1. An extremely energetic cosmic ray observed by a surface detector arrayR. U. Abbasi, M. Allen, R. Arimura, J. W. Belz, Douglas R. Bergman, S. A. Blake, K. Shin, I. J. Buckland, B. G. Cheon, Jon Paul Lundquist, 2023, izvirni znanstveni članek Opis: Cosmic rays are energetic charged particles from extraterrestrial sources, with the highest-energy events thought to come from extragalactic sources. Their arrival is infrequent, so detection requires instruments with large collecting areas. In this work, we report the detection of an extremely energetic particle recorded by the surface detector array of the Telescope Array experiment. We calculate the particle’s energy as 244 +- 29 (stat.) +51,-76 (syst.)
exa–electron volts (~40 joules). Its arrival direction points back to a void in the large-scale structure of the Universe. Possible explanations include a large deflection by the foreground magnetic field, an unidentified source in the local extragalactic neighborhood, or an incomplete knowledge of particle physics. Ključne besede: ultra-high-energy cosmic rays, telescope array, extremely energetic cosmic-ray event Objavljeno v RUNG: 23.04.2025; Ogledov: 265; Prenosov: 2
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2. Mass composition of ultrahigh energy cosmic rays from distribution of their arrival directions with the Telescope ArrayR. U. Abbasi, Y. Abe, T. Abu-Zayyad, M. Allen, Y. Arai, R. Arimura, E. Barcikowski, J. W. Belz, Douglas R. Bergman, Jon Paul Lundquist, 2024, izvirni znanstveni članek Opis: We use a new method to estimate the injected mass composition of ultrahigh cosmic rays (UHECRs) at energies higher than 10 EeV. The method is based on comparison of the energy-dependent distribution of cosmic ray arrival directions as measured by the Telescope Array (TA) experiment with that calculated in a given putative model of UHECR under the assumption that sources trace the large-scale structure (LSS) of the Universe. As we report in the companion Letter, the TA data show large deflections with respect to the LSS which can be explained, assuming small extragalactic magnetic fields (EGMF), by an intermediate composition changing to a heavy one (iron) in the highest energy bin. Here we show that these results are robust to uncertainties in UHECR injection spectra, the energy scale of the experiment and galactic magnetic fields. The assumption of weak EGMF, however, strongly affects this interpretation at all but the highest energies E > 100 EeV, where the remarkable isotropy of the data implies a heavy injected composition even in the case of strong EGMF. This result also holds if UHECR sources are as rare as 2 × 10[sup]−5 Mpc[sup]−3, that is the conservative lower limit for the source number density. Ključne besede: ultrahigh energy cosmic rays, large-scale structure, extragalactic magnetic fields, UHECR propagation, Telescope Array, UHECR mass composition, UHECR arrival directions Objavljeno v RUNG: 23.04.2025; Ogledov: 276; Prenosov: 2
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3. Isotropy of Cosmic Rays beyond 10[sup]20 eV Favors Their Heavy Mass CompositionR. U. Abbasi, Jon Paul Lundquist, 2024, izvirni znanstveni članek Opis: We report an estimation of the injected mass composition of ultrahigh energy cosmic rays (UHECRs) at energies higher than 10 EeV. The composition is inferred from an energy-dependent sky distribution of UHECR events observed by the Telescope Array surface detector by comparing it to the Large Scale Structure of the local Universe. In the case of negligible extragalactic magnetic fields (EGMFs), the results are consistent with a relatively heavy injected composition at E ∼ 10 EeV that becomes lighter up to E ∼ 100 EeV, while the composition at E > 100 EeV is very heavy. The latter is true even in the presence of highest experimentally allowed extragalactic magnetic fields, while the composition at lower energies can be light if a strong EGMF is present. The effect of the uncertainty in the galactic magnetic field on these results is subdominant. Ključne besede: ultrahigh energy cosmic rays (UHECRs), Large Scale Structure, extragalactic magnetic fields, UHECR propagation, Telescope Array surface detector, UHECR mass composition, UHECR arrival directions Objavljeno v RUNG: 23.04.2025; Ogledov: 281; Prenosov: 2
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4. Intermediate fluence downward terrestrial gamma ray flashes as observed by the Telescope Array Surface DetectorR. U. Abbasi, N. Kieu, P. R. Krehbiel, J. W. Belz, M. M. F. Saba, W. Rison, M. A. Stanley, D. Rodeheffer, D. Mazzucco, Jon Paul Lundquist, 2024, izvirni znanstveni članek Opis: On 11 September 2021, two small thunderstorms developed over the Telescope Array Surface Detector (TASD) that produced an unprecedented number of six downward terrestrial gamma ray flashes (TGFs) within one‐hour timeframe. The TGFs occurred during the initial stage of negative cloud‐to‐ground flashes whose return strokes had increasingly large peak currents up to 223 kA, 147 GeV energy deposit in up to 25 1.2 km‐spaced surface detectors, and intermittent bursts of gamma‐rays with total durations up to 717 s. The analyses are based on observations recorded by the TASD network, complemented by data from a 3D lightning mapping array, broadband VHF interferometer, fast electric field change sensor, high‐speed video camera, and the National Lightning Detection Network. The TGFs of the final two flashes had gamma fluences of and 8, logarithmically bridging the gap between previous TASD and satellite‐based detections. The observations further emphasize the similarity between upward and downward TGF varieties, suggesting a common mechanism for their production. Ključne besede: Telescope Array Surface Detector, terrestrial gamma ray flashes, 3D lightning mapping array, broadband VHF interferometer, fast electric field change sensor, high‐speed video camera, National Lightning Detection Network, TGF fluence measurement Objavljeno v RUNG: 23.04.2025; Ogledov: 279; Prenosov: 4
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5. First time-resolved leader spectra associated with a downward terrestrial gamma-ray flash detected at the Telescope Array Surface DetectorN. Kieu, R. U. Abbasi, M. M. F. Saba, J. W. Belz, P. R. Krehbiel, M. A. Stanley, F. J. Gordillo-Vazquez, M. Passas-Varo, T. Warner, Jon Paul Lundquist, 2024, izvirni znanstveni članek Opis: Optical emissions associated with Terrestrial Gamma ray Flashes (TGFs) have recently become important subjects in space‐based and ground‐based observations as they can help us understand how TGFs are produced during thunderstorms. In this paper, we present the first time‐resolved leader spectra of the optical component associated with a downward TGF. The TGF was observed by the Telescope Array Surface Detector (TASD) simultaneously with other lightning detectors, including a Lightning Mapping Array (LMA), an INTerFerometer (INTF), a Fast Antenna (FA), and a spectroscopic system. The spectroscopic system recorded leader spectra at 29,900 frames per second (33.44 s time resolution), covering a spectral range from 400 to 900 nm, with 2.1 nm per pixel. The recordings of the leader spectra began 11.7 ms before the kA return stroke and at a height of 2.37 km above the ground. These spectra reveal that optical emissions of singly ionized nitrogen and oxygen occur between 167 s before and 267 s after the TGF detection, while optical emissions of neutrals (H I, 656 nm; N I, 744 nm, and O I, 777 nm) occur right at the moment of the detection. The time‐dependent spectra reveal differences in the optical emissions of lightning leaders with and without downward TGFs. Ključne besede: Telescope Array Surface Detector, terrestrial gamma‐ray flashes, time‐resolved tgf leader spectra Objavljeno v RUNG: 22.04.2025; Ogledov: 299; Prenosov: 2
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6. Measurement of cosmic-ray proton and helium spectra from the ISS-CREAM experimentG. H. Choi, R. U. Abbasi, Y. Abe, T. Abu-Zayyad, M. Allen, Yasuhiko Arai, R. Arimura, E. Barcikowski, J. W. Belz, Douglas R. Bergman, Jon Paul Lundquist, 2023, objavljeni znanstveni prispevek na konferenci Opis: The Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM) experiment successfully recorded data for 539 days from Aug. 2017 to Feb. 2019. The ISS-CREAM instrument consists of a Silicon Charge Detector (SCD), carbon targets, a calorimeter (CAL), a top counting detector (TCD), a bottom counting detector (BCD), and a boronated scintillator detector (BSD). In this analysis, the SCD was used for the charge measurements. It comprises four layers, and each SCD layer is finely segmented with 2,688 silicon pixels to minimize charge misidentification due to the backscattered particles. The CAL was used for the energy measurements. It comprises 20 layers of tungsten/scintillating fibers. Each tungsten/scintillating-fiber layer consists of a 50 cm × 50 cm × 3.5 mm tungsten plate, followed by a layer of fifty 1 cm-wide 50 cm-long scintillating-fiber ribbons. The CAL also provides the incident cosmic-ray track and the high-energy trigger. For the low-energy trigger, the TCD and BCD were used. In this paper, we present the proton spectrum from the ISS-CREAM experiment in the energy range of 1.6 - 655 TeV and the preliminary helium spectrum in the energy range of 2.7 TeV - 1.1 PeV Ključne besede: Telescope Array, TAx4, indirect detection, hybrid detection Objavljeno v RUNG: 10.10.2023; Ogledov: 2500; Prenosov: 9
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7. Effect of optical properties of FDs on reconstruction analysisDaiki Sato, R. U. Abbasi, Y. Abe, T. Abu-Zayyad, M. Allen, Yasuhiko Arai, R. Arimura, E. Barcikowski, J. W. Belz, Douglas R. Bergman, 2023, objavljeni znanstveni prispevek na konferenci Opis: The TA experiment uses fluorescence telescopes to observe cosmic ray air showers. The telescope camera uses PMTs as Pixels. The telescope’s PMT pointing direction has an uncertainty of 0.1°, and more precise measurements of the telescope's optical properties are needed to more accurately reconstruct the cosmic ray air showers. We have developed the Opt-copter which is a light source mounted on a drone that can be flown within the telescope's field of view. Observational experiments with the Opt-copter have provided a more accurate analysis of the telescope viewing direction.
In this study, we estimate the effect of this measurement of accurate telescope viewing direction on the reconstruction of cosmic ray air showers. Ključne besede: Telescope Array, indirect detection, fluorescence detection, ultra-high energy, cosmic rays, composition, calibration, Xmax Objavljeno v RUNG: 10.10.2023; Ogledov: 2686; Prenosov: 9
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8. Effects of atmospheric transparency on Telescope Array air shower analysisK. Mizuno, R. U. Abbasi, Y. Abe, T. Abu-Zayyad, M. Allen, Yasuhiko Arai, R. Arimura, E. Barcikowski, J. W. Belz, Douglas R. Bergman, Jon Paul Lundquist, 2023, objavljeni znanstveni prispevek na konferenci Opis: The Telescope Array (TA) experiment continues to observe Ultra High Energy Cosmic Rays (UHECRs) both with its original TA detectors as well as with the new TAx4 expansion detectors. These observations employ Fluorescence Detectors (FDs) to capture the air shower induced by the primary UHECRs. The FD observes fluorescence light emitted from atmospheric nitrogen molecules excited by air shower particles. Observation of the FD extends over tens of kilometers, and the fluorescence light is attenuated by scattering from atmospheric molecules and aerosols during the propagation process. Seasonal dependence was found when evaluating the attenuation of fluorescence by aerosols. We will report on the effects of this seasonal dependence on TA air shower analysis. Ključne besede: Telescope Array, TAx4, indirect detection, hybrid detection Objavljeno v RUNG: 10.10.2023; Ogledov: 2646; Prenosov: 10
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9. Updates of the surface detector array of the TAx4 experimentEiji Kido, R. U. Abbasi, Y. Abe, T. Abu-Zayyad, M. Allen, Yasuhiko Arai, R. Arimura, E. Barcikowski, J. W. Belz, Douglas R. Bergman, Jon Paul Lundquist, 2023, objavljeni znanstveni prispevek na konferenci Opis: The TAx4 experiment plans to realize an Ultra High Energy Cosmic Rays (UHECR) detection area four times larger than that of the TA experiment. TAx4 will include five hundreds new surface detectors (SD) spaced at 2.08 km and two new fluorescence detectors (FD), which provides hybrid observation of UHECRs. We deployed 257 SDs in 2019 and completed building 2 FD stations in 2020, all operating stably. The data acquisition of the SDs is made via six communication towers, and inter-tower triggers have been recently implemented. Ključne besede: Telescope Array, TAx4, indirect detection, hybrid detection Objavljeno v RUNG: 10.10.2023; Ogledov: 2122; Prenosov: 11
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10. Anisotropies in the arrival direction distribution of ultra-high energy cosmic rays measured by the Telescope Array surface detectorJihyun Kim, R. U. Abbasi, Y. Abe, T. Abu-Zayyad, M. Allen, Yasuhiko Arai, R. Arimura, E. Barcikowski, J. W. Belz, Douglas R. Bergman, Jon Paul Lundquist, 2023, objavljeni znanstveni prispevek na konferenci Opis: Ultra-high energy cosmic rays (UHECRs) are extremely energetic, charged particles with energies greater than 10^18 eV, originating from outer space. We investigate anisotropic patterns in the arrival direction distribution of UHECRs to identify their source locations. The Telescope Array (TA) experiment, the largest UHECR observatory in the northern hemisphere, has observed evidence of two intermediate-scale anisotropies in UHECR arrival direction distributions: the TA Hotspot and the Perseus-Pisces supercluster excess. In this presentation, we will describe an oversampling analysis that we performed to find the excess of events using the data measured by the TA surface detector array. We will report the latest results of the TA Hotspot and Perseus-Pisces supercluster excesses. Ključne besede: Telescope Array, TALE, low energy extension, indirect detection, hybrid detection Objavljeno v RUNG: 10.10.2023; Ogledov: 2196; Prenosov: 6
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