Trigger observed by Fermi, Integral.

I think these are the original optical references: 23. One-Meter Two-Hemisphere (1M2H) collaboration, GRB Coordinates Network 21529 (2017). 24. D. A. Coulter, et al., Science, doi:10.1126/science.aap9811 (2017).

The transient was discovered optically by the 1M2H (1m telescopes in 2 hemispheres) collaboration, and I think that is the Coulter+17 paper above.

Discovery optical Observations ~ 11 hr after trigger. First optical spectra 11.75 hrs after spectra Shappee+17; Earliest NIR spectrum 1.5 d, CHornock+17.