COSMIC RAY ACCELERATION and TRANSPORT LECTURE 3: Research Topics

1. COSMIC RAY ACCELERATION andTRANSPORTLECTURE 3: Research Topics Pasquale Blasi INAF/Arcetri Astrophysical Observatory 4th School on Cosmic Rays and Astrophysics UFABC - Santo André - São Paulo – Brazil

2. WHAT NEXT? • We have found the elegant results of the theory of DIFFUSIVE SHOCK • ACCELERATION in the TEST PARTICLE approximation and also found • some of its limitations: • TOO LARGE EFFICIENCIES TO EXPECT TEST PARTICLES • THE EXPECTED DIFFUSION COEFFICIENT LEADS TO TOO LOW EMAX • IF PARTICLES DIFFUSE THEY ALSO LEAD TO WAVE GROWTH ALL THESE PHENOMENA SUGGEST THAT WE NEED TO MOVE BEYONDTHE TEST PARTICLE APPROXIMATION NON LINEAR THEORY OF DIFFUSIVE SHOCK ACCELERATION

3. Dynamical Reaction of Accelerated Particles PRECURSOR Velocity Profile v SUBSHOCK Undisturbed Medium Shock Front subshock Precursor Conservation of Momentum Transport equation for cosmic rays

4. WHAT SHOULD BE EXPECT? UPSTREAM • PARTICLES WITH HIGH P FEEL • LARGER COMPRESSION FACTOR • THEN LOW P PARTICLES • 2. THE TOTAL COMPRESSION • BECOMES LARGER THAN 4 • 3. THE SPECTRUM SHOULD BE NO • LONGER A POWER LAW! • 4. AT HIGH P THE SLOPE SHOULD • BE FLATTER THAN 2 !!! • 5. THE GAS BEHIND THE SHOCK • SHOULD BE COOLER THAN FOR • AN ORDINARY SHOCK High p Velocity SUBSHOCK Rtot Rsub PRECURSOR

5. INJECTION THIS IS THE LEAST UNDERSTOOD ASPECTS OF ALL ! Ideal Collisionless Shock (More) Real Collisionless Shock rL WHICH PARTICLES AND HOW MANY PARTICLES ENTER THE ACCELERATION CYCLE?

6. INJECTION…cont’d f(p) Maxwellian for the Downstream gas T2 T1 Relation between Rsub, ξand η p Pinj =  pth,2 OUTPUT OF THE CALCULATIONS

7. SHOCK HEATING and SPECTRA REDUCED HEATING SHOCK MODIFICATION PB, Gabici & Vannoni 2005

8. Particle Diffusion  Wave Growth Remember that we showed that a particle diffuses along a direction z where there is an ordered magnetic field B0 because of a small perturbation dB perpendicular to B0. In this process the particles lose momentum in the z direction and this p Is transferred to the dB waves. This equals the momentum gained by the waves: And imposing a perfect balance: In the ISM this is ~10-3 yr-1 but close to a shock front the grow can be even larger!!! dB IS AMPLIFIED BY PARTICLES

9. MAGNETIC FIELD AMPLIFICATION Bell 2004, Amato & PB 2009 SMALL PERTURBATIONS IN THE LOCAL B-FIELD CAN BE AMPLIFIED BY THE SUPER-ALFVENIC STREAMING OF THE ACCELERATED PARTICLES SHOCK Particles are accelerated because there is High magnetic field in the acceleration region High magnetic field is present because particles Are accelerated efficiently Without this non-linear process, no acceleration of cr to High energies (and especially not to the knee!)

10. Successes of the SNR paradigm1. Observation of X-ray rims TYPICAL THICKNESS OF FILAMENTS: ~ 10-2 pc The synchrotron limited thickness is:

11. Chandra SN 1006 Chandra Cassiopeia A

13. Successes of the SNR paradigm2. Max energy and the knee 107 106 105 104 Magnetic field amplification leads to higher values of the Maximum energy MAXIMUM MOMENTUM PROTON KNEE pmax/mc Bohm Diff without B-amplification 50 100 150 200 M0 PB, Amato & Caprioli, 2007

14. Observed proton spectrum Data from Bertaina et al. 2008

15. Successes of the SNR paradigm3. evidence for a CR precursor ? PRECURSOR REGION RIM Morlino, Amato, PB & Caprioli 2010

16. Successes of the SNR paradigm4. Balmer dominated shocks DOWNSTREAM ION Temperature LOWER because of CR acceleration NEUTRAL Temperature HIGHER because of charge exchange + + BROAD BALMER LINE IS NARROWER NARROW BALMER LINE IS WIDER

17. Observations of Balmer dominated shocks Helder et al. 2009 INFERRED EFFICIENCY of CR ACCELERATION 50-60% !!!

18. Observation of Balmer dominated shocksbroader narrow Balmer line Sollerman et al. 2003 Broadening of the narrow line hints to a mechanism for heating of the neutrals upstream on scales shorter than ionization scales TURBULENT HEATING CHARGE EXCHANGE UPSTREAM

19. Observation of Balmer dominated shocks:Possible evidence for a CR precursor in the narrow Balmer line A broadened narrow Ha line from upstream shows that the neutrals and ions have some level of charge exchange  different bulk velocities and/or T’s between the two components  CR precursor

21. HADRONIC RXJ1713 RXJ1713 LEPTONIC Morlino, Amato & PB 2009

22. RXJ1713 with fermi data • e/p Equilibration downstream? (Morlino et al. 2009) • Very low value of Kep at given time • Lines from non-equilibrium ionization ? (Ellison et al. 2010) • What are those Fermi data points telling us?

23. A Puzzling situation Courtesy of S. Funk • Most SNR detected by Fermi have steep spectra (some exceptions, such as • RXJ1713) • The predicted spectra would naively require steep diffusion D(E)~E0.7 in conflict • with anisotropy measurements

24. A small print in the theory of DSA: a point as important as poorly known Velocity of scattering centers in the shock frame NOT velocity of the plasma In general the velocity of scattering centers is small and there is no problem BUT AMPLIFIED MAGNETIC FIELD  high velocity ??? VERY MACROSCOPIC CONSEQUENCES ON SPECTRA!

25. ROLE OF NUCLEI Caprioli, PB, Amato 2010 The dynamical reaction of nuclei on the shock structure turns out to be VERY IMPORTANT

26. ROLE OF NUCLEI: The knee Caprioli, PB, Amato 2010

27. WHERE DO GALACTIC CR end? • The SNR paradigm hints to a galactic CR spectrum • ending at ~a few 1017 eV • Observations of chemical composition also suggest • the same trend ?

28. PROPAGATION OF PROTONS from extragalactic sources DIP GZK 100 Mpc

29. HOW DOES THE SPECTRUM LOOK LIKE? THE DIP Dip structure Berezinsky et al. 2005 Aloisio et al. 2007

30. HISTORICAL INTERPRETATION OF THE TRANSITION: THE ANKLE

31. ALTERNATIVE INTERPRETATION OF THE TRANSITION: MIXED COMPOSITION Allard et al. 2005-2008

32. UNDERSTANDING THE DIFFERENCE: DIP VS MIXED From Kampert 2008

33. UNDERSTANDING THE DIFFERENCE: DIP VS ANKLE DIP ANKLE Aloisio, Berezinsky, PB & Ostapchenko 2008

34. XMAX and RMS OF XMAX Auger HiRes