Propagation and Composition of Propagation and Composition of Ultra High Energy Cosmic RaysUltra High Energy Cosmic Rays

Roberto Aloisio Roberto Aloisio INFN – Laboratori Nazionali del Gran Sasso

Challenges in Particle Astrophysics6th Rencotres du Vientnam

Hanoi 6-12 August 2006

The spectrum of CR's

Knee2nd Knee Ankle

GZK

ns 10-5 Mpc-3

E 1020eV

4 1019eV E 1020 eV

The first fuzzy picture of the UHECR sky

Small angle clustering gives indications about the source

number densitynS

As nS decreases (fixed flux)

sources become brighterwith an increase in

clustering probability40 sources within 100 Mpc

(~20 degrees between sources)

Using many realizations (MC)

Blasi & De Marco (2003)Kachelriess & Semikoz (2004)

At most one source in the angular bin of 3 degrees! The sources should have been seen in particular

at 1020 eV

Correlation???

if no correlations found

Bursting Sources???or

High Magnetic Fields???or

Exotic Models???

CAVEAT

Recently Blasi, De Marco and Olinto founda 5σ inconsistency between the spectrum and the small scale anisotropies measured by AGASA.

Chemical Composition

Hires, HiresMIA, Yakutsk proton composition

Fly’s Eye, Haverah Park, Akeno mixed composition

Hires elongation rateProton composition at E>1018 eVnot disfavored by experimental

observations

Fly's Eye [Dawson et al. 98]

Transition from heavy (at 1017.5 eV) to light composition (at ~1019 eV)

Haverah Park [Ave et al. 2001]

No more than 54% can be Iron above 1019 eVNo more than 50% can be photons above 4 1019 eV

Similar limits from AGASASimilar limits from AGASA

No conclusive observations at energies E>1018 eV

Pair production

p p e+ e-

Photopion production

p p 0 n

100 Mpc

1000 Mpc

log10

[ E (eV)]

log 10

[ l at

t (M

pc)]

Universe size

UHE Proton energy losses

CMBpro

tons

Adiabatic lossesUniverse expansion

UHE Nuclei energy losses Pair production

A e+ e-

Universe size

Iron

Universe size

helium

Photodisintegration

A (A-1) N (A-2) 2N

Depletion of the flux Iron E 20 eV Helium E eV

Pair production has no particular effect on the flux

Continuum Energy Losses

Protons lose energy but do not disappear.Fluctuations in the pγ interaction start to be important only at E>5 1019 eV.

Discrete sources the UHECR sources are discretely distributed with a spacing d.

γg > 2 injection power law

Lp source luminosity

ns (d)

source density (spacing)

model parameters

Injection spectrum number of particles injectedat the source per unit time and energy

Jp

unm(E) only redshift energy lossesJ

p(E) total energy losses

Modification factor

Blasi, D

e Marco, O

linto (2003)Protons propagation in Intergalactic Space

Uniform distribution of sources the UHECR sources are continuously distributed with a density n

s.

The energy losses suffered by protons leave their imprint on the spectrum

CMBp+ p + e+ + e–DIP GZK CMBp+ N +

sources distribution (mainly GZK) injection spectrum (mainly DIP) way of propagation (magnetic fileds)

These features depend on

UHECR proton spectrum

Akeno AGASA

Proton DipExperimental evidence of the Dip

Berezinsky et al. (2002-2005)

Best fit values:γ

g = 2.7

<Lp> = 4 erg/s

ns = 3 -5 Mpc-3

Robustness and Caveats

The interpretation of the DIP in terms of protons pair-production FAILS if:

the injection spectrum has g< 2.4

RA

, Berezinsky, G

rigorieva (2006)

heavy nuclei fraction at E>1018 eV larger than 15% (primordial He

has nHe

/nH)

Berezinsky et al. (2004)Allard et al. (2005)RA et al. (2006)

Protons in the Dip come from large distances, up to 103 Mpc. The Dip does not depend on:

inhomogeneity, discreteness of sources maximum energy at the source intergalactic magnetic fields (see later...)

Maximum energy distribution

The maximum acceleration energy is fixed by the geometry of the source and its magnetic field

g 2.0 2.2Diffusive shock acceleration tipically shows

the overall UHECR generation rate has a steepening at some energy Ec

(minimal Emax

O(1018 eV))

If the sources are distributed over Emax

: (β ≈ 1.5)

Q inj E E g

Q inj E E g 1

E Ec

E EcKachelriess and Semikoz (2005)RA, Berezinsky, Blasi, Grigorieva, Gazizov. (2006)

Energy calibration by the DipDifferent experiments show different systematic in energy determination

Calibrating the energy through the Dip gives an energy shift E→ λE (fixed by χ2)

λAGASA

= 0.90 λHiRes

= 1.21 λAuger

= 1.26

NOTE: λ<1 for on-ground detectors and λ>1 for fluorescence light detectors (Auger energy calibration by the FD)

Very poor experimental evidences

Faraday rotation

Synchrotron and ICS emission

Magnetic field concentrated around sources, i.e. in Large Scale Structures

No appreciable field in most part of theuniverse volume

Large Scale Structures are characterizedby magnetic field produced from compression and twisting of the primordial field

Voids are characterized by an appreciablemagnetic field

Astrophysical sources

Cosmological origin

Effect of IMF on UHECR

deflection diffusion isotropization

Intergalactic Magnetic Fields

Numerical simulations

Puzzling results by different groups

Numerical determination of the IMF is based on LSS and MHD simulations

Sigl, Miniati & Ensslin use anunconstrained simulation

putting the observer * close to a cluster

Dolag, Grasso, Springel & Tkachev use constrained simulations, being able

to reproduce the local Universe

High B (100 nG in filaments and 1 nG in voids)

High deflection angles: up to 20° at 1020 eV

UHECR astronomy nearly impossible

Low B (0.1 nG in filaments and 0.01 nG in voids)

Low deflection angles: < 1° at 4 1019 eV

UHECR astronomy is allowed

The IMF effect on the UHE proton spectrum

B0 1nG , lc 1Mpc

Steepening in the flux at E1018 eV 2nd Knee

no IMFThe DIP survives also with IMF

g=2.7

Magnetic Horizon – Low Energy Steepening The diffusive flux presents an exponential suppression at low energy and a

steepening at larger energies.

The low energy cut-off is due to a suppression in the maximal contributing distance (magnetic horizon), its position depends on the IMF.

The steepening is independent of the IMF, it depends only on the proton energy losses and coincides with the observed 2nd Knee.

The low energy behavior (E<1018 eV) depends on the diffusive regime.RA & Berezinsky (2005)

Lemoine (2005)

Galactic Cosmic Rays

Rigidity models can be rigidity-confinement models or rigidity-acceleration models.

The energy of spectrum bending (knee) for nucleus Z is Ez = Z Ep, where Ep 3×1015 eV is the proton knee. For Iron E

Fe 8eV.

Ep

proton

EHe

helium

?

Kascade data 2005:different results with different Monte Carlo

approaches in data reconstruction. Rigidity scenario not confirmed.

Kascade data Kascade data 2003:seem to confirm the rigidity

model.

BUT

Galactic and ExtraGalactic IThe Galactic CR spectrum ends in the energy range 1017 eV, 1018 eV.

2nd Knee appears naturally in the extragalactic proton spectrum as the steepening energy corresponding to the transition from adiabatic energy losses to pair production energy losses. This energy is universal for all propagation modes (rectilinear or diffusive): E

2K1018 eV.

with IMF without IMF

g=2.7

g=2.7

RA

& B

erezinsky (2005)

Traditionally (since 70s) the transition Galactic-ExtraGalactic CR was placed at the ankle ( 1019 eV).

In this context ExtraGalactic protons start to dominate the spectrum only at the ankle energy with a more conservative injection spectrum

g 2.0

2.2.

Problems for the Galactic component

Galactic acceleration: Maximum acceleration energy required is very high E

max1019 eV

Composition: How the gap between Iron knee E

Fe1017eV and the ankle (1019 eV)

is filled

Galactic and ExtraGalactic II

Conclusions

2. Is there a dip? Spectrum in the range 1018 - 1019 eV could be a signature of proton interaction with CMB (as the GZK feature).

3. Where is the transition Galactic-ExtraGalactic CRs? Precise determination of the mass composition in the energy range 1018 - 1019 eV.

ExtraGalactic CR (protons) at E ≥ 1018 eV discovery of proton interaction with CMB

confirmation of conservative models for Galactic CRmodels for the acceleration of UHECR with γ

g > 2.4

Galactic CR (nuclei) at E ≥ 1018 eV

challenge for the acceleration of CR in the Galaxy (Emax

EFe

)

1. Is there the GZK feature? Auger will soon clarify this point. First results seem to favor the GZK picture.