Transcript 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
16 June 2005
Auger - GC Workshop
Contents
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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
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The status of the Auger Observatory
Sky exposure, low-energy events and analysis
methods to study anisotropies at the EeV
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Conclusion : perspectives to study the GC
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UHECRs
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Power law spectrum with slight
spectral index changes
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Remarkably isotropic
background, excepted for a
few features (still to be
confirmed)
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Composition : a priori
hadronic, large uncertainties
(see recent Kascade results @
E ~ PeV)
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At E > 100 EeV : unknown
flux (“GZK cutoff” expected)
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AGASA excess at EeV energies
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Akeno Giant Air Shower Array
At 1018 eV :
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~ 20 % energy systematics
3° angular resolution @ 1 EeV
R.A. analysis
Solar day analysis
0
4 km
Rayleigh analysis of the events in Right Ascension:
Compute the amplitude:
Then Pisotropy = exp(-K) with K = nA2/4
P(iso) = exp(-K)
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AGASA excess at EeV energies
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Akeno Giant Air Shower Array
At 1018 eV :
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~ 20 % energy systematics
3° angular resolution @ 1 EeV
R.A. analysis
Solar day 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
P(iso) = exp(-K)
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AGASA excess (2)
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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
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Other observations
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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
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Gamma ray – EeV connection?
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Nuclei acceleration in GC object(s) to EeV
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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
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Gamma ray – EeV connection?
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Nuclei acceleration in GC object(s) to EeV
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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)
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Expected signal at the EeV
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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
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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
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The Pierre Auger Observatory
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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
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Southern Site
Pampa Amarilla; Province of Mendoza
3000 km2, 875 g/cm2, 1400 m
Surface Array (SD):
Lat.: 35.5° south
LOMA AMARILLA
1600 Water Tanks
1.5 km spacing
3000 km2
Fluorescence Detectors (FD):
4 Sites (“Eyes”)
6 Telescopes per site (180° x 30°)
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70 km
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Water Tank in the Pampa
Communication
antenna
GPS antenna
Electronics enclosure
40 MHz FADC,
local triggers, 10 Watts
Battery
box
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Solar Panel
three 9”
PMTs
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Plastic tank with
12 tons of water
Installation Chain
installation of electronics
receiving ~20 tanks/week
Tank Preparation and Assembly
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Transportation into field
Water deployment
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Six Telescopes viewing 30°x30° each
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Camera with 440 PMTs
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Workshop
(Photonis
XP 3062)
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
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A stereo hybrid event
~70°
Coihueco
Fluores. Telescope
~37 km
Lateral Distribution Function
~8·1019eV
~24km
Los Leones
Fluores. Telescope
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global view
~37 km
~24km
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Shower Profile
~7·1019eV
(SD: ~8·1019eV)
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Exposure estimation methods
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Need background estimation
to analyse event maps
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Systematics can appear:
Array instabilities
Weather effects at the
threshold
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 Large-scale modulation of the background
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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
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“Low energy” data
3-ToT
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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
• Low energy threshold (largely below 1 EeV)
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Preliminary raw event map : 3-ToT,
3 tanks kept for reconstruction
(Jan-Sept. 2004, no energy cut)
Galactic coordinates
Cross-checks
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Large-scale feature analysis methods
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Rayleigh analysis
Fitting a dipole from the event
map
Aublin, Parizot, astro-ph/0504575
Reconstructing the angular
power spectrum Cℓ from the
event map Deligny et al., JCAP 0410:008 (2004)
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Auger South exposure is large
enough to do so!
Needs accurate exposure knowledge to measure
large scale anisotropies of order ~ few %
 Stable detector operation.
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MCMC
: 10%
: small
GC dipole injected
Recovered
Dipole direction
angular
reconstruction
power spectrum
Source searches
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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
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Preliminary
Small subset!
No energy cut!
Method : a fixed excess
probability P = 0.001 is distributed
over a few a priori targets.
GC
3 nearby objects (Cen A, NGC 0253,
NGC 3256)
Targets can be changed in view of
the data (blind searches)
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15°
(2004, >4 tanks subset,
3° smoothing, exposure subtracted)
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Perspectives
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Excesses correlated with galactic features have been claimed at the
EeV
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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:
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Various features claimed
All need to be checked
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
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