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.

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