TITLE: GCN CIRCULAR NUMBER: 39213 SUBJECT: GRB 250129A: ABObservatory SLOAN r’ afterglow detection DATE: 25/02/07 18:49:05 GMT FROM: A. Brosio at ABObservatory Rosarno antonino.brosio@gmail.com

A. Brosio (ABObservatory), S. Savaglio (University of Calabria), S. Tosi, S. Zappatore & P. Cianfarra (University of Genoa), S. Benatti (INAF Palermo), M. Rainer (INAF Brera), D. Ricci (INAF Padova), A. Di Dato (INAF Capodimonte), S. Masiero & A. Nastasi (GAL Hassin), L. Betti (Osservatorio Polifunzionale del Chianti), D. Liguori (Osservatorio “G. Galilei” Cariati) for the NOCTIS team report:

We observed the field of GRB 250129A, which was detected by Swift (Beardmore et al., GCN 39066) with the 30-cm automated telescope at ABObservatory (Rosarno, Italy) using the SLOAN r’ filter. Observations began on 2025 January 30 at 23:41:31 UT, approximately 43 hours after the Swift trigger. The observation consisted of 10 exposures of 240 seconds each, with variable conditions due to passing clouds during the session. The mid-exposure time was 00:07:31 UT, and the final exposure ended at 00:33:31 UT.

From photometry, we detect the optical counterpart in our images at the position of the previously reported afterglow (Francile et al., GCN 39065; 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).

The measured magnitude is:

r’ = 19.32 +/- 0.13 (AB, calibrated against the Pan-STARRS catalogue on SIMBAD) at a mid-time of t - t0 = 00:12:43 after the trigger.

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