Midwest Magnetic Field 2011
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Transcript of Midwest Magnetic Field 2011
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Midwest Magnetic Field 2011
MotivationTheoryResults
Discussion
Acceleration of Cosmic-rays by Super-Alfvenic turbulence
Hyeseung LeeUniversity of Wisconsin-Madison
Alex LazarianUniversity of Wisconsin-Madison
Reinhard SchlikeiserUniversity of Bochum, Germany
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Cosmic RayGalaxy Cluster
Cosmic Ray Spectrum
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1GeV ~ Knee : Galactic Origin (Supernovae)
Knee ~ Ankle: Larger Shocks (Galactic wind - Neutron Stars, Superbubbles, Reaccelerated heavy
nuclei) and SN explosions into stellar windsUHECR (Ultra High Energy Cosmic rays)
Slope ϒ=-2.7
Slope ϒ=-3.1
Slope ϒ=-2.7
MotivationTheoryResults
Discussion
Viktor Hess(1912)
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Galaxy Cluster
Hillas Plot
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UHECR (Ultra High Energy Cosmic rays)
Extragalactic (GRB, AGN, Galaxy Cluster)
MotivationTheoryResults
Discussion
rlar < L
It need astrophysical acceleration mechanism
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Stochastic Acceleration
Second-order Fermi Acceleration
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Fermi(1949)Galactic CRs are acceleratedas the result of many collision with massive, magnetized cloud
Particle in head-on collisions gains energyParticle in an overtaking collisions loses energy
θexit : <cosθout’> = 0θenter : ν - Vcosθin
On average,net energy gain
MotivationTheoryResults
Discussion
But, head-on collisions are more frequentStochastic Acceleration by MHD turbulence
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Acceleration by MHD turbulenceMotivation
TheoryResults
Discussion
Property of MHD Turbulence
Midwest Magnetic Field 2011
The acceleration by sub-Alfvenic turbulence had been discussed by Cho & Lazarian 2006.
Sub-Alfvenic turbulence ( Vl < VA )(Cho & Lazarian 2006)
Super-Alfvenic turbulence ( Vl > VA )
35A kkE 35s kkE
23f kkE
Goldreich-Sridhar 95 scaling
ISOTROPIC
Super-Alfvenic turbulence evolves along the hydrodynamic isotropic Kolmogorov cascade
Assume that compression follows Kolmogorov scaling
For example :
Cho & Larzarin (2002)
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MHD turbulenceMotivation
TheoryResults
Discussion
Diffuse by MHD turbulence
Midwest Magnetic Field 2011
MHD turbulence can change particle momentum Diffusion Coefficient
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MHD turbulenceMotivation
TheoryResults
Discussion
Diffuse by MHD turbulence
Midwest Magnetic Field 2011
MHD turbulence can change particle momentum Diffusion Coefficient
Pitch-angle Scattering
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MHD turbulenceMotivation
TheoryResults
Discussion
Diffuse by MHD turbulence
Midwest Magnetic Field 2011
MHD turbulence can change particle momentum Diffusion Coefficient
Pitch-angle Scattering
Large-scale compressible motion
Fast diffusion time
Slow diffusion time
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MHD turbulenceMotivation
TheoryResults
Discussion
Diffuse by MHD turbulence
Midwest Magnetic Field 2011
MHD turbulence can change particle momentum Diffusion Coefficient
Pitch-angle Scattering
Large-scale compressible motion
Fast diffusion time
Slow diffusion time
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The acceleration by large-scale turbulence is relative to the momentum diffusion coefficient
MHD turbulenceMotivation
TheoryResults
Discussion
Comparison of D
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tvptp
222
pDPitch-angle Scattering
Large scale compression Fast Diffusion Limits Slow Diffusion Limits
ptlmfp
AA
vlLv
Lvp2~pitch
pD
DL
LvL
2
~ t , vA
A
A vv
t , v~
ptlmfp
A
A
LA
vlLv
vv
Lvp
22
~Alf-suppD A
A
LA Mvv
Lvp
22
~
Alf-suppD
For super-alfvenic turbulence, pitchalfvensuppp DD
Large-Scale motion dominates acceleration of cosmic- ray !!!
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SUMMARY1. Super-Alfvenic turbulence is present in astrophysicsal environment
: galaxy clusters
2. For super-Alfvenic acceleration by large scale motions dominates resonance scattering.
3. The acceleration by super-Alfvenic turbulence should be taken into account in models for galaxy cluster and molecular cloud.
MotivationTheoryResults
Summary
Midwest Magnetic Field 2011