angela v. olinto the university of chicago anisotropies at the highest energies
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Angela V. OlintoThe University of Chicago
Anisotropies at the Highest Energies
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CMB vs UHECR Anisotropies
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1. UHECRS are Charged, should ‘point’ above ~ 10 EeV Z
Halo B?
Extra-galactic B?B < nG
weak deflection
RL = kpc Z-1 (E / EeV) (B / G)-1
RL = Mpc Z-1 (E / EeV) (B / nG)-1
where EeV=1018 eV
kpc
10 kpc
strong deflection
Milky wayB ~ G
E > 1019eV
E < 1018eV
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2. Cosmic RaySpectrum is Power law
Non-thermal Phenomena
Extreme Accelerators
Emax > 1020 eV
E-2.7
E-3.1
12 orders of magnitude
32 o
rder
s of
mag
nit
ud
e
RH
IC
Teva
tron
LH
C
Ankle (1 particle /km2 yr)
Ecm = PeV (Euhecr /ZeV)1/2 (2A)1/2
Swordy ‘02
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3. ‘Pointing” UHECRS E ~ 100s TeV CM
ankle
knee
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E = Ze B L
10% efficiency
1020eV Protons1020eV Iron
Log B(G)
Log L(cm)
others
GRBs
LHC
4. No known mechanism acceleration nor clear
Counterparts
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Cosmologically Meaningful TerminationGZK CutoffGreisen, Zatsepin, Kuzmin
1966
p+cmb + p + 0
n + +
Proton Horizon~1020 eV
5. Extragalactic propagation GZK imprint
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Attenuation length
e+e–
Interaction length
Attenuation length
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6. GZK Effect Anisotropies
Spectral Feature
+ LSS Anisotropic Sky Distribution
Charged Particle Astronomy!!!
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GZK Horizon - Protons
Allard, AO, Parizot 08
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Horizons:
Gpc
1019 eV ~ 1 Gpc
1020 eV < 100 Mpc
100 Mpc
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Inhomogeneous Galaxy Distribution
2MASS - Two Micron All Sky Survey
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Horizons:
Gpc
1019 eV ~ 1 Gpc
1020 eV < 100 Mpc
100 Mpc
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The Pierre Auger Observatoryof Ultra-High Energy Cosmic
Rays
Southern site
3 000 km2
Northern site20 000 km2
ArgentinaAustraliaBrasilBolivia*Croatia*Czech Rep.France Germany ItalyMexicoNetherlands
> 400 PhD scientists from > 70 Institutions and 18 countries
PolandPortugalSlovenia
Spain UKUSAVietnam*
*Associate Countries
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18 Countries 70 Institutions, > 400 scientists
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Many Candidates to win the World Cup 2010!!!
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1660 tanks = 3,000 km2
Surface Array4 Fluorescence Detector SitesScience Data since 2004 Completed in June 2008
Auger South
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surface detector
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tanks aligned seen from Los Leones
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4 Fluorescence Detector Sites
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1st - 4 Fold Hybrid Event
20 May 2007 E ~ 1019 eV
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Statistical 14% @ 50 EeVSystematic 22%
Less than 1 degree @ 50 EeV
> ~1 degree “astronomy” @ 50 EeV
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Observed Spectrum showns GZK GZK
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Unclear Trend in Observed Composition
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Anisotropy Analysis
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Auger Anisotropy Result 2007Highest energy cosmic rays have an anisotropic distribution!
Correlation with z < 0.018 AGNs in
the 12th Véron-Cetty/Véron catalogue
The observed correlationdid not identify the CR sources
but established anisotropy at 99% c.l.
Data: 27 events above 57 EeV from 1/1/2004 to 31/8/2007 (exposure of 8890 km2 sr y)
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Auger 2007 Anisotropy ResultAuger 2007 Anisotropy Result
* - VCV AGN catalogue 3.2o- 27 highest energy event
Blue shades: equal integrated exposure
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Challenges of the Analysis:
1. LOW STATISTICS!!!!!
2. Choice of catalogs
Véron-Cetty / Véron, 12th Edition, 2006
“This catalogue should not be used for any statistical analysis as it is not complete in any sense, except that it is, we hope, a complete survey of the literature.”
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Significance of the anisotropy result
Not an “AGN correlation” result!1st step: search for correlations between arrival directions of
UHECR and various source catalogues
Very large “raw significance” found w/ 12th VCV catalogue of AGNs
Did not seem to be fluctuation
Auger collaboration set up a prescription for future data
Even after generous penalty factors for a posteriori searches and scanning of parameter space
(data from 2004/01/01 to 2006/05/27)
12 out of 15 events E > 56 EeV closer than 3.1° from an AGN in 12th VCV with z ≤ 0.018 (D ≤ 75 Mpc)
Most significant a posteriori “correlation signal”:
3.2 expected from isotropic distribution
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Exploratory scan (Period I): 1 Jan 2004-27 May 2006Integrated exposure: 4390 km2 sr y
Scan in ψ(angular distance between CR and AGN), Eth (CR energy), zmax (AGN distance)
Scan implemented to find the minimum of the binomial probability P that ≥ k out of N events correlate by chance
Minimum value of P: Eth = 56 EeV ψ = 3.1o zmax = 0.01812/15 events correlate (3.2 expected by chance, p(z, ψ) = 0.21)
Scan proper penalization difficult to calculate Prescription adopted
p(z, ψ)= exposure-weighted chanceprobability for a CR to fall within ψ of the sources
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≤ 3.1°z ≤ 0.018
(D ≤ 75 Mpc)E ≥ 56 EeV
3 Parameter Scan3 Parameter Scan
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correlation is most significant above E = 56 EeV where the CR flux drops…
Energy Threshold makes senseEnergy Threshold makes sense
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Significance of the anisotropy result
2nd step: predefine a region in the sky of excess CR flux & test if next UHECRs come from this region
Independent data set, prescribed parameters, unambiguous significance
21% chance from isotropic distribution
Nearby VCV AGN 21% sky
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Independent data (Period II): 27/5/2006-31/8/2008Integrated exposure: 4500 km2 sr y
A-priori fixed parameters: Eth = 56 EeV ψ = 3.1o zmax = 0.018
8/13 events correlate (2.7 expected by chance)
Probability to happen by chance from an isotropic flux: P≈1.7 10-3
Test built to have 1% probability to incorrectly reject isotropy.
Test passed: 99% c.l. anisotropy
Note: it does not show that VCV AGN are UHECR sources!
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First 27 events
Exploratory scan – 12/15 events correlated (3.2 expected)Prescription passed when 8/13 correlated (2.7 expected)
NOTE: original set became 14 events when reconstructed with new energy analysis, 14+13 = 27
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References
Science 318 (2007), 939“Correlation of the highest energy cosmic rays with nearby extragalactic objects”
Astroparticle Physics 29 (2008), 188“Correlation of the highest-energy cosmic rays with the positions of nearby active galactic nuclei”
arXiv:0906.234731st International Cosmic Ray Conference, Lodz , Poland, July 2009“Astrophysical Sources of Cosmic Rays and Related Measurements with the Pierre Auger Observatory”
NEW Update to come soon...
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ICRC Update 2009ICRC new data (Period III): 27/5/2006-31/3/2009after exploratory period (II+III) integrated exposure: 12650 km2sr y
Updated event reconstruction: 56 EeV 55 EeV
31 new events E > 55 EeV: 44 post-prescription events
A-priori fixed parameters: Eth = 55 EeV ψ = 3.1º zmax = 0.018
mask = cut outGalactic Plane
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ICRC 2009Likelihood ratio: binomial probability of correlationover binomial probability in isotropic case (piso=0.21)
17/44 events in correlation (P=0.006)Isotropy still rejected at 99% c.l.
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Time Ordered Degree of correlation (p=k/N)
pdata=17/44=0.38±0.07Correlation degree decreased wrt our previous report
but still more than 2 s.d. from isotropy
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A Posteriori Analysis
Point source searches
Different methods & Catalogs (w/ ICRC 2009 Data):
I. Cross-correlationII. Log-likelihoodIII. 2-fold correlation
Laura Watson: Bayesian Methods applied to 2007 data Fred Kuehn: Methos used in the collaboration
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Centaurus A
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Centaurus A
KS test: 2% of isotropic realizations have a maximum departurefrom isotropy ≥ the maximum observed departure
Integral number of events vsangular distance from Cen A
Maximum excess @ 18o radius: 12 observed events vs 2.7 expected
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1. X-ray AGNs in 22-months SWIFT-BAT catalogue (261 objects)
2. Galaxies in the HIPASS survey (3058 galaxies, radio, flux-limited, HI sources)
3. HIPASS-HL: sub-sample of HIPASS (the 765 most luminous galaxies)
4. Galaxies in the 2MRS compilation (|b|>10¡, 23000 most luminous galaxies from 2MASS, full-sky, IR)
Other (Better) Catalogs
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Cross Correlation
e.g.: volume selected galaxies(D<200 Mpc) from 2MRS (1940 obj)
Measures the excess of pairs within a given angular separation wrt isotropy (departures are larger if CRs correlate with denser regions of the catalogues)
No weight by distance or luminosity (equal contribution to CR flux from every source)
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Smoothed Maps from Catalogs For each catalogue: Smoothed probability maps of arrival directionsWeight catalogue sources by flux x GZK attenuation
2 free parameters: smoothing angle σ and isotropic background (catalogue incompleteness + lower en. spill)
Fc(n) = density map value in the direction n
Use data to find the best values of (σ, fiso) by maximizing the LogLikelihood
Parameters weakly constrained
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Likelihood Test
Simulate 104 samples with the same number of data as in the real set
Draw events according to catalogue density map or isotropically
Compare the likelihood distributions with the value obtained from data
Better agreement with Catalog models vs Isotropy
LL sensitive to data points “in or out” of high density catalogue regions
Simulated data sets based on isotropy (I) and Catalog models (II) compared to data (black line/point).
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Complementary method to testoverall proportionality betweenmodels and data
Based on the computation of twocoefficients: correlation (testmatch between models and data)and concentration (test clusteringproperties of data)
Data compatible with all themodels
The map based on SWIFT givesthe most discriminant test againstisotropy
2-fold correlation method
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up to 3/31/2009, exposure 17,000 km2sr.y, 58 CRs w E>55 EeV
Update on the correlation with VCV objects (a-priori analysis) Isotropy rejected at 99% c.l. Degree of correlation lower than in early data
A-posteriori analysis: Excess of events close to Cen A (?) Distribution of arrival directions compatible with several catalogs that trace the distribution of nearby extra-galactic matterX-rays AGNs (e.g., SWIFT-BAT) interesting correlationsMore statistics needed to discriminate possible source scenarios
“Only” collect ≈ 2 UHECR/monthOnly look in the Southern Sky
Conclusions
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Auger North 10 yr
Black – 2MASS catalog z<0.02Blue – Auger North simul Data – energy proportional to circle sizeRed – Auger South Data
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50 CERN, 11 December 2007
— Particle Physics Seminar: Auger
results on UHECRs —
NEED MUCH HIGHER STATISTICS!!!!
The poorest, but very energetic!
THANKS!!!