Answers are grounded in this paper and cite their sources.
Gamma-ray burst outflows may entrain small blobs or filaments of dense, highly ionized metal-rich material. Such inhomogeneities, accelerated by the flow to Lorentz factors in the range 10-100, could have a significant coverage factor and give rise to broad features, especially because of Fe K edges, which influence the spectrum below the MeV range, leading to a progressively decreasing hardness ratio.
No takes yet. Share an insight, caveat, or question.
A 1998 study studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: