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