16 June 2005Auger - GC Workshop Auger potentiality and analysis methods to study the Galactic Center E. Armengaud (APC/IAP) Auger Collaboration

16 June 2005 Auger - GC Workshop Contents Ultra High Energy Cosmic Rays : results from previous experiments concerning the GC at ~ EeV ( = eV) Models for EeV cosmic ray anisotropies from the GC region The status of the Auger Observatory Sky exposure, low-energy events and analysis methods to study anisotropies at the EeV Conclusion : perspectives to study the GC

16 June 2005 Auger - GC Workshop UHECRs Power law spectrum with slight spectral index changes Remarkably isotropic background, excepted for a few features (still to be confirmed) Composition : a priori hadronic, large uncertainties (see recent Kascade E ~ PeV) At E > 100 EeV : unknown flux (“GZK cutoff” expected)

16 June 2005 Auger - GC Workshop AGASA excess at EeV energies Akeno Giant Air Shower Array At eV :  ~ 20 % energy systematics  3° angular 1 EeV 0 4 km Rayleigh analysis of the events in Right Ascension: Compute the amplitude: Then P isotropy = exp(-K) with K = nA 2 /4 R.A. analysis Solar day analysis P(iso) = exp(-K)

16 June 2005 Auger - GC Workshop AGASA excess at EeV energies Akeno Giant Air Shower Array At eV :  ~ 20 % energy systematics  3° angular 1 EeV 0 4 km R.A. analysis Solar day analysis “Stable operation day” selection  70% of the events (~100,000) K ~ E > EeV  4% amplitude Should not be due to weather modulation of the event rate P(iso) = exp(-K)

16 June 2005 Auger - GC Workshop AGASA excess (2) Excess map in the a posteriori energy band [ – ] eV 20° top-hat window GC out of exposure, but near : 308 obs / 242 expected (4σ) Exposure assumed to be R.A.- invariant Other excesses : near Cygnus (3σ) and anti-GC (-3.7σ) Event excess map (n obs /n exp ) 20° A large-scale feature

16 June 2005 Auger - GC Workshop Other observations SUGAR Array (Southern hemisphere, 70’s)  Small EeV  5.5° angular resolution < E < : 3732 events Direction (α = 274°, δ = -22°) shifted ~ 7° from the GC Compatible with a point source Obs/Expected ~ 22/12 Flux ~ (9 + 3) m -2 s -1 Sugar excess probability map GC Agasa excess contours Fly’s Eye experiment (USA) : excess from the Galactic EeV but fluorescence detector  large-scale feature analysis difficult

16 June 2005 Auger - GC Workshop Gamma ray – EeV connection? Nuclei acceleration in GC object(s) to EeV  1) Hadronic scattering pp  pp + π°  Gamma flux with α ~ 2.2 if α proton ~ 2.2  2) pp  np + π + pγ IR  n via pion photoproduction / nuclei photodisintegration  Neutron flux 3 EG J source? TeV HESS source ~ SGR A* ? Crocker et al., ApJ,622: (2005) Grasso, Maccione, astro-ph/

16 June 2005 Auger - GC Workshop Gamma ray – EeV connection? Nuclei acceleration in GC object(s) to EeV  1) Hadronic scattering pp  pp + π°  Gamma flux with α ~ 2.2 if α proton ~ 2.2  2) pp  np + π + pγ IR  n via pion photoproduction / nuclei photodisintegration  Neutron flux UHECR anisotropy (neutron showers = proton showers)

16 June 2005 Auger - GC Workshop Expected signal at the EeV d(GC - Earth) ~ 8 kpc vs. d(n  p) ~ 9 EeV Neutron point source from the GC n  p which then diffuse in galactic B field Large-scale feature Shape and amplitude should depend on B field model (regular + random components) Bossa et al., J.Phys.G29: (2003) Normalizing the fluxes using Hess or Egret sources or Chandra flux (+equipartition assumption), estimations: Source / CR background ~ 1 in a 2.5° [1-3] EeV around the GC Large-scale feature of order of magnitude compatible with AGASA excess

16 June 2005 Auger - GC Workshop The Pierre Auger Observatory Main goal : spectrum and sources of UHECR above 10 EeV Low flux  ~ 3000 km 2 collecting area Understand systematic errors + improve angular and energy resolution: Hybrid Approach Hybrid Approach Independent EAS-observation techniques Shower-by-Shower in one experiment

16 June 2005 Auger - GC Workshop 70 km Southern Site Pampa Amarilla; Province of Mendoza 3000 km 2, 875 g/cm 2, 1400 m Lat.: 35.5° south Surface Array (SD): 1600 Water Tanks 1.5 km spacing 3000 km 2 Surface Array (SD): 1600 Water Tanks 1.5 km spacing 3000 km 2 Fluorescence Detectors (FD): 4 Sites (“Eyes”) 6 Telescopes per site (180° x 30°) Fluorescence Detectors (FD): 4 Sites (“Eyes”) 6 Telescopes per site (180° x 30°) LOMA AMARILLA

16 June 2005 Auger - GC Workshop Water Tank in the Pampa Solar Panel Electronics enclosure 40 MHz FADC, local triggers, 10 Watts Communication antenna GPS antenna Battery box Plastic tank with 12 tons of water three 9” PMTs

16 June 2005 Auger - GC Workshop receiving ~20 tanks/week Tank Preparation and Assembly Transportation into field Water deployment installation of electronics Installation Chain

16 June 2005 Auger - GC Workshop Six Telescopes viewing 30°x30° each Camera with 440 PMTs (Photonis XP 3062)

16 June 2005 Auger - GC Workshop Current state of the Observatory Los Leones (FD) Coihueco (FD) Los Morados (FD) 2/4 FD telescope sites fully running ~750/1600 tanks working in the fields

16 June 2005 Auger - GC Workshop Coihueco Fluores. Telescope Los Leones Fluores. Telescope ~8 · eV Lateral Distribution Function ~37 km ~24km ~70° global view A stereo hybrid event

16 June 2005 Auger - GC Workshop ~37 km ~24km

16 June 2005 Auger - GC Workshop Shower Profile ~7 · eV (SD: ~8 · eV)

16 June 2005 Auger - GC Workshop Angular reconstruction and resolution SD : Iterative fit with the arrival times of particles from the shower:  Shower front ~ plane surface  Global fit using tank signal amplitudes  core location estimation  If 4 tanks are hit : (variable) radius of curvature included Angular resolution ~ 10 EeV Hybrid data (~10%) : adding information from only ONE tank to the FD events improves greatly the resolution ~ 10 EeV Angular resolution depends a lot on: Energy Zenith angle But still a good resolution at ~ EeV Hybrid data (+ “doublets of tanks”) allows to check the resolution directly from the data (no MC) Preliminary figures

16 June 2005 Auger - GC Workshop Exposure estimation methods Need background estimation to analyse event maps Systematics can appear:  Array instabilities  Weather effects at the threshold  Large-scale modulation of the background 2 strategies : 1. Use our knowledge of detector acceptance 2. Direct exposure derivation from the events (scrambling) Preliminary raw event map (2004 subset : “T5 hexagons + Herald + >4 tanks hit”) Equatorial coordinates – 3° smoothing Crucial analysis for large scale feature studies

16 June 2005 Auger - GC Workshop “Low energy” data An efficient trigger : the “Compact 3-ToT”  events reconstructed with 3 tanks sending long signals in a compact configuration Angular resolution ~ EeV Preliminary raw event map : 3-ToT, 3 tanks kept for reconstruction (Jan-Sept. 2004, no energy cut) Galactic coordinates Excellent statistics at energies ~ EeV (not the first goal of Auger) 3-ToT + Hybrid data : FD reconstruction significantly improved with the signal from only 1 tank Less statistics Better angular resolution ~ EeV Low energy threshold (largely below 1 EeV) Cross-checks

16 June 2005 Auger - GC Workshop Large-scale feature analysis methods Rayleigh analysis Fitting a dipole from the event map Aublin, Parizot, astro-ph/ Reconstructing the angular power spectrum C ℓ from the event map Deligny et al., JCAP 0410:008 (2004)  Auger South exposure is large enough to do so! Needs accurate exposure knowledge to measure large scale anisotropies of order ~ few %  Stable detector operation. MC : 10% GC dipole injected Dipole direction reconstruction MC : small dipole injected Recovered angular power spectrum

16 June 2005 Auger - GC Workshop Source searches Method : a fixed excess probability P = is distributed over a few a priori targets. Current ‘targets’ defined at ICRC 2003:  “Agasa/Sugar direction” : 3° radius, E < 3.2 EeV  GC : 5° radius, E < 3.2 EeV  GC : 15° radius, all E  3 nearby objects (Cen A, NGC 0253, NGC 3256) Targets can be changed in view of the data (blind searches) 15° (2004, >4 tanks subset, 3 ° smoothing, exposure subtracted) Preliminary Small subset! No energy cut! GC

16 June 2005 Auger - GC Workshop Perspectives Excesses correlated with galactic features have been claimed at the EeV  Various features claimed  All need to be checked There could be EeV couterparts of “low-energy” gamma sources The Auger Southern Observatory has many advantages to analyse a possible GC excess at the EeV for the first time:  An efficient “low-energy” trigger  Unprecedented statistics  A good angular resolution at EeV (excellent with hybrid data)  But... Energy determination can be systematically shifted compared to previous experiments (depending on the nature of UHECR in particular) A GC point source can be checked with SD as well as hybrid data. Large-scale pattern searches are more involved but very good impression even with an array still under construction First Auger results at ICRC 2005