49,009 research outputs found
On the afterglow from the receding jet of gamma-ray burst
According to popular progenitor models of gamma-ray bursts, twin jets should
be launched by the central engine, with a forward jet moving toward the
observer and a receding jet (or the counter jet) moving backwardly. However, in
calculating the afterglows, usually only the emission from the forward jet is
considered. Here we present a detailed numerical study on the afterglow from
the receding jet. Our calculation is based on a generic dynamical description,
and includes some delicate ingredients such as the effect of the equal arrival
time surface. It is found that the emission from the receding jet is generally
rather weak. In radio bands, it usually peaks at a time of d,
with the peak flux nearly 4 orders of magnitude lower than the peak flux of the
forward jet. Also, it usually manifests as a short plateau in the total
afterglow light curve, but not as an obvious rebrightening as once expected. In
optical bands, the contribution from the receding jet is even weaker, with the
peak flux being orders of magnitude lower than the peak flux of the
forward jet. We thus argue that the emission from the receding jet is very
difficult to detect. However, in some special cases, i.e., when the
circum-burst medium density is very high, or if the parameters of the receding
jet is quite different from those of the forward jet, the emission from the
receding jet can be significantly enhanced and may still emerge as a marked
rebrightening. We suggest that the search for receding jet emission should
mostly concentrate on nearby gamma-ray bursts, and the observation campaign
should last for at least several hundred days for each event.Comment: A few citations added, together with a few minor revisions, main
conclusions unchanged, accepted for publication in A&A, 7 figures, 10 Page
GRBs and fundamental physics
Gamma-ray bursts (GRBs) are short and intense flashes at the cosmological
distances, which are the most luminous explosions in the Universe. The high
luminosities of GRBs make them detectable out to the edge of the visible
universe. So, they are unique tools to probe the properties of high-redshift
universe: including the cosmic expansion and dark energy, star formation rate,
the reionization epoch and the metal evolution of the Universe. First, they can
be used to constrain the history of cosmic acceleration and the evolution of
dark energy in a redshift range hardly achievable by other cosmological probes.
Second, long GRBs are believed to be formed by collapse of massive stars. So
they can be used to derive the high-redshift star formation rate, which can not
be probed by current observations. Moreover, the use of GRBs as cosmological
tools could unveil the reionization history and metal evolution of the
Universe, the intergalactic medium (IGM) properties and the nature of first
stars in the early universe. But beyond that, the GRB high-energy photons can
be applied to constrain Lorentz invariance violation (LIV) and to test
Einstein's Equivalence Principle (EEP). In this paper, we review the progress
on the GRB cosmology and fundamental physics probed by GRBs.Comment: 38 pages, 18 figures, Review based on ISSI workshop "Gamma-Ray
Bursts: a Tool to Explore the Young Universe" (2015, Beijing, China),
accepted for publication in Space Science Review
Nonconical theory of flow past slender wing bodies with leading-edge separation
Nonconical theory of flow past slender wing bodies with leading edge separatio
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