Post on 30-Dec-2015
Interaction among Interaction among cosmic Rays, waves and cosmic Rays, waves and large scale turbulencelarge scale turbulence
Interaction among Interaction among cosmic Rays, waves and cosmic Rays, waves and large scale turbulencelarge scale turbulence
Huirong Yan
Kavli Institute of Astronomy & Astrophysics, Peking U
Collaboration: A. Lazarian (UW-Madison), R. Schlickeiser (U Ruhr-Bochum)
ImportanceImportanceImportanceImportance
Propagation:
Acceleration:
CMB synchrotron foreground Diffuse ɣ ray emissionDiffuse ɣ ray emission
diffuse Galactic 511 keV radiation
Magnetic “clouds” Stochastic
Acceleration:Fermi (49)
Gamma ray burstGamma ray burstSolar FlareSolar Flare
Big simulation itself is not adequate
Big simulation itself is not adequate
big numerical simulations fit results due to the existence of "knobs" of free parameters (see, e.g., http://galprop.stanford.edu/).
Self-consistent picture can be only achieved on the basis of theory with solid theoretical foundations and numerically tested.
Compressible Turbulence Compressible Turbulence dominates CR scatteringdominates CR scatteringCompressible Turbulence Compressible Turbulence dominates CR scatteringdominates CR scattering
Sca
tter
ing
freq
uenc
y
(Kolmogorov)
Alfven modes
Big difference!!!
(Chandran 2000)
The often adopted Alfven modes are useless. Fast modes dominate CR scattering (Yan & Lazarian 02,04,08).
eddies
l|| l
⊥
modesmodes momodes
Depends ondamping
dam damping
fast modes
CR Transport varies from place CR Transport varies from place to place!to place!
CR Transport varies from place CR Transport varies from place to place!to place!
Flat dependence of mean free path can occur due to collisionless damping (Yan & Lazarian 2008).
CR Transport in ISM
Mean
fre
e p
ath
(p
c)
Kinetic energy
haloWIMText from Bieber et al
1994
Palmer Palmer consensusconsensus
Feedback of Cosmic Rays (CRs) on MHD turbulence
Feedback of Cosmic Rays (CRs) on MHD turbulence
Slab modes with
Lazarian & Beresnyak 2006 , Yan & Lazarian 2011
Gyroresonance Instability Gyroresonance Instability
Turbulence compression
Scattering by instability generated slab wave
A
β≝ Pgas/Pmag < 1, fast modes (isotropic cascade +anisotropic damping )β > 1 slow modes (GS95) Wave Growth is limited by Nonlinear
Suppression!
Scattering by growing wavesScattering by growing waves
Anisotropy cannot reach δv/vA, the value predicted earlier (Lazarian & Beresnyak 2006), and the actual growth is slower and smaller amplitude due to nonlinear suppression (Yan
&Lazarian 2011).
By balancing it with the rate of increase due to turbulence compression , we can get
Bottle-neck of growth due to energy constraint:
Simple estimates:
Gyroresonance instabiltiy of cosmic rays
Gyroresonance instabiltiy of cosmic rays
domains for different regimes of CR scattering
domains for different regimes of CR scattering
Damped by background turbulence
λfb
cutoff due to linear damping
Hydronic picture of gamma ray emission near SNR
Hydronic picture of gamma ray emission near SNR
Supernova remnantTextText
streaming CRs
molecular clouds
Acceleration is limited by the wave growth at the shock frontAcceleration is limited by the
wave growth at the shock front
for MHD turbulence with k⊥ >> k||
maximum energy at a give epoch
maximum energy at a give epoch
Maximum energy accelerated at a given shock radius is higher than the case when the
background turbulence is assumed isotropic.
Accelerated CR flux and γ ray emission
Accelerated CR flux and γ ray emission
D<<DISM
Result is self-consistent! Result is self-consistent!
Steaming instability due to increased CR flux is sufficient to overcome the damping by
turbulence.
SummarySummarySummarySummaryCompression by large scale turbulence results in anisotropic distribution of CRs, which induces gyroresonance instability. Compression by large scale turbulence results in anisotropic distribution of CRs, which induces gyroresonance instability.
The growth of the instability is balanced by the feedback of the slab waves on the anisotropy of CRs. The growth of the instability is balanced by the feedback of the slab waves on the anisotropy of CRs.
Small scale slab waves are generated in compressible turbulence by gyroresonance instability, dominating the scattering of low energy Small scale slab waves are generated in compressible turbulence by gyroresonance instability, dominating the scattering of low energy CRs (<100GeV). CRs (<100GeV).
Feedback of CRs on turbulence should be included in future turbulence simulations. Feedback of CRs on turbulence should be included in future turbulence simulations.
The flux of CRs near SNRs is increased enough to create strong streaming instability that can overcome the damping by background The flux of CRs near SNRs is increased enough to create strong streaming instability that can overcome the damping by background turbulence for the energy range considered.turbulence for the energy range considered.
The enhanced scattering by the instability is enough to reproduce the observed gamma ray flux from molecular clouds. at the The enhanced scattering by the instability is enough to reproduce the observed gamma ray flux from molecular clouds. at the proximity of SNR. proximity of SNR.
\item The enhanced scattering by the instability is enough to reproduce the observed gamma ray flux from molecular clouds at the \item The enhanced scattering by the instability is enough to reproduce the observed gamma ray flux from molecular clouds at the proximity of SNR. The interaction of streaming instability and background turbulence determines the maximum energy of accelerated proximity of SNR. The interaction of streaming instability and background turbulence determines the maximum energy of accelerated particles.particles.
For perpendicular transport:For perpendicular transport:
Perpendicular transportPerpendicular transport