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New Abstracts of Interest
A cumulative list of titles for the current year can be found here (new window). Previous years' titles: 2002 | 2003 | 2004 | 2005 | 2006 | 2007 (new window). Abstract: 0811.2897 Full Text: [ PostScript, PDF] Title: Very-High Energy Gamma-Ray Flux Limits for Nearby Active Galactic Nuclei(Submitted on 18 Nov 2008)
Abstract: Combining the results of targeted observations, H.E.S.S. has accumulated a large amount of extra-galactic exposure at TeV energies. Due to its large field of view a considerable part of the sky (0.6 sr) has been observed with high sensitivity outside the targeted observation positions. Since this exposure region contains little inherent bias, it is well suited for studies of extra-galactic source populations. Given the correlation between ultra-high energy cosmic rays and nearby extra-galactic objects recently claimed by the Auger collaboration, this unbiased sky sample by H.E.S.S. is of interest since it includes (besides the targeted sources) 63 AGN within 100 Mpc, for which very-high energy gamma-ray flux limits are derived.
Abstract: 0811.1671 Full Text: [ PostScript, PDF] Title: First Results from the IceTop Air Shower Array(Submitted on 11 Nov 2008)
Abstract: IceTop is a 1 km^2 air shower detector presently under construction as a part of the IceCube Observatory at South Pole. It will consist of 80 detector stations, each equipped with two ice Cherenkov tanks, which cover 1 km^2. In 2008, the detector is half completed. One of the design goals of the detector is to investigate cosmic rays in the energy range from the knee up to approaching 1 EeV and study the mass composition of primary cosmic rays.
Abstract: 0811.2520 Full Text: [ PostScript, PDF] Title: AURA - A radio frequency extension to IceCube(Submitted on 15 Nov 2008)
Abstract: The excellent radio frequency transparency of cold polar ice, combined with the coherent Cherenkov emission produced by neutrino-induced showers when viewed at wavelengths longer than a few centimeters, has spurred considerable interest in a large-scale radio-wave neutrino detector array.
Abstract: 0811.2408 Full Text: [ PostScript, PDF] Title: An 84 microGauss Magnetic Field in a Galaxy at Redshift z=0.692(Submitted on 14 Nov 2008)
Abstract: The magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars. The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ~ 3 microGauss. The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain. Here we report a measurement of a magnetic field of B ~ 84 microGauss in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 microGauss in the neutral interstellar gas of our Galaxy. This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past rather than stronger. Abstract: 0811.1848 Full Text: [ PostScript, PDF] Title: Active Galactic Nuclei: Sources for ultra high energy cosmic rays?(Submitted on 12 Nov 2008 (v1), last revised 18 Nov 2008 (this version, v2))
Abstract: The origin of ultra high energy cosmic rays promises to lead us to a deeper understanding of the structure of matter, through the study of particle collisions at center-of-mass energies in interactions far larger than anything possible with the Large Hadron Collider, albeit at the substantial cost of no control over the sources and interaction sites. For the extreme energies we have to identify and understand the sources first, before trying to use them as physics laboratories. Here we describe the current stage of this exploration. The most promising contenders as sources are radio galaxies and gamma ray bursts. The sky distribution of observed events yields a hint favoring radio galaxies. Key in this quest are the intergalactic and galactic magnetic fields, whose strength and structure are not yet fully understood. Current data and statistics do not yet allow a final judgment. We outline how we may progress in the near future.
Abstract: 0811.1919 Full Text: [ PostScript, PDF] Title: Air Shower Measurements with the LOPES Radio Antenna Array(Submitted on 12 Nov 2008)
Abstract: LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from Extensive Air Showers. Since radio waves suffer very little attenuation, radio measurements allow the detection of very distant or highly inclined showers. These waves can be recorded day and night, and provide a bolometric measure of the leptonic shower component. LOPES is designed as a digital radio interferometer using high bandwidths and fast data processing and profits from the reconstructed air shower observables of KASCADE-Grande. The LOPES antennas are absolutely amplitude calibrated allowing to reconstruct the electric field strength which can be compared with predictions from detailed Monte Carlo simulations. We report about the analysis of correlations present in the radio signals measured by the LOPES 30 antenna array. Additionally, LOPES operates antennas of a different type (LOPES-STAR) which are optimized for an application at the Pierre Auger Observatory. Status, recent results of the data analysis and further perspectives of LOPES and the possible large scale application of this new detection technique are discussed.
Abstract: 0811.2230 Full Text: [ PostScript, PDF] Title: Lorentz Invariance Violation and the Observed Spectrum of Ultrahigh Energy Cosmic Rays(Submitted on 13 Nov 2008)
Abstract: 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.
Links to: arXiv, astro-ph, find, abs
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