ISAPP School 2018 : “LHC meets Cosmic Rays” CERN, Geneva, Switzerland (Oct. 29th – Nov. 2nd)
Extragalactic cosmic rays and the Galactic/extragalactic transition
Étienne Parizot (APC, Université Paris Diderot)
E.T. d’Orion @parizot etienne.parizot
Mixity & gender equity Extreme Universe Space Observatory [2] Overview
✧ UHECRs: very brief phenomenology UHECR = Ultra-high-energy cosmic rays ✧ Acceleration ✧ Propagation ✧ Energy spectrum ✧ Composition ✧ Arrival directions (anisotropies)
✧ The GCR/EGCR transition GCR = Galactic cosmic rays ✧ What is the issue, why is it important? EGCR = extragalactic cosmic rays ✧ How can we learn something about it? ✧ What can we learn from it?
✧ Lessons from the GCR/GCR transition ✧ General phenomenology of a transition ✧ Lessons for the GCRs ✧ Lessons for the EGCRs ✧ An example of a “working”, two-component model
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [3] Preliminary comment
✧ Cosmic rays gave birth to Particle Physics ✧ First window opened onto the subatomic world ✧ Discovery of antimatter (1932) ✧ Discovery of the muon (1936) ✧ Discovery of pions (1947) ✧ Discovery of “strange particles”, K, L, X, S… (1949–1953)
✧ Particle Physics repudiated cosmic rays
✧ CERN created in 1954 ✧ Particle physics doesn’t need cosmic rays anymore (so she believes!)
✧ Cosmic rays are back and welcome!
✧ LHC: 1013 eV ; UHECRs: 1020 eV ✧ Particle physics needs cosmic rays => “LHC meets cosmic rays”… again! ✧ Cosmic rays need particle physics (showers)
✧ But cosmic rays are also interesting for themselves!
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [4]
> 12 orders of magnitude! Cosmic rays
4 per cm2 ✧ Major phenomenon ! per second ✧ Universal ✧ 32 orders of magnitude ( /m Out of equilibrium!!!
✧ Major role in Galactic ecology !
✧ Energy density ~ star light, thermal, B field ✧ Regulate the equilibrium between the different phases of the interstellar medium ✧ Control ionisation, heating ✧ Regulate star formation 2
/ ✧ Control astrochemistry sr /GeV ) /GeV ✧ Generate turbulent magnetic field ✧ Produce Li, Be and B!
✧ Major unknown !
1 per m2 per ✧ Sources are unknown (Galactic and Extragal.) billion years ✧ Acceleration processes are uncertain
#IMHO: CRs are so important that our current state of ignorance is truly exciting!
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [5] Cosmic rays
✧ A few significant structures à clues to understand/constrain underlying phenomena NB: at “low” energy:
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) GCR/EGCR transition (1)
Galactic cosmic rays
extragalactic cosmic rays [7] GCR/EGCR transition
✧ Low-energy cosmic rays are Galactic! ✧ Many possible sources à how could extragalactic sources dominate? Superbubbles, SNRs, pulsars, magnetic reconnection, AGN episodes, starburst episodes, GRBs, TDEs, etc.
✧ Observational proof: Magellanic clouds have a lower gamma-ray emissivity from π0 decay than the Milky-Way => lower cosmic ray flux => ∃ internal Galactic sources CR flux in LMC ~ 15% of GCR flux (even lower in SMC)
✧ Very-high-energy cosmic rays are (almost certainly) extragalactic
✧ Loss of confinement in the Galaxy and its magnetic halo ✧ Large anisotropy would result from active Galactic sources
✧ So there must be a transition somewhere! à where?
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [8] Transition between two components
✧ Case 1: Same spectrum continuity ✧ Case 1.a: Same normalisation ( à Which one is which?) very unlikely!
✧ Case 1.b: First one is higher drop (wherever the first one stops)
✧ Case 1.c: First one is lower bump (wherever the second one starts)
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [9] Transition between two components
✧ Case 2: from steeper to flatter, i.e. “ankle-like”
ankle ankle ankle
Produces an ankle at whichever energy where the second one overcomes the first one
à very natural and simple phenomenology
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [10] Transition between two components
✧ Case 3: from flatter to steeper
à “knee-like”?
knee
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [11] Transition between two components
✧ Case 3: from flatter to steeper
In fact no! à “knee-like”? Ankle-like!
knee ankle
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [12] Transition between two components
✧ Case 3: from flatter to steeper
In fact no! à “knee-like”? Ankle-like!
knee ankle
Unless the second one starts “exactly” where … and with the same flux! the first one stops…
knee Painful break
=> very unlikely!
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [13] Transition in the data?
✧ All-particle data: there is an ankle indeed! Natural candidate for the GCR/EGCR transition!
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [14] Transition in the data?
✧ KASCADE-Grande data: evidence for a “light-ankle” (protons?)
Natural candidate for a GCR/EGCR transition in the light component!
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [15] GCR/EGCR transition: a key issue!
✧ Immediate consequences ✧ EGCRs must go as low in energy as the transition! ✧ GCRs must go as high in energy as the transition!
✧ Forget PeVatrons: think EeVatrons! ✧ Galactic sources must accelerate particles to much high energies than the knee à crucial constraint!
✧ Magnetic confinement ✧ Galactic magnetic field should confine particles up to the ankle!
✧ Magnetic horizon ✧ Extragalactic magnetic field should not prevent ankle particles from reaching us from extragalactic sources GCR EGCR ✧ EGCR flux level & UHECR spectrum!
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) UHECRs: crash course summary [17] UHECRs: crash course summary
✧ Observables: 3 spectral dimensions ✧ Energy à energy spectrum ✧ Nature of the cosmic ray à composition (or mass spectrum) ✧ Arrival direction à anisotropies, angular spectrum
✧ Acceleration ✧ What are the sources? ✧ What is the acceleration process? ✧ What is the power imparted to cosmic rays? ✧ What is the energy spectrum at and out of the source? ✧ What is the maximum energy? (or energies!) ✧ What is the source composition?
✧ Propagation
✧ Modification of the spectrum: energy losses ✧ Modification of the composition: nucleon losses ✧ Modification of the trajectories: pointing losses
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [18] UHECRs: crash course summary
✧ Observables: 3 spectral dimensions ✧ Energy à energy spectrum Revolutionary data ✧ Nature of the cosmic ray à composition (or mass spectrum) since ~10 years New generation of ✧ Arrival direction à anisotropies, angular spectrum detectors needed ✧ Acceleration Unknown ✧ What are the sources? Unknown ✧ What is the acceleration process? ✧ What is the power imparted to cosmic rays? few 1044 erg Mpc−3 yr−1 ✧ What is the energy spectrum at and out of the source? Unknown ✧ What is the maximum energy? (or energies!) Unknown ✧ What is the source composition? Unknown ✧ Propagation
✧ Modification of the spectrum: energy losses Well understood ✧ Modification of the composition: nucleon losses Well understood ✧ Modification of the trajectories: pointing losses Well understood, but unknown magnetic field!
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [19] Energy dimension: acceleration
✧ Acceleration up to 1020 eV is VERY challenging!
✧ No permanent E fields in the universe, except at “machines” like pulsars/magnetars
Emax <
✧ Transitory E fields: reconnection ✧ “Change-of-frame acceleration” (shock waves + turbulence)
✧ Emax <
✧ Confinement problem ✧ Keep the particles in the accelerator!
Emax <
✧ => large magnetic fields and/or large size needed!
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [20] Energy dimension: acceleration
✧ Acceleration up to 1020 eV is VERY challenging!
✧ Source power ✧ Magnetic energy passing through the source
✧ Minimum power requirement:
Emax Emax <
✧ Put in efficiencies and loss processes!
✧ Conclusion: VERY challenging indeed… especially for protons!
But Emax (Fe) = 26 × Emax (proton) (if no losses or photo-dissociation)
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [21] Energy dimension: propagation (= transport from the sources to the Earth)
✧ Interaction of Galactic cosmic rays with the ambient medium
✧ At low energy: spallation, ionisation losses, Bremsstrahlung, pion production, Inverse Compton… (cf. Pasquale Blasi’s lecture)
✧ At high energy, say above 10 GeV : negligible! (GRCs leak out of the Galaxy unaffected)
✧ Steepening of GCR spectrum through energy-dependent confinement
Simplified propagation equation source term (“leaky box”)
confinement time
Steady state solution steeper spectrum:
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [22] Energy dimension: propagation
flux
Propagated spectrum
à change of slope!
Source spectrum
energy
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [23] Energy dimension: propagation
flux Propagated spectrum
Knee!
Change in the transport regime à change in the confinement regime! à change of spectral index!
Source spectrum
energy
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [24] UHECR propagation
✧ Interaction of extragalactic cosmic rays with the ambient medium
✧ It’s almost empty… but full of photons! The GZK effect! (Greisen, Zatsepin, Kuz’min)
Cosmological microwave background (CMB)
UHE protons e- π g p Proton rest frame e+ Eg > 1 MeV Eg > 160 MeV
e- p g p “Cosmic frame” e+ π
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [25] UHECR propagation
✧ The GZK effect for protons
[cross section] x [inelasticity] Attenuation length
1
production de pions 0,1
0,01
0,001 (mbarn)
σκ 0,0001 production de paires e+/e-
10-5
10-6 106 107 108 109 1010 E (en eV) γ
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [26] UHECR propagation
✧ The GZK effect for protons
z = 0.01, i.e. D ∼ 60 Mpc
10-11 a E × Flux
GZK cutoff
10-12 1017 1018 1019 1020 1021 Energie (en eV)
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [27] UHECR propagation
✧ The GZK effect for protons pair prod. pions prod.
z = 0.1 accumulation 10-11
accumulation
a z = 0.01 E
× Flux D ≈ 530 Mpc
GZK cutoff
D ≈ 60 Mpc
10-12 1017 1018 1019 1020 1021 protonEnergie energy (en (ineV) eV)
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [28] UHECR propagation
✧ The GZK effect for protons
10 Spectre propagé (source unique au redshift z ) s z = 0.1 s )
-1 z = 0.3 s sr -1 s
-2 1 m 2 (eV
2.3 E
×
(E) z = 0.01 z = 1 s Φ s 0,1 z =0.65 z = 0.5 s s
0,1 1 10 100 1000 Energie (eV)
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [29] UHECR propagation
✧ The GZK effect for protons
With a uniform source distribution
pure proton sources 1025 ) -1 sr -1 s -2
m 24 2 10 (eV GZK suppression (E) Φ 3
E 1023
18 18,5 19 19,5 20 20,5 log E (eV) 10
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [30] UHECR propagation
✧ The GZK effect for nuclei
Nuclei interact with CMB and IR photons ® photo-dissociation + energy losses
+
✧ Nuclear cascade in the intergalactic medium
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [31] UHECR propagation
✧ The GZK effect for nuclei
Horizon effect, similar to that of protons
Attenuation length Horizon effect 104
Proton Fe Helium 103 Oxygen Iron
102 He O (Mpc)
75 H χ 101
100
10-1 1019 1020 1021 E (eV)
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [32] UHECR propagation
✧ The GZK effect for nuclei
1025 pure Fe sources ) -1 sr -1 s -2
m 24 2 10 (eV (E) Φ 3
E 1023
18 18,5 19 19,5 20 20,5 log E (eV) 10
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [33] UHECR propagation
✧ Evidence for a GZK feature in the UHECR spectrum
pure proton sources 25 pure Fe sources 1025 10 ) ) -1 -1 sr sr -1 -1 s s -2 -2 m
m 24
24 2 2 10 10 (eV (eV (E) (E) Φ Φ 3 3 E
E 23 1023 10
18 18,5 19 19,5 20 20,5 18 18,5 19 19,5 20 20,5 log E (eV) log E (eV) 10 10
but no information on the source composition!
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [34] UHECR propagation
✧ Just for fun!
He only (at sources) E = Z × 1020.3 eV pure He sources 25 max 10 (800 EeV) β = 2.0 ) 1 sr -1 s -2
m 24 2 10 H (eV (E) Φ
3 He E 1023
18,4 18,8 19,2 19,6 20 20,4 log E eV 10
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [35] UHECR propagation
✧ Just for fun!
CNO only (at sources) E = Z × 1020.3 eV pure CNO sources 1025 max β = 2.0 ) 1 sr -1 s -2
m 24 2 10 H (eV
(E) CNO Φ 3 E H 1023 He
18,4 18,8 19,2 19,6 20 20,4 log E eV 10
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [36] UHECR propagation
✧ Just for fun!
Si only (at sources) E = Z × 1020.3 eV pure Si sources 1025 max β = 2.05 ) 1 sr -1 s -2
m 24 2 10 p (eV
F-Ne-Na (E)
Φ Mg-Al-Si 3 E CNO 1023
He
18,4 18,8 19,2 19,6 20 20,4 log E eV 10
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [37] UHECR propagation
✧ Just for fun!
Fe only (at sources) E = Z × 1020.3 eV pure Fe sources 1025 max β = 2.3 ) 1 sr -1 s -2
m 24 2 10 20 ≤ Z ≤ 26 (eV
(E) 12 ≤ Z ≤ 19 Φ 3 E 1023 protons
9 ≤ Z ≤ 11
18,4 18,8 19,2 19,6 20 20,4 log E eV 10
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [38] UHECR propagation
✧ Just for fun!
70% H + 30% Fe (at sources) E = Z × 1019.3 eV 70% H + 30% Fe at source 1025 max β = 2.0 ) 1 sr -1 s -2
m 24 2 10 20 ≤ Z ≤ 26
(eV p (E) Φ 3 E
23 12 ≤ Z ≤ 19 10 p
9 ≤ Z ≤ 11
18,4 18,8 19,2 19,6 20 20,4 log E eV 10
CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [39] GZK horizon effect
1
20.4 0,8 20.2 20.0
0,6 19.8 19.6 P(d 0,2 Protons 10 100 1000 D(Mpc) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [40] GZK horizon effect 1 20.0 0,8 19.8 0,6 19.6 19.4 P(d 0,2 CNO 10 100 1000 D(Mpc) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [41] What do the data say? ✧ Energy spectrum measured at the Pierre Auger Observatory CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [42] What do the data say? ✧ CR composition estimated at the Pierre Auger Observatory Energy E, mass A same A, higher E same E, higher A Xmax Xmax Xmax X (g/cm2) X (g/cm2) X (g/cm2) Higher energy => deeper shower Higher mass => shallower shower Higher mass => smaller fluctuations CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [43] What do the data say? ✧ CR composition estimated at the Pierre Auger Observatory CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [44] What do the data say? ✧ CR composition estimated at the Pierre Auger Observatory CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [45] What do the data say? ✧ CR composition estimated at the Pierre Auger Observatory CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [46] What do the data say? ✧ CR composition estimated at the Pierre Auger Observatory CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [47] Natural interpretation: low proton Emax ² The Auger results clearly show a transition towards a heavier composition around a few 1018 eV ² This is either puzzling… • because protons are by far the most abundant nuclear species in the universe • because the transition occurs at energies much lower than the expected GZK cut-off (so it cannot be due to a propagation effect) ² …or very easy to understand – and very comforting! • there is a “non GZK” cut-off of the protons à it must be at the source! à simple, generic and natural explanation: the low proton Emax scheme! CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [48] Natural interpretation: low proton Emax ² Very sensible interpretation, from the astrophysical point of view! ² Maximum energy at the source proportional to Z for different nuclei Charged particles trajectories and energy gains only depend on rigidity ² Relaxes a critical problem: very hard to build acceleration models providing maximum proton energies above1020 eV! 18 19 à More “comfortable” to have Emax(p) ~ between a few 10 eV and 10 eV ² à transition towards heavier component by extinction of the light one! ² NB: also in line with the absence of any marked anisotropy in the UHECR sky (would be hard to explain within a p-dominated scenario!) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [49] Natural interpretation: low proton Emax GCR CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [50] Natural interpretation: low proton Emax Allard et al. (2005) § source spectrum & acceleration § Interpretation of the ankle CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [51] Natural interpretation: low proton Emax ² But this has an important implication: The source spectrum must be hard! with x < 2 or even x ~ 1 GCR ² Not a problem! • requires less energy in total • obtained in a natural way in some models ² But a hard proton spectrum implies a low EGCR proton fraction at 1018 eV… ² And GCRs must reach the ankle > 1018 eV! CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) Back to the GCR/EGCR transition [53] Combined composition data ICRC 2015 CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [54] Combined composition data light heavy ICRC 2015 light heavy CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 55 Is there a proton crisis at the ankle? GC R ² Important constraint: CRs are light-dominated at 1018 eV But light CRs at 1018 eV cannot be Galactic! à that would violate isotropy data! (Auger results) And light CRs at 1018 eV cannot be extragalactic if they have the hard spectrum inferred from the light-to-heavy UHECR transition! ² => either there is an additional component to fill the gap, GCR/EGCR or the spectrum of light elements is different! transition is key! CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 56 Lessons from GCRs à Can we attack the problem from below the ankle? à The knee + new data from KASCADE-Grande! à GCRs become heavier at the knee CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 57 What is the GCR knee? ² Is it a feature of the acceleration process? • Cut-off at the source? à usually advocated by people who hold SNRs responsible for the GCRs • Change of slope due to reducing number of sources? à in some versions of the SNR-GCR connection scheme ² Is it a feature of cosmic ray propagation/confinement? • Change of diffusion regime? à expected due to maximum turbulence scale (ànon resonant scattering off magnetic inhomogeneities) • Influence of a Galactic wind? à advection? ² Is it a local effect (space-time distribution of sources)? ² In all cases, a rigidity-dependent effect can be expected… CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 58 Kascade-Grande: the light ankle! Kascade Grande Collaboration (2013) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 59 Kascade-Grande: light ankle/heavy knee Kascade Grande Collaboration (2013) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 60 Kascade-Grande results Kascade Grande Collaboration (2013) ankle 5 1018 eV CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 61 Quite a simple and natural picture! CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 62 Quite a simple and natural picture! knee 3 1015 eV CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 63 Quite a simple and natural picture! knee E-2.7 pre-knee slope slope x = 3.3 3 1015 eV CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 64 Quite a simple and natural picture! knee E-2.7 pre-knee slope slope x = 3.3 • same slope! • natural match to the knee! slope x = 3.3 3 1015 eV CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 65 Quite a simple and natural picture! Fe knee knee E-2.7 pre-knee slope slope x = 3.3 • same slope! • natural match to the knee! slope x = 3.3 3 1015 eV CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 66 Very appealing GCR/EGCR transition picture protons Fe GCR E-2.7 EGCR 3 1015 eV 8 1016 1017 3 1018 eV CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 67 Very appealing GCR/EGCR transition picture protons Fe GCR E-2.7 EGCR 3 1015 eV 8 1016 1017 3 1018 eV UHECRs CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 68 Very appealing GCR/EGCR transition picture protons Fe GCR E-2.7 EGCR 3 1015 eV 8 1016 1017 3 1018 eV à But it requires Galactic protons up to ~1017 eV and Galactic Fe nuclei up to the ankle! UHECRs Not SNRs! à Is there a second GCR component? CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 69 Do we have a hardness crisis? Low proton Emax models imply The EGCR proton component hard source spectra seems to be much softer! protons Fe GCR EGCR 3 1015 eV 8 10161017 3 1018 eV Does this require an additional component? In fact, no: a softer spectrum for EGCR protons (compared to EGCR nuclei) works as well! CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) [70] Example: acceleration model in GRBs CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) Example of a simple, generic model that meets the transition and UHE constraints - One single GCR component, with rigidity dependence only - One single EGCR component, from a GRB source model gamma-ray burst 72 Particle acceleration at mildly relativistic shocks ² Monte Carlo simulation of Fermi acceleration: Ø Full calculation of particle trajectories and shock crossings => energy gains + particle escape (both upstream and downstream) ² Resulting spectra (no energy losses): Ø Escape upstream : high pass filter (selects particles in the weak scattering regime) Ø Escape downstream : should become a high pass filter in the presence of energy losses (particles must leave before being cooled by energy losses) E r (E ) = max ≡ λ L max eZB max CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 73 Particle acceleration with energy losses ² Competition between acceleration and energy losses Ø Take into account all energy loss processes (expansion, synchrotron, pair production, photo-dissociation, photo-pion, hadronic interactions) ² Resulting spectra of escaping particles, integrated over the whole GBR evolution Ø For each GRB luminosity Ø For each of three different energy partition models (A, B and C) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 74 Particle acceleration with energy losses 51 Lwind = 10 erg/s | twind = 2 s | metallicity = 10×GCRs mass hierarchy for Emax + very hard spectrum! CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 75 Particle acceleration with energy losses 53 Lwind = 10 erg/s | twind = 2 s | metallicity = 10×GCRs mass hierarchy for Emax + very hard spectrum! CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 76 Particle acceleration with energy losses 55 Lwind = 10 erg/s | twind = 2 s | metallicity = 10×GCRs CERN LOOK AT THE— NEUTRONISAPP School 2018 — COMPONENT!!! E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 77 Resulting UHECR propagated spectra ² Implement the GRB rate, GRB luminosity function, and redshift evolution from Wanderman & Piran (2010) a = 1.2 b = 2.4 n1 = 2.1 n2 = -1.4 z* = 3 CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 78 Resulting UHECR propagated spectra 1025 Model A, isotropic, Bext = 0.1nG Auger 24 ) 10 -1 sr -1 s -2 23 10 m 2 22 10 dndE (eV 3 E 21 10 20 10 17.5 18.0 18.5 19.0 19.5 20.0 20.5 log10E (eV) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 79 Resulting UHECR propagated spectra 1025 Model C, isotropic, Bext = 0.1nG Auger 24 ) 10 -1 sr -1 s -2 23 10 m 2 22 10 dndE (eV 3 E 21 10 20 10 17.5 18.0 18.5 19.0 19.5 20.0 20.5 log10E (eV) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 80 Resulting UHECR propagated spectra 1025 Model B, isotropic, Bext = 0.1nG Auger 24 ) 10 -1 sr -1 s -2 23 10 m 2 22 10 dndE (eV 3 E 21 10 20 10 17.5 18.0 18.5 19.0 19.5 20.0 20.5 log10E (eV) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 81 Global GCR/EGCR model Globus, Allard & EP (Phys. Rev. D, 2015) • Let’s put GCR and EGCR models together! • IT WORKS! • All the spectral features and composition measurements can be reproduced, both qualitatively and quantitatively! • Only two components are needed: 1 GCR + 1 EGCR CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 82 Global GCR/EGCR model ² GCRs: broken power law at the knee (either source or propagation effect), with measured abundances at low E (below the knee): purely rigidity-dependent spectrum ² EGCRs: fit of Auger spectrum data with the GRB acc. model + cosmological evolution of the sources (but could be different GRB wind model, etc.) à 1 extra parameter CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 83 Global GCR/EGCR model: spectrum CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 84 Global GCR/EGCR model: spectrum CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 85 Global GCR/EGCR model: composition CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 86 2. Global GCR/EGCR model: composition CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 87 2. Global GCR/EGCR model: composition CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 88 Implications ² Two dominant components are sufficient to account for the general CR phenomenology over the entire spectrum ² But then the EGCR component must have a low maximum energy (with a charge/mass dependence) and softer proton spectrum ² The GCR proton component should extend up to ~1017 eV à Seems very hard for SNR models (which have other severe problems, by the way!) ² NB: the GRB acceleration model is probably not unique: strongly magnetized media with high photon density would produce the same key features (presumably) ² Other schemes are possible, with additional components à other types of implications and questions CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 89 Main message ² The GCR/EGCR transition region is very important to study ² It is constrained from above by EGCRs and from below by GCRs ² In turn, it constraints GCRs and EGCRs! ² Studies must involve energy spectrum, composition and anisotropies (and their energy evolution) CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7) 90 Perspectives ² More data are needed on the GCR/EGCR transition region ² The knee needs to be understood à data needed! ² Detailed anisotropy studies will be important (at all energies) ² Find GCR sources! à keep an open mind beyond isolated SNRs! ² Find EGCR sources! à take advantage of the GZK horizon effect: look deep into the cut-off, with larger exposure and full sky coverage NB: important efforts of the JEM-EUSO Collaboration to develop space-based UHECR studies à stay tuned ;-) ² Develop multi-messenger astronomy! Cosmogenic neutrinos + electromagnetic cascades à neutrino and gamma-ray backgrounds + individual sources CERN — ISAPP School 2018 — E. Parizot 1/11/2018 “Extragalactic cosmic rays and the Galactic/extragalactic transition” (APC, Paris 7)