Recent results from Pierre Auger Observatory

J. R. T. de Mello Neto

Universidade Federal do Rio de Janeiro

XI International Conference on Hadron Spectroscopy – HADRON 05

CBPF- Rio de Janeiro

Outline

• Open questions• The Auger Observatory • The detector’s performance• The model-independent energy spectrum• Anisotropies• Blind source search• Photon fraction limit• Perspectives

Ref: Auger contributions in the proceedings of ICRC 05 – Pune, India

S. Swordy

Cosmic flux vs. Energy

Roughly a single power law

Indication of Fermi shock acceleration mechanism?

Spectrum extends beyond the energies that can be produced with shock acceleration in known shocks.

8.2E

UHECR • one particle per century per km2

• many interesting questions

Open questions

• How 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?

eV 1019E

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 eV

Universe is opaque for E > EGZK !

n

pp k0

3

MeVE 300

Photon-pion production

nFeFe k 563

56 Photon dissociation

Detection techniques

Particles 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 dependent

Fluorescence 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

The Auger Observatory: Hybrid design• A 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.

Pierre Auger South Observatory

3000 km2

A surface array station

Communications antenna GPS antenna

Electronicsenclosure Solar panels

Battery box

3 photomultiplier tubes looking into the water collect light left

by the particles

Plastic tank with 12 tons of very pure water

Electronics temperature and VEM charge Electronics temperature and VEM charge evolution over a week in April 2005evolution over a week in April 2005

Surface detectorStation 102

Los Leones

Coihueco

Los Morados

Loma

Amarilla

Trigger rates: T1: First level triggerTrigger rates: T1: First level trigger

T2: Second lever triggerT2: Second lever trigger

ToT: Time over ThresholdToT: Time over Threshold

Surface detectorCorrelation of the trigger rate with temperature:

T1 -0.04 ± 0.03 % per degree

T2 0.08 ± 0.05 % per degree

ToT 0.20 ± 0.50 % per degree

SD 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 detector

Los Leones telescope

The fluorescence telescope

30 deg x 30 deg x 30 km field of view per eye

Atmospheric monitoring and FD detector calibration

Atmospheric monitoring Central Laser Facility (laser optically linked to adjacent surface detector tank)

• Atmospheric monitoring

• Calibration checks

• Timing checks

Absolute calibration

Drum 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 detector

Absolute 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 detection

Golden events: independent triggers

Simultaneus detection in the sky and in the ground

Sub-threshold events: FD promoted triggers

Hybrid detector

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

Construction progress

1208 surface detector stations deployed

951 with eletronics and sending data

Three fluorescence buildings complete each with 6 telescopes

In construction

Angular resolution

Hybrid events: 0.6°

Surface detector: 2.2° for 3-fold events (E < 4 EeV)

1.7° for 4-fold events (3 < E < 10 EeV)

1.4° for 5 or more stations (E > 8 EeV)

SD only Comparison hybrid and SD only

= 1.54 ± 0.05

2 47.84 / 14

= 1.30 ± 0.04

2 61.50 / 14

SD Hyb = 1.2

SD Hyb = 1.1

= 1.24 ± 0.07

2 37.05 / 14

= 0.98 ± 0.06

2 29.49 / 12

Sd Hyb = 0.66

Sd Hyb = 0.72

High energy events

The highest energy SD event (86 EeV)

Properties of the 20 most energetic events

A Hybrid event

Spectrum: previous claims

Continuation beyond the GZKlimit?

Extragalatic sources distributeduniformly

AGASA

M. Takeda et al., PRL 81 (1998) 1163

Spectrum: previous claims

HiRes

HiRes mono spectrum consistentwith GZK suppresion

HiRes Collab., arXiv:astro-ph/0501317

Fit to unbroken power law:

0.32 dof

Fit taking into account GZK suppression: 2.12 dof

Energy spectrum for Auger Observatory

• Based on fluorescence and surface detector data• First model- and mass-independent energy spectrum• Power of the statistics and well-defined exposure of the

surface detector• Hybrid data stablishes conection between ground

parameter S and shower energy• Hybrid data confirm that SD event trigger is fully efficient

above 3x1018 eV for θ<60o

• Energy scale of the fluorescence detector (nearly calorimetric, model independent energy measurement)

Constant intensity cut

Cosmic rays are nearly isotropic: Constant intensity cut ↔ constant energy cut

For a fixed I0 find S(1000) at each θ such that I(>S(1000)) = I0

The relative values of S(1000) give CIC(θ)

Normalized so that CIC(38o) = 1; 38o is the median zenith angle

Define the energy parameter S38= S(1000)/CIC(θ) for each shower :“the S(1000) it would have produced if it had arrived at 38o zenith angle”

Energy spectrum for Auger Observatory

Constant Intensity Cut Correlation FD-SD

Energy spectrum for Auger Observatory

Estimated Spectrum Percentage deviation from the best-fit power law

Error bars Poisson statisticsSystematic uncertainty: double arrowsat two different energies

dI

d(lnE)E

dI

dE

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

Source at the Galactic center

AGASA

)4.5( 6.413

506

expected

observed

20o scales

1018 – 1018.4 eV

N. Hayashida et al., Astroparticle Phys. 10 (1999) 303

Significance (σ)

• Cuts are a posteriori • Chance probability is not well defined

22% excess

)280,15(),(

Source at Galactic center

J.A. Bellido et al., Astroparticle Phys. 15 (2001) 167

SUGAR

)2.9( 8.11

8.21

expected

observed

85% excess

1018 – 1018.4 eV

5.5o cone)274,22(),(

Source at the Galactic Center

SignificanceCoverage map 1.5o scale

3.7o scale (SUGAR like) 13.3o scale (AGASA like)

Source at the Galatic center

AGASA

Original Cuts (1.0 – 2.5 EeV)

top hat 20° 1155 / 1160.7 ratio = 1.00 ± 0.03

Enlarge energy range (0.8 – 3.2 EeV)

top hat 20° 1896 / 1853.06

SUGAR (0.8 – 3.2 EeV)

top hat 5° 144 / 150.9 ratio = 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 plane

A) GP 1-5 EeV 5077 / 5083.3

B) SGP > 5 EeV 241 / 232.8 C) SGP > 10 EeV 68 /67.4

Prescription results

For each target: specify a priory probability levels and angular scalesavoids uncertainties from “penalty factors” due to a posteriori probability estimation

Targets: • low energy: Galactic center and AGASA-SUGAR location• high energy: nearby violent extragalactic objects

Blind search for point sourcesExposure map

Events map

Galactic coordinates

1 – 5 EeV smoothed top-hat window 5o

HEALPIX pixielization

Blind search for point sources

Li, Ma ApJ 272, 317-324 (1983)

significance

All distributionsconsistent withisotropy

Primary photon fraction upper limit

Limited by statistics,

Considerable increase in a near future.

Obtain a bound at higher energy

Primary photon fraction upper limit

Further exploit surface detector observables

ConclusionsJanuary 2004 - June 2005

SD Array:

• Unprecedented statistics in southern hemisphere Unprecedented statistics in southern hemisphere ((anisotropyanisotropy))

• Exposure 1750 kmExposure 1750 km22 sr yr (1.07 total AGASA) sr yr (1.07 total AGASA)

• On time 94.3%On time 94.3%

• Gain one order of magnitude within the next two years (1500 Gain one order of magnitude within the next two years (1500 physical events per day)physical events per day)

Hybrid:Hybrid:

Unprecedented core location and direction precision Unprecedented core location and direction precision excellent excellent shower development and energy measurements shower development and energy measurements

((energy spectrum & photon limitsenergy spectrum & photon limits))

This is just the beginning! We have a lot of work ahead, including the Auger North Observatory!

Thanks!