Transcript GROUP V: Summary talk

Group 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 Numbers
Mode
Symbol
Log (Energy)
April 21, 2002
July 23, 2002
UB
32.3 ± 0.3
32.3 ± 0.3
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
SXR Radiation
UR
31.3
31.0
Total Radiation
UR
> 31.7
> 31.6
Kinetic
UK
32.3 ± 0.3
32.0 ± 0.3
Potential
U
30.7 ± 0.3
31.1 ± 0.3
UP
31.5 ± 0.6
< 30
Magnetic
Flare
Intermediate
Final
CME
SEPs
X/ -ray spectrum
Thermal components
T= 2 10 7 K
T= 4 10 7 K
Electron
bremsstrahlung
-ray lines
(ions > 3 MeV/nuc)
Ultrarelativistic
Electron
Bremsstrahlung
SMM/GRS
Phebus/Granat
Observations
GAMMA1
GRO
GONG
RHESSI
Energy range
Pion decay radiation
(ions > 100 MeV/nuc)
sometimes with neutrons
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)
Vilmer et al (1999)
BATSE
• For 2 PHEBUS events
o if Wi>1MeV/nuc  We>20
keV
o No detectable GRL
above continuum
o Weak GRL flares?
PHEBUS
non-thermal
thermal
RHESSI
two component fits:
T, EM
γ, F35
spectral index
flux
Energy dependent photon spectral index
Interval 3 (peak of the flare)
Spectral index evolution:
Mean Electron Spectrum: Temporal evolution
1234 5
RHESSI Lightcurves
3-12keV;
12-25keV;
25-50keV;
50-300keV
Temporal evolution of the
Regularized Mean Electron
Spectrum (20s time intervals)
3
12 4 5
Non-thermal preflare coronal sources
GOES 1-8 A
DERIVATIVE
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 1AU
Typical electron spectrum can
be fitted with broken power law:
Break around: 30-100 keV
Steeper 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.
-ray line emission can be
delayed from hard X-rays
from <2 to 10’s of sec.
50- 180 keV
275- 325 keV
4 – 6.4 MeV
|-----20 sec----|
50- 180 keV
275- 325 keV
4 – 6.4 MeV
|------100 sec------|
60000
60
06:44
06:48
06:52
06:56
28-53 keV
40000
40
20000
20
0
7-15 MeV
20.01. 2005 FLARE
0
60
Background subructed
40000
53-150 KeV
20000
15-26 MeV
40
20
0
0
60
8000
0.15-0.5 MeV
4000
CORONAS
SONG DATA
26-41 MeV
Red horisontal bars
indicate the time intervals
used for the speactra
construction.
40
20
0
0
25
1200
20
41-60 MeV
0.5-1.3 MeV
15
800
10
400
5
0
0
400
15
counts s
-1
60-100 MeV
1.3-4 MeV
300
12
9
200
6
100
3
0
0
120
2.5
4-7 MeV
100-200 MeV
10 points smoothing
2.0
80
1.5
40
1.0
0
06:44
06:48
06:52
Time, UT
06:56
0.5
06:44
06:48
06:52
Time, UT
06:56
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
Geometry
The MHD incompressible equations are solved to study magnetic
reconnection in a current layer in slab geometry:
Periodic boundary conditions
along y and z directions
Dimensions of the domain:
-lx < x < lx, 0 < y < 2ly, 0 < z < 2lz
Description of the simulations: equations and geometry
Incompressible, viscous, dimensionless MHD equations:
V
1 2
 ( V   ) V   P  (  B)  B   V
t
Rv
B
1 2
   ( V  B) 
 B
t
RM
B  0
V  0
B is the magnetic field, V the plasma velocity and P the
kinetic pressure.
RM and Rv are the magnetic and kinetic Reynolds
numbers.
Time 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 time
<E> (erg)
t=400
t=300
t (s)
Total final energy of particles:
34
10 erg
Magnetic energy:
30
10 erg
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 p
4-5 for e
1.5 for p
1.8 for p
2.2 for e
4-5 for p
2.0 for e
1.8 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
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
HXR looptop
HXR footpoints
Outflow Shock Signatures During the Impulsive Phase
Solar Event of October 28, 2003:
• X17.2 flare
• RHESSI & INTEGRAL data (Gros et al. 2004)
The event was able to produce electrons
up to 10 MeV.
• termination shock radio signatures start
at the time of impulsive HXR rise
• signatures end when impulsive
HXR burst drops off
Discussion I
basic coronal parameters at 150 MHz
Ne  2.8  108 cm 3
B o  4 .7 G
( 160 Mm for 2 x Newkirk (1961))
(Dulk & McLean, 1978)
(flare plasma)
T  10 MK
 v th, e  12.300 km / s
v A  610 km / s
shock parameter
Ndown / Nup  B down / Bup  2

v s  1500 km / s
A shock  64 (Mm )2
total electron flux through the shock
Pe  No  A shock  v A  MA  2.5  10 34 s 1
 MA  2.32
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