Transcript ppt
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