TITLE:   GCN CIRCULAR
NUMBER:  40334
SUBJECT: GRB 250502A: NOT optical observations
DATE:    25/05/03 12:59:00 GMT
FROM:    Gregory Corcoran  at University College Dublin  <gregory.corcoran@ucdconnect.ie>

G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), A. de Ugarte Postigo (LAM), D. Xu (NAOC), A. Saccardi (CEA/Irfu), N. Pyykkinen (NOT and Turku), report on behalf of a larger collaboration:

We observed the field of GRB 250502A detected by SVOM/ECLAIRs (Wang et al., GCN 40313), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained exposures in the SDSS g, r, i (3x300 s each) and z (5x200 s) bands, starting at 21:41:17 UT on 2025-05-02 (12.914 hr after the SVOM/ECLAIRs trigger).

The optical counterpart reported by Rakotondrainibe et al. (GCN 40315), An et al. (GCN 40319), Li et al. (GCN 40320), Ghosh et al. (GCN 40322), de Ugarte Postigo et al. (GCN 40328), Pérez-Fournon et al. (GCN 40330), Odeh & Guessoum (GCN 40331), Bochenek & Perley (GCN 40333) with a redshift of z = 2.163 (de Ugarte Postigo et al., GCN 40328) is well detected in all our frames. We measure the following preliminary magnitude (mid time 13.23 hr after the trigger):

r = 20.71 +/- 0.03  (AB).

The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitudes are not corrected for Galactic extinction.