TITLE: GCN CIRCULAR NUMBER: 39131 SUBJECT: GRB 250129a: Liverpool Telescope optical follow-up DATE: 25/02/03 14:47:32 GMT FROM: A. Bochenek at Liverpool John Moores University a.m.bochenek@2023.ljmu.ac.uk

A. Bochenek and D. A. Perley (LJMU) report:

We observed the field of GRB250129a (Beardmore et al., GCN 39066) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 10x90s exposures in the SDSS r’ filter starting at 2025-02-02 02:53:56 UT, approximately 4.93 days after the trigger.

We report a detection of the optical transient (Beardmore et al., GCN 39066) in the stacked images of r = 21.80 ± 0.11 mag. Our detection is consistent with other late-time observations (Schlekat et al., GCN39110, Gompertz et al., GCN 39114, Moskvitin et al., GCN39130), and suggests the afterglow is now decaying faster, with a temporal index of approx. -2.2 (fit to observations after 2.5 days post-trigger).

The photometry was obtained using nearby PanSTARRS standards and was not corrected for extinction.

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