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Opis: Telescope Array (TA) and Auger experiments reported anisotropies in the arrival direction of ultrahigh-energy cosmic rays (UHECRs). In particular, Auger Collaboration reported a correlation between UHECR events and the flux model of assumed sources and suggested a contribution of starburst galaxies (SBGs) to the anisotropy of UHECRs. However, in their study, the effect of coherent deflections by the galactic magnetic field (GMF) is not taken into account. In this study, we investigated the effect of the GMF on the arrival directions of UHECRs using the cosmic ray propagation code CRPropa3. We used a backtracking technique which consists of propagating antiparticles to map the flux outside the galaxy to at the earth. We estimate the systematic effects caused by GMF in the reported likelihood analysis. We conduct likelihood analysis for mock UHECR datasets based on the flux pattern through the GMF model. We found systematic decrease of (f_ani, �) due to GMF. As prospects for the TAx4 experiment and joint analysis of Auger and TA collaborations, we develop the likelihood analysis method with the convolution of the rigidity spectrum.
Ključne besede: Telescope Array, TAx4, ultra-high energy, cosmic rays, anisotropy, galactic magnetic field, starburst galaxies
Objavljeno v RUNG: 29.09.2023; Ogledov: 621; Prenosov: 5
Celotno besedilo (1,97 MB)
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Opis: The Telescope Array (TA) is the largest cosmic ray observatory in the Northern Hemisphere. It is designed to measure the properties of cosmic rays over a wide range of energies. TA with it's low energy extension (TALE) observe cosmic-ray induced extensive air showers between 2 PeV and 100 EeV in hybrid mode using multiple instruments, including an array of scintillator detectors at the Earth's surface and telescopes to measure the fluorescence and Cerenkov light. The statistics at the highest energies is being enhanced with the ongoing construction of the TAx4 experiment which will quadruple the surface area of the detector. We review the present status of the experiments and most recent physics results on the cosmic ray anisotropy, chemical composition and energy spectrum. Notable highlights include a new feature in the energy spectrum at about 10^19.2 eV, and a new clustering of events in the direction of Perseus-Pisces supercluster above this energy. We also report on updated diffuse photon flux limits and new spectrum and composition results in the lower energy range from the TALE extension.
Ključne besede: Telescope Array, TALE, low energy extension, TAx4, indirect detection, hybrid detection, ground array, fluorescence detection, Cherenkov light, ultra-high energy, cosmic rays, energy spectrum, composition, anisotropy
Objavljeno v RUNG: 26.09.2023; Ogledov: 662; Prenosov: 5
Celotno besedilo (6,75 MB)
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Opis: Clusters of galaxies are the largest gravitationally-bound structures in the Universe. They are composed of galaxies and gas (approximately 15% of the total mass) mostly dark matter (DM, accounts up to 85% of the total mass). If the DM is composed of Weakly Interacting Massive Particles (WIMPs), galaxy clusters represent one of the best targets to search for gamma-ray signals induced by the decay of WIMPs, with masses around the TeV scale. Due to its sensitivity and energy range of operation (from 20 GeV to 300 TeV), the Cherenkov Telescope Array (CTA) Observatory has a unique opportunity to test WIMPs with masses close to the unitarity limit. This will complement the searches for DM from other gamma-ray observatories as well as direct and collider experiments. The CTA Observatory is planning to search for gamma-ray emission, either its origin may be cosmic-ray (CR) or DM related, in the Perseus galaxy cluster during the first years of operation. In this poster, we will present the software created to perform the analysis using the ctools software and the corresponding results.
Ključne besede: Cherenkov Telescope Array, CTA, dark matter, standard model, dwarf spheroidal galaxies
Objavljeno v RUNG: 26.09.2023; Ogledov: 616; Prenosov: 4
Celotno besedilo (1,33 MB)
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Opis: Blazars are active galactic nuclei (AGN) with a relativistic jet oriented toward the observer. This jet is composed of accelerated particles which can display emission over the entire electromagnetic spectrum. Spectral variability has been observed on short- and long-time scales in AGN, with a power spectral density (PSD) that can show a break at frequencies below the well-known red-noise process. This break frequency in the PSD has been observed in X-rays to scale with the accretion regime and the mass of the central black hole. It is expected that a break could also be seen in the very-high-energy gamma rays, but constraining the shape of the PSD in these wavelengths has not been possible with the current instruments. The Cherenkov Telescope Array (CTA) will be more sensitive by a factor of five to ten depending on energy than the current generation of imaging atmospheric Cherenkov telescopes, therefore it will be possible with CTA to reconstruct the PSD with a high accuracy, bringing new information about AGN variability. In this work, we focus on the AGN long-term monitoring program planned with CTA. The program is proposed to begin with early-start observing campaigns with CTA precursors. This would allow us to probe longer time scales on the AGN PSD.
Ključne besede: Cherenkov Telescope Array, CTA, dark matter, standard model, dwarf spheroidal galaxies
Objavljeno v RUNG: 26.09.2023; Ogledov: 685; Prenosov: 7
Celotno besedilo (3,48 MB)
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Opis: Dark matter (DM) is one of the major components in the Universe. However, at present its existence is still only inferred through indirect astronomical observations. DM particles can annihilate or decay, producing final-state Standard Model pairs that subsequently annihilate into high-energy �-rays. The dwarf spheroidal galaxies (dSphs) in the Milky Way DM halo have long been considered optimal targets to search for annihilating DM signatures in GeV-to-TeV �-ray spectra due to their high DM densities (hence high astrophysical factors), as well as the expected absence of intrinsic �-ray emission of astrophysical origin. For such targets, it is important to compute the amount of DM in their halos in a consistent way to optimize the �-ray data analysis. Such estimates directly affect the observability of DM signals in dSphs, as well as the DM constraints that can be derived in case of null detection. In this contribution, we present the results on the sensitivity of the Cherenkov Telescope Array (CTA) for DM annihilation and decay searches using planned observations of the Milky Way dSphs. We select the most promising targets among all presently known dwarf satellites, providing new determinations of their expected DM signal. This study shows an improvement of approximately an order of magnitude in sensitivity compared to current searches in similar targets. We also discuss the results in terms of cuspy and cored DM models, and investigate the sensitivity obtained by the combination of observations from different dSphs. Finally, we explore the optimal strategies for CTA observations of dSphs.
Ključne besede: Cherenkov Telescope Array, CTA, dark matter, standard model, dwarf spheroidal galaxies
Objavljeno v RUNG: 26.09.2023; Ogledov: 687; Prenosov: 4
Celotno besedilo (4,11 MB)
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