Repository of University of Nova Gorica

Search the repository
A+ | A- | Help | SLO | ENG

Query: search in
search in
search in
search in
* old and bologna study programme

Options:
  Reset


61 - 70 / 129
First pagePrevious page3456789101112Next pageLast page
61.
62.
On the GeV Emission of the Type I BdHN GRB 130427A
Remo Ruffini, Rahim Moradi, Jorge Armando Rueda, Carlo Luciano Bianco, Christian Cherubini, Simonetta Filippi, Yen-Chen Chen, Mile Karlica, Narek Sahakyan, Yu Wang, She Sheng Xue, Laura Beccera, 2019, original scientific article

Abstract: 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.
Keywords: black hole physics, binaries, gamma-ray burst, neutron stars, supernovae, Astrophysics - High Energy Astrophysical Phenomena
Published in RUNG: 20.07.2020; Views: 2761; Downloads: 0
This document has many files! More...

63.
Fermi Large Area Telescope fourth source catalog
S. Abdollahi, Fabio Acero, M. Ajello, W. B. Atwood, M. Axelsson, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, Gabrijela Zaharijas, 2020, original scientific article

Keywords: astronomy, gamma rays, sky surveys
Published in RUNG: 22.05.2020; Views: 2784; Downloads: 200
URL Link to full text
This document has many files! More...

64.
TeV dark matter search at the Galactic center with the CTA
Gabrijela Zaharijas, unpublished invited conference lecture

Keywords: gamma rays, dark matter, Cherenkov Telescope Array
Published in RUNG: 16.05.2020; Views: 2548; Downloads: 0
This document has many files! More...

65.
The bursts of high energy events observed by the telescope array surface detector
R.U. Abbasi, Jon Paul Lundquist, 2017, original scientific article

Abstract: 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.
Keywords: High energy radiation, Lightning, Terrestrial gamma-ray flash
Published in RUNG: 30.04.2020; Views: 2531; Downloads: 0
This document has many files! More...

66.
Gamma Ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders
R.U. Abbasi, Jon Paul Lundquist, 2018, original scientific article

Abstract: 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.
Keywords: gamma rays, lightning, gamma ray bursts, surface detector
Published in RUNG: 30.04.2020; Views: 3004; Downloads: 0
This document has many files! More...

67.
Search for point sources of ultra-high-energy photons with the Telescope Array surface detector
R.U. Abbasi, Jon Paul Lundquist, 2020, original scientific article

Abstract: 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.
Keywords: methods: data analysis, cosmic rays, gamma-rays: general
Published in RUNG: 29.04.2020; Views: 2559; Downloads: 0
This document has many files! More...

68.
Search forγ-ray emission from dark matter particle interactions from theAndromeda and Triangulum galaxies with the Fermi Large Area Telescope
Gabrijela Zaharijas, 2019, original scientific article

Keywords: gamma rays, dark matter
Published in RUNG: 20.02.2020; Views: 2475; Downloads: 0
This document has many files! More...

69.
FermiandSwiftObservations of GRB 190114C: Tracing the Evolution of High-energyEmission from Prompt to Afterglow
Gabrijela Zaharijas, 2020, original scientific article

Keywords: gamma-ray bursts
Published in RUNG: 20.02.2020; Views: 2503; Downloads: 88
.pdf Full text (1,71 MB)

70.
Search done in 0.06 sec.
Back to top