Group V: ReportGroup V: Report

Regular Members: K. Arzner, A. Benz, C. Dauphin, G. Emslie, M. Onofri, N. Vilmer, L. Vlahos

Visitors: E. Kontar, G. Mann, R. Lin, V. Zharkova

Main Goals

1. Constrains on particle acceleration from the RHESSI data (close collaboration with all WGs) and other available sources of information on high energy particles

2. Discuss new theories on particle acceleration

3. Connecting theories on particle acceleration with the global magnetic topologies hosting flares and CMEs

Constraints on Acceleration/Transport(Electrons)

• Must produce an electron flux of at least 1037 electrons per second

• Must be able to accelerate electrons on time scales at most 10 milliseconds

• Must sometimes produce electron energies greater than at least 10’s of GeV

• Mechanism must be able to produce a flattening of the electron distribution at energies on the order of 500 keV

• Higher nonthermal hard X-ray flux statistically associated with harder spectra

The Electron “Problem”

• Efficiency of bremsstrahlung production ~ 10-5 (ergs of X-rays per erg of electrons)

Electron flux ~ 105 hard X-ray flux• Electron energy can be 1032 – 1033 ergs in large

events• Total number of accelerated electrons up to

1040 (cf. number of electrons in loop ~1038).– replenishment and current closure necessary

Revised NumbersMode Symbol Log (Energy)

April 21, 2002 July 23, 2002

Magnetic UB 32.3 ± 0.3 32.3 ± 0.3

Flare

Intermediate

Thermal Uth 31.3 (+0.4,-1) 31.1 (+0.4,-1)

Electrons Ue 31.3 (+?, -0.5) 31.5 (+?, -0.5)

Ions Ui < 31.6 31.9 ± 0.5

Final

SXR Radiation UR 31.3 31.0

Total Radiation

UR > 31.7 > 31.6

CME

Kinetic UK 32.3 ± 0.3 32.0 ± 0.3

Potential U 30.7 ± 0.3 31.1 ± 0.3

SEPs UP 31.5 ± 0.6 < 30

X/ -ray spectrum

RHESSI Energy range

Pion decay radiation(ions > 100 MeV/nuc)sometimes with neutrons

Ultrarelativistic ElectronBremsstrahlung

Thermal components

Electronbremsstrahlung

-ray lines (ions > 3 MeV/nuc)

T= 2 10 7 KT= 4 10 7 K

SMM/GRSPhebus/GranatObservationsGAMMA1GROGONG

Electron-Dominated Events• First observed with SMM

(Rieger et al, 1993)

• Short duration (s to 10 s) high energy (> 10 MeV) bremsstrahlung emission

• No detectable GRL flux• Photon spectrum > 1

MeV (X-1.5—2.0)

• For 2 PHEBUS events o if Wi>1MeV/nuc We>20 keV

o No detectable GRL above continuum

o Weak GRL flares?

Vilmer et al (1999)

PHEBUS

BATSE

thermal

non-thermal

RHESSItwo component fits:T, EMγ, F35

Grigis & B.

flux

spectral index

Energy dependent photon spectral indexEnergy dependent photon spectral index

Interval 3 (peak of the flare)

Spectral index evolution:

Mean Electron Mean Electron Spectrum: Temporal evolutionSpectrum: Temporal evolution

Temporal evolution of the Regularized Mean Electron Spectrum (20s time intervals)

1234 5

1 2

3

54

RHESSI Lightcurves3-12keV;12-25keV;25-50keV;50-300keV

GOES 1-8 ADERIVATIVE

Non-thermal preflare coronal sources

RHESSI SPECTRA 5-50 keV Thermal+broken powerlaw Preflare period: 01:02:00-01:11:00

Broken powerlaw extends down to 5 keV Thermal component

never dominates EM and T are poorly

determined Chisquare ~ 1 if EM=0

White = photons, Green = thermal model,Red = broken powerlaw, Purple = background

(NB similar source in July 23rd 2002 event)

Electron spectrum at 1AUTypical electron spectrum can be fitted with broken power law:

Break around: 30-100 keVSteeper at higher energies

Oakley, Krucker, & Lin 2004

Ions

• Tens of MeV ions and hundreds of MeV particles can be accelerated at the same time;

• We also see cases where we see a stage when hundreds of MeV ions are primarily accelerated.

|-----20 sec----|

|------100 sec------|

50- 180 keV

50- 180 keV

275- 325 keV

275- 325 keV

4 – 6.4 MeV

4 – 6.4 MeV

-ray line emission can be delayed from hard X-rays from <2 to 10’s of sec.

Background subructed

Red horisontal bars indicate the time intervals used for the speactra construction.

coun

ts s

-1

CORONAS SONG DATA

20.01. 2005 FLARE

06:44 06:48 06:52 06:560.5

1.0

1.5

2.0

2.5

Time, UT

100-200 MeV10 points smoothing

0

3

6

9

12

1560-100 MeV

0

5

10

15

20

25

41-60 MeV

0

20

40

60

26-41 MeV

0

20

40

60

15-26 MeV

0

20

40

6006:44 06:48 06:52 06:56

7-15 MeV

06:44 06:48 06:52 06:560

40

80

120

Time, UT

4-7 MeV

0

100

200

300

400

1.3-4 MeV

0

400

800

12000.5-1.3 MeV

0

4000

80000.15-0.5 MeV

0

20000

40000

53-150 KeV

0

20000

40000

60000

28-53 keV

June 3, 1982 - Evidence for delayed high-energy emission

Constraints for Theory

Radio spectral features and flares

• Connection between hard X-ray features and spikes in the range 300-3000 MHz, corresponding to densities of 109 -1011, has always been a promising diagnostic of energy release

• But there are some aspects hard to understand: frequently the spikes occur in a narrow frequency range for 10s of seconds, implying a fixed density in the energy release site. Energy release widespread over a large volume would produce spikes over a wide frequency (i.e. density) range

• Wide range of burst types in this frequency range is hard to understand: what controls frequency drift rates of different features?

Radio Emission at Decimetric Wavelengths

Constraints for Theory

Magnetic configuration of flares in the low corona

• See configurations of all types in radio images: single “loops”, double “loops”, complex configurations

• Frequently see magnetic connections over very large spatial scales

• Magnetic field strength: spectra typically imply 500-1000 G in the radio source

• But radio spectra are frequently flat-topped: hard to model, range of fields in the source (need FASR)

• See both prompt precipitation, implying either rapid scattering of electron pitch angles or loops with little height dependence for B, and trapping, where radio is strong but X-rays are weak, implying little pitch angle scattering.

Radio Flare Loop

The MHD incompressible equations are solved to study magnetic reconnection in a current layer in slab geometry:

Periodic boundary conditionsalong y and z directions

GeometryGeometry

Dimensions of the domain:-lx < x < lx, 0 < y < 2ly, 0 < z < 2lz

Description of the simulations: equations and geometryDescription of the simulations: equations and geometryIncompressible, viscous, dimensionless MHD equations:

0

0

1)(

1)()(

2

2

V

B

BBVB

VBBVVV

M

v

Rt

RP

t

B B is the magnetic field, is the magnetic field, VV the plasma velocity and the plasma velocity and PP the the kinetic pressure.kinetic pressure.

MR vRand are the magnetic and kinetic Reynolds are the magnetic and kinetic Reynolds numbersnumbers.

Time evolution of the electric fieldTime evolution of the electric field

The surfaces are drawn for E=0.005 from t=200 to t=300

Kinetic energy as a function of timeKinetic energy as a function of time

<E> (erg)

t (s)

t=400

t=300

Total final energy of particles: Magnetic energy:1034erg 10

30erg

Energy spectra: e (blue) and p (black)upper panel – neutral, middle – semi-neutral,

lower – fully separated beams

1.8 for p 2.2 for e

1.7 for p4-5 for e

1.5 for p 1.8 for e

4-5 for p2.0 for e

1.8 for p 2.2 for e

The suggested scheme of proton/electron acceleration and precipitation

Pure electron beams, compensated by return current, precipitate in 1s

Proton beam compensated by proton-energised electrons precipitate about 10s

Electron Acceleration in Solar Flares

basic question: particle acceleration in the solar corona

energetic electrons non-thermal radio and X-ray radiation

HXR footpoints

HXR looptop

electron acceleration mechanisms:

direct electric field acceleration (DC acceleration) (Holman, 1985; Benz, 1987; Litvinenko, 2000;

Zaitsev et al., 2000)

stochastic acceleration via wave-particle interaction (Melrose, 1994; Miller et al., 1997)

shock waves (Holman & Pesses,1983; Schlickeiser, 1984; Mann & Claßen, 1995; Mann et al., 2001)

outflow from the reconnection site (termination shock)

(Forbes, 1986; Tsuneta & Naito, 1998; Aurass, Vrsnak & Mann, 2002)

radio observations of termination shock signatures

Outflow Shock Signatures During the Impulsive Phase

• X17.2 flare

• RHESSI & INTEGRAL data (Gros et al. 2004)

• termination shock radio signatures start at the time of impulsive HXR rise

• signatures end when impulsive HXR burst drops off

Solar Event of October 28, 2003:

The event was able to produce electrons up to 10 MeV.

basic coronal parameters at 150 MHz

( 160 Mm for 2 x Newkirk (1961))

(Dulk & McLean, 1978)

(flare plasma)

s/km610v

s/km300.12v

MK10T

G7.4B

cm108.2N

A

e,th

o

38e

2shock

s

Aupdownupdown

)Mm(64A

s/km1500v

32.2M2B/BN/N

shock parameter

Discussion I

total electron flux through the shock

134AAshockoe s105.2MvANP

Summary

The termination shock is able to efficiently generate energetic electrons up to 10 MeV.

Electrons accelerated at the termination shock could be the source of nonthermal hard X- and -ray radiation in chromospheric footpoints as well as in coronal loop top sources.

The same mechanism also allows to produce energetic protons (< 16 GeV).

Summary

• The constrains on the acceleration are becoming so many and the ability of a single acceleration to handle all this become impossible- No unique acceleration

• Shocks, stochastic E-Fields and turbulent acceleration enters into the picture

• Synchronized from photosheric motions complex magnetic topologies maybe be the answer