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

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

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

<----- 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

Krucker & Lin 2003

RHESSI –Hα movie

Krucker & Lin 2004

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

HXR footpoint motion movie, all

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

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

_ _

Spectral Components

511 keV- positron annihilation

Neutron-capture2.2 MeV power law - electron bremsstrahlung

De-excitation lines -narrow

broad

total model

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)

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

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

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)

Mason et al., 2000

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)

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 altitudeCME is already severalSolar 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