Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The State of the Circumstellar Medium Surrounding Gamma-Ray Burst
  Sources and its Effect on the Afterglow Appearance   We present a numerical investigation of the contribution of the presupernova
ejecta of Wolf-Rayet stars to the environment surrounding gamma-ray bursts
(GRBs), and describe how this external matter can affect the observable
afterglow characteristics. An implicit hydrodynamic calculation for massive
stellar evolution is used here to provide the inner boundary conditions for an
explicit hydrodynamical code to model the circumstellar gas dynamics. The
resulting properties of the circumstellar medium are then used to calculate the
deceleration of a relativistic, gas-dynamic jet and the corresponding afterglow
light curve produced as the shock wave propagates through the shocked-wind
medium. We find that variations in the stellar wind drive instabilities that
may produce radial filaments in the shocked-wind region. These comet-like tails
of clumps could give rise to strong temporal variations in the early afterglow
lightcurve. Afterglows may be expected to differ widely among themselves,
depending on the angular anisotropy of the jet and the properties of the
stellar progenitor; a wide diversity of behaviors may be the rule, rather than
the exception.

2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph