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41.
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, published scientific conference contribution

Abstract: 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.
Keywords: Pierre Auger Observatory, Telescope Array, ultra-high energy cosmic rays, fluorescence detectors
Published in RUNG: 22.01.2024; Views: 285; Downloads: 5
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42.
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, original scientific article

Abstract: 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.
Keywords: ultra high energy cosmic rays, cosmic ray experiments, Pierre Auger Observatory, active galactic nuclei
Published in RUNG: 19.01.2024; Views: 309; Downloads: 7
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43.
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, published scientific conference contribution

Abstract: 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.
Keywords: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array, CTA sensitivity, gamma-ray bursts, POpulation Synthesis Theory Integrated project for very high-energy emission
Published in RUNG: 04.12.2023; Views: 406; Downloads: 3
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44.
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, published scientific conference contribution

Abstract: 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.
Keywords: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array, CTA sensitivity, gamma-ray bursts, population Synthesis Theory, very high-energy emission
Published in RUNG: 04.12.2023; Views: 530; Downloads: 1
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45.
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, published scientific conference contribution

Abstract: 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.
Keywords: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array, CTA performances, transient VHE sources, CTA science
Published in RUNG: 04.12.2023; Views: 478; Downloads: 4
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46.
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, published scientific conference contribution

Abstract: 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.
Keywords: neutrons, cosmic ray, Pierre Auger Observatory, Crab Nebula, proton, high-energy neutron flux
Published in RUNG: 14.11.2023; Views: 506; Downloads: 5
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47.
Ferrite-based magnets by high pressure consolidation
Cesár De Julián Fernández, Blaž Belec, Aleksander Učakar, Petra Jenuš, 2023, published scientific conference contribution abstract

Abstract: M-type hexaferrite magnets constitute together the rare-earth magnets the most employed magnets in the world. Even if ferrite magnets have smaller energy product and lower magnetization saturation than rare-earth permanent magnets (PMs), currently ferrite magnets represent the most widely used PMs, covering 80% of the PM market production [1,2]. Recently, a strong effort is being performed to improve the magnetic properties of ferrites with the scope of substituting partially rare-earth magnets. Most of the strategies involve the nanostructuration of the ferrites and/or the development of hybrid compounds [3]. A bottleneck for the production of these magnets is that standard sintering process requires high temperatures and oxidizing atmosphere that produces the destruction of the nanostructure and several chemical changes. Different novel strategies as out-of-equilibrium or cold sintering processes are mainly considered[2,4]. In our presentation we will show the production of dense ferrite-based magnets by high pressure multi-Anvil press at low temperatures. This press applies quasi-isotropic pressures in the range up to 20 GPa and temperatures up to 1200°C. We demonstrate that the consolidation of micrometric hexaferrite (SrFe12O19) powders is possible at temperatures below 1000°C, below the standard sintering temperatures. In addition, dense hybrid magnets were obtained composed of micrometric hexaferrites and soft high magnetization metal Fe or FeCo NPs applying pressures up to 6 GPa and low temperatures (250°C). A deep study, including structural, morphological and magnetic characterizations, has been performed to determine the influence of the temperature and pressure consolidation conditions in the properties of these novel magnets. Magnetic characterizations show that hybrid magnets exhibit larger magnetization than ferrites and single step hysteresis loops. Single Point Detection characterizations indicate that the anisotropy field of the hybrid magnets is similar to that of the ferrite magnets. These results suggest that the two moieties componing the high pressure consolidated magnets have similar properties than the original micro and nano powders, but they are magnetic coupled during the reversal process. High pressure consolidation appears as a promising technique to obtain nano-based metal-oxide hybrid magnets with promising hard properties.
Keywords: ferrite magnets, high pressure consolidation, low temperatures
Published in RUNG: 19.10.2023; Views: 634; Downloads: 5
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48.
AugerPrime surface detector electronics
A. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, original scientific article

Abstract: 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.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, AugerPrime detector upgrade, surface detector array, surface detector electronics
Published in RUNG: 18.10.2023; Views: 602; Downloads: 5
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49.
The Cherenkov Telescope Array. Science Goals and Current Status
Rene A. Ong, Christopher Eckner, Gašper Kukec Mezek, Samo Stanič, Serguei Vorobiov, Lili Yang, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, published scientific conference contribution (invited lecture)

Abstract: The Cherenkov Telescope Array (CTA) is the major ground-based gamma-ray observatory planned for the next decade and beyond. Consisting of two large atmospheric Cherenkov telescope arrays (one in the southern hemisphere and one in the northern hemisphere), CTA will have superior angular resolution, a much wider energy range, and approximately an order of magnitude improvement in sensitivity, as compared to existing instruments. The CTA science programme will be rich and diverse, covering cosmic particle acceleration, the astrophysics of extreme environments, and physics frontiers beyond the Standard Model. This paper outlines the science goals for CTA and covers the current status of the project.
Keywords: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array (CTA), cosmic particle acceleration, astrophysics of extreme environments, physics beyond the Standard Model
Published in RUNG: 11.10.2023; Views: 496; Downloads: 7
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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, published scientific conference contribution

Abstract: 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.
Keywords: ultra-high-energy (UHE) cosmic rays (CRs), Pierre Auger Observatory, UHE neutrinos, multi-messenger astrophysics
Published in RUNG: 11.10.2023; Views: 678; Downloads: 5
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