Establish the angular isotropy of the comoving emissivity

Establish whether the comoving emissivity of the prompt-emitting shells is isotropic, an assumption required by the transformation used to infer the angular structure of the GW170817 jet.

Background

The radiative-transfer equation used in the paper assumes an emissivity that is isotropic in the comoving frame. The authors argue that a common anisotropy would largely cancel in the ratio between GRB 090510 and GW170817, whereas a difference between the two bursts could alter the inferred exponent.

The assumption remains empirically unresolved because the available observations do not directly test it.