Download Galactic Center is a - Instituto de Física / UFRJ

Cosmic ray anisotropy from
Pierre Auger Observatory
J. R. T. de Mello Neto
(for the Auger Collaboration)
Universidade Federal do Rio de Janeiro
V Nova Física no Espaço
Campos do Jordão - SP
Outline
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Open questions
Coverage map
Previous anisotropy claims
Galactic center
Prescription results
Blind source search
Perspectives
Ref: Auger contributions in the proceedings of
ICRC 05 – Pune, India
Cosmic flux vs. Energy
Roughly a single power law
E 2.8
Indication of Fermi shock
acceleration mechanism?
Spectrum extends beyond the
energies that can be produced
with shock acceleration in
known shocks.
S. Swordy
UHECR
• one particle per century per km2
• many interesting questions
Open questions
19
E

10
eV ?
• 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?
Anisotropy
UHECR spatial distribution constrains models and sources :
point-like for E > 10 EeV
galactic magnetic diffusion for E < 10 EeV
If anisotropy/sources are seen
• Start “charged particle astronomy”
• probe magnetic fields
• spectrometry
If no anisotropy/sources are seen
• indication of top-down origin
• re-think propagation
• ???
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.
Angular resolution
SD only
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)
Coverage map
Check the proposition: what is observed is compatible
with what is expected from an isotropic distribution;
Need: • isotropic background expectations (coverage map)
• statistical estimator of the overdensity
Acurate determination of the coverage map is the real issue!
• detector growing
• weather effects
• true large scale anisotropies
Coverage determination
Two techniques for coverage map determination:
• semi-analytical method
• shuffling (two flavours)
Acceptance almost independent of sidereal time and azimuth
Four independent groups calculated the coverage.
Shuffling method (2D)
• MC based method :
• Make N new realisations of the data arrival
direction by resampling them :
– 5 zenith angle bins
– for each event : keep zenith, sample a new
arrival time and a new azimuth from data in the
same zenith angle bin
• Average the N datasets in the window
centered around the observed direction
• This gives you the expected number of
events in that direction
Shuffling method (1D)
• MC based method :
• Make N new realisations of the data arrival
direction by resampling them :
– 5 zenith angle bins
– for each event : keep zenith, sample a new day
and a new UTC hours from data in the same
zenith angle bin and draw phi uniformily
• Average the N datasets in the window
centered around the observed direction
• This gives you the expected number of
events in that direction
Semi-analytical coverage map
• Start with events zenith angle distribution
• Fit it with some smooth functions : splines or
polynomials times a Fermi-Dirac.
• Convert the fitted zenith angle shape into a
declination distribution (analytical)
• Assume RA uniformity or use weather data to model
RA variation
• Integrate through the window
• You have the expected number of events in any
direction
Semi-analytical method
Isotropic simulation 10k events
Coverage map in galactic coordinates
Mollweide projection
Li-Ma significance map
Nev  S  B
Nco  B
Nev  Nco
Nsig 
Nev  Nco
Galactic center
• Galactic Center is a “natural” site
for cosmic ray acceleration
– Supermassive black hole
– Dense clusters of stars
– Stellar remnants
– SNR (?) Sgr A East
• SUGAR excess is consistent with
a point source, indicating neutral
primaries
• Neutrons would go undeflected,
and neutron decay length at 1018
eV is comparable to the distance
to the Galactic center (~8.5 kpc)
Chandra
Source at the Galactic center
AGASA
Significance (σ)
20o scales
( ,  )  (15,280)
1018 – 1018.4 eV
observed
506

(4.5 )
expected 413.6
22% excess
• Cuts are a posteriori
• Chance probability is
not well defined
N. Hayashida et al., Astroparticle Phys. 10 (1999) 303
Source at Galactic center
SUGAR
5.5o cone
( ,  )  (22,274)
1018 – 1018.4 eV
observed 21.8

(2.9 )
expected 11.8
85% excess
J.A. Bellido et al., Astroparticle Phys. 15 (2001) 167
Source at the Galactic Center
Coverage map
3.7o scale (SUGAR like)
1.5o scale
Significance
13.3o scale (AGASA like)
Source at the Galactic 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 center
SD only:
Gaussian filtering 1.5 degree
exp/obs 24.3/23.9
if S  CR then for 0.8 EeV < E < 3.2 EeV
S < 2.5    10-15 m-2 s-1 @ 95 %
 uncertainty in CR flux
 Iron/proton detection efficiency ratio
Hybrid :
Top hat window 1.0 degree
Exp/obs 4/3.4
if S  CR then for E > 0.1 EeV
S < 1.2   10-13 m-2 s-1 @ 95 %
Excess / Significance maps build
using the individual pointing
direction of the events.
Galactic plane and Super Galactic plane
A) GP 1-5 EeV
5077 / 5083.3
B) SGP > 5 EeV
241 / 232.8
Origin CR change galactic -> extra-galactic
1 – 10 EeV
C) SGP > 10 EeV
68 /67.4
Prescription results
For each target: specify a priory probability levels and angular scales
avoids 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 sources
significance
Li, Ma ApJ 272,
317-324 (1983)
All distributions
consistent with
isotropy
Conclusions
January 2004 - June 2005
SD Array:
• Unprecedented statistics in southern hemisphere
(anisotropy)
• Exposure 1750 km2 sr yr (1.07 total AGASA)
• On time 94.3%
• Gain one order of magnitude within the next two years (1500
physical events per day)
Hybrid:
Unprecedented core location and direction precision  excellent
shower development and energy measurements
No previous claims of anisotropy were confirmed !
This is just the beginning! We have a lot of work ahead,
including the Auger North Observatory!
Thanks!
6 doublets 1 triplet
above 4 x 1019 eV
AGASA
< 2.5 deg
above 1019 eV
Log E>19.4
Log E>19.6
Agasa clustering
• Agasa claimed high significance for their
clustering
• Analysis was done by tuning for maximum
significance
• No penalty factor or separate data set used
Significant peak in the autocorrelation plots at zero degrees: implying presence
of compact UHECR sources
HiRes
No clustering seen so far!
HiRes-I Monocular Data, E > 1019.5 eV
HiRes-I Monocular Data, E > 1018.5 eV
HiRes Stereo
Upper limit of 4 doublets (90% c.l.)
in HiRes-I monocular dataset.
GKZ suppression
• Cosmic rays E = 1020 eV interact with 2.7 K photons
• In the proton frame E  300MeV
p   3k    p   0
 n 
56
Fe   3k 56Fe  n

Photon-pion production
Photon dissociation
• Proton with less energy, eventually below the cutoff energy
EGZK= 5x 1019 eV
Universe is opaque for E > EGZK !
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
Pierre Auger South Observatory
3000 km2
A surface array station
Communications
antenna
Electronics
enclosure
GPS antenna
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
Surface detector
Station 102
Loma Amarilla
Coihueco
Los Morados
Los Leones
Trigger rates:
T1: First level trigger
T2: Second lever trigger
ToT: Time over Threshold
Electronics temperature and VEM charge
evolution over a week in April 2005
Surface detector
Correlation 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)
Absolute calibration
• Atmospheric
monitoring
• Calibration
checks
• Timing checks
Lidar at each
fluorescence eye for
atmospheric
profiling - “shooting
the shower”
Drum for uniform
illumination of each
fluorescence camera
– part of end to end
calibration .
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
Simultaneus detection in the sky and in the ground
Golden events: independent triggers
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
In construction
1208 surface detector
stations deployed
951 with eletronics and
sending data
Three fluorescence
buildings complete each
with 6 telescopes
Spectrum: previous claims
AGASA
Continuation beyond the GZK
limit?
Extragalatic sources distributed
uniformly
M. Takeda et al., PRL 81 (1998) 1163
Spectrum: previous claims
HiRes
HiRes mono spectrum consistent
with GZK suppresion
Fit to unbroken power law:
 2 dof  3.0
Fit taking into account GZK
suppression:
 2 dof  1.2
HiRes Collab., arXiv:astro-ph/0501317
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
dI
dI
E
d(ln E )
dE

Error bars Poisson statistics
Systematic uncertainty: double arrows
at two different energies
Percentage deviation from the
best-fit power law
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
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
High energy events
The highest energy SD event (86 EeV)
Properties of the 20 most energetic events
A Hybrid event