24,595 research outputs found
Deviation of light curves of gamma-ray burst pulses from standard forms due to the curvature effect of spherical fireballs or uniform jets
As revealed previously, under the assumption that some pulses of gamma-ray
bursts are produced by shocks in spherical fireballs or uniform jets of large
opening angles, there exists a standard decay form of the profile of pulses
arising from very narrow or suddenly dimming local (or intrinsic) pulses due to
the relativistic curvature effect (the Doppler effect over the spherical shell
surface). Profiles of pulses arising from other local pulses were previously
found to possess a reverse S-feature deviation from the standard decay form. We
show in this paper that, in addition to the standard decay form shown in Qin et
al. (2004), there exists a marginal decay curve associated with a local
function pulse with a mono-color radiation. We employ the sample of
Kocevski et al. (2003) to check this prediction and find that the phenomenon of
the reverse S-feature is common, when compared with both the standard decay
form and the marginal decay curve. We accordingly propose to take the marginal
decay curve (whose function is simple) as a criteria to check if an observed
pulse could be taken as a candidate suffered from the curvature effect. We
introduce two quantities and to describe the mentioned deviations
within and beyond the position of the decay phase, respectively. The
values of and of pulses of the sample are calculated, and the
result suggests that for most of these pulses their corresponding local pulses
might contain a long decay time relative to the time scale of the curvature
effect.Comment: 24 pages, 7 figures, 1 table accepted for publication in MNRA
Large-time Behavior of Solutions to the Inflow Problem of Full Compressible Navier-Stokes Equations
Large-time behavior of solutions to the inflow problem of full compressible
Navier-Stokes equations is investigated on the half line .
The wave structure which contains four waves: the transonic(or degenerate)
boundary layer solution, 1-rarefaction wave, viscous 2-contact wave and
3-rarefaction wave to the inflow problem is described and the asymptotic
stability of the superposition of the above four wave patterns to the inflow
problem of full compressible Navier-Stokes equations is proven under some
smallness conditions. The proof is given by the elementary energy analysis
based on the underlying wave structure. The main points in the proof are the
degeneracies of the transonic boundary layer solution and the wave interactions
in the superposition wave.Comment: 27 page
Two types of softening detected in X-ray afterglows of Swift bursts: internal and external shock origins?
The softening process observed in the steep decay phase of early X-ray
afterglows of Swift bursts has remained a puzzle since its discovery. The
softening process can also be observed in the later phase of the bursts and its
cause has also been unknown. Recently, it was suggested that, influenced by the
curvature effect, emission from high latitudes would shift the Band function
spectrum from higher energy band to lower band, and this would give rise to the
observed softening process accompanied by a steep decay of the flux density.
The curvature effect scenario predicts that the terminating time of the
softening process would be correlated with the duration of the process. In this
paper, based on the data from the UNLV GRB group web-site, we found an obvious
correlation between the two quantities. In addition, we found that the
softening process can be divided into two classes: the early type softening
() and the late type softening ().
The two types of softening show different behaviors in the duration vs.
terminating time plot. In the relation between the variation rates of the flux
density and spectral index during the softening process, a discrepancy between
the two types of softening is also observed. According to their time scales and
the discrepancy between them, we propose that the two types are of different
origins: the early type is of internal shock origin and the late type is of
external shock origin. The early softening is referred to the steep decay just
following the prompt emission, whereas the late decay typically conceives the
transition from flat decay to late afterglow decay. We suspect that there might
be a great difference of the Lorentz factor in two classes which is responsible
for the observed discrepancy.Comment: 20 pages, 5 figures, 2 tables, Accepted for Publication to Journal of
Cosmology and Astroparticle Physics (JCAP
- …