Ultra-High Energy Cosmic Rays (III)

Transcription

1 Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Ultra-High Energy Cosmic Rays (III) Ralph Engel Forschungszentrum Karlsruhe & Karlsruhe Institute of Technology

2 Outline Brief overview (experimental results) UHECR sources & injection spectra Propagation: energy loss processes Model predictions for fluxes Propagation: magnetic fields Physics of extensive air showers (composition)

3 Propagation: role of magnetic fields Part 1: Galactic fields

4 Arrival direction distribution E > 2 ev +6 o +3 o 24 h GC h 12 h!3 o AGASA: 5 doublets, 1 triplet for Δθ < 2.5, E > 4x 19 ev HiRes: no confirmation (different statistics & systematics) > 19 ev!6 o

5 AGASA auto-correlation function + Δb E > 19 ev E > ev E > 19.7 ev - Δl ~3.5 σ - Z + (Cosmic rays from outer Galaxy region) ξ( l, b) = dldb ρ(l,b) ρ(l l,b b) (Teshima et al., ICRC21) ρ(l,b) = i [ 1 exp (l l i) 2 2πσ l,i σ b,i σ 2 l,i (b b i) 2 σ 2 b,i ]

6 Possible interpretation of correlation Source with continuous injection spectrum Source NGP z F E >E 1 2 l= y l=27 E 1 v B E 2 x b 1 b 2 > l=18 Observer l=9 (Alvarez-Muniz et al., ApJ 22)

7 Magnetic fields in our Galaxy (I) Rotation measure of pulsars projected onto Galactic plane (open/filled symbols: negative/positive RM) (Han et al., 25)

8 Magnetic fields in our Galaxy (II) halo disk Galactic Center Sun 3 pc 15 kpc 2-4 kpc Disk field: bisymmetrical spiral 8 kpc Bðr jj ; Þ ¼ B Halo field: A dynamo B x ¼ 3l G sin cos cos =r 3 B y ¼ 3l G sin cos sin =r 3 ; B z ¼ l G ð1 3 sin 2 Þ=r 3 ; R r jj ð jj cos ln r jj r Þ ¼ ¼ ¼

9 Map of expected deflection angles Deflection E > 4x 19 ev Galactic coordinates (Stanev, ApJ 479, 1997) -6 strong deflection near Galactic Center

10 Correlation studies 2.14E+3 Deflection angle 3.92E+3 1.6E+3 1.6E E E+ -5!l (deg) E E E E+ -5!l (deg) E E E+2!b (deg) E+ -5!l (deg) 5!b (deg) E+3 3.2E E+3 1.6E+3 "5 7.94E+2 " " "5!l (deg) E E E E+2 Point source at 2 kpc 1.3E E E+3 (Alvarez-Muniz et al., ApJ 22) E E+ (+4) b=-15 (+3) b= (+2) b=15 (+) 3 2 l=157.5 b= E+ 2.8E+3!b (deg)!b (deg) deflection!" (deg.) 5!b (deg)!b (deg) 6 19 b= energy log( E/eV ) Galactic mag. field can be used for cosmic ray charge measurement 21

11 Galactic center as cosmic ray source? Significance map of AGASA data E > 18 ev ~ 4σ excess Galactic center outside FOV ~ 4σ deficit (AGASA, APP, 1999)

12 Energy dependence of anisotropy Statistical significance: AGASA P chance = exp( K) Data set: 114, events Dipole amplitude: 4% for E > 18 ev Cannot be checked by HiRes (aperture, statistics) (AGASA, APP, 1999)

13 Neutron point source model Neutron decay length: AGASA Full Sky d dec 9kpc ( E ) 18 ev Anisotropy (%) Field-of-view limitation Proton gyro-radius ~.4 kpc Galactic Center: TeV γ-ray source (H.E.S.S.) hadron accelerator neutron point source log(e/ev) (Medina-Tanco & Watson ICRC 21; Bossa et al., JPG29, 23)

14 Auger data: Galactic Center AGASA SUGAR Auger 26: much higher statistics AGASA local excess excluded limit on neutron point source N Significance (Auger, 26) Z Emax E min Φ source de ξ.8km 2 yr 1 (95% CL)

15 Comparison in numbers AGASA event numbers (2 circular region): n obs /n exp = 56/413.6 = 1.22 ±.5, Auger event numbers (same region): E min [ev] E max [ev] n obs /n exp / = 1.1 ±.2(stat) ±.1(syst) / =.98 ±.2(stat) ±.1(syst) (Auger, 26) e / =.99 ±.3(stat) ±.1(syst)

16 Propagation: role of magnetic fields Part 2: extra-galactic fields

17 Propagation in inter-galactic mag. field

18 Deflection angle distribution 7 dn/d!, sr Mpc 8 Mpc 32 Mpc B = 1nG lcoh = kpc 128 Mpc Protons, E = 21.5 ev Simulation of propagation with energy loss Turbulent mag. field with Kolmogorov spectrum arrival angle! arr, deg 512 Mpc Flux isotropic after propagation over GZK distance (Stanev et al., PRD62, 2)

19 Proton propagation (magnetic fields) Diffusion theory ( ) B 2 ( ) E 2 ( )( ) t del yr Z 2 lcoh D 2 1nG 2 ev 1Mpc Mpc ) 1/2 ( α rms 3.5 Z ( B )( E ) 1 ( lcoh 1nG 2 ev 1Mpc (Achterberg et al., 1999) ) D 1/2 Mpc

20 Magnetic fields in structured universe Clusters mag. field strength Voids Unconstrained simulation of large scale structure (z=6, Gaussian fluctuations) Large deflection in and near clusters and filaments (Sigl, Miniati, Enßlin, 25)

21 Cosmological simulation with ideal MHD Dolag et al., 24: constrained structure formation simulation (Gadget 2) MHD simulation for mag. field amplification Initial (z=2) dark matter distribution constrained by observed galaxy distribution Saturation Seed field: B = B(z ini )(1 + z ini ) G Shear Shear + Turbulence + Major Merger relative baryon density

22 Total deflection angle Virgo Coma Centaurus Hydra A3627 Perseus Pavo Deflection of protons E = 4x 19 ev, 1 Mpc distance, no energy loss (Dolag et al. 24)

23 Cosmic ray composition

24 Extensive air showers: overview X shower size N e 12 km 2 7 X max α ln(e /A) N e(max) α E Z h ρ air dl = X(h) 6 km slant depth (g/cm 2 ) 3 12 sea level vertical shower sea level zenith angle of 3 deg. Shower particles mainly e ±, γ 8-95% of initial energy converted to ionization energy Up to 11 particles

25 Proton-initiated air shower

26 Iron-initiated air shower

27 Photon-initiated air shower

28 Heitler s model for em. showers depth X E After n generations: λ int X = n λ int N part = 2 n = 2 X/λint E part = E 2 X/λ int Assumption: cascade stops at E part E crit N max = E /E crit X max λ int ln(e /E crit )

29 Muon production in hadronic showers E Primary particle proton E /n tot n tot = n ch+ n neut π decay immediately 2 tot E /(n ) ( n ch ) 2 π ± initiate new cascades E /(n ) tot n (n ch ) n N µ = ( E E dec ) α Assumptions: cascade stops at E part = E dec each hadron produces one muon α = lnn ch lnn tot

30 Superposition model Characteristics of proton showers: N max = E /E crit X max λ int ln(e ) N µ = ( E E dec ) α Assumption: Nucleus with mass A and total energy E can be replaced by A nucleons of energy En = E/A N A max = AE n /E crit = E /E crit X A max λ int ln(e n ) λ int ln(e /A) N A µ = A ( En E dec = A 1 α N µ ) α

31 Composition analysis using shower profiles ) 9 Number of charged particles (x proton, E= Auger shower ev 6 Height a.s.l. (m) 4 2 ) 9 Number of charged particles (x !-ray, E= Auger shower ev 6 Height a.s.l. (m) Slant depth (g/cm ) Slant depth (g/cm ) ) Height a.s.l. (m) 4 2 Example: event measured by Auger Collab. (ICRC 23) Number of charged particles (x iron, E= Auger shower ev Energy well determined Primary particle type: mean and fluctuations of shower depth of maximum Slant depth (g/cm )

32 X max (g/cm 2 ) 12 1 Fly s Eye HiRes-MIA HiRes 24 Yakutsk 1993 Yakutsk 21 CASA-BLANCA gamma with preshower Interpretation strongly model dependent HEGRA-AIROBICC SPASE-VULCAN DICE TUNKA gamma proton 6 Mean depth of 5 shower maximum 4 iron DPMJET 2.55 nexus 2 QGSJET 1 SIBYLL 2.1 nexus E lab (ev)

33 Electron-muon number correlation Model prediction for Ne-Nμ Very good agreement with expectations from superposition model Number of muons N µ (E µ >1 GeV) QGSJet, proton iron 14 ev 15 ev 16 ev Shower size N e (E e >1 MeV) 18 ev 17 ev

34 Hybrid measurement: HiRes-MIA HiRes (prototype): shower profile MIA: muon density at ground Phys.Rev.Lett. 84(2)4276 Shower profile: composition changes to protons Muon density: very heavy, iron-like composition

35 Example: Auger stereo-hybrid event LDF fit Signal [VEM] r [km]

36 Hybrid measurement: A n g l e Pierre Auger Observatory S h o w e r p l a n e 29th International Cosmic Ray Conference Pune (25), 1 6 First Estimate of the Primary Cosmic Ray Energy Spectrum above 3 EeV from the Pierre Auger Observatory The Pierre Auger Collaboration Presenter: P. Sommers (sommers@physics.utah.edu) F l y ' s E y e w i t h activated phototubes Measurements of air showers are accumulating at an increasing rate while construction proceeds at the Pierre Auger Observatory. Although the southern site is only half complete, the cumulative exposure is already similar to those achieved by the largest forerunner experiments. A measurement of the cosmic ray energy spectrum in the southern sky is reported here. The methods are simple and robust, exploiting the combination of fluorescence detector (FD) and surface detector (SD). The methods do not rely on detailed numerical simulation or any assumption about the chemical composition. I m p a c t p o i n t C e r e n k o v t a n k s Simulation: particles at ground would correspond to 25% higher shower energy than measured shower profile P. Sommers et al. astro-ph/5715 Caution: within current systematic uncertainty

37 Equivalent c.m. energy s pp (GeV) ) 1.5 sec -1 sr -1 ev ATIC PROTON RUNJOB 3 4 KASCADE (QGSJET 1) KASCADE (SIBYLL 2.1) MSU Akeno 5 HiRes-MIA HiRes I HiRes II AGASA Auger 25 6 J(E) (m Scaled flux E fixed target (p-a) HERA (!-p) RHIC (p-p) Tevatron (p-p) LHC (p-p) LHC (C-C) Energy (ev/particle) Statistical errors only!

38 Summary / Outline Experimental results UHECR sources & injection spectra Propagation: energy loss processes Model predictions for fluxes Propagation: magnetic fields Physics of extensive air showers (composition) Little known so far -- very exciting times ahead!