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 1 - 4 / 41 1.A search for Galactic transients disguised as gamma-ray burstsValentina La Parola, Cristiano Guidorzi, Aurora Clerici, 2015, original scientific articleAbstract: A significant fraction of cosmological gamma-ray bursts (GRBs) are characterised by a fast rise and exponential decay (FRED) temporal structure. This is not a distinctive feature of this class, since it is observed in many Galactic transients and is likely descriptive of a sudden release of energy followed by a diffusion process. Possible evidence has recently been reported by Tello et al. (2012) for a Galactic contamination in the sample of FRED GRBs discovered with Swift. We searched for possible Galactic intruders disguised as FRED GRBs in the Swift catalogue up to September 2014. We selected 181 FRED GRBs (2/3 with unknown redshift) and considered different subsamples. We tested the degree of isotropy through the dipole and the quadrupole moment distributions, both with reference to the Galaxy and in a coordinate-system-independent way, as well as with the two-point angular autocovariance function. In addition, we searched for possible indicators of a Galactic origin among the spectral and temporal properties of individual GRBs. We found marginal (~3 sigma) evidence for an excess of FREDs with unknown redshift towards the Galactic plane compared with what is expected for an isotropic distribution corrected for the non-uniform sky exposure. However, when we account for the observational bias against optical follow-up observations of low-Galactic latitude GRBs, the evidence for anisotropy decreases to ~2 sigma. In addition, we found no statistical evidence for different spectral or temporal properties from the bulk of cosmological GRBs. We found marginal evidence for the presence of a disguised Galactic population among Swift GRBs with unknown redshift. The estimated fraction is f=(19 +- 11)%, with an upper limit of 34% (90% confidence).Found in: ključnih besedahSummary of found: ...gamma-ray burst, statistical, Galactic transient...Keywords: gamma-ray burst, statistical, Galactic transientPublished: 03.02.2016; Views: 3404; Downloads: 0 Fulltext (173,64 KB) 2.GRB 160227A: NOT redshiftTanja Petrushevska, Dong Xu, 2016, final research reportFound in: ključnih besedahSummary of found: ...Gamma Ray Burst classification, GRB, Nordic Optic Telescope...Keywords: Gamma Ray Burst classification, GRB, Nordic Optic TelescopePublished: 24.01.2018; Views: 2246; Downloads: 0 Fulltext (49,11 KB) 3.Fermi -LAT Observations of LIGO / Virgo Event GW170817Gabrijela Zaharijas, 2018, original scientific articleFound in: ključnih besedahSummary of found: ... gamma-ray burst, gamma rays, gravitational waves...Keywords: gamma-ray burst, gamma rays, gravitational wavesPublished: 23.08.2018; Views: 2146; Downloads: 0 Fulltext (5,09 MB) 4.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 besedahSummary of found: ...this "inner engine" can operate in a gamma-ray burst (GRB) for thousands of years. By...Keywords: black hole physics, binaries, gamma-ray burst, neutron stars, supernovae, Astrophysics - High Energy Astrophysical PhenomenaPublished: 20.07.2020; Views: 1454; Downloads: 0 Fulltext (1,09 MB)
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