Monocular UHECR Spectra as Measured by HiRes

We have measured the spectrum of UHE cosmic rays in monocular mode using separately both detectors the High Resolution Fly's Eye experiment. We describe the two detectors and the basic methods of analysis, and we present our measured spectra. We compare these spectra with that produced by an astrophysical source model with galactic and uniformly distributed extra-galactic sources. We also compare our spectra to the spectra produced by the AGASA experiment.Comment: 3 pages, 4 figures. Contribution to the proceedings of ICHEP 200

Cerenkov Events Seen by The TALE Air Fluorescence Detector

The Telescope Array Low-Energy Extension (TALE) is a hybrid, Air Fluorescence Detector (FD) / Scintillator Array, designed to study cosmic ray initiated showers at energies above $\sim3\times10^{16}$ eV. Located in the western Utah desert, the TALE FD is comprised of 10 telescopes which cover the elevation range 31-58$^{\circ}$ in addition to 14 telescopes with elevation coverage of 3-31$^{\circ}$. As with all other FD's, a subset of the shower events recorded by TALE are ones for which the Cerenkov light produced by the shower particles dominates the total observed light signal. In fact, for the telescopes with higher elevation coverage, low energy Cerenkov events form the vast majority of triggered cosmic ray events. In the typical FD data analysis procedure, this subset of events is discarded and only events for which the majority of signal photons come from air fluorescence are kept. In this talk, I will report on a study to reconstruct the "Cerenkov Events" seen by the high elevation viewing telescopes of TALE. Monte Carlo studies and a first look at real events observed by TALE look very promising. Even as a monocular detector, the geometrical reconstruction method employed in this analysis allows for a pointing accuracy on the order of a degree. Preliminary Monte Carlo studies indicate that, the expected energy resolution is better than 25$$. It may be possible to extend the low energy reach of TALE to below $10^{16}$ eV. This would be the first time a detector designed specifically as an air fluorescence detector is used as an imaging Cerenkov detector.Comment: Presentation at the DPF 2013 Meeting of the American Physical Society Division of Particles and Fields, Santa Cruz, California, August 13-17, 2013. 5 pages, 2 figure

A Measurement of the UHECR Spectrum with the HiRes FADC Detector

We have measured the energy spectrum of ultra-high energy cosmic rays (UHECR) with the HiRes FADC detector (HiRes-2) in monocular mode. A detailed Monte Carlo simulation of the detector response to air showers has been used to calculate the energy dependent acceptance of the air fluorescence detector. The measured spectrum complements the measurement by the HiRes-1 detector down to lower energies. Systematic effects of the assumed input spectrum and composition on the aperture are presented, as well as systematics due to the atmosphere.Comment: 6 pages, 8 figures, to be included in the CRIS '04 (Cosmic Ray International Seminar) proceedings (Nucl. Phys. B

Fitting the HiRes Spectra and Monocular Composition

This paper consists of two sections. In the first section, we discuss our fits to the latest HiRes monocular spectra. We find that the best fit for the extragalactic component has a spectral index of $\gamma=-2.38\pm0.04$ with a distribution of sources varying with a evolution parameter $m=2.8\pm0.3$. In the second section, we discuss preliminary results from a new composition measurement using HiRes monocular data. We find a predominantly light spectrum above $10^{17.6}$ eV.Comment: 6 pages, 8 figures; to appear in the proceedings of CRIS 2004, Catania, Italy, 31 May - 4 June 200

A novel non-spreading variant of transformed hamster fibroblasts

Using repeated plating on fibronectin-coated surfaces as a selection procedure, I isolated three different mutants unresponsive to fibronectin, from thioguanine resistant Py-BHK (TG) cells in a simple assay of cell spreading. All three were recloned on soft agar. Two had morphologies similar to lines which had been selected previously, FI and F2. The mutant F3, then a unique isolate, had a different morphology in culture. Whereas F1 colonies contain exclusively rounded cells, and F2 have a few partially spread cells, more scattered than F1, F3 has a spread epithelial-like morphology in culture. I selected F3 from TG cells, on the basis that this mutant is non- responsive to fibronectin. However, in spreading assays, I found that F3 spreads on fibronectin, when the simple saline in the assay (HEPES-buffered Hanks') is supplemented with foetal bovine serum, or replaced by Ham's F10. Unexpectedly, I found that the active component stimulating spreading of F3 was pyruvate. To explain the pyruvate requirement, I searched for an abnormality of glucose utilisation in F3. Glucose uptake, studied using 14C- labelled glucose, suggested there could be some such abnormality. However, separating metabolites from TG and F3 by one and two dimensional paper chromatography gave inconclusive results. The activity of mitochondrial dehydrogenases of TG and F3, measured using MTT, responded similarly to glucose, suggesting that pyruvate in F3 is more likely needed to supply metabolites than as an energy source. The possible identity of such metabolites and explanation for how F3 came to be selected, are discussed

The Effect of Clouds on Air Showers Observation from Space

Issues relating to extensive air showers observation by a space-borne fluorescence detector and the effects of clouds on the observations are investigated using Monte Carlo simulation. The simulations assume the presence of clouds with varying altitudes and optical depths. Simulated events are reconstructed assuming a cloud-free atmosphere. While it is anticipated that auxiliary instruments, such as LIDAR (LIght Detection And Ranging), will be employed to measure the atmospheric conditions during actual observation, it is still possible that these instruments may fail to recognize the presence of a cloud in a particular shower observation. The purpose of this study is to investigate the effects on the reconstructed shower parameters in such cases. Reconstruction results are shown for both monocular and stereo detectors and for the two limiting cases of optically thin, and optically thick clouds.Comment: 31 pages, 13 figure

Measurements of the Muon Content of UHECR Air Showers with the Pierre Auger Observatory

The Pierre Auger Observatory, recently completed, has been operational since 2004. As a hybrid experiment, it allows for a wide range of measurements of UHECR-induced extensive air showers (EAS), including measurements of the EAS particle content on ground which is sensitive to high-energy hadronic interactions. We present the results of several independent measurements of the EAS muon content on ground in Auger data at a primary energy of 10 EeV. We discuss implications on high-energy hadronic interaction models and cosmic ray composition.Comment: 6 pages, 5 figures; proceedings of ISVHECRI 2008 - XV International Symposium on Very High Energy Cosmic Ray Interaction

Influence of shower fluctuations and primary composition on studies of the shower longitudinal development

We study the influence of shower fluctuations, and the possible presence of different nuclear species in the primary cosmic ray spectrum, on the experimental determination of both shower energy and the proton air inelastic cross section from studies of the longitudinal development of atmospheric showers in fluorescence experiments. We investigate the potential of track length integral and shower size at maximum as estimators of shower energy. We find that at very high energy (~10^19-10^20 eV) the error of the total energy assignment is dominated by the dependence on the hadronic interaction model, and is of the order of 5%. At lower energy (~10^17-10^18 eV), the uncertainty of the energy determination due to the limited knowledge of the primary cosmic ray composition is more important. The distribution of depth of shower maximum is discussed as a measure of the proton-air cross section. Uncertainties in a possible experimental measurement of this cross section introduced by intrinsic shower fluctuations, the model of hadronic interactions, and the unknown mixture of primary nuclei in the cosmic radiation are numerically evaluated.Comment: 12 pages, 11 figures, 4 table