**6.7. Anisotropic Fireballs**

It is unlikely that a realistic fireball will be spherically
symmetric. In fact strong deviation from spherical symmetry are
expected in the most promising neutron star merger model, in which the
radiation is expected to emerge through funnels along the rotation
axis. The initial motion of the fireball might be fairly complex but
once
>> 1 the motion of each fluid element decouples from the
motion of its neighbors with angular distance larger than
^{-1}.
This motion can be described by the same asymptotic solution, as if it
is a part of a spherical shell.
We define the angular range over which different
quantities vary as .
Additionally now the motion is not radially outwards and
*u*^{r} *u*.
We define the spread angle
as
*u*^{r}
*u* cos.
The spherical fireball equations hold locally if:

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