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PARTICLE ACCELERATION IN SUPERNOVA REMNANTS: IMPLICATIONS FOR THE ORIGIN OF GALACTIC COSMIC RAYS

PARTICLE ACCELERATION IN SUPERNOVA REMNANTS: IMPLICATIONS FOR THE ORIGIN OF GALACTIC COSMIC RAYS. Pasquale Blasi INAF/Arcetri Astrophysical Observatory. Geneva, 28/03/2012. OUTLINE. GENERAL COSMIC RAY FACTS BASICS OF PARTICLE ACCELERATION IN THE NON LINEAR REGIME

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PARTICLE ACCELERATION IN SUPERNOVA REMNANTS: IMPLICATIONS FOR THE ORIGIN OF GALACTIC COSMIC RAYS

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  1. PARTICLE ACCELERATION IN SUPERNOVA REMNANTS: IMPLICATIONS FOR THE ORIGIN OF GALACTIC COSMIC RAYS Pasquale Blasi INAF/Arcetri Astrophysical Observatory Geneva, 28/03/2012

  2. OUTLINE • GENERAL COSMIC RAY FACTS • BASICS OF PARTICLE ACCELERATION IN THE NON LINEAR REGIME • MAGNETIC FIELD AMPLIFICATION • WHAT ARE GAMMA RAY OBSERVATIONS TELLING US ? • PARTICLE ACCELERATION IN PARTIALLY IONIZED MEDIA

  3. THE BASIC PROBLEM OF COSMIC RAY PHYSICS CONSISTS IN FIGURING OUT THE PHYSICS OF ACCELERATION AND PROPAGATION GIVEN BASICALLY THREE OBSERVABLES: • SPECTRUM OF CHEMICALS (protons, He, CNO, MgAlSi, Fe) • SECONDARY/PRIMARY RATIOS • ANISOTROPY • SOURCES  MULTIFREQUENCY OBSERVATION vs MODELS • THE PROPAGATION OF COSMIC RAYS BOTH INSIDE THE SOURCES AND IN THE GALAXY IS DIFFUSIVE IN NATURE, AND IS USUALLY DESCRIBED BY USING A DIFFUSION COEFFICIENT D(E) (ALTHOUGH A DIFFUSION TENSOR SHOULD BE USED)

  4. CR move diffusively in the Galaxy ALL THESE MEASUREMENTS TELL US THAT ON AVERAGE CR STAY IN THE GALAXY FOR A FEW TENS MILLIONYEARS BEFORE ESCAPING THE GALAXY

  5. DIFFUSIVE MOTION H Rd 2h disc Halo Particle escape THE DIFFUSIVE MOTION LEADS TO ESCAPE TIMES ~H2/D(E) >> H/c D(E)=(1/3) v l(E) is the diffusion coefficient and l(E) is the scattering Length as a function of energy E

  6. Secondary/Primary ratios Primary/Primary CREAM 2008

  7. Simple scaling relations IN ORDER FOR INJECTION AND ESCAPE TO LEAD TO A STATIONARY SITUATION ONE HAS TO REQUIRE: DURING PROPAGATION CR PRODUCE SECONDARY NUCLEI AT A RATE AND AGAIN IN A STATIONARY REGIME:

  8. PAMELA CREAM

  9. The B/C ratio as a diffusion indicator IN PRINCIPLE B/C ~ 1/D(E) IN THE HIGH RIGIDITY REGIME BUT UNCERTAINTIES ARE STILL LARGE NOT EASY TO DISCRIMINATE AMONG DIFFERENT DIFFUSION COEFFICIENTS Adapted from Obermeier et al. 2011

  10. BASICS of the SNR PARADIGM Zwicky (mid 30s) and Ginzburg & Sirovatsky (mid 60s) realized that On energetic grounds SNR are the only viable source of CR in the Galaxy TOTAL CR LUMINOSITY OF THE GALAXY ~ 3x1040 erg/s IN PRINCIPLE AN EFFICIENCY OF ORDER 10% PER SN IS SUFFICIENT TO ACCOMMODATE THE COSMIC RAY ENERGETICS THE BIG QUESTION IS HOW DOES NATURE PERFORM THE ENERGY CONVERSION? ACCELERATION MECHANISM

  11. SUPERNOVA BLAST WAVE FREE EXPANSION VELOCITY: THE EXPANSION SPEED DROPS DOWN DURING THE SEDOV-TAYLOR PHASE, BUT THE MACH NUMBER IS ~100 A STRONG SHOCK WAVE DEVELOPS

  12. THEORY OF CR ACCELERATION IN SNRs Diffusive Shock Acceleration PB 2002, 2004, Amato & PB 2005, 2006, Caprioli +, 2007-2011, Morlino + 2007-2012

  13. The first order FERMI ACCELERATIONTest particle theory Downstream Upstream DIFFUSION OF CHARGED PARTICLES BACK AND FORTH THROUGH THE SHOCK LEADS TO PARTICLES ARE ACCELERATED TO A POWER LAW SPECTRUM THE SLOPE OF THE SPECTRUM ONLY DEPENDS ON THE COMPRESSION NOT ON THE DIFFUSION COEFFICIENT FOR STRONG SHOCKS: E-2 U2 U1 SHOCK FRONT

  14. NON LINEAR THEORY • A theory of particle acceleration that allows one • to describe: • Dynamical reaction of accelerated particles • CR-induced B-field and their reaction • Recipe for injection (self-regulation) • 4. Escape of particles (Cosmic Rays)

  15. DIFFUSIVE ACCELERATION AT COLLISIONLESS NEWTONIAN SHOCKSnon linear theory: BASIC PHYSICAL ASPECTS COMPRESSION FACTOR BECOMES FUNCTION OF ENERGY SPECTRA ARE NOT PERFECT POWER LAWS (CONCAVE) GAS BEHIND THE SHOCK IS COOLER FOR EFFICIENT SHOCK ACCELERATION SYSTEM SELF REGULATED EFFICIENT GROWTH OF B-FIELD IF ACCELERATION EFFICIENT VELOCITY PROFILE 0 1 2

  16. Basics of CR streaming instability SHOCK FRONT THE UPSTREAM PLASMA REACTS TO THE UPCOMING CR CURRENT BY CREATING A RETURN CURRENT TO COMPENSATE THE POSITIVE CR CHARGE THE SMALL INDUCED PERTURBATIONS ARE UNSTABLE (ACHTERBERG 1983, ZWEIBEL 1978, BELL 1978, BELL 2004, AMATO & PB 2009) + + + + + + + + + + + ++ ++++++++ ++++++++ ++++++++ + + + ++ ++ ++ JCR=nCRVs q B0 CR MOVE WITH THE SHOCK SPEED (>> VA). THIS UNSTABLE SITUATION LEADS THE PLASMA TO REACT IN ORDER TO SLOW DOWN CR TO <VA BY SCATTERING PARTICLES IN THE PERP DIRECTION (B-FIELD GROWTH)

  17. Particle Diffusion  Wave Growth In the ISM this is ~10-3 yr-1 but close to a shock front the growth can be much larger!!! dB IS AMPLIFIED BY PARTICLES

  18. MAGNETIC FIELD AMPLIFICATION SMALL PERTURBATIONS IN THE LOCAL B-FIELD CAN BE AMPLIFIED BY THE SUPER-ALFVENIC STREAMING OF THE ACCELERATED PARTICLES 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!)

  19. X-ray rims and B-field amplification TYPICAL THICKNESS OF FILAMENTS: ~ 10-2 pc The synchrotron limited thickness is: In some cases the strong fields are confirmed by time variability of X-rays Uchiyama & Aharonian, 2007

  20. SPECTRA THE SPECTRA OF ACCELERATED PARTICLES ARE IN GENERAL CONCAVE AND FLATTER THAN E-2 AT HIGH ENERGY THE MAXIMUM ENERGY WITH B-FIELD AMPLIFICATION REACHS UP TO ~1015 eV FOR PROTONS (Z TIMES HIGHER FOR NUCLEI) THESE SPECTRA SHOULD REFLECT IN THE GAMMA RAY SPECTRA (IF DUE TO PP SCATTERING) AND OF NEUTRINOS BUT THE OBSERVED SPECTRA OF GAMMAS ARE TYPICALLY ~ E-2.3 CLEARLY INCOMPATIBLE WITH LEPTONIC MODELS! BUT ALSO NOT COMPATIBLE WITH THE SIMPLEST PREDICTION OF NLDSA: E-2

  21. THE EFFECT OF THE VELOCITY OF WAVES One should remember that the compression factor that counts in shock acceleration is not that of fluid velocity, but that of the scattering centers velocity When the magnetic field is amplified the Alfven speed is not well defined and one may argue that it should be calculated in the amplified field (it depends on helicity!): THIS EFFECT LEADS TO STEEPER SPECTRA WHEN ACCELERATION IS EFFICIENT (BUT VERY MODEL DEPENDENT)

  22. Trouble with slopes ? VERY SURPRISING TO SEE THAT THE REQUIRED ACCELERATION EFFIC. ARE HIGH BUT THE SPECTRA ARE STEEP Caprioli 2011

  23. Caprioli 2011

  24. The case of RX J1713 Morlino et al. 2009 Morlino, Amato & PB 2009

  25. The case of Tycho STEEP SPECTRUM BASICALLY IMPOSSIBLE TO EXPLAIN WITH LEPTONS Morlino&Caprioli 2011

  26. CR spectra and SNRs Blasi & Amato 2011 Deficit compensated by extragalactic CRs

  27. Chemicals and the KNEE Blasi & Amato 2011 d=1/3 He p Fe ONLY FOR d=1/3 SPECTRUM OF He HARDER THAN SPECTRUM OF PROTONS AS A RESULT OF SPALLATION

  28. Large Scale CR Anisotropy Naïve expectation: proportional to Ed d=1/3 d=0.6 Blasi & Amato 2011

  29. Effect of spiral arms PB and Amato 2011 Broad Arms Tight Arms

  30. Dependence of Halo Size PB and Amato 2011

  31. EFFECT OF EXTRAGALACTIC CR WITHOUT EXTRAGALACTICCOMPONENT WITH EXTRAGALACTIC COMPONENT

  32. SOME NEW DIRECTIONS COLLISIONLESS SNR SHOCKS IN PARTIALLY IONIZED MEDIA

  33. SUBTLE ASPECTS OF ACCELERATION AT A COLLISIONLESS SHOCK NEUTRALS AND IONS SHOCK VELOCITY PB+, 2012 CHARGE EXCHANGE  BROAD BALMER LINE (NEUTRALS THAT MADE CHARGE EXCHANGE) REFLECTING THE TEMPERATURE OF IONS… BUT THE LATTER AFFECTED BY EFFICIENT CR ACCELERATION + + Hot ion Cold ion Cold neutral hot neutral

  34. BROAD BALMER LINES NARROWER THAN FOR UNMODIFIED SHOCKS Helder et al. 2009 INFERRED EFFICIENCY of CR ACCELERATION 50-60% !!! (BUT model dependent)

  35. narrow BALMER LINES broader THAN FOR UNMODIFIED SHOCKS Sollerman et al. 2003 NEUTRALS VELOCITY PROFILE IONS CHARGE EXCHANGE OCCURS NOW IN THE CR INDUCED PRECURSOR NARROW BALMER LINE BROADER THAN FOR AN UNMODIFIED SHOCK

  36. The neutral return flux NEUTRALS AND IONS PB + 2012 SHOCK VELOCITY A NEUTRAL ATOM CAN CHARGE EXCHANGE WITH AN ION WITH V<0, THEREBY GIVING RISE TO A NEUTRAL WHICH IS NOW FREE TO RETURN UPSTREAM THIS NEUTRAL RETURN FLUX LEADS TO ENERGY AND MOMENTUM DEPOSITION UPSTREAM OF THE SHOCK! Vperp=0 V<0 1 v/(Vs/4)

  37. Neutrals as collisionless particles Neutrals are describing through the Vlasov equation: Stationary + charge exch • Charge exch and • ionization

  38. Relevant cross sections n=1 n=2

  39. Ions as a plasma Mass conservation Momentum Conservation Energy Conservation Mass flux of neutrals Momentum flux of neutrals Energy flux of neutrals

  40. Distribution Functions in phase space PB+2012 UPSTREAM DOWNSTREAM NEUTRAL RETURN FLUX THE DISTRIBUTION FUNCTIONS OF NEUTRALS ARE NOT MAXWELLIAN IN SHAPE BUT APPROACH SUCH SHAPE AT DOWNSTREAM INFINITY

  41. SHOCK MODIFIED BY THE NEUTRAL RETURN FLUX NEUTRAL INDUCED PRECURSOR EFFECT of IONIZATION PB+2012

  42. NEUTRAL INDUCED PRECURSOR PB+2012 EVEN FOR A STRONG SHOCK (M>>1) THE EFFECTIVE MACH NUMBER OF THE PLASMA IS DRAMATICALLY REDUCED DUE TO THE ACTION OF THE NEUTRAL RETURN FLUX

  43. ACCELERATION OF TEST PARTICLES PB+ 2012 1 GeV 10 GeV 100 GeV 1 TeV

  44. CONCLUSIONS THE SN PARADIGM EXPLAINS THE ROUGH OBSERVATIONAL PICTURE OF THE ORIGIN OF COSMIC RAYS BUT MISSING PIECES: STEEP SPECTRA, ANISOTROPY, SPECTRAL FEATURES IN THE NUCLEAR SPECTRA MAGNETIC FIELD AMPLIFICATION INDUCED BY CR IS NOW ONE OF THE HOT TOPICS IN EXPLAINING X-RAY MORPHOLOGY AND REACH THE KNEE THE KNEE CAN BE EXPLAINED REASONABLY WELL IN TERMS OF CHANGE OF CHEMICAL COMPOSITION, BUT TRANSITION AT THE DIP (NOT ANKLE) PRESENCE OF NEUTRALS EXTREMELY IMPORTANT DIAGNOSTIC TOOL FOR CR ACCELERATION AS WELL AS POSSIBLE CAUSE FOR SPECTRAL STEEPENING

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