6,464 research outputs found
A Two-Component Explosion Model for the Giant Flare and Radio Afterglow from SGR1806-20
The brightest giant flare from the soft -ray repeater (SGR) 1806-20
was detected on 2004 December 27. The isotropic-equivalent energy release of
this burst is at least one order of magnitude more energetic than those of the
two other SGR giant flares. Starting from about one week after the burst, a
very bright ( mJy), fading radio afterglow was detected. Follow-up
observations revealed the multi-frequency light curves of the afterglow and the
temporal evolution of the source size. Here we show that these observations can
be understood in a two-component explosion model. In this model, one component
is a relativistic collimated outflow responsible for the initial giant flare
and the early afterglow, and another component is a subrelativistic wider
outflow responsible for the late afterglow. We also discuss triggering
mechanisms of these two components within the framework of the magnetar model.Comment: 7 pages including 3 figures, emulateapj5.sty, accepted for
publication in ApJ Letter
Electrical conductance at initial stage in epitaxial growth of Pb on modified Si(111) surface
The electrical conductance and RHEED intensities as a function of the
coverage have been measured during Pb depositions at 105 K on Si(111)-(6x6)Au
with up to 4.2 ML of annealed Pb. The experiments show the strong influence of
used substrates on the behavior of the conductance during the epitaxy of Pb
atoms, especially for very initial stage of growth. Oscillations of the
conductance during the layer-by-layer growth are correlated with RHEED
intensity oscillations. The analysis of the conductance behavior is made
according to the theory described by Trivedi and Aschcroft (Phys.Rev.B 38,12298
(1988)).Comment: 5 pages, 3 figures. Surf. Sci. - accepte
The preliminary lattice QCD calculation of meson decay width
We present a direct lattice QCD calculation of the meson decay width
with the s-wave scattering phase shift for the isospin pion-kaon () system. We employ a special finite size formula, which is the extension of
the Rummukainen-Gottlieb formula for the system in the moving frame, to
calculate the scattering phase, which indicates a resonance around
meson mass. Through the effective range formula, we extract the effective
coupling constant GeV and
decay width MeV. Our simulations are done with the MILC
gauge configurations with flavors of the "Asqtad" improved staggered
dynamical sea quarks on a lattice at and lattice spacing fm.Comment: To make it concise. arXiv admin note: text overlap with
arXiv:1110.1422, but much of v1 text overlap with articles by same and other
authors remove
Jet Precession Driven by Neutrino-Cooled Disc for Gamma-Ray Bursts
A model of jet precession driven by a neutrino-cooled disc around a spinning
black hole is present in order to explain the temporal structure and spectral
evolution of gamma-ray bursts (GRBs). The differential rotation of the outer
part of a neutrino dominated accretion disc may result in precession of the
inner part of the disc and the central black hole, hence drives a precessed jet
via neutrino annihilation around the inner part of the disc. Both analytic and
numeric results for our model are present. Our calculations show that a black
hole-accretion disk system with black hole mass ,
accretion rate , spin parameter
and viscosity parameter may drive a precessed jet with period P=1
s and luminosity erg s, corresponding to the scenario for
long GRBs. A precessed jet with s and erg s may be
powered by a system with , , , and , possibly being responsible for the
short GRBs. Both the temporal and spectral evolution in GRB pulse may explained
with our model. GRB central engines likely power a precessed jet driven by a
neutrino-cooled disc. The global GRB lightcurves thus could be modulated by the
jet precession during the accretion timescale of the GRB central engine. Both
the temporal and spectral evolution in GRB pulse may be due to an viewing
effect due to the jet precession.Comment: 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
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