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Auger potentiality and analysis methods to study the Galactic Center

Auger potentiality and analysis methods to study the Galactic Center. E. Armengaud (APC/IAP) Auger Collaboration. Contents. Ultra High Energy Cosmic Rays : results from previous experiments concerning the GC at ~ EeV ( = 10 18 eV) Models for EeV cosmic ray anisotropies from the GC region

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Auger potentiality and analysis methods to study the Galactic Center

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  1. Auger potentiality andanalysis methods to study the Galactic Center E. Armengaud (APC/IAP) Auger Collaboration Auger - GC Workshop

  2. Contents • Ultra High Energy Cosmic Rays : results from previous experiments concerning the GC at ~ EeV ( = 1018 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 Auger - GC Workshop

  3. 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 results @ E ~ PeV) • At E > 100 EeV : unknown flux (“GZK cutoff” expected) Auger - GC Workshop

  4. AGASA excess at EeV energies • Akeno Giant Air Shower Array • At 1018 eV : • ~ 20 % energy systematics • 3° angular resolution @ 1 EeV R.A. analysis 0 4 km Rayleigh analysis of the events in Right Ascension: Compute the amplitude: Solar day analysis Then Pisotropy = exp(-K) with K = nA2/4 P(iso) = exp(-K) Auger - GC Workshop

  5. AGASA excess at EeV energies • Akeno Giant Air Shower Array • At 1018 eV : • ~ 20 % energy systematics • 3° angular resolution @ 1 EeV R.A. analysis 0 4 km • “Stable operation day” selection •  70% of the events (~100,000) • K ~ 7 @ E > EeV  4% amplitude • Should not be due to weather modulation • of the event rate Solar day analysis P(iso) = exp(-K) Auger - GC Workshop

  6. AGASA excess (2) • Excess map in the a posteriori energy band [1017.9 – 1018.3] 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 (nobs/nexp)20° A large-scale feature Auger - GC Workshop

  7. Other observations Agasa excess contours • SUGAR Array (Southern hemisphere, 70’s) • Small statistics @ EeV • 5.5° angular resolution • 1017.9 < E < 1018.5 : 3732 events • Direction (α = 274°, δ = -22°) shifted ~ 7° from the GC • Compatible with a point source • Obs/Expected ~ 22/12 • Flux ~ (9 + 3) 10-14 m-2 s-1 GC Sugar excess probability map • Fly’s Eye experiment (USA) : • excess from the Galactic Plane @ EeV • but fluorescence detector  large-scale • feature analysis difficult Auger - GC Workshop

  8. 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 αproton~ 2.2 • 2) pp  np + π+ pγIR  n via pion photoproduction / nuclei photodisintegration  Neutron flux 3 EG J1746-2851 source? TeV HESS source ~ SGR A* ? Crocker et al., ApJ,622:892-909 (2005) Grasso, Maccione, astro-ph/0504323 Auger - GC Workshop

  9. 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 αproton~ 2.2 • 2) pp  np + π+ pγIR  n via pion photoproduction / nuclei photodisintegration  Neutron flux UHECR anisotropy (neutron showers = proton showers) Auger - GC Workshop

  10. Expected signal at the EeV • d(GC - Earth) ~ 8 kpc vs. d(np) ~ 9 kpc @ 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.G29:1409-1422 (2003) • Normalizing the fluxes using Hess or Egret sources or Chandra • flux (+equipartition assumption), estimations: • Source / CR background ~ 1 in a 2.5° window @ [1-3] EeV around the GC • Large-scale feature of order of magnitude compatible with AGASA excess Auger - GC Workshop

  11. The Pierre Auger Observatory • Main goal : spectrum and sources of UHECR above 10 EeV • Low flux  ~ 3000 km2 collecting area • Understand systematic errors + improve angular and energy resolution: Hybrid Approach Independent EAS-observation techniques Shower-by-Shower in one experiment Auger - GC Workshop

  12. LOMA AMARILLA Southern Site Pampa Amarilla; Province of Mendoza 3000 km2, 875 g/cm2, 1400 m Surface Array (SD): 1600 Water Tanks 1.5 km spacing 3000 km2 Lat.: 35.5° south Fluorescence Detectors (FD): 4 Sites (“Eyes”) 6 Telescopes per site (180° x 30°) Auger - GC Workshop 70 km

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

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

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

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

  17. A stereo hybrid event ~70° global view Coihueco Fluores. Telescope ~37 km Lateral Distribution Function ~8·1019eV ~24km Los Leones Fluores. Telescope Auger - GC Workshop

  18. ~37 km ~24km Auger - GC Workshop

  19. Shower Profile ~7·1019eV (SD: ~8·1019eV) Auger - GC Workshop

  20. 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 : • Use our knowledge of detector acceptance • 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 Auger - GC Workshop

  21. “Low energy” data 3-ToT • An efficient trigger : the “Compact 3-ToT”  events reconstructed with 3 tanks sending long signals in a compact configuration • Angular resolution ~ 2° @ EeV Excellent statistics at energies ~ EeV (not the first goal of Auger) • + Hybrid data : • FD reconstruction significantly • improved with the signal from only 1 tank • Less statistics • Better angular resolution ~ 1° @ EeV • Lowenergy threshold (largely below 1 EeV) Preliminary raw event map : 3-ToT, 3 tanks kept for reconstruction (Jan-Sept. 2004, no energy cut) Galactic coordinates Cross-checks Auger - GC Workshop

  22. Large-scale feature analysis methods • Rayleigh analysis • Fitting a dipole from the event map Aublin, Parizot, astro-ph/0504575 • Reconstructing the angular power spectrum Cℓ from the event mapDeligny et al., JCAP 0410:008 (2004) • Auger South exposure is large enough to do so! MC : small dipole injected Recovered angular power spectrum MC : 10% GC dipole injected Dipole direction reconstruction Needs accurate exposure knowledge to measure large scale anisotropies of order ~ few %  Stable detector operation. Auger - GC Workshop

  23. Source searches Preliminary Small subset! No energy cut! • Method : a fixed excess probability P = 0.001 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) GC 15° (2004, >4 tanks subset, 3°smoothing, exposure subtracted) Auger - GC Workshop

  24. 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 Auger - GC Workshop

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