1. Inference of the Mass Composition of Cosmic Rays with Energies from 10[sup]18.5 to 10[sup]20 eV Using the Pierre Auger Observatory and Deep LearningA. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, original scientific article Abstract: We present measurements of the atmospheric depth of the shower maximum Xmax,
inferred for the first time on an event-by-event level using the Surface Detector
of the Pierre Auger Observatory. Using deep learning, we were able to extend
measurements of the Xmax distributions up to energies of 100 EeV (10[sup]20 eV),
not yet revealed by current measurements, providing new insights into the mass
composition of cosmic rays at extreme energies.
Gaining a 10-fold increase in statistics compared to the Fluorescence Detector data,
we find evidence that the rate of change of the average Xmax with the logarithm
of energy features three breaks at 6.5 ± 0.6 (stat) ± 1 (sys) EeV,
11 ± 2 (stat) ± 1 (sys) EeV, and 31 ± 5 (stat) ± 3 (sys) EeV, in the vicinity to the three
prominent features (ankle, instep, suppression) of the cosmic-ray flux.
The energy evolution of the mean and standard deviation of the measured Xmax
distributions indicates that the mass composition becomes increasingly heavier
and purer, thus being incompatible with a large fraction of light nuclei between
50 EeV and 100 EeV.
Keywords: ultra-high-energy cosmic rays (UHECRs), extensive air showers, Pierre Auger Observatory, UHECR mass composition, depth of the shower maximum, fluorescence detector, surface detector, deep learning
Published in RUNG: 20.01.2025; Views: 174; Downloads: 1
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2. Measurement of the depth of maximum of air-shower profiles with energies between ▫$10^{18.5} and 10^{20}$▫ eV using the surface detector of the Pierre Auger Observatory and deep learningA. Abdul Halim, P. Abreu, M. Aglietta, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, original scientific article Abstract: We report an investigation of the mass composition of cosmic rays with energies
from 3 to 100 EeV (1 EeV = 10[sup]18 eV) using the distributions of the depth of shower
maximum Xmax. The analysis relies on ∼50,000 events recorded by the surface detector
of the Pierre Auger Observatory and a deep-learning-based reconstruction algorithm.
Above energies of 5 EeV, the dataset offers a 10-fold increase in statistics with respect to
fluorescence measurements at the Observatory. After cross-calibration using
the fluorescence detector, this enables the first measurement of the evolution of the mean
and the standard deviation of the Xmax distributions up to 100 EeV.
Our findings are threefold: (i) The evolution of the mean logarithmic mass toward a heavier
composition with increasing energy can be confirmed and is extended to 100 EeV.
(ii) The evolution of the fluctuations of Xmax toward a heavier and purer composition
with increasing energy can be confirmed with high statistics. We report a rather heavy
composition and small fluctuations in Xmax at the highest energies.
(iii) We find indications for a characteristic structure beyond a constant change
in the mean logarithmic mass, featuring three breaks that are observed in proximity
to the ankle, instep, and suppression features in the energy spectrum.
Keywords: ultra-high-energy cosmic rays, UHECRs, extensive air showers, Pierre Auger Observatory, UHECR mass composition, depth of shower maximum, fluorescence detector, surface detector, deep learning
Published in RUNG: 20.01.2025; Views: 184; Downloads: 0
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3. Combined fit of spectrum and composition for FR0 radio-galaxy-emitted ultra–high energy cosmic rays with resulting secondary photons and neutrinosJon Paul Lundquist, Serguei Vorobiov, Lukas Merten, Anita Reimer, Margot Boughelilba, Paolo Da Vela, Fabrizio Tavecchio, Giacomo Bonnoli, Chiara Righi, 2025, original scientific article Abstract: This study comprehensively investigates the gamma-ray dim population of Fanaroff–Riley
Type 0 (FR0) radio galaxies as potentially significant sources of ultra–high energy cosmic rays
(UHECRs, E > 10[sup]18 eV) detected on Earth. While individual FR0 luminosities are relatively
low compared to the more powerful Fanaroff–Riley Type 1 and Type 2 galaxies, FR0s are
substantially more prevalent in the local universe, outnumbering the more energetic galaxies
by a factor of ∼5 within a redshift of z ≤ 0.05. Employing CRPropa3 simulations, we estimate
the mass composition and energy spectra of UHECRs originating from FR0 galaxies for energies
above 10[sup]18.6 eV. This estimation fits data from the Pierre Auger Observatory (Auger)
using three extensive air shower models; both constant and energy-dependent observed
elemental fractions are considered. The simulation integrates an approximately isotropic
distribution of FR0 galaxies, extrapolated from observed characteristics, with UHECR
propagation in the intergalactic medium, incorporating various plausible configurations of
extragalactic magnetic fields, both random and structured. We then compare the resulting
emission spectral indices, rigidity cutoffs, and elemental fractions with recent Auger results.
In total, 25 combined energy-spectrum and mass-composition fits are considered. Beyond
the cosmic-ray fluxes emitted by FR0 galaxies, this study predicts the secondary photon and
neutrino fluxes from UHECR interactions with intergalactic cosmic photon backgrounds.
The multimessenger approach, encompassing observational data and theoretical models,
helps elucidate the contribution of low-luminosity FR0 radio galaxies to the total cosmic-ray
energy density.
Keywords: ultra-high-energy cosmic rays, UHECRs, UHECR energy spectrum, Pierre Auger Observatory, UHECR mass composition, UHECR sources, extragalactic magnetic fields, UHECR propagation, CRPropa tool
Published in RUNG: 06.01.2025; Views: 224; Downloads: 6
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4. Large-scale cosmic-ray anisotropies with 19 yr of data from the Pierre Auger ObservatoryA. Abdul Halim, P. Abreu, M. Aglietta, Ingo Allekotte, K. Almeida Cheminant, Jon Paul Lundquist, Shima Ujjani Shivashankara, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2024, original scientific article Abstract: We present results of the measurement of large-scale anisotropies in the arrival directions of
ultra–high-energy cosmic rays detected at the Pierre Auger Observatory during 19 yr of operation,
prior to AugerPrime, the upgrade of the observatory. The 3D dipole amplitude and direction are
reconstructed above 4 EeV in four energy bins. Besides the established dipolar anisotropy in right
ascension above 8 EeV, the Fourier amplitude of the 8–16 EeV energy bin is now also above the 5σ
discovery level. No time variation of the dipole moment above 8 EeV is found, setting an upper limit
to the rate of change of such variations of 0.3% per year at the 95% confidence level. Additionally,
the results for the angular power spectrum are shown, demonstrating no other statistically
significant multipoles. The results for the equatorial dipole component down to 0.03 EeV are
presented, using for the first time a data set obtained with a trigger that has been optimized for
lower energies. Finally, model predictions are discussed and compared with observations, based
on two source emission scenarios obtained in the combined fit of spectrum and composition above 0.6 EeV.
Keywords: ultra–high-energy cosmic rays, UHECRs, UHECR anisotropies, Pierre Auger Observatory, dipolar anisotropy in right ascension, Fourier amplitude analysis, angular power spectrum, equatorial dipole component, UHECR source emission scenarios
Published in RUNG: 26.11.2024; Views: 408; Downloads: 1
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5. Multi-messenger astrophysics with the Pierre Auger ObservatoryMassimo Mastrodicasa, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, published scientific conference contribution Abstract: The Pierre Auger Observatory is sensitive to ultra-high energy neutral particles, such as photons, neutrinos, and neutrons, and can take part in Multi-Messenger searches in collaboration with other observatories. Photons and neutrinos are searched by exploiting the design of the Pierre Auger Observatory and profiting from the different properties of the induced showers caused by different particles. Diffuse and point source fluxes of photons and neutrinos are searched for. Furthermore, photon and neutrino follow-ups of the gravitational wave events observed by the LIGO/Virgo Collaboration are conducted. The Pierre Auger Observatory is also used to search for neutrons from point-like sources. In contrast to photons and neutrinos, neutrons induce air showers that cannot be distinguished from those produced by protons. For this reason, the search for neutrons from a given source is performed by searching for an excess of air showers from the corresponding direction. All these searches have resulted in stringent upper limits on the corresponding fluxes of the considered particles, allowing, together with the results obtained by other experiments, to shed some light on the most energetic phenomena of our Universe. An overview of the Multi-Messenger activities carried out within the Pierre Auger Collaboration is presented.
Keywords: ultra-high-energy cosmic rays, UHE photons, UHE neutrinos, UHE neutrons, Pierre Auger Observatory, multi-messenger astrophysical studies
Published in RUNG: 04.10.2024; Views: 627; Downloads: 6
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6. Probing hadronic interactions using the latest data measured by the Pierre Auger ObservatoryCaterina Trimarelli, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, published scientific conference contribution Abstract: The Pierre Auger Observatory is the world’s largest ultra-high energy cosmic ray observatory. Its hybrid detection technique combines the observation of the longitudinal development of extensive air showers and the lateral distribution of particles arriving at the ground. In this contribution, a review of the latest results on hadronic interactions using measurements from the Pierre Auger Observatory is given. In particular, we report on the self-consistency tests of the post-LHC models using measurements of the depth of the shower maximum and the main features of the muon component at the ground. The tensions between the model predictions and the data, considering different shower observables, are reviewed.
Keywords: ultra-high-energy cosmic rays, hadronic interactions, extensive air showers, maximum depth, EAS muon content, Pierre Auger Observatory, post-LHC hadronic interaction models
Published in RUNG: 04.10.2024; Views: 608; Downloads: 7
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7. Expected performance of the Auger Radio DetectorFelix Schlüter, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2023, published scientific conference contribution Abstract: The Auger Radio Detector (RD) will increase the sky coverage and overall aperture for mass- sensitive measurements of ultra-high-energy cosmic rays with the Pierre Auger Observatory. The installation of over 1600 dual-polarized short aperiodic loaded loop antennas (SALLAs) on an area of about 3000 sq. km will enable the detection of highly inclined air showers via the emitted electromagnetic radiation in coincidence with the Auger water-Cherenkov detector array (SD). The combination of complementary information from both detectors yields a strong sensitivity to the mass composition of cosmic rays.
We will present the expected performance of the RD to detect and reconstruct inclined air showers. This study features comprehensive sets of Monte-Carlo generated air showers, utilizes a complete description of the instrumental response of the radio antennas, and in-situ recorded background. The estimation of an energy- and direction-dependent aperture yields an expectation of about 3900 events with energies above 10[sup]19 eV being detected during 10 years of operation. From a full event reconstruction, we quantify the achievable energy resolution to be better than 10% at and beyond 10[sup]19 eV. With this at hand, the potential to measure the number of muons and discriminate between different cosmic-ray primaries in combination with the SD using inclined air showers is presented. The discrimination between proton- and iron-induced air showers yields a figure-of-merit of 1.6.
Keywords: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, Auger Radio Detector, Auger water-Cherenkov detector array, mass-sensitive UHECR measurements
Published in RUNG: 03.10.2024; Views: 601; Downloads: 6
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8. The depth of the shower maximum of air showers measured with AERABjarni Pont, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2023, published scientific conference contribution Abstract: The Auger Engineering Radio Array (AERA) is an array of 153 radio antennas spanning an area of 17 sq. km, currently the largest of its kind, that probes the nature of ultra-high energy cosmic rays at energies around the transition from Galactic to extra-galactic origin. It measures the MHz radio emission of extensive air showers produced by cosmic rays hitting our atmosphere. The elemental composition of cosmic rays is a crucial piece of information in determining what the sources of cosmic rays are and how cosmic rays are accelerated. This composition can be obtained from the mass-sensitive parameter Xmax, the depth of the shower maximum. We reconstruct Xmax with a likelihood analysis by comparing the measured radio footprint on the ground to an ensemble of footprints from Monte-Carlo CORSIKA/CoREAS air shower simulations. We compare our Xmax reconstruction with fluorescence Xmax measurements on a per-event basis, a setup unique to the Pierre Auger Observatory, and show the methods to be compatible. Furthermore, we extensively validate our reconstruction by identifying and correcting for systematic uncertainties. We determine the resolution of our method as a function of energy and reach a precision better than 15 g/cm[sup]2 at the highest energies. With a bias-free set of around 600 showers, we find a light to light-mixed composition at energies between 10[sup]17.5 to 10[sup]18.8 eV, also in agreement with Auger fluorescence measurements.
Keywords: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, UHECR mass composition
Published in RUNG: 03.10.2024; Views: 546; Downloads: 5
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9. Simulations of antenna response for the Radio Detector of the Pierre Auger ObservatoryU. G. Giaccari, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2023, published scientific conference contribution Abstract: After more than 15 years of successful operation, the Pierre Auger Observatory is currently undergoing a major upgrade called AugerPrime. The aim is to study the mass composition of ultra-high-energy cosmic rays. Part of the upgrade program consists in installing a Short Aperiodic Loaded Loop Antenna (SALLA) atop each of the 1660 water-Cherenkov detectors.
To obtain an absolute calibration for the SALLA, the frequency and directionally dependent antenna response (or vector effective length) must be known. The characteristics of the SALLA depend on various parameters, most prominent is the considered frequency of reception and the antenna geometry. Moreover, the interaction with the structure elements and the presence of the ground has an impact. The measurement of the characteristics of the SALLA is a complex experimental effort. In this view, investigation by numerical antenna simulations provides an important and useful tool. In this contribution, we describe the method used to calculate the vector equivalent length of the SALLA with an advanced and widely used software for antenna simulations like the Numerical Electromagnetics Code (NEC).
Keywords: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, AugerPrime upgrade
Published in RUNG: 03.10.2024; Views: 512; Downloads: 5
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10. Absolute calibration and investigation of ageing of the AERA radio detectorsRogerio M. De Almeida, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2023, published scientific conference contribution Abstract: The Auger Engineering Radio Array (AERA) is currently the largest facility to measure radio emissions from extensive air showers. Located at the Pierre Auger Observatory in Argentina,
it comprises 153 autonomous radio-detector stations, covering an area of 17 sq. km, and measures radio waves in the frequency range from 30 to 80 MHz. For the correct interpretation of data collected by AERA stations, the detector response has to be carefully calibrated. In the past, this was done by measuring the analogue chain in the laboratory, in addition to simulating and measuring the directional response of the antenna. In this work, we perform an absolute calibration by using the radio emission from the Galaxy. A model of the full radio sky is propagated through the system response, including the antenna, filters and amplifiers, and compared to the average spectra recorded by the stations. The method to determine the calibration constants, as the results, for each antenna will be presented. The behavior of the calibration constants is studied as a function of time from 2014 to 2020. There is no relevant ageing effect over a timescale of 10 years, showing that radio detectors could help to monitor possible ageing effects of other detector systems during long-term operations, stressing their importance in determining an absolute energy scale.
Keywords: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, engineering radio array
Published in RUNG: 03.10.2024; Views: 549; Downloads: 1
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