Transcript Magnetic fields in the local universe and the propagation

Deflections of Ultra High Energy Cosmic
Rays by Intergalactic Magnetic Fields
Based on astro-ph/0310902
with
Klaus Dolag (Dipartimento di Astronomia - Padova
Volker Springel (Max Planck Institute for Astrophysics - Munich)
Igor Tkachev (CERN )
Ultra High Energy Cosmic Rays
Cosmic Rays spectrum
UHECR
Why UHECRs are so interesting?
• Likely, they are of extra-galactic origin
• The acceleration mechanism is unknown and it may involve new physics
• Galactic magnetic field are not expected to deflect them significantly

UHECR may point their sources
if intergalactic magnetic fields are not too strong
Plan of the talk
• Observational situation: UHECR energy spectrum and
angular distribution
• Why, most likely, UHECR come from astrophysical
sources
• How far UHECR can travel; why they are nuclei
• Galactic and intergalactic magnetic fields and their origin
• Reconstructing the IGMF by numerical simulations
• Maps of deflections and general results
• Conclusions
The observational situation
Extensive Air Showers
Ground Arrays
either scintillators or water cherenkov
tanks are deployed on a large region.
The energy of the particle is obtained
by measuring the density of particles
at 600 m from the core of the shower.
Fluorescence
Telescope antennas are used to detect
the isotropic 300-400 nm radiation
emitted by fluorescence from the
nitrogen molecules in the atmosphere.
Energy and composition are measured
from the position of the maximum of the
shower.
EAS experiments
THE PRESENT:
AGASA: ground detector
[acceptance 160 km2 sr , angular resolution ~ 20]
HiRes (monocular): fluorescence detector
[350 km2 sr, angular resolution ~ 1o (binocular)]
THE FUTURE:
AUGER (ground + florescence)
[accep. 7000 km2 sr, res. 1.5o]
EUSO ( fluorescence from the space)
[accep. 35000-70000 km2 sr] 
Energy spectrum: AGASA vs HiRes
• AGASA ~ 900 events with E > 1019 eV
– ~ 100 “
– ~ 15 “
“ 4  1019 eV
“ 1020 eV
• HiRes 2 events with E > 1020 eV (expected 20 by assuming AGASA flux)
Energy spectrum: AGASA vs HiRes
By correcting for possible systematic in the energy determination
Blasi, De Marco & Olinto ‘03
- 15 %
+ 15 %
- discrepancy reduces at ~ 2  between the two experiments
- AGASA is compatible with the GZK cut-off at 2.3 
Hopefully this will be settled by AUGER which combine both techniques !
The composition of UHECR
From the study of EAS development
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 48% of the inclined showers can be photons above 1019 eV
No more than 54% can be Iron above 1019 eV
No more than 50% of the showers can be photons above 4 1019 eV
Neutrinos are excluded (if the cross section is not enhanced)
Similar limits from AGASA
Angular distribution
Galactic plane
Doublets and triplets
Qui ckTime™ e un decompressor e TIFF (Non compresso) sono necessar i per vi suali zzar e q uest'i mmagi ne.
E > 10 20 eV
E > 4  1019 eV
Supergalactic plane
• Fly’s Eye + AGASA: excess of events (4 %) for 0.4 <E < 1.0  1018 eV in the
direction of the galactic center
• For E > 4  1019 eV AGASA and HIRes find no evidence of a large scale anisotropy
UHECR must be extragalactic or be produced in an extended halo !!
No evidence of an excess along the supergalactic plane
The Local Super Cluster (LSC)
~ 10 Mpc
~ 40 Mpc
How far UHECRs may come from ?
The GZK cut-off and the composition of UHECR
PROTONS
Energy losses due to
p +  CMB  n(p) +  0 (+)
p +  CMB  e + e + p




1 E  1
lE (E)  

E x 
lE (E = 4 1019 eV)  1 Gpc
lE (E = 11020 eV)  20  50 Mpc
The GZK cut-off
Qui ckTime™ e un decompressor e TIFF (Non compresso) sono necessari per visuali zzar e q uest'immag ine.
AGASA ONLY !!
may be due to a systematics
or
to a local excess of sources
(top-down models)
or
To a local confinement of UHECRs
due to strong magnetic fields
in the LSC
NEUTRONS
They decay after travelling a distance
 E 
E
Rn   n
 1  20
 Mpc
10 eV 
mn
COMPOSITE NUCLEI
(Less interesting in this context since they smaller Larmor radius)

Same energy losses as for the proton + photodisintegration
At 1020 eV they cannot travel more than ~ 10 Mpc
PHOTONS
(electromagnetic showers)
 +  bg  e  + e _
e +  bg  e + 
 +  bg  e  + e _

(NO MAGNETIC FIELDS)

Protheroe & Johnson ‘96
The large scale isotropy is not a problem for protons
For E ≤ 5  1019 eV
lE ≥ 1 Gpc
The flux is dominated by far source 
No expected excess along the Supergalatic plane !
The some doesn’t hold for photons since
lE() < 10 Mpc
A large component of UHECRs is composed by protons or nuclei
Why UHECR sources are astrophysical:
• The spectrum of CR is practically a single power law
• There are evidence for small scale clustering
• Hints for a correlation between UHECR and BL-Lacs
Small scale clustering
AGASA: 92 events with E > 41019 eV - 8 doublets - 2 triplets
Chance probability to reproduce them with a homogeneous distribution of sources:
Pchance < 1 %
AGASA + Yakutsk [Tiniakov & Tkachev, 01]
Pchance < 10 -5 (different treatment of triplets)
SIGNIFICANT INDICATION THAT SOURCES MAY BE POINT LIKE
The BL-Lacs - UHECR connection
Tinyakov & Tkachev astro-ph/0102476
•
•
Chance probability to reproduce that with uniform sources P < 10-4
– From a sample of 22 BL-Lacs 5 coincide with UHECR arr.dir.
Crossing BL-Lacs catalogue with EGRET sources gives 12 BL-Lacs
– 4 UHECR source candidates are among these 12 !
– The remaining 10 correlate with UHECR after correcting for the galactic
field ( if Q = + 1). Gobunov et al. astro-ph/0204360
Galactic and intergalactic magnetic fields
Observations
Galactic magnetic field

Breg  110 G
lc  1 kpc
Btur  110 G
lc  10  100 pc

Nuclei Deflections in the Milky Way
 E 10- 6 G 
E
rL (E) =
 10 kpc 19

 >> L C small defl. regime
10 eV  B 
ZeB
1019 eV   B  L 
L
o
 
 8 Z 

 

-6
rL (E)
 E  2 10 G 1 kpc

rms
regular field
1019 eV B  L 1/2  L C 1/2
 1.5 Z 


 

-6
 E 2 10 G 1 kpc 50 pc
o
random field
– the regular field give rise to undetectable deflections at 1020 eV
the galactic disk signature should be visible if sources are galactic and UHECR
are not heavy nuclei
– Sizeable deflections at 1019 eV which, however, can be disentangled !
[See e.g. Tinyakov & Tkachev ‘03]
– The random field produce ~ 1 o deflections
Magnetic fields in galaxy clusters
I X  f(ne, n )
Coma cl. : visible
X-rays

Synchrotron emission
X-ray non-thermal emissions
radio
IS  ne B perp
I X (n e, n )
 B = 0.1  1 G
2

Faraday Rotation Measurments (RMs)
Coma RMs

RM  2
obs
 l 2
= 812  ne (l)   B(l) dl
obs 
0
L
 BC   1  10 G
rad m-2
lCoh = 10  100 kpc
MF in the Inter-Galactic Medium (IGM)
Only upper limits are available based on the Faraday Rotation Measurements
of Quasars’ radio emission at cosmological distance (z ~ 1)
LC
First limit by Kronberg’94 who, however assumed ne = const. and b = 1 !!
Then Blasi, Burles and Olinto, `99 accounted for ne inhomogen. in Ly-alpha clouds
 9

BH -1  10
G


 9
G
 B 50 Mpc  6  10
 8

G

 B1 Mpc  10
UHECR deflections may be large if these limits are saturated !
Possible origin of magnetic fields
1.
Primordial seed + dynamo amplification in galaxies + pollution of
the IGM by galactic winds
2.
Ejection from AGN’s + amplification during the cluster accrection
3.
Battery + amplification during the cluster accrection
4.
Primordial origin ( phase transitions in the early universe,
generation at neutrino decoupling, the inflation) + amplification
during the cluster accrection
[For a review see D.G. & Rubinstein ‘01]
MHD SIMULATIONS FAVOUR 2-4
MSPH simulations in galaxy clusters
MSPH: Magnetic Smooth Particle Hydrodynamics
[Dolag, Bartelmann & Lesch, astro-ph/0109541, 0202272]
N-body simulations of DM + gas hydrodynamics (SPH) + MHD
The initial DM fluctuations are fixed
at z = 20 compatibly with CDM
DM “particle”
gas “particle” + magnetic field
Smoothing length
.
Magnetic field evolution
The MF is evolved starting from a seed (AGNs, battery or primordial)
The electric conductivity of the IGM is practically infinite
The magnetic field is amplified by:
ADIABATIC COMPRESSION:
B = const  B R  
-2
Cosmologically this implies
:
2/3
gas
B(z)  (1 + z)2
MHD amplification by shear flows:
B
=   v  B + Bin
t

The memory of the initial power spectrum is erased !

Simulated RMs
low :
B0  0.5  10- 12 G
m edium: B0  2.5  10- 12 G
high:

• RMs profile is reproduced
for

B0  1  10- 11 G
B0  B(zin ) (1 + zin )2
5  10- 13  B0  1  10 - 11 G
Reconstructing the magnetic structure
of the local universe
Basic assumption: magnetic fields in galaxy clusters are originated by
a uniform primordial seed generated at high redshift
Motivations: - this is easier to be implemented numerically
- it should give the largest deflections of UHECRs
Approach:
- we combine MSPH simulations previously performed for galaxy
clusters with constrained simulations of the local universe LSS
Simulations of IGMF in the local universe
REQUIREMENTS
•
We need a realistic 3D simulation of the LSS such that the size and position of
simulated structures (clusters) coincide with those observed on the sky.
•
We need to know the observer position in the magnetized structure.
•
The size of the simulation volume has to be > 50 Mpc such to enclose
the Local Super Cluster (LSC)
the GZK sphere
Constrained simulations
Initial conditions (density fluctuations) are chosen randomly from a Gaussian field
with a power spectrum compatible with CMD cosmology but constrained so that
the smoothed density field coincide with that observed.
Simulations of this kind have been performed, successfully, to simulate the local flow
[Mathis, Springel, White et al. , astro-ph/0111099]
OUR SIMULATION
CONSTRAINED SIMULATION OF DM AND GAS + MSPH
• Simulation volume: 80/h Mpc = 107/h70 Mpc
gas mass resolution 5 x 108 Msun ; max spatial resolution ~ 10 kpc
• Initial redshift: z = 60
• Initial magnetic field: B0 = 1 x 10 -11 G
lC = ∞
We use IRAS 1.2 galaxy catalogue to constrain initial conditions
Results of the MHD simulation
•
CLUSTERS: Bc = 1 - 10 G - OK with RMs LC << L: no memory of the initial field structure
•
High density FILAMENTS: Bc = 10-2 - 10-3 G ; (no memory)
•
Low density FILAMENTS: Bc = 10-4 G ; field aligned with the fil. axis
RAY TRACING
Smoothed gas particle
• We sum deflections produced by every gas particle
• If  > 5 o trajectories are ignored
• Proton energy: E = 4  1019 eV 
Energy losses can be neglected up to ~ 1 Gpc
( deflections at larger energies can only be smaller !! )
Deflections up to 107 Mpc
What we learn from these maps ?
• UHECR cannot be isotropized !!
• Large deflections are produced only in gal. clusters which
cover only a tiny fraction of the sky
• Filaments produce small deflections (< 2o)
• At large distances the bulk of deflections is due to
filaments
• No observable deflections in the local region and in the
voids

Sky fraction covered by observable deflections

For d > 50 Mpc
A(
th,d)  (d /d0 )
  0.8
Self-similarity is consistent with a uniform density of deflectors (filaments)
For d   a large number of filaments is crossed, each time giving a random 
   0.5
There is a considerable fraction of the sky where correlation with source is preserved !!
OK with small scale clustering and UHECR-BL Lacs correlation
The effect of a possible unclustered field
To be expected only if the field is of primordial origin
1/2
1/2
19








4 10 eV
B
L
lC
  0.2o Z 
 - 11 
 

E

10 G 1 Gpc 1 Mpc
 Observable only if lC > 20 Mpc
Quite hard to get unless the field is primordial and generated during the inflation
Conclusions
• We performed the first simulation of the magnetic structure in the local
universe
• The simulation reproduce MF observed in galaxy clusters and give
new hints on the MF in less dense regions like filaments
• According to our results the LSC is weakly magnetized
• UHE protons undergoes large deflections only when they pass trough
clusters and ~ 1o deflections in filaments
• Our results are compatible with small scale clustering and
UHECR-BL Lacs correlation
CHARGE PARTICLE ASTRONOMY SHOULD BE POSSIBLE