Heavy element nucleosynthesis associated with a gamma-ray burst

• DOI: 10.48550/arxiv.2308.00633
• Publication Date: 2023-01-01
• Authors: James H. Gillanders; E. Troja; Chris L. Fryer; Marko Ristić; Brendan O’Connor; Christopher J. Fo...; Yu-Han Yang; Nanae Domoto; Salma Rahmouni; Masaomi Tanaka; Ori D. Fox; S. Dichiara
• Keywords: Kilonova; Opacity; r-process

Kilonovae are a novel class of astrophysical transients, and the only observationally-confirmed site rapid neutron capture nucleosynthesis (the r-process) in Universe. To date, handful kilonovae have been detected, with just single spectroscopically-observed event (AT 2017gfo). Spectra AT 2017gfo provided evidence for formation elements heavier than iron; however, these spectra were collected during first ~ 10 days, when emission from light r-process dominates observations. Heavier elements, if synthesised, expected to shape late-time evolution kilonova, beyond phases which we spectral Here present spectroscopic observations rapidly-reddening thermal transient, following gamma-ray burst, GRB 230307A. Early (2.4 day) optical spectroscopy identifies presence hot (T 6700 K) continuum. By 29 this component has expanded cooled significantly 640 K), yet it remains optically thick, indicating high-opacity ejecta. We show that properties can be explained by merger compact objects, further, leads us infer production heavy lanthanide elements. identify several features (in both absorption emission), whose cause newly-synthesised This marks second recorded synthesis observed at such late times.