arXiv subjects

R. Anderson

Publications and source records attributed to R. Anderson.

30 records · Page 2Linked to original sources

arXiv2013

Energy Spectrum of Ultra-High Energy Cosmic Rays Observed with the Telescope Array Using a Hybrid Technique

We measure the spectrum of cosmic rays with energies greater than $10^{18.2}$ eV with the Fluorescence Detectors (FDs) and the Surface Detectors (SDs) of the Telescope Array Experiment using the data taken in our first 2.3-year observation from May 27 2008 to September 7 2010. A hybrid air shower reconstruction technique is employed to improve accuracies in determination of arrival directions and primary energies of cosmic rays using both FD and SD data. The energy spectrum presented here is in agreement with our previously published spectra and the HiRes results.

astro-ph.HE↗

arXiv2013

The Energy Spectrum of Ultra-High-Energy Cosmic Rays Measured by the Telescope Array FADC Fluorescence Detectors in Monocular Mode

We present a measurement of the energy spectrum of ultra-high-energy cosmic rays performed by the Telescope Array experiment using monocular observations from its two new FADC-based fluorescence detectors. After a short description of the experiment, we describe the data analysis and event reconstruction procedures. Since the aperture of the experiment must be calculated by Monte Carlo simulation, we describe this calculation and the comparisons of simulated and real data used to verify the validity of the aperture calculation. Finally, we present the energy spectrum calculated from the merged monocular data sets of the two FADC-based detectors, and also the combination of this merged spectrum with an independent, previously published monocular spectrum measurement performed by Telescope Array's third fluorescence detector (Abu-Zayyad {\it et al.}, {Astropart. Phys.} 39 (2012), 109). This combined spectrum corroborates the recently published Telescope Array surface detector spectrum (Abu-Zayyad {\it et al.}, {Astrophys. Journ.} 768 (2013), L1) with independent systematic uncertainties.

astro-ph.HE↗

arXiv2013

The Cosmic Ray Energy Spectrum Observed with the Surface Detector of the Telescope Array Experiment

The Telescope Array (TA) collaboration has measured the energy spectrum of ultra-high energy cosmic rays with primary energies above 1.6 x 10^(18) eV. This measurement is based upon four years of observation by the surface detector component of TA. The spectrum shows a dip at an energy of 4.6 x 10^(18) eV and a steepening at 5.4 x 10^(19) eV which is consistent with the expectation from the GZK cutoff. We present the results of a technique, new to the analysis of ultra-high energy cosmic ray surface detector data, that involves generating a complete simulation of ultra-high energy cosmic rays striking the TA surface detector. The procedure starts with shower simulations using the CORSIKA Monte Carlo program where we have solved the problems caused by use of the "thinning" approximation. This simulation method allows us to make an accurate calculation of the acceptance of the detector for the energies concerned.

astro-ph.HE↗

arXiv2012

Search for Anisotropy of Ultra-High Energy Cosmic Rays with the Telescope Array Experiment

We study the anisotropy of Ultra-High Energy Cosmic Ray (UHECR) events collected by the Telescope Array (TA) detector in the first 40 months of operation. Following earlier studies, we examine event sets with energy thresholds of 10 EeV, 40 EeV, and 57 EeV. We find that the distributions of the events in right ascension and declination are compatible with an isotropic distribution in all three sets. We then compare with previously reported clustering of the UHECR events at small angular scales. No significant clustering is found in the TA data. We then check the events with E>57 EeV for correlations with nearby active galactic nuclei. No significant correlation is found. Finally, we examine all three sets for correlations with the large-scale structure of the Universe. We find that the two higher-energy sets are compatible with both an isotropic distribution and the hypothesis that UHECR sources follow the matter distribution of the Universe (the LSS hypothesis), while the event set with E>10 EeV is compatible with isotropy and is not compatible with the LSS hypothesis at 95% CL unless large deflection angles are also assumed. We show that accounting for UHECR deflections in a realistic model of the Galactic magnetic field can make this set compatible with the LSS hypothesis.

astro-ph.HE↗

arXiv2012

The surface detector array of the Telescope Array experiment

The Telescope Array (TA) experiment, located in the western desert of Utah,USA, is designed for observation of extensive air showers from extremely high energy cosmic rays. The experiment has a surface detector array surrounded by three fluorescence detectors to enable simultaneous detection of shower particles at ground level and fluorescence photons along the shower track. The TA surface detectors and fluorescence detectors started full hybrid observation in March, 2008. In this article we describe the design and technical features of the TA surface detector.

astro-ph.IM↗

arXiv2012

The Energy Spectrum of Telescope Array's Middle Drum Detector and the Direct Comparison to the High Resolution Fly's Eye Experiment

The Telescope Array's Middle Drum fluorescence detector was instrumented with telescopes refurbished from the High Resolution Fly's Eye's HiRes-1 site. The data observed by Middle Drum in monocular mode was analyzed via the HiRes-1 profile-constrained geometry reconstruction technique and utilized the same calibration techniques enabling a direct comparison of the energy spectra and energy scales between the two experiments. The spectrum measured using the Middle Drum telescopes is based on a three-year exposure collected between December 16, 2007 and December 16, 2010. The calculated difference between the spectrum of the Middle Drum observations and the published spectrum obtained by the data collected by the HiRes-1 site allows the HiRes-1 energy scale to be transferred to Middle Drum. The HiRes energy scale is applied to the entire Telescope Array by making a comparison between Middle Drum monocular events and hybrid events that triggered both Middle Drum and the Telescope Array's scintillator Ground Array.

astro-ph.IM↗

arXiv2011

New air fluorescence detectors employed in the Telescope Array experiment

Since 2007, the Telescope Array (TA) experiment, based in Utah, USA, has been observing ultra high energy cosmic rays to understand their origins. The experiment involves a surface detector (SD) array and three fluorescence detector (FD) stations. FD stations, installed surrounding the SD array, measure the air fluorescence light emitted from extensive air showers (EASs) for precise determination of their energies and species. The detectors employed at one of the three FD stations were relocated from the High Resolution Fly's Eye experiment. At the other two stations, newly designed detectors were constructed for the TA experiment. An FD consists of a primary mirror and a camera equipped with photomultiplier tubes. To obtain the EAS parameters with high accuracies, understanding the FD optical characteristics is important. In this paper, we report the characteristics and installation of new FDs and the performances of the FD components. The results of the monitored mirror reflectance during the observation time are also described in this report.

astro-ph.IM↗

arXiv2010

New g'r'i'z' Photometry of the NGC 5128 Globular Cluster System

We present new photometry for 323 of the globular clusters in NGC 5128 (Centaurus A), measured for the first time in the $g'r'i'z'$ filter system. The color indices are calibrated directly to standard stars in the $g'r'i'z'$ system and are used to establish the fiducial mean colors for the blue and red (low and high metallicity) globular cluster sequences. We also use spectroscopically measured abundances to establish the conversion between the most metallicity-sensitive colors ($(g'-r')_0$, $(g'-i')_0$) and metallicity, [Fe/H].

astro-ph.GA↗

arXiv2008

QU Carinae: a SNeIa progenitor?

Optical spectra obtained in 2006-07 of the nova-like cataclysmic variable QU Car are studied for radial velocities, line profiles, and line identifications. We are not able to confirm the reported 10.9 hr orbital period from 1982,partly because our sampling is not ideal for this purpose and also, we suspect, because our radial velocities are distorted by line profile changes due to an erratic wind. P-Cygni profiles are found in several of the emission lines, including those of C IV. Carbon lines are abundant in the spectra, suggesting a carbon enrichment in the doner star. The presence of [O III] 5007Åand [N II] 6584Åis likely due to a diffuse nebula in the vicinity of the system. The wind signatures in the spectra and the presence of nebular lines are in agreement with the accretion wind evolution scenario that has been suggested to lead to SNeIa. We argue that QU Car is a member of the V Sge subclass of CVs, and a possible SNeIa progenitor. It is shown that the recent light curve of QU Car has ~1 mag low states, similar to the light curve of V Sge, strengthening the connection of QU Car with V Sge stars, supersoft x-ray sources, and SNeIa progenitors.

astro-ph↗

arXiv2006

Effect of Magnetization Inhomogeneity on Magnetic Microtraps for Atoms

We report on the origin of fragmentation of ultracold atoms observed on a permanent magnetic film atom chip. A novel technique is used to characterize small spatial variations of the magnetic field near the film surface using radio frequency spectroscopy of the trapped atoms. Direct observations indicate the fragmentation is due to a corrugation of the magnetic potential caused by long range inhomogeneity in the film magnetization. A model which takes into account two-dimensional variations of the film magnetization is consistent with the observations.

physics.atom-ph↗

arXiv2006

Condensate splitting in an asymmetric double well for atom chip based sensors

We report on the adiabatic splitting of a BEC of $^{87}$Rb atoms by an asymmetric double-well potential located above the edge of a perpendicularly magnetized TbGdFeCo film atom chip. By controlling the barrier height and double-well asymmetry the sensitivity of the axial splitting process is investigated through observation of the fractional atom distribution between the left and right wells. This process constitutes a novel sensor for which we infer a single shot sensitivity to gravity fields of $δg/g\approx2\times10^{-4}$. From a simple analytic model we propose improvements to chip-based gravity detectors using this demonstrated methodology.

cond-mat.other↗

arXiv2005

Optical Spectroscopy of a Flare on Barnard's Star

We present optical spectra of a flare on Barnard's star. Several photospheric as well as chromospheric species were enhanced by the flare heating. An analysis of the Balmer lines shows that their shapes are best explained by Stark broadening rather than chromospheric mass motions. We estimate the temperature of the flaring region in the lower atmosphere to be >8000 K and the electron density to be ~10^14 cm^{-3}, similar to values observed in other dM flares. Because Barnard's star is considered to be one of our oldest neighbors, a flare of this magnitude is probably quite rare.

astro-ph↗