Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Identifying Gamma-Ray Burst Remnants Through Positron Annihilation
  Radiation   We model the annihilation of relic positrons produced in a gamma-ray burst
(GRB) after its afterglow has faded. We find that the annihilation signal from
at least one GRB remnant in the Milky Way galaxy should be observable with
future space missions such as INTEGRAL and EXIST, provided that the gas
surrounding the GRB source has the typical density of the interstellar medium,
< 1 cm^-3. Three fortunate circumstances conspire to make the signal
observable. First, unlike positrons in a standard supernova, the GRB positrons
initially travel at a relativistic speed and remain ahead of any
non-relativistic ejecta until the ejecta become rarefied and the annihilation
time becomes long. Second, the GRB remnant remains sufficiently hot (T > 5 x
10^5 K) for a strong annihilation line to form without significant smearing by
three-photon decay of positronium. Third, the annihilation signal persists over
a time longer than the average period between GRB events in the Milky Way
galaxy.

17
The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
31
The categories of this paper are: ao-sci
1
The categories of this paper are: cs
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat