TITLE:   GCN CIRCULAR
NUMBER:  43208
SUBJECT: GRB 251222A / EP251222b: LCO  optical observations
DATE:    25/12/23 07:17:11 GMT
FROM:    SVOM_group <svomgroup@bao.ac.cn>

A. Saccardi, J. T. Palmerio (CEA/Irfu), C. Wu, L.P. Xin (NAOC), H. Yang, S. Guillot (IRAP) report on behalf of the SVOM mission team:

We observed the field of GRB 251222A (Yang et al., GCN 43188; Fermi GBM team, GCN 43186; Wang et al., GCN 43202; Guo et al., GCN 43201) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument.

Our observation started at 2025-12-22T19:31:31 (about 2.43 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical counterpart reported by Palmerio et al. (GCN 43189) is clearly detected in our images.

We measure the following magnitudes, calibrated against the  Pan-STARRS1 catalog, and not corrected for Galactic extinction:

r = 18.55 +/- 0.01 AB (mid-time of 3.04 hr after the trigger);
z = 18.17 +/- 0.01 AB (mid-time of 2.59 hr after the trigger).

This result is consistent with the reports (An et al., GCN 43194; Durbak et al., GCN 43197, Li et al., GCN 43203).

This project is funded by the SVOM collaboration.