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Motivation Theory Results Discussion. Acceleration of Cosmic-rays by Super- Alfvenic turbulence. Hyeseung Lee University of Wisconsin-Madison Alex Lazarian University of Wisconsin-Madison Reinhard Schlikeiser University of Bochum, Germany. Midwest Magnetic Field 2011. Motivation - PowerPoint PPT Presentation
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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
Cosmic RayGalaxy Cluster
Cosmic Ray Spectrum
Midwest Magnetic Field 2011
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)
Galaxy Cluster
Hillas Plot
Midwest Magnetic Field 2011
UHECR (Ultra High Energy Cosmic rays)
Extragalactic (GRB, AGN, Galaxy Cluster)
MotivationTheoryResults
Discussion
rlar < L
It need astrophysical acceleration mechanism
Stochastic Acceleration
Second-order Fermi Acceleration
Midwest Magnetic Field 2011
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
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)
MHD turbulenceMotivation
TheoryResults
Discussion
Diffuse by MHD turbulence
Midwest Magnetic Field 2011
MHD turbulence can change particle momentum Diffusion Coefficient
MHD turbulenceMotivation
TheoryResults
Discussion
Diffuse by MHD turbulence
Midwest Magnetic Field 2011
MHD turbulence can change particle momentum Diffusion Coefficient
Pitch-angle Scattering
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
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
The acceleration by large-scale turbulence is relative to the momentum diffusion coefficient
MHD turbulenceMotivation
TheoryResults
Discussion
Comparison of D
Midwest Magnetic Field 2011
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 !!!
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
