Collisionless Dynamics II: Orbits Collisionless Dynamics II: Orbits.
Radiation from Poynting Jets and Collisionless Shocks Edison Liang, Koichi Noguchi
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Transcript of Radiation from Poynting Jets and Collisionless Shocks Edison Liang, Koichi Noguchi
Radiation from Poynting Jets and Collisionless Shocks
Edison Liang, Koichi NoguchiShinya Sugiyama, Rice University
Acknowledgements: Scott Wilks, Bruce LangdonBruce Remington
Talk given at Glast Symposium, Feb 2007(see http://spacibm.rice.edu/~liang/picsim
and spacibm.rice.edu/~knoguchi)
Internal shocksHydrodynamic Outflow
Poynting fluxElectro-magnetic-dominated outflow
Popular Paradigms for the radiation of relativistic outflows in GRBs & Blazars
e+e-ions
e+e-
What is energy source? How are the e+e/ion accelerated?How do they radiate?
shock-raysSSC, EC… -rays
B
>>1PIC sims can address
difficultmicrophysics
Highlight We have developed a Particle-In-Cell code that
simultaneously computes total radiation output from each superparticle.
We find that in-situ radiation output of highest energy electrons accelerated by Poynting Flux (and some Collisionless Shocks) are much below that predicted by the classical synchrotron formula.
This may solve the problem of too rapid synchrotron cooling in many internal shock models of GRBs.
Question: How do particles radiate while they are
being accelerated to high energies?
We compute the power radiated simultaneously from the force terms
used in the particle movers of the PIC code:
Prad = 2e2(F|| 2+ 2F+2) /3m3c
where F|| is force along vand F+ is force orthogonal to v
(we have carefully calibrated our procedureagainst analytic results)
p
By
Ez
k
In Poynting flux acceleration, most energeticparticles ~ comoving with local EM field
Prad ~ e22sin4< Psyn ~e
22
where is angle between v and Poynting vector k.
critical frequencycr ~ e2sin2crsyn~ e2
<< 1 in the limit Ez ~ By
and ~ wave
By
Ez
Jz
Plasma
JxB force pushes all surface particles upstream:<> ~ max(B2/4nmec2, ao)“Leading PoyntingAccelerator” (LPA)
Plasma
JxB force pulls out surface particles. Loaded EM pulse (speed < c) stays in-phase with the fastest particles, but gets “lighter” as slower particles fall behind. It accelerates indefinitely over time: <> >> B2 /4nmec2, ao “Trailing Poynting Accelerator”(TPA).
(Liang et al. PRL 90, 085001, 2003)
Entering
Exiting
Two different kinds ofPoynting Flux Acceleration via
induced j x B(ponderomotive) force
x
x
EM pulse
By
x
y
z
Ez
Jz JxB
k
Prad
Panalytic ~e22sin4x
px
pz
ByPrad
Electrons accelerated by LPA radiate at a level ~ 10- 4
of classical synchrotron formula, due to sin ~ pz/px ≤ 0.1
2e2~105
50
px
Prad
By
Evolution of e+e- plasma accelerated by Poynting flux (LPA) shows decline of radiative power output Prad
despite increase of
x
By
Ez
Jz
Plasma
JxB force pushes all surface particles upstream:<> ~ max(B2/4nmec2, ao)“Leading PonderomotiveAccelerator” (LPA)
Plasma
JxB force pulls out surface particles. Loaded EM pulse (speed < c) stays in-phase with the fastest particles, but gets “lighter” as slower particles fall behind. It accelerates indefinitely over time: <> >> B2 /4nmec2, ao “Trailing Ponderomotive Accelerator” (TPA).
(Liang et al. PRL 90, 085001, 2003)
Entering
Exiting
Relativistic Poynting Flux Accelerationvia induced j x B(ponderomotive) force
x
x
EM pulse
By
x
y
z
Ez
Jz JxB
k
t.e=800 t.e=10000
magnify
e/pe =10
TPAOccurs
whenever EM-
dominated plasma is rapidly
unconfined(Liang &
NishimuraPRL 91,175005 2004)
te=1000
5000
10000
18000
Fourier peak wavelength scales as ~ c.m/ pe
logdN/dE
logE
Epk~200 keV
~0--1.5
β~-2--2.5
time
Epk
dN/dthard-to-soft GRB spectralevolution
diverseandcomplexBATSElightcurves
TPA produces Power-Law spectra with low-energy cut-off.Peak(bulk) Lorentz factor m corresponds roughly to the
profile/group velocity of the EM pulse
logdN/dE
logE
Epk~200 keV
~0--1.5
β~-2--2.5
time
Epk
dN/dt
m
the maximum max ~ e E(t)βzdt /mc where E(t) is the comoving electric field
Typical GRB spectrum
β=(n+1)/2
The power-law index (p ~ 3 - 4) is remarkably robust independent of initial plasma size or temperature
and only weakly dependent on B
f()
-3.5
Lo=105rce
Lo= 104rce
PhotonIndex
β=(p+1)/2~ 2 -2.5
x
300px
By*100
Prad
2e2~3x106
Prad from TPA << Psyn (~ 2e2)
QuickTime™ and aGraphics decompressor
are needed to see this picture.
Prad
Panalytic ~e22sin4
In TPA, we also find Prad ~ Panalytic
for the highest energy particles
In TPA jets, Prad asymptotes to ~ constant level at late timesas increase in is compensated by decrease in and B
Lo=120c/eLo=105c/e
po=10
PradPrad
x x
Inverse Compton scattering against ambient photons can slow or stop PF acceleration (Sugiyama et al 2005)
n=10-4ne n=10-2ne n=ne
1 eV photon field epe=100
We have studied radiation from Collisionless Shocks
3 Examples:
1. e+e-/e+e- Magnetic Shock (B2 ~ bulk KE)
2. e+e- /e-ion Magnetic Shock (B2 ~ bulk KE)
3. e+e- Nonmagnetic Shocks (B2 << bulk KE)
QuickTime™ and a decompressor
are needed to see this picture.
B
Poynting jet running into cool e-ion ambient plasma
(movie by Noguchi)
ejecta e+
ejecta e-ambient ion
ambient e-
f()-10pxe-10pxej
100pxi
100Ex
100By
Magnetized collisionless shock produced by collision of e+e- Poynting Jet with cold e-ion plasma .
radiative shock layer
x
swept-up e- radiation snapshots
The radiative shock layer gets thicker and bifurcates with time due to ion drag, but max Prad stays ~ constant
x
Prad
SUMMARY
1. Radiation power of Poynting Flux accelerated electrons are orders of magnitude below classical synchrotron formula due to Force ~ parallel to velocity. This result may be generic and also applies to
some Collisionless Shocks.
2. Structure and radiation power of collisionless shocks are highly sensitive to magnetization and ion loading. Shocked radiative layer in e-ion shocks is much thicker and bifurcates.
3. Inverse Compton of external photons may dominate synchrotron and SSC.
4. Critical frequency of PF acceleration radiation is much lower than the classical synchrotron critical frequency.