Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An origin for short g-ray bursts unassociated with current star
  formation   Two short (<2 s) g-ray bursts (GRBs) have recently been localized and fading
afterglow counterparts detected. The combination of these two results left
unclear the nature of the host galaxies of the bursts, because one was a
star-forming dwarf, while the other was probably an elliptical galaxy. Here we
report the X-ray localization of a short burst (GRB 050724) with unusual g-ray
and X-ray properties. The X-ray afterglow lies off the centre of an elliptical
galaxy at a redshift of z=0.258, coincident with the position determined by
ground-based optical and radio observations. The low level of star formation
typical for elliptical galaxies makes it unlikely that the burst originated n a
supernova explosion. A supernova origin was also ruled out for GRB 050709, even
though that burst took place in a galaxy with current star formation. The
isotropic energy for the short bursts is 2-3 orders of magnitude lower han that
for the long bursts. Our results therefore suggest that an alternative source
of bursts -- the of binary systems of neutron stars or a neutron star-black
hole pair -- are the progenitors of short bursts.

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The categories of this paper are: hep-ph
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
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The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
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The categories of this paper are: cond-mat
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol
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The categories of this paper are: math
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
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The categories of this paper are: solv-int
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The categories of this paper are: stat