Particle Acceleration and Radiation from Relativistic Colliding Plasmas

1
Particle Acceleration and Radiation from
Relativistic Colliding Plasmas Edison Liang,
Koichi Noguchi Orestes Hastings, Rice
University Acknowledgements Scott Wilks,
Giovanni Lapenta, Bruce Remington Talk given at
DPP meeting 2007 Work partially supported by NSF,
LLNL, LANL
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Blazars, Gamma-ray Bursts, Pulsar Wind Nebulae
efficiently convert outflow energy from a central
engine into high-energy radiation. How do
relativistic plasma collisions and interactions
dissipate their energy and radiate? To address
this, We have developed a PIC code that includes
in-situ radiation from each superparticle
self-consistently, allowing for radiation damping
and Compton drag if necessary.
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Electrostatic 2-stream and Weibel instabilities
are dominant dissipation mechanisms in
unmagnetized collisions
Head-on collision of cold ee- plasmas at 0.9c in
1-D leads to growth of pure electrostatic
2-stream instability. No electron holes are
formed. Some particles are accelerated to to
twice initial energy
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Px vs x
By vs x
Head-on ee- collision of ee- at 0.9c in 3D
leads to Weibel Instability using Quicksilver.
Early growth of field energies agrees with linear
theory. Some particles are accelerated
to energies gt twice initial energy (Hastings
Liang 2007)
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Comparison of collisions hot ee- running into
B0 ee- cold plasma Ejecta
low-By, G10 B0, NR
100By
100By
100Ex
100Ex
Weibel is inhibited relative to 2-stream. 2.7
power law is produced in the relativistic case,
in agreement with other groups.
-px swept-up
-pxswrpt-up
2.7
ejecta
ejecta
swept-up
swept-up
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PIC simulation can compute the
radiation power directly from the force terms
Prad 2e2(F 2 g2F2) /3c where
F is force along v and F is force orthogonal
to v
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Calibration of PIC calculation again analytic
formula
Ppic
Psyn
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Simulation of warm magnetized ee-
colliding with B0 ee-
B
B0
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We use ray-tracing to compute the intensity and
critical frequencies of radiation measured by
detector Use approximation I Prad g2/p for
qg-1 I0 for q gt g-1 wcr reciprocal of time it
takes emission cone to Sweep past detector
Detector
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Details of ee- Poynting Shock (nejecta40no)
By100
ejecta
px
ambient
f(g)
decelerated ejecta spectral evolution
swept-up ambient spectral evolution
g
g
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Movie showing ee- Poynting Jet sweeping up
cold e-ion plasma
B
(movie made by Noguchi)
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Poynting shock with e-ion plasma is very complex.
Swept-up electrons are accelerated by
ponderomotive (jxB) force. Swept-up ions are
accelerated by charge separation electric fields.

100pxi
100By
Prad
100Ex
f(g)
ejecta e
-10pxe
-10pxej
ambient ion
ejecta e-
ambient e-
g
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Poynting shock of ee- sweeping up cold e-ion
plasma Poynting flux decays via mode conversion
and acceleration and heating of electrons.
pi
px/mc
ambient ion
ambient e-
ejecta e
x
pi10
By
By100
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Evolution of f(g) vs . g
ejecta e-
ejecta e
swept-up e-
ion
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• SUMMARY
• Structure and radiative power of collisionless
  shocks are highly dependent on ejecta
  (downstream) B field and Lorentz factor.
• Radiative efficiency appears to be low in all
  cases. This may pose a
• problem for astrophysics, especially GRBs and
  blazars.
• 3. In Weibel shocks, electrons are accelerated
  by self-generated EM
• turbulence. No evidence of first-order Fermi
  process.
• In electrostatic shocks, electrons are
  accelerated by Langmuir
• turbulence to form power-law of index 2.5-2.8
• 5. In strongly magnetized shocks, swept-up
  electrons are accelerated by ponderomotive force
  and electrostatic turbulence. Swept-up ions are
  accelerated by charge separation.