The Auger Project

Seeking the Source of Ultra High Energy Cosmic Rays

A New Window on Astronomy

Generic Colloquium SlidesPrepared December 11, 1997

David F. NitzUniversity of Michigan

Outline

• Introduction– Historical Perspective– CR Spectrum– Extensive Air Showers– Array layout– EeV data

• Possible Sources of Cosmic Rays– “Standard” Acceleration– Propagation and GZK– Top down (topological defects)– Monopoles– Gamma Ray Bursts

• Observations and Physics Issues– Magnetic fields– Point Sources– AGASA pairs– Sky Coverage

• Auger Detectors & Techniques– Fluorescence detectors– Tanks– Hybrid Operation– Timing– Trigger– Front-end electronics– Communications network– Energy, Direction, Composition resolution

The Beginning

Ever since Victor Hess discovered

cosmic rays in 1912, a primary question has been "Where do they come from?". After more than 80 years of research

this question remains largely unanswered. The origin of the

highest energy cosmic rays remains one of the great unsolved

mysteries of physics.

The Observed Cosmic Ray Spectrum

Layman’s Terms?

Energy Scales

The Highest Energy Particle Ever Observed

E = 3 x 1020eV 50 J!50 J!

Flux of EeV Particles

The Question

The International Collaboration

A 1019 eV Extensive Air Shower

Auger Array Layout

Two Hemispheres

Anu Talvari is an artist of Estonian origin, born in Sweden and living in Buenos Aires -- a

background not unlike the world-wide composition of the Auger Collaboration. She describes the

painting thusly: “Earth. The Blue Planet. The known space is enclosed in the

lower left corner. The unknown space opens in the upper right

corner. Two Auger Observatories installed in both hemispheres.

Two eyes looking for information from the unknown space.”

The Auger Project is named after the late French physicist Pierre Auger, who discovered extensive air showers. He received a Nobel Prize for his work on “Auger electrons” and was influential in the founding of CERN.

Auger Observatory Sites

#S

#S

Northern Hemisphere Site

Southern Hemisphere SiteArgentinaArgentina

Site Photos

Astrophysical Miscellanea

Possible SourcesPossible Sources

• Diffusive shock acceleration (Fermi) in extended objects– Lobes of radio galaxies (Biermann)

– Galaxy cluster accretion shocks (Kang, et. al)

– Collisions of galaxies (Cesarsky)

– Motion of galaxies in ISM

• Acceleration in strong fields associated with accretion disks and compact rotating galaxies (Colgate)

Astrophysical Acceleration Mechanisms

Black Hole(Artist’s Conception)

NGC4151

Caveats?

Limits to Acceleration

cZeBLE max

Attenuation of Cosmic Rays

All known particles except neutrinos undergointeractions with the CMBR:

This is the GZK cutoff

Distance Scales

The GZK Cutoff

Possible SourcesPossible Sources

• Top down models – Decay of topological defects (Kibble, Bhattacharjee,

Hill, ..)– Window to Post-Inflationary Reheating Epoch?

(Kuzmin & Rubakov) – Decaying Vortons (Masperi & Solva)– Relic monopoles (Kephart & Weiler) (Escobar &

Vazquez : “No”)

• Acceleration in catastrophic events – In association with gamma ray bursts (Waxman, Vietri,

Milgrom)

• Other New Physics – Supersymmetric particles (Chung, Farrar, & Kolb) – Strongly interacting neutrinos (Bordes)– Needs to be at few Gev or cross section too low => not

likely - ruled out by accelerator data (Halzen)– Decay of energetic new long lived progenator

(Frampton, Keszthelyi, & Ng)

Exotic Mechanisms

Topological Defect Model

CASA/MIA

Auger Neutrino Detection

(A recent analysis by Ralstan et al. suggests the cross section is likely to be closer to MRS)

Neutrino rates for 2 extreme extrapolations of the cross section

00.20.40.60.8

11.21.41.61.8

2

17 18 19 20 21

Log10 Electron Neutrino Energy

Log

10 k

m**

3 sr

wat

er

equi

vale

nt

Magnetic Magnetic MonopolesMonopoles

• Consideration of relic monopoles motivated by 2 interesting facts:– Observed CR flux >1020 eV similar to Parker Bound

• Higher flux would have violated bound• Lower flux would not have been observed

– Dirac monopoles can be accelerated to >1020 eV with typical galactic magnetic field strengths and field coherence lengths

• Must be relativistic to initiate observed air showers==> masses <1019 eV

• Observational consequences:– Energetic monopoles may be distributed preferentially in the direction of local

galactic magnetic field– Air showers produced by monopoles may have distinctive characteristics

• Detailed modeling of interactions of monopoles in upper atmosphere not yet been carried out.

– Not known whether monopole can produce showers like those observed by AGASA and Fly’s Eye

Auger is designed to be sensitive to air shower structure

N.A. Porter, Nuov. Cim. 16 958 (1960)T.W. Kephart and T.J. Weiler, Astropart. Phys. 4, 271 (1996)

k M

G pc

M

kpc

E q BL N

B

B

L

L

R

R

~/ /

6 1020

300

1 2

30

1 2

eV

F M lM H c

~ .0 2 1025 3 3

eV / cm / sec / sr2F

M

PL 10 15 / cm / sec / sr2

M lc H

1020 eV

RM

M M

M

PL

E F

F~ 10

108

20

eV

Horizon size Phase transition correlation length

Monotonic relationship betweenmonopole flux & mass

(Parker bound)

(Doesn’t overclose Universe)

==>

AssociationAssociation with Gamma Ray with Gamma Ray BurstsBursts

• If cosmological, power needed to account for flux of highest energy cosmic rays is comporable to average power in gamma rays

• Observed spectrum consistent with Fermi acceleration in region and cosmological distribution

• Observed rate– 2 CR events above 2 x 1020 eV observed in 26 months– ~1 GRB per 50 years within field of view of experiments and within 100 Mpc

(GZK cutoff)==> Requires 1020 eV protons produced in distant GRB burst are dispersed in time

>50 years==> Inter-Galactic Magnetic Field >10-12 G

• Each of 2 highest energy CR within ~5o of a strong BATSE GRB (but not statistically compelling)

• If highest energy CRs associated with distant GRBs– GZK cutoff– If GRB sources associated with luminous matter, expect CR anisotropy related to

large scale structure of local (<100 Mpc) universe– Energy dependent delays in arrival times induced by IGMF

• Brightest sources may be different at different energies

• If highest energy CRs associated with local GRBs– No GZK cutoff– New >1020 eV events should be correlated with GRBs– Isotropic CR distribution due to observed isotropy of GRBs

E. Waxman, Phys. Rev. Lett. 75, 386 (1995)M. Vietri, Astrophys. J. 453, 883 (1995)E. Waxman, Astrophys. J. 444, L1 (1995)E. Waxman & P. Coppi, astro-ph/9603144M. Milgrom & V. Usov, Astrophys. J. 448, L37 (1995)M. Vietri, Mon. Not. R. Astron. Soc. 278, L1 (1996)J. Miralda-Escude & E. Waxman, astro-ph/9601012

Possible Source Conclusions

No really satisfactory model has emerged

Magnetic Field Deflection

AGASA pairs

• 2-3 cases of 2 cosmic rays coming from the same direction within 1.6 deg. angular resolution

– 1% random chance if isotropic distribution– 2% if use >4 x 1019 eV

• One pair includes highest energy event observed by AGASA

– Assume same species & source– Trace back 30-50 Mpc to source

Need more data, more sky coverageWe expect >50 events in Auger from this sourcein same length of time (5 years)

20 events eV 5 1019

36 events > 4 10 eV19

B h B e h( ) ( ) . 0 0 8 2

(Parker)

Auger Philosophy

• Large aperture (>10X previous generation)

• Uniform sky coverage

• Hybrid operation

• Good energy & direction measurement

• Composition sensitivity

Northern Observatory Exposure

AGASA Events(E > 5x1019eV)

Havarah Park Events (E > 5x1019eV)

Southern Observatory Exposure

Auger Observatory Exposure

AGN Catalog of Huchra (< 100 Mpc)

D ~ cz/H (for small z)

Hybrid Operation

Fluorescence Detector

Surface Detector Station

GPS Timing

Tandar Test Tank

White top: 55 ns

Black top: 21 ns

Data Simulation (Pryke)

Trigger Hierarchy

Auger Communications System Functional

Overview

Control Center

Concentrator

Remote Station1600/site

Fluorescence Eye

~0.5 Mbits/s each

~1.1Mbits/s aggregate 1600 stations

Level 2 Triggers~20 Hz @24 bits each Poisson distributed

Event Data ~15 Kbits/s @ ~2600 interval Poisson distributed

Monitoring Data ~200 bits/s mean program controlled

Software Download ~2 Mbits/hr infrequently

Control 100 bits/s?

+ ACK, NAK as required

Level 3 Trig. 0.2 hz

Test Tank at AGASA

1020 eV event

1.7 km from core

30o zenith angle

Ground Array Energy Reconstruction

Can probably remove offset

Primary Composition Sensitivity

Performance Summary

Conclusions