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41.
The time evolution of the surface detector of the Pierre Auger Observatory
Orazio Zapparrata, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The surface detector array of the Pierre Auger Observatory, consisting of 1660 water Cherenkov tanks, has been in operation for nearly 20 years. During this long period of data acquisition, ageing effects in the detector response have been observed. The temporal evolution of the signals recorded by the surface detector is mostly compensated by continuous calibration with atmospheric muons; however, effects persist in the signal rise time and in high-level data analysis using neural networks. We have implemented a detailed description of the time evolution of the detector response and of the uptimes of individual stations in GEANT4-based detector simulations. These new simulations reproduce the observed time dependencies in the data. Using air-shower simulations that take into account the evolution of individual stations, we show that the reconstructed energy is stable at the sub-percent level, and its resolution is affected by less than 5% in 15 years. For a few specific stations, the collected light produced by muons has decreased to the point where it is difficult to distinguish it from the electromagnetic background in the calibration histograms. The upgrade of the Observatory with scintillator detectors mitigates this problem: by requiring a coincidence between the water-Cherenkov and scintillator detectors, we can enhance the muon relative contribution to the calibration histogram. We present the impact and performance of this coincidence calibration method.
Ključne besede: surface detector, Pierre Auger Observatory, neural networks, air-shower simulations
Objavljeno v RUNG: 22.01.2024; Ogledov: 312; Prenosov: 4
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42.
Constraining models for the origin of ultra-high-energy cosmic rays with spectrum, composition, and arrival direction data measured at the Pierre Auger Observatory
Teresa Bister, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The distribution of cosmic-ray arrival directions shows a better agreement with models in which a fraction of the flux is associated with catalogs of nearby source candidates, such as starburst galaxies, than with isotropy. To investigate this further, we use a novel approach, fitting simultaneously the energy spectrum, distributions of shower maxima, and arrival directions at the highest energies measured with the Pierre Auger Observatory. The astrophysical model consists of homogeneously distributed background sources as well as an adaptable contribution from nearby source candidates. Propagation effects and a rigidity-dependent magnetic field blurring are taken into account, producing a rising level of anisotropy with the energy. We demonstrate that a model containing a flux fraction of around 20% from the starburst galaxy catalog at 40 EeV, with a hard, nitrogen-dominated injection spectrum, provides a good description of the data. By investigating a scenario with Cen A as a single source in combination with the homogeneous background, we show that this region of the sky provides the dominant part to the observed anisotropy signal. Models based on jetted active galactic nuclei whose cosmic-ray flux scales with the gamma-ray emission are disfavored. The modeled energy evolution of the arrival directions, the spectra of individual sources, as well as the statistical significance of the results, including the influence of experimental systematic effects, will be discussed in this contribution.
Ključne besede: anisotropies, Pierre Auger Observatory, ultra-high energy cosmic-rays, arrival directions
Objavljeno v RUNG: 22.01.2024; Ogledov: 281; Prenosov: 4
.pdf Celotno besedilo (1,47 MB)
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43.
An update on the arrival direction studies made with data from the Pierre Auger Observatory
Geraldina Golup, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The search for anisotropies in the arrival directions of ultra-high-energy cosmic rays plays a key role in the efforts to understand their origin. The observed first-harmonic modulation in right ascension above 8 EeV, detected by the Pierre Auger Observatory with a current significance of 6.9�, suggests an extragalactic origin above this energy. Furthermore, there are indications, at the ∼4� significance level, of anisotropies at intermediate angular scales, which are obtained when comparing the arrival directions against the distribution of potential sources from astrophysical catalogs, in particular that of nearby starburst galaxies, and around the Centaurus region. In this contribution, we present the status of the different searches for anisotropies at small, intermediate and large angular scales. We use the latest available data set, with 19 years of operation that has yielded 135,000 km^2 yr sr of accumulated exposure, covering the sky at declinations from −90◦ to 45◦. At small and intermediate scales, we report updates of the all-sky blind search for localized excesses, the study around the Centaurus region, and the likelihood analysis with catalogs of candidate sources. We have also studied the regions of the sky from which the Telescope Array Collaboration has reported hints of excesses in their data and we find no significant effects in the same directions with a data set of comparable size. At large angular scales, the dipolar and quadrupolar amplitudes in energy bins are updated. We discuss the prospects of these searches, both in regards to increases in statistics and in relation to the future inclusion of event-by-event mass estimators in these analyses through the upgrade of the Observatory, AugerPrime.
Ključne besede: anisotropies, Pierre Auger Observatory, ultra-high energy cosmic-rays, arrival directions
Objavljeno v RUNG: 22.01.2024; Ogledov: 285; Prenosov: 5
.pdf Celotno besedilo (2,45 MB)
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44.
Depth of maximum of air-shower profiles : testing the compatibility of the measurements at the Pierre Auger Observatory and the Telescope Array
A. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The Pierre Auger Observatory (Auger) and the Telescope Array (TA), located, respectively, in the Southern and Northern hemispheres, are the largest ultra-high-energy cosmic ray (UHECR) observatories. The Auger and TA Collaborations have collected unprecedented statistics providing us with a unique opportunity to search for the differences between the UHECR energy spectra and mass compositions in the complementary sky regions. To correctly attribute such differences to the properties of the UHECR sources or propagation, the systematic effects in the measurements of each observatory should be considered properly. In this context, the task of the Auger – TA mass composition working group is to identify possible differences of astrophysical origin in the measurements of the depth of the maximum of air-shower profiles, X_max, performed at both observatories using the fluorescence technique. Due to distinct approaches to event selection and analysis atAuger and TA, theworking group uses a specially designed method to transfer the Auger X_max distributions into the TA detector. To this end, dedicated air-shower and detector simulations for the TA Black Rock Mesa and Long Ridge fluorescence detector stations were performed with the Sibyll 2.3d hadronic interaction model. From the comparison of the first two moments and the shapes of X_max distributions for energies above 10^18.2 eV, no significant differences between the Auger and TA measurements were found.
Ključne besede: Pierre Auger Observatory, Telescope Array, ultra-high energy cosmic rays, fluorescence detectors
Objavljeno v RUNG: 22.01.2024; Ogledov: 332; Prenosov: 5
.pdf Celotno besedilo (1,19 MB)
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45.
Constraining models for the origin of ultra-high-energy cosmic rays with a novel combined analysis of arrival directions, spectrum, and composition data measured at the Pierre Auger Observatory
A. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2024, izvirni znanstveni članek

Opis: The combined fit of the measured energy spectrum and shower maximum depth distributions of ultra-high-energy cosmic rays is known to constrain the parameters of astrophysical models with homogeneous source distributions. Studies of the distribution of the cosmic-ray arrival directions show a better agreement with models in which a fraction of the flux is non-isotropic and associated with the nearby radio galaxy Centaurus A or with catalogs such as that of starburst galaxies. Here, we present a novel combination of both analyses by a simultaneous fit of arrival directions, energy spectrum, and composition data measured at the Pierre Auger Observatory. The model takes into account a rigidity-dependent magnetic field blurring and an energy-dependent evolution of the catalog contribution shaped by interactions during propagation. We find that a model containing a flux contribution from the starburst galaxy catalog of around 20% at 40 EeV with a magnetic field blurring of around 20◦ for a rigidity of 10EV provides a fair simultaneous description of all three observables. The starburst galaxy model is favored with a significance of 4.5σ (considering experimental systematic effects) compared to a reference model with only homogeneously distributed background sources. By investigating a scenario with Centaurus A as a single source in combination with the homogeneous background, we confirm that this region of the sky provides the dominant contribution to the observed anisotropy signal. Models containing a catalog of jetted active galactic nuclei whose flux scales with the γ-ray emission are, however, disfavored as they cannot adequately describe the measured arrival directions.
Ključne besede: ultra high energy cosmic rays, cosmic ray experiments, Pierre Auger Observatory, active galactic nuclei
Objavljeno v RUNG: 19.01.2024; Ogledov: 330; Prenosov: 7
.pdf Celotno besedilo (3,93 MB)
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46.
Update on the offline framework for AugerPrime and production of reference simulation libraries using the VO Auger grid resources
Eva Santos, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Taking data stably since 2004, the Pierre Auger Observatory has published numerous results regarding the properties of ultra-high-energy cosmic rays with unprecedented statistics. However, questions about their origin and mass composition remain unanswered, motivating us to build AugerPrime, a major upgrade of our surface detector array with improved electronics and new detectors. The upgrade is swiftly approaching its completion. Phase II of the Pierre Auger Observatory has begun, which called for an update of the Offline software Framework and modules to handle the additional detectors and the new electronics. Thanks to its modular structure, Offline has proved flexible enough to accommodate all the changes required to handle AugerPrime data reconstruction and event simulation. Additionally, new reference libraries of shower and detector simulations, including dedicated libraries envisaging the searches for neutral particles, such as ultra-high-energy photons and neutrinos, profiting from the new AugerPrime detectors with the upgraded electronics, are in the pipeline. In this contribution, we report on the current status and prospects for the Auger Off line Framework and the production of reference Monte Carlo libraries for AugerPrime.
Ključne besede: AugerPrime, Pierre Auger Observatory, cosmic rays, surface detectors
Objavljeno v RUNG: 16.01.2024; Ogledov: 334; Prenosov: 7
.pdf Celotno besedilo (1,52 MB)
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47.
Najvišje energije v vesolju
mIHA Živec, druga izvedena dela

Opis: Zgodovinski pregled in trenutno stanje astrofizike visokih energij.
Ključne besede: nevtrini, kozmični delci, žarki gama, observatorij Pierre Auger, polje teleskopov Čerenkova
Objavljeno v RUNG: 11.12.2023; Ogledov: 358; Prenosov: 0
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48.
Search for evidence of neutron fluxes using Pierre Auger Observatory data
Danelise De Oliveira Franco, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Astrophysical neutral particles, such as neutrons, can point directly to their sources since they are not affected by magnetic fields. We expect neutron production in the immediate vicinity of the acceleration sites due to cosmic ray interactions. Hence, a high-energy neutron flux could help to identify sources of cosmic rays in the EeV range. Free neutrons, although unstable, can travel a mean distance of 9.2 kpc times their energy in EeV. Due to the neutron instability, we limit the searches to Galactic candidate sources. Since air showers initiated by a neutron are indistinguishable from those generated by a proton, we would recognize a neutron flux as an excess of events from the direction of its source. Previous searches using events with a zenith angle up to 60^◦ and energies above 1 EeV found no surplus of events that would indicate a neutron flux. We present the results of the search for evidence of high-energy neutron fluxes using a data set about three times larger than the previous work. We investigate the sky in the field of view of the Pierre Auger Observatory, narrowing down to specific directions of candidate sources. With respect to previous works, we extend the angular range up to zenith angles of 80^◦ , reaching declinations from −90^◦ to +45^◦ , and the energy range going as low as 0.1 EeV. The extension in the field of view provides exposure to the Crab Nebula for the first time.
Ključne besede: neutrons, cosmic ray, Pierre Auger Observatory, Crab Nebula, proton, high-energy neutron flux
Objavljeno v RUNG: 14.11.2023; Ogledov: 532; Prenosov: 5
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49.
AugerPrime surface detector electronics
A. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, izvirni znanstveni članek

Opis: Operating since 2004, the Pierre Auger Observatory has led to major advances in our understanding of the ultra-high-energy cosmic rays. The latest findings have revealed new insights that led to the upgrade of the Observatory, with the primary goal of obtaining information on the primary mass of the most energetic cosmic rays on a shower-by-shower basis. In the framework of the upgrade, called AugerPrime, the 1660 water-Cherenkov detectors of the surface array are equipped with plastic scintillators and radio antennas, allowing us to enhance the composition sensitivity. To accommodate new detectors and to increase experimental capabilities, the electronics is also upgraded. This includes better timing with up-to-date GPS receivers, higher sampling frequency, increased dynamic range, and more powerful local processing of the data. In this paper, the design characteristics of the new electronics and the enhanced dynamic range will be described. The manufacturing and test processes will be outlined and the test results will be discussed. The calibration of the SD detector and various performance parameters obtained from the analysis of the first commissioning data will also be presented.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, AugerPrime detector upgrade, surface detector array, surface detector electronics
Objavljeno v RUNG: 18.10.2023; Ogledov: 644; Prenosov: 5
.pdf Celotno besedilo (2,07 MB)
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50.
Ultrahigh-Energy multi-messengers at the Pierre Auger Observatory
Francisco 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: 716; Prenosov: 5
.pdf Celotno besedilo (1,69 MB)
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