2,256 research outputs found
Analyses of celestial pole offsets with VLBI, LLR, and optical observations
This work aims to explore the possibilities of determining the long-period
part of the precession-nutation of the Earth with techniques other than very
long baseline interferometry (VLBI). Lunar laser ranging (LLR) is chosen for
its relatively high accuracy and long period. Results of previous studies could
be updated using the latest data with generally higher quality, which would
also add ten years to the total time span. Historical optical data are also
analyzed for their rather long time-coverage to determine whether it is
possible to improve the current Earth precession-nutation model
Jet-cloud/star interaction as an interpretation of neutrino outburst from the blazar TXS 0506+056
Recently, a high-energy neutrino event IceCube-170922A in the spatial and
temporal coincidence with the flaring gamma-ray blazar TXS 0506+056 was
reported. A neutrino outburst between September 2014 and March 2015 was
discovered in the same direction by a further investigation of years of
IceCube data, while the blazar is in a quiescent state during the outburst with
a gamma-ray flux only about one-fifth of the neutrino flux. In this letter, we
propose the neutrino outburst originates from the interaction between a
relativistic jet and a dense gas cloud which may be formed via the tidally
disrupted envelope of a red giant being blown by the impact of the jet.
Gamma-ray photons and electron/positron pairs that are produced correspondingly
will induce electromagnetic cascades. Comptonization of the cascade emission
inside the cloud forms an X-ray photon field with Wien distribution. GeV flux
is suppressed due to the absorption by the Comptonized photon field and, as a
result, a hard spectrum above 10 GeV is formed. The gamma-ray spectrum
predicted in our model is consistent with the Fermi-LAT data of TXS 0506+056.Comment: 6 pages, 3 figure
Hadronic origin of prompt high-energy emission of gamma-ray bursts revisited: in the case of a limited maximum proton energy
The high-energy (> 100MeV) emission observed by Fermi-LAT during the prompt
phase of some luminous gamma-ray bursts (GRBs) could arise from the cascade
induced by interactions between accelerated protons and the radiation field of
GRBs. The photomeson process, which is usually suggested to operate in such a
hadronic explanation, requires a rather high proton energy (> 10^17eV) for an
efficient interaction. However, whether GRBs can accelerate protons to such a
high energy is far from guaranteed, although they have been suggested as the
candidate source for ultrahigh-energy cosmic rays. In this work, we revisit the
hadronic model for the prompt high-energy emission of GRBs with a smaller
maximum proton energy than the usually adopted value estimated from the Bohm
condition. In this case, the Bethe-Heitler pair production process becomes
comparably important or even dominates over the photomeson process. We show
that with a relatively low maximum proton energy with a Lorentz factor of 10^5
in the comoving frame, the cascade emission can still reproduce various types
of high-energy spectrum of GRBs. For most GRBs without high-energy emission
detected, the maximum proton energy could be even lower and relax the
constraints on the parameters of GRB jet resulting from the fact of
non-detection of GRB neutrinos by IceCube.Comment: 36 pages, 13 figures, accepted for publication in Ap
Domain wall brane in a reduced Born-Infeld- theory
The Born-Infeld theory is reduced from the Born-Infeld determinantal
gravity in Weitzenb\"ock spacetime. We investigate a braneworld scenario in
this theory and obtain an analytic domain wall solution by utilizing the
first-order formalism. The model is stable against the linear tensor
perturbation. It is shown that the massless graviton is localized on the brane,
but the continuous massive gravitons are non-localized and will generate a tiny
correction with the behavior of to the Newtonian potential.
The four-dimensional teleparallel gravity is recovered as an effective infrared
theory on the brane. As a physical application, we consider the
(quasi-)localization property of spin-1/2 Dirac fermion in this model.Comment: 9 pages, 2 figures, published versio
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