Post on 04-Feb-2018
Galactic Cosmic Rays
Alexandre Marcowith
Laboratoire Univers &Particules de Montpellier
9/14/12 A.Marcowith‐Seminar‐IPAG 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
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100 years of cosmic rayresearch(1912-2012)
• Viktor HESS (1883-1969)– Discovery of cosmic rays:
altitude ionization effect
– Nobel price 1936
• Pierre Auger (1899-1993)– Discovery of electromagnetic
showers (1938): start ofastroparticle physics
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Introduction
• Cosmic Rays in 3D– Energy spectrum
– Angular spectrum: anisotropy
– Mass spectrum: composition
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⊗
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Galactic Cosmic Rays
GCR
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Sources of galactic cosmic rays
• Supernova remnants: Hadrons + electrons-positrons
• Massive star clusters: Hadrons+ electrons-positrons
• Pulsars and pulsar wind nebulae: Electrons-positrons (+ Hadrons)
• X-ray binaries: Electron-positron + Hadrons
Drury+01 (SSR,vol.99)
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Les restes de supernova• Base du modèle “standard”:
– Argument énergétique:• Densité d’énergie du RC eRC ~ 1.5 eV/cm3
• Temps de résidence tres~10 M ansPcr = Vgal eRC / tr ~ 1041 erg/s soit 10% PSN
– 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)
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HistoricalSNRs
CassiopeiaA SN ~ 1681Type II (type IIb)Distance 3.4 kpc (+0.3
-0.1)Radius 2.5 pcShock speed ~5000km/s
ChandraChandra Chandra + HST
Tycho SN 1572Type IaDistance 3.8 kpc (+1.5
-0.9)Radius 3.4 pcShock speed ~ 4600km/s
SN 1006Type IaDistance 2.2 kpc (+/-0.1)
Radius 9 pcShock speed ~ 3000km/s
+ Kepler (type Ia) 1604 6.1 kpc+ RCW86 (type II? ) 185(?) 2.8 kpc
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Young SN remnant structure
<----------Ejecta --------->
2 shocksInterstellar mediumCassiopaeAbyChandra
Court.ADecourchelle
Analysisrestrictedto“young”SNrwithageafew103yearsFreeexpansion–earlySedovphase.
Green: 4-6 keV
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Observations: radio• Non‐thermalradiation:radio(Greencatalog;Green’08):
synchrotron(polarizedemission)F(ν)∝ν‐α;<α>=0.55(0.4‐0.7)s=(1.8‐2.4)
•Inagreementwithdiffusiveshockacceleration(DSA)s=2
Kepler
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Young SNR: X-rays
CasA Tycho
SN1006 Kepler
RCW86
Blue:synchrotronnon‐thermalX‐rays@keV(Vink’08)
Filamentsize%Rsh
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X - ray Filaments: consequencies• Downstream: within asynchrotron losstimescaletsyn(Eph,B)
- Advection with a speedVav⇒Advection length : ΔRdif
‐Diffusion with acoefficient D⇒Diffusion length : ΔRadv
To be compared with thefilament size ΔRx⇒ConstraintoverB
Shock restframe view
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X-ray Filaments: Magnetic field
Parizot,AM,Ballet,Gallant’06
DownstreamMF=>2ordersofmagnitudeabovestandardISMvalues:Amplification
Magnetic field amplification is required
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X-ray stripes
Eriksen+11Tycho
• Turbulence pattern? Bykov+11
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Supernova remnants: gamma-rays
Detected at one (GeV/TeV) or both GeV-TeV wavebands• Historical SNRs:
– Tycho, SN1006, Cassiopeia A, RCW86
• other SNRs:– RX J1713-3946.5, Vela Jr, HESS 1731-347
• 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
Par
t-II
Par
t-I
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Emission mechanisms• Non-thermal particle
distribution :N(E)=N0E‐s
• Leptonic : Inverse Compton– Source of low energy photons:
Cosmic microwave backgroundbut sometimes IR, UV
– Luminosity∝neE‐(s‐1)/2
(Thompson regime).
– IC/synchrotron => B in a one-zone model
+ Bremsstrahlung (NT electrons)– Luminosity ∝nenISME‐s
•Hadronic : Neutral pion production– Cross section increases only inlog(E): gamma-ray and hadronindices similar above 1 GeV.
– Luminosity∝∫nISMnCRdV
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TeV
GeV
TychoCassiopeia A SN 1006
Acciari+11
Uchiyama+11Abdo+10
Acero+10
x
Albert+07
+Chandra & CO data
+XMM newton
+XMM newton
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Tycho
CasA
Abdo+10
Hadronic model
sGeV =2.3 may be up to VHEECR consistent with 10% ofESN for next=0.3 cm-3
Fermi data more consistent withhadronic model.
Hadronic modelsGeV=2.1 + cut off at 10 TeV (blue)sGeV =2.3 no cut off (red)
ECR =3.2 x 1049 erg = 1/30 ESNfor next = 10 cm-3
Density possibly smaller.Leptonic (Inverse Compton) modelalso possible.
Uchiyama+11
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Other SNRs
Vela junior SNR
Type Ic ? Iyudin+10
Age ~ 450-900 yrs ?
Distance ~ 150-1000 pc
Radius 13 pc (D=750 pc)
RXJ 1713.7-3946
Type ?
Age ~ 1600 yrs (SN 393 ?)
Distance ~ 1 kpc
Radius 20 pc
Aharonian+07 Aharonian+07
Both powerful gamma-ray objects and show X-ray filaments
+ASCA
+ROSAT
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Spectra
Abdo+11
• RX J1713: data more consistent withleptonic models: index sGeV =2 and amean MF = 10mG <=> X-ray filaments ?• Inclusion of hadrons in a mixedmodel: ECR < 30% ESN but a hardspectrum is required.
• Cut off beyond 10 TeV: if hadronsare present: several hundred TeVparticles.
• Vela Jr: both models are possiblebut hadronic model requires a lot ofenergy into hadrons (50% ESN) andleptonic model difficult to reconcilewith X-ray filaments
Hadronic/Mixed
Leptonic
RXJ1713
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Short summary: Young SNRand 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• ECR is < 10% (CasA) but 10% Tycho.
• Emax-CR < knee (max: RXJ 1713, Tycho)
– Leptonic origin difficult to reconcile with high MF deducedfrom 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 beweakly magnetized.
– Injection dependence wrt the mean magnetic field direction(SN1006) ?
• No definite observational proofs that historicalyoung isolated SNR are the sources of GCR YET!
• What about theory ?
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l’accélération de Fermi (1erordre)
Accélération diffusive par ondede choc (ADOC ou DSA)
• Cas linéaire
• Cas non-linéaire
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Non-linear DSA in young SNR
• (too ?) Efficient mechanism (Drury & Voelk’81)
– PCR ~ [0.1-0.5] ρush2
– continuity conditions (Rankine-Hugoniot) haveto include PCR => modification of the shockprofile
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CR retro-action
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MFA feed-back• MFA mainly has a negative feed-back
- MFA in the shock precursor => increase of the Alfvén velocity
Btot=(δB2+〈B〉2)1/2,ūa=Btot/(4πρ)1/2⇒ Decrease scattering center velocity Vsh-ua => 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
Caprioli+09
Va (B0): no MFATrans: Ua in thekinetic CR Eq.Trans+Ampl: Ua
in the kineticCR Eq.+growthrate
Fluidvelocity
Particledistribution
Spectralindex
Magneticenergydensity
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Collisionless shockmicrophysics
• How to simultaneously explain:1/ High energy CR production including
the non-linear effects
2/ MF amplification
3/ High energy emission
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Multiple species and scales• Still quite challenging
– Completeness:• Need to include: plasma
waves, magnetized fluidand energetic particles +radiation.
– Scale description:• Requires to compute
acceleration processfrom thermal to ultra-relativistic particlescales.
• Intrinsic linear & non-linear process (scaleback-reaction).
Plasma fluctuations Energeticparticles
Magnetized thermalparticles
Hea
ting,
dam
ping
Generation, scattering,
stochastic acceleration
Com
pression, adiabatic
losses
Photons
Radiation, cooling
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Streaming instability
• Principle
• Recent developments
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JCR
F(x,p)
Non‐resonantinstabilityλ<rL=E/ZeB,left‐handcircularlypolarized
Resonantinstabilityλ>rL=E/ZeB,right‐handcircularlypolarized
Γ(k=1/λ)=ūa(kkc)1/2;kc=Jcr/B0
Γ(k)=Χ0|k//|ūa,Χ0=Pcr/Ubtot
Btot=(δB2+〈B〉2)1/2,ūa=Btot/(4πρ)1/2Vch
Shock precursor
MIS
Skilling’75,McKenzie&Völk’82,Bell&Lucek’01,Bell’04,Pelletier,Lemoine,AM‘06,AM,Pelletier,Lemoine’06,Amato&Blasi’09…Bykov+12(review)
PrincipleShock moving upstream
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MF amplification• Non-resonant instability:
– Fastest especially at highshock velocity (Pelletier,Lemoine, AM’06)
– Expected MF amplitude atthe shock front (B ∝ Vsh
3/2)
– But:• only small scales : Issue for
confinement of high-energyparticles
Bturb
BISM
!
" #
$
% &
2
= Ma
2 ush
c
!
"
$
%
PCR
'ush
2
!
" #
$
% & = 500( )
2(1/50)(1/5) = 1000
Voelk’05
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Different numericalapproaches
Particle‐In‐Cell(PIC):allspecieskinetic:Smallscalesl~rthi:instabilitiesthatmediatethe
shockformation‐injectionproblem.
“Hybrid”(electronasfluid,ionsaskinetic):Dominantinstabilityforparticleacceleration‐
backreactionovertheCRcurrentKinetic‐magneto‐hydrodynamic(MHD)(electron+ionfluid,
energeticparticlesaskinetic):Largescalesl~rCR‐longtermevolutionofthedominant
Instability‐CRtransportandescape.
Microscopic M
esoscopic Macroscopic
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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, ionizationdegree), shock properties (MF obliquity, shock velocity)
1. Fluctuations produciton• PIC:Hybrid Riquelme & Spitkovsky’10, Gagrgaté & Spitkovsky’12• MHD/kinetic Bykov+12, Reville & Bell’12
2. Turbulence properties• Upstream (Pelletier+06) downstream (AM & Casse’10)
3. Particle transport• Kinetic/MHD Reville+08, AM & Casse’10
4. High shock speeds studies• Very young SNR Renaud,AM+ in prep
• Gamma-ray burst Lemoine & Pelletier’11
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Conclusions: shockmicrophysics
• MFA likely connected to energetic particles assource 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- anddownstream => Maximum energy
• Not clear answer about SNR as sources of CRs maybe valuable to look after alternative sources …
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Other sources of energeticparticles/photons
• Massive star clusters• SNR/Molecular clouds interaction
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Massive starclusters
• Cygnus X cocoon by Fermi– Extended hard gamma emission
Tibaldo+11
Cygnus X cocoonspectrum: index close to 2.(calorimeter?)
Hadrons seem to bemandatory => E > 3 eV/cm-3
Photon residual map 10-100 GeV
Fermi MSX 8 micron
Ackerman+11
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CR acceleration: collectiveprocesses
• 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 PeVbut theory difficult due to strong non-linear feed-backs.
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CR solutions
F(p) distributionSpectral indexCase of a cluster with N=100starsFerrand & AM’10
Test-particle solutions Non-linear solutions
Ferrand+08, Ferrand & AMin prep.
MFI+FII FI
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Massive star sample
θ* = tFII/tesc and ransition hard-soft at p*=1/θ* GeV
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SNR in interaction withmolecular clouds
Uchiyama+10
Green: VLA data, ellipses CO cloud (a),black/white crosses OH masers
Aharonian+08a/b, Acciari+09, Fiasson+09
Triangle(c)/open(b) crosses: OH masers, stars: HIIregions(d)/PWN(c) White(a,b)/black contours(c): COdata
CTB 37a
TeVGeV
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IC443
Abdo+10, + Agile Tavani+10
Age: 3-30 kyrsDistance ~ 1.5 kpc?Size ~ 19 pc
• Shock/dense materials interaction(OH masers).
• Good fit provided by a hadronic modelwith broken power-law.
• ECR~0.6-2.2x1049 erg
Also W44:
=> Neutral pion decay nicely reproducedcombining Agile and Fermi dataGiuliani+11
FermiEgretVeritasMagic
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Shock/cloudinteraction
• MF Amplification due toturbulent medium (shockrippling) 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 densecloud limit)
– Behind the blast wave =>propagate in an ionizedmedium.
Ino
ue+0
9+1
0
2D MHD simulations (perpstrong shock)
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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 multipleweak shock re-acceleration + High energy spectrumsofter spectrum due to secondary shocks
– Hadrons from the cloud re-accelerated at theshock front (Blandford & Cowie’82,Uchiyama+10)
– Hadrons escaping the SNR and interacting withMCs (Gabici+07+09, Torres+08, Casanova+10)
9/14/12 A.Marcowith‐Seminar‐IPAG 45
Illuminated clouds ?• Probe of the diffusion coefficient around CR sourceGabici+09, Ohira+10:⇒ One can expect soft GeV and hard TeV spectra especiallyfor 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 diffusivelength: Diffusion coefficient (HESS1801, and HESS 1800a/b)~ 6% ISM values Gabici+10• See also Torres+08 in the case of IC443 ~ % ISM values.
CR spectrum at a MC atdifferent times (Gabici+09)
32000 yr 8000 yr 2000 yr 500 yr
But OH masersdetected Hewitt& Yusef-Zadeh’09
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Ion radicals measurements:dense gas
• Probe CR ionization rates in different environments usinglines produced by different ion radicals
Dense shocked gas:
1. W51c: Ionization in dense region probed by [DCO+/HCO+]Ceccarelli+11 ξ~10-15s => 2 orders of magnitude above standardvalues
2. IC443 [H3+] Indriolo+10 ξ> 10-15s
IC443
Ionization rates
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Some challenges• Inducing LE-CR spectrum
– Local deconvolution from the solar wind modulationeffect likely ≠ Around SNR/MC shocks.
– MeV protons and keV electrons: interface betweenthermal 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 ionizationhas been observed too).
• NO yet detailed modeling either for sourcespectrum or for transport– Only reference : heliospheric shock
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Importance of LE CRs
• LE CRs important for:– Ionization and ISM heating through wave production.
– Chemistry.
– Spallation => MeV Astrophysics.
– Dynamical effects => pressure gradients largelyoverlooked.
Influence over ISM
– Spatial: A source has influence on its local environmentover 100-200 pc.
– Timescales: 104 => 107 yrs
– Sources are usually in clusters
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Conclusions• Young (historical) SNRs: CR spectrum
– HE particle acceleration + MF amplification likelyconnected to non-resonant streaming instability.
– HE particles dominate EP pressure and largelycontrol the Fermi process and escape.
– No yet observational/theoretical proof the SNRare 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 ofFermi SNRs
• Evidences of LE-CR ionization
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Perspectives• Theory: numerical calculations
– Injection: PIC-Hybrid effects of obliquity andISM
– Fermi process: Hybrid-MHD parametric studiesand 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 studiesAcero+12
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Back-up
1. Simulations of turbulence in SNRs
2. Neutral damping effects
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Numerical highlights
PICRiquelme&Spitkovsky’09
HybridGargaté&Spitkovsky’12
Non-resonant instability saturationby CR feed-back
Non-thermal acceleration bythe Fermi process for differentAlfvén Mach numbers (// shock)
Solid blue: 3D simulationstransvers MFDotted: longitudinal MF
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Draw-backs• PIC/Hybrid methods cannot catch large
scales and are limited in time evolution.
• Simulation regime not in correspondencewith SNR conditions– Vsh > 0.5c– Biases in PIC mp/me < 1836– Low Ma (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.
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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
Mean square displacement at different particle energies vs time:Sampling over a large amount of particles implementedrandomly in space and in pitch-angle
Reville+08
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MHD-Kinetic calculationsKepler:MFadvecteddownstreamX(synchrotron)andg‐ray(InverseCompton)profilesproducedbyelectrons
Kepler:MFrelaxingdownstream
AM&Casse’10
=>Neutralpion(Acero+inprep)=>CTA
SDE+HD1Dspherical
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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: E1
for waves with ω=kVa>Γ– Maximum energy of particles if acceleration is limited by ion-
neutral damping: E2
1. If E2 < E1 then acceleration highly reduced compared to theneutral free case.
2. If E2 > E1 then acceleration slightly reduced compared to theneutral free case.
E1
= 8GeVT
104K
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#
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%0.4ni
1cm%3
!
"
#
$
%3 / 2B
1µG
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sh
103km /s
!
"
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0.1
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104K
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• High speed shocks ~1000 km/s are more likely in case 2.• Low speed shocks ~100 km/s: E2 < 1 GeV and likely in case 1.
9/14/12 A.Marcowith‐Seminar‐IPAG 57
High MFA limit (δB2/B2>1)
Ion-neutraldamping
Ptuskin & Zirakashvili’03
SNR/MC Young SNR
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Particle acceleration performancesHomogeneous-ionised-’low
density’ medium• Adiabatic high speed phases last
longer.
• Streaming instability likely togenerate strong magnetic fields
• Internal injection from the heatedthermal plasma unlesspropagating in massive starclusters regions
• Acceleration up to very highenergies (PeV and more).
• TeV particles observed from X andGamma-rays.
Inhomogeneous-partiallyneutral-’dense’ medium
• Faster shock aging. Lowervelocities.
• Alfvèn waves damped by ion-neutraldamping.
• Magnetic field compression ? Theclouds can have magnetic fields >10 µGauss.
• External energetic particlesinjection likely important
• Importance of re-acceleration/Coulomb losses at lowenergy (keV-MeV).
• Acceleration performances to betested versus wave damping and lowshock velocities.
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Break & spectral indices
• Spectral break:– Strong shock: balance tFI=tdamping => E~1-10 GeV
Ptuskin & Zirakashvili’03
• Index at low energy:– Strong shock: sGeV = 2
• Index at high energy:– Multiple weak shocks: sTeV > 2
– E.g. dense cloud case M=√5 gives s=2(M2+1)/(M2-1) => 3
Inoue+10