Search For Large-scale Anisotropy Research Articles

Search for Large-scale Anisotropy on Arrival Directions of Ultra-high-energy Cosmic Rays Observed with the Telescope Array Experiment

Abstract Motivated by the detection of a significant dipole structure in the arrival directions of ultra-high-energy cosmic rays above 8 EeV reported by the Pierre Auger Observatory (Auger), we search for a large-scale anisotropy using data collected with the surface detector array of the Telescope Array Experiment (TA). With 11 yr of TA data, a dipole structure in a projection of the R.A. is fitted with an amplitude of 3.3% ± 1.9% and a phase of 131° ± 33°. The corresponding 99% confidence-level upper limit on the amplitude is 7.3%. At the current level of statistics, the fitted result is compatible with both an isotropic distribution and the dipole structure reported by Auger.

Summary of the main results of the KASCADE and KASCADE-Grande experiments

The KASCADE and KASCADE-Grande experiments operated in KIT-Campus North, Karlsruhe (Germany) from 1993 to 2012. The two experiments studied primary cosmic rays in the energy range from 1014 eV to 1018 eV, investigating the change of slope of the spectrum detected at 2 - 4 × 1015 eV, the so called knee. We briefly review the performance of the experiments and then the main results obtained in the operation of both experiments: the test of hadronic interaction models, the all particle primary spectrum, the elemental composition of primary cosmic rays (with the first claim of a knee-like feature of the heavy primaries spectrum) and the search for large scale anisotropies.

KASCADE-Grande experiment measurements of the cosmic ray spectrum and large scale anisotropy

The KASCADE-Grande experiment operated at KIT from January 2004 to November 2012, measuring Extensive Air Showers (EAS) generated by primary cosmic rays in the 1016–1018eV energy range. The experiment measured, for each single event, with a high resolution, the total number of charged particles (Nch) and of muons (Nμ).In this contribution we summarize the results obtained about:(i) the measurement of the all particle energy spectrum, discussing the influence of the hadronic interaction model used to derive the energy calibration of the experimental data.(ii) The energy spectra derived separating the events according to the Nμ/Nch ratio. This technique allowed us to unveil a steepening of the spectrum of heavy primaries at E∼1016.92±0.04eV and a hardening of the spectrum of light primaries at E∼1017.08±0.08eV.(ii) A search for large scale anisotropies.

Latest results from the KASCADE-Grande experiment

The KASCADE-Grande experiment operated at KIT from January 2004 to November 2012, measuring EAS generated by primary cosmic rays in the 1016–1018eV energy range. The experiment detected, for each single event, with a high resolution, the total number of charged particles (Nch) and of muons (Nμ).In this contribution we present the latest results about:(i)The measurement of the all particle energy spectrum, discussing the influence of the hadronic interaction model used to derive the energy calibration of the experimental data.(ii)The energy spectra derived separating the events according to the Nμ/Nch ratio. This technique allowed us to unveil a steepening of the spectrum of heavy primaries at E~1016.92±0.04eV and a hardening of the spectrum of light primaries at E~1017.08±0.08eV.(iii)The elemental spectra (for five mass groups) obtained applying a detailed unfolding analysis technique.(iv)A search for large scale anisotropies.

CONSTRAINTS ON THE ORIGIN OF COSMIC RAYS ABOVE 10 18 eV FROM LARGE-SCALE ANISOTROPY SEARCHES IN DATA OF THE PIERRE AUGER OBSERVATORY

A thorough search for large scale anisotropies in the distribution of arrival directions of cosmic rays detected above $10^{18}$ eV at the Pierre Auger Observatory is reported. For the first time, these large scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above $10^{18}$ eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions.

LARGE-SCALE DISTRIBUTION OF ARRIVAL DIRECTIONS OF COSMIC RAYS DETECTED ABOVE 1018 eV AT THE PIERRE AUGER OBSERVATORY

ABSTRACT A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above 1018 eV at the Pierre Auger Observatory is presented. This search is performed as a function of both declination and right ascension in several energy ranges above 1018 eV, and reported in terms of dipolar and quadrupolar coefficients. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Assuming that any cosmic-ray anisotropy is dominated by dipole and quadrupole moments in this energy range, upper limits on their amplitudes are derived. These upper limits allow us to test the origin of cosmic rays above 1018 eV from stationary Galactic sources densely distributed in the Galactic disk and predominantly emitting light particles in all directions.

Large scale anisotropy studies with the Pierre Auger Observatory

Completed at the end of 2008, the Pierre Auger Observatory has been continuously operating for more than seven years. We present here the analysis techniques and the results about the search for large scale anisotropies in the sky distribution of cosmic rays, reporting both the phase and the amplitude measurements of the first harmonic modulation in right ascension in different energy ranges above 2.5×1017eV. Thanks to the collected statistics, a sensitivity of 1% at EeV energies can be reached. No significant anisotropies have been observed, upper limits on the amplitudes have been derived and are here compared with the results of previous experiments and with some theoretical expectations.

The effect of the geomagnetic field on cosmic ray energy estimates and large scale anisotropy searches on data from the Pierre Auger Observatory

We present a comprehensive study of the influence of the geomagnetic field on the energy estimation of extensive air showers with a zenithangle smaller than 60°, detected at the Pierre Auger Observatory.The geomagnetic field induces an azimuthal modulation of the estimated energy of cosmic rays up to the ∼ 2% level at large zenith angles.We present a method to account for this modulation of the reconstructed energy. We analyse the effect of the modulation on large scale anisotropy searches in the arrival direction distributions of cosmic rays. At a given energy, the geomagnetic effect is shown to induce a pseudo-dipolar pattern at the percent level in the declination distribution that needs to be accounted for.

Study of penetrating cosmic ray muons and search for large scale anisotropies at the Gran Sasso Laboratory

The MACRO detector, located in the underground Gran Sasso Laboratory, had its initial data run from February 27 to May 30, 1989, using the first supermodule (SΩ∼800 m 2 sr) . Approximately 245 000 muon events were recorded. Here are reported the results of the analysis of penetrating muons which determine the measured vertical muon flux at depths greater than 3000 m.w.e. In addition the data have been used to search for large scale anisotropies.