signatures of protons in uhecr transition from galactic to extragalactic cosmic rays
DESCRIPTION
Signatures of Protons in UHECR Transition from Galactic to Extragalactic Cosmic Rays. Roberto Aloisio. INFN – Laboratori Nazionali del Gran Sasso. Aspen Workshop on Cosmic Rays Physics. Aspen 15-19 April 2007. Chemical Composition. Fly's Eye [Dawson et al. 98]. - PowerPoint PPT PresentationTRANSCRIPT
Signatures of Protons in UHECR Signatures of Protons in UHECR Transition from Galactic to Transition from Galactic to Extragalactic Cosmic RaysExtragalactic Cosmic Rays
Roberto Aloisio Roberto Aloisio INFN – Laboratori Nazionali del Gran Sasso
Aspen Workshop on Cosmic Rays PhysicsAspen Workshop on Cosmic Rays PhysicsAspen 15-19 April 2007
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
Chemical Composition
Hires, HiresMIA, Yakutsk proton composition
Fly’s Eye, Haverah Park, Akeno mixed composition
Proton composition at E>1018 eVnot disfavored by experimental
observations
No conclusive observations at energies E>1018 eV
HiRes elongation rate
The last HiReS analysis confirms the expected Greisen Zatzepin Kuzmin suppression in the flux with E1/2=1019.730.07 eV in perfect agreement with the theoretically predicted value for protons E1/2=1019.72 (Berezinsky & Grigorieva 1988)
The End of the CR Spectrum?
Strong evidences of an astrophysical proton dominated flux at the highest energies
HiR
es collaboration (2007)
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 energy lossesproduce an early onset in the
photo-disintegration flux depletion
Berezinsky, G
rigorieva, Gazizov (2006)
Continuum Energy LossesProtons lose energy but do not disappear.Fluctuations in the pγ interaction start to be important only at E>51019 eV.
Discrete sources the UHECR sources are discretely distributed with a spacing d.
γ > 2 injection power law
Jp=Lp nS
source emissivity
model parameters
Protons propagation in Intergalactic Space
Injection spectrum number of particles injectedat the source per unit time and energy
€
Qinj
=Lp(γ − 2)
EC
2
EEC
⎛
⎝ ⎜
⎞
⎠ ⎟
−γ
Uniform distribution of sources the UHECR sources are continuously distributed with a density n
s.
Jp
unm(E) only redshift energy losses
Jp(E) total energy losses
€
η =J p(E)
J punm (E)
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
Modification Factor
DIP (p + CMB p + e+ + e- ) GZK cut-off (p + CMB N + )
Tiny dependence on the injection spectrum
Proton Dip
Berezinsky et al. (2002-2005)
Best fit values:γ
= 2.7
Jp = O(erg s-1Mpc-3
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 minimum χ2)
λHiRes
= 1.21 λAuger
= 1.26NOTE: λ<1 for on-ground detectors and λ>1 for fluorescence light detectors (Auger energy calibration by the FD)
λAGASA
= 0.90
RobustnessProtons in the Dip come from large distances, up to 103 Mpc. The Dip does not depend on:
inhomogeneity, discreteness of sources source cosmological evolution maximum energy at the source intergalactic magnetic fields (see later…)
The interpretation of the observed Spectrum in terms of protonspair-production losses FAILS if:
the injection spectrum has < 2.4
CaveatsR
A, B
erezinsky, Grigorieva (2007)
heavy nuclei fraction at E>1018 eV larger than 15% (primordial He has n
He/n
H)
Berezinsky et al. (2004)Allard et al. (2005)RA et al. (2006)
Diffusive shock acceleration tipically shows
2.1 2.3
Maximum energy distribution
The maximum acceleration energy is fixed by the geometry of the source and its magnetic field
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)
Kachelriess and Semikoz (2005)RA, Berezinsky, Blasi, Grigorieva, Gazizov (2006)
€
Qinj (E)∝ E−γ
Qinj (E)∝ E−γ−β+1
E < Ec
E > Ec
€
dndE
max
∝ Emax
−β
The IMF effect on the UHE proton spectrum
Magnetic Horizon – Low Energy Steepening The diffusive flux presents a steeping due to proton energy losses and at lower energies an exponential suppression due to the magnetic horizon.
Steepening in the flux at E1018 eV 2nd Knee
no IMFThe DIP survives also with IMF
=2.7
B0=1 nG, lc=1 Mpc
The beginning of 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 cut-off is due to a suppression in the maximal contributing distance its position depends on the IMF.
The low energy behavior (E<1018 eV) depends on the diffusive regime.
RA & Berezinsky (2005)Lemoine (2005)
Combination of the UHECR low energy tail with the HE tail of galactic CR(transition Galactic-ExtraGalactic see later)
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
2K 1018 eV.
with IMF without IMF
=2.7 =2.7
RA
& B
erezinsky (2005)dip scenario
Allard, P
arizot, Olinto (2005-2007)
Galactic and ExtraGalactic II The transition is placed at Etr 31018 eV
The composition is dominated by galactic nuclei at E<Etr ,
by extra-galactic nuclei at E>Etr and by extra-galactic protons at the highest energies
mix comp scenario
High (Emax>1018 eV) maximum energy of galactic CR
Difficult to detect (nuclei before and after the transition)
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
2.1
2.3.
Problems in the Galactic component
Galactic acceleration: Maximum acceleration energy required is very high E
max 1019 eV
Composition: How the gap between Iron knee E
Fe
1017eV and the ankle (1019 eV) is filled
Galactic and ExtraGalactic III ankle scenario
Conclusions
1. Observation of the dip Spectrum in the range 1018 - 1019 eV could represent a signature of the proton interaction with CMB (as the GZK feature).
2. 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 (dip scenario)
discovery of proton interaction with CMBconfirmation of conservative models for Galactic CRchallenge for the acceleration of UHECR (steep injection γ
> 2.4)
Galactic CR (nuclei) at E ≥ 1018 eV (ankle and mixed composition scenario)
challenge for the acceleration of CR in the Galaxy (high Emax)