TITLE: GCN CIRCULAR NUMBER: 41370 SUBJECT: GRB 250813B: NOT observations of the optical afterglow DATE: 25/08/14 12:18:54 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group antonio.martin-carrillo@ucd.ie
G. Corcoran (UCD), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), B. P. Gompertz (Birmingham), V. Vuolteenaho (Univ. of Oulu), report on behalf of a larger collaboration:
We observed the field of the SVOM/ECLAIRs GRB 250813B (Xie et al., GCN 41352; Xie et al., GCN 42354), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 6x150 s exposures in the r-band and 5x200 s in the z-band, starting at 2025-08-14 00:05:04 UT (1.231 hr after the trigger).
The optical afterglow reported by Jelinek et al. (GCN 41355), de Ugarte Postigo et al. (GCN 41356), Schneider et al. (GCN 41363) and Xin et al. (GCN 41369) is well detected with a preliminary magnitude of
r = 21.00 +/- 0.08 (AB, mid-time 1.379 hr after trigger); z = 20.04 +/- 0.09 (AB, mid-time 1.689 hr after trigger).
The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitudes are not corrected for Galactic extinction.
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