170 research outputs found
Early Afterglows of Gamma-Ray Bursts in a Stratified Medium with a Power-Law Density Distribution
A long-duration gamma-ray burst (GRB) has been widely thought to arise from
the collapse of a massive star, and it has been suggested that its ambient
medium is a homogenous interstellar medium (ISM) or a stellar wind. There are
two shocks when an ultra-relativistic fireball that has been ejected during the
prompt gamma-ray emission phase sweeps up the circumburst medium: a reverse
shock that propagates into the fireball, and a forward shock that propagates
into the ambient medium. In this paper, we investigate the temporal evolution
of the dynamics and emission of these two shocks in an environment with a
general density distribution of (where is the radius) by
considering thick-shell and thin-shell cases. A GRB afterglow with one smooth
onset peak at early times is understood to result from such external shocks.
Thus, we can determine the medium density distribution by fitting the onset
peak appearing in the light curve of an early optical afterglow. We apply our
model to 19 GRBs, and find that their values are in the range of 0.4 - 1.4,
with a typical value of , implying that this environment is neither a
homogenous interstellar medium with nor a typical stellar wind with
. This shows that the progenitors of these GRBs might have undergone a new
mass-loss evolution.Comment: 32 pages, 5 figures, 1 table, published in Ap
Higher-order properties and Bell-inequality violation for the three-mode enhanced squeezed state
By extending the usual two-mode squeezing operator to the three-mode squeezing operator , we
obtain the corresponding three-mode squeezed coherent state. The state's
higher-order properties, such as higher-order squeezing and higher-order
sub-Possonian photon statistics, are investigated. It is found that the new
squeezed state not only can be squeezed to all even orders but also exhibits
squeezing enhancement comparing with the usual cases. In addition, we examine
the violation of Bell-inequality for the three-mode squeezed states by using
the formalism of Wigner representation
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