TITLE:   GCN CIRCULAR
NUMBER:  39102
SUBJECT: GRB 250129A: continued KAIT observations indicating steep decay after 28.5h
DATE:    25/01/30 22:40:51 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, continued observing the afterglow of the

GRB 250129A (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; Zheng et al. GCN 39090; Schlekat et al.,

GCN 39091; Antier et al., 39096; Odeh et al., GCN 39097; Ferro

et al., GCN 39098; Bochenek et al., GCN 39099; Malesani et al.,

GCN 39100; Romanov, GCN 39101) in the clear (roughly R) band.

Observation started at ~28.5h after the burst and lasted for ~5.0h.

The OT was still clearly detected in every individual image. Our

photometry results show that the OT was in a single power-law decay

phase, decayed from ~18.6 mag (~28.5h) to ~19.5 mag (~33.5h) with

a decay index of ~4.1, much steeper compared to the value of ~0.85

reported by Bochenek et al. (GCN 39099). This indicating the OT is

likely in a post jet-break phase.