Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The radio afterglow from the giant flare of SGR 1900+14: the same
  mechanism as afterglows from classic gamma-ray bursts?   A radio afterglow was detected following the 1998 August 27 giant flare from
the soft gamma repeater (SGR) 1900+14. Its short-lived behavior is quite
different from the radio nebula of SGR 1806-20, but very similar to radio
afterglows from classic gamma-ray bursts (GRBs). Motivated by this, we attempt
to explain it with the external shock model as invoked in the standard theory
of GRB afterglows. We find that the light curve of this radio afterglow is not
consistent with the forward shock emission of an ultra-relativistic outflow,
which is suggested to be responsible for the initial hard spike of the giant
flare. Nevertheless, shock emission from a mildly or sub-relativistic outflow
expanding into the interstellar medium could fit the observations. The possible
origin for this kind of outflow is discussed, based on the magnetar model for
SGRs. Furthermore, we suggest that the presence of an ultra-relativistic
fireball from SGR giant flares could be tested by rapid radio to optical
follow-up observations in the future.

10
The categories of this paper are: q-bio
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
29
The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
33
The categories of this paper are: plasm-ph