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1.
2.
Constraints on upward-going air showers using the Pierre Auger Observatory data
Emanuele De Vito, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution

Abstract: The fluorescence detector (FD) of the Pierre Auger Observatory is sensitive to upward-going air showers with energies above 1017 eV. Given its operation time and wide field of view, the FD has the potential to support or constrain the “anomalous” observations by the ANITA detector, interpreted as upward-going air showers that would be indicative of Beyond Standard Model (BSM) physics. To this end, a search for upward-going air showers with the FD has been performed applying selection criteria that were optimized using 10% of FD data. Dedicated background simulations (downward-going events) have been performed to estimate our capability to distinguish candidates from false positives. Also dedicated signal simulations (upward-going events) have been used to estimate our sensitivity to such showers with a focus on the energy region close to the ANITA observations. Improved and updated results of the Pierre Auger Observatory exposure to upward-going showers will be presented after the unblinding of 14 years of FD data. Extensive simulations allow the FD exposure to be obtained at lower energies which are particularly relevant for the comparison with the ANITA results. A refinement of the method for signal discrimination and background rejection has also been applied. The implications are discussed under the assumption that the ANITA events were due to upward-going events.
Keywords: Pierre Auger Observatory, ultra-high energy cosmic rays, air showers, beyond standard model, fluorescence detectors, ANITA
Published in RUNG: 23.01.2024; Views: 526; Downloads: 6
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3.
Measurements of cloud base height and coverage using elastic multiangle lidar scans at the Pierre Auger Observatory
Juan Pallotta, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution

Abstract: Cloud features significantly affect the reconstruction of extensive air showers, and their characterization plays an important role in atmospheric monitoring. A multi-directional characterization of the cloud pattern is provided by a combination of several instruments of the atmospheric monitoring network at the Pierre Auger Observatory (Mendoza Province, Argentina). In this work, we present the results of an analysis of the cloud measurements using data taken from 2007 to 2022 by the elastic lidars positioned in the proximity of the fluorescence detector (FD) sites. These systems provide hourly measurements of cloud coverage and base height above FD. The ansatz of horizontal homogeneity of cloud structures is tested by comparing the hourly measurements of cloud base height and coverage done simultaneously at different lidar locations. These results allow a detailed description of cloud patterns observed above the array throughout the whole period. The variation of cloud parameters is shown and quantitative conclusions about cloud homogeneity across the array of the Pierre Auger Observatory are given.
Keywords: ultra-high energy cosmic rays, Pierre Auger Observatory, surface detectors, fluorescence detectors
Published in RUNG: 23.01.2024; Views: 501; Downloads: 6
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4.
Investigating multiple ELVES and halos above strong lightning with the fluorescence detectors of the Pierre Auger Observatory
Roberto Mussa, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution

Abstract: ELVES are being studied since 2013 with the twenty-four FD Telescopes of the Pierre Auger Observatory, in the province of Mendoza (Argentina), the world’s largest facility for the study of ultra-high energy cosmic rays. This study exploits a dedicated trigger and extended readout. Since December 2020, this trigger has been extended to the three High Elevation Auger Telescopes (HEAT), which observe the night sky at elevation angles between 30 and 60 degrees, allowing a study of ELVES from closer lightning. The high time resolution of the Auger telescopes allows us to upgrade reconstruction algorithms and to do detailed studies on multiple ELVES. The origin of multiple elves can be studied by analyzing the time difference and the amplitude ratio between flashes and comparing them with the properties of radio signals detected by the ENTLN lightning network since 2018. A fraction of multi-ELVES can also be interpreted as halos following ELVES. Halos are disc-shaped light transients emitted at 70-80 km altitudes, appearing at the center of the ELVES rings, due to the rearrangement of electric charges at the base of the ionosphere after a strong lightning event.
Keywords: ultra-high energy cosmic rays, Pierre Auger Observatory, surface detectors, fluorescence detectors
Published in RUNG: 23.01.2024; Views: 486; Downloads: 5
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5.
The dynamic range of the upgraded surfac-detector stations of AugerPrime
Gioacchino Alex Anastasi, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution

Abstract: The detection of ultra-high-energy cosmic rays by means of giant detector arrays is often limited by the saturation of the recorded signals near the impact point of the shower core at the ground, where the particle density dramatically increases. The saturation affects in particular the highest energy events, worsening the systematic uncertainties in the reconstruction of the shower characteristics. The upgrade of the Pierre Auger Observatory, called AugerPrime, includes the installation of an 1-inch Small PhotoMultiplier Tube (SPMT) inside each water-Cherenkov station (WCD) of the surface detector array. The SPMT allows an unambiguous measurement of signals down to about 250m from the shower core, thus reducing the number of events featuring a saturated station to a negligible level. In addition, a 3.8m2 plastic scintillator (Scintillator Surface Detector, SSD) is installed on top of each WCD. The SSD is designed to match the WCD (with SPMT) dynamic range, providing a complementary measurement of the shower components up to the highest energies. In this work, the design and performances of the upgraded AugerPrime surface detector stations in the extended dynamic range are described, highlighting the accuracy of the measurements. A first analysis employing the unsaturated signals in the event reconstruction is also presented.
Keywords: ultra-high energy cosmic rays, Pierre Auger Observatory, fluorescence detectors, scintillator surface detectors
Published in RUNG: 23.01.2024; Views: 561; Downloads: 6
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6.
A novel tool for the absolute end-to-end calibration of fluorescence telescopes : the XY-scanner
Christoph Schäfer, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution

Abstract: The Pierre Auger Observatory uses 27 large-aperture wide-angle Schmidt telescopes to measure the longitudinal profile of air showers using the air-fluorescence technique. Up to the year 2013, the absolute calibration of the telescopes was performed by mounting a uniform large-diameter light source on each of the telescopes and illuminating the entire aperture with a known photon flux. Due to the high amount of work and person-power required, this procedure was only carried out roughly once every three years, and a relative calibration was performed every night to track short-term changes. Since 2013, only the relative calibration has been performed. In this paper, we present a novel tool for the absolute end-to-end calibration of the fluorescence detectors, the XY-Scanner. The XY-Scanner uses a portable integrating sphere as a light source, which has been absolutely calibrated. This light source is installed onto a motorized rail system and moved across the aperture of each telescope. We mimic the illumination of the entire aperture by flashing the light source at ∼1700 positions evenly distributed across the telescope aperture. For the absolute calibration of the light source, we built a dedicated setup that uses a NIST-calibrated photodiode to measure the average photon flux and a PMT to track the pulse-to-pulse stability. We present the laboratory setups used to study the characteristics of the employed light sources and discuss the inter-calibration between selected telescopes.
Keywords: ultra-high energy cosmic rays, Pierre Auger Observatory, fluorescence detectors, longitudinal profile
Published in RUNG: 23.01.2024; Views: 624; Downloads: 6
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7.
Depth of maximum of air-shower profiles : testing the compatibility of the measurements at the Pierre Auger Observatory and the Telescope Array
A. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution

Abstract: The Pierre Auger Observatory (Auger) and the Telescope Array (TA), located, respectively, in the Southern and Northern hemispheres, are the largest ultra-high-energy cosmic ray (UHECR) observatories. The Auger and TA Collaborations have collected unprecedented statistics providing us with a unique opportunity to search for the differences between the UHECR energy spectra and mass compositions in the complementary sky regions. To correctly attribute such differences to the properties of the UHECR sources or propagation, the systematic effects in the measurements of each observatory should be considered properly. In this context, the task of the Auger – TA mass composition working group is to identify possible differences of astrophysical origin in the measurements of the depth of the maximum of air-shower profiles, X_max, performed at both observatories using the fluorescence technique. Due to distinct approaches to event selection and analysis atAuger and TA, theworking group uses a specially designed method to transfer the Auger X_max distributions into the TA detector. To this end, dedicated air-shower and detector simulations for the TA Black Rock Mesa and Long Ridge fluorescence detector stations were performed with the Sibyll 2.3d hadronic interaction model. From the comparison of the first two moments and the shapes of X_max distributions for energies above 10^18.2 eV, no significant differences between the Auger and TA measurements were found.
Keywords: Pierre Auger Observatory, Telescope Array, ultra-high energy cosmic rays, fluorescence detectors
Published in RUNG: 22.01.2024; Views: 602; Downloads: 5
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8.
Highlights from the Telescope Array Experiment
J. Kim, Jon Paul Lundquist, 2023, published scientific conference contribution (invited lecture)

Abstract: The Telescope Array (TA) is the largest ultra-high energy cosmic ray (UHECR) observatory in the Northern Hemisphere. Together with the TA Low Energy Extension (TALE), TA×4, and TALE infill detector, the TA measures the properties of UHECR-induced extensive air showers (EAS) in the energy region from 10^15 eV to over 10^20 eV. Each of these uses a hybrid system with an array of scintillators to sample the footprint of the EAS at the Earth’s surface along with telescopes that measure the fluorescence and Cherenkov light from the EAS. The statistics at the highest energies are being enhanced with the TA×4 detector, half completed but still under construction, which will quadruple the surface detector area with telescopes. The TALE infill surface detectors were recently deployed to further lower the hybrid energy threshold of TALE. We present the status of the experiment and recent results on the energy spectrum, mass composition, and anisotropy, including new features in the energy spectrum at about 10^19.2 eV and in the UHECR arrival direction anisotropy.
Keywords: Telescope Array, TALE, low energy extension, TAx4, indirect detection, hybrid detection, ground array, surface detection, fluorescence detection, cerenkov light, ultra-high energy, cosmic rays, energy spectrum, composition, anisotropy
Published in RUNG: 10.10.2023; Views: 752; Downloads: 6
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9.
Effect of optical properties of FDs on reconstruction analysis
Daiki Sato, R. U. Abbasi, Y. Abe, T. Abu-Zayyad, M. Allen, Yasuhiko Arai, R. Arimura, E. Barcikowski, J. W. Belz, Douglas R. Bergman, 2023, published scientific conference contribution

Abstract: 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.
Keywords: Telescope Array, indirect detection, fluorescence detection, ultra-high energy, cosmic rays, composition, calibration, Xmax
Published in RUNG: 10.10.2023; Views: 832; Downloads: 6
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10.
Systematic uncertainty in the analysis of the TA fluorescence detector from fluorescence yield models
Kohei Komori, R. U. Abbasi, Y. Abe, T. Abu-Zayyad, M. Allen, Yasuhiko Arai, R. Arimura, E. Barcikowski, J. W. Belz, Douglas R. Bergman, 2023, published scientific conference contribution

Abstract: Ultra-high energy cosmic rays have been observed by various experiments such as Telescope Array (TA) and the Pierre Auger Observatory (Auger). There are differences in the energy spectra measured by TA and Auger. One reason for this difference is systematic uncertainty in the energy determination. The fluorescence yield model, which consists of fluorescence emission efficiencies and spectra, is one of the most significant components of this systematic uncertainty. Fluorescence emission efficiencies and spectra have been measured in various experiments, and different measurements are currently used to determine the energy of the TA and Auger experiments. In this study, we estimate the influence of the fluorescence yield model on the systematic uncertainty in the energy determination of the TA fluorescence detector.
Keywords: Telescope Array, TAx4, indirect detection, fluorescence detection, fluorescence yield, ultra-high energy, cosmic rays, energy uncertainty
Published in RUNG: 09.10.2023; Views: 883; Downloads: 5
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