Particle Acceleration in Solar Energetic Particle (SEP) Events and Solar Flares R. P. Lin Physics Department & Space Sciences Laboratory University of California, Berkeley, CA, USA For fall 2009 semester: School of Space Research, Kyung Hee University, Yongin, Gyeonggi , South Korea, Thanks to the RHESSI team & the Wind 3DP team

Forbush, S., Phys. Rev. Lett., 70, 771, 1946 “…unusual increases… nearly simultaneous with a solar flare…” “…may have been caused by charged particles actually being emitted by the Sun…”

The Sun is the most energetic particle accelerator in the solar system: - Ions up to ~ 10s of GeV - Electrons up to ~100s of MeV Acceleration 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 2000 Solar Flare

23 July 2002 X4.8 Flare ( Lin et al 2003) Thermal Plasma ~3x10 7 K Accelerated Electrons ~10 keV to >10s MeV Accelerated Ions ~1 to >100s of MeV

SPECTROSCOPY Π 0 Decay Nonthermal Bremsstrahlung Thermal Bremsstrahlung Solar Flare Spectrum Positron and Nuclear Gamma-Ray lines T = 2 x 10 7 K T = 4 x 10 7 K hot loop HXR footpoints soft X-rays hard X-rays g -rays  photosphere  RHESSI Energy Coverage 

Imaging spectroscopy

Krucker & Lin 2004

e-e- e-e- HXR v in v fp e-e- e-e- HXR v in t1t1 t2t2 v fp ? ? HXR source motions in magnetic reconnection models photosphere B fp BcBc v in = coronal inflow velocity B c = coronal magnetic field strength v fp = HXR footpoint velocity B fp = magnetic field strength in HXR footpoint ~ photospheric value v in B c = v fp B fp

Velocity-HXR flux correlation Rough correlation between v and HXR flux d F = B v a dt Reconnection rate d F /dt= B v a ~ 2x10 18 Mx/s E = vB ~ 5 kV/m v= velocity B= magnetic field strength a=footpoint diameter

g -ray imaging with RHESSI Before RHESSI, no imaging in the g -ray range available RHESSI g -ray imaging at 35” and 180” resolution (compared to 2” for HXRs, i.e. electrons) Low photon statistics: integration over total flare duration needed 2.2MeV line is best candidate (Hurford et al. 2003, 2006) photosphere p+p+ p+p+ g -ray footpoints? low density high density Where are the g -ray footpoints relative to the HXR footpoints?

Protons vs Electrons >~30 MeV p (2.223 MeV n-capture line) > 0.2 MeV e ( MeV bremsstrahlung X- rays) e & p separated by ~10 4 km, but close to flare ribbons

Energetics – 23 July 2002 Flare Accelerated Electrons: > ~2 x ergs ~3 x ergs/s = ~3 x (~50 keV) electrons/s for ~600s Accelerated Ions (>2.5 MeV) : ~ ergs ~ ergs/s = ~10 33 (~10 MeV) protons/s for ~1000s Thermal Plasma: ~ ergs + losses dE/dt = ~5x10 28 ergs/s energy release rate for ~1000s

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)

Cliver et al, 1994

Tylka & Lee, 2006

Large (L)SEP events - tens/year at solar maximum - >10 MeV protons (small e/p ratio) - Normal coronal composition (but sometimes 3 He & 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 the inner heliosphere, 2-40 solar radii

Mewaldt et al 2005

(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).

Tycho Supernova Remnant X-ray picture from Chandra

Diffusive shock acceleration: r g >> d Compressive discontinuity of the plasma flow leads to acceleration of particles reflecting at both sides of the discontinuity: diffusive shock acceleration (1st order Fermi) u1u1 u2u2 R = u 1 /u 2 in the shock rest frame where u = u 1 -u 2 1st order acceleration shock compression Δp~ (u/v) p

Gopalswamy et al. 2004

January 20, 2005 SEP event (from Mewaldt et al. 2005) Very short time to maximum intensity (30 min) Very hard spectrum

2002 Aug 03, X Sep 19, M1.9 SHH SHS

“soft-hard-soft” (SHS) vs. “soft-hard-harder” (SHH) (non-thermal HXR spectral behavior during flares) Power law spectrum: lower gamma value = flatter, ‘harder’ spectrum

SHS behavior: (more common) SHH behavior: (~15-20% of flares) time HXR Emission

Results 60 of the 84 events had determinable spectral behavior and SEP occurrence 23 of 60 had only partial observations and no SHH, finally leaving 37 events SEPs?Yes:No: Yes: 120 No: 619 SHH?

very large source (>200 arcsec) expanding and rising October 27, 2002 CME velocity ~2000 km/s size motion

very large source (>200 arcsec) expanding and rising October 27, 2002 CME velocity ~2000 km/s size motion 300”

very large source (>200 arcsec) expanding and rising October 27, 2002 ~400 km/s ~800 km/s CME velocity ~2000 km/s size motion 300” HXR emission from electrons in magnetic structures related to coronal mass ejections. speed of CME front ~ 2000 km/s filament behind ~ 1000 km/s

X-ray spectrum 14 MK, low EM (1e46 cm -3 )  density ~10 8 cm -3 relatively hard/flat spectrum (  ~3.3) extending down to ~10 keV Number of non-thermal electrons are 10% of number of thermal electrons.

NASA Solar Probe + ESA Solar Orbiter Solar Sentinels

Protons >30 MeV (2.223 MeV Line Fluence, corrected for limb darkening) (Shih et al 2009) GOES Soft X-ray Peak flux

Cliver et al, 1994

Evidence for the Formation of Large- Scale, Reconnecting Current Sheet Linhui Sui, Gordon D. Holman Cusp-shaped loop; Possible formation of current sheet? ribbon From Shibata limb

Evidence for the Formation of Large- Scale, Reconnecting Current Sheets Linhui Sui, Gordon D. Holman HXR emissions from 1)footpoints 2)source in corona? or projection effect?

Temperature gradient is observed keV keV keV 8-10 keV keV keV footpoints (Sui & Holman 2003)

Above-the-loop-top HXR source limb thermal loop HXR footpointsHXR above the loop top source YOHKOH HXT observations: Only very rarely seen! 6 good events in 10 years. The most famous one is the so-called Masuda flare (Masuda et al. 1994)

Above-the-loop-top HXR source limb HXR above the loop top source Spectral resolution of Masuda flare is poor Thermal (~200 MK) or non- thermal emission?

RHESSI and STEREO observations of a partially disk-occulted flare C8 class flare on December 31, 2007

Krucker et al, 2009 thermal emission rapid time variations Nobeyama observations: thermal component (constant spectrum) gyro-synchrotron emission (decreasing spectrum)

STEREO view shows flare ribbons and post flare loops impulsive phase 1 hour later (post flare loops) (Krucker et al, 2009)

HXR imaging (Krucker et al, 2009) HXR peak (impulsive phase) SXR peak HXR source is above the SXR loops!

Microwave imaging (Krucker et al, 2009) HXR peak (impulsive phase) SXR peak microwave limb is higher up, 17 GHz co-spatial.

HXR spectra (Krucker et al, 2009) Power-law spectrum index g ~ 4.2  accelerated electrons have power law spectrum with index d ~3.7 N HXR > N thermal means * almost all energy is in accelerated electrons * collisional heating is fast ALL electrons are accelerated Masuda flare emission from before HXR burst

Microwave spectrum: non-thermal ( Krucker et al, 2009) gyro-synchrotron emission a ~ 1.8 d m wave ~ 3.4 B ~ G RHESSI: d thin ~ 3.7  power law spectrum from ~16 keV up to the MeV range

Summary: measured parameters ~ cm 3 ~ G ~ cm -3 ~ 3.4 volume magnetic field strength B pre-flare density acc. electron density power law distribution with d from ~15 keV up to a few MeV

Summary: measured parameters ~ cm 3 ~ G ~ cm -3 ~ 3.4 ~ 0.01 ~ 1 volume magnetic field strength B pre-flare density acc. electron density power law distribution with d from ~15 keV up to a few MeV pre-flare b (T=2 MK) b during HXR burst  energy density of the accelerated electrons is comparable to that of the magnetic field ions?

Discussion of models turbulence (e.g. Liu et al. 2007) Contracting islands (Drake et al. 2006) time evolution given by acceleration and escape. Drake et al. extended acc. region all electrons are acc. power law distribution 1 b ~1 stops contraction 1 b ~1 stops acceleration

Temperature kT Magnetic Reconnection at a Magnetar (?) (Hurley, et al., Nature 2005; Boggs et al., 2007 ) RHESSI > 20 keV X-rays Time in seconds

~100 times RHESSI sensitivity at 10 keV 12” FWHM resolution ~ keV Si strip detectors (NeXT mission, Takahashi san) launch: 2010, ~7 minute flight FOSXI (Focusing Optics Solar X-ray Imager) NASA Low Cost Access to Space program, PI Krucker detectors optics 2 m Optics assemblies (7) focal plane Detectors (7) recovery system Science: HXR emission from quiet corona (search for non-thermal emission from nanoflares) 2 m

HXR footpoints photosphere present day observations show us where electrons are lost. Future X-ray observations will image acceleration region and track flare accelerated electrons. “Spectroscopic imaging of the electron acceleration regions and tracking energetic electrons in the corona.” Future spacecraft mission

GRIPS (Gamma-Ray Imaging Polarimeter for Solar Flares) balloon payload R. Lin, PI Energy range: 20 keV-10 MeV Energy Res.: ~2-5 keV FWHM Angular Res.: ~10 arcsec Field of View: ~1 degree Polarization: ~3% in large flare Multi-pitch Rotating Modulator 3D position-sensitive germanium detectors in active shield Ultra-long duration Balloon

Mewaldt et al 2005

Gradual SEP event with 3 He (Mason, Mazur, & Dwyer, 1999)

Tylka & Lee, 2006

Tylka & Lee 2006

Zurbuchen 2004

Solar Reconnection – Breakout CME Model 3D simulation Lynch et al (2007) Null-point ahead of ejected plasmoid Bipolar reconnection behind

Computed wave spectra (Leamon et al 1998)

Reames & Ng 1998

Proton spectrum: RHESSI Gamma-rays (lines) vs SEPs at 1AU (blue points)

Comparison of SEP spectral indices from in-situ and g -ray data (Krucker, Mewaldt, Murphy, & Share, RHESSI workshop 2005) W5 6 E0 8

Electron - 3 He-rich SEP events - ~1000s/year at solar maximum - dominated by: - electrons of ~0.1 (!) to ~100 keV energy - 3 He ~10s keV/nuc to ~MeV/nuc x10-x10 4 (!) enhancements - heavy nuclei: Fe, Mg, Si, S enhancements - high charge states - associated with: - small flares/coronal microflares - Type III radio bursts - Impulsive soft X-ray bursts (so also called Impulsive SEP events )

LSEP event with 3He (Mason, Mazur, & Dwyer, 1999)

Gloeckler et al 2003