ABSTRACT: We search for ultra-high energy photons by analyzing geometrical properties
of shower fronts of events registered by the Telescope Array surface detector.
By making use of an event-by-event statistical method, we derive upper limits
on the absolute flux of primary photons with energies above 10^19, 10^19.5 and
10^20 eV based on the first three years of data taken.
ABSTRACT: 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
ABSTRACT: 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 5 x 10^(18)
eV and a steepening at 5 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.
ABSTRACT: 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.
ABSTRACT: 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.
ABSTRACT: 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.
ABSTRACT: The purpose of The Telescope Array experiment is to identify origin of the ultra high energy cosmic rays. The Telescope Array is a hybrid detector consists of a surface detector array and air fluorescence detectors. This hybrid detector is observing extensive air showers to measure the energy spectrum, anisotropy and composition of Ultra High Energy Cosmic Rays. The detector construction has been completed in March 2008, and the hybrid observation with the full configuration has been running since that time. In this talk, the status of observation and our prospects are described.
Journal of Physics Conference Series 05/2011; 293(1):012035.
ABSTRACT: We describe a method for restoring information lost during statistical
thinning in extensive air shower simulations. By converting weighted particles
from thinned simulations to swarms of particles with similar characteristics,
we obtain a result that is essentially identical to the thinned shower, and
which is very similar to non-thinned simulations of showers. We call this
method dethinning. Using non-thinned showers on a large scale is impossible
because of unrealistic CPU time requirements, but with thinned showers that
have been dethinned, it is possible to carry out large-scale simulation studies
of the detector response for ultra-high energy cosmic ray surface arrays. The
dethinning method is described in detail and comparisons are presented with
parent thinned showers and with non-thinned showers.
ABSTRACT: A simple method for the parallelization of extensive air shower simulations
is described. A shower is simulated at fixed steps in altitude. At each step,
daughter particles below a specified energy threshold are siphoned off and
tabulated for further simulation. Once the entire shower has been tabulated,
the resulting list of particles is concatenated and divided into separate list
files where each possesses a similar projected computation time. These lists
are then placed on a computation cluster where the simulation can be completed
in a piecemeal fashion as computing resources become available. Once the
simulation is complete, the outputs are reassembled as a complete air shower
simulation. The original simulation program (in this case CORSIKA) is in no way
altered for this procedure. Verification is obtained by comparisons of
10^(16.5) eV showers produced with and without parallelization.
ABSTRACT: The Telescope Array is a detector of extensive air shower produced by ultra High energy cosmic ray. This detector is located on Utah, USA. The construction have been completed and the full operation has been running from March 2008. In this talk, the status of observation and our prospects are described.
AIP Conference Proceedings. 05/2010; 1238(1):365-368.
ABSTRACT: We report studies of ultrahigh-energy cosmic-ray composition via analysis of depth of air shower maximum (X(max)), for air shower events collected by the High-Resolution Fly's Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate d<X(max)>/d[log(E)] of 47.9+/-6.0(stat)+/-3.2(syst) g/cm2/decade for energies between 1.6 and 63 EeV, and are consistent with a predominantly protonic composition of cosmic rays when interpreted via the QGSJET01 and QGSJET-II high-energy hadronic interaction models. These measurements constrain models in which the galactic-to-extragalactic transition is the cause of the energy spectrum ankle at 4x10(18) eV.
Physical Review Letters 04/2010; 104(16):161101. · 7.37 Impact Factor
ABSTRACT: Stereo data collected by the HiRes experiment over a six year period are examined for large-scale anisotropy related to the inhomogeneous distribution of matter in the nearby Universe. We consider the generic case of small cosmic-ray deflections and a large number of sources tracing the matter distribution. In this matter tracer model the expected cosmic ray flux depends essentially on a single free parameter, the typical deflection angle theta. We find that the HiRes data with threshold energies of 40 EeV and 57 EeV are incompatible with the matter tracer model at a 95% confidence level unless theta is larger than 10 degrees and are compatible with an isotropic flux. The data set above 10 EeV is compatible with both the matter tracer model and an isotropic flux. Comment: 9 pages, 5 Postscript figures
ABSTRACT: We report studies of ultra-high energy cosmic ray composition via analysis of depth of airshower maximum (Xmax), for airshower events collected by the High Resolution Fly's Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate d /d(log(E)) of 47.9 +- 6.0 (stat.) +- 3.2 (syst.)g/cm^2/decade for energies between 1.6 EeV and 63 EeV, and are consistent with a predominantly protonic composition of cosmic rays when interpreted via the QGSJET01 and QGSJET-II high-energy hadronic interaction models. These measurements constrain models in which the galactic-to-extragalactic transition is the cause of the energy spectrum "ankle' at 4 EeV. Comment: 11 pages, 4 figures, accepted for publication in Physical Review Letters
ABSTRACT: The High Resolution Fly's Eye experiment has measured the flux of ultrahigh energy cosmic rays using the stereoscopic air fluorescence technique. The HiRes experiment consists of two detectors that observe cosmic ray showers via the fluorescence light they emit. HiRes data can be analyzed in monocular mode, where each detector is treated separately, or in stereoscopic mode where they are considered together. Using the monocular mode the HiRes collaboration measured the cosmic ray spectrum and made the first observation of the Greisen-Zatsepin-Kuzmin cutoff. In this paper we present the cosmic ray spectrum measured by the stereoscopic technique. Good agreement is found with the monocular spectrum in all details. Comment: 20 pages, 10 figures
ABSTRACT: Data taken in stereo mode by the High Resolution Fly's Eye (HiRes) air fluorescence experiment are analyzed to search for correlations between the arrival directions of ultrahigh-energy cosmic rays with the positions of BL Lacertae objects. Several previous claims of significant correlations between BL Lac objects and cosmic rays observed by other experiments are tested. These claims are not supported by the HiRes data. However, we verify a recent analysis of correlations between HiRes events and a subset of confirmed BL Lac objects from the 10th Veron Catalog, and we study this correlation in detail. Due to the a posteriori nature of the search, the significance level cannot be reliably estimated and the correlation must be tested independently before any claim can be made. We identify the precise hypotheses that will be tested with statistically independent data.
The Astrophysical Journal 12/2008; 636(2):680. · 6.02 Impact Factor
ABSTRACT: The composition of ultra-high-energy cosmic rays is measured with the High Resolution Fly's Eye cosmic-ray observatory data using the Xmax technique. Data were collected in stereo between 1999 November and 2001 September. The data are reconstructed with well-determined geometry. Measurements of the atmospheric transmission are incorporated in the reconstruction. The detector resolution is found to be 30 g cm-2 in Xmax and 13% in energy. The Xmax elongation rate between 1018.0 and 1019.4 eV is measured to be 54.5 ± 6.5 ± 4.5 g cm-2 per decade. This is compared with predictions using the QGSJet01 and SIBYLL 2.1 hadronic interaction models for both protons and iron nuclei. CORSIKA-generated extensive air showers are incorporated directly into a detailed detector Monte Carlo program. The elongation rate and the Xmax distribution widths are consistent with a constant or slowly changing and predominantly light composition. A simple model containing only protons and iron nuclei is compared with QGSJet and SIBYLL. The best agreement between the model and the data is for 80% protons for QGSJet and 60% protons for SIBYLL.
The Astrophysical Journal 12/2008; 622(2):910. · 6.02 Impact Factor
ABSTRACT: The High Resolution Fly's Eye (HiRes) experiment is an air fluorescence detector which, operating in stereo mode, has a typical angular resolution of 06 and is sensitive to cosmic rays with energies above 1018 eV. The HiRes cosmic-ray detector is thus an excellent instrument for the study of the arrival directions of ultra-high-energy cosmic rays. We present the results of a search for anisotropies in the distribution of arrival directions on small scales (<5°) and at the highest energies (>1019 eV). The search is based on data recorded between 1999 December and 2004 January, with a total of 271 events above 1019 eV. No small-scale anisotropy is found, and the strongest clustering found in the HiRes stereo data is consistent at the 52% level with the null hypothesis of isotropically distributed arrival directions.
The Astrophysical Journal 12/2008; 610(2):L73. · 6.02 Impact Factor
ABSTRACT: The fluorescence yield in air is reported for wavelength and pressure ranges of interest to ultra-high energy cosmic ray detectors. A 28.5 GeV electron beam was used to excite the fluorescence. Central to the approach was the system calibration, using Rayleigh scattering of a nitrogen laser beam. In atmospheric pressure dry air, at 304 K, the yield is 20.8±1.6 photons per MeV.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2008; 175(1):472. · 1.21 Impact Factor
ABSTRACT: A key assumption in the reconstruction of extensive air showers using
the air fluorescence technique is that fluorescence is proportional to
energy deposition at all depths in the shower. This ansatz, along with
the supposition that particle distribution and energy loss can be well
modeled by modern shower simulation software, must be thoroughly
verified. We report here the results of the first direct measurement of
air fluorescence yield as a function of shower depth, as performed in
the thick-target phase of the FLASH (FLuorescence in Air from SHowers)
experimental program at the SLAC Final-Focus Test Beam facility. We
compare observed fluorescence light yields as a function of shower depth
to concurrently measured charged particle yields, to the energy
deposition predictions of the EGS and GEANT software packages, and to
empirical energy-deposition models. We also examine the extent to which
the relative yield versus shower depth is independent of wavelength
within the fluorescence spectrum. We find the proportionality hypothesis
to be well supported by the data, validating the use of fluorescence
profiles in the study of ultra high energy cosmic rays.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 10/2008; 597:37-40. · 1.21 Impact Factor
ABSTRACT: Telescope Array (TA) is a hybrid detector of a surface detector array and fluorescence telescopes. This hybrid detector will measure the energy spectrum, anisotropy and composition of ultra-high energy cosmic rays (UHECRs) to identify their origin. The almost construction of the detector has been completed in May 2007, and the detector is running under test and adjustments. The first hybrid observation with the full configuration is planned in beginning of 2008. In this paper the status and prospects of TA detector is described.
Journal of Physics Conference Series 07/2008; 120(6):062027.