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Anisotropic Plasma Astrophysics

Roger Blandford Paul Simeon Yajie Yuan KIPAC Stanford. Anisotropic Plasma Astrophysics. Describing Cosmic Plasma. Fluid description P ,  , v , B… Magneto Fluid Dynamics Flux-freezing, conservation of mass, momentum, energy P ~    isotropic ! Relativistic flows

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Anisotropic Plasma Astrophysics

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  1. Roger Blandford Paul Simeon Yajie Yuan KIPAC Stanford Anisotropic PlasmaAstrophysics AronsFest

  2. Describing Cosmic Plasma • Fluid description • P, , v, B… • Magneto Fluid Dynamics • Flux-freezing, conservation of mass, momentum, energy • P ~ isotropic! • Relativistic flows • Electromagnetic Flows • Kinetic description • f(p,x,t), E, B… • Collisionless plasmas • Vlasov equation for f • Nonthermal distributions • Transport effects • Ultrarelativistic plasmas Need a hybrid approach to tacklecontemporaryproblem AronsFest

  3. Anisotropic MHD • MHD commonly developed and computed assuming isotropic pressure • Collisionless plasmas are observed and expected to be anisotropic • How and when can we discuss this at the fluid level using a pressure tensor? • Interesting and possibly different when dominant pressure (and current) is due to ultrarelativistic particles while the flow is locally non-relativistic • Dissipation due to radiation not collisions or plasma instabilities • Diffusive Shock Acceleration – SNR, clusters… • Pinches - PWN, jets… AronsFest

  4. Particle Acceleration Unipolar Induction Stochastic Acceleration V ~  I ~ V / Z0 Z0~100 P ~ V I ~ V2/Z0 U DE/E ~ +/-u/c ln(E) ~ u/c (Rt)1/2  c AronsFest

  5. Cosmic Rays protons heavies? protons?? Cahill Dedication, Caltech AronsFest GeVTeVPeVEeVZeV

  6. Cosmic Rays solar system supernova remnants pulsars? active galactic nuclei ?? Cahill Dedication, Caltech AronsFest GeVTeVPeVEeVZeV

  7. Cas A Tycho SN1006 Crab Nebula Chandra Supernova remnants SN1006 X-ray Cassiopeia A X-ray Radio Cosmic rays W44 . AronsFest

  8. Particle acceleration in SNR SN1006 • ~ 100TeV gamma rays • ~0.3 PeV cosmic rays • Hadronic and leptonic (Fermi) • Variable X-rays • 100 TeV electrons • ~ 1 mG magnetic field • Shocks also amplify magnetic field • Details controversial Cas A Tycho Perseus Cluster AronsFest

  9. Ultra High Energy Cosmic Rays • Zevatrons? • Top down exotica • GZK cutoff • EM channel not seen and hard to avoid • Massive BH in AGN (~30-50 Mpc) • AGN may be too weak • Acceleration must be remote from BH • Gamma-Ray Bursts • Stellar BH or millisecond magnetar? • Too distant? Too much radiation? • Cluster Shocks (Norman,Ryu,Bohringer…) • High Mach accretion shocks • Hard to accelerate p to ZeV energy • Heavy elements may be predicted • e.g. Fe; range ~ 10 Mpc? • Composition controversial • Analysis should be aided by LHC AronsFest

  10. Entropy Matters • Sgas=1.5 ln[(T/Trec)(n/nrec)-2/3]k (relative to recombination) • Much more in CMB • Shocks create gas entropy • DS[M]=1.5ln[(5M2/4-1/4)(1/4+3/4M2)5/3]k • Before reionization • Weak shocks M ~ 1-3 • DS < k • During reionization (z~10) • Ionization entropy • Moderate shocks M ~1-20 • DS <3k • After reionization • May need DS as large as 10k • Would imply M~100 • e.g. V~1000, s~10 km s-1 M Simionescu et al Perseus Sgas/k 18 17 r 16 15 14 13 Recent strong evidence for presence of high M accretion shocks around clusters AronsFest

  11. Shocks in Structure Formation Simulations (Ryu et al 2003) rgas Lx pancake filament Ms T cluster (100 Mpc/h)2 2D slice Simulations exhibit high M shocks LCDM simulation with 10243 cells, computational box: (100h-1 Mpc)3 , TVD: grid-based Eulerian hydro code AronsFest

  12. GeVg-rays from Clusters of Galaxies Keith Bechtol • Active Galactic Nuclei • Primordial cosmic rays • Dark Matter Annihilation Han et al 2012 Upper limits are interesting! AronsFest

  13. UHECR at accretion shocks?? Norman Ryu Bohringer… • Accretion shocks • Invisible • v~500-1000 km/s? • R ~ 3-10Mpc • B ~ 3 x 1020V/v R ~10mG! • However, SNR generate phenomenal fields • OK if UHECR is Fe • Counter-evolutionary tendency AronsFest

  14. Collisionless Shocks Scatter off magnetic waves Explain intensity and spectrum of Galactic cosmic rays AronsFest

  15. Too good to be true! • Diffusion: CR create their own magnetic irregularities ahead of shock through instability if <v>>a • Instability likely to become nonlinear - Bohm limit • What happens in practice? • Parallel vs perpendicular diffusion? • Cosmic rays are not test particles • Include in Rankine-Hugoniot conditions • u=u(x) • Include magnetic stress too? • Acceleration controlled by injection • Cosmic rays are part of the shock • What happens when v ~ u? • Relativistic shocks • Energy cutoff? • E < euBR ~ PeV for mG magnetic field AronsFest

  16. 0.1 P(E) / u2 P(E) / u2 E Shock TeV GeV PeV GeV TeV PeV X Particle Transport Cosmic Ray Pressure dominates Magnetic and Gas Pressure far ahead of Shock • Alfven waves scatter cosmic rays •  ~ (B/B)2rL • Bohm? • D ~ c/3 • Parallel vs perpendicular • L ~ D/u > 100rL ~ 100 EPeVBG-1Z-1pc • RSNR < 10pc • Highest energy cosmic rays stream furthest ahead of shock • L ~ E ? • “Magnetic Bootstrap” • Firehose and other instabilities AronsFest

  17. RB Funk 2007 Magnetic Bootstrap • Assume: • Cosmic rays accelerated by DSA at shock front to ~PeV energy • PCR ~ 0.1u2 E9-0.2 • Magnetic field amplified upstream l > rL • Dynamical effects on background small • Wave turbulence maintained at Bohmlevel mainly by Firehosemodes • Also mirror, gyroresonant, Bell-Lucek • Transport by field line modeling • “Uniform” field is turbulent field created by higher energy upstream • Cosmic rays with energy ~ Emax stream away from the shock • Firehose dominates if u > (aISM c)1/2 (PCR/u2)-1/4 ~1000 km s-1 • Fermi observations are instructive! AronsFest

  18. Magnetic Bootlaces CR th P mag • How can a small magnetic pressure mediate the interaction between two particle “fluids”? X j X AronsFest

  19. Extragalactic Jets M87 Cygnus A PictorA Pictor A 3C273 3C31 NGC 326 3C75 AronsFest

  20. McKinney Tschekhoskoy RB 2012 AronsFest

  21. Crab Nebula AronsFest

  22. Flaring behavior Buehler et al April 2011 Power~1029W Singular events or power spectrum?No variation seen in other bands AronsFest

  23. Spectrum of “Flare” synchrotron spectrum AronsFest Electron synchrotron radiation: E~PeV, g~109; B~100nT

  24. Where does the variation originate ? =10,000mas • Long term variation of nebula likely due to changes in magnetic field • Peak power is ~ 3 percent of nebular power • Flare energy equals that stared in a region of size L~ 20B-71/2 ltd ~ 2B-71/2 arcsec • We want to learn where and how nature accelerates particles to high energy • Not the Pulsar • No correlation with rotation frequency • Wind shocks when momentum flux equals nebular pressure • Wind, Shock, Jet, Torus are all possibilities W P J S T 1 lt hr = 3 mas Larmor radius= 60g9B-7-1mas AronsFest

  25. Pinch? E • Resistance in line current • Current carried byhigh energy particles • Resistance due to radiation reaction • Pairs undergo poloidal gyrations which radiate in all directions • Relativistic drift along direction of current Jet!! • Compose current from orbits self-consistently • Illustration of Poynting’s theorem! • Variation intrinsic due to instability j X Bf r AronsFest

  26. MHD with Pressure Tensor Linear Perturbations etc Double Adiabatic Ansatz (CGL) etc First invariant has validity but second is questionable in real plasmas (Kulsrud…). However something like this may be a reasonable approximation for some problems including those of current interest AronsFest

  27. Friedrich Diagrams Vf(q) AronsFest

  28. Firehose (and mirror) instabilities AronsFest

  29. Conjectures • Relativistic CR ahead of nonrelativistic shock wave behave like a highly anisotropic fluid with an equation of state and this dictates the growth of magnetic field • Firehose dominates, resonant, Bell, Weibel… • Cosmic ray acceleration kinetics can be solved self-consistently in this background AronsFest

  30. Particle drifts and current Normal approach is to analyze particle orbits and deduce currents Can also start from static equilibrium and understand what is happening Curvature perpendicular magnetization gradient ExB Parallel current contains a part that is magnetization drift Also a part that is resistive – collisional/radiative AronsFest

  31. Conjectures • Unipolar inductor potential differences maintained into jets and nebulae • Pinches (relatively) stabilized by flow, expansion… • Highest energy particles with largest gyro radii carry current and dissipate resistively through radiation • Steady and explosive instability generic leading to in situ acceleration and emission AronsFest

  32. Summary • Major challenges to particle acceleration from Crab, blazar flares UHECR… • Hybrid – fluid/kinetic problems • Currents may be carried by highest energy particles and dissipation can be primarily radiative • May be possible to gain insight at fluid level using anisotropic RMHD • Drift currents etc can emerge from MHD rather than vice versa • Particle trajectories must still be solved in this background AronsFest

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