Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetohydrodynamic simulations of the collapsar model for early and
  late evolution of gamma-ray bursts   I present results from magnetohydrodynamic (MHD) simulations of a gaseous
envelope collapsing onto a black hole. These results support the notion that
the collapsar model is one of most promising scenarios to explain the huge
release of energy in a matter of seconds associated with Gamma Ray Bursts
(GRB). Additionally, the MHD simulations show that at late times, when the mass
supply rate is expected to decrease, the region in the vicinity of the black
hole can play an important role in determining the rate of accretion, its time
behaviour, and ultimately the energy output. In particular, the magnetic flux
accumulated around the black hole can repeatedly stop and then restart the
energy release. As proposed by Proga and Zhang, the episode or episodes of
reoccurring of accretion processes can correspond to X-ray flares discovered
recently in a number of GRBs.

2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
16
The categories of this paper are: stat
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn