The Solar System: A Laboratory for
the Study of the Physics of Particle
Acceleration
R. P. Lin
Physics Dept & Space Sciences Laboratory
University of California, Berkeley
October 2008, Krakow, Poland
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
Bastille Day Flare
Thermal Plasma
~3x107 K
23 July 2002
X4.8 Flare
(Lin et al 2003)
Accelerated Electrons
~10 keV to >10s MeV
Accelerated Ions
~1 to >100s of MeV
hot loop
Solar Flare Spectrum
Thermal Bremsstrahlung
T = 2 x 107 K
T = 4 x 107 K
HXR
footpoints
photosphere
Nonthermal Bremsstrahlung
soft X-rays
Positron and Nuclear
Gamma-Ray lines
hard X-rays g-rays 
Π0 Decay
<----- RHESSI coverage ----->
Krucker &
Lin 2003
RHESSI –
Hα movie
Krucker &
Lin 2004
Bc
t1
vin
ephotosphere
t2
eHXR
HXR
vin
HXR source motions
in magnetic reconnection
models
vin
?
?
Bfp
vin
e-
e-
HXR
HXR
vfp
vfp
vin = coronal inflow velocity
Bc = coronal magnetic field
strength
vfp = HXR footpoint velocity
Bfp = magnetic field strength
in HXR footpoint
~ photospheric value
vin Bc = vfpBfp
HXR footpoint motion movie, all
Velocity-HXR flux correlation
Rough correlation
between v and HXR flux
dF = B v a dt
Reconnection rate
dF/dt= B v a
~ 2x1018 Mx/s
E = vB ~ 5 kV/m
v= velocity
B= magnetic field strength
a=footpoint diameter
Mean Electron Flux Fit
2002 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
Spectral Components
total model
broad
De-excitation lines -narrow
Neutron-capture2.2 MeV
511 keV- positron
annihilation
power law - electron
bremsstrahlung
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
Multi-island reconnection
(Drake, et al., 2006)
uup
y
CAx
x
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
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
Protons
>30 MeV
(2.223 MeV
Line Fluence,
corrected for
limb
darkening)
(Shih et al
2008)
Electrons >0.3 MeV (Bremsstrahlung Fluence >0.3 MeV)
Mason et
al., 2000
3
Electron - He-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 energy
x10-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)
A series of He3 rich impulsive electron
Krucker & Weidenbeck, private comm 2003
Reconstruct event geometry
Adapted
from
Gloeckler
et al 2006
Mewaldt et al
2004
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
Ion acceleration
Kahler 1994:
Compare ion release time
near Sun with CME front
altitude
CME is already several
Solar radii away from the Sun
(Mewaldt et al. 2004)
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).
Tylka & Lee, 2006
Tylka & Lee, 2006
Tylka & Lee 2006
Tylka & Lee 2006
Cliver & Ling, 2007
Gradual SEP events
Zurbuchen 2004
Ng et al 2003
Solar Probe +
Oct-Nov 2003
Simulation
• Thanks to the RHESSI team, and many
colleagues