Galactic Cosmic Rays. Alexandre Marcowith Laboratoire Univers & Particules de Montpellier

Transcription

1 Galactic Cosmic Rays Alexandre Marcowith Laboratoire Univers & Particules de Montpellier

2 Outlines Introduction: Cosmic Rays spectra in 3D Historical Supernova remnants Sources of high energy photons and cosmic rays Fermi acceleration Collisionless shock physics Other energetic particle sources Massive star clusters Supernova remnant/molecular clouds interaction Low energy cosmic rays Conclusions Perspectives A.Marcowith Seminar IPAG 2

3 100 years of cosmic ray research( ) Viktor HESS ( ) Discovery of cosmic rays: altitude ionization effect Nobel price 1936 Pierre Auger ( ) Discovery of electromagnetic showers (1938): start of astroparticle physics A.Marcowith Seminar IPAG 3

4 Introduction Cosmic Rays in 3D Energy spectrum Angular spectrum: anisotropy Mass spectrum: composition A.Marcowith Seminar IPAG 4

5 A.Marcowith Seminar IPAG 5

6 Galactic Cosmic Rays GCR A.Marcowith Seminar IPAG 6

7 Sources of galactic cosmic rays Supernova remnants: Hadrons + electronspositrons Massive star clusters: Hadrons+ electronspositrons Pulsars and pulsar wind nebulae: Electronspositrons (+ Hadrons) X-ray binaries: Electron-positron + Hadrons Drury+01 (SSR,vol.99) A.Marcowith Seminar IPAG 7

8 Les restes de supernova Base du modèle standard : Argument énergétique: Densité d énergie du RC e RC ~ 1.5 ev/cm 3 Temps de résidence t res ~10 M ans P cr = V gal e RC / t r ~ erg/s soit 10% P SN Argument de composition: Requiert d accélérer la matière du MIS. Argument spectral: Spectre source proche de celui d accélération diffusion par onde de choc (c.f. + loin) A.Marcowith Seminar IPAG 8

9 Chandra Historical SNRs CassiopeiaA SN ~ 1681 Type II (type IIb) Distance 3.4 kpc ( ) Radius 2.5 pc Shock speed ~5000 km/s + Kepler (type Ia) kpc + RCW86 (type II? ) 185(?) 2.8 kpc Chandra Chandra + HST Tycho SN 1572 Type Ia Distance 3.8 kpc ( ) Radius 3.4 pc Shock speed ~ 4600 km/s A.Marcowith Seminar IPAG SN 1006 Type Ia Distance 2.2 kpc (+/-0.1) Radius 9 pc Shock speed ~ 3000 km/s 9

10 Young SN remnant structure Interstellar medium 2 shocks Cassiopae A by Chandra < Ejecta > Court. A Decourchelle Green: 4-6 kev Analysis restricted to young SNr with age a few 10 3 years Free expansion early Sedov phase. A.Marcowith Seminar IPAG 10

11 Observations: radio Non thermal radiation: radio (Green catalog; Green 08) : synchrotron (polarized emission) F(ν) ν α ; <α> = 0.55 ( ) s=( ) Kepler In agreement with diffusive shock acceleration (DSA) s=2 A.Marcowith Seminar IPAG 11

12 Young SNR: X-rays CasA Tycho Filament size %R sh RCW86 SN1006 Kepler Blue: synchrotron non thermal X kev (Vink 08) A.Marcowith Seminar IPAG 12

13 X - ray Filaments: consequencies Downstream: within a synchrotron loss timescale t syn (E ph, B) - Advection with a speed V av Advection length : ΔR dif Diffusion with a coefficient D Diffusion length : ΔR adv Shock restframe view To be compared with the filament size ΔR x Constraint over B A.Marcowith Seminar IPAG 13

14 X-ray Filaments: Magnetic field Parizot, AM, Ballet, Gallant 06 Downstream MF => 2 orders of magnitude above standard Magnetic field amplification is required ISM values: Amplification A.Marcowith Seminar IPAG 14

15 X-ray stripes Eriksen+11 Turbulence pattern? Bykov+11 Tycho A.Marcowith Seminar IPAG 15

16 Supernova remnants: gammarays Detected at one (GeV/TeV) or both GeV-TeV wavebands Historical SNRs: Tycho, SN1006, Cassiopeia A, RCW86 other SNRs: RX J , Vela Jr, HESS SNR in interaction with molecular clouds: IC443, W28, W51c, W44, CTB37a, W49b, W30 Evolved SNRs: Cygnus loop + star forming regions and massive star clusters: W1, W2, Cygnus X (données Milagro), LMC GeV: Fermi, Agile TeV: HESS, MAGIC, Veritas, CangarooIII Part-II Part-I A.Marcowith Seminar IPAG 16

17 Emission mechanisms Non-thermal particle distribution : N(E)=N 0 E s Leptonic : Inverse Compton Source of low energy photons: Cosmic microwave background but sometimes IR, UV Luminosity n e E (s 1)/2 (Thompson regime). IC/synchrotron => B in a onezone model + Bremsstrahlung (NT electrons) Luminosity n e n ISM E s Hadronic : Neutral pion production Cross section increases only in log(e): gamma-ray and hadron indices similar above 1 GeV. Luminosity n ISM n CR dv A.Marcowith Seminar IPAG 17

18 Cassiopeia A Tycho SN XMM newton GeV x Abdo+10 Uchiyama+11 +XMM newton TeV +Chandra & CO data Albert+07 Acciari+11 A.Marcowith Seminar IPAG Acero+10 18

19 Tycho Hadronic model s GeV =2.3 may be up to VHE E CR consistent with 10% of E SN for n ext =0.3 cm -3 Uchiyama+11 Fermi data more consistent with hadronic model. CasA Hadronic model s GeV =2.1 + cut off at 10 TeV (blue) s GeV =2.3 no cut off (red) E CR =3.2 x erg = 1/30 E SN for n ext = 10 cm -3 Abdo+10 Density possibly smaller. Leptonic (Inverse Compton) model also possible. A.Marcowith Seminar IPAG 19

20 Aharonian+07 Other SNRs Aharonian+07 +ASCA +ROSAT Vela junior SNR RXJ Type Ic? Iyudin+10 Type? Age ~ yrs? Age ~ 1600 yrs (SN 393?) Distance ~ pc Distance ~ 1 kpc Radius 13 pc (D=750 pc) Radius 20 pc Both powerful gamma-ray A.Marcowith Seminar IPAG objects and show X-ray filaments 20

21 RXJ1713 Hadronic/Mixed Spectra Abdo+11 Leptonic RX J1713: data more consistent with leptonic models: index s GeV =2 and a mean MF = 10mG <=> X-ray filaments? Inclusion of hadrons in a mixed model: E CR < 30% E SN but a hard spectrum is required. Cut off beyond 10 TeV: if hadrons are present: several hundred TeV particles. Vela Jr: both models are possible but hadronic model requires a lot of energy into hadrons (50% ESN) and leptonic model difficult to reconcile with X-ray filaments A.Marcowith Seminar IPAG 21

22 Short summary: Young SNR and cosmic rays Several issues: Most of historical SNR are weak gamma-ray sources but emit non-thermal X-rays => particle accelerators. Cosmic ray content in question E CR is < 10% (CasA) but 10% Tycho. E max-cr < knee (max: RXJ 1713, Tycho) Leptonic origin difficult to reconcile with high MF deduced from X-ray filaments MF relaxation? (Rettig & Pohl 12, A.M. & Casse 10, Pohl+05) Time dependent turbulent features? (Bykov+08) Contribution from the reverse shock (CasA)? Thought to be weakly magnetized. Injection dependence wrt the mean magnetic field direction (SN1006)? No definite observational proofs that historical young isolated SNR are the sources of GCR YET! A.Marcowith Seminar IPAG 22 What about theory?

23 l accélération de Fermi (1er ordre) Accélération diffusive par onde de choc (ADOC ou DSA) Cas linéaire Cas non-linéaire A.Marcowith Seminar IPAG 23

24 A.Marcowith Seminar IPAG 24

25 Non-linear DSA in young SNR (too?) Efficient mechanism (Drury & Voelk 81) P CR ~ [ ] ρu sh 2 continuity conditions (Rankine-Hugoniot) have to include P CR => modification of the shock profile A.Marcowith Seminar IPAG 25

26 CR retro-action A.Marcowith Seminar IPAG 26

27 MFA feed-back MFA mainly has a negative feed-back - MFA in the shock precursor => increase of the Alfvén velocity B tot = (δb 2 + B 2 ) 1/2, ū a = B tot /(4πρ) 1/2 Decrease scattering center velocity V sh -u a => smaller compression Stationary solution closer to the test particle one : s=4 or even harder (AM, Lemoine & Pelletier 06) - A part of the turbulence energy => pre-heating (but not too much) => smaller compressibility Magnetic energy density Fluid velocity Particle distribution Spectral index V a (B 0 ): no MFA Trans: U a in the kinetic CR Eq. Trans+Ampl: U a in the kinetic CR Eq.+growth rate Caprioli+09 A.Marcowith Seminar IPAG 27

28 Collisionless shock microphysics How to simultaneously explain: 1/ High energy CR production including the non-linear effects 2/ MF amplification 3/ High energy emission A.Marcowith Seminar IPAG 28

29 Multiple species and scales Still quite challenging Completeness: Need to include: plasma waves, magnetized fluid and energetic particles + radiation. Scale description: Requires to compute acceleration process from thermal to ultrarelativistic particle scales. Intrinsic linear & nonlinear process (scale back-reaction). Heating, damping Plasma fluctuations Magnetized thermal particles Generation, scattering, stochastic acceleration Compression, adiabatic losses Energetic particles Radiation, cooling Photons A.Marcowith Seminar IPAG 29

30 Streaming instability Principle Recent developments A.Marcowith Seminar IPAG 30

31 Shock moving upstream J CR Principle Non resonant instability λ < r L =E/ZeB, lefthand circularly polarized Γ(k=1/λ)= ū a (k kc) 1/2 ; k c =J cr /B 0 F(x,p) V ch MIS B tot = (δb 2 + B 2 ) 1/2, ū a = B tot /(4πρ) 1/2 Resonant instability λ > r L =E/ZeB, righthand circularly polarized Shock precursor Γ(k) = Χ 0 k// ū a, Χ 0 = P cr /U btot Skilling 75, McKenzie & Völk 82, Bell & Lucek 01, Bell 04, Pelletier, Lemoine,AM 06, AM, Pelletier, Lemoine 06, Amato & Blasi 09 Bykov+12 (review) A.Marcowith Seminar IPAG 31

32 MF amplification Non-resonant instability: Fastest especially at high shock velocity (Pelletier, Lemoine, AM 06) Expected MF amplitude at the shock front (B V sh 3/2 )! # " B turb B ISM $ & % 2 2! u = M sh $! a " c % # " P CR 2 'u sh $ & = 500 % ( ) 2 (1/50)(1/5) = 1000 But: only small scales : Issue for confinement of high-energy particles Voelk 05 A.Marcowith Seminar IPAG 32

33 Different numerical approaches Particle In Cell (PIC): all species kinetic: Small scales l ~ r thi :instabilities that mediate the shock formation injection problem. Hybrid (electron as fluid, ions as kinetic): Dominant instability for particle acceleration back reaction over the CR current Kinetic magneto hydrodynamic (MHD) (electron+ion fluid, energetic particles as kinetic): Large scales l~r CR long term evolution of the dominant Instability CR transport and escape. Microscopic Mesoscopic Macroscopic A.Marcowith Seminar IPAG 33

34 Développements Instability studies Shock formation Particle injection at supra-thermal energies Acceleration process High energy cosmic rays tansport and instabilities => versus: ISM properties (magnetization, temperature, ionization degree), shock properties (MF obliquity, shock velocity) 1. Fluctuations produciton PIC:Hybrid Riquelme & Spitkovsky 10, Gagrgaté & Spitkovsky 12 MHD/kinetic Bykov+12, Reville & Bell Turbulence properties Upstream (Pelletier+06) downstream (AM & Casse 10) 3. Particle transport Kinetic/MHD Reville+08, AM & Casse High shock speeds studies Very young SNR Renaud,AM+ in prep Gamma-ray burst Lemoine A.Marcowith Seminar IPAG & Pelletier 11 34

35 Conclusions: shock microphysics MFA likely connected to energetic particles as source of free energy: Streaming Pressure gradient => Sonic waves Debates: Master instability depending on the ISM and shock properties Saturation process and turbulence properties Simulations: Injection Fermi acceleration at work Role of high CRs controling the turbulence up- and downstream => Maximum energy Not clear answer about SNR as sources of CRs may be valuable to look after alternative sources A.Marcowith Seminar IPAG 35

36 Other sources of energetic particles/photons Massive star clusters SNR/Molecular clouds interaction A.Marcowith Seminar IPAG 36

37 Massive star Photon residual map GeV clusters Cygnus X cocoon by Fermi Extended hard gamma emission Tibaldo+11 Fermi Ackerman+11 MSX 8 micron Cygnus X cocoon spectrum: index close to 2. (calorimeter?) Hadrons seem to be mandatory => E > 3 ev/cm -3 A.Marcowith Seminar IPAG 37

38 CR acceleration: collective processes In massive star clusters (Bykov 01, Parizot, AM+04, Ferrand & AM 10 ) Strong SNR shocks Multiple weak shocks Super-sonic/alfvenic turbulence: second order Fermi acceleration => Efficient CR accelerators up to 100 PeV but theory difficult due to strong nonlinear feed-backs. A.Marcowith Seminar IPAG 38

39 Test-particle solutions CR solutions Non-linear solutions MFI+FII FI F(p) distribution Spectral index Case of a cluster with N=100 stars Ferrand & AM 10 Ferrand+08, Ferrand & AM in prep. A.Marcowith Seminar IPAG 39

40 Massive star sample θ * = t FII /t esc and ransition hard-soft at p * =1/θ * GeV A.Marcowith Seminar IPAG 40

41 SNR in interaction with molecular clouds GeV CTB 37a TeV Uchiyama+10 Green: VLA data, ellipses CO cloud (a), black/white crosses OH masers Triangle(c)/open(b) crosses: OH masers, stars: HII regions(d)/pwn(c) White(a,b)/black contours(c): CO data A.Marcowith Seminar IPAG 41 Aharonian+08a/b, Acciari+09, Fiasson+09

42 IC443 Age: 3-30 kyrs Distance ~ 1.5 kpc? Size ~ 19 pc Fermi Egret Veritas Magic Shock/dense materials interaction (OH masers). Good fit provided by a hadronic model with broken power-law. E CR ~ x10 49 erg Also W44: => Neutral pion decay nicely reproduced combining Agile and Fermi data Giuliani+11 Abdo+10, + Agile Tavani+10 A.Marcowith Seminar IPAG 42

43 Shock/cloud interaction 2D MHD simulations (perp A.Marcowith Seminar IPAG strong shock) Inoue MF Amplification due to turbulent medium (shock rippling) that is shocked B grows due to velocity shear along mean B B => few hundred microg Network secondary shocks M < 2 (M= 5 in the dense cloud limit) Behind the blast wave => propagate in an ionized medium. 43

44 SNR/MC Several explanations: Hadrons accelerated from the thermal pool (Drury+96, Bykov & Uvarov 00, Inoue+10, Malkov & Diamond 11 W44). Single shock acceleration + Break due to loss cone transition between single strong shock and multiple weak shock re-acceleration + High energy spectrum softer spectrum due to secondary shocks Hadrons from the cloud re-accelerated at the shock front (Blandford & Cowie 82, Uchiyama+10) Hadrons escaping the SNR and interacting with MCs (Gabici+07+09, Torres+08, Casanova+10) A.Marcowith Seminar IPAG 44

45 Illuminated clouds? Probe of the diffusion coefficient around CR source Gabici+09, Ohira+10: One can expect soft GeV and hard TeV spectra especially for young SNR and/or close MCs. If we know SNR-MC distance and the CR released time => probe the diffusion coefficient around the sources. W28 case: if 1801 & 1800a and b are within a diffusive length: Diffusion coefficient (HESS1801, and HESS 1800 a/b)~ 6% ISM values Gabici+10 See also Torres+08 in the case of IC443 ~ % ISM values yr 8000 yr 2000 yr 500 yr CR spectrum at a MC at different times (Gabici+09) But OH masers detected Hewitt & Yusef- Zadeh 09 A.Marcowith Seminar IPAG 45

46 Ion radicals measurements: dense gas Probe CR ionization rates in different environments using lines produced by different ion radicals Dense shocked gas: 1. W51c: Ionization in dense region probed by [DCO+/HCO+] Ceccarelli+11 ξ~10-15 s => 2 orders of magnitude above standard values 2. IC443 [H3+] Indriolo+10 ξ> s Ionization rates IC443 A.Marcowith Seminar IPAG 46

47 Some challenges Inducing LE-CR spectrum Local deconvolution from the solar wind modulation effect likely Around SNR/MC shocks. MeV protons and kev electrons: interface between thermal and non-thermal components. Enhanced LE-CRs around sources: LE CR may be released differently depending on the upstream region: shock aging effect Transport to diffuse clouds (where enhanced ionization has been observed too). NO yet detailed modeling either for source spectrum or for transport Only reference : heliospheric shock A.Marcowith Seminar IPAG 47

48 Importance of LE CRs LE CRs important for: Ionization and ISM heating through wave production. Chemistry. Spallation => MeV Astrophysics. Dynamical effects => pressure gradients largely overlooked. Influence over ISM Spatial: A source has influence on its local environment over pc. Timescales: 10 4 => 10 7 yrs Sources are usually in clusters A.Marcowith Seminar IPAG 48

49 Conclusions Young (historical) SNRs: CR spectrum HE particle acceleration + MF amplification likely connected to non-resonant streaming instability. HE particles dominate EP pressure and largely control the Fermi process and escape. No yet observational/theoretical proof the SNR are the sources of GCR Other sources of EP and likely CRs Massive star clusters => promising candidates to be tested SNR/MC Aged shocks but still (re)accelerate particles =>most of Fermi SNRs Evidences of LE-CR ionization A.Marcowith Seminar IPAG 49

50 Perspectives Theory: numerical calculations Injection: PIC-Hybrid effects of obliquity and ISM Fermi process: Hybrid-MHD parametric studies and role of HE CRs Escape: go towards 3D simulations Shock/cloud interaction: impact of neutrals, decide among different scenarii. Observations: CTA Improved sensitivity : spectral studies Important role of angular resolution => population studies Acero+12 A.Marcowith Seminar IPAG 50

51 Back-up 1. Simulations of turbulence in SNRs 2. Neutral damping effects A.Marcowith Seminar IPAG 51

52 Numerical highlights PIC Riquelme & Spitkovsky 09 Non-resonant instability saturation by CR feed-back Solid blue: 3D simulations transvers MF Dotted: longitudinal MF Hybrid Gargaté & Spitkovsky 12 Non-thermal acceleration by the Fermi process for different Alfvén Mach numbers (// shock) A.Marcowith Seminar IPAG 52

53 Draw-backs PIC/Hybrid methods cannot catch large scales and are limited in time evolution. Simulation regime not in correspondence with SNR conditions V sh > 0.5c Biases in PIC m p /m e < 1836 Low M a (except Gargaté & Spitkovsky 12) Cover a part of the parameter space Upstream magnetization + MF Obliquity (but Gargaté & Spitkovsky 12) Ionization degree: shock/molecular cloud regions. A.Marcowith Seminar IPAG 53

54 PIC-MHD simulations particles propagate into a MHD solution. Statistical reconstruction of the transport properties => diffusion coefficient. Only done in test-particle case (but see Reville & Bell 12) Turbulent Magnetic field Reville+08 Mean square displacement at different particle energies vs time: Sampling over a large amount of particles implemented randomly in space and in pitch-angle A.Marcowith Seminar IPAG 54

55 MHD-Kinetic calculations Kepler: MF advected downstream X (synchrotron) and g ray (Inverse Compton) profiles produced by electrons Kepler: MF relaxing downstream => Neutral pion (Acero+ in prep) => CTA SDE+HD 1D spherical AM & Casse 10 A.Marcowith Seminar IPAG 55

56 Ion-neutral damping Case of resonant Alfvén waves (weak turbulence limit; δb < B) (Drury et al 96) Typical energy where ion-neutral damping is the strongest: E 1 for waves with ω=kv a >Γ Maximum energy of particles if acceleration is limited by ionneutral damping: E 2 1. If E 2 < E 1 then acceleration highly reduced compared to the neutral free case. 2. If E 2 > E 1 then acceleration slightly reduced compared to the neutral free case. %0.4! T # E 1 = 8GeV " 10 4 K$ U sh! # E 2 = 1TeV " 10 3 km /s$ n i! " 1cm %3 3! " # $ %3 / 2 P #! T 0.1$ " 10 4 K! B # & ' " 1µG $ %0.4 # $ 2 n i! " 1cm %3 High speed shocks ~1000 km/s are more likely in case 2. Low speed shocks ~100 km/s: E 2 < 1 GeV and likely in case 1. # $ 0.5 %1! n n # " 1cm %3 $ A.Marcowith Seminar IPAG 56

57 High MFA limit (δb 2 /B 2 >1) SNR/MC Young SNR Ionneutral damping Ptuskin & Zirakashvili 03 A.Marcowith Seminar IPAG 57

58 Particle acceleration performances Homogeneous-ionised- low density medium Adiabatic high speed phases last longer. Streaming instability likely to generate strong magnetic fields Internal injection from the heated thermal plasma unless propagating in massive star clusters regions Acceleration up to very high energies (PeV and more). TeV particles observed from X and Gamma-rays. Inhomogeneous-partially neutral- dense medium Faster shock aging. Lower velocities. Alfvèn waves damped by ion-neutral damping. Magnetic field compression? The clouds can have magnetic fields > 10 µgauss. External energetic particles injection likely important Importance of reacceleration/coulomb losses at low energy (kev-mev). Acceleration performances to be tested versus wave damping and low shock velocities. A.Marcowith Seminar IPAG 58

59 Break & spectral indices Spectral break: Strong shock: balance t FI =t damping => E~1-10 GeV Ptuskin & Zirakashvili 03 Index at low energy: Strong shock: s GeV = 2 Index at high energy: Multiple weak shocks: s TeV > 2 E.g. dense cloud case M= 5 gives s=2(m 2 +1)/(M 2-1) => 3 Inoue+10 A.Marcowith Seminar IPAG 59