Cosmic ray anisotropy from Pierre Auger ObservatoryJ. R. T. de Mello Neto (for the Auger Collaboration)Universidade Federal do Rio de JaneiroV Nova Fsica no Espao Campos do Jordo - SP

OutlineOpen questionsCoverage mapPrevious anisotropy claimsGalactic centerPrescription resultsBlind source searchPerspectivesRef: Auger contributions in the proceedings of ICRC 05 Pune, India

Cosmic flux vs. EnergyS. SwordyRoughly a single power lawIndication of Fermi shock acceleration mechanism?Spectrum extends beyond the energies that can be produced with shock acceleration in known shocks.UHECR one particle per century per km2 many interesting questions

Open questionsHow cosmic rays are accelerated at ?What are the sources? How can they propagate along astronomical distances at such high energies?Are they substantially deflected by magnetic fields?Can we do cosmic ray astronomy?What is the mass composition of cosmic rays?

AnisotropyUHECR spatial distribution constrains models and sources : point-like for E > 10 EeVgalactic magnetic diffusion for E < 10 EeVIf anisotropy/sources are seen Start charged particle astronomy probe magnetic fields spectrometryIf no anisotropy/sources are seen indication of top-down origin re-think propagation ???

The Auger Observatory: Hybrid designA large surface detector array combined with fluorescence detectors results in a unique and powerful design;

Simultaneous shower measurement allows for transfer of the nearly calorimetric energy calibration from the fluorescence detector to the event gathering power of the surface array.

A complementary set of mass sensitive shower parameters contributes to the identification of primary composition.

Different measurement techniques force understanding of systematic uncertainties in each.

Angular resolutionSD only

Coverage mapCheck the proposition: what is observed is compatible with what is expected from an isotropic distribution; Need: isotropic background expectations (coverage map) statistical estimator of the overdensityAcurate determination of the coverage map is the real issue! detector growing weather effects true large scale anisotropies

Coverage determinationTwo techniques for coverage map determination: semi-analytical method shuffling (two flavours)Acceptance almost independent of sidereal time and azimuthFour independent groups calculated the coverage.

Shuffling method (2D) MC based method : Make N new realisations of the data arrival direction by resampling them : 5 zenith angle bins for each event : keep zenith, sample a new arrival time and a new azimuth from data in the same zenith angle bin Average the N datasets in the window centered around the observed direction This gives you the expected number of events in that direction

Shuffling method (1D) MC based method : Make N new realisations of the data arrival direction by resampling them : 5 zenith angle bins for each event : keep zenith, sample a new day and a new UTC hours from data in the same zenith angle bin and draw phi uniformily Average the N datasets in the window centered around the observed direction This gives you the expected number of events in that direction

Semi-analytical coverage map Start with events zenith angle distribution Fit it with some smooth functions : splines or polynomials times a Fermi-Dirac. Convert the fitted zenith angle shape into a declination distribution (analytical) Assume RA uniformity or use weather data to model RA variation Integrate through the window You have the expected number of events in any direction

Semi-analytical methodIsotropic simulation 10k eventsCoverage map in galactic coordinatesMollweide projection

Li-Ma significance map

Galactic centerGalactic Center is a natural site for cosmic ray accelerationSupermassive black holeDense clusters of starsStellar remnantsSNR (?) Sgr A EastSUGAR excess is consistent with a point source, indicating neutral primariesNeutrons would go undeflected, and neutron decay length at 1018 eV is comparable to the distance to the Galactic center (~8.5 kpc)

Chandra

Source at the Galactic centerAGASA20o scales1018 1018.4 eV N. Hayashida et al., Astroparticle Phys. 10 (1999) 303Significance () Cuts are a posteriori Chance probability is not well defined22% excess

Source at Galactic centerJ.A. Bellido et al., Astroparticle Phys. 15 (2001) 167SUGAR85% excess1018 1018.4 eV 5.5o cone

Source at the Galactic CenterSignificanceCoverage map1.5o scale3.7o scale (SUGAR like)13.3o scale (AGASA like)

Source at the Galactic centerAGASA Original Cuts (1.0 2.5 EeV)top hat 201155 / 1160.7ratio = 1.00 0.03

Enlarge energy range (0.8 3.2 EeV)top hat 201896 / 1853.06

SUGAR (0.8 3.2 EeV)top hat 5144 / 150.9ratio = 0.95 0.08

Point sources at the Galactic centerSD only:Gaussian filtering 1.5 degreeexp/obs 24.3/23.9if S CR then for 0.8 EeV < E < 3.2 EeVS < 2.5 10-15 m-2 s-1 @ 95 %

Hybrid :Top hat window 1.0 degreeExp/obs 4/3.4if S CR then for E > 0.1 EeVS < 1.2 10-13 m-2 s-1 @ 95 %Excess / Significance maps build using the individual pointing direction of the events. uncertainty in CR flux Iron/proton detection efficiency ratio

Galactic plane and Super Galactic planeA) GP 1-5 EeV 5077 / 5083.3 B) SGP > 5 EeV 241 / 232.8 C) SGP > 10 EeV 68 /67.4Origin CR change galactic -> extra-galactic 1 10 EeV

Prescription resultsFor each target: specify a priory probability levels and angular scalesavoids uncertainties from penalty factors due to a posteriori probability estimationTargets: low energy: Galactic center and AGASA-SUGAR location high energy: nearby violent extragalactic objects

Blind search for point sourcesLi, Ma ApJ 272, 317-324 (1983)significanceAll distributionsconsistent withisotropy

ConclusionsJanuary 2004 - June 2005SD Array: Unprecedented statistics in southern hemisphere (anisotropy) Exposure 1750 km2 sr yr (1.07 total AGASA) On time 94.3% Gain one order of magnitude within the next two years (1500 physical events per day)Hybrid: Unprecedented core location and direction precision excellent shower development and energy measurements No previous claims of anisotropy were confirmed !This is just the beginning! We have a lot of work ahead, including the Auger North Observatory! Thanks!

6 doublets 1 triplet above 4 x 1019 eV< 2.5 degabove 1019 eVLog E>19.6Log E>19.4AGASA

Agasa clusteringAgasa claimed high significance for their clusteringAnalysis was done by tuning for maximum significanceNo penalty factor or separate data set usedSignificant peak in the autocorrelation plots at zero degrees: implying presenceof compact UHECR sources

HiResNo clustering seen so far!

HiRes-I Monocular Data, E > 1019.5 eV

HiRes-I Monocular Data, E > 1018.5 eV

Upper limit of 4 doublets (90% c.l.) in HiRes-I monocular dataset.HiRes Stereo

GKZ suppression Cosmic rays E = 1020 eV interact with 2.7 K photons

In the proton frame

Proton with less energy, eventually below the cutoff energy EGZK= 5x 1019 eVUniverse is opaque for E > EGZK ! Photon-pion productionPhoton dissociation

Detection techniquesParticles at ground level large detector arrays (scintillators, water Cerenkov tanks, etc) detects a small sample of secondary particles (lateral profile) 100% duty cicle aperture: area of array (independent of energy) primary energy and mass compostion are model dependentFluorescence of N2 in the atmosphere calorimetric energy measurement as function of atmospheric depth only for E > 1017 eV only for dark nights (14% duty cicle) requires good knowledge of atmospheric conditions aperture grows with energy, varies with atmosphere

Pierre Auger South Observatory3000 km2

A surface array stationCommunications antennaGPS antennaElectronicsenclosureSolar panelsBattery box3 photomultiplier tubes looking into the water collect light left by the particlesPlastic tank with 12 tons of very pure water

Surface detectorElectronics temperature and VEM charge evolution over a week in April 2005Trigger rates: T1: First level trigger T2: Second lever trigger ToT: Time over Threshold

Surface detectorCorrelation of the trigger rate with temperature:T1-0.04 0.03 % per degreeT2 0.08 0.05 % per degreeToT 0.20 0.50 % per degreeSD array operates with stable trigger threshold even with 20 degrees daily temperature variations Surface detector array on-time in 2004: 94.3%Evolution of the physics event rate as a function of time. It is roughly related to the number of active stations by 0.9 event per day per station

The fluorescence detectorLos Leones telescope

The fluorescence telescope30 deg x 30 deg x 30 km field of view per eye

Atmospheric monitoring and FD detector calibrationAtmospheric monitoringCentral Laser Facility (laser optically linked to adjacent surface detector tank) Atmospheric monitoring Calibration checks Timing checksAbsolute calibrationDrum for uniform illumination of each fluorescence camera part of end to end calibration .Lidar at each fluorescence eye for atmospheric profiling - shooting the shower

Fluorescence detectorAbsolute calibration has been performed with a precision of 12%, with improvements planned to reduce this uncertainty to 8%The estimated systematic uncertainty in the reconstructed shower energy is 25%, with activity underway to reduce this significantly

Hybrid detectionGolden events: independent triggersSimultaneus detection in the sky and in the groundSub-threshold events: FD promoted triggers

Hybrid detectorThe hybrid analysis benefits from the calorimetry of the fluorescence technique and the uniformity of the surface detector aperture

Construction progress1208 surface detector stations deployed 951 with eletronics and sending dataThree fluorescence buildings complete each with 6 telescopesIn construction

Spectrum: previous claimsContinuation beyond the GZKlimit?Extragalatic sources distributeduniformlyAGASAM. Takeda et al., PRL 81 (1998) 1163

Spectrum: previous claimsHiResHiRes mono spectrum consistentwith GZK suppresion HiRes Collab., arXiv:astro-ph/0501317Fit to unbroken power law: Fit taking into account GZK suppression:

Energy spectrum for Auger ObservatoryBased on fluorescence and surface detector dataFirst model- and mass-independent energy spectrumPower of the statistics and well-defined exposure of the surface detectorHybrid data stablishes conection between ground parameter S and shower energyHybrid data confirm that SD event trigger is fully efficient above 3x1018 eV for

Constant intensity cutCosmic rays are nearly isotropic: Constant intensity cut constant energy cutFor a fixed I0 find S(1000) at each such that I(>S(1000)) = I0The relative values of S(1000) give CIC()Normalized so that CIC(38o) = 1; 38o is the median zenith angle Define the energy parameter S38= S(1000)/CIC() for each shower :the S(1000) it would have produced if it had arrived at 38o zenith angle

Energy spectrum for Auger ObservatoryConstant Intensity Cut Correlation FD-SD

Energy spectrum for Auger ObservatoryEstimated Spectrum Percentage deviation from the best-fit power law Error bars Poisson statisticsSystematic uncertainty: double arrowsat two different energies

Energy spectrum for Auger Observatory No events above 1020 in spectrum Two sigma upper limit is consistent with AGASA flux With current level of statistics and systematics, no solid conclusion is possible

Primary photon fraction upper limitLimited by statistics, Considerable increase in a near future. Obtain a bound at higher energy

Primary photon fraction upper limitFurther exploit surface detector observables

High energy events

A Hybrid event