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Register a new userUpdate on the correlation of the highest energy cosmic rays with nearby extragalactic matter
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Miguel Mostafa Miguel Mostafa
Publication date
2010
fields
Physics
and research's language is
English
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Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuzmin energy threshold, obreak{$6times 10^{19}$eV}. The anisotropy was measured by the fraction of arrival directions that are less than $3.1^circ$ from the position of an active galactic nucleus within 75 Mpc (using the Veron-Cetty and Veron $12^{rm th}$ catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating fraction is $(38^{+7}_{-6})%$, compared with $21%$ expected for isotropic cosmic rays. This is down from the early estimate of $(69^{+11}_{-13})%$. The enlarged set of arrival directions is examined also in relation to other populations of nearby extragalactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-rays by the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has the largest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation function is shown for the enlarged set of arrival directions and compared to the isotropic expectation.
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We examine the anisotropy of the arrival directions of twenty seven ultra high energy cosmic rays detected by the Pierre Auger Collaboration. We confirm the anisotropy of the arrival directions of these events and find a significant correlation with the updated definition of the supergalactic plane at distances up to 70 Mpc, A Monte Carlo calculation of isotropic source distribution suggests a chance probability for isotropic event arrival direction distribution of 2-6$times10^{-4}$.
One of several working groups established for this workshop was charged with examining results and methods associated with the UHECR energy spectrum. We summarize the results of our discussions, which include a better understanding of the analysis choices made by groups and their motivation. We find that the energy spectra determined by the larger experiments are consistent in normalization and shape after energy scaling factors are applied. Those scaling factors are within systematic uncertainties in the energy scale, and we discuss future work aimed at reducing these systematics.
In this paper we review the extragalactic propagation of ultrahigh energy cosmic-rays (UHECR). We present the different energy loss processes of protons and nuclei, and their expected influence on energy evolution of the UHECR spectrum and composition. We discuss the possible implications of the recent composition analyses provided by the Pierre Auger Observatory. The influence of extragalactic magnetic fields and possible departures from the rectilinear case are also mentioned as well as the production of secondary cosmogenic neutrinos and photons and the constraints their observation would imply for the UHECRs origin. Finally, we conclude by briefly discussing the relevance of a multi messenger approach for solving the mystery of UHECRs.
More than 100 years after the discovery of cosmic rays and various experimental efforts, the origin of ultra-high energy cosmic rays (E > 100 PeV) remains unclear. The understanding of production and propagation effects of these highest energetic particles in the universe is one of the most intense research fields of high-energy astrophysics. With the advent of advanced simulation engines developed during the last couple of years, and the increase of experimental data, we are now in a unique position to model source and propagation parameters in an unprecedented precision and compare it to measured data from large scale observatories. In this paper we revisit the most important propagation effects of cosmic rays through photon backgrounds and magnetic fields and introduce recent developments of propagation codes. Finally, by comparing the results to experimental data, possible implications on astrophysical parameters are given.
Observation of Ultra High Energy Cosmic Rays (UHECR) -whose energy exceeds $10^20$eV- is still a puzzle for modern astrophysics. The transfer of more than 16 Joules to a microscopic particle can hardly be achieved, even in the most powerful cosmic accelerators such as AGNs, GRBs or FR-II radio galaxy lobes. Potential sources must also lie within 100 Mpc of the Earth as the interaction length of protons, nuclei or photons is less than 10Mpc. However no visible counterpart of those sources has been observed. Calling upon new physics such as Topological Defect interactions or Super Massive Relic Particle decays is therefore very tempting, but such objects are yet to be proven to exist. Due to the very low flux of UHECR only very large dedicated experiments, such as the Auger observatories, will allow to shed some light on the origin of those cosmic rays. In this quest neutrinos, if they can be detected, are an invaluable messengers of the nature of the sources.
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