Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session H8: Ultra High Energy Cosmic Rays |
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Sponsoring Units: DAP Chair: Todor Stanev, University of Delaware Room: Governor's Square 17 |
Sunday, May 3, 2009 10:45AM - 10:57AM |
H8.00001: Update of the correlation of UHECRs with nearby extragalactic objects David Thomas The Pierre Auger Observatory has become the largest cosmic ray detector ever built. Among our first results, the announcement of the correlation of 20 out of 27 arrival directions of the highest energy events ($E > 5.7\times10^{19}$~eV) with nearby ($d < 75$~Mpc) active galactic nuclei has triggered a surge of interest in source models of ultra-high energy cosmic ray origin as well as forecast studies of neutrino and gamma-ray expected signals from these objects. In this talk I will present the updated results of the correlation between the arrival directions of ultra-high energy cosmic rays detected with the Pierre Auger Observatory and nearby extragalactic objects. [Preview Abstract] |
Sunday, May 3, 2009 10:57AM - 11:09AM |
H8.00002: Small-Scale Clustering of Ultrahigh Energy Cosmic Rays at the Pierre Auger Observatory Carl Pfendner The Pierre Auger Observatory is a hybrid cosmic ray observatory located in Malargue, Argentina. One of the main goals of the experiment is the search for the sources of cosmic rays with energies above several 10$^{18}$ eV. A promising approach to finding the sources is the statistical search for anisotropies in the cosmic ray arrival direction distribution in itself. Compact sources of cosmic rays could for example manifest themselves in a significant amount of event clusters (doublets, triplets,...) on small angular scales. We present results on searches for significant small-scale clustering in the arrival direction distribution of cosmic rays with energies above 4$\cdot $10$^{19}$ eV on angular scales up to 10\r{ }. The method, results, and error studies will be discussed. [Preview Abstract] |
Sunday, May 3, 2009 11:09AM - 11:21AM |
H8.00003: Search for Correlations between HiRes Events' Pointing Directions and Local Large Scale Structure Gordon Thomson We have searched for correlations in the pointing directions of cosmic ray showers collected by the High Resolution Fly's Eye (HiRes) experiment and the large scale structure of galaxies in our vicinity. HiRes stereo events were used for the analysis. The analysis will be described and the results presented. [Preview Abstract] |
Sunday, May 3, 2009 11:21AM - 11:33AM |
H8.00004: Ultra high energy cosmic rays from black hole jets of radio galaxies Charles Dermer, S. Razzaque, J.D. Finke, A. Atoyan The Auger Collaboration reports [1, 2] that the arrival directions of $>$60 EeV ultra-high energy cosmic rays (UHECRs) cluster along the supergalactic plane and correlate with active galactic nuclei (AGN) within 100 Mpc. The association of several events with the nearby radio galaxy Centaurus A supports the paradigm that UHECRs are powered by supermassive black-hole engines and accelerated to ultra- high energies in the shocks formed by variable plasma winds in the inner jets of radio galaxies. The GZK horizon length of 60 EeV UHECR protons is 100 Mpc, consistent with a largely proton composition of the UHECRs. In this scenario, the sources of UHECRs are FR II radio galaxies and FR I galaxies like Cen A with scattered radiation fields that enhance UHECR neutral-beam production. Radio galaxies with jets pointed away from us can still be observed as UHECR sources due to deflection of UHECRs by magnetic fields in the radio lobes of these galaxies. A broadband $\sim$ 1 MeV - 10 EeV radiation component in the spectra of blazar AGN is formed by UHECR-induced cascade radiation in the extragalactic background light (EBL). This emission is too faint to be seen from Cen A, but could be detected from more luminous blazars. [Preview Abstract] |
Sunday, May 3, 2009 11:33AM - 11:45AM |
H8.00005: A Three-Point Cosmic Ray Anisotropy Method John Hague, Bernard Becker, Michael Gold, John Matthews The two-point angular correlation function is a traditional method used to search for deviations from expectations. In this paper we develop and explore a new three-point (shape-strength) method with the intended application being the search for deviations from isotropy in the highest energy cosmic rays. We compare the sensitivity of two-point and shape-strength methods for a variety of Monte-Carlo simulated (mock data) anisotropic signals. Studies are done with anisotropic source signals diluted by an isotropic background. Type I and II errors for rejecting the hypothesis of isotropic cosmic ray arrival directions are evaluated for four different event sample sizes: 27, 40, 60 and 80 events consistent with near term data expectations from the Pierre Auger Observatory. In all cases the ability to reject the isotropic hypothesis improves with event size and with the fraction of anisotropic signal. While $\sim 80$ event data sets should be sufficient for reliable identification of anisotropy in cases of rather extreme (highly anisotropic) data, much larger data sets are suggested for reliable identification of more subtle anisotropies. The shape-strength method consistently performs better than the two point correlation. Applying these methods to the 27 events above 57 EeV published by the Pierre Auger Observatory we find a 3 probability of isotropy using the two-point method and 0.2\% probability using the shape-strength method. [Preview Abstract] |
Sunday, May 3, 2009 11:45AM - 11:57AM |
H8.00006: Stereoscopic Measurement of the Flux of Ultra High Energy Cosmic Rays by the High Resolution Fly's Eye Observatory William Hanlon The High Resolution Fly's Eye (HiRes) experiment has measured the flux of ultrahigh energy cosmic rays using the stereoscopic air fluorescence technique. The HiRes experiment consists of two detectors that observe cosmic ray air showers via the fluorescence light they emit. HiRes data can be analyzed in monocular mode, where each detector is treated separately, or in stereoscopic mode where they are considered together. Using the monocular mode, the HiRes collaboration measured the cosmic ray spectrum and made the first observation of the Greisen-Zatsepin-Kuz'min cutoff. The cosmic ray spectrum measured by the stereoscopic technique is presented here. Good agreement is found with the monocular spectrum in all respects. [Preview Abstract] |
Sunday, May 3, 2009 11:57AM - 12:09PM |
H8.00007: On Estimating the Relative Flux of the Brightest Cosmic Ray Source above 6x10$^{19}$ eV Patrick Younk Recent observations by the the Pierre Auger Observatory support the hypothesis that ultra-high energy cosmic rays originate in astrophysical environments external to the galaxy and that the Greisen-Zatsepin-Kuz'min (GZK) effect is in operation. The GZK effect is a prediction made 40 years ago that the highest energy cosmic rays suffer energy losses due to interactions with the cosmic microwave background and that the majority of cosmic rays above 6x10$^{19}$ eV (super-GZK) must originate from sources within 200 Mpc. In this talk, we will demonstrate that this hypothesis implies that the relative flux of the brightest super-GZK source is at the few percent level or above. This prediction is robust with regard to assumptions on the source type or source space density. The Pierre Auger Observatory observes approximately 20 super-GZK events per year. Therefore, it is expected that over the course of several years, tens of events from a single extragalactic cosmic ray source will be seen. This will be enough statistics to measure specific properties of the source; cosmic ray astronomy will have begun. [Preview Abstract] |
Sunday, May 3, 2009 12:09PM - 12:21PM |
H8.00008: Lorentz Invariance Violation and the Observed Spectrum of Ultrahigh Energy Cosmic Rays Floyd Stecker, Sean Scully There has been much interest in possible violations of Lorentz invariance, particularly motivated by quantum gravity theories. It has been suggested that a small amount of Lorentz invariance violation (LIV) could turn off photomeson interactions of ultrahigh energy cosmic rays (UHECRs) with photons of the cosmic background radiation and thereby eliminate the resulting sharp steepening in the spectrum of the highest energy CRs predicted by Greisen Zatsepin and Kuzmin (GZK). Recent measurements of the UHECR spectrum reported by the HiRes and Auger collaborations, however, indicate the presence of the GZK effect. We present the results of a detailed calculation of the modification of the UHECR spectrum caused by LIV using the formalism of Coleman and Glashow. We then compare these results with the experimental UHECR data from Auger and HiRes. We find an upper limit on the amount of LIV of $5 \times 10^{-23}$. Within that limit we discuss how a small amount of LIV that is consistent with the experimental data can still lead to a recovery of the cosmic ray flux at higher energies than presently observed. [Preview Abstract] |
Sunday, May 3, 2009 12:21PM - 12:33PM |
H8.00009: Large scale Cosmic Rays Anisotropy as Observed With IceCube Rasha Abbasi IceCube is a neutrino observatory under construction at the geographic South Pole. When completed it will comprise 80 strings deployed in the deep ice between 1,450 and 2,450 meters depth, each string containing 60 optical sensors. From April 2007 to March 2008 data were collected with 22 deployed strings. An analysis was performed on this data to measure large-scale cosmic-rays anisotropy with $\sim $4.3 billion events with a median cosmic ray energy of $\sim $ 14 TeV. A two-dimensional skymap is presented with an evidence of $\sim $ 0.1{\%} large-scale anisotropy. This result bears implications to our understanding of cosmic rays, galactic magnetic field and possible origin for this anisotropy. [Preview Abstract] |
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