52° congresso sait 2008 raffaella bonino* for the pierre auger collaboration ( * ) ifsi – infn...
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52° Congresso SAIt 200852° Congresso SAIt 2008
Raffaella BoninoRaffaella Bonino** for the Pierre Auger Collaboration for the Pierre Auger Collaboration((**)) IFSI – INFN – Università di Torino IFSI – INFN – Università di Torino
08/05/2008 SAIt 2008 Raffaella Bonino
OutlineOutlineThe origin of the highest energies cosmic rays (>1019 eV) is expected to be extra-galacticextra-galactic What are these extra-galactic sources? search for correlations
Somewhere downwards in the spectrum, the transitiontransition from galactic to extra-gal. must occur Where? study of large scale anisotropies (change in the large scale angular distribution)
The Galactic CenterGalactic Center is one of the most interesting galactic target look for localized excesses of CRs in the GC region at ~ 1018 eV
Required tools: knowledge of the angular resolution of the Surface Detector angular reconstruction and timing uncertainty model
08/05/2008 SAIt 2008 Raffaella Bonino
Auger Surface DetectorAuger Surface Detector
08/05/2008 SAIt 2008 Raffaella Bonino
SD arrival directionsSD arrival directionsarrival times and angular arrival times and angular
resolutionresolution Especially for the analysis of small scale anisotropy a good angular
resolution and detector stability are required
The angular resolution is strictly dependent on the accuracy in the arrival time measurement of the particles in the tanks
The arrival direction is measured from the delays among the hit tanks
08/05/2008 SAIt 2008 Raffaella Bonino
““Start TimeStart Time””It should correspond to the arrival time of the shower front to the detectors
It’s identified with the arrival time of the first particle detected ⇒ the first bin above a fixed threshold in a 2 or 3-fold coincidence
Start Time
08/05/2008 SAIt 2008 Raffaella Bonino
SD angular resolutionSD angular resolutionComputed on an event by event basis:→ and derived from the fit of the arrival
time of the first particle on the tank
Based on:Parabolic shower front model
Semi-empirical timing uncertainty model
Angular resolution ≡ angular radius that would contain 68% of the showers coming from a point-like source
08/05/2008 SAIt 2008 Raffaella Bonino
SD angular resolutionSD angular resolution
Comparison with hybrid reconstruction (~0.6°) confirms the
SD-only result
SD-only Hybrid
Large scale anisotropy Large scale anisotropy studiesstudies
08/05/2008 SAIt 2008 Raffaella Bonino
OverviewOverviewObjective: galactic: %-level modulation (models of gal. propagation)
CR’s origin at ~1018eV extra-gal.: no structure except for a CMB-dipole (~0.6%) at higher energies: GZK cut-off → sources → anisotropy
Difficulties: control of spurious modulationssky exposureinstabilities due to atmospheric and instrumental effectsnot constant acceptance
3 complementary analysis in the EeV (=1018eV) range (5·105 events)
08/05/2008 SAIt 2008 Raffaella Bonino
Auger resultsAuger resultsResults from the search for large-scale patterns:
no modulation in RAno modulation in RA95% c.l. upper limit = 1.4% 95% c.l. upper limit = 1.4% for 1 < E < 3 EeV
Exposure-independent cross-checks confirm the lack of significant pattern
The AGASA 4% modulation is not confirmed (but the observed regions of the sky are different)
The Galactic CenterThe Galactic Centerregionregion
08/05/2008 SAIt 2008 Raffaella Bonino
Why the Galactic Center?Why the Galactic Center?GC contains a super-massive black hole → possible candidate to accelerate CR
It passes only 6° away from the AUGER zenith
Claims in the past from other experiments of large excesses in GC region:
SUGARSUGAR:excess = 85%
E = 1017.9-1018.5 eV(,) = (274°,-22°)
AGASAAGASA:excess = 22%
E = 1018-1018.4 eV(,) = (280°,-17°)
H.E.S.S.H.E.S.S. detected a TeV -ray
source close to Sagittarius A*
08/05/2008 SAIt 2008 Raffaella Bonino
Auger resultsAuger results as extended source
In our analysis GC treated both as point-like source
Data set divided into 2 energy bands:
0.1 < E < 1 EeV
1 < E < 10 EeV
Conclusions:No significant CRs flux excess in both energy rangesDistribution of Li-Ma overdensity significances consistent with isotropic sky
08/05/2008 SAIt 2008 Raffaella Bonino
08/05/2008 SAIt 2008 Raffaella Bonino
UHECR sourcesUHECR sources
Sizes and magnetic field strengths
of astronomical objects that are
possible candidates as CR sources
AGN
Radio Galaxies
)()()(max KpcRGBZeVE
Hillas plot
BUT…GZK cut- off : only nearby sources (within ~ 100-200 Mpc) should
contribute to the flux above EGZK = 6·1019 eV
08/05/2008 SAIt 2008 Raffaella Bonino
Ultra High Energy Cosmic Ultra High Energy Cosmic RaysRays
Particles with E ~ 1020 eV exist and have been detectedwhat are and where do they come from?what are and where do they come from?
Complementary studies:
Energy spectrum and composition
Origin → study of anisotropy in arrival directions:
LARGE SCALE: transition from galactic to extra-galactic origin = change in the large scaleangular distribution because of different mechanisms of propagation
SMALL SCALE: above 5·1019 eV cosmic rays are only slightly deflected (2°-3°) by magnetic fields → direct way to search for UHECR sourcesIf sources are nearby and not uniformly distributed, an anisotropic arrival directionsdistribution is expected (“clustering”)
08/05/2008 SAIt 2008 Raffaella Bonino
SD angular resolutionSD angular resolutionComputed on an event by event basis:→ and derived from the fit of the arrival
time of the first particle on the tank
Based on:Parabolic shower front modelSemi-empirical timing uncertainty model [C.Bonifazi et al., astro-[C.Bonifazi et al., astro-ph0705.1856]ph0705.1856]
Space-angle uncertainty computed from and :
Angular resolution ≡ angular radius that would contain 68% of the showers comingfrom a point-like source:
sinF
FAR .
08/05/2008 SAIt 2008 Raffaella Bonino
11stst method method - - Fourier time Fourier time analysisanalysis
Spectral analysis on the « modified time » of the events : tmod=t+RA-LST
fsid
fsol
fantisid
All energiesΔf
Results: no signal in sidereal frequency solar modulation of 3.2% due to atmospheric effects analysis repeated in 3 different energy ranges → no significant sid. modulation
At sidereal frequency, recover the RA modulation
Frequency resolution Δf ~1/Tacquis
Compare the sidereal signal to: - the antisidereal signal - the average noise in other freq.
08/05/2008 SAIt 2008 Raffaella Bonino
Characteristics: Differential method Allows to remove direction-independent phenomena
(i.e. atmospheric and not-constant acceptance effects)
)()()()()()()(
)()()(
)()()(
tWtEttWtEttIttI
tttItW
tttItE
ttWtEtI
dtdI
)()()('
22ndnd method method - - East-West method East-West method
where I(t) = physical CR intensity
First harmonic analysis on (E-W) amplitude of the sidereal modulation of I(t)
08/05/2008 SAIt 2008 Raffaella Bonino
Results (using the whole data set: Emedian ~ 6· 1017 eV) : solar modulation: reduced from 4.2% to 0.8% (±0.4%)
sidereal modulation: (0.7±0.4)% corresponding to PRayleigh=24%
antisidereal modulation = (0.5±0.4)%
95% c.l. upper limit = 1.4%95% c.l. upper limit = 1.4%
amplitudes
95% c.l. upper limits
Scan in energy
(4.2 ± 0.4)% (0.8 ± 0.4)%
22ndnd method method - - East-West method East-West method
08/05/2008 SAIt 2008 Raffaella Bonino
33rdrd method method - - Exposure-based Exposure-based studystudy
Resid
ual m
odul
atio
n 1 < E < 3 EeV
A scan in energy has been done no significant excess
Energy (EeV) nb events -(expected noise)
sid. ampl. –(phase)
antisid. ampl.
upper limits 95% c.l.
1 < E < 3 69641 (0.7%) 0.74% (330º) 0.6% 1.4%
3 < E < 10 7722 (2.0%) 1.2% (100º) 1.1% 3.2%
E > 10 1437 (4.7%) 3.5% (70º) 4.2% 8.6%
Measure the residual modulation after dividing by the exposure - modulations compatible with the
statistical + systematic errorsUpper limit derived from MC, taking into account the measured modulation
Results:
08/05/2008 SAIt 2008 Raffaella Bonino
Large scale anisotropyLarge scale anisotropy1st method
2nd method
3rd methodAll energies
fsid
fsol
fsid
95% c.l. upper limits
amplitudes
Scan in energy
Scan in energy
Correlation of UHECR Correlation of UHECR with with
nearby extra-gal. nearby extra-gal. objectsobjects
08/05/2008 SAIt 2008 Raffaella Bonino
What are AGN ?What are AGN ?
Active Galactic Nuclei:Active Galactic Nuclei: galaxies hosting central black holes that feed on gas and stars
and may eject vast plasma jets into intergalactic space
Different names → unified scheme
08/05/2008 SAIt 2008 Raffaella Bonino
Other possible UHECR Other possible UHECR sourcessources
BL – Lacs = subclass of blazars, active galaxies with beamed emission from a relativistic jet aligned toward our line of sight → potential sources of UHECRs
AUGER results:AUGER results:
AUGER doesn’t support correlations reported by AGASA, YakutskAGASA, Yakutsk and HiResHiRes data no excess from an extended search
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