Gamma-ray bursts [1] are a class of observations, not single event. Some of them may originate from relativistic jets [2] emitted by massive, spinning, charged objects colliding (e.g. black holes). Those jets' intensity is not uniform; if it's pointed at the Earth, that's worse than if it's pointed perpendicularly to it.
There are other mechanisms proposed that columnate the emission [3][4]. These involve a star's rotation creating a radiating column along the star's axis. (I'm not sure if the atoms in that column radiate with a bias.)
[1] https://en.wikipedia.org/wiki/Gamma-ray_burst
[2] https://en.wikipedia.org/wiki/Astrophysical_jet
Many stellar objects rotate and/or have a magnetic field, and thus an "up", "down", and "side" in spite of being a sphere. Pulsars (extinguished stars that emit radio waves from their poles) are another famous example.