1. Multimessenger studies with the Pierre Auger ObservatoryJon Paul Lundquist, Andrej Filipčič, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: 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. Ključne besede: high-energy particle physics, astrophysics, ultra-high energy cosmic rays, neutrinos, gravitional waves Objavljeno v RUNG: 22.04.2025; Ogledov: 273; Prenosov: 0
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2. A new view of UHECRs with the Pierre Auger ObservatoryDenise Boncioli, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: In its Phase I, the Pierre Auger Observatory has led to several observations, driving the field of ultra- high-energy cosmic ray (UHECR) research over the last 20 years. Major achievements obtained so far include the unprecedented precise energy spectrum and its features, the observables linked to the UHECR mass composition and the distribution of arrival directions of the most energetic events. These results, together with the non-observation of high-energy neutrinos and photons, strongly disfavor the pre-Auger pure-proton paradigm.
In this talk, we will provide an overview on the main results of the Observatory, and describe possible astrophysical scenarios for their interpretation. The prospects of improving the current understanding about UHECR characteristics during the Phase II of the Observatory will be also shown. Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE neutrinos, UHE photons, Auger Phase I, AugerPrime upgrade, Auger Phase II, UHECR mass composition, UHECR energy spectrum, UHECR anisotropy studies, UHECR astrophysical scenarios, UHECR data interpretation Objavljeno v RUNG: 24.03.2025; Ogledov: 460; Prenosov: 4
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3. Searches for UHE neutrinos and upward-going showers at the Pierre Auger ObservatoryJaime Alvarez-Muňiz, 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, as a key actor in multi-messenger astronomy, is playing a crucial role in searching for and following-up cosmic phenomena across different channels. Data from the Observatory have been utilized for nearly 20 years to search for showers induced by Ultra-High-Energy (UHE) neutrinos with energies exceeding 0.1 EeV. Neutrino-induced showers at high zenith angles are likely to develop deep in the atmosphere, resulting in a significant electromagnetic component that distinguishes them from the cosmic-ray background. This enables the identification of candidate events from both neutrinos interacting in the atmosphere and Earth-skimming τ neutrinos. Searches have been conducted for both diffuse and point sources using data collected by the Surface Detector, a large array of over 1660 water-Cherenkov stations spread over an area of 3000 square km. Additionally, the Fluorescence Detector consisting of 27 telescopes has been employed to search for upward-developing air showers, as predicted by several interpretations of the 'anomalous' events detected by the ANITA detector. In this contribution, we summarize the main results obtained in these searches and discuss their astrophysical implications. Ključne besede: ulti-messenger astronomy, ultra-high-energy neutrino search, down-going neutrinos, Earth-skimming τ neutrinos, search for upward-developing air showers, ANITA detector, Pierre Auger Observatory Objavljeno v RUNG: 24.03.2025; Ogledov: 401; Prenosov: 6
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4. The Pierre Auger Observatory and physics beyond the standard modelR. Aloisio, 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, the world’s largest cosmic ray detector, plays a pivotal role in exploring the frontiers of physics beyond the standard model of particle physics. By the observation of ultra-high energy cosmic rays, Auger provides critical insights into two major scenarios: super heavy dark matter and Lorentz invariance violation. Super heavy dark matter, hypothesized to originate in the early universe, offers a compelling explanation for the dark matter problem and is constrained by Auger through searches for photons and neutrinos resulting from its decay. Lorentz invariance violations, motivated by quantum gravity theories implying deviations from fundamental symmetries, are probed by Auger through alterations of the particle dispersion relation and the energy thresholds of their interactions with astrophysical photons backgrounds. Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE neutrinos, UHE photons Objavljeno v RUNG: 24.03.2025; Ogledov: 379; Prenosov: 4
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5. Multi-messenger and transient astrophysics with the Cherenkov Telescope ArrayŽ. Bošnjak, Anthony M. Brown, Alessandro Carosi, M. Chernyakova, Pierre Cristofari, F. Longo, A. López Oramas, M. Santander, Serguei Vorobiov, Danilo Zavrtanik, 2021, drugi sestavni deli Opis: The discovery of gravitational waves, high-energy neutrinos or the very-high-energy counterpart of gamma-ray bursts has revolutionized the high-energy and transient astrophysics community. The development of new instruments and analysis techniques will allow the discovery and/or follow-up of new transient sources. We describe the prospects for the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory, for multi-messenger and transient astrophysics in the decade ahead. CTA will explore the most extreme environments via very-high-energy observations of compact objects, stellar collapse events, mergers and cosmic-ray accelerators. Ključne besede: multi-messenger astrophysics, gravitational waves, very-high-energy (VHE) gamma rays, cosmic rays, VHE neutrinos, transient astrophysical phenomena, Cherenkov Telescope Array Observatory Objavljeno v RUNG: 13.01.2025; Ogledov: 661; Prenosov: 7
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6. 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, objavljeni znanstveni prispevek na konferenci Opis: 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. Ključne besede: ultra-high-energy cosmic rays, UHE photons, UHE neutrinos, UHE neutrons, Pierre Auger Observatory, multi-messenger astrophysical studies Objavljeno v RUNG: 04.10.2024; Ogledov: 1100; Prenosov: 6
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7. Ultrahigh-Energy multi-messengers at the Pierre Auger ObservatoryFrancisco Pedreira, Andrej Filipčič, Gašper Kukec Mezec, Ahmed Saleh, Samo Stanič, Marta Trini, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, objavljeni znanstveni prispevek na konferenci Opis: The study of correlations between observations of different messengers from extreme sources of the Universe has emerged as an outstanding way to make progress in astrophysics. The Pierre Auger Observatory is capable of significant contributions as an ultra-high energy particle detector, particularly through its capability to search for inclined showers produced by neutrinos. We describe the neutrino searches made with
the Observatory with particular emphasis on the recent results following the detections of
gravitational waves from binary mergers with Advanced LIGO and VIRGO, leading to competitive limits. Ključne besede: ultra-high-energy (UHE) cosmic rays (CRs), Pierre Auger Observatory, UHE neutrinos, multi-messenger astrophysics Objavljeno v RUNG: 11.10.2023; Ogledov: 3139; Prenosov: 11
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8. TA SD analysis for inclined air showersK. Takahashi, Jon Paul Lundquist, 2023, objavljeni znanstveni prispevek na konferenci Opis: The origin of UHECRs is an open question which is complicated due to not very well-known deflections of the charged particles in Galactic and intergalactic magnetic fields. Finding the EeV neutrinos from astronomical sources will be a key to solve the problem of the origin. EeV neutrinos are expected to produce extensive air showers which are observable by the current operational air shower arrays. To search for neutrino-induced showers, it is important to increase both the interaction probability and background rejection power in the analysis of the inclined showers. We study a reconstruction method of the Telescope Array surface detector (TA SD) data for the neutrino-induced inclined air showers. The prime target is to improve the angular resolution for the astronomical objects. In this contribution, we present the detail of analysis method, angular resolution and total exposure of TA SD for neutrinos from the astronomical objects as a function of the declination. Ključne besede: Telescope Array, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, inclined showers, neutrinos Objavljeno v RUNG: 09.10.2023; Ogledov: 2999; Prenosov: 6
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9. Telescope Array Combined Fit to Cosmic Ray Spectrum and CompositionD. Bergman, Jon Paul Lundquist, 2022, objavljeni znanstveni prispevek na konferenci Opis: We present the result of fits of an astrophysical model of UHECR sources to the energy spectrum measured using the Telescope Array (TA) surface detectors and the composition data measured by TA fluorescence detectors in stereo mode. The astrophysical model consists of identical sources, uniformly distributed with a density which evolves with age, where groups of nuclei with varying fractions are accelerated producing a power law source with a rigidity-dependent cutoff. The model includes the propagation effects of photo-pion production, photo-nuclear disintegration and general energy loss from universal expansion. Comparison of model data with detector data in both the energy and the Xmax distributions is done via a forward-folding description of detector effects. A prediction of the cosmogenic neutrino flux at Earth resulting from the cosmic rays produced in the model with these fit values is also presented. The predicted flux is considerably higher than other similar fits to Auger data have previously predicted. Ključne besede: Telescope Array, indirect detection, stereo detection, fluorescence detection, ultra-high energy, cosmic rays, energy spectrum, composition, combined fit, cosmogenic neutrinos, multimessenger Objavljeno v RUNG: 02.10.2023; Ogledov: 2353; Prenosov: 6
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10. Science with the Global Cosmic-ray Observatory (GCOS)Rafael Alves Batista, M. Ahlers, Pedro Assis, Markus Gottfried Battisti, J. A. Bellido, S. Bhatnagar, K. Bismark, Teresa Bister, Martina Boháčová, Serguei Vorobiov, 2023, objavljeni znanstveni prispevek na konferenci Opis: The Global Cosmic-ray Observatory (GCOS) is a proposed large-scale observatory for studying
ultra-high-energy cosmic particles, including ultra-high-energy cosmic rays (UHECRs), photons,
and neutrinos. Its primary goal is to characterise the properties of the highest-energy particles in
Nature with unprecedented accuracy, and to identify their elusive sources. With an aperture at least a ten-fold larger than existing observatories, this next-generation facility should start operating after 2030, when present-day detectors will gradually cease their activities. Here we briefly review the scientific case motivating GCOS. We present the status of the project, preliminary ideas for its design, and some estimates of its capabilities. Ključne besede: ultra-high-energy cosmic rays, UHE photons, UHE neutrinos, the Global Cosmic-ray Observatory project Objavljeno v RUNG: 27.09.2023; Ogledov: 2834; Prenosov: 7
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