The optical constants and grain sizes of interstellar dust measured directly using the dust-scattered X-ray halo of GRB221009A

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Table 1

Model comparison using various dust grain-size distributions [(MRN Mathis et al. 1977), (HD Hensley & Draine 2023)] and various assumptions for refractive index models (e.g. ADT or RG).

Model	Framework	a₊ [μm]	χ²/DOF
MRN	ADT	${0.235}_{- 0.006}^{+ 0.007}$ $\[0.235_{-0.006}^{+0.007}\]$	6950/5838
MRN	RG	${0.212}_{- 0.006}^{+ 0.008}$ $\[0.212_{-0.006}^{+0.008}\]$	8312/5842
HD	ADT	~0.6	8302/5841
HD*	ADT	~0.5	7925/5836
MRN	Mg_2–xFe_xSiO₄^†	0.236 ± 0.004	7536/5841
MRN	MgSiO₃+Fe	0.241 ± 0.005	7527/5841
MRN	MgSiO₃+Fe+C	0.236 ± 0.006	7522/5840

Notes. The HD with fiducial and optimised (HD*) parameters is shown in Fig. 6 (alongside an MRN distribution). The bottom three rows show similar maximum grain sizes and χ² for various dust compositions, as analysed in Figs. 9, 10, and 11. ^†The Fe/Mg ratio is represented by x/2, where 0 ≤ x ≤ 2.

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