TITLE:   GCN CIRCULAR
NUMBER:  39099
SUBJECT: GRB 250129a: Liverpool Telescope optical follow-up
DATE:    25/01/30 14:06:13 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 6x90s exposures in the SDSS r’ filter starting at 2025-01-30 04:53:17 UT, approximately 24.1 hours after the trigger. Three of the images had to be discarded due to autoguider issues.
 
We report a detection in the stacked images of r = 18.91 ± 0.03 mag. Our detection is consistent with the re-brightening (Brivio et al., GCN 39079, Zheng et al., GCN 39090) and subsequent observations of the afterglow (Odeh et al., GCN39097, Ferro et al. GCN39098). This implies slow decay, approx. 2 magnitudes in r-band from (clear) R ~17.1 at 6.9h post trigger (Zheng et al., GCN 39090) to this work’s r = 18.91 at 24.1h, with the decay index of approximately ~0.85.
 
The photometry was obtained using nearby PanSTARRS standards and was not corrected for extinction.