What is baryon loading in the context of gamma ray bursts (GRBs)?

I've read that with short hard gamma ray bursts (shGRBs) associated with the coalescence of NS-NS and NS-BH binaries are expected to be beamed along the axis of the orbital angular momentum (i.e. perpendicular to the orbital plane) because the "baryon loading is lowest there". Here, NS = neutron star, BH = (stellar mass) black hole.

1. What is meant by baryon loading?

2. Why is it lowest along the direction of the orbital angular momentum?

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