1. Astrophysical models to interpret the Pierre Auger Observatory dataJuan Manuel González, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The Pierre Auger Observatory has measured the spectrum of ultra-high-energy cosmic rays with unprecedented precision, as well as the distribution of the depths of the maximum of the shower development in the atmosphere, which provide a reliable estimator of the mass composition. The measurements above 10[sup]17.8 eV can be interpreted assuming two populations of uniformly distributed sources, one with a soft spectrum dominating the flux below few EeV, and another one with a very hard spectrum dominating above that energy. When considering the presence of intense extragalactic magnetic fields between our Galaxy and the closest sources and a high-energy population with low spatial density, a magnetic horizon appears, suppressing the cosmic ray's flux at low-energies, which could explain the very hard spectrum observed at Earth. The distribution of arrival directions, which at energies above 32 EeV shows indications of a correlation with a population of starburst galaxies or the radio galaxy Centaurus A (Cen A), are also important to constrain the sources. It is shown that adding a fractional contribution from these sources of about 20% on top of an homogeneous background leads to an improvement of the model likelihood.
Ključne besede: ultra-high-energy cosmic rays, UHECR energy spectrum, UHECR mass composition, UHECR anisotropies, UHECR propagation, UHECR data interpretation, extragalactic magnetic fields, starburst galaxies, Centaurus A, Pierre Auger Observatory
Objavljeno v RUNG: 24.03.2025; Ogledov: 293; Prenosov: 7
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2. The flux of UHECRs along the supergalactic plane using Pierre Auger Observatory dataArmando Di Matteo, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: We use the latest dataset from the surface detector array of the Pierre Auger Observatory, with events detected up to 31 December 2022 and a total exposure of 135,000 km² sr yr, to search for possible excesses in the flux of the most energetic cosmic rays on an intermediate angular scale (top-hat radius 27°, based on our previous results) from regions along the supergalactic plane. We find no indication for any such excesses other than the previously reported one in the Centaurus region, with a post-trial significance around 3σ, which we find extends down to lower energies than previously studied. In particular, the field of view of our dataset overlaps both regions in the northern celestial hemisphere from which excesses of events have been reported by the Telescope Array. With our integral exposures over these regions comparable to the Telescope Array ones, we find no indication of any flux excesses from there, with event counts in good agreement with the expectations from an isotropic distribution.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, anisotropies, Centaurus region
Objavljeno v RUNG: 24.03.2025; Ogledov: 307; Prenosov: 5
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3. Very high-energy gamma-ray signature of ultrahigh-energy cosmic-ray acceleration in Centaurus AJagdish Joshi, Marlui Miranda, Lili Yang, Soebur Razzaque, 2017, objavljeni povzetek znanstvenega prispevka na konferenci Opis: The association of at least a dozen ultrahigh-energy cosmic-ray (UHECR) events with energy 54 EeV or higher detected by the Pierre Auger Observatory from the direction of Centaurus-A, the nearest radio galaxy, supports the scenario of UHECR acceleration in the jets of radio galaxies. Multiwavelength observations of Centaurus-A suggest that the inner jet is likely the site for particle acceleration, which emits in X-ray to very high-energy (VHE) gamma-ray. We model broadband spectral energy distribution with emission from shock-accelerated electrons and protons in a combined synchrotron-self-Compton and photo-hadronic scenario. The UHECR flux from Centaurus-A, required to explain Pierre Auger data, successfully explains observed VHE gamma rays as photo-hadronic emission.
Ključne besede: Centaurus A, gamma ray, cosmic rays
Objavljeno v RUNG: 17.01.2018; Ogledov: 5446; Prenosov: 0
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