R. P. Lin Physics Dept & Space Sciences Laboratory University of California, Berkeley
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R. P. Lin
Physics Dept & Space Sciences LaboratoryUniversity of California, Berkeley
The Solar System: A Laboratory for the Study of the Physics of Particle
Acceleration
October 2008, Krakow, Poland
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The Sun is the most energetic particle accelerator in the solar system:
- Ions up to ~ 1-10 GeV - Electrons up to ~100s of MeV
Acceleration to these energies occurs in transient energy releases, in two (!) processes:
- Large Solar Flares, in the lower corona- Fast Coronal Mass Ejections (CMEs), in the inner heliosphere, ~2-40 solar radii
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Bastille Day Flare
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23 July 2002 X4.8 Flare
(Lin et al 2003)
Thermal Plasma
~3x107 K
Accelerated Electrons
~10 keV to >10s MeV
Accelerated Ions
~1 to >100s of MeV
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<----- RHESSI coverage ----->
Π0 Decay
Nonthermal Bremsstrahlung
Thermal Bremsstrahlung
Solar Flare Spectrum
Positron and NuclearGamma-Ray lines
T = 2 x 107 K
T = 4 x 107 K
hot loop
HXRfootpoints
soft X-rays hard X-rays -rays
photosphere
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Krucker & Lin 2003
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RHESSI –Hα movie
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Krucker & Lin 2004
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e-e-
HXR HXR
vinvin
vfp
e-e-
HXR HXR
vinvin
t1
t2
vfp
?
?
HXR source motions in magnetic reconnection
models
photosphere Bfp
Bc
vin = coronal inflow velocity Bc = coronal magnetic field
strengthvfp = HXR footpoint velocityBfp = magnetic field strength
in HXR footpoint ~ photospheric value
vin Bc = vfpBfp
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HXR footpoint motion movie, all
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Velocity-HXR flux correlationRough correlation between v and HXR flux
d = B v a dt
Reconnection rate d/dt= B v a
~ 2x1018 Mx/s
E = vB ~ 5 kV/m
v= velocityB= magnetic field strengtha=footpoint diameter
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Mean Electron Flux Fit2002 July 23 Flare
• 00:30:00 – 00:30:20 UT,
•Isothermal component + double power-law
•T = 37 MK
• EM = 4.1 × 1049 cm-3
• nVF = 6.9 × 1055 cm-2 s-1
• Ec = 34 keV
• δL = 1.5
• EB = 129 keV
• δU = 2.5
_ _
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Spectral Components
511 keV- positron annihilation
Neutron-capture2.2 MeV power law - electron bremsstrahlung
De-excitation lines -narrow
broad
total model
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Energetics – 23 July 2002 Flare
• Accelerated Electrons: > ~2 x 1031 ergs ~3 x 1028 ergs/s = ~3 x 1035 (~50 keV) electrons/s for ~600s
• Accelerated Ions (>2.5 MeV) : ~ 1031 ergs~ 1028 ergs/s = ~1033 (~10 MeV) protons/s for ~1000s
• Thermal Plasma: ~ 1031 ergs + losses
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Multi-island reconnection (Drake, et al., 2006)
Large energy gains require interaction with multiple magnetic islands - energy gain linked to geometrical change of island aspect ratio
Consider a reconnection region with multiple islands in 3-D with a stochastic magnetic field -Electrons can wander from island to island
Stochastic region assumed to be macroscopic
uup
CAx
x
y
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Protons vs Electrons
>~30 MeV p (2.223 MeV
n-capture line)
> 0.2 MeV e (0.2-0.3 MeV
bremsstrahlung X-rays)
e & p separated by ~104 km, but
close to flare ribbons
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Electrons >0.3 MeV (Bremsstrahlung Fluence >0.3 MeV)
Protons >30 MeV
(2.223 MeV Line Fluence, corrected for limb darkening)
(Shih et al 2008)
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Mason et al., 2000
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Electron -3He-rich SEP events
- ~1000s/year at solar maximum
- dominated by: - electrons of ~0.1 (!) to ~100 keV energy
- 3He ~10s keV/nuc to ~MeV/nuc energyx10-x104 (!) enhancements
- heavy nuclei: Fe, Mg, Si, S enhancements
- high charge states, e.g., Fe+20
- associated with:
- small flares/coronal microflares - Type III radio bursts - Impulsive soft X-ray bursts (so also called
Impulsive SEP events)
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A series of He3 rich impulsive electron
Krucker & Weidenbeck, private comm 2003
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Reconstruct event geometry
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Adapted from
Gloeckler et al 2006
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Mewaldt et al 2004
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Large (L)SEP events - tens/year at solar maximum
- >10 MeV protons (small e/p ratio)- Normal coronal composition
(but sometimes 3He & Fe/O enhanced)- Normal coronal charge states, Fe+10
(but sometimes enhanced )
- SEPs seen over >~100º of solar longitude
- associated with: - Fast Coronal Mass Ejections (CMEs)- Large flares (but sometimes missing) - Gradual (hours) soft X-ray bursts (also called Gradual SEP events)
* Acceleration by fast CME driven shock wave in inner heliosphere, 2-40 solar radii
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Ion acceleration
Kahler 1994:Compare ion release time near Sun with CME front altitudeCME is already severalSolar radii away from the Sun
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(Mewaldt et al. 2004)
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Mewaldt et al, 2005
If these SEPs are accelerated by CME-driven shocks, they use
a significant fraction of the CME kinetic energy (up to
20%)
(see also Emslie et al. 2004).
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Tylka & Lee, 2006
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Tylka & Lee, 2006
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Tylka & Lee 2006
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Tylka & Lee 2006
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Cliver & Ling, 2007
Gradual SEP events
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Zurbuchen 2004
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Ng et al 2003
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Solar Probe +
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Oct-Nov 2003 Simulation
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• Thanks to the RHESSI team, and many colleagues
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