Test the robustness of launch-radius dependence in GRB jet inferences

Determine whether the inferred dependence of GRB jet parameters on launch radius persists within individual ejecta shells and whether combining prompt spectra with afterglow, polarization, or independent engine-size constraints can resolve the degeneracy among launch radius, efficiency, and spectral decomposition.

Background

The paper derives conditional jet parameters for eight Fermi/GBM gamma-ray bursts using the non-dissipative photospheric prescriptions of H2013 and G2015. Both frameworks show that increasing the assumed launch radius generally lowers the inferred thermal fraction and raises the inferred magnetization, but the analysis is limited by the small, selected sample, effective time-integrated blackbody inputs, assumed efficiencies, and model-dependent spectral decompositions.

The authors identify the launch radius, radiative efficiency, and spectral decomposition as a joint degeneracy rather than determining a unique, model-independent jet composition. They propose testing whether the observed radius dependence is intrinsic to individual ejecta shells and whether independent observations can constrain the degenerate parameters.