Lorentz Center Workshop Cosmic Ray Interactions: Bridging High and Low Energy Astrophysics 1 Cosmic Rays: high/low energy connections Etienne Parizot APC University of Paris 7
2 Cosmic rays: messages and messengers
Cosmic rays are very important! 3 Key subject in astrophysics! One of the main components of the Galaxy (> 1 ev/cm 3 ) CRs control the ionization of the interstellar medium + heating + turbulent magnetic field + astro-chemistry CRs regulate star formation + LiBeB nucleosynthesis! + biological evolution! Still very poorly understood Sources are unknown! (even at low energy!) Key problem slowing down the progress of high-energy astrophysics and astroparticle physics
Main questions 4 What are the sources of the cosmic rays? What is the acceleration mechanism? What is the role of cosmic rays in the Galactic ecology? + Can we use them to learn something about the sources? Physical conditions Dynamics Power Energy and EM/hadron balance Source history cloud tomography Structure of the ISM
5 A few grams of matter Cosmic rays (CRs) = high-energy nuclei filling the whole Galaxy and even the extragalactic space Cosmic rays make the Earth heavier with matter coming from distant galaxies! in a world of light All that is known about the universe is deduced from the observation of photons (+ knowledge of physical laws!) the astronomical messenger except for a few non-photonic particles : cosmic rays! new messengers new messages? (But with CRs, the messenger itself is mysterious!)
6 Matter? What is it worth? Photons: energy arrival direction energy spectrum angular spectrum Cosmic rays: energy arrival direction nuclear type energy spectrum angular spectrum mass spectrum
The CR problem 7
The CR problem 8 Cosmic rays are not rays! We are blinded by a magnetic mist! Larmor radius: r g = 1 pc E PeV B µg -1 Z -1 10 15 ev
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The CR problem suggests its own solution 10 low energy higher energy even higher energy still higher energy
11 The way out of the mist Turn cosmic rays into real rays (that go straight!) Turn charged CR into neutral particles Interactions with ambient medium : secondary photons + secondary neutrinos Go to the highest energies, to overcome magnetic deflection How high? Do CRs with high enough energies exist? Are they observationally accessible?
CRs: an amazing natural phenomenon! 12
CRs: an amazing natural phenomenon! 13
UHECRs: extremely rare, but not inexistent! 14 1 part/m 2 /s 1 part/m 2 /year knee Limit for satellites ankle 1 /km 2 /century!
15 Observing cosmic rays
16 Observing cosmic rays The solar modulation effect Key problem 1: only secondary particles at ground level Key problem 2: extremely low fluxes at high E
17 Observing cosmic rays The solar modulation effect Key problem 1: only secondary particles at ground level Key problem 2: extremely low fluxes at high E (Key problem 3: I m not an expert!)
18 Most CRs are NOT observed Most of the CR energy is carried by low-energy CRs (LECRs), which do not make it to the Earth! The solar modulation effect Interaction of the charged cosmic rays with the magnetized wind of the Sun equivalent electric field energy losses + outward flow (at very low E: thermalization before reaching the heliosphere!)
19 Low-energy cutoff solar attenuation 1 GeV/n 1 GeV/n 10 MeV/n 10 MeV/n
20 Solar modulation (solar minimum) (solar minimum) 1965 1987 1977 1987 1969 (solar maximum) 1969 (solar maximum)
21 Solar modulation Flux variation in coincidence with solar cycles Sun spot activity CR intensity
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Solar modulation: voyager and Pioneer data 23
Moderate energy CRs 24 Interactions in the atmosphere secondary particles go to space or high-altitude to measure the primary CRs balloons and satellites JACEE, CREAM, RUNJOB, ATIC, BESS Japanese American Cooperative Emulsion Experiment Cosmic Ray Energetics And Mass RUssian-Nippon JOint Balloon Advanced Thin Ionization Calorimeter Balloon-borne Experiment with a Superconducting Magnet AMS, PAMELA Alpha Magnetic Spectrometer (launch: April, 19th) Payload for Antimatter Matter Exploration and Light nuclei Astrophysics
25 H He
High energy CRs 26 The flux is too low for a balloon or satellite detection on-ground detectors indirect detection :-( High-Energy CRs produce extensive atmospheric showers Particle cascades developing at ~ the speed of light accross the astmosphere, hitting large surfaces on the ground and exciting molecules over large volume detect the showers instead of the cosmic rays reconstruct the showers, i.e. infer the energy, arrival direction and mass of the incoming particle Surface detectors (SD) vs Fluorescence detectors (FD) detect the particles in the shower detect the fluorescence light from the excited molecules
Hybrid HECR detection 27 comparison of observables with MC simulations grammage (g/cm 2 ) Fluorescence photons from atmosphere longitudinal shower development (sensible to EM sub-shower) Density of shower particles on the ground lateral distribution (sensible to EM and hadronic sub-showers)
One of the Auger stations 28 (Cherenkov water tank) Comms antenna GPS antenna Solar pannel PMT battery Diffusive white liner Plastic tank 12 m 3 of clean water
4 times 6 telescopes overlooking the site 29 Now completed!
One of the fluorescence eyes 30 440 PMT camera 1.5 per pixel segmented spherical mirror
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32 Independent analyses of stereo events E = 4.8 10 19 ev E = 4.9 10 19 ev E = 5.3 10 19 ev E em calculated by fitting a GH profile and integrating
First 4-fold hybrid event! 33 20 May 2007 E ~ 10 19 ev
Energy reconstruction with surface detector 34 SD energy estimator: interpolated signal in a tank at 1000 meters and 38 timing information available for triangulation geometry reconstruction (arrival direction) No.4 Theta = 59.9 [degree]
Example of a Hybrid Event 35
Cross-calibration of the detectors 36 SD energy estimator FD energy
Main composition observable 37 Depth of shower maximum development: X max atmospheric depth (g/cm 2 ) low E high E high E low A high A Stochastic process large fluctuations small fluctuations
Atmospheric depth of shower maximum 38 Expectations from different hadronic models
Fluctuations of depth of shower maximum 39 Expectations from different hadronic models
40 High-E/low-E interplay 1- Galactic/Extragalactic transitions
41 The GZK effect Greisen (1966) + Zatsepin & Kuz min (1966) Energy losses through e + /e - pair and pions production! Proton rest frame γ p e - e + Cosmic frame p γ p Threshold : E γ 2 m e c 2 in the proton rest frame E γ > 1 MeV Threshold : E γ m π c 2 in the proton rest frame E γ > 160 MeV
42 [cross section] x [inelasticity] 1 0,1 Pion production production de pions!" (mbarn) 0,01 0,001 0,0001 production de paires e + /e - e + e - pair production 10-5 10-6 10 6 10 7 10 8 10 9 10 10 (in ev) E # (en ev)
Attenuation length particle horizon 43 10 4 proton attenuation length (in CMB) 1000! att (Mpc) 100 10 19 19,5 20 20,5 21 log(e) (ev)
44 "Propagated" spectrum 10-11 z = 0.01, i.e. D " 60 Mpc accumulation Flux! E a Source spectrum: E -2.3 up to infinity... GZK cutoff 10-12 10 17 10 18 10 19 10 20 10 21 proton Energie energy (en ev) (in ev)
45 pair prod. pions prod. 10-11 z = 0.1 accumulation Flux! E a accumulation D 530 Mpc z = 0.01 D 60 Mpc GZK cutoff 10-12 10 17 10 18 10 19 10 20 10 21 Energie (en ev) proton energy (in ev)
46 10 Spectre propagé (source Propagated unique au spectrum redshift z s ) (unique source at redshift z s ) z s = 0.1!(E) " E 2.3 (ev 2 m -2 s -1 sr -1 ) 1 0,1 z s = 1 z s =0.65 z s = 0.3 z s = 0.5 z s = 0.01 0,1 1 10 100 1000 Energie (ev)
47 Uniform source distribution 10 26 AGASA Stereo Fly's Eye Akeno 1 km2 distribution uniforme de sources de z=0.001 à z=1 (spectre source en E -2.5 )!(E) " E 3 (ev 2 m -2 s -1 sr -1 ) 10 25 10 24 GZK suppression 10 23 10 17 10 18 10 19 10 20 10 21 Energie (ev)
48 Horizon (proton) 1 0,8 20.4 20.2 20.0 P(d<D) 0,6 19.8 19.6 0,4 19.4 19.2 0,2 Protons 10 100 1000 D(Mpc)
Auger spectrum 49 Cut off confirmed with high significance
UHE Nuclei propagation 50 2D nuclear scheme
51 Horizon (Helium) 1 0,8 19.8 P(d<D) 0,6 19.6 19.4 0,4 19.2 0,2 He 10 100 1000 D(Mpc)
52 Horizon (CNO) 1 0,8 20.0 19.8 P(d<D) 0,6 19.6 19.4 0,4 19.2 0,2 CNO 10 100 1000 D(Mpc)
Proton and nuclei loss length 53 10 4 10 3 Fe Proton Helium Oxygen Iron! 75 (Mpc) 10 2 10 1 He O H 10 0 10-1 10 19 10 20 10 21 E (ev) GZK horizon structure is essentially the same for protons and Fe nuclei
Fitting the spectrum 54 E 3!(E) (ev 2 m -2 s -1 sr -1 ) 10 25 10 24 10 23 pure proton sources Auger data 18 18,5 19 19,5 20 20,5 log 10 E (ev)
Fitting the spectrum 55 E 3!(E) (ev 2 m -2 s -1 sr -1 ) 10 25 10 24 10 23 pure Fe sources Auger data 18 18,5 19 19,5 20 20,5 log 10 E (ev)
Fitting the spectrum 56 10 25 He only (at sources) E max = Z # 10 20.3 ev " = 2.0 (800 EeV) pure He sources E 3!(E) (ev 2 m -2 s -1 sr1) 10 24 H He total 10 23 Auger data 18,4 18,8 19,2 19,6 20 20,4 log 10 E ev
Fitting the spectrum 57 10 25 CNO only (at sources) E max = Z # 10 20.3 ev " = 2.0 pure CNO sources E 3!(E) (ev 2 m -2 s -1 sr1) 10 24 10 23 H He total H CNO 18,4 18,8 19,2 19,6 20 20,4 log 10 E ev
Fitting the spectrum 58 10 25 Si only (at sources) E max = Z # 10 20.3 ev " = 2.05 pure Si sources E 3!(E) (ev 2 m -2 s -1 sr1) 10 24 Mg-Al-Si total p F-Ne-Na 10 23 CNO He 18,4 18,8 19,2 19,6 20 20,4 log 10 E ev
Fitting the spectrum 59 10 25 Fe only (at sources) E max = Z # 10 20.3 ev " = 2.3 pure Fe sources E 3!(E) (ev 2 m -2 s -1 sr1) 10 24 10 23 total 20 Z 26 12 Z 19 protons 9 Z 11 18,4 18,8 19,2 19,6 20 20,4 log 10 E ev
Fitting the spectrum 60 10 25 70% H + 30% Fe (at sources) E max = Z # 10 19.3 ev " = 2.0 70% H + 30% Fe E 3!(E) (ev 2 m -2 s -1 sr1) 10 24 p total 20 Z 26 10 23 12 Z 19 p 9 Z 11 18,4 18,8 19,2 19,6 20 20,4 log 10 E ev
Fitting the spectrum 61 E max (p) = 10 19 ev total Fe p
Are there nuclei among EGCRs? 62 Pure protons Mixed composition 10 protons only (uniform source distribution) Q(E) ~ E - 2.6 HiRes 1 (mono) HiRes 2 (mono) 10 mixed composition (uniform source distribution) Q(E) ~ E - 2.3 HiRes 1 (mono) HiRes 2 (mono)!(e) " E 3 (10 24 ev 2 m -2 s -1 sr -1 ) 1 with low E cut with cut inferred Galactic components!(e) " E 3 (10 24 ev 2 m -2 s -1 sr -1 ) 1 inferred Galactic component 0,1 0,1 17 17,5 18 18,5 19 19,5 20 20,5 17 17,5 18 18,5 19 19,5 20 20,5 log E (ev) log E (ev) 10 10 Source spectrum in E -2.6 Source spectrum in E -2.3 Ankle = "pair production dip" Ankle = gal./extragal. transition
Auger results about composition 63
Auger results about composition 64
Auger results about composition 65 transition towards a heavier composition or (strong!) modification of hadronic physics
66 High-E/low-E interplay 1- Galactic/Extragalactic transition 2- Same source/mechanism?
Viability conditions of a holistic model 67 Assume there is only one type of sources producing cosmic rays at all energies --> their physical properties (spectrum, power, composition) must be able to explain both galactic AND extragalactic fluxes [No freedom on the relative normalisation of the Gal. and extragal. components] Each galaxy injects CRs at a rate: In the Galaxy Outside the Galaxy
Viability conditions of a holistic model 68 Cosmological evolution of sources: f(z)
Viability conditions of a holistic model 69 Each galaxy injects CRs at a rate: In the Galaxy Outside the Galaxy
Viability conditions of a holistic model 70 A single free parameter : the slope of the source sprectrum, E x Galactic flux known, say, at 1 GeV Extragalactic flux known, say at 10 19 ev Astrophysical parameters solution: α 2.23 ± 0.07!
71 A striking result A single free parameter: source spectrum in E -2.2 E -2.3 Now this is already known to be the best fit at low energy (standard phenomenology of the galactic CR + diffusion theory) This is also the best fit at high energy, if one does not neglect the nuclei in the CR sources (just as required for a holistic model!) (This is also the source spectrum predicted by the acceleration models involving a relativistic shock wave) That may be a coincidence, but it nevertheless shows that there is some interest in considering cosmic-rays globally
72 There is NO standard model for cosmic rays Please don t oversell supernova remnants! ;-)
Last week s PAMELA results 73 Puzzling and exciting! Abstract: [ ] (www.sciencemag.org 3rd March 2011)
74 H He
75 H He
76 p/he ratio rigidity (GV)
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78 H He
Conclusions 79 CR sources are unknown at ALL energies! The majority of the CRs, and especially those most relevant to the science of the interstellar medium, are NOT observed! just unknown! + don t forget Li, Be and B don t rely on common thoughts Low-E CRs are Galactic, High-E CRs are extragalactic, but where does the transition occur? depends on composition UHECRs are challenging, but can be very helpful: high rigidity individual source identification! UHECR phenomenology is rich; composition is very important All CRs could be coming from the same sources, perhaps unknown yet!!! The common picture is not a standard model: not supported by observations, and sometimes in contradiction with them! Beware: energetic particle is different from cosmic ray
80 Thank you!