Transition from Galactic to Extragalactic Cosmic Rays Roberto - PowerPoint PPT Presentation

Transition from Galactic to Extragalactic Cosmic Rays Roberto Aloisio Gran Sasso Science Institute INFN – Laboratori Nazionali del Gran Sasso Symposium 20 th Anniversary of the Foundation of the Pierre Auger Observatory 14-16 November 2019, Malargue, Mendoza Province, Argentina.

CR Observations and the transition GCR-EGCR ALL PARTICLE SPECTRUM In Cosmic Rays physics we can study sources, production mechanisms and the physics of propagation only through three basic observables ü Spectrum ü Anisotropy ü Mass composition KNEE T R A N ü The all particle S II KNEE I T I spectrum is a broken O N power law with few structures: knee, ANKLE second knee, ankle, strong suppression at UHE.

Ultra High Energy Cosmic Rays – Spectrum log (E/eV) 10 Spectral features 17 18 19 20 ] 2 ü Second knee: ~2x10 17 eV eV 38 10 -1 ü Ankle: ~3x10 18 eV sr -1 yr -2 [km Transition GCR-EGCR SD 1500m < 60 degrees θ 3 37 10 ü Expected changes in the mass E SD 1500m > 60 degrees θ × composition across the hybrid J(E) transition region: from heavy SD 750m to light (see later). Cherenkov ü Anisotropy observations can 17 18 19 20 10 10 10 10 provide stringent limits on the E [eV] transition region. Auger Collaboration (2019)

Ultra High Energy Cosmic Rays – Anisotropy ü Large scale anisotropy: dipole E>8 EeV (5.2 ! ) Extragalactic origin 90 0.44 Flux[km -2 sr -1 yr -1 ] 0.40 360 0 Auger Collaboration (2019) 0.36 -90 ü Intermediate anisotropy: E>38 EeV (3.8 ! ) Hints of sources (Starburst, AGN)

log (E/eV) 10 17 18 19 20 ] 2 eV 38 10 Hotspot: Sources -1 sr -1 yr -2 Dipole: Extragalactic [km SD 1500m < 60 degrees θ 37 3 10 E SD 1500m > 60 degrees θ × hybrid J(E) SD 750m Cherenkov 17 18 19 20 10 10 10 10 E [eV]

Galactic CR: knees and acceleration ü The knee as a signature of a rigidity dependent acceleration ü The all particle spectrum is the result of the sum of the spectra of different species, with a cut-off energy rigidity dependent E Z = ZE p 0 ✓ E ◆ ✏ c � − ∆ �  d Φ Z ✏ c dE ( E ) = Φ 0 X E � 1 + Z E Z J.R. Horandel et al. (2003) ü Maximum energy of accelerated protons (need for “Pevatron” sources) E p 0 & 1PeV E. G. Berezhko, H. J. Volk (2008)

Diffusive Shock Acceleration U 1 U 2 -39 RXJ-1713, X and gamma 100 100 80 -39.5 Tycho, X 60 40 20 0 -40 ü Diffusion of charged particles back and forth PSF -40.5 through the shock leads to 17h15m 17h10m ∆ E ' E (4 / 3)( U 1 � U 2 ) /c X-rays observations ü Particles are accelerated to a power law Typical size of the observed filaments ~ 10 -2 parsec spectrum Q ( E ) ∝ E − γ ü The slope of the spectrum depends only on the shock compression factor, in the case of strong shock (M>>1) Q~E -2 . Comparison with the observed thickness ü The maximum acceleration energy depends leads to a B-field estimate only on diffusion in the shock region. The B ' O(100 µ G) ISM magnetic turbulence (as it follows from B/C observation) is too low (providing only CR at GeV energy). It is needed additional turbulence to reach E max ~10 5 -10 6 GeV.

The case of Tycho 8 7 Brightness � erg � s � cm 2 � Hz � sr � X � ray profile � 1 keV ü SNIa exploded in roughly homogeneous ISM 6 (regular spherical shape) 5 ü From X-ray observations B~300 µ G 4 3 ü Maximum energy protons E max ~500 TeV 4. 2 1 0.94 0.95 0.96 0.97 0.98 0.99 1.00 Morlino & Caprioli 2011 Steep spectrum hard to explain with R � R sh leptonic emission ü Leptonic emission. ICS of relativistic electrons on photon background has a flatter spectrum respect to CR: E -(γ+1)/2 ü Hadronic emission. pp→π 0 →γγ conserves the same spectrum of CR: E -γ ü Important experimental confirmation of the credibility level of theories based on DSA. Space resolved gamma ray observations would test different theoretical hypothesis. Morlino & Caprioli 2011

Escape of CR from accelerator – maximum energy Caprioli et al. 2009 Streaming instability Escape is the physical phenomenon that transforms accelerated particles into CR. Super-Alfvenic streaming of CR leads to the excitation of ESCAPE FROM SNR magnetic turbulence δB at the AFTER EXPANSION resonant wavenumber k=1/r L . Locally at the shock front this turbulence can reach δB/B ~ ESCAPE FLUX FROM 50, while in the ISM δB/B<<1. BOUNDARY CR injected ü particles escaped during the free expansion and Sedov- Taylor phases (emission peaked on p max ) Maximum energy D ( E max ) ü particles released in the ISM ü particles escape χ < 1 ' χ R sh V sh after expansion ü NOTE: Hillas criterion is an upper limit, r L ( E max ) = R sh overestimates the actual maximum energy by a factor of c/V sh

Blasi 2019 Galactic CR acceleration ü Type Ia SN ü In the framework of DSA ◆ � 2 / 3 ✓ E SN ✓ ξ CR ◆ ✓ M ej ◆ ⇣ n ISM ⌘ E p in SNRs the maximum max = 0 . 05 PeV 10 51 erg cm � 3 0 . 1 M � attainable energy seems somewhat lower than needed. ü Type II SN core collapse in its own wind ! 1 / 2 ✓ E SN ◆ � 1 ˙ ✓ ξ CR ◆ ✓ M ej ◆ ✓ ◆ M V w E p max = 0 . 3 PeV 10 � 5 M � yr � 1 10 51 erg 10 kms � 1 0 . 1 M �

Galactic Cosmic Rays – The knee structure P+HE SPECTRUM (YAC1-Tibet) All particle and light components (Argo-YBJ) ) -1 sr -1 Preliminary s -2 m 4 10 1.6 (GeV Ω dAdtd ARGO-YBJ G4 ARGO-YBJ G1 dN ARGO-YBJ Bayes-G4 ARGO-YBJ Bayes-G1 3 10 ARGO-YBJ WFCTA (p + He) ARGO-YBJ strip (p + He) E d Tibet III (QGSJET-II) 2008 Tibet III (SIBYLL) 2008 KASCADE (QGSJET-II) 2005 KASCADE (SIBYLL) 2005 × Tunka-25 2013 Tunka-133 2012 2.6 DICE 2000 Icetop 2013 E KASCADE-Grande 2012 EAS-Top 1999 BLANCA 2001 CASA-MIA 1999 RUNJOB JACEE 2 KASCADE p KASCADE (He + C + Si) 10 KASCADE Fe YAC-I TibetIII (p + He) SIB 2013 CREAM (p + He) 2011 Horandel (p + He) 2003 Horandel (p+He) 2003 Horandel (All particle) 2003 knee at Z × 1 PeV Gaisser et al. 2013 (p + He) Gaisser et al. 2013 (p+He+Fe+CNO) Direct measurements comb. (p + He) Direct measurements (All particle) 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Log (E/TeV) 10 I. De Mitri, A. D’Amone, L. Perrone, A. Surdo (2016) J. Huang (2013) YAC1-Tibet and Argo-YBJ ü Knee in the all particle spectrum ~ 2 PeV ü Knee in the light component ~ 0.1 PeV

Kascade and Kascade-Grande 19 10 Kascade and Kascade -Grande EAS-TOP (Astrop.Phys.10(1999)1) Akeno (J.Phys.G18(1992)423) KASCADE (Astrop.Phys.24(2005)1) direct data ) AGASA (ICRC 2003) 1.5 KASCADE H ü Knee in the all particle 18 HiResI (PRL100(2008)101101) KASCADE He 10 eV KASCADE heavy HiResII (PRL100(2008)101101) TIBET-III (ApJ678(2008)1165) AUGER (ICRC 2009) -1 spectrum ~ 2 PeV GAMMA (J.Phys.G35(2008)115201) sr TUNKA (ICRC-Beijing(2011)) 17 -1 10 IceTop (2012-arXiv:1202.3039v1) sec Yakutsk (NewJ.Phys11(2008)065008) KASCADE-Grande (QGSJET II) Nch-N ü Knee in the heavy KASCADE-Grande heavy -2 J(E) (m KASCADE-Grande light+medium 16 10 component ~ 80 PeV 2.5 15 dI/dE x E ü ”Recovery” in the light 10 component ~ 100 PeV 14 10 13 10 13 14 15 16 17 18 19 20 21 10 10 10 10 10 10 10 10 10 ü The position of the p+He Energy (eV/particle) A. Haungs et al. (2013) knee is not clearly determined, discrepancies ) 1.7 ) 1.7 eV all-particle -- PRL 107 light (sep. between He-CNO) eV among experiments (high vs -1 all-particle -1 s s band of systematic uncertainty -1 19 10 heavy (sep. between He-CNO) -1 sr 2506 low altitudes?) sr -2 1487 -2 (m (m 882 2.7 2.7 539 dI/dE x E dI/dE x E 19 10 322 144 ü Uncertainties in the 92 43 195 55 8 18 40 hadronic interaction models light (sep. between CNO-Si) -- PRL 107 light (sep. between CNO-Si) ü Uncertainty in the maximum light (sep. between He-CNO) γ = -3.25 ± 0.05, γ = -2.79 ± 0.08, log (E /eV) = 17.08 ± 0.08 18 10 1 2 10 break, light light (sep. on He) 16.6 16.8 17 17.2 17.4 17.6 17.8 18 18.2 acceleration energy of 16.4 16.6 16.8 17 17.2 17.4 17.6 17.8 18 18.2 18.4 log (E/eV) log (E/eV) 10 10 W.D. Apel et al. (2013) galactic CR.

Ultra High Energy Cosmic Rays – Composition Mixed Composition At the lowest energies log(E/eV)=17.5 an increasing light component till log(E/eV)=18.5, with Auger Collaboration (2019) increasing energy the composition turns heavier. Uncertainties due to the hadronic interaction model assumed.

Caveats on UHE nuclei Composition It is impossible to observe at the Earth a pure heavy nuclei spectrum, even if sources inject only heavy nuclei of a RA, Berezinsky, Grigorieva (2009-2013) fixed specie at the Earth we will observe all secondaries (protons too) produced by photo-disintegration. Critical Lorentz factor The critical Lorentz factor fixes the scale at which photo-disintegration becomes relevant, for heavy nuclei it is almost independent of the nuclei specie