8,005 research outputs found
Relation between phase and dwell times for quantum tunneling of a relativistically propagating particle
The general and explicit relation between the phase time and the dwell time
for quantum tunneling of a relativistically propagating particle is
investigated and quantified. In analogy with previously obtained
non-relativistic results, it is shown that the group delay can be described in
terms of the dwell time and a self-interference delay. Lessons concerning the
phenomenology of the relativistic tunneling are drawn
On the average Gamma-Ray Burst X-ray flaring activity
Gamma-ray burst X-ray flares are believed to mark the late time activity of
the central engine. We compute the temporal evolution of the average flare
luminosity in the common rest frame energy band of 44 GRBs taken from
the large \emph{Swift} 5-years data base. Our work highlights the importance of
a proper consideration of the threshold of detection of flares against the
contemporaneous continuous X-ray emission. In the time interval ; this implies
that the flare isotropic energy scaling is . The decay of the continuum underlying the flare emission closely
tracks the average flare luminosity evolution, with a typical flare to
steep-decay luminosity ratio which is : this
suggests that flares and continuum emission are deeply related to one another.
We infer on the progenitor properties considering different models. According
to the hyper-accreting black hole scenario, the average flare luminosity
scaling can be obtained in the case of rapid accretion () or
when the last \sim 0.5 M_{\sun} of the original 14 M_{\sun} progenitor star
are accreted. Alternatively, the steep behaviour could be
triggered by a rapid outward expansion of an accretion shock in the material
feeding a convective disk. If instead we assume the engine to be a rapidly
spinning magnetar, then its rotational energy can be extracted to power a jet
whose luminosity is likely to be between the monopole () and
dipole () cases. In both scenarios we suggest the variability,
which is the main signature of the flaring activity, to be established as a
consequence of different kinds of instabilities.Comment: MNRAS accepte
Conditional entropy of glueball states
The conditional entropy of glueball states is calculated using a holographic
description. Glueball states are represented by a supergravity dual picture,
consisting of a 5-dimensional graviton-dilaton action of a dynamical
holographic AdS/QCD model. The conditional entropy is studied as a function of
the glueball spin and of the mass, providing information about the stability of
the glueball states.Comment: 6 pages, 4 figure
The X-ray light curve of Gamma-ray bursts: clues to the central engine
We present the analysis of a large sample of gamma-ray burst (GRB) X-ray
light curves in the rest frame to characterise their intrinsic properties in
the context of different theoretical scenarios. We determine the morphology,
time scales, and energetics of 64 long GRBs observed by \emph{Swift}/XRT
\emph{without} flaring activity. We furthermore provide a one-to-one comparison
to the properties of GRBs \emph{with} X-ray flares. We find that the steep
decay morphology and its connection with X-ray flares favour a scenario in
which a central engine origin. We show that this scenario can also account for
the shallow decay phase, provided that the GRB progenitor star has a
self-similar structure with a constant envelope-to-core mass ratio . However, difficulties arise for very long duration
( s) shallow phases. Alternatively, a spinning-down magnetar
whose emitted power refreshes the forward shock can quantitatively account for
the shallow decay properties. In particular we demonstrate that this model can
account for the plateau luminosity vs. end time anticorrelation.Comment: 12 pages, 8 figures, accepted for publication in A&
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