1. Reconstructing air-shower observables using a universality-based modelMaximilian Stadelmaier, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: Air-Shower universality describes the regularity in the longitudinal, lateral, and energy distributions of electromagnetic shower particles, as motivated by solutions of the cascade equations. To reconstruct air-shower observables from ultra-high-energy cosmic rays, we employ a universality-based model of shower development that incorporates hadronic particle components. Depending on the input parameters, the model can be used, for example, to estimate the depth of the shower maximum or the number of muons on event level. In this context, we present the expected performance for the reconstruction using air-shower simulations and data from the Pierre Auger Observatory. Keywords: ultra-high-energy cosmic rays, extensive air showers, air-shower universality, Pierre Auger Observatory, UHECR event reconstruction, air-shower maximum depth, muonic shower component Published in RUNG: 09.06.2025; Views: 328; Downloads: 3
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2. The Pierre Auger Observatory open dataV. Scherini, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: During almost 20 years of regular data acquisition, the Pierre Auger Observatory, the world's largest facility for measuring ultra-high energy cosmic rays, has collected a vast and diverse amount of data covering complementary research fields from astroparticle and fundamental physics to space weather science.
The Pierre Auger Collaboration has embraced the concept of open access to research data since its foundation. Since then, a gradual release process has been initiated, and a dedicated task force has been established to implement and sustain this effort over the long term. In line with the FAIR (Findable, Accessible, Interoperable, and Reusable) principles, the mandate of the task force includes the selection of data samples and the documented translation of in-house analyses codes into popular and available software for easy exploration and manipulation of the data.
The Pierre Auger Open Data Portal was launched in February 2021 and contains 10% of the cosmic-ray data and 100% of the atmospheric and space-weather data. Since its initial release, the Portal has been extended and updated with new data samples. It also includes a detailed catalog of the showers created by the highest-energy particles and an outreach section aimed at engaging the general public in cosmic-ray science. The foreseen increase of the fraction of released cosmic-ray data to 30% and the inclusion of new detectors will further boost the scientific community's interest in the Observatory's data and their use for education and outreach initiatives. Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, open data, FAIR data principles, the Pierre Auger Open Data Portal Published in RUNG: 29.05.2025; Views: 364; Downloads: 9
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3. The core software and simulation activities for data analysis at the Pierre Auger ObservatoryEva Santos, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: The Pierre Auger Observatory, located near the town Malargüe in the province of Mendoza, Argentina, is the largest cosmic-ray detector in existence, covering an area of 3000 sq. km. The upgraded Observatory, in Phase II of operations, consists of a surface array of 1660 stations combining water Cherenkov, scintillator, and radio detectors. A subset of stations also includes underground muon detectors. Additionally, fluorescence detectors located at four sites overlook the array. The science goals for the enhanced Observatory include the measurement of the properties of ultra-high-energy cosmic rays with large statistics and high sensitivity to the primary composition. The Observatory is also sensitive to photons and neutrinos at the highest energies, allowing it to participate in multi-messenger studies. The Auger Offline Framework provides the tools to perform detailed simulations, using the Geant 4 toolkit, of all components of the Observatory and the analysis of both data and simulated events. It proved to have the flexibility needed to evolve during the lifetime of the Observatory, to accommodate new sub-detectors and, recently, changes to the station readout electronics. A new challenge is interfacing the framework with Machine Learning tools for both the development and execution of neural-network-based algorithms. Independent of the framework, CORSIKA 7 is used to simulate particles, fluorescence light, and radio signals produced by air showers. The production of simulations is coordinated
centrally to provide standard libraries for analyses and to optimize the use of computing resources. We will describe the evolution and status of the Offline Framework and the tools used to coordinate the simulation efforts. We will also discuss the challenges of the massive simulation efforts and the resources consumed to provide the simulation libraries required by the Collaboration. Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, air-shower simulations, extensive air showers, detector simulations Published in RUNG: 29.05.2025; Views: 380; Downloads: 6
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4. Neural networks for photon searches with AugerPrimeEzequiel Rodriguez, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: Ultra-high-energy photons (E ≥ 10[sup]17 eV) are expected as by-products of interactions between ultra-high-energy cosmic rays (UHECRs) and background radiation fields or galactic matter, as well as from decay of super-heavy dark matter. Despite these various production mechanisms, the diffuse photon flux is too low for direct detection. Consequently, photon searches at UHE must rely on large ground-based detector arrays. In this contribution, we present a method for photon-hadron discrimination based on deep learning algorithms applied to detector simulations within the context of the Pierre Auger Observatory. Our method correlates information from the Surface Detector (SD), sensitive to air-shower particles arriving to the ground, and the Underground Muon Detector (UMD), sensitive to muons with energies above ∼ 1 GeV. We chose graph neural networks (GNNs) for their effectiveness in handling the discrimination task, allowing for an easy and flexible correlation of information from the SD and UMD. This approach is particularly suitable for handling the irregular structures found in SD and UMD configurations, where stations may be missing due to technical issues. Using simulations, the performance indicates that the method has strong potential for identifying photons, suffering at most 10[sup]−4 background contamination at 0.5 signal efficiency. Future studies will delve into how much that background contamination can be diminished. Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE photons, extensive air showers, AugerPrime upgrade Published in RUNG: 29.05.2025; Views: 351; Downloads: 5
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5. Estimation of muons on the surface and correlation with the muonic signal of AugerPrimeCarmina Perez Bertolli, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: This work focuses on estimating the muon density at ground level using simulations and investigating its correlation with the muonic signal recorded by the Water Cherenkov Detectors (WCDs) of the Pierre Auger Observatory. The study is motivated by the need to validate the estimation of the muonic signal in the WCDs. The methodology involves the development of a parameterization for the surface muon density based on simulated muon data from the Underground Muon Detector (UMD) of AugerPrime—an upgrade to the Pierre Auger Observatory. Our results indicate a negligible bias and a resolution better than 40 at energies above 10[sup]17.5 eV. Furthermore, we find a strong positive correlation between the estimated muon density and the simulated muonic signals in the WCDs. Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, AugerPrime upgrade, muonic air-shower component Published in RUNG: 29.05.2025; Views: 315; Downloads: 7
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6. Search for neutrons from Galactic sources with the Pierre Auger ObservatoryMiguel Alexandre Martins, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: Astrophysical neutral particles, such as neutrons, are produced through interactions of charged cosmic rays in the vicinity of their acceleration sites and are not deflected by magnetic fields during propagation. Therefore, they can be traced back to their sources. Despite being unstable particles, neutrons can travel approximately 9.2 kpc per EeV of energy before decaying, confining the search for their possible sources to the Milky Way. In this study, which was carried out with 19 years of data collected by the Pierre Auger Observatory, we analysed data sets nearly three times larger than those used in previous analyses. We extended the search to declinations up to +45◦ and to lower energy showers by including data sets with reconstructed primary energies down to 0.1 EeV. This extensive, high-quality dataset is studied in correlation with catalogues of over 800 Galactic candidate sources, including the Crab Nebula, which is studied for the first time in this type of analysis. The analysis method we present has been specifically developed for this study, allowing us to establish upper limits on the neutron flux from the sources under investigation. Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE neutrons, Galactic sources, Crab Nebula Published in RUNG: 29.05.2025; Views: 329; Downloads: 8
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7. Prospects of a composition-enhanced search for large-scale anisotropy with the Pierre Auger ObservatoryEdyvania Emily Martins, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: The Pierre Auger Observatory has been collecting data for over 19 years, reaching more than 135 000 sq. km yr sr of accumulated exposure, with the surface detectors spread over 3000 sq. km. A remarkable discovery is the large-scale dipole structure with a total amplitude of 7.4% for energies above 8 EeV. The observed modulation in right ascension has a statistical significance of 6.8 sigma. The dipolar pattern in the events with energies between 8 and 16 EeV has a statistical significance of over 5 sigma. The Pierre Auger Collaboration has also reported an increase in the dipole amplitude with energy. This anisotropy is understood to be of extragalactic origin, as the maximum of the dipolar component is located ∼ 115◦ away from the Galactic Center. In the same energy range, the observed evolution of the depth of maximum shower development with energy indicates a progression towards heavier composition of cosmic rays with increasing energy. This contribution presents a novel approach to a search for composition-enhanced large-scale anisotropy. On the one hand, lighter events have higher rigidity than their heavier counterparts with similar energy; therefore, their trajectories are less affected by magnetic fields. The expected effect is a higher anisotropy in the arrival direction of a subset of events with smaller mass and charge than the anisotropy in the overall flux of cosmic rays. On the other hand, the attenuation length is distinct for each mass group, leading to different horizon of cosmic ray sources for each of them. Under a source-agnostic model, we investigate the dipole amplitude as a function of rigidity. Using a simulation library, we analyze the possibility of measuring a separation in total dipole amplitude between two sub-populations distinct in mass of the Auger Phase I dataset. Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHECR arrival directions, UHECR mass composition, large-scale anisotropy Published in RUNG: 29.05.2025; Views: 259; Downloads: 2
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8. Search for a diffuse flux of photons with energies above tens of PeV at the Pierre Auger ObservatoryA. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, original scientific article Abstract: Diffuse photons of energy above 0.1 PeV, produced through the interactions between cosmic rays and either interstellar matter or background radiation fields, are powerful tracers of the distribution of cosmic rays in the Galaxy. Furthermore, the measurement of a diffuse photon flux would be an important probe to test models of super-heavy dark matter decaying into gamma-rays. In this work, we search for a diffuse photon flux in the energy range between 50 PeV and 200 PeV using data from the Pierre Auger Observatory. For the first time, we combine the air-shower measurements from a 2 sq. km surface array consisting of 19 water-Cherenkov surface detectors, spaced at 433 m, with the muon measurements from an array of buried scintillators placed in the same area. Using 15 months of data, collected while the array was still under construction, we derive upper limits to the integral photon flux ranging from 13.3 to 13.8 per sq. km, per steradian, and per year above tens of PeV. We extend the Pierre Auger Observatory photon search program towards lower energies, covering more than three decades of cosmic-ray energy. This work lays the foundation for future diffuse photon searches: with the data from the next 10 years of operation of the Observatory, this limit is expected to improve by a factor of ∼20. Keywords: ultra-high-energy (UHE) cosmic rays, UHE photons, Pierre Auger Observatory, diffuse photon flux, extensive air showers, water-Cherenkov surface detectors, underground muon detectors Published in RUNG: 26.05.2025; Views: 349; Downloads: 6
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9. A 1.8 m class pathfinder Raman LIDAR for the Northern Site of the Cherenkov Telescope Array Observatory : performancePedro José Bauzá-Ruiz, O. Blanch Bigas, Paolo G. Calisse, Anna Campoy-Ordaz, Sidika Merve Çolak, Michele Doro, Darko Kolar, Samo Stanič, Marko Zavrtanik, Miha Živec, 2025, original scientific article Abstract: The Barcelona Raman LIDAR (BRL) will provide continuous monitoring of the aerosol extinction profile along the line of sight of the Cherenkov Telescope Array Observatory (CTAO). It will be located at its Northern site (CTAO-N) on the Observatorio del Roque de Los Muchachos. This article presents the performance of the pathfinder Barcelona Raman LIDAR (pBRL), a prototype instrument for the final BRL. Power budget simulations were carried out for the pBRL operating under various conditions, including clear nights, moon conditions, and dust intrusions. The LIDAR PreProcessing (LPP) software suite is presented, which includes several new statistical methods for background subtraction, signal gluing, ground layer and cloud detection and inversion, based on two elastic and one Raman lines. Preliminary test campaigns were conducted, first close to Barcelona and later at CTAO-N, albeit during moonlit nights only. The pBRL, under these non-optimal conditions, achieves maximum ranges up to about 35 km, range resolution of about 50 m for strongly absorbing dust layers, and 500 m for optically thin clouds with the Raman channel only, leading to similar resolutions for the LIDAR ratios and Ångström exponents. Given the reasonable agreement between the extinction coefficients obtained from the Raman and elastic lines independently, an accuracy of aerosol optical depth retrieval in the order of 0.05 can be assumed with the current setup. The results show that the pBRL can provide valuable scientific results on aerosol characteristics and structure, although not all performance requirements could be validated under the conditions found at the two test sites. Several moderate hardware improvements are planned for its final upgraded version, such as gated PMTs for the elastic channels and a reduced-power laser with a higher repetition rate, to ensure that the data acquisition system is not saturated and therefore not affected by residual ringing. Keywords: Barcelona Raman LIDAR, BRL, Cherenkov Telescope Array Observatory, CTAO, remote sensing, lidar, Raman lidar Published in RUNG: 26.05.2025; Views: 329; Downloads: 5
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10. Galactic transient sources with the Cherenkov Telescope Array ObservatoryK. Abe, Saptashwa Bhattacharyya, Christopher Eckner, Judit Pérez Romero, Samo Stanič, Serguei Vorobiov, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, Miha Živec, 2025, original scientific article Abstract: A wide variety of Galactic sources show transient emission at soft and hard X-ray energies: low- and high-mass X-ray binaries containing compact objects, isolated neutron stars exhibiting extreme variability as magnetars as well as pulsar-wind nebulae. Although most of them can show emission up to MeV and/or GeV energies, many have not yet been detected in the TeV domain by Imaging Atmospheric Cherenkov Telescopes. In this paper, we explore the feasibility of detecting new Galactic transients with the Cherenkov Telescope Array Observatory (CTAO) and the prospects for studying them with Target of Opportunity observations. We show that CTAO will likely detect new sources in the TeV regime, such as the massive microquasars in the Cygnus region, low-mass X-ray binaries with low-viewing angle, flaring emission from the Crab pulsar-wind nebula or other novae explosions, among others. Since some of these sources could also exhibit emission at larger time-scales, we additionally test their detectability at longer exposures. We finally discuss the multiwavelength synergies with other instruments and large astronomical facilities. Keywords: very-high-energy gamma-rays, Cherenkov Telescope Array Observatory, galactic transient sources, microquasars, X-ray binaries, flaring emission, crab pulsar-wind nebula, novae explosions Published in RUNG: 21.05.2025; Views: 506; Downloads: 7
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