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Confirm the near-infrared line identification for GRB 230307A

Establish whether the broad near-infrared emission feature at approximately 2.15 µm observed for the counterpart of GRB 230307A is Te III at redshift z = 0.065, thereby confirming the kilonova origin and r-process production for this event.

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Background

GRB 230307A shows a broad near-infrared emission feature claimed to be Te III at z = 0.065, similar to a feature observed in AT 2017gfo. A definitive identification of this line would strengthen evidence for a kilonova origin and confirm r-process production in this long GRB event.

References

This was claimed to be Te III at z = 0.065 (Gillanders et al. 2023; Levan et al. 2024) although the identification is not definitive. A broad emission feature was observed for AT 2017gfo at a similar (but not exact) rest-frame wavelength, also proposed to be Te III (Hotokezaka et al. 2023). If the identification is correct, this spectroscopically validates that the GRB 230307A derived from an NS merger and that the excess was an r-process KN.

— Where has all the $r$-process gone? Timescales for GRB-Kilonovae to Enrich their Host Galaxies (2410.00095 - Nugent et al., 30 Sep 2024) in Section 2.1. GRB-Kilonova Sample