  I this paper, which is a sequel to math.AG/0310361, we study Bessel models of
representations of GSp_4 over a local non archimedian field in the framework of
the geometric Langlands program.
  The Bessel module over the nonramified Hecke algebra of GSp_4 admits a
geometric counterpart, the Bessel category of perverse sheaves on some
ind-algebraic stack. We use it to prove a geometric version of the multiplicity
one for Bessel models. It implies a geometric Casselman-Shalika type formula
for these models. The strategy of the proof is the same as in the paper of
Frenkel, Gaitsgory and Vilonen math.AG/9907133.
  We also propose a geometric framework unifying Whittaker, Waldspurger and
Bessel models.
