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, original scientific article Abstract: 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.
Keywords: ultra-high-energy cosmic rays, telescope array, extremely energetic cosmic-ray event
Published in RUNG: 23.04.2025; Views: 58; Downloads: 0
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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, original scientific article Abstract: 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.
Keywords: ultrahigh energy cosmic rays, large-scale structure, extragalactic magnetic fields, UHECR propagation, Telescope Array, UHECR mass composition, UHECR arrival directions
Published in RUNG: 23.04.2025; Views: 54; Downloads: 0
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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, original scientific article Abstract: 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.
Keywords: ultrahigh energy cosmic rays (UHECRs), Large Scale Structure, extragalactic magnetic fields, UHECR propagation, Telescope Array surface detector, UHECR mass composition, UHECR arrival directions
Published in RUNG: 23.04.2025; Views: 63; Downloads: 0
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4. Multimessenger studies with the Pierre Auger ObservatoryJon Paul Lundquist, Andrej Filipčič, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: The Pierre Auger Observatory, the world’s largest ultra-high-energy (UHE) cosmic ray (CR) detector, plays a crucial role in multi-messenger astroparticle physics with its high sensitivity to UHE photons and neutrinos. Recent Auger Observatory studies have set stringent limits on the diffuse and point-like fluxes of these particles, enhancing constraints on dark-matter models and UHECR sources. Although no temporal coincidences of neutrinos or photons with LIGO/Virgo gravitational wave events have been observed, competitive limits on the energy radiated in these particles have been established, particularly from the GW170817 binary neutron star merger. Additionally, correlations between the arrival directions of UHECRs and high-energy neutrinos have been explored using data from the IceCube Neutrino Observatory, ANTARES, and the Auger Observatory, providing additional neutrino flux constraints. Efforts to correlate UHE neutron fluxes with gamma-ray sources within our galaxy continue, although no significant excesses have been found. These collaborative and multi-faceted efforts underscore the pivotal role of the Auger Observatory in advancing multi-messenger astrophysics and probing the most extreme environments of the Universe.
Keywords: high-energy particle physics, astrophysics, ultra-high energy cosmic rays, neutrinos, gravitional waves
Published in RUNG: 22.04.2025; Views: 119; Downloads: 0
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5. 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, original scientific article Abstract: 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.
Keywords: ultra-high-energy cosmic rays (UHECRs), extensive air showers, Pierre Auger Observatory, open data, UHECR event data, space weather data, Auger Open Data Portal
Published in RUNG: 03.04.2025; Views: 369; Downloads: 8
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6. 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, original scientific article Abstract: 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.
Keywords: ultra-high-energy cosmic rays, extensive air showers, upward-going air showers, Pierre Auger Observatory, Fluorescence Detector, anomalous ANITA events
Published in RUNG: 28.03.2025; Views: 356; Downloads: 5
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7. 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, published scientific conference contribution Abstract: 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.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, AugerPrime upgrade
Published in RUNG: 28.03.2025; Views: 349; Downloads: 7
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8. 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, published scientific conference contribution Abstract: 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.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, radio emission
Published in RUNG: 28.03.2025; Views: 335; Downloads: 5
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9. 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, published scientific conference contribution Abstract: 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.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, UHECR mass composition
Published in RUNG: 28.03.2025; Views: 342; Downloads: 8
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10. Testing the declination dependency of the spectrum measured by the Pierre Auger ObservatoryDiego Ravignani, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: The distribution of the arrival directions of cosmic rays observed by the Pierre Auger Observatory has a dipolar component that implies a flux dependence on declination. Previously, we showed that the spectrum built from events arriving with a zenith angle less than 60° is qualitatively consistent with the dipole. In this work, we go one step further and show that the Auger spectrum cannot reject the hypothesis of a declination-independent flux. By using events of up 80°, we extend the previous survey from +25° of declination to +45°, thus covering 85% of the sky.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHECR arrival directions, large-scale dipolar anisotropy
Published in RUNG: 28.03.2025; Views: 334; Downloads: 6
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