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arXiv2007

Superluminal motion and closed signal curves

We discuss some properties of Lorentz invariant theories which allow for superluminal motion. We show that, if signals are always sent forward in time, closed curves along which signals propagate can be formed. This leads to problems with causality and with the second law of thermodynamics. Only if one singles out one frame with respect to which all signals travel forward in time, the formation of 'closed signal curves' can be prevented. However, the price to pay is that in some reference frames perturbations propagate towards the past or towards the future, depending on the direction of emission.

astro-ph↗

arXiv2007

Composition-sensitive parameters measured with the surface detector of the Pierre Auger Observatory

A key step towards the understanding of the origin of ultra-high energy cosmic rays is their mass composition. Primary photons and neutrinos produce markedly different showers from nuclei, while showers of different nuclear species are not easy to distinguish. To maximise the discrimination with the Pierre Auger Observatory ideally all mass-sensitive observables should be combined, but the 10% duty cycle of the fluorescence detector limits the use of direct measurements of shower maximum at the highest energies. Therefore, we investigate mass-sensitive observables accessible with the surface detectors alone. These are the signal risetime in the Cherenkov stations, the curvature of the shower front, the muon-to-electromagnetic ratio, and the azimuthal signal asymmetry. Risetime and curvature depend mainly on the depth of the shower development in the atmosphere, and thus on primary energy and mass. The muon content of a shower depends on the primary energy and the number of nucleons, while asymmetry about the shower core is due to geometric effects and attenuation, which are dependent on the primary mass. The mass sensitivity of these variables is demonstrated and their application for composition studies is discussed.

astro-ph↗

arXiv2007

Limits to the diffuse flux of UHE tau neutrinos at EeV energies from the Pierre Auger Observatory

With the Pierre Auger Observatory we have the capability of detecting ultra-high energy neutrinos by searching for very inclined showers with a significant electromagnetic component. In this work we discuss the discrimination power of the instrument for earth skimming tau neutrinos with ultra-high energies. Based on the data collected since January 2004 an upper limit to the diffuse flux of neutrinos atEeV energies is presented and systematic uncertainties are discussed.

astro-ph↗

arXiv2007

New method for atmospheric calibration at the Pierre Auger Observatory using FRAM, a robotic astronomical telescope

FRAM - F/(Ph)otometric Robotic Atmospheric Monitor is the latest addition to the atmospheric monitoring instruments of the Pierre Auger Observatory. An optical telescope equipped with CCD camera and photometer, it automatically observes a set of selected standard stars and a calibrated terrestrial source. Primarily, the wavelength dependence of the attenuation is derived and the comparison between its vertical values (for stars) and horizontal values (for the terrestrial source) is made. Further, the integral vertical aerosol optical depth can be obtained. A secondary program of the instrument, the detection of optical counterparts of gamma-ray bursts, has already proven successful. The hardware setup, software system, data taking procedures, and first analysis results are described in this paper.

astro-ph↗

arXiv2007

Search for correlation of UHECRs and BL Lacs in Pierre Auger Observatory data

Several analyses of the data collected by other experiments have found an excess of cosmic rays in correlation with subclasses of BL Lacs. Data from the Pierre Auger Observatory do not support previously reported excesses. The number of events correlated with BL Lac positions is compatible with that expected for an isotropic flux.

astro-ph↗

arXiv2007

Systematic study of atmosphere-induced influences and uncertainties on shower reconstruction at the Pierre Auger Observatory

A wide range of atmospheric monitoring instruments is employed at the Pierre Auger Observatory: two laser facilities, elastic lidar stations, aerosol phase function monitors, a horizontal attenuation monitor, star monitors, weather stations, and balloon soundings. We describe the impact of analyzed atmospheric data on the accuracy of shower reconstructions, and in particular study the effect of the data on the shower energy and the depth of shower maximum (Xmax). These effects have been studied using the subset of golden hybrid events - events observed with high quality in the fluorescence and surface detector - used in the calibration of the surface detector energy spectrum.

astro-ph↗

arXiv2007

Studies of clustering in the arrival directions of cosmic rays detected at the Pierre Auger Observatory above 10 EeV

If clustering of the arrival directions of ultra high energy cosmic rays is discovered, this would provide important information about their origin, composition, and the galactic and extragalactic magnetic fields. We present here the analysis of the autocorrelation function of the data from the Pierre Auger Observatory as a function of the angular scale and the energy threshold. We compare our results with the signals found by previous experiments.

astro-ph↗

arXiv2007

The GRB afterglow onset observed by REM: fireball Lorentz factor and afterglow fluence

We report observations of the early light curves of GRB 060418 and GRB 060607A, carried out with the pink robotic telescope REM. A clear peak is detected for both events, which is interpreted as the onset of the afterglow, that is the time at which the fireball starts decelerating. This detection allows to directly measure the initial fireball Lorentz factor, which was found to be Gamma_0 ~ 400 for both events, fully confirming the ultrarelativistic nature of gamma-ray burst fireballs. Sampling the light curve before the peak also allows to compute the bolometric fluence of the afterglow, which is 16% of the prompt one in the case of GRB 060418.

astro-ph↗

arXiv2007

HD 114839 - An Am star showing both delta Scuti and gamma Dor pulsations discovered through MOST photometry

Using MOST (Microvariability and Oscillations of STars) satellite guide star photometry, we have discovered a metallic A star showing hybrid p- and g-mode pulsations. HD 114839 was observed nearly continuously for 10 days in March, 2005. We identify frequencies in three groups: the first centered near 2 cycles/day, in the gamma Dor pulsation range, and two others near 8 and 20, both in the delta Scuti range. This is only the fourth known such hybrid pulsator, including another MOST discovery (Rowe et al. 2006, this issue).

astro-ph↗

arXiv2007

Test of hadronic interaction models with data from the Pierre Auger Observatory

The Pierre Auger Observatory allows the measurement of both longitudinal profiles and lateral particle distributions of high-energy showers. The former trace the overall shower development, mainly of the electromagnetic component close to the core where the latter reflect the particle densities in the tail of the shower far away from the core and are sensitive to both the muonic and electromagnetic components. Combining the two complementary measurements, predictions of air shower simulations are tested. In particular the muon component of the tank signals, which is sensitive to hadronic interactions at high energy, is studied with several independent methods. Implications for the simulation of hadronic interactions at ultra-high energy are discussed.

astro-ph↗

arXiv2007

Applying Extensive Air Shower Universality to Ground Detector Data

Air shower universality states that the electromagnetic part of hadron-induced extensive air showers (EAS) can be completely described in terms of the primary energy and shower age. In addition, simulations show that the muon part is well characterized by an overall normalization which depends on the primary particle and hadronic interaction model. We investigate the consequences of EAS universality for ground arrays, which sample EAS at large core distances, and show how universality can be used to experimentally determine the muon content as well as the primary energy of cosmic ray air showers in a model-independent way.

astro-ph↗

arXiv2007

Spacetime Indeterminacy and Holographic Noise

A new kind of quantum indeterminacy of transverse position is shown to arise from quantum degrees of freedom of spacetime, based on the assumption that classical trajectories can be defined no better than the diffraction limit of Planck scale waves. Indeterminacy of the angular orientation of particle trajectories due to wave/particle duality at the Planck scale leads to indeterminacy of a nearly-flat spacetime metric, described as a small nonvanishing quantum commutation relation between transverse position operators at different events along a null trajectory. An independent derivation of the same effect is presented based on the requirement of unitarity in black hole evaporation. The indeterminacy is interpreted as a universal holographic quantum spacetime noise, with a frequency-independent spectrum of metric perturbation amplitude, h_H^2^{1/2} \simeq \sqrt{l_P}=2.3 \times 10^{-22} /\sqrt{Hz}, where l_P denotes the Planck length. The effect is estimated to be directly measurable using current interferometer technology similar to LIGO and LISA.

gr-qc↗

arXiv2007

Probing CP violation in neutrino oscillations with neutrino telescopes

Measurements of flavor ratios of astrophysical neutrino fluxes are sensitive to the two yet unknown mixing parameters $θ_{13}$ and $δ$ through the combination $\sinθ_{13}\cosδ$. We extend previous studies by considering the possibility that neutrino fluxes from more than a single type of sources will be measured. We point out that, if reactor experiments establish a lower bound on $θ_{13}$, then neutrino telescopes might establish an upper bound on $|\cosδ|$ that is smaller than one, and by that prove that CP is violated in neutrino oscillations. Such a measurement requires several favorable ingredients to occur: (i) $θ_{13}$ is not far below the present upper bound; (ii) The uncertainties in $θ_{12}$ and $θ_{23}$ are reduced by a factor of about two; (iii) Neutrino fluxes from muon-damped sources are identified, and their flavor ratios measured with accuracy of order 10% or better. For the last condition to be achieved with the planned km^3 detectors, the neutrino flux should be close to the Waxman-Bahcall bound. It motivates neutrino telescopes that are effectively about 10 times larger than IceCube for energies of O(100 TeV), even at the expense of a higher energy threshold.

hep-ph↗

arXiv2007

Measurement of the UHECR energy spectrum using data from the Surface Detector of the Pierre Auger Observatory

At the southern site of the Pierre Auger Observatory, which is close to completion, an exposure that significantly exceeds the largest forerunner experiments has already been accumulated. We report a measurement of the cosmic ray energy spectrum based on the high statistics collected by the surface detector. The methods developed to determine the spectrum from reconstructed observables are described. The energy calibration of the observables, which exploits the correlation of surface detector data with fluorescence measurements in hybrid events, is presented in detail. The methods are simple and robust, exploiting the combination of fluorescence detector (FD) and surface detector (SD) and do not rely on detailed numerical simulation or any assumption about the chemical composition. Besides presenting statistical uncertainties, we address the impact of systematic uncertainties.

astro-ph↗

arXiv2007

Prompt muons in extended air showers

We present results of simulations of a muon content in the air showers induced by very high energy cosmic rays. Muon energy distributions and muon densities at ground level are given. We discuss a prompt muon component generated by decays of charm mesons. The method combines standard Monte Carlo generators incorporated in the CORSIKA code and phenomenological estimates of the charm hadroproduction.

astro-ph↗

arXiv2007

GRB Cosmology

Current observations are about to open up a direct window into the final frontier of cosmology: the first billion years in cosmic history when the first stars and galaxies formed. Even before the launch of the James Webb Space Telescope, it might be possible to utilize Gamma-ray Bursts (GRBs) as unique probes of cosmic star formation and the state of the intergalactic medium (IGM) up to redshifts of several tens, when the first (Population III) stars had formed. The Swift mission, or future satellites such as EXIST, might be the first observatories to detect individual Population III stars, provided that massive metal-free stars were able to trigger GRBs. Spectroscopic follow-up observations of the GRB afterglow emission would allow to probe the ionization state and metal enrichment of the IGM as a function of redshift.

astro-ph↗

arXiv2007

Singular Sources of Energy in Stars and Planets

If primordial low-mass black holes (PBH) exist in the Universe than many of stars and planetary bodies appear to be infected by them. This is also true in regard to the Sun and likely Jupiter and Saturn. The availability of even the very low-mass inner relativistic reactor may lead to essential changes in evolution scenario of a celestial body on its lifetime scale. Black holes in stellar interior may be found either in consequence of captures process or incorporation during the formation of a star from interstellar clouds. Surprisingly that in the equilibrium state a PBH growth is a long-lived process with e-folding rise time of billion years. One can envision a PBH orbiting inside the Sun. Our considerations showed that the PBH experiences very little friction in passing through the stellar matter. If the BH mass is above 10^{-5}M_{sun} the major contribution to the luminosity comes from the relativistic gravitational reactor. In such a case a star evolves towards the Eddington limit. This should lead to considerable expansion of a star and a global stability loss. Microscopic PBHs can exist in the interior of planetary bodies too. To produce the required excess of thermal energy on Jupiter and Saturn the masses of PBH captured are assumed to be reached of 4 10^{19} and 7 10^{18} g, respectively. These microscopic objects are comparable to the hydrogen atom in size. One can envision even a planet with the PBH acting as the self-sufficient source of heating. Such a planet does not need a sun to maintain animal life on its surface. This may last eons.

astro-ph↗

arXiv2007

Practical wavelet design on the sphere

We address the question of designing isotropic analysis functions on the sphere which are perfectly limited in the spectral domain and optimally localized in the spatial domain. This work is motivated by the need of localized analysis tools in domains where the data is lying on the sphere, e.g.{} the science of the Cosmic Microwave Background. Our construction is derived from the localized frames introduced by Narcowich, Petrushev, Ward, 2006. The analysis frames are optimized for given applications and compared numerically using various criteria.

math.NA↗