Transcript The Ultra-High Energy Cosmic Rays

The Ultra-High Energy Cosmic
Rays
Introduction
Data
Acceleration and propagation
Numerical Simulations
(Results)
Conclusions
Isola Claudia
Ecole Polytechnique / IAP- Paris
07/05/2003 Valencia
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Introduction
 12 orders of magnitude on the
energy and 30 orders on the
spectrum
 Two cut-off : at the knee and at
the ankle (galactic to extragalactic
component)
 At around 109 eV solar origin
 Between 109 eV and 1015 eV
Galactic origin (SNR)
 Between 1015 eV and 1018 eV
probably Galactic origin but yet
unclear
 Above 1019 eV unknown origin
but very probably extra-galactic
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The showers
They reveal their existence
only by indirect effects
Charged hadronic particles,
electrons and muons are
recorded on the ground
1010-1011 particles on the
ground
99% electrons (red) and
gamma (green) in the MeV
energy range
1% muons (blue) in the GeV
energy range
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Detection:two techniques
• Direct observation of CR primaries is only possible from space
• Such detectors are limited in size - The highest energies require big
surfaces
They are detected on the ground
Water Cherenkov
or scintillation detectors
AGASA
The energy of the primary from the
particle density at 600m from
the shower core; the mass of
the primary from e/
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Fluorescence detector
HiRes
The energy of the primary
from the quantity of light
produced; the mass of primary
from the column depth Xmax
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Data
• Questions: their origin, their nature and
where does the spectrum ends?
• Three quantities: arrival direction,
mass of the primary particle, energy of
the primary particle
• The angular distribution, the chemical
composition, the spectrum
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The angular distribution
• Energy in the
range (1-4) x1019
eV
•
Energy in the
range (4-10) x1019
eV

Energy ≥ 1020 eV
•
•
Doublets
Triplet
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The chemical composition
• Fly’s eye data
o Theoretical prediction for
the iron
 Theoretical prediction
for protons
 Simple two component
model
Transition from « heavy »
to « light » component
Transition from galactic to
extragalactic origin
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The spectrum
AGASA and HIres
are not consistent
at the highest
energies
Does a GZK
cut-off exist?
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The Pierre Auger Project
A combination of a ground array
and one or more fluorescence
detectors
 Effective aperture about 200
times as large as the AGASA array
1700 particle detectors covering
about 3000 Km2
50-100 events per year above 1020
eV
 It is planned to construct one site
in each hemisphere (Argentina and
Utah)
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How can they achieve these
energies?
Top-Down
• Decay from a
supermassive paticle X
• Topological defects or
metastable particles
from inflation
• Final products: ,,
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Bottom-Up
• Statistical acceleration
in a magnetized plasma
• Fermi mechanism
• Power law spectrum
• Supernovae, Hot spot of
radio galaxies, Actif
galactic nuclei
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The GZK cut-off
Physics beyond the Standard Model?
• The nucleons interact with the background
photons
• Threshold energy for a photo-pion reaction
1
  
Eth  3.4 10  3  eV
 10 eV 
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• Energy loss
E p
Ep
• Mean free path
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m

 10%
mp
1
l 
  nCMB
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The cross section for the
photo-pion reaction
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Attenuation lenght
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Few objets as possible sources
Emax
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 B  L 
 EeV

 Z 
 1G  1Kpc 
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In general we cannot achieve the maximal value Emax
because of the energy losses at the source from
synchrotron radiation and photo-pion reaction
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The angular distribution
Two possibilities
1)Many Sources
2)A few sources but a strong magnetic field
This could explain the absence of correlation
between the arrival direction and powerful
astrophysical objects
The isotropy at large scale as a diffusion effect
The clusters at small scales as a magnetic lensing
effects
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The numerical simulation
The purpose is to test theoretical
models by using a numerical code
The code simulates the propagation of
charged particle in an extragalactic
magnetic field by taking into account
the energy losses
The results are strongly affected by the
magnetic field
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The effect of magnetic fields
Deflection
Time delay
Diffusion
1
1/ 2
 E   d 
 ( E , d )  0.8 Z 

 
20
10
Mpc
 10 eV  


3 2
 ( E , d )  1.5  10 Z 


 10 eV 
E
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2
1/ 2
 c 


1
Mpc


 B 


9 
 10 G 
2
B
 d   c   

 
 9  yr
 10Mpc   1Mpc  10 G 
2
1
 ZB 
 Mpc  d

 10 eV  1G 

rL  0.11
E
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They affect the angular distribution, the clusters, the
spectrum and the chemical composition
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The code
• We assume a random turbulent magnetic field
B(k )  k
nB
for 2 / L  k  2 / lc
• We use nB=-11/3 ->Kolmogorov turbulence
• L characterize the coherence length of the
magnetic field
• 5000 trajectories are computed for each magnetic
field realization
• 20 realizations in total
• Each trajectory is followed for a maximal time of
10 Gyr
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Centaurus A (I)
One single source at 3.4 Mpc
B=0.3G
B=0.3G
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Centaurus A (II)
B=0.3G
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B=1G
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The Local SuperCluster
• Distribution of sources
We take a discrete distribution of sources centered at
20 Mpc from Earth and distributed on a sheet of
thickness 3 Mpc and radius 20 Mpc, with the source
density following the profile of the shee
• The auto-correlation function
1
1 if  ij is in same bin as 
N ( ) 
Rij ( ) Rij    

2S ( ) j i
0 otherwise

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Auto-correlation function (I)
100 sources and B=0.05 µG
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100 sources and B=0.3 µG
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Auto-correlation function (II)
5 sources and B=0.3 µG
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10 sources and B=0.3 µG
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The spectrum
10 sources and B=0.3 µG
E-2 injection spectrum
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Sources in a sphere of 40 Mpc
around the Local Supergalactic
center
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Centaurus A (again)
Agasa exposure
function
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Auger exposure function
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Heavy nuclei
The maximal acceleration energy
depends linearly on the charge Ze
The deflection is also proportional
to the charge Ze
Heavy nuclei are attenuated basically by two processes:
photodisintegration on the diffuse photon backgrounds and
creation of e± pairs

R( A,i )
2 
1 d
' '
'

n
(

)
d



(

)
A,i
2  2

2 0 
0
n() is the photon density of the ambient radiation
We include the contributions from three different components:
infra-red, CMB and Universal Radio Background
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The energy loss time
Helium
Silicon
Carbon
Iron
A
Reff , A
; Reff , A
dA

  iR A,i
dt
i
At energies above 1020 eV the
heaviest nuclei start to
disintegrate more quickly
The multi-nucleon emission
becomes more important
compared to one or two
nucleon emission
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Chemical composition
-12
B=10
G
f i (d ) 
ni ( d )
 ni ( d )
B=2x10-8G
i
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The observed spectra
All particle spectrum observed at distances d=1.5,
2.3,3.2,4.8,7.1,10.5,15.5,33.9,50 Mpc (dotted line)
B=10-12G
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B=2x10-8G
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Applications
Anchordoqui et al. Iron nuclei
accelerated in two nearby starbust
galaxies. Hard injection spectrum.
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Ahn et al. UHECR originate from M87,
deflected in a powerful galactic
magnetic field. The two highest
energy events He nuclei.
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Conclusions
• Many questions are still open on the Ultra High
Energy Cosmic Rays
• Their origin (source and acceleration mechanism),
their nature and the end of the spectrum
• We used a numerical code to simulate some possible
scenarios and we were able to ruled out some of the
scenarios proposed
• We plan to implement our code and combine it with
the new statistics coming from Auger
• The very next future years will be crucial to solve
this mistery
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