Paper: astro-ph/0507099
Date: Tue, 5 Jul 2005 16:22:59 GMT (650kb)

Title: Torus Formation in Neutron Star Mergers and GRB 050509b

Authors: R. Oechslin, H.-Th. Janka (MPI for Astrophysics, Garching)
Comments: 6 pages, 6 figures, high-resolution color figures available on
request; submitted to MNRAS letters
\\
Merging neutron stars (NSs) are hot candidates for the still enigmatic
sources of short gamma-ray bursts (GRBs). If the central engines of the huge
energy release are accreting relic black holes (BHs) of such mergers, it is
important to understand how the properties of the BH-torus systems, in
particular disc masses and mass and rotation rate of the compact remnant, are
linked to the characterizing parameters of the NS binaries. For this purpose we
present relativistic smoothed particle hydrodynamics simulations with
conformally flat approximation of the Einstein field equations and a physical,
non-zero temperature equation of state. Disc formation is highlighted as a
dynamical process caused by angular momentum transfer through tidal torques
during the merging process of asymmetric systems or in the rapidly spinning
triaxial post-merger object. Our simulations support the possibility that the
first well-localized short and hard GRB 050509b has originated from a NS merger
event. If so, its low energy output and short duration suggest that the merger
remnant has collapsed to a BH within less than roughly 100 ms, leaving an
accretion torus with a small mass of less or about 0.01 M_sun.

\\ ( http://arXiv.org/abs/astro-ph/0507099 , 650kb)