  The long and short gamma-ray bursts are believed to be produced due to
collapse of massive stars and merger of compact binaries respectively. All
these objects are rich in neutron and the jet outflow from these objects must
have a neutron component in it. By postulating the neutron anti-neutron
oscillation in the gamma-ray burst fireball, we show that, 19-38 GeV neutrinos
and anti-neutrinos can be produced due to annihilation of anti-neutrons with
the background neutrons. These neutrinos and anti-neutrinos will be produced
before the 5-10 GeV neutrinos due to dynamical decoupling of neutrons from the
rest of the fireball. Observation of these neutrinos will shed more light on
the nature of the GRB progenitors and also be a unique signature of physics
beyond the standard model. A possible way of detecting these neutrinos in
future is also discussed.
