approach of astrophysics, which starts with physical concepts from first principles and analyzes astronomical data with the goal to confirm or disprove theoretical models. In this review we attempt to bridge this yawning gap and aim to present the recent developments in solar flare high-energy physics from a physical point of view, structuring the observations and analysis results according to physical processes, such as particle acceleration, propagation, energy loss, kinematics, and radiation signatures. |
Contents
1 Introduction | 3 |
2 Magnetic Topology of Acceleration Regions | 4 |
21 BIPOLAR RECONNECTION MODELS | 8 |
22 TRIPOLAR RECONNECTION MODELS | 9 |
23 QUADRUPOLAR RECONNECTION MODELS | 12 |
24 SPINE AND FAN RECONNECTION MODELS | 15 |
31 MAGNETIC TOPOLOGY CONSTRAINTS ON THE ACCELERATION REGION | 16 |
32 DIRECT HARD XRAY DETECTION OF THE ACCELERATION REGION | 17 |
62 KINEMATICS OF PARTICLE ACCELERATION | 108 |
63 KINEMATICS OF PARTICLE PROPAGATION | 111 |
64 KINEMATICS OF COMBINED ACCELERATION AND PROPAGATION | 116 |
65 KINEMATICS OF PARTICLE INJECTION | 121 |
66 KINEMATICS OF PARTICLE TRAPPING | 123 |
67 KINEMATICS OF PARTICLE PRECIPITATION | 131 |
68 KINEMATICS OF PARTICLE ENERGY LOSS | 137 |
7 Gamma Ray Emission | 142 |
33 TIMEOFFLIGHT LOCALIZATION OF THE ACCELERATION REGION | 21 |
34 CONJUGATE FOOTPOINT CONSTRAINTS | 28 |
35 REMOTE FOOTPOINT DELAYS | 32 |
36 BIDIRECTIONAL ELECTRON BEAMS | 33 |
37 HARD XRAY AND RADIOCOINCIDENT ELECTRON BEAMS | 36 |
38 ELECTRON DENSITY IN ACCELERATION SITES | 38 |
4 Dynamics of Acceleration Region | 40 |
42 DYNAMICS OF MAGNETIC RECONNECTION | 46 |
43 DYNAMICS INFERRED FROM FAST TIME STRUCTURES | 55 |
44 DYNAMICS INFERRED FROM SPATIOTEMPORAL FRAGMENTATION | 63 |
45 DYNAMICS INFERRED FROM SPATIAL EVOLUTION | 69 |
5 Accelerating Electromagnetic Fields and Waves | 76 |
51 ELECTRIC DC FIELD ACCELERATION | 77 |
52 STOCHASTIC ACCELERATION | 86 |
53 SHOCK ACCELERATION | 95 |
6 Particle Kinematics | 102 |
61 KINEMATICS OF RELATIVISTIC PARTICLES | 105 |
72 ACCELERATION AND PROPAGATION OF PROTONS | 144 |
73 INVERSE BREMSSTRAHLUNG OF PROTONS | 149 |
75 LONGTERM TRAPPING OF HIGHENERGY PARTICLES | 150 |
76 GAMMARAYS FROM BEHINDTHELIMB FLARES | 153 |
77 PITCHANGLE DISTRIBUTION OF HIGHENERGY PARTICLES | 154 |
78 INTERPLANETARY HIGHENERGY PARTICLES | 156 |
8 Hard XRay Emission | 157 |
82 TIMEDEPENDENT HARD XRAY SPECTRA | 160 |
83 HARD XRAY SPECTRA | 168 |
84 SPATIAL STRUCTURE OF HARD XRAY SOURCES | 173 |
9 Radio Emission | 178 |
91 RADIO DIAGNOSTIC OF ELECTRON ACCELERATION | 179 |
92 RADIO DIAGNOSTIC OF ELECTRON PROPAGATION | 185 |
93 RADIO DIAGNOSTICS OF ELECTRON TRAPPING | 205 |
10 Conclusions | 213 |
REFERENCES | 218 |
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Common terms and phrases
accelerated particles acceleration region arcade Aschwanden Astrophys Benz bremsstrahlung CGRO chromospheric chromospheric evaporation cm³ coalescence collisional deflection collisionless component coronal current sheet cusp detected distribution dynamic electric field electron beams electron density electron energy electron time-of-flight energy-dependent time delays fast shock Figure filament flare loop footpoint gamma-ray geometry hard X-ray emission hard X-ray flux hard X-ray pulses hard X-ray sources images injection function interplanetary ions kinematics Kliem Loop radius losscone magnetic field lines magnetic islands magnetic mirror magnetic reconnection Masuda measured nonthermal nullpoints observed particle acceleration peak photospheric pitch angle plasma emission plasma frequency powerlaw propagation protons radio bursts radio emission Ramaty reconnection models reconnection point reconnection region scale scenario shown in Fig soft X-ray solar flares spatial spectra spectral slope stochastic acceleration thick-target time-of-flight time-of-flight distance TOF distance trapped electrons tripolar type III bursts upflows velocity waves X-point Yohkoh Yohkoh/HXT