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 61 - 70 / 7512345678 61.FermiandSwiftObservations of GRB 190114C: Tracing the Evolution of High-energyEmission from Prompt to AfterglowGabrijela Zaharijas, 2020, original scientific articleFound in: ključnih besedahKeywords: gamma-ray burstsPublished: 20.02.2020; Views: 665; Downloads: 35 Fulltext (1,71 MB) 62.Search forγ-ray emission from dark matter particle interactions from theAndromeda and Triangulum galaxies with the Fermi Large Area TelescopeGabrijela Zaharijas, 2019, original scientific articleFound in: ključnih besedahKeywords: gamma rays, dark matterPublished: 20.02.2020; Views: 664; Downloads: 0 Fulltext (11,40 MB) 63.Search for point sources of ultra-high-energy photons with the Telescope Array surface detectorJ. P. Lundquist, R.U. Abbasi, 2020, original scientific articleAbstract: The surface detector (SD) of the Telescope Array (TA) experiment allows us to detect indirectly photons with energies of the order of 10^18 eV and higher, and to separate photons from the cosmic ray background. In this paper, we present the results of a blind search for point sources of ultra-high-energy (UHE) photons in the Northern sky using the TA SD data. The photon-induced extensive air showers are separated from the hadron-induced extensive air shower background by means of a multivariate classifier based upon 16 parameters that characterize the air shower events. No significant evidence for the photon point sources is found. The upper limits are set on the flux of photons from each particular direction in the sky within the TA field of view, according to the experiment’s angular resolution for photons. The average 95 per cent confidence level upper-limits for the point-source flux of photons with energies greater than 10^18, 10^18.5, 10^19, 10^19.5 and 10^20 eV are 0.094, 0.029, 0.010, 0.0073 and 0.0058 km−2yr−1, respectively. For energies higher than 10^18.5 eV, the photon point-source limits are set for the first time. Numerical results for each given direction in each energy range are provided as a supplement to this paper.Found in: ključnih besedahSummary of found: ...methods: data analysis, cosmic rays, gamma-rays: general...Keywords: methods: data analysis, cosmic rays, gamma-rays: generalPublished: 29.04.2020; Views: 663; Downloads: 0 Fulltext (1,05 MB) 64.Gamma Ray Showers Observed at Ground Level in Coincidence With Downward Lightning LeadersJ. P. Lundquist, R.U. Abbasi, 2018, original scientific articleAbstract: Bursts of gamma ray showers have been observed in coincidence with downward propagating negative leaders in lightning flashes by the Telescope Array Surface Detector (TASD). The TASD is a 700‐km^2 cosmic ray observatory located in southwestern Utah, USA. In data collected between 2014 and 2016, correlated observations showing the structure and temporal development of three shower‐producing flashes were obtained with a 3‐D lightning mapping array, and electric field change measurements were obtained for an additional seven flashes, in both cases colocated with the TASD. National Lightning Detection Network information was also used throughout. The showers arrived in a sequence of 2–5 short‐duration (≤10 μs) bursts over time intervals of several hundred microseconds and originated at an altitude of ≃3–5 km above ground level during the first 1–2 ms of downward negative leader breakdown at the beginning of cloud‐to‐ground lightning flashes. The shower footprints, associated waveforms and the effect of atmospheric propagation indicate that the showers consist primarily of downward‐beamed gamma radiation. This has been supported by GEANT simulation studies, which indicate primary source fluxes of ≃10^12–10^14 photons for 16° half‐angle beams. We conclude that the showers are terrestrial gamma ray flashes, similar to those observed by satellites, but that the ground‐based observations are more representative of the temporal source activity and are also more sensitive than satellite observations, which detect only the most powerful terrestrial gamma ray flashes.Found in: ključnih besedahKeywords: gamma rays, lightning, gamma ray bursts, surface detectorPublished: 30.04.2020; Views: 797; Downloads: 0 Fulltext (1,14 MB) 65.The bursts of high energy events observed by the telescope array surface detectorJ. P. Lundquist, R.U. Abbasi, 2017, original scientific articleAbstract: The Telescope Array (TA) experiment is designed to detect air showers induced by ultra high energy cosmic rays. The TA ground Surface particle Detector (TASD) observed several short-time bursts of air shower like events. These bursts are not likely due to chance coincidence between single shower events. The expectation of chance coincidence is less than 10^-4 for five-year's observation. We checked the correlation between these bursts of events and lightning data, and found evidence for correlations in timing and position. Some features of the burst events are similar to those of a normal cosmic ray air shower, and some are not. On this paper, we report the observed bursts of air shower like events and their correlation with lightning.Found in: ključnih besedahKeywords: High energy radiation, Lightning, Terrestrial gamma-ray flashPublished: 30.04.2020; Views: 725; Downloads: 0 Fulltext (1,70 MB) 66.TeV dark matter search at the Galactic center with the CTAGabrijela Zaharijas, unpublished invited conference lectureFound in: ključnih besedahKeywords: gamma rays, dark matter, Cherenkov Telescope ArrayPublished: 16.05.2020; Views: 582; Downloads: 0 Fulltext (107,91 KB)This document has many files! More... 67.Fermi Large Area Telescope fourth source catalogS. Abdollahi, F. Acero, M. Ajello, W. B. Atwood, M. Axelsson, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, Gabrijela Zaharijas, 2020, original scientific articleFound in: ključnih besedahKeywords: astronomy, gamma rays, sky surveysPublished: 22.05.2020; Views: 602; Downloads: 26 Fulltext (2,55 MB)This document has many files! More... 68.Sensitivity of the Cherenkov Telescope Array for probing cosmology and fundamental physics with gamma-ray propagationSerguei Vorobiov, Samo Stanič, Christopher Eckner, R. Adam, A. Acharyya, F. Acero, H. Abe, H. Abdalla, Gabrijela Zaharijas, Marko Zavrtanik, Danilo Zavrtanik, Miha Živec, 2021, original scientific articleAbstract: 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.Found in: ključnih besedahKeywords: Cherenkov Telescope Array, active galactic nuclei, gamma-ray experiments, axions, extragalactic magnetic fieldsPublished: 02.03.2021; Views: 161; Downloads: 5 Fulltext (0,00 KB)This document has many files! More... 69.On the GeV Emission of the Type I BdHN GRB 130427ALaura Beccera, She Sheng Xue, Yu Wang, Narek Sahakyan, Mile Karlica, Yen-Chen Chen, Simonetta Filippi, Christian Cherubini, Carlo Luciano Bianco, Jorge Armando Rueda, Rahim Moradi, Remo Ruffini, 2019, original scientific articleAbstract: We propose that the inner engine of a type I binary-driven hypernova (BdHN) is composed of Kerr black hole (BH) in a non-stationary state, embedded in a uniform magnetic field B_0 aligned with the BH rotation axis and surrounded by an ionized plasma of extremely low density of 10^−14 g cm−3. Using GRB 130427A as a prototype, we show that this inner engine acts in a sequence of elementary impulses. Electrons accelerate to ultrarelativistic energy near the BH horizon, propagating along the polar axis, θ = 0, where they can reach energies of ~10^18 eV, partially contributing to ultrahigh-energy cosmic rays. When propagating with $\theta \ne 0$ through the magnetic field B_0, they produce GeV and TeV radiation through synchroton emission. The mass of BH, M = 2.31M ⊙, its spin, α = 0.47, and the value of magnetic field B_0 = 3.48 × 10^10 G, are determined self consistently to fulfill the energetic and the transparency requirement. The repetition time of each elementary impulse of energy ${ \mathcal E }\sim {10}^{37}$ erg is ~10^−14 s at the beginning of the process, then slowly increases with time evolution. In principle, this "inner engine" can operate in a gamma-ray burst (GRB) for thousands of years. By scaling the BH mass and the magnetic field, the same inner engine can describe active galactic nuclei.Found in: ključnih besedahKeywords: black hole physics, binaries, gamma-ray burst, neutron stars, supernovae, Astrophysics - High Energy Astrophysical PhenomenaPublished: 20.07.2020; Views: 514; Downloads: 0 Fulltext (1,09 MB) 70.Constraining dark matter particle properties with Fermi-LAT and the Cherenkov Telescope ArrayChristopher Eckner, 2020, doctoral dissertationFound in: ključnih besedahKeywords: dark matter, astroparticle physics, high-energy gamma-ray astronomy, cosmic rays, Imaging Atmospheric Cherenkov Telescope, Cherenkov Telescope Array, Fermi Large Area TelescopePublished: 29.09.2020; Views: 629; Downloads: 26 Fulltext (68,77 MB)
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