2 research outputs found
Cross-Correlation between UHECR Arrival Distribution and Large-Scale Structure
We investigate correlation between the arrival directions of
ultra-high-energy cosmic rays (UHECRs) and the large-scale structure (LSS) of
the Universe by using statistical quantities which can find the angular scale
of the correlation. The Infrared Astronomical Satellite Point Source Redshift
Survey (IRAS PSCz) catalog of galaxies is adopted for LSS. We find a positive
correlation of the highest energy events detected by the Pierre Auger
Observatory (PAO) with the IRAS galaxies inside within the angular
scale of . This positive correlation observed in the southern
sky implies that a significant fraction of the highest energy events comes from
nearby extragalactic objects. We also analyze the data of the Akeno Giant Air
Shower Array (AGASA) which observed the northern hemisphere, but the obvious
signals of positive correlation with the galaxy distribution are not found.
Since the exposure of the AGASA is smaller than the PAO, the cross-correlation
in the northern sky should be tested using a larger number of events detected
in the future. We also discuss the correlation using the all-sky combined data
sets of both the PAO and AGASA, and find a significant correlation within . These angular scales can constrain several models of intergalactic
magnetic field. These cross-correlation signals can be well reproduced by a
source model in which the distribution of UHECR sources is related to the IRAS
galaxies.Comment: 21 pages,7 figure
Small Scale Anisotropy Predictions for the Auger Observatory
We study the small scale anisotropy signal expected at the Pierre Auger
Observatory in the next 1, 5, 10, and 15 years of operation, from sources of
ultra-high energy (UHE) protons. We numerically propagate UHE protons over
cosmological distances using an injection spectrum and normalization that fits
current data up to \sim 10^{20}\eV. We characterize possible sources of
ultra-high energy cosmic rays (UHECRs) by their mean density in the local
Universe, Mpc, with between 3 and 6.
These densities span a wide range of extragalactic sites for UHECR sources,
from common to rare galaxies or even clusters of galaxies. We simulate 100
realizations for each model and calculate the two point correlation function
for events with energies above 4 \times 10^{19}\eV and above 10^{20}\eV, as
specialized to the case of the Auger telescope. We find that for r\ga 4,
Auger should be able to detect small scale anisotropies in the near future.
Distinguishing between different source densities based on cosmic ray data
alone will be more challenging than detecting a departure from isotropy and is
likely to require larger statistics of events. Combining the angular
distribution studies with the spectral shape around the GZK feature will also
help distinguish between different source scenarios.Comment: 15 pages, 6 figures, 6 tables, submitted to JCA