Possibility of Using a Satellite-Based Detector for Recording Cherenkov Light from Ultrahigh-Energy Extensive Air Showers Penetrating into the Ocean Water

We have estimated the reflected component of Cherenkov radiation, which arises in developing of an extensive air shower with primary energy of 10^20 eV over the ocean surface. It has been shown that, under conditions of the TUS experiment, a flash of the reflected Cherenkov photons at the end of the fluorescence track can be identified in showers with zenith angles up to 20 degrees.Comment: 5 pages, 3 figures. This preprint corrects errors which appeared in the English version of the article published in Bull. Rus. Acad. Sci. Phys., 2011, Vol. 75, No. 3, p. 381. The original russian text was published in Izv. RAN. Ser. Fiz., 2011, Vol. 75, No. 3, p. 41

Observation of the Ankle and Evidence for a High-Energy Break in the Cosmic Ray Spectrum

We have measured the cosmic ray spectrum at energies above $10^{17}$ eV using the two air fluorescence detectors of the High Resolution Fly's Eye experiment operating in monocular mode. We describe the detector, PMT and atmospheric calibrations, and the analysis techniques for the two detectors. We fit the spectrum to models describing galactic and extragalactic sources. Our measured spectrum gives an observation of a feature known as the ``ankle'' near $3\times 10^{18}$ eV, and strong evidence for a suppression near $6\times 10^{19}$ eV.Comment: 14 pages, 9 figures. To appear in Physics Letters B. Accepted versio

A Measurement of Time-Averaged Aerosol Optical Depth using Air-Showers Observed in Stereo by HiRes

Air fluorescence measurements of cosmic ray energy must be corrected for attenuation of the atmosphere. In this paper we show that the air-showers themselves can yield a measurement of the aerosol attenuation in terms of optical depth, time-averaged over extended periods. Although the technique lacks statistical power to make the critical hourly measurements that only specialized active instruments can achieve, we note the technique does not depend on absolute calibration of the detector hardware, and requires no additional equipment beyond the fluorescence detectors that observe the air showers. This paper describes the technique, and presents results based on analysis of 1258 air-showers observed in stereo by the High Resolution Fly's Eye over a four year span.Comment: 7 pages, 3 figures, accepted for publication by Astroparticle Physics Journa

Constraints on the Local Sources of Ultra High-Energy Cosmic Rays

Ultra high-energy cosmic rays (UHECRs) are believed to be protons accelerated in magnetized plasma outflows of extra-Galactic sources. The acceleration of protons to ~10^{20} eV requires a source power L>10^{47} erg/s. The absence of steady sources of sufficient power within the GZK horizon of 100 Mpc, implies that UHECR sources are transient. We show that UHECR "flares" should be accompanied by strong X-ray and gamma-ray emission, and that X-ray and gamma-ray surveys constrain flares which last less than a decade to satisfy at least one of the following conditions: (i) L>10^{50} erg/s; (ii) the power carried by accelerated electrons is lower by a factor >10^2 than the power carried by magnetic fields or by >10^3 than the power in accelerated protons; or (iii) the sources exist only at low redshifts, z<<1. The implausibility of requirements (ii) and (iii) argue in favor of transient sources with L>10^{50} erg/s.Comment: 7 pages, 1 figure, submitted to JCA

Photon air showers at ultra-high energy and the photonuclear cross-section

Experimental conclusions from air shower observations on cosmic-ray photons above 10^19 eV are based on the comparison to detailed shower simulations. For the calculations, the photonuclear cross-section needs to be extrapolated over several orders of magnitude in energy. The uncertainty from the cross-section extrapolation translates into an uncertainty of the predicted shower features for primary photons and, thus, into uncertainties for a possible data interpretation. After briefly reviewing the current status of ultra-high energy photon studies, the impact of the uncertainty of the photonuclear cross-section for shower calculations is investigated. Estimates for the uncertainties in the main shower observables are provided. Photon discrimination is shown to be possible even for rapidly rising cross-sections. When photon-initiated showers are identified, it is argued that the sensitivity of photon shower observables to the photonuclear cross-section can in turn be exploited to constrain the cross-section at energies not accessible at colliders.Comment: Based on a talk presented at the international conference "From Colliders to Cosmic Rays", Prague, September 7-13 (2005

A Likelihood Method for Measuring the Ultrahigh Energy Cosmic Ray Composition

Air fluorescence detectors traditionally determine the dominant chemical composit ion of the ultrahigh energy cosmic ray flux by comparing the averaged slant depth of the shower maximum, $X_{max}$, as a function of energy to the slant depths expect ed for various hypothesized primaries. In this paper, we present a method to make a direct measurement of the expected mean number of protons and iron by comparing the shap es of the expected $X_{max}$ distributions to the distribution for data. The advantages of this method includes the use of information of the full distribution and its ability to calculate a flux for various cosmic ray compositi ons. The same method can be expanded to marginalize uncertainties due to choice of spectra, hadronic models and atmospheric parameters. We demonstrate the technique with independent simulated data samples from a parent sample of protons and iron. We accurately predict the number of protons and iron in the parent sample and show that the uncertainties are meaningful.Comment: 11 figures, 22 pages, accepted by Astroparticle Physic

Alternative Methods to Finding Patterns in HiRes Stereo Data

In this paper Ultra High Energy Cosmic Rays UHECRs data observed by the HiRes fluorescence detector in stereo mode is analyzed to search for events in the sky with an arrival direction lying on a great circle. Such structure is known as the arc structure. The arc structure is expected when the charged cosmic rays pass through the galactic magnetic field. The arcs searched for could represent a broad or a small scale anisotropy depending on the proposed source model for the UHECRs. The Arcs in this paper are looked for using Hough transform were Hough transform is a technique used to looking for patterns in images. No statistically significant arcs were found in this study

eIF2B bodies and their role in the integrated stress response

Eukaryotic initiation factor 2 (eIF2) is a G protein comprised of 3 subunits (α, β and γ) that is critical for translation. It is tightly regulated in the integrated stress response (ISR) via the phosphorylation of its α subunit following the induction of cellular stress. In its phosphorylated form eIF2α inhibits the guanine nucleotide exchange factor (GEF) eukaryotic initiation factor 2B (eIF2B), resulting in the attenuation of global protein synthesis. eIF2B is a multisubunit protein comprised of regulatory and catalytic subunits. The catalytic subunits are responsible for the GEF activity whereas the regulatory subunits mediate inhibition by phosphorylated eIF2α. Through studying the localisation of eIF2B subunits, cytoplasmic eIF2B bodies were identified in mammalian cells. A relationship between body size and the eIF2B subunits localising to them exists; larger bodies contain all subunits and smaller bodies contain predominantly catalytic subunits. eIF2 localises to eIF2B bodies and moves through these bodies in a manner that correlates with eIF2B GEF activity. Upon the induction of cellular stress phosphorylated eIF2α localises predominately to larger eIF2B bodies which contain regulatory subunits and a decrease in the movement of eIF2 through these bodies is observed. Interestingly, drugs that inhibit the ISR can rescue the movement of eIF2 through these eIF2B bodies, in a manner that correlates to cellular levels of phosphorylated eIF2α. In contrast, smaller eIF2B bodies, which contain predominately catalytic subunits, show increased movement of eIF2 during cellular stress. This increase in movement is accompanied by an increase in the localisation of eIF2Bδ to these bodies, suggesting the formation of a novel eIF2B subcomplex. This response is mimicked by ISR-inhibiting drugs, providing insight into their potential mechanisms of action. This study provides the first evidence that the composition and function of mammalian eIF2B bodies is regulated by the ISR and the drugs that control it

Evidence for Declination Dependence of Ultrahigh Energy Cosmic Ray Spectrum in the Northern Hemisphere

The energy of the ultrahigh energy spectral cutoff was measured, integrating over the northern hemisphere sky, by the Telescope Array (TA) collaboration, to be 10^19.78±0.06 eV, in agreement with the High Resolution Fly\u27s Eye (HiRes) experiment, whereas the Pierre Auger experiment, integrating over the southern hemisphere sky, measured the cutoff to be at 10^19.62±0.02 eV. An 11% energy scale difference between the TA and Auger does not account for this difference. However, in comparing the spectra of the Telescope Array and Pierre Auger experiments in the band of declination common to both experiments ( −15.7∘<δ<24.8∘ ) we have found agreement in the energy of the spectral cutoff. While the Auger result is essentially unchanged, the TA cutoff energy has changed to 10^19.59±0.06 eV. In this paper we argue that this is an astrophysical effect

Search for Anisotropy in the Ultra High Energy Cosmic Ray Spectrum using the Telescope Array Surface Detector

The Telescope Array (TA) experiment is located in the western desert of Utah, USA, and observes ultra high energy cosmic rays (UHECRs) in the Northern hemisphere. At the highest energies, E>10~EeV, the shape of cosmic ray energy spectrum may carry an imprint of the source density distribution along the line of sight different in different directions of the sky. In this study, we search for such directional variations in the shape of the energy spectrum using events observed with the Telescope Array\u27s surface detector. We divide the TA field of view into two nearly equal-exposure regions: the "on-source" region which we define as ±30∘ of the supergalactic plane containing mostly nearby structures, and the complementary "off-source" region where the sources are further away on average. We compare the UHECR spectra in these regions by fitting them to the broken power law and comparing the resulting parameters. We find that the off-source spectrum has an earlier break at highest energies. The chance probability to obtain such or larger difference in statistically equivalent distributions is estimated as 6.2±1.1×10−4 (3.2σ) by a Monte-Carlo simulation. The observed difference in spectra is in a reasonable quantitative agreement with a simplified model that assumes that the UHECR sources trace the galaxy distribution from the 2MRS catalogue, primary particles are protons and the magnetic deflections can be neglected