Speaker
Description
GRB 191019A was a long Gamma-ray burst (GRB) that triggered Swift/BAT and lasted about 65 s and, as such, originally thought to have a core-collapse origin. However, no associated supernova was detected following the optical afterglow despite deep follow-up, which suggested that the burst was caused by the merger of two compact stellar objects. This is also supported by the published properties of its host-galaxy (z=0.248), which is a massive and passive galaxy, unusual for a collapsar event.
We thus re-analyzed unpublished GROND multi-band (g'r'i'z'JHKs) data obtained between 0.4 and 15 days post trigger and obtained additional late-time LBT imaging. Image subtraction confirmed the optical counterpart in all four optical bands and suggested the presence of a rebrightening around 1-2 days, with magnitude and peak timescale compatible with an AT2017gfo-like KN at the same redshift.
Incorporating publicly available Swift-XRT data, a joint fit of an afterglow plus a kilonova model revealed a better match than an afterglow-only scenario. Our findings strongly suggest that GRB 191019A belongs to the increasing list of binary-merger long GRBs like GRB 211211A and GRB 230307A.
