TITLE:   GCN CIRCULAR
NUMBER:  42481
SUBJECT: GRB 251027A: LCO optical upper limit
DATE:    25/10/27 15:13:55 GMT
FROM:    SVOM_group <svomgroup@bao.ac.cn>

A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), D. Turpin (CEA/Irfu), B. Cordier (CEA/Irfu), Y. H. Cheng (YNU), Y. F. Liang (PMO), report on behalf of the SVOM mission team:

We observed the field of the GRB 251027A detected by SVOM/ECLAIRs (Cheng et al., GCN 42471) with the LCO 1m telescope at McDonald Observatory equipped with the Sinistro instrument.

Our observation started on 2025-10-27 at 10:22:43 UT (~45 min after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/ECLAIRs position (Cheng et al., GCN 42471), in agreement with the results reported by Dornic et al. (GCN 42480).

We derived the following upper limit r > 22 AB mag (5-sigma) calibrated against Pan-STARRS1 catalogue and not corrected for Galactic extinction.

This project is funded by the SVOM collaboration.