Solar Electrons

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Planetary, Solar and Astrophysical
Relativistic Electrons Common Energization
Mechanisms?
SSL Colloquium Oct 20 2006 Ilan
Roth Space Sciences UC Berkeley, CA
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Different active magnetized plasma environments
are susceptible to a variety of intense
enhancements in fluxes of relativistic
electrons. Is there a common denominator in the
underlying physical processes?
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I. Artists view of the magnetosphere
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Active Magnetosphere Electron Signatures
Fluxes of relativistic electrons increase often
in the storm recovery phase due to substantial
sub-storm activity
L
Injection of low energy electrons - substorm
reconfiguration
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II. Flaring Solar Corona - Electron Signatures
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Solar Magnetic Reconfigurations
Coronal Mass Ejection
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Heliospheric field
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CIR Co-rotating Interaction Regions
interaction between fast/slow SW
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III. Gamma Ray Bursts (GRB)
High temperature heating of relativistically
expanding plasmas produced due to neutron star
(black hole) binary mergers (short burst) or
core collapse of a massive star (long
burst). Scenario fireball of electron-positron
pairs and radiation, moving with a Lorentz
factor ? 100-1000 with respect to the external
medium. Electron signature 0.1-1.0 MeV short
burst, then X, optical and radio afterglow
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Artists view of GRB - Gamma Ray Bursts
1MeV
CIR
CME
Synchrotron emission boosted by large Lorentz
factor due to super-relativistic electrons
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Solar/heliospheric (delayed) Relativistic
Electrons Magnetospheric (localized)
Relativistic Electrons Non-heliospheric
Relativistic Electrons Bootstrap Mechanism for
Relativistic Electrons
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A. Solar Electrons
Solar electrons are
detected a) In situ by orbiting satellites (1
AU) b) X ray thin target emissions (hard X ray
flare) c) Absorption in lower coronal regions
(soft X ray flare) d) Microwave emissions
(synchrotron)
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B. Magnetospheric Electrons
Magnetospheric electrons are
detected a) In situ by orbiting satellites (1
AU) b) X ray thin target emissions balloons
(hard X ray flare) c) Absorption in lower
auroral regions (soft X ray flare) d)
Microwave pulsations (synchrotron intense at
Jupiter)
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C. Non-heliospheric GRB Electron Physics
Gamma Ray Burst
electrons are deduced
remotely via
the observed synchrotron (jitter) or
inverse Compton electromagnetic
radiation, which
due to the large Lorentz factor is
observed at ?, X , optical
and radio wavelengths.
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Electrons are excellent tracers of magnetic field
and a major source of electromagnetic radiation

• Electromagnetic emissions include coherent
  radiation due to collective plasma processes, and
  incoherent single particle emissions due to
  interaction with plasma or with the magnetic
  field.

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It is hard to accelerate electrons they are good
indicators of magnetic fields, but due to their
small gyroradius, are not easily detached from
them. Magic astrophysical energization
configurations (a) Shock waves (b)
Reconnection Regions (c) Turbulent/meandering
fields In the presence of magnetic fields
electron energization ? violation of adiabatic
invariant(s)
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Motion of charged particles in an inhomogeneous
magnetic field
Energization ltgt violation of adiabatic invariants
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In situ Electron Observations Crucial
ingredient timing Correlation with other
phenomena
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Solar/heliospheric Relativistic Electrons

• Solar electrons are detected
• Remotely
• via varying electromagnetic emissions from the
  solar corona or along their heliospheric
  propagation path
• (b) in situ
• by spacecraft mainly at 1AU, at varying
  energies and pitch angles

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• Low Corona Signatures of Electrons in
  Flare-related Emissions
• Flare related electron fluxes streaming down the
  coronal loops, interacting with the dense
  chromospheric foot-points
• Hard X-Rays (HXR) via Bremsstrahlung (20 100
  keV)
• Chromospheric heating and evaporation results in
  UV and soft X-ray (SXR)
  emissions (lt10 keV).
• More energetic electron fluxes at the lower solar
  atmosphere gyrating around the magnetic field
  (gyro)synchrotron microwave emissions (1-10 GHz).
• 
  

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• Propagating-beam Signatures of non-thermal
  Electrons
• Fluxes (along) from the corona to the
  interplanetary medium excite Langmuir waves at
  the local plasma frequency, which are converted
  into electromagnetic radiation.
• ? 9000 n (sec )
• Frequency of this radiation determines the local
  density (time dependent location of the
  propagating beam)
• Wavelength
• at the chromosphere gt 1-10 cm at 1 AU
  gt 15km
• (b) Drift of the frequency reveals the electron
  momentum (energy) of the exciter - (few keV).

1/2
-1
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Remotely observed electrons from 1AU
Type III shock accelerated
Type II backbone
Two distinct propagation speeds shock and
impulsive electrons
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Classic event (Krucker, 1999)
Electrons at 1AU
Radio spectrogram
Energies and fluxes of the non thermal electrons
are deduced remotely via electromagnetic
radiations they emit, and in situ along the IP
field
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What processes may connect the closed coronal /
open interplanetary field lines?
Coronal (Moreton) EIT (Imaging Telescope) wave
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Heliospheric Signatures Injection of rel
electrons into heliosphere follows coronal
perturbations
Relation between coronal and IP perturbations
164 MHz NRH images
LASCO/SOHO
CME
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Connectivity to coronal restructuring
Radio waves at 100 MHz observed with CME
propagation
Perturbed Coronal field observed in tandem with
propagating IP structure
LASCO
NRH
Long-lived injection sites exist far behind CME
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Timing of the electromagnetic emissions vs
electrons

• Is there a delay between the onset of the X-ray,
  synchrotron, electromagnetic
• type III emissions and the inferred electron
  release time?
• Are electrons at different energies ejected
  simultaneously?

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In situ electrons at 1AU
Bieber et al, 2002
Higher energy fluxes peak later
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Two different populations type III and delayed
(energetic)
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Double injection
Subtracted type III onset
Langmuir
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14 MHz emissions occur at plasma density
of 10 cc. Time subtracted 500 sec for
waves, 1.2 AU/v for electrons Impulsive semi
relativistic electron events 10-30 min delay
with respect to the electromagnetic emissions
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Timing of the electromagnetic emissions - results

• HXR and microwaves few seconds
• HXR and 300 MHz seconds
• Relativistic electron events in IP medium are
  delayed by up to 30 min vs HXR, microwaves and H
  alpha

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Mildly relativistic fluxes are delayed vs
Microwave/hard X rays and soft X rays
Haggerty Roelof
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Mildly relativistic electron fluxes are delayed
vs low energy type III fluxes
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Relativistic electrons vs CME shocks
Mildly relativistic
Relativistic electrons
Em emissions (low energy)
CME
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Corrected
CME 2500 km/s
Injection
relativistic
Flare, type III
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Imaging Energization occurs behind the CME
External injection gt relativistic electrons
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Observations
The delayed relativistic electrons are
correlated to an uplift of coronal transient
(CME). They are not correlated to type III
emissions. They are not correlated to X-ray
emissions. They are correlated to NRH
emissions. How are the relativistic electrons
energized?
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• Explanation Attempts of the delayed
  Relativistic Fluxes
• Corona EIT/CME Shock Waves the flare forms the
  low energy electrons, while EIT energizes
  relativistic electrons
• 2) Reconnection behind Coronal Shock Large
  scale restructuring, far from flare site, maybe
  due to EIT or CME.
• 3) Complicated Geometry/Propagation
• 4) Hand-waving
• Big flare syndrome
• Fast CME intense flares coronal shock big
  particle events occur in temporal proximity
• QUESTION accelerating mechanism

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Magnetospheric Relativistic Electrons
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MAGNETOSPHERIC ELECTRON SCENARIO
Enhanced radiation belt radial diffusion
Slow diffusion across geomagnetic field
lines due to enhanced ULF activity by external
pressures
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However.
Often fluxes increase mainly in LOWER shells at
a FAST rate
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Calculated vs observed distributions
Radial diffusion does NOT describe the spatial
evolution
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Electron Fluxes over Consecutive Spacecraft
Crossings Black initial Red final
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Waves observed in space
(Meredith)
Strong correlation between kHz oscillations and
relativistic electron enhancement
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Whistler ray trajectories Bortnik et al 2004
Same in the solar corona?
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Waves observed on
ground Signatures on ground of chorus waves
strongly related to geomagnetic substorm,
energization of electrons and precipitation (loss
of the radiation belts) in the recovery phase of
the magnetic storm
Substorm injection
External injection gt relativistic electrons
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Geometric optics for whistler wave propagation
Electrons gyrate along the field line and
interact with the oblique whistler waves via
multiple resonances
B(x,y,z), n(z), e(?,k,z)
Z
electron
k
The wave propagates as a ray with a changing
wavenumber due to varying density/magnetic
field an electron interacts with the wave via
numerous resonances along its path
k v ? n O
Inhomogeneous magnetic field
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Resonance Doppler shifted frequency n
gyrofrequency Electron
characteristics
f(v) J (k ?) exp i (k z (? nO)t)
The effect at higher/anomalous harmonics is
more pronounced for more energetic electrons.
n
Non-isotropic lower energy electrons excite waves
which diffusively energize the high energy
electrons
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The crucial ingredient in the energization stems
from the ability of an electron to interact with
many wave modes (characteristics) as it
propagates/bounces along the inhomogeneous
magnetic field. The whistler wave changes its
phase velocity along its propagation.
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Non-heliospheric Relativistic Electron Physics
Gamma Ray Bursts
(GRB) Scenario fireball of electron-positron
pairs and radiation. Model for cosmic gamma ray
burst sources High temperature shock heating of
relativistically expanding plasmas produced due
to (possibly) neutron star binary mergers or core
collapse of massive star . Some energy is
deposited in baryons with ? 100-1000, which
transfer part of it to electrons through shock
acceleration these electrons cool off through
synchrotron emissions which are seen in GRB
(internal shocks between adjacent fireball
shells) and in the afterglow (external shocks
between fireball and interstellar medium).
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• Two major questions relevant to GRB/afterglow
  emissions
• An important ingredient in the GRB synchrotron
  emission is the necessary enhancement of the
  magnetic fields due to plasma processes Weibel
  Instability
  Magnetic fields need to be enhanced
• 2) Then, the ultra-relativistic electrons in the
  presence of enhanced magnetic field emit
  gyrosynchrotron radiation at a peeak frequency
  which is shifted to high frequencies due to
  Lorentz factor.
• ? ? B
• Electrons need to be energized
• (also synchrotron cooling requires
  re-energization)

2
c
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Models of a synchrotron spectrum
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Prototype of simulations
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1) Formation of localized magnetic fields
Cross section of longitudinal current
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Electron current/density due to electron/positron
interaction
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Electron-positron plasma
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Simulated Magnetic Field Lines
Jet injected into perpendicular B
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Computational Procedure
The background plasma is determined by the
background density n(x) and magnetic field
B(x). To make it generic to magnetospheric, solar
and other applications an inhomogeneous field
model is used B (x) B z
x / L B (x) B z y / L
B (x) B (1 z z /L
) Dispersion relation is solved LOCALLY, at the
position of the electron, with the resulting
eigenvectors of the electric and magnetic fields.
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x
o
2
y
o
2
z
o
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Geometric optics for whistler wave propagation
Electrons gyrate along the field line and
interact with the oblique whistler waves via
multiple resonances
B(x,y,z), n(z), e(?,k,z)
Z
electron
k
The wave propagates as a ray with a changing
wavenumber due to varying density/magnetic
field an electron interacts with the wave via
numerous resonances along its path
k v ? n O
Inhomogeneous magnetic field
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Short time evolution
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Medium term evolution
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Longer-term evolution
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Whistler diffusion time scale increases with
electron energy and is much faster than
magnetospheric ULF or solar Alfvenic time scale
For 5 mV/m ? ? 100 keV/ minute
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Bootstrap Mechanism Ingredients Large-scale
inhomogeneity of the magnetic field External
Perturbation with field reconfiguration and
injection of low energy, non-isotropic
electrons Excitation of obliquely propagating
whistler waves Whistler-electron tail resonant
interaction Energization/Diffusion time scales
with the wave amplitude, inversely with external
magnetic field scale. Therefore.
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Bootstrap Energization Model
Magnetospheric Scenario Injection of 10
keV-50 keV anisotropic electron distribution due
to a distant reconnection (sub-storm
reconfiguration of the magnetic field) these
anisotropic distributions excite whistler waves
which diffuse in pitch angle the low energy
electrons while energizing the tail of the
electron population. The low energy electrons
transfer energy to the high energy electrons
while diffusing in pitch angle.
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Bootstrap Energization Model
Solar Scenario Injection of 10
keV-50 keV anisotropic electron distribution due
to a distant reconfiguration due to coronal
perturbation these anisotropic distributions
excite whistler waves which diffuse in pitch
angle the low energy electrons while energizing
the tail of the electron population. CME plays
role in opening a venue to the IP medium. The
low energy electrons transfer energy to the high
energy electrons while diffusing in pitch angle.
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Bootstrap Energization Model
RGB scenario Relativistic Weibel instability
forms strongly inhomogeneous magnetic field
patches. Simulations indicate
that the energization occurs BEHIND the shock
front NOT Fermi acceleration. The localized
reversal of field topology injects anisotropic
electrons which emit whistler waves. Due to their
relativistic energies, the interaction with the
many high harmonics of the whistler is very
efficient, forming an energetic tail over very
short time scales.
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Low(er) energy electrons provide the seed, the
means and the energy for the relativistic
electrons