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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
.pdf Celotno besedilo (743,29 KB)
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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: 283; 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: 330; 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.
The Cherenkov Telescope Array
Daniel Mazin, 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: The Cherenkov Telescope Array (CTA) is the next generation ground-based observatory for gamma-ray astronomy at very-high energies. It will be capable of detecting gamma rays in the energy range from 20 GeV to more than 300 TeV with unprecedented precision in energy and directional reconstruction. With more than 100 telescopes of three different types it will be located in the northern hemisphere at La Palma, Spain, and in the southern at Paranal, Chile. CTA will be one of the largest astronomical infrastructures in the world with open data access and it will address questions in astronomy, astrophysics and fundamental physics in the next decades. In this presentation we will focus on the status of the CTA construction, the status of the telescope prototypes and highlight some of the physics perspectives.
Ključne besede: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array, CTA sensitivity, gamma-ray bursts, POpulation Synthesis Theory Integrated project for very high-energy emission
Objavljeno v RUNG: 04.12.2023; Ogledov: 432; Prenosov: 3
.pdf Celotno besedilo (27,92 MB)
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48.
POSyTIVE : a GRB population study for the Cherenkov Telescope Array
Maria Grazia Bernardini, 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 central scientific goals of the next-generation Cherenkov Telescope Array (CTA) is the detection and characterization of gamma-ray bursts (GRBs). CTA will be sensitive to gamma rays with energies from about 20 GeV, up to a few hundred TeV. The energy range below 1 TeV is particularly important for GRBs. CTA will allow exploration of this regime with a ground-based gamma-ray facility with unprecedented sensitivity. As such, it will be able to probe radiation and particle acceleration mechanisms at work in GRBs. In this contribution, we describe POSyTIVE, the POpulation Synthesis Theory Integrated project for very high-energy emission. The purpose of the project is to make realistic predictions for the detection rates of GRBs with CTA, to enable studies of individual simulated GRBs, and to perform preparatory studies for time-resolved spectral analyses. The mock GRB population used by POSyTIVE is calibrated using the entire 40-year dataset of multi-wavelength GRB observations. As part of this project we explore theoretical models for prompt and afterglow emission of long and short GRBs, and predict the expected radiative output. Subsequent analyses are performed in order to simulate the observations with CTA, using the publicly available ctools and Gammapy frameworks. We present preliminary results of the design and implementation of this project.
Ključne besede: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array, CTA sensitivity, gamma-ray bursts, population Synthesis Theory, very high-energy emission
Objavljeno v RUNG: 04.12.2023; Ogledov: 583; Prenosov: 1
.pdf Celotno besedilo (1,50 MB)
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49.
Cherenkov Telescope Array Science : a multi-wavelength and multi-messenger perspective
Ulisses Barres de Almeida, 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: The Cherenkov Telescope Array (CTA) will be the major global observatory for VHE gamma-ray astronomy over the next decade and beyond. It will be an explorer of the extreme universe, with a broad scientific potential: from understanding the role of relativistic cosmic particles, to the search for dark matter. Covering photon energies from 20 GeV to 300 TeV, and with an angular resolution unique in the field, of about 1 arc min, CTA will improve on all aspects of the performance with respect to current instruments, surveying the high energy sky hundreds of times faster than previous TeV telescopes, and with a much deeper view. The very large collection area of CTA makes it an important probe of transient phenomena. The first CTA telescope has just been inaugurated in the Canary Islands, Spain, and as more telescopes are added in the coming years, scientific operation will start. It is evident that CTA will have important synergies with many of the new generation astronomical and astroparticle observatories. In this talk we will review the CTA science case from the point of view of its synergies with other instruments and facilities, highlighting the CTA needs in terms of external data, as well as the opportunities and strategies for cooperation to achieve the basic CTA science goals.
Ključne besede: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array, CTA performances, transient VHE sources, CTA science
Objavljeno v RUNG: 04.12.2023; Ogledov: 521; Prenosov: 4
.pdf Celotno besedilo (1,16 MB)
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50.
Koraki razvoja Slovenskega nacionalnega superračunalniškega omrežja
Samo Stanič, 2023, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: superračunalniki, SLING, Vega, ARNES
Objavljeno v RUNG: 17.11.2023; Ogledov: 507; Prenosov: 6
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