1. The Radio Detector of the Pierre Auger ObservatoryJ. R. Hörandel, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: To measure the properties of the highest-energy particles in the Universe with unprecedented precision, we have upgraded the Pierre Auger Observatory. A crucial component of this upgrade is the Radio Detector. Radio antennas have been added to all 1660 positions of the surface detector array, covering an area of 3000 sq. km. The antennas detect radio emission, emitted by extensive air showers in the frequency band from 30 to 80 MHz in two polarization directions - one parallel and one perpendicular to the Earth magnetic field. For inclined air showers with zenith angles above 60 degrees, the radio antennas provide a clean measurement of the electromagnetic shower component, while the water-Čerenkov detectors measure the muonic component. Large-scale deployment in the Argentinian Pampa Amarilla started around June 2023 and has been completed in 2024. The deployment is accompanied by extensive calibration efforts both, in the laboratory and in the field. The signal chain is characterized in the laboratory. Galactic radio emission is used as a reference signal and the antenna patterns are verified through in-situ calibrations with a reference antenna. Commissioning of the system is in full progress as well as the analysis of first measured air showers. We present first air showers measured with the largest radio detector for cosmic rays in the world.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, surface detectors, Water-Cherenkov detectors, Surface Scintillator detectors
Objavljeno v RUNG: 16.05.2025; Ogledov: 76; Prenosov: 0
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2. Machine learning-based analyses using surface detector data of the Pierre Auger ObservatorySteffen Hahn, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The Pierre Auger Observatory is the largest detector for the study of extensive air showers induced
by ultra-high-energy cosmic rays (UHECRs). Its hybrid detector design allows the simultaneous
observation of different parts of the shower evolution using various detection techniques. To
accurately understand the physics behind the origin of UHECRs, it is essential to determine their
mass composition. However, since UHECRs cannot be measured directly, estimating their masses
is highly non-trivial. The most common approach is to analyze mass-sensitive observables, such as
the number of secondary muons and the atmospheric depth of the shower maximum.
An intriguing part of the shower to estimate these observables is its footprint. The shower footprint is detected by ground-based detectors, such as the Water-Cherenkov detectors (WCDs) of the Surface Detector (SD) of the Observatory, which have an uptime of nearly 100%, resulting in a high number of observed events. However, the spatio-temporal information stored in the shower footprints is highly complex, making it very challenging to analyze the footprints using analytical and phenomenological methods. Therefore, the Pierre Auger Collaboration utilizes machine learning-based algorithms to complement classical methods in order to exploit the measured data with unprecedented precision. In this contribution, we highlight these machine learning-based analyses used to determine high-level shower observables that help to infer the mass of the primary particle, with a particular focus on analyses using the shower footprint detected by the WCDs and the Surface Scintillator Detectors (SSD) of the SD. We show that these novel methods show promising results on simulations and offer improved reconstruction performance when applied to measured data.
Ključne besede: ultra-high-energy cosmic rays (UHECRs), extensive air showers, Pierre Auger Observatory, surface detector, Water-Cherenkov detectors (WCDs), Surface Scintillator Detectors (SSDs), UHECR mass composition, air-shower footprint, machine learning
Objavljeno v RUNG: 16.05.2025; Ogledov: 31; Prenosov: 0
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3. Investigations of CORSIKA thinning levels suitable for studies of photon-hadron discrimination at ultra-high energiesFiona Ellwanger, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: Cosmic ray detectors like the 3000 sq. km surface array of the Pierre Auger Observatory are
capable of observing high-energy photons in the range of 10[sup]18 to 10[sup]20 eV if the flux
is sufficiently high.
However, no clear candidates for ultra-high-energy photons have been identified yet, so
simulations must be used to study typical trigger patterns and observables for discriminating photons from hadrons, e.g., with neural networks.
Thinning algorithms are applied to keep the computation time and file sizes in a manageable range since the simulation of ultra-high-energy particle showers is computationally expensive.
In CORSIKA, particles with energies below a certain fraction of the primary energy, the thinning level, are exposed to thinning.
In the case of thinning, only one of the particles emerging from an interaction is tracked.
By assigning a corresponding weight, this particle then represents a number of its siblings.
However, the weights of particles that originate from electromagnetic interactions can be 100 times larger than for hadronic interactions.
In contrast to hadronic showers, where a major part of the signal in a surface detector
is produced by muons, photon showers are almost purely electromagnetic.
Using simulations of photon-induced showers with two different thinning levels, the influence
on different observables used for photon-hadron discrimination is investigated.
Effects deriving from both statistical sampling and detector simulations are considered.
Possible influences on station-level as well as event-level observables are probed.
With this study, we are reassured that the optimal thinning parameters determined for
hadron-induced showers are also sufficient for photon-induced showers.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, CORSIKA air-shower simulator
Objavljeno v RUNG: 16.05.2025; Ogledov: 67; Prenosov: 0
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4. Improved calibration methods and reconstruction of the underground muon detector of the Pierre Auger ObservatoryJoaquín De Jesús, A. Abdul Halim, P. Abreu, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: As part of the upgrade of the Pierre Auger Observatory, known as AugerPrime, the Underground
Muon Detector is being deployed in the low-energy extension of the Surface Detector. It comprises
an array of 30 m[sup]2 plastic scintillator muon counters, buried 2.3 meters underground near the water-Cherenkov detectors, allowing for direct measurement of the muonic component of air showers in the energy range of 10[sup]16.5 − 10[sup]19 eV. To achieve an extended dynamic range, the detector operates in two modes: the binary mode, which is optimized for low muon densities, and the ADC mode, designed for high muon densities. In this contribution, we present the latest improvements to the calibration procedure of the ADC mode and to the data reconstruction of the binary mode. We assess their performance with simulations.
Ključne besede: ultra-high-energy cosmic rays (UHECRs), extensive air showers, Pierre Auger Observatory, AugerPrime upgrade, Auger underground muon detector (UMD), muonic air-shower component, detector calibration, data reconstruction
Objavljeno v RUNG: 30.04.2025; Ogledov: 470; Prenosov: 5
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5. Amplifying UHECR arrival direction information using mass estimators at the Pierre Auger ObservatoryLorenzo Apollonio, A. Abdul Halim, P. Abreu, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The origin of Ultra-High-Energy Cosmic Rays (UHECRs) is one of the biggest mysteries in modern astrophysics. Since UHECRs are deflected by Galactic and extragalactic magnetic fields, their arrival directions do not point to their sources. Previous analyses conducted on the arrival directions of high-energy events (E ≥ 32 EeV) recorded by the Surface Detector of the Pierre Auger Observatory have not shown significant anisotropies. The largest excess found in the first 19 years of data - at the 4.0 sigma level - is in the region around Centaurus A, and it is also the driving force of a correlation of UHECR arrival directions with a catalog of Starburst Galaxies, which is at the 3.8 sigma level. Since UHECRs are mostly nuclei, the lightest ones (least charged) are also the least deflected. While the mass of the events can be estimated better using the Fluorescence Detector of the Pierre Auger Observatory, the Surface Detector provides the necessary statistics needed for astrophysical studies. The introduction of novel mass-estimation techniques, such as machine learning models and an algorithm based on air-shower universality, will help identify high-rigidity events in the Surface Detector data of the Pierre Auger Observatory. With this work, we present how event-per-event mass estimators can help enhance the sensitivity in the search for anisotropies in the arrival directions of UHECRs at small and intermediate angular scales using simulations.
Ključne besede: ultra-high-energy cosmic rays (UHECRs), extensive air showers, Pierre Auger Observatory, UHECR propagation, UHECR arrival directions, UHECR mass composition, Centaurus A radio galaxy, starburst galaxies, air-shower universality
Objavljeno v RUNG: 30.04.2025; Ogledov: 356; Prenosov: 6
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6. The Pierre Auger Observatory open dataA. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, izvirni znanstveni članek Opis: The Pierre Auger Collaboration has embraced the concept of open access to their research data since its foundation, with the aim of giving access to the widest possible community. A gradual process of release began as early as 2007 when 1% of the cosmic-ray data was made public, along with 100% of the space-weather information. In February 2021, a portal was released containing 10% of cosmic-ray data collected by the Pierre Auger Observatory from 2004 to 2018, during the first phase of operation of the Observatory. The Open Data Portal includes detailed documentation about the detection and reconstruction procedures, analysis codes that can be easily used and modified and, additionally, visualization tools. Since then, the Portal has been updated and extended. In 2023, a catalog of the highest-energy cosmic-ray events examined in depth has been included. A specific section dedicated to educational use has been developed with the expectation that these data will be explored by a wide and diverse community, including professional and citizen scientists, and used for educational and outreach initiatives. This paper describes the context, the spirit, and the technical implementation of the release of data by the largest cosmic-ray detector ever built and anticipates its future developments.
Ključne besede: ultra-high-energy cosmic rays (UHECRs), extensive air showers, Pierre Auger Observatory, open data, UHECR event data, space weather data, Auger Open Data Portal
Objavljeno v RUNG: 03.04.2025; Ogledov: 475; Prenosov: 8
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7. Search for the anomalous events detected by ANITA using the Pierre Auger ObservatoryA. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, izvirni znanstveni članek Opis: A dedicated search for upward-going air showers at zenith angles exceeding 110° and energies E>0.1 EeV has been performed using the Fluorescence Detector of the Pierre Auger Observatory. The search is motivated by two “anomalous” radio pulses observed by the ANITA flights I and III that appear inconsistent with the standard model of particle physics. Using simulations of both regular cosmic-ray showers and upward-going events, a selection procedure has been defined to separate potential upward-going candidate events and the corresponding exposure has been calculated in the energy range [0.1–33] EeV. One event has been found in the search period between January 1, 2004, and December 31, 2018, consistent with an expected background of 0.27 ± 0.12 events from misreconstructed cosmic-ray showers. This translates to an upper bound on the integral flux of (7.2±0.2)×10[sup]−21 cm[sup]−2 sr[sup]−1 y[sup]−1 and (3.6±0.2)×10−20 cm[sup]−2 sr[sup]−1 y[sup]−1 for an E[sup]−1 and E[sup]−2 spectrum, respectively. An upward-going flux of showers normalized to the ANITA observations is shown to predict over 34 events for an E[sup]−3 spectrum and over 8.1 events for a conservative E[sup]−5 spectrum, in strong disagreement with the interpretation of the anomalous events as upward-going showers.
Ključne besede: ultra-high-energy cosmic rays, extensive air showers, upward-going air showers, Pierre Auger Observatory, Fluorescence Detector, anomalous ANITA events
Objavljeno v RUNG: 28.03.2025; Ogledov: 448; Prenosov: 5
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8. Subluminal pulses in the surface-scintillator detectors of AugerPrimeTobias Schulze, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: In extensive air showers, the signals from the electromagnetic and muonic components typically span a few microseconds in scintillation detectors.
Neutrons are the only stable neutral hadrons over the timescale of air showers.
They lose energy exclusively through hadronic interactions and quasi-elastic scattering, which results in their high abundance at ground level.
These neutrons can produce delayed pulses in scintillation detectors, appearing up to several milliseconds after the primary shower signal.
This allows us to probe hadronic interactions in the development of air showers.
In this study, we characterize such subluminal pulses using the first measurements from the scintillator surface detectors of the AugerPrime upgrade of the Pierre Auger Observatory.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, AugerPrime upgrade
Objavljeno v RUNG: 28.03.2025; Ogledov: 440; Prenosov: 7
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9. Highlights from the Auger Engineering Radio ArrayBjarni Pont, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The Auger Engineering Radio Array (AERA) at the Pierre Auger Observatory is an array of 153 radio-antenna stations that measure the 30−80 MHz radio emission produced in extensive air showers in the energy range between 0.1 and 10 EeV. It has been taking data for over a decade. In this contribution, we present the recent results of AERA. We show the measurements of the depths of the shower maxima (Xmax) using the radio footprint and using interferometry, demonstrating compatibility and competitiveness with the established fluorescence detection method. We also show the measurement of the stability of the radio signal over close to a decade determined using the Galactic radio background as a calibration source, demonstrating that a radio detector can be used to lower systematic uncertainties on the energy scale of, for example, fluorescence and water-Cherenkov detectors.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, radio emission
Objavljeno v RUNG: 28.03.2025; Ogledov: 437; Prenosov: 5
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10. Mass composition of ultra-high-energy cosmic rays at the Pierre Auger ObservatoryThomas Fitoussi, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: For the past 20 years, the Pierre Auger Observatory has collected the largest dataset of
ultra-high-energy cosmic rays (UHECRs) ever achieved using a hybrid detector. The study
of this dataset has led to numerous unexpected discoveries that enhance our understanding
of the origins of UHECRs. One of the key points in this study is their mass composition.
In this work, we will present the most recent results regarding the mass composition of UHECRs at the Pierre Auger Observatory. In particular, we will focus on the measurement of the depth
of the maximum of air-shower profiles, denoted as Xmax . This determination has been achieved through both direct measurements from the Fluorescence Detector data and the application of machine learning for estimating Xmax on an event-by-event basis using the Surface Detector data. The latter has allowed us to extend the measurement to energies up
to 100 EeV and indicates a correlation between changes in composition and three features
of the energy spectrum (ankle, instep, steepening). Moreover, the results provide evidence
of a heavy and nearly pure primary beam for energies greater than 50 EeV that is independent
of the hadronic interaction model. The implications of these findings for astrophysics and
for modelling hadronic interactions will be discussed.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, UHECR mass composition
Objavljeno v RUNG: 28.03.2025; Ogledov: 426; Prenosov: 9
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