Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Jets in GRBs   In several GRBs afterglows, rapid temporal decay is observed which is
inconsistent with spherical (isotropic) blast-wave models. In particular, GRB
980519 had the most rapidly fading of the well-documented GRB afterglows, with
t^{-2.05\pm 0.04} in optical as well as in X-rays. We show that such temporal
decay is more consistent with the evolution of a jet after it slows down and
spreads laterally, for which t^{-p} decay is expected (where p is the index of
the electron energy distribution). Such a beaming model would relax the energy
requirements on some of the more extreme GRBs by a factor of several hundreds.
It is likely that a large fraction of the weak (or no) afterglow observations
are also due to the common occurrence of beaming in GRBs, and that their jets
have already transitioned to the spreading phase before the first afterglow
observations were made. With this interpretation, a universal value of p~2.5 is
consistent with all data.

33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an