Hisono Tokuno

Tokyo Institute of Technology

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Kazuhiro Machida

University of Yamanashi

Jon Paul Lundquist

University of Nova Gorica

I. Tkachev

Institute for Nuclear Research

Yuta Tanoue

Osaka Metropolitan University

Y. Tsunesada

Osaka Metropolitan University

Heungsu Shin

Osaka Metropolitan University

M. Kuznetsov

Institute for Nuclear Research

T. Nonaka

The University of Tokyo

Toshihiro Fujii

University of Chicago

Yuma Shibasaki

Shinshu University

Cooperative Institutions

Consejo Nacional de Investigaciones Científicas y Técnicas

457

Instituto de Tecnologías en Detección y Astropartículas

411

University of Buenos Aires

400

Universidad Nacional de La Plata

392

National Technological University

367

Pierre Auger Observatory

364

Institute of Astronomy and Space Physics

362

National University of General San Martín

355

Institute of Scientific and Technical Research for Defense

262

Karlsruhe Institute of Technology

126

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Joint analysis of the energy spectrum of ultra-high-energy cosmic rays as measured at the Pierre Auger Observatory and the Telescope Array

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

Y. Tsunesada Rasha Abbasi T. Abu‐Zayyad Monica Allen Yuto Arai

The measurement of the energy spectrum of ultra-high-energy cosmic rays (UHECRs) is of crucial importance to clarify their origin and acceleration mechanisms. The Pierre Auger Observatory in Argentina and the Telescope Array (TA) in the US have reported their measurements of UHECR energy spectra observed in the southern and northern hemisphere, respectively. The region of the sky accessible to both Observatories ($[-15,+24]$ degrees in declination) can be used to cross-calibrate the two spectra. The Auger-TA energy spectrum working group was organized in 2012 and has been working to understand the uncertainties in energy scale in both experiments, their systematic differences, and differences in the shape of the spectra. In previous works, we reported that there was an overall agreement of the energy spectra measured by the two observatories below 10 EeV while at higher energies, a remaining significant difference was observed in the common declination band. We revisit this issue to understand its origin by examining the systematic uncertainties, statistical effects, and other possibilities. We will also discuss the differences in the spectra in different declination bands and a new feature in the spectrum recently reported by the Auger Collaboration.

Pierre Auger Observatory

Right ascension

10.22323/1.395.0337

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The UHECR dipole and quadrupole in the latest data from the original Auger and TA surface detectors

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

P. Tinyakov Rogério de Almeida Rasha Abbasi T. Abu‐Zayyad Monica Allen

The sources of ultra-high-energy cosmic rays are still unknown, but assuming standard physics, they are expected to lie within a few hundred megaparsecs from us. Indeed, over cosmological distances cosmic rays lose energy to interactions with background photons, at a rate depending on their mass number and energy and properties of photonuclear interactions and photon backgrounds. The universe is not homogeneous at such scales, hence the distribution of the arrival directions of cosmic rays is expected to reflect the inhomogeneities in the distribution of galaxies; the shorter the energy loss lengths, the stronger the expected anisotropies. Galactic and intergalactic magnetic fields can blur and distort the picture, but the magnitudes of the largest-scale anisotropies, namely the dipole and quadrupole moments, are the most robust to their effects. Measuring them with no bias regardless of any higher-order multipoles is not possible except with full-sky coverage. In this work, we achieve this in three energy ranges (approximately 8--16 EeV, 16--32 EeV, and 32--$\infty$ EeV) by combining surface-detector data collected at the Pierre Auger Observatory until 2020 and at the Telescope Array (TA) until 2019, before the completion of the upgrades of the arrays with new scintillator detectors. We find that the full-sky coverage achieved by combining Auger and TA data reduces the uncertainties on the north-south components of the dipole and quadrupole in half compared to Auger-only results.

Pierre Auger Observatory

10.22323/1.395.0375

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A study of analysis method for the identification of UHECR source type

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

Fugo Yoshida Rasha Abbasi T. Abu‐Zayyad Monica Allen Yuto Arai

The autocorrelation analysis using the arrival direction of Ultra High Energy Cosmic Rays (UHECRs) has been previously reported by the Telescope Array (TA) experiment. It is expected that the autocorrelation function reflects the source distribution. We simulate the expected arrival direction distribution of the cosmic rays using the catalogs of candidate sources. We take into account random deflection in the magnetic fields, with the magnitude of deflection determined by the charge and energy of the cosmic rays, coherence length and magnitude of the extragalactic magnetic field (EGMF), and by distance to source. In addition, in order to compare with the results of TA experiment, we consider the TA exposure. We compare the autocorrelation of the arrival directions corresponding to different source catalogs with the isotropic distribution. We calculate the autocorrelation function for each type of source candidates using this procedure. We will discuss the ability of this method to identify the source type of UHECRs.

10.22323/1.395.0242

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UHECR mass composition from anisotropy of their arrival directions with the Telescope Array SD

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

M. Kuznetsov P. Tinyakov Rasha Abbasi T. Abu‐Zayyad Monica Allen

We propose a new method for the estimation of ultra-high energy cosmic ray (UHECR) mass composition from a distribution of their arrival directions. The method employs a test statistic (TS) based on a characteristic deflection of UHECR events with respect to the distribution of luminous matter in the local Universe modeled with a flux-weighed 2MRS catalog. Making realistic simulations of the mock UHECR sets, we show that this TS is robust to the presence of galactic and non-extreme extra-galactic magnetic fields and sensitive to the mass composition of events in a set. We apply the method to Telescope Array surface detector data for 11 years and derive new independent constraints on fraction of protons and iron in p-Fe mix at $E > 10$ EeV. At $10 < E < 100$ EeV the data favors increase of allowed proton fraction and decrease of allowed iron fraction, while at $E > 100$ EeV --- pure iron or even more massive composition. This result is in tension with Auger composition model inferred from spectrum-$X_{max}$ fit at $2.7\sigma$ ($2.0\sigma$) for PT'11 (JF'12) regular GMF model.

Mass fraction

10.22323/1.395.0294

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Effects of Galactic magnetic field on the UHECR anisotropy studies

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

Ryo Higuchi K. Kawata Rasha Abbasi T. Abu‐Zayyad Monica Allen

Telescope Array (TA) and Auger experiments reported anisotropies in the arrival direction of ultra-high-energy cosmic rays (UHECRs). In particular, Auger Collaboration reported a correlation between UHECR events and the flux model of assumed sources and suggested a contribution of starburst galaxies (SBGs) to the anisotropy of UHECRs. However, in their study, the effect of coherent deflections by the galactic magnetic field (GMF) is not taken into account. In this study, we investigated the effect of the GMF on the arrival directions of UHECRs using the cosmic ray propagation code CRPropa3. We used a backtracking technique which consists of propagating antiparticles to map the flux outside the galaxy to at the earth. We estimate the systematic effects caused by GMF in the reported likelihood analysis. We conduct likelihood analysis for mock UHECR datasets based on the flux pattern through the GMF model. We found systematic decrease of $(f_{\rm ani}, \:\theta)$ due to GMF. As prospects for the TAx4 experiment and joint analysis of Auger and TA collaborations, we develop the likelihood analysis method with the convolution of the rigidity spectrum.

Air shower

10.22323/1.395.0358

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The status of the TALE surface detector array and TALE infill project

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

S. Ogio Rasha Abbasi T. Abu‐Zayyad Monica Allen Yuto Arai

Routine hybrid observations of the surface detectors (SD) in conjunction with the fluorescence detectors (FD) of the Telescope Array Low-energy Extension (TALE) began in November 2018. In this presentation, we will describe the simulation studies of detector aperture and resolution of the TALE SD, and report on the latest observation results other than the energy spectrum. We are also in the process of expanding the experiment by 50 SDs, with even smaller nearest-neighbor spacing, in order lower the energy threshold to match that of the Cherenkov-dominated events seen by the FD. Details of the upgrade and expected performance of this new extension will be discussed.

Upgrade

Aperture (computer memory)

10.22323/1.395.0255

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Analysis of TAx4 hybrid trigger and events

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

Sang‐Woo Kim Rasha Abbasi T. Abu‐Zayyad Monica Allen Yuto Arai

'The Telescope Array is the largest ultra-high energy cosmic ray hybrid detector in the Northern hemisphere. While the TAx4 Surface Detector (TAx4 SD) has a duty cycle of ~ 100%, it should be noted that the TAx4 Fluorescence Detector (TAx4 FD) observes the full longitudinal profile of the cosmic ray air showers and therefore is able to determine their energies more accurately than TAx4 SD. In addition, observing cosmic rays in hybrid mode (“hybrid events”) has several advantages. Events seen in hybrid mode by the TAx4 FD and SD are used to establish the energy scale of the TAx4 SD. Moreover, the FD longitudinal profile is used to determine the mass composition of the primary comic ray particles, when the event geometries are well constrained by FD and SD measurements simultaneously. Despite large differences in the TAx4 SD/FD stand-alone performances, both detector types complement each other in measuring important physical quantities. Since August 2019, direction, energy, and Xmax can be obtained from reconstructing hybrid events. In this poster, preliminary analysis of TAx4 hybrid trigger and TAx4 hybrid events will be presented with focus on energy and Xmax observations.'

Duty cycle

10.22323/1.395.0332

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The measurements of the cosmic ray energy spectrum and the depth of maximum shower development of Telescope Array Hybrid trigger events

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

Heungsu Shin Rasha Abbasi T. Abu‐Zayyad Monica Allen Yuto Arai

The Telescope Array experiment is an ultra-high energy cosmic ray observatory located in Millard County, Utah, USA. The observatory consists of 3 fluorescence detector (FD) stations and 507 surface detectors (SD) that cover an area of ~$700~ {\rm km}^2$. Hybrid trigger is an external trigger system for the SD arrays that prompts the SD to perform data acquisition when an FD detects a shower-like event. In comparison with the SD autonomous trigger, hybrid trigger allows the SD to collect the data of an air shower that has primary energy below $10^{18.5}~\rm eV$, where the efficiency of SD autonomous trigger decreases rapidly. We present the measurements of the cosmic ray energy spectrum and the depth of maximum shower development of hybrid trigger events observed from October 2010 to September 2014.

Air shower

Shower

Energy spectrum

10.22323/1.395.0305

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Citations (4)

Cosmic Ray Composition between 2 PeV and 2 EeV measured by the TALE Fluorescence Detector

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

T. Abu‐Zayyad Rasha Abbasi T. Abu‐Zayyad Monica Allen Yuto Arai

The Telescope Array (TA) cosmic rays detector located in the State of Utah in the United States is the largest ultra high energy cosmic rays detector in the northern hemisphere. The Telescope Array Low Energy Extension (TALE) fluorescence detector (FD) was added to TA in order to lower the detector's energy threshold, and has succeeded in measuring the cosmic rays energy spectrum down to PeV energies, by making use of the direct Cherenkov light produced by air showers. In this contribution we present the results of a measurement of the cosmic-ray composition using TALE FD data collected over a period of $\sim$7 years. TALE FD data is used to measure the $X_{\rm max}$ distributions of showers seen in the energy range of $10^{15.3}$ - $10^{18.3}$eV. The data distributions are fit to Monte Carlo distributions of {H, He, N, Fe} cosmic-ray primaries for energies up to $10^{18}$eV. Mean $X_{\rm max}$ values are measured for the full energy range. TALE observes a light composition at the "Knee", that gets gradually heavier as energy increases toward the "Second-Knee". An increase in the $X_{\rm max}$ elongation rate is observed at energies just above $10^{17.3}$eV indicating a change in the cosmic rays composition from a heavier to a lighter mix of primaries.

10.22323/1.395.0346

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FOV direction and image size calibration of Fluorescence Detector using light source on UAV

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019) (2021)

Arata Nakazawa Rasha Abbasi T. Abu‐Zayyad Monica Allen Yuto Arai

In the Telescope Array (TA) experiment, we have been observing cosmic rays using a Fluorescence Detector (FD). More than 10 years have passed since we started this observation, and the accuracy of the observation has become more important than ever. We have developed the "Opt-copter" as a calibration device for the FDs. The Opt-copter is an unmanned aerial vehicle (UAV) equipped with a light source and can fly freely within the FD's field of view (FOV). In addition, the Opt-copter is equipped with a high-precision RTK-GPS, which enables it to accurately determine the position of the light source in flight. With this device, we can obtain detailed information on the optical characteristics of the FD. So far, we have reported on the configuration of the device and the analysis of the FOV direction. In this presentation, we will report on the new FOV analysis and image size analysis.

Field of view

10.22323/1.395.0196

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Citations (1)