Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: What we learn from the afterglow of GRB 021211   The behaviour of the afterglow (AG) of gamma-ray bursts (GRBs) directly
provides, in the cannonball (CB) model, information about the environment of
their progenitor stars. The well observed early temporal decline of the AG of
GRB 021211 is precisely the one predicted in the presence of a progenitor's
``wind'' which resulted in a density profile $\propto 1/r^2$ around the star.
The subsequent fast fading --which makes this GRB ``quasi-dark''-- is the one
anticipated if, further away, the interstellar density is roughly constant and
relatively high. The CB-model fit to the AG clearly shows the presence of an
associated supernova akin to SN1998bw, and allows even for the determination of
the broad-band spectrum of the host galaxy. GRB 990123 and GRB 021004, whose
AGs were also measured very early, are also discussed.

24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat