Transcript Jetapr01 - Obserwatorium Astronomiczne Uniwersytetu

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New Relativistic Particle-In-Cell Simulation Studies of
Prompt and Early Afterglows from GRBs
Ken Nishikawa
National Space Science & Technology Center/CSPAR (UAH)
Collaborators:
P. Hardee (Univ. of Alabama, Tuscaloosa)
Y. Mizuno (Univ. Nevada, Las Vegas/CSPAR)
M. Medvedev (Univ. of Kansas)
B. Zhang (Univ. Nevada, Las Vegas)
Å. Nordlund (Neils Bohr Institute)
J. Frederiksen (Neils Bohr Institute)
J. Niemiec (Institute of Nuclear Physics PAN)
Y. Lyubarsky (Ben-Gurion University)
H. Sol (Meudon Observatory)
D. H. Hartmann (Clemson Univ.)
G. J. Fishman (NASA/MSFC )
KINETIC MODELING OF ASTROPHYSICAL PLASMA S, October 7, 2008
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Outline of talk
• Recent 3-D particle simulations of relativistic jets
* e±pair jet into e±pair and electron-ion ambient plasmas
 = 12.57, 1 <  <30 (avr ≈ 12.6)
• Radiation from two electrons
• One example of jitter radiation in turbulent magnetic
field created by the Weibel instability
• Summary
• Future plans of our simulations of relativistic jets
Calculation of radiation based on particle trajectories
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Schematic GRB from a massive stellar progenitor
(Meszaros, Science 2001)
Simulation box
Prompt emission
Polarization ?
Accelerated particles emit waves at shocks
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3-D simulation
with MPI code
injected at z = 25Δ
X
Y
105×105×4005
grids
(not scaled)
1.2 billion particles
Z
jet front
3-D isosurfaces of density of jet particles and Jz for narrow jet (γv||=12.57)
electron-ion
ambient
t = 59.8ωe-1
electron-positron
ambient
jet electrons (blue), positrons (gray)
-Jz (red), magnetic field lines (white)
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Isosurfaces of z-component of current density
for narrow jet (γv = 12.57)
||
electron-ion
ambient plasma
electron-positron
ambient plasma
(+Jz: blue, -Jz:red) local magnetic field lines (white curves)
3-D isosurfaces of z-component of current Jz for narrow jet (γv||=12.57)
electron-ion ambient
t = 59.8ωe-1
-Jz (red), +Jz (blue), magnetic field lines (white)
Particle acceleration due to the local
reconnections during merging current
filaments at the nonlinear stage
thin filaments
merged filaments
Ion Weibel instability
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ion current
E  B acceleration
electron trajectory
(Hededal et al 2004)
t = 59.8ωe-1 9/39
Magnetic field generation and particle
acceleration with narrow jet (u|| = γv|| = 12.57)
B
electron-positron
ambient
εBmax = 0.012
jet electrons
electron-ion
ambient
εBmax = 0.061
jet electrons
ambient positrons
ambient ions
red dot: jet electrons
blue dots: ambient (positrons and ions)
(Ramirez-Ruiz, Nishikawa, Hededal 2007)
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New simulation results using new MPI_Tristan
γ = 15.02, nj/nb = 0.676
t = 1500ωpe−1
electron-positron jet
x/Δ = 400
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New simulation results using new MPI_Tristan
γ = 15.02, nj/nb = 0.676
t = 1950ωpe−1
x/Δ = 400
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Present theory of Synchrotron radiation
(Nakar’s talk on Monday)
• Fermi acceleration (Monte Carlo simulations are not selfconsistent; particles are crossing at the shock surface many
times and accelerated, the strength of turbulent magnetic
fields are assumed), New simulations show Fermi
acceleration (Spitkovsky 2008)
• The strength of magnetic fields is assumed based on the
equipartition (magnetic field is similar to the thermal
energy) (B)
• The density of accelerated electrons are assumed by the
power low (F() = p; p = 2.2?) (e)
• Synchrotron emission is calculated based on p and B
• There are many assumptions in this calculation
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Self-consistent calculation of radiation
• Electrons are accelerated by the
electromagnetic field generated by the
Weibel instability (without the assumption used in
test-particle simulations for Fermi acceleration)
• Radiation is calculated by the particle trajectory in
the self-consistent magnetic field
• This calculation include Jitter radiation
(Medvedev 2000, 2006) which is different from
standard synchrotron emission
• Some synchrotron radiation from electron is
reported (Nishikawa et al. 2008 (astroph/0801.4390;0802.2558)
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Radiation from collisionless shock
New approach: Calculate radiation
from integrating position, velocity,
and acceleration of ensemble of
particles (electrons and positrons)
Hededal, Thesis 2005 (astroph/0506559)Nishikawa et al. 2008 (astroph/0802.2558)
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Synchrotron radiation from gyrating electrons in a uniform magnetic field
electron trajectories
B

β
β
n

β
radiation electric field observed at long distance
observer
β
n
spectra with different viewing angles
time evolution of three frequencies
0°
4°
3° 2° 1°
6°
5°
theoretical synchrotron spectrum
f/ωpe = 8.5, 74.8, 654.
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Synchrotron radiation from propagating electrons in a uniform magnetic field
electron trajectories
B
radiation electric field observed at long distance
θ
observer
spectra with different viewing angles
gyrating
θΓ = 13.5°
Nishikawa et al. astro-ph/0809.5067
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(Nishikawa et al. astro-ph/0809.5067)
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Case A
(Nishikawa et al. astro-ph/0809.5067)
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Case B
(Nishikawa et al. astro-ph/0809.5067)
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Case C
(Nishikawa et al. astro-ph/0809.5067)
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Case D
(Nishikawa et al. astro-ph/0809.5067)
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Case E
(Nishikawa et al. astro-ph/0809.5067)
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Case F
(Nishikawa et al. astro-ph/0809.5067)
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Radiation from collisionless shock
☺
Power
observer
Shock simulations
GRB
Hededal Thesis:
Hededal & Nordlund 2005, submitted to ApJL (astro-ph/0511662)
Summary
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• Simulation results show electromagnetic stream
instability driven by streaming e± pairs are
responsible for the excitation of near-equipartition,
turbulent magnetic fields.
• Ambient ions assist in generation of stronger
magnetic fields.
• Weibel instability plays a major role in particle
acceleration due the quasi-steady radial electric field
around the current filaments and local reconnections
during merging filaments in relativistic jets.
• Broadband (not monoenergetic) jets sustain the
stronger magnetic field over a longer region.
• The magnetic fields created by Weibel instability
generate highly inhomogeneous magnetic fields,
which is responsible for jitter radiation (Medvedev,
2000, 2006; Fleishman 2006).
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Future plans for particle acceleration in relativistic jets
• Further simulations with a systematic parameter
survey will be performed in order to understand
shock dynamics with larger systems
• Simulations with magnetic field may accelerate
particles further?
• In order to investigate shock dynamics further
diagnostics will be developed
• Investigate synchrotron (jitter) emission, and/or
polarity from the accelerated electrons in
inhomogeneous magnetic fields and compare with
observations (Blazars and gamma-ray burst
emissions) (Medvedev, 2000, 2006; Fleishman 2006)
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Gamma-Ray Large Area Space Telescope (GLAST)
(launched on June 11, 2008)
Compton Gamma-Ray
http://www-glast.stanford.edu/
Observatory (CGRO)
Burst And Transient
Source Experiment
(BATSE) (1991-2000)
PI: Jerry Fishman
GLAST
All sky monitor
• Large Area Telescope (LAT) PI: Peter Michaelson:
gamma-ray energies between 20 MeV to about 300 GeV
• GLAST Burst Monitor (GBM) PI: Chip Meegan (MSFC):
X-rays and gamma rays with energies between 8 keV and
25 MeV (http://gammaray.nsstc.nasa.gov/gbm/)
The combination of the GBM and the LAT provides a
powerful tool for studying radiation from relativistic
jets and gamma-ray bursts, particularly for timeresolved spectral studies over very large energy band.
GRB progenitor
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relativistic jet
Fushin
(god of wind)
emission
(shocks, acceleration)
Raishin
(god of lightning)
(Tanyu Kano 1657)