1. 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, izvirni znanstveni članek Opis: 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.
Ključne besede: 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
Objavljeno v RUNG: 26.11.2024; Ogledov: 202; Prenosov: 0
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2. Cherenkov Telescope Array potential in the search for Galactic PeVatronsE.O. Angüner, Christopher Eckner, Gašper Kukec Mezek, Samo Stanič, Serguei Vorobiov, Lili Yang, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, objavljeni znanstveni prispevek na konferenci Opis: One of the major scientific objectives of the future Cherenkov Telescope Array (CTA) Observatory is the search for PeVatrons. PeVatrons are cosmic-ray factories able to accelerate nuclei at least up to the knee feature seen in the spectrum of cosmic rays measured near the Earth. CTA will perform a survey of the full Galactic plane at TeV energies and beyond with unprecedented sensitivity. The determination of efficient criteria to identify PeVatron candidates during the survey is essential in order to trigger further dedicated observations. Here, we present results from a study based on simulations to determine these criteria. The outcome of the study is a PeVatron figure of merit, defined as a metric that provides relations between spectral parameters and spectral cutoff energy lower limits. In addition, simulations of the PeVatron candidate HESS J1641−463 and its parental particle spectrum are presented and discussed. Eventually, our work is applied to simulated population of Galactic PeVatrons, with the aim to determine the sensitivity of CTA.
Ključne besede: Galactic cosmic rays, very-high-energy gamma rays, Galactic PeVatrons, Cherenkov Telescope Array (CTA) Observatory, Galactic plane survey, H.E.S.S. J1641−463 PeVatron candidate
Objavljeno v RUNG: 08.11.2024; Ogledov: 241; Prenosov: 5
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3. Prospects for a survey of the galactic plane with the Cherenkov Telescope ArrayK. Abe, Saptashwa Bhattacharyya, Judit Pérez Romero, Samo Stanič, Veronika Vodeb, Serguei Vorobiov, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, Miha Živec, 2024, izvirni znanstveni članek Opis: Approximately one hundred sources of very-high-energy (VHE) gamma rays are known in the Milky Way, detected with a combination of targeted observations and surveys. A survey of the entire Galactic Plane in the energy range from a few tens of GeV to a few hundred TeV has been proposed as a Key Science Project for the upcoming Cherenkov Telescope Array Observatory (CTAO). This article presents the status of the studies towards the Galactic Plane Survey (GPS). We build and make publicly available a sky model that combines data from recent observations of known gamma-ray emitters with state-of-the-art physically-driven models of synthetic populations of the three main classes of established Galactic VHE sources (pulsar wind nebulae, young and interacting supernova remnants, and compact binary systems), as well as of interstellar emission from cosmic-ray interactions in the Milky Way. We also perform an optimisation of the observation strategy (pointing pattern and scheduling) based on recent estimations of the instrument performance. We use the improved sky model and observation strategy to simulate GPS data corresponding to a total observation time of 1620 hours spread over ten years. Data are then analysed using the methods and software tools under development for real data. Under our model assumptions and for the realisation considered, we show that the GPS has the potential to increase the number of known Galactic VHE emitters by almost a factor of five. This corresponds to the detection of more than two hundred pulsar wind nebulae and a few tens of supernova remnants at average integral fluxes one order of magnitude lower than in the existing sample above 1 TeV, therefore opening the possibility to perform unprecedented population studies. The GPS also has the potential to provide new VHE detections of binary systems and pulsars, to confirm the existence of a hypothetical population of gamma-ray pulsars with an additional TeV emission component, and to detect bright sources capable of accelerating particles to PeV energies (PeVatrons). Furthermore, the GPS will constitute a pathfinder for deeper follow-up observations of these source classes. Finally, we show that we can extract from GPS data an estimate of the contribution to diffuse emission from unresolved sources, and that there are good prospects of detecting interstellar emission and statistically distinguishing different scenarios. Thus, a survey of the entire Galactic plane carried out from both hemispheres with CTAO will ensure a transformational advance in our knowledge of Galactic VHE source populations and interstellar emission.
Ključne besede: very-high-energy gamma rays, Cherenkov Telescope Array Observatory, CTAO Galactic Plane Survey, galactic cosmic rays, pulsar wind nebulae, supernova remnants, galactic PeVatrons, binary systems, diffuse emission
Objavljeno v RUNG: 28.10.2024; Ogledov: 339; Prenosov: 0
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4. Prospects for ▫$\gamma-ray$▫ observations of the Perseus galaxy cluster with the Cherenkov Telescope ArrayK. Abe, Saptashwa Bhattacharyya, Judit Pérez Romero, Samo Stanič, Veronika Vodeb, Serguei Vorobiov, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, Miha Živec, 2024, izvirni znanstveni članek Opis: Galaxy clusters are expected to be both dark matter (DM) reservoirs and storage rooms for the cosmic-ray protons (CRp) that accumulate along the cluster’s formation history. Accordingly, they are excellent targets to search for signals of DM annihilation and decay at γ-ray energies and are predicted to be sources of large-scale γ-ray emission due to hadronic interactions in the intracluster medium (ICM). In this paper, we estimate the sensitivity of the Cherenkov Telescope Array (CTA) to detect diffuse γ-ray emission from the Perseus galaxy cluster. We first perform a detailed spatial and spectral modelling of the expected signal for both the DM and the CRp components. For each case, we compute the expected CTA sensitivity accounting for the CTA instrument response functions. The CTA observing strategy of the Perseus cluster is also discussed. In the absence of a diffuse signal (non-detection), CTA should constrain the CRp to thermal energy ratio X500 within the characteristic radius R500 down to about X500 < 0.003, for a spatial CRp distribution that follows the thermal gas and a CRp spectral index αCRp = 2.3. Under the optimistic assumption of a pure hadronic origin of the Perseus radio mini-halo and depending on the assumed magnetic field profile, CTA should measure αCRp down to about ∆αCRp ≃ 0.1 and the CRp spatial distribution with 10% precision, respectively. Regarding DM, CTA should improve the current ground-based γ-ray DM limits from clusters observations on the velocity- averaged annihilation cross-section by a factor of up to ∼ 5, depending on the modelling of DM halo substructure. In the case of decay of DM particles, CTA will explore a new region of the parameter space, reaching models with τχ > 10[sup]27 s for DM masses above 1 TeV. These constraints will provide unprecedented sensitivity to the physics of both CRp acceleration and transport at cluster scale and to TeV DM particle models, especially in the decay scenario.
Ključne besede: cosmic ray experiments, dark matter experiments, galaxy clusters, gamma ray experiments, very-high energy gamma rays, Cherenkov Telescope Array Observatory, Perseus galaxy cluster
Objavljeno v RUNG: 09.10.2024; Ogledov: 404; Prenosov: 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, 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: 457; Prenosov: 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, objavljeni znanstveni prispevek na konferenci Opis: 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.
Ključne besede: ultra-high-energy cosmic rays, hadronic interactions, extensive air showers, maximum depth, EAS muon content, Pierre Auger Observatory, post-LHC hadronic interaction models
Objavljeno v RUNG: 04.10.2024; Ogledov: 411; Prenosov: 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, objavljeni znanstveni prispevek na konferenci Opis: 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.
Ključne besede: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, Auger Radio Detector, Auger water-Cherenkov detector array, mass-sensitive UHECR measurements
Objavljeno v RUNG: 03.10.2024; Ogledov: 437; Prenosov: 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, objavljeni znanstveni prispevek na konferenci Opis: 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.
Ključne besede: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, UHECR mass composition
Objavljeno v RUNG: 03.10.2024; Ogledov: 403; Prenosov: 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, objavljeni znanstveni prispevek na konferenci Opis: 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).
Ključne besede: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, AugerPrime upgrade
Objavljeno v RUNG: 03.10.2024; Ogledov: 384; Prenosov: 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, objavljeni znanstveni prispevek na konferenci Opis: 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.
Ključne besede: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, engineering radio array
Objavljeno v RUNG: 03.10.2024; Ogledov: 411; Prenosov: 1
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