1. Particle Acceleration GeV-TeV Astrophysics in the GLAST era SLAC Sep 30 2004 Roger Blandford KIPAC

2. Aug 12 042 Direct Evidence for SNR Acceleration  Electron acceleration to TeV energies  TeV gamma rays sometimes observed Model -dependent evidence for ion acceleration Efficient acceleration but not to knee  EGRET, GLAST (GeV)  Hess, VERITAS (TeV)  pion decay Cas A

3. Aug 12 043 Proton spectrum GeV TeV PeV EeV ZeV ~MWB Energy Density E ~ 50 J c -1fm s -1 c -1km H 0 ~ GRB Energy Density

4. Aug 12 044 “Relativistic Jets”

5. Aug 12 045 GeV-TeV electron emission  T gyro E<  f  ~ 100 MeV => C -1 emission  If electrons radiate efficiently on time of flight and  <1 =>Modest electron energies in KN regime =>n(E -1 )  T R<10, P 2, relativistic sources quite likely Not a great challenge! Must beat radiative loss Protons?

6. Aug 12 046 Particle Accleleration  Stochastic  Shocks  Reconnection  Electrostatic  Currents

7. Aug 12 047 Traditional Fermi Acceleration  Magnetic field lazy-electric field does the work! Frame change creates electric field and changes energy  CR bounce off magnetic disturbances moving with speed  c   E/E|~  Second order process  dE/dt ~  2 (c/ )E - E/t esc t acc >r L /c  2  =>Power law distribution function IF, t esc do not depend upon energy THEY DO!

8. Aug 12 048 Shock Acceleration  Non-relativistic shock front Protons scattered by magnetic inhomogeneities on either side of a velocity discontinuity Describe using distribution function f(p,x) uu / r B u B L

9. Aug 12 049 Transmitted Distribution Function where =>N(E)~E -2 for strong shock with r=4 Consistent with Galactic cosmic ray spectrum allowing for energy-dependent propagation

10. Aug 12 0410 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  Cosmic rays are not test particles Include in Rankine-Hugoniot conditions u=u(x)  Acceleration controlled by injection Cosmic rays are part of the shock  What mediates the shock, Parallel vs Perpendicular Firehose? Weibel when low field? Ion skin depth

11. Aug 12 0411 Relativistic Shock Waves  Not clear that they exist as thin discontinuities May not be time to establish subshock, magnetic scattering Weibel instability => large scale field???  Returning particles have energy x  2 if elastically scattered  Spectrum N(E)~E -2.3     eg Keshet &Waxman

12. Aug 12 0412 Flares and Reconnection May be intermittent not steady Strong, inductive EMF? Hall effects important Most energy -> heat Create high energy tail Theories are highly controversial! Relativistic reconnection barely studied at all

13. Aug 12 0413 Unipolar Induction B M  V~    P ~ V 2 / Z 0  Crab Pulsar B ~ 100 MT, ~ 30 Hz, R ~ 10 km V ~ 30 PV; I ~ 3 x 10 14 A; P ~ 10 31 W  Massive Black Hole in AGN B ~ 1T, ~ 10  Hz, R ~1 Pm V ~300 EV, I ~ 3EA, P ~ 10 39 W  GRB B ~ 1 TT, ~ 1  Hz, R~10 km V ~ 30 ZV, I ~ 300 EA, P ~ 10 43 W

14. Aug 12 0414 Pictor A Active collimation?

15. Aug 12 0415 (Implicit) conventional view is that electromagnetic energy dissipated close to source and outflow is fluid dynamical. Perhaps the transport is primarily electromagnetic. Nonthermal emission is ohmic dissipation of current flow? 10 17 or 10 18 A?

16. Aug 12 0416 Is particle acceleration ohmic dissipation of electrical current?  Jets delineate the current flow?  Organized dominant electromagnetic field  Shocks weak and ineffectual  Tap electromagnetic reservoir Poynting flux along jet and towards jet  Jet core has equipartition automatically  Unlikely to be direct electrostatic acceleration above GeV-TeV

17. Aug 12 0417 Let there be Light  Faraday  Maxwell  Initial Condition  Definition =>Maxwell Tensor, Poynting Flux

18. Aug 12 0418 Force-Free Condition  Ignore inertia of matter  =U M /U P >>  2, 1  Electromagnetic stress acts on electromagnetic energy density  Fast and Alfven wave modes  B 2 -E 2 > 0, normally

19. Aug 12 0419 Surfing  Relativistic wind eg from pulsar  V=ExB/B 2 E->B, V->c  More generally force-free electrodynamics, limit of MHD when inertia ignorable evolves to give regions where E/B increases to, and sometimes through, unity  cf wake-field acceleration

20. Aug 12 0420 Stochastic acceleration  Line and sheet currents break up due to instabilities like filamentation?  Create electromagnetic wave spectrum  Nonlinear wave-wave interactions give electrons stochastic kicks Inner scale where waves are damped by particles Are there local power laws? kU k k 2N2N 

21. Aug 12 0421 Summary  GeV-TeV emission - inverse Compton scattering by relativistic electrons Protons?  Shock acceleration likely to be dominant in gas- dominated regions - eg SNR  Ultrarelativistic outflows may be electromagnetically dominated and require different acceleration mechanisms Stochastic acceleration, Surfing, shear drift acceleration

22. Aug 12 0422 Abundances ● (Li, Be, B)/(C, N, O) ● ~ 10 (E/1GeV) -0.6 g cm -2 ● S(E) ~ E -2.2 ● L ~ U CR M gas c    ~ 3 x 10 40 erg s -1 ~ 0.03 L SNR ~ 0.001L gal

23. Aug 12 0423 Sources  t ~ 15 Myr (eg 10 Be etc)   t > 10 5 yr (eg 59 Ni/Co) ● Heavy element injection Ionization Potential Volatility Injected as grains? ACE

24. Aug 12 0424 UHE Cosmic Rays  Range ~30 Mpc (GZK) luminosity density ~ GCR  Probably not  Fe?  Probably not ``top down'’  Excess  -ray background  Sources Isotropy, clustering? - permanent not transient? Limits on B  Need better statistics  => Auger(S)...

25. Aug 12 0425 -35 -36 -37 -38 9 12 15 18 21 eV Galactic Extragalactic Luminosity density (cgs)

26. Aug 12 0426 Cosmic Ray Propagation  Larmor radius: r L ~E 21 /B pc  Larmor period:t L ~20 E 21 /B yr  Resonant scattering by magnetic disturbances (wave modes) with k~r L -1 Random walk in pitch angle Mean free path: ~(B/  B res ) 2 r L > r L Non-resonant scattering: ~kr L 2 > r L  Diffusion coefficient: D~ c/3 Bohm Diffusion: D~ 0.1 r L c

27. Aug 12 0427 Local Cosmic Ray Sources  Magnetosphere, Jupiter, Sun  Interplanetary traveling and standing shocks  Solar Wind Termination Shock  Galaxy (SNR, hot stars?)

28. Aug 12 0428 UHE Cosmic Rays  L>r L /  ;  =u/c BL>E 21 G pc=>I>3 x 10 18 E 21 A! Lateral diffusion  P>P EM ~B 2 L 2  c/4  3 x 10 39 E 21 2  -1 W Powerful extragalactic radio sources,  ~1  Relativistic motion eg gamma ray bursts P EM ~  2 (E/e  ) 2 /Z 0 ~ (E/e) 2 /Z 0  Radiative losses; remote acceleration site P mw < 10 36 (L/1pc)W  Adiabatic losses E~  /L  Observational association with dormant AGN?

29. Aug 12 0429 “Relativistic Jets”

30. Aug 12 0430 Pictor A Wilson et al

31. Aug 12 0431 UHE Cosmic Rays  L>r L /  ;  =u/c BL>E 21 G pc=>I>3 x 10 18 E 21 A! Lateral diffusion  P>P EM ~B 2 L 2  c/4  3 x 10 39 E 21 2  -1 W Powerful extragalactic radio sources,  ~1  Relativistic motion eg gamma ray bursts P EM ~  2 (E/e  ) 2 /Z 0 ~ (E/e) 2 /Z 0  Radiative losses; remote acceleration site P mw < 10 36 (L/1pc)W  Adiabatic losses E~  /L  Observational association with dormant AGN?

32. Aug 12 0432 Second order acceleration  N ~  -2  L ~ N 1/2 ~   Similar requirements to shock model

33. Aug 12 0433 Electrostatic Acceleration  Establish static potential difference  Gaps  Double Layers  Aurorae  Pulsars  P EM > (E/e) 2 /Z 0

34. Aug 12 0434 Pulsar Wind Nebulae

35. Aug 12 0435 Problems  Unlikely to make full potential difference available for electrostatic acceleration 1TV creates pair discharge in pulsars 1GV is all that is needed in AGN The larger the EMF the harder it is to dissipate the current

36. Aug 12 0436 Solar Flares Magnetic instability and reconnection SOHO YOHKOH Trace

37. Aug 12 0437 Magnetars  Neutron stars with 10 14-15 G field  Repeating gamma ray sources  Magnetically powered  Radiative and adiabatic losses severe?  Galactic source as extragalactic, magnetar luminosity density too low  Fe?

38. Aug 12 0438 Magnetars Slowly spinning, high field neutron star May spin rapidly at birth.

39. Aug 12 0439 Shear Layer  E z =sinh kz; B y =cosh kz; V x =-c tanh kz   E + j x B = 0  Analytic solutions  eg u x =-(1-k 2 ) 1/2 t; u z =(1-k 2 ) 1/2 /k  Electric, gradient, polarization drifts  Energy bounded by electrostatic potential difference  P em >(E/e) 2 /Z 0 E B x V

40. Aug 12 0440 Relativistic Outflows  Enormous particle energies possible in principle through “magnetic slingshot”  Can particles slide smoothly along field lines?  Radiative losses

41. Aug 12 0441 Summary  Basic astrophysical accelerators -shocks, holes, magnetars, winds- not ruled out  All pose serious problems  New idea or top down solution (also hard)  Auger should rule out many possibilities

42. Aug 12 0442 General References  Blandford (2000) Phys. Scripta T85 191- 193  Anchordoqui, Paul, Reucroft & Swain (2003) Int.J.Mod.Phys. A18 2229-2366  Olinto (2004) astro-ph 0404114 (XXVIII ICRC)  Ong (2003) SSI03 vugrafs

43. Aug 12 0443 Acceleration Mechanisms  Statistical Acceleration Shock Waves  Electrostatic Acceleration Unipolar Induction  Flares Magnetars  Surfing Relativistic Outflows