The footprint of large scale cosmic
structure on the UHECRs (and gamma) distribution
Alessandro Cuoco, Università degli studi di
Napoli Federico II
OtrantoSeptember 1 0
2006
Cuoco A, D’Abrusco R, Longo G, Miele G and Serpico P D, 2006 JCAP. 0601:009
Sky Distribution•For E>4-5 x1019 eV galactic and extragalactic magnetic fields are negligible and charged particles propagate almost rectilinearly: is it possible UHECRs astronomy?
•Energy losses impose that sources must be near (100-200 Mpc) (GZK Cutoff)
•Data from AGASA (50 events) indicate an isotropic distribution (extragalactic origin) except for a small scale clustering (point sources?)…
Energy Spectrum (2)
Cosmic-rayCosmic-rayspectrum spectrum E E2.72.7
The change in slope is generally due to a change in composition and/or The change in slope is generally due to a change in composition and/or a change in astrophysical origin or in the acceleration mechanism… a change in astrophysical origin or in the acceleration mechanism…
Unsolved problem… Unsolved problem…
The spectrum is a Piecewise Power Law:
E-γ = 2.7- 3.0- 2.8
Clearly visible the Kneeat E=1015 eV and the Ankle at E=5x1018 eV
Pierre Auger Observatory
•Auger observatory will use hybrid techniques reducing considerably the sistematics…
•Statistics of events of about 50-100 UHECRs with E>4x1019 eV per year
Southern hemisphere:
MalargüeProvincia dede Mendoza
Argentina
3000 Km2
surface
Large Scale Structures (LSS)
SDSS mesurements have confirmed the results of numerical (hydrodynamical) simulation: Universe has a foam-like Structure rich of voids and filaments along which the galaxies are aligned; The structures start to be homogeneous and isotropic by about 100 Mpc and are visible till the farest explored regions at about 1Gpc
SDSS Galaxies and Structures
1Gpc
Local Universe (200 Mpc)
2MASS Survey
Local Universe (Eq. Coordinates)
Redshift informations
IRAS PSCz Survey
Worst quality respect to 2MASS: • About 15.000 Gal. in PSCz against 1.5 millions of 2MASS, and less sky coverage, but easier to manage
• Better quality in redshifts: spectroscopic redshifts available with negligible errors
• For 2MASS only photometry is available from which photometric redshifts are calculable only with great errors (tipically 20-30%)
Mask and sky distribution of the PSCz sources
Redshift distribution and selection function
Propagation of particles
Energy Loss and Interaction Length (dE/dz)/E for a proton injected at z=0.2 and Energy=100 EeV.
Photopion Production
Bhete-Heitler Pair Production :
P + γCMB p + e+e-
Cosmological Redshift
Combined effect
Energy Loss
z
Mp
c10 E
eV
Interaction Length not always constant, expecially for photopion production due to the tight dependence of cross section on energy: exponential weight and attenuation not truly valid
Model prediction
Propagation
Can we test the hypothesis that the UHECRs come from local sources (the GZK sphere)?
Resulting Resulting UHECRs flux UHECRs flux integrated integrated from a lower from a lower threshold of threshold of 5x105x101919 eV eV
Some assumption is needed:• Sources are numerous and follow the distribution of LSS• GZK is true (quite a consequence…)• Standard propagation and particles (protons)• Magnetic fields not very strong (rectilinear propagation)
Energy Cut DependenceEcut=30 EeV Ecut=50 EeV
Ecut=70 EeV Ecut=90 EeV
Equal area Hammer–Aitoff projections of the smoothed UHECR arrival directions distribution in galactic coordinates obtained for fixed s = 2.0 and
Ecut = 3, 5, 7, 9 × 1019 eV. The smoothing angle is σ = 3◦. The contours enclose 95%, 68%, 38%, 20% of the corresponding distribution.
Method
Comparison cell by cell with a pure uniform
distribution random generated with 2 statistics:
0 50 100 150 200 250 300 350
-75
-50
-25
0
25
50
75
2
k1
Ncell #eventskmeank2meank
How many events to How many events to detect detect
the anisotropies? the anisotropies?
Forecast predictions
About 600 events required to distinguish structures froman isotropic background
Alternatives: top-down,Strong magnetic fields,
Point sources…
Dis
trib
uti
on
s n
orm
alize
d t
o U
nit
Are
a
Reduced 2: r2
2 distribution obtained from 10.000
Montecarlo simulations
AUGER proper sky coverage and exposure included:600 events about4-5 years of AUGER
200 events
400 events
600 events
800 events
Comparison of LSS model andisotropic model distributions
Power Spectrum
m
maC12
2
Strong dipole and quadrupole anisotropy!Strong dipole and quadrupole anisotropy!
Non gaussian Non gaussian features: Power features: Power
spectrum spectrum contains only contains only part of the full part of the full
map information!map information!
Magnetic Fields
In some cases strong deflections up to 50 degrees seems possible making particle astronomy not possible, but intergalactic magnetic fields are very poor known…
Worth testing!
Map of deflection Map of deflection angles from the local angles from the local
clustersclusters
Cumulative Cumulative distribution of distribution of
deflection anglesdeflection angles
From G.Sigl
Gamma Analogy
•Photon interactions at TeV energy give a gamma horizon of the same order size of GZK horizon
•The main interaction is: γγe+e-
pair production with e+e- cascading
Gamma Horizon E-z Gamma Horizon E-z PlanePlane
Critical (Critical (=1) contour=1) contour
: Optical Depth Attenuation = Exp(-
)
Stecker et al. astro-ph/0510449
Satellite and Ground based gamma ray astronomy
CANGAROO III(Australia & Japan)
Spring 20044 telescopes 10
meters ØWoomera, Australia
Windhoek, NamibiaHESS
(Germany & France)
Summer 20024 (16)
telescopes12 meters Ø
Roque delos Muchachos, Canary Islands
MAGICMAGIC(Germany, Spain, Italy)(Germany, Spain, Italy)
Summer 2003Summer 20031 telescope 17 meters 1 telescope 17 meters
ØØMontosa Canyon,Arizona
VERITAS(USA &
England)2005?
7 telescopes10 meters Ø
Air Shower Cerenkov telescopesEnergy Range > 50 GeV
GLAST: to be launched in 2007Energy Range 10 MeV-500 GeV
Wide-angle instruments surveying ~ 2-3
“Threshold” Sens. (1 y)Milagro ~ 2 TeV ~ 0.5 CrabTibet III shower array ~ 3 TeV ~ 1 CrabARGO YBJ 0.5 – 1 TeV ~ 0.5 Crab
Crab signalTibet arrayMilagro ARGO
Ground Based Surveys
Milagro Galactic Plane
• GP diffuse excess clearly visible from l=25° to l=90°• Cygnus Region at l=65°-85° and |b|<3° shows extended excess• FCygnus ~ 2 x Fcrab
Sig
nifi
can
ce
Preliminary
From B.Dingus, Elba06From B.Dingus, Elba06
Cuoco A, Hannestad S, Haugbølle T, Miele G, Serpico
PD & Tu H In Progress…
TeV Gamma SkyTeV Gamma Sky
From Large Scale Structures
TeV angular Power Spectra
Halo Model N-body Simulation
Summary and Conclusions
• In a standard scenario of composition (protons) and propagation of UHECRs GZK limits the sources to be no far than 100 Mpc (the GZK sphere)
• Anisotropies in the arrival distribution and flux of the UHECRs is expected to correlate with the local cosmological structures
• All sky astronomical surveys (2MASS, IRAS) and propagation codes can be used to construct a realistic model of the expected flux anisotropy
• Statistical analysis indicates order few hundreds events are required to distinguish the structures from isotropic background, corresponding to 4-5 years of AUGER
• Given enough statistics the model can be confirmed or ruled out: in both cases valuable conclusion: beginning of UHECRs astronomy in first case or confirmation of non standard feature in the second: strong magnetic fields, atypical sources, exotic particles and propagation…