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1.
Astrophysical interpretation of energy spectrum and mass composition of cosmic rays as measured at the Pierre Auger Observatory
Eleonora Guido, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The combined interpretation of the spectrum and composition measurements plays a key role in the quest for the origin of ultra-high-energy cosmic rays (UHECRs). The Pierre Auger Observatory, thanks to its huge exposure, provides the most precise measurement of the energy spectrum of UHECRs and the most reliable information on their composition, exploiting the distributions of the depth of maximum of the showers in the atmosphere. A combined fit of a simple astrophysical model of UHECR sources to the spectrum and mass composition measurements is used to evaluate the constraining power of the data measured by the Pierre Auger Observatory on the source properties. We find that our data across the “ankle” feature are well reproduced if two extragalactic populations of sources are considered, one emitting a very soft spectrum which dominates the region below the ankle, and the other taking over at energies above the ankle, with an intermediate mixed composition, a hard spectrum and a low rigidity cutoff. Interestingly, similar results can also be obtained if the medium-mass contribution at lower energy is provided by an additional galactic component.
Ključne besede: Pierre Auger Observatory, ultra-high energy cosmic rays, UHECR energy spectrum, UHECR mass composition
Objavljeno v RUNG: 24.01.2024; Ogledov: 279; Prenosov: 7
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2.
Investigation of multi-messenger properties of FR0 radio galaxy emitted ultra-high energy cosmic rays
Jon Paul Lundquist, Lukas Merten, Serguei Vorobiov, Margot Boughelilba, Albert Reimer, Paolo Da Vela, F. Tavecchio, G. Bonnoli, C. Righi, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Low luminosity Fanaroff-Riley type 0 (FR0) radio galaxies are amongst potential contributors to the observed flux of ultra-high energy cosmic rays (UHECRs). Due to FR0s’ much higher abundance in the local universe than more powerful radio galaxies (e.g., about five times more ubiquitous at redshifts z≤0.05 than FR1s), they could provide a substantial fraction of the total UHECR energy density. In the presented work, we determine the mass composition and energy spectrum of UHECRs emitted by FR0 sources by fitting simulation results from the CRPropa3 framework to the recently published Pierre Auger Observatory data. The resulting emission spectral characteristics (spectral indices, rigidity cutoffs) and elemental group fractions are compared to the Auger results. The FR0 simulations include the approximately isotropic distribution of FR0s extrapolated from the measured FR0 galaxy properties and various extragalactic magnetic field configurations, including random and large-scale structured fields. We predict the fluxes of secondary photons and neutrinos produced during UHECR propagation through cosmic photon backgrounds. The presented results allow for probing the properties of the FR0 radio galaxies as cosmic-ray sources using observational high-energy multi-messenger data.
Ključne besede: ultra-high energy cosmic rays, UHECRs, Pierre Auger Observatory, UHECR propagation, UHECR interactions, UHECR energy spectrum, UHECR mass composition, UHECR sources, Fanaroff-Riley (FR) radio galaxies, FR0 galaxies
Objavljeno v RUNG: 24.01.2024; Ogledov: 319; Prenosov: 5
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3.
Measurement of UHECR energy spectrum with the Pierre Auger Observatory and the Telescope Array
Douglas R. Bergman, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The measurement of the energy spectrum of ultra-high-energy cosmic rays (UHECRs) is of crucial importance to clarify their origin, acceleration mechanisms, and propagation processes in inter-Galactic and Galactic space. The Pierre Auger Observatory in Argentina and the Telescope Array (TA) in the US have reported their measurements of UHECR energy spectra observed in the southern and northern hemisphere, respectively. The Auger–TA energy spectrum working group was established in 2012 and has been working to understand the uncertainties in energy scale in both experiments, their systematic differences, and differences in the shape of the spectra. In previous works, we reported that there was an overall agreement of the energy spectra measured by the two observatories below 10 EeV while at higher energies, a remaining significant difference was observed in the common declination band. This time we revisit the energy scales of both experiments, including the fluorescence yield and the invisible energy corrections. Another new approach to investigate a possible source of energy systematic difference is to reconstruct simulated showers of common energy and zenith angle using the detector simulation and reconstruction programs of both experiments that are independently tuned and optimized for data from their own detectors. The results will be presented at the conference.
Ključne besede: Pierre Auger Observatory, ultra-high energy cosmic rays, Telescope Array, energy spectrum
Objavljeno v RUNG: 23.01.2024; Ogledov: 283; Prenosov: 5
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4.
Measurement of the cosmic ray spectrum with the Pierre Auger Observatory
Daniela Mockler, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, objavljeni znanstveni prispevek na konferenci

Opis: The flux of ultra-high energy cosmic rays above 3×10[sup]17 eV has been measured with unprecedented precision at the Pierre Auger Observatory. The flux of the cosmic rays is determined by four different measurements. The surface detector array provides three data sets, two formed by dividing the data into two zenith angle ranges, and one obtained from a nested, denser detector array. The fourth measurement is obtained with the fluorescence detector. By combining all four data sets, the all-sky flux of cosmic rays is determined. The spectral features are discussed in detail and systematic uncertainties are addressed.
Ključne besede: ultra-high-energy cosmic rays (UHECRs), Pierre Auger Observatory, UHECR energy spectrum
Objavljeno v RUNG: 11.10.2023; Ogledov: 586; Prenosov: 6
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5.
Results from the Pierre Auger Observatory
Esteban Roulet, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, objavljeni znanstveni prispevek na konferenci

Opis: Some of the results on ultrahigh-energy cosmic rays that have been obtained with the Pierre Auger Observatory are presented. These include measurements of the spectrum, composition and anisotropies. Possible astrophysical scenarios that account for these results are discussed.
Ključne besede: ultra-high-energy cosmic rays (UHECRs), Pierre Auger Observatory, UHECR energy spectrum, UHECR anisotropies, UHECR mass composition
Objavljeno v RUNG: 11.10.2023; Ogledov: 607; Prenosov: 5
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6.
Performance of the 433 m surface array of the Pierre Auger Observatory
G. Silli, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, objavljeni znanstveni prispevek na konferenci

Opis: The Pierre Auger Observatory, located in western Argentina, is the world's largest cosmic-ray observatory. While it was originally built to study the cosmic-ray flux above 10^18.5 eV, several enhancements have reduced this energy threshold. One such enhancement is a surface array composed of a triangular grid of 19 water-Cherenkov detectors separated by 433 m (SD-433) to explore the energies down to about 10^16 eV. We are developing two research lines employing the SD-433. Firstly, we will measure the energy spectrum in a region where previous experiments have shown evidence of the second knee. Secondly, we will search for ultra-high energy photons to study PeV cosmic-ray sources residing in the Galactic center. In this work, we introduce the SD-433 and we show that it is fully efficient above 5×10^16 eV for hadronic primaries with θ<45∘. Using seven years of data, we present the parametrization of the lateral distribution function of measured signals. Finally, we show that an angular resolution of 1.8∘ (0.5∘) can be attained at the lowest (highest) primary energies. Our study lays the goundmark for measurements in the energy range above 10^16 eV by utilizing the SD-433 and thus expanding the scientific output of the Auger surface detector.
Ključne besede: Pierre Auger Observatory, SD-433, indirect detection, surface detection, low energy extension, ultra-high energy, cosmic rays, energy spectrum, photons, multimessenger
Objavljeno v RUNG: 04.10.2023; Ogledov: 614; Prenosov: 5
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7.
Combined fit of the energy spectrum and mass composition across the ankle with the data measured at the Pierre Auger Observatory
E. Guido, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, objavljeni znanstveni prispevek na konferenci

Opis: The combined fit of the energy spectrum and mass composition data above 5 EeV suggested the presence of extragalactic sources ejecting ultra-high-energy cosmic rays with relatively low maximum energies, hard spectral indices and mixed chemical compositions, dominated by the contribution of intermediate mass groups. Here we present an extension of the fit to lower energies, to include the feature observed near 5 EeV in the all-particle energy spectrum, the so-called ankle. We show that it is possible to generate such a change of slope assuming that the flux below the ankle is provided by the superposition of different contributions. The simplest extension of this sort consists of introducing a supplemental extragalactic component at low energy, characterised by different physical parameters with respect to the one being dominant above the ankle: such a component may originate from a different population of sources or be provided by interactions occurring in the acceleration sites. In this framework we also explore the possibility of including the end of a Galactic contribution at low energies. The fit suggests that these scenarios provide a reasonable description of the measurements across the ankle, without significantly affecting the interpretation obtained for the above-ankle region. In order to evaluate our capability to constrain the source models, we finally discuss the impact of the main experimental systematic uncertainties and of the theoretical models choice on the fit results.
Ključne besede: Pierre Auger Observatory, indirect detection, fluorescence detection, hybrid detection, surface detection, ultra-high energy, cosmic rays, composition, energy spectrum, combined fit
Objavljeno v RUNG: 03.10.2023; Ogledov: 486; Prenosov: 4
.pdf Celotno besedilo (1,09 MB)
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8.
Energy spectrum of cosmic rays measured using the Pierre Auger Observatory
V. Novotný, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, objavljeni znanstveni prispevek na konferenci

Opis: We present the energy spectrum of cosmic rays measured at the Pierre Auger Observatory from 6×10^15 eV up to the most extreme energies where the accumulated exposure reaches about 80 000 km^2sr yr. The wide energy range is covered with five different measurements, namely using the events detected by the surface detector with zenith angles below 60 degrees and applying different reconstruction method also above 60 degrees, those collected by a denser array, the hybrid events simultaneously recorded by the surface and fluorescence detectors, and using those events in which the signal is dominated by Cherenkov light registered by the high-elevation telescopes. In this contribution, we report updates of the analysis techniques and present the spectrum obtained by combining the five different measurements. Spectral features occurring in the wide energy range covered by the Observatory are discussed.
Ključne besede: Pierre Auger Observatory, indirect detection, fluorescence detection, surface detection, hybrid detection, ultra-high energy, cosmic rays, cerenkov light, energy spectrum, inclined showers
Objavljeno v RUNG: 03.10.2023; Ogledov: 484; Prenosov: 5
.pdf Celotno besedilo (1,45 MB)
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9.
Large-scale and multipolar anisotropies of cosmic rays detected at the Pierre Auger Observatory with energies above 4 EeV
R. de Almeida, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, objavljeni znanstveni prispevek na konferenci

Opis: More than half a century after the discovery of ultra-high energy cosmic rays (UHECRs), their origin is still an open question. The study of anisotropies in the arrival directions of such particles is an essential ingredient to solve this puzzle. We update our previous analysis of large-scale anisotropies observed by the Pierre Auger Observatory using the latest data collected before the AugerPrime upgrade. We select events with zenith angles up to 80 degrees, implying a sky coverage of 85%, and energies above 4 EeV, for which the surface detector of the Observatory is fully efficient. Dipolar and quadrupolar amplitudes are evaluated through a combined Fourier analysis of the event count rate in right ascension and azimuth. The analysis is performed in three energy bins with boundaries at 4, 8, 16 and 32 EeV and two additional cumulative bins with energies above 8 and 32 EeV. The most significant signal is a dipolar modulation in right ascension for energies above 8 EeV, as previously reported, with statistical significance of 6.6σ. Additionally, we report the measurements of the angular power spectrum for the same energy bins with the same dataset.
Ključne besede: Pierre Auger Observatory, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, anisotropy, dipole, quadropole, angular power spectrum, inclined showers
Objavljeno v RUNG: 03.10.2023; Ogledov: 544; Prenosov: 4
.pdf Celotno besedilo (1,14 MB)
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10.
Joint analysis of the energy spectrum of ultra-high-energy cosmic rays as measured at the Pierre Auger Observatory and the Telescope Array
Y. Tsunesada, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, objavljeni znanstveni prispevek na konferenci

Opis: The measurement of the energy spectrum of ultra-high-energy cosmic rays (UHECRs) is of crucial importance to clarify their origin and acceleration mechanisms. The Pierre Auger Observatory in Argentina and the Telescope Array (TA) in the US have reported their measurements of UHECR energy spectra observed in the southern and northern hemisphere, respectively. The region of the sky accessible to both Observatories ([−15,+24] degrees in declination) can be used to cross-calibrate the two spectra. The Auger-TA energy spectrum working group was organized in 2012 and has been working to understand the uncertainties in energy scale in both experiments, their systematic differences, and differences in the shape of the spectra. In previous works, we reported that there was an overall agreement of the energy spectra measured by the two observatories below 10 EeV while at higher energies, a remaining significant difference was observed in the common declination band. We revisit this issue to understand its origin by examining the systematic uncertainties, statistical effects, and other possibilities. We will also discuss the differences in the spectra in different declination bands and a new feature in the spectrum recently reported by the Auger Collaboration.
Ključne besede: Telescope Array, Pierre Auger Observatory, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, energy spectrum, anisotropy, declination dependence, fully sky
Objavljeno v RUNG: 02.10.2023; Ogledov: 502; Prenosov: 6
.pdf Celotno besedilo (1,02 MB)
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