TITLE: GCN CIRCULAR NUMBER: 39090 SUBJECT: GRB 250129A: KAIT optical observations of the rebrightening around 5.1 hours DATE: 25/01/29 22:21:18 GMT FROM: Weikang Zheng at UC Berkeley <weikang@berkeley.edu> WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, responded to GRB 250129A detected by Swift (Beardmore et al., GCN 39066) starting at 09:25 UT, ~4.68h after the bust. Observations were performed in the clear (roughly R) filter with a set of 60s exposures and lasted for ~2.2h. The optical afterglow (Francile et al., GCN 39065; Beardmore et al., GCN 39066; Schneider et al., GCN 39071; Belkin et al., GCN 39072; Izzo et al., GCN 39073; Izzo & Malesani, GCN 39074; Gosh et al., GCN 39077; Schneider et al., GCN 39078; Brivio et al., GCN 39079; Siegel et al., GCN 39085) was clearly detected in every individual image. Our photometry results show that the OT rebrightened since ~4.68h (~16.7 mag) and reached a double peak at ~4.99h (~16.3 mag) and again at 5.2h (~16.3 mag), then decayed afterword, with small flares during decay phase, till ~17.1 mag at ~6.90h. View this GCN Circular online at https://gcn.nasa.gov/circulars/39090. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...