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21.
Telescope Array Hot/Coldspot Study – Intermediate Scale Anisotropy
J. P. Lundquist, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: Indications of energy dependent intermediate scale anisotropy has been found in the arrival directions of ultra high energy cosmic rays with energies above 20 EeV in the northern hemisphere, using 7 years of TA surface detector data. The previously reported “hotspot‘” excess for E>57 EeV is found to correspond to a deficit, or “coldspot ”, of events for energies 2057 EeV has a Li Ma statistical significance of 4.62σ, and the deficit for energies 20Najdeno v: ključnih besedah
Ključne besede: cosmic rays, energy spectrum, anisotropy, magnetic deflection
Objavljeno: 28.04.2020; Ogledov: 617; Prenosov: 0
.pdf Polno besedilo (2,25 MB)

22.
Energy-position correlation anisotropy of ultra-high energy cosmic rays with Telescope Array Data
J. P. Lundquist, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: Indication of an energy dependent intermediate-scale anisotropy has been found in the arrival directions of ultra-high energy cosmic rays with energies above 20 EeV in the northern hemisphere, using 7 years of TA surface detector data. The previously reported “hotspot“ excess for E>57 EeV is found to correspond to a deficit, or “coldspot“, of events for energies 2057 EeV has a Li-Ma statistical significance of 4.62σ, and the deficit for energies 20Najdeno v: ključnih besedah
Ključne besede: UHECR, energy spectrum, anisotropy, magnetic deflection
Objavljeno: 29.04.2020; Ogledov: 628; Prenosov: 0
.pdf Polno besedilo (1,84 MB)

23.
Search for anisotropy of ultrahigh energy cosmic rays with the Telescope Array experiment
J. P. Lundquist, T. Abu-Zayyad, 2012, izvirni znanstveni članek

Opis: We study the anisotropy of Ultra-High Energy Cosmic Ray (UHECR) events collected by the Telescope Array (TA) detector in the first 40 months of operation. Following earlier studies, we examine event sets with energy thresholds of 10 EeV, 40 EeV, and 57 EeV. We find that the distributions of the events in right ascension and declination are compatible with an isotropic distribution in all three sets. We then compare with previously reported clustering of the UHECR events at small angular scales. No significant clustering is found in the TA data. We then check the events with E > 57 EeV for correlations with nearby active galactic nuclei. No significant correlation is found. Finally, we examine all three sets for correlations with the large-scale structure (LSS) of the universe. We find that the two higher-energy sets are compatible with both an isotropic distribution and the hypothesis that UHECR sources follow the matter distribution of the universe (the LSS hypothesis), while the event set with E > 10 EeV is compatible with isotropy and is not compatible with the LSS hypothesis at 95% CL unless large deflection angles are also assumed. We show that accounting for UHECR deflections in a realistic model of the Galactic magnetic field can make this set compatible with the LSS hypothesis.
Najdeno v: ključnih besedah
Ključne besede: acceleration of particles, astroparticle physics, cosmic rays, magnetic fields, methods: statistical, relativistic processes
Objavljeno: 19.05.2020; Ogledov: 638; Prenosov: 0
.pdf Polno besedilo (1,04 MB)

24.
Evidence for a Supergalactic Structure of Magnetic Deflection Multiplets of Ultra-High Energy Cosmic Rays
J. P. Lundquist, R. Abbasi, 2020, izvirni znanstveni članek

Opis: Evidence for a large-scale supergalactic cosmic ray multiplet (arrival directions correlated with energy) structure is reported for ultra-high energy cosmic ray (UHECR) energies above 10^19 eV using seven years of data from the Telescope Array (TA) surface detector and updated to 10 years. Previous energy-position correlation studies have made assumptions regarding magnetic field shapes and strength, and UHECR composition. Here the assumption tested is that, since the supergalactic plane is a fit to the average matter density of the local Large Scale Structure (LSS), UHECR sources and intervening extragalactic magnetic fields are correlated with this plane. This supergalactic deflection hypothesis is tested by the entire field-of-view (FOV) behavior of the strength of intermediate-scale energy-angle correlations. These multiplets are measured in spherical cap section bins (wedges) of the FOV to account for coherent and random magnetic fields. The structure found is consistent with supergalactic deflection, the previously published energy spectrum anisotropy results of TA (the hotspot and coldspot), and toy-model simulations of a supergalactic magnetic sheet. The seven year data post-trial significance of this supergalactic structure of multiplets appearing by chance, on an isotropic sky, is found by Monte Carlo simulation to be 4.19σ. The ten years of data post-trial significance is 4.09σ. Furthermore, the starburst galaxy M82 is shown to be a possible source of the TA Hotspot, and an estimate of the supergalactic magnetic field using UHECR measurements is presented.
Najdeno v: ključnih besedah
Ključne besede: astroparticle physics, cosmic rays, UHECR, supergalactic plane, multiplets, magnetic deflection, large-scale structure of universe
Objavljeno: 19.05.2020; Ogledov: 561; Prenosov: 0
.pdf Polno besedilo (4,40 MB)

25.
Element-resolved study on the influence of a magnetic dopant on the exchange interaction in FePt on ultrashort timescales
Jurij Urbančič, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: In this study, we investigate the optically induced ultrafast demagnetization dynamics of a FePt alloy doped with Mn atoms on the characteristic timescale of the exchange interaction of a few femtoseconds. We use high harmonic generation with photon energies in the XUV to gain elemental resolution in a femtosecond magneto-optical Kerr-effect experiment [1] in transversal geometry. Following up on earlier experiments, which showed the importance of the exchange interaction in the demagnetization process in alloys [2,3], we see clear differences in the dynamical responses of the three elements Fe, Pt, and Mn. Our results suggest, that the exchange coupling between the magnetic moments of the FePt alloy and the Mn dopant changes on ultrashort timescales.
Najdeno v: ključnih besedah
Ključne besede: FePt, High Harmonic Generation, Laser, Magnetic Materials
Objavljeno: 22.05.2020; Ogledov: 719; Prenosov: 0

26.
Sensitivity of the Cherenkov Telescope Array for probing cosmology and fundamental physics with gamma-ray propagation
Serguei Vorobiov, Samo Stanič, Christopher Eckner, R. Adam, A. Acharyya, F. Acero, H. Abe, H. Abdalla, Gabrijela Zaharijas, Marko Zavrtanik, Danilo Zavrtanik, Miha Živec, 2021, izvirni znanstveni članek

Opis: The Cherenkov Telescope Array (CTA), the new-generation ground-based observatory for γ astronomy, provides unique capabilities to address significant open questions in astrophysics, cosmology, and fundamental physics. We study some of the salient areas of γ cosmology that can be explored as part of the Key Science Projects of CTA, through simulated observations of active galactic nuclei (AGN) and of their relativistic jets. Observations of AGN with CTA will enable a measurement of γ absorption on the extragalactic background light with a statistical uncertainty below 15% up to a redshift z=2 and to constrain or detect γ halos up to intergalactic-magnetic-field strengths of at least 0.3 pG . Extragalactic observations with CTA also show promising potential to probe physics beyond the Standard Model. The best limits on Lorentz invariance violation from γ astronomy will be improved by a factor of at least two to three. CTA will also probe the parameter space in which axion-like particles could constitute a significant fraction, if not all, of dark matter. We conclude on the synergies between CTA and other upcoming facilities that will foster the growth of γ cosmology.
Najdeno v: ključnih besedah
Ključne besede: Cherenkov Telescope Array, active galactic nuclei, gamma-ray experiments, axions, extragalactic magnetic fields
Objavljeno: 02.03.2021; Ogledov: 160; Prenosov: 5
URL Polno besedilo (0,00 KB)
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Evidence for a supergalactic structure of magnetic deflection multiplets of ultra-high-energy cosmic rays
R. U. Abbasi, T. Abu-Zayyad, Mitsuhiro Abe, M. Allen, R. Azuma, E. Barcikowski, J. W. Belz, D. R. Bergman, S. A. Blake, Jon Paul Lundquist, 2020, izvirni znanstveni članek

Opis: Evidence for a large-scale supergalactic cosmic-ray multiplet (arrival directions correlated with energy) structure is reported for ultra-high-energy cosmic-ray (UHECR) energies above 1019 eV using 7 years of data from the Telescope Array (TA) surface detector and updated to 10 years. Previous energy–position correlation studies have made assumptions regarding magnetic field shapes and strength, and UHECR composition. Here the assumption tested is that, because the supergalactic plane is a fit to the average matter density of the local large-scale structure, UHECR sources and intervening extragalactic magnetic fields are correlated with this plane. This supergalactic deflection hypothesis is tested by the entire field-of-view (FOV) behavior of the strength of intermediate-scale energy–angle correlations. These multiplets are measured in spherical cap section bins (wedges) of the FOV to account for coherent and random magnetic fields. The structure found is consistent with supergalactic deflection, the previously published energy spectrum anisotropy results of the TA (the Hotspot and Coldspot), and toy-model simulations of a supergalactic magnetic sheet. The seven year data posttrial significance of this supergalactic structure of multiplets appearing by chance, on an isotropic sky, is found by Monte Carlo simulation to be 4.2σ. The 10 years of data posttrial significance is 4.1σ. Furthermore, the starburst galaxy M82 is shown to be a possible source of the TA Hotspot, and an estimate of the supergalactic magnetic field using UHECR measurements is presented.
Najdeno v: ključnih besedah
Ključne besede: extragalactic magnetic fields, ultra-high-energy cosmic radiation, cosmic rays, high energy astrophysics, astrophysical magnetism, cosmic ray astronomy, cosmic ray sources
Objavljeno: 05.02.2021; Ogledov: 256; Prenosov: 9
URL Polno besedilo (0,00 KB)
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30.
Observational evidence in favor of scale-free evolution of sunspot groups
Alexander Shapoval, Jean-Louis Le Mouël, M. Shnirman, Vincent Courtillot, 2018, izvirni znanstveni članek

Najdeno v: ključnih besedah
Ključne besede: sunspots, sun, magnetic fields, data analysis
Objavljeno: 23.03.2021; Ogledov: 173; Prenosov: 5
.pdf Polno besedilo (451,74 KB)
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