TITLE:   GCN CIRCULAR
NUMBER:  41394
SUBJECT: GRB 250813B: Liverpool Telescope optical upper limits
DATE:    25/08/15 14:54:03 GMT
FROM:    Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515@gmail.com>

A. Kumar, J. R. Maund (RHUL), N. C. Sun (UCAS), W. X. Li, Y. N. Wang (NAOC), and K. Wiersema (Herts) report:

Using the IO:O imager on the 2.0 m Liverpool Telescope, we observed the field of the SVOM/ECLAIRs–triggered GRB 250813B (Xie et al., GCNs 41352, 41354), also detected by EP–FXT (Wu et al., GCN 41361), SVOM/MXT (Götz et al., GCN 41368), Fermi/GBM (Smith et al., GCN 41376), and SVOM/GRM (Tan et al., GCN 41383). Observations in the r and z bands were obtained on 2025-08-15 at 02:42:32.1 UT and 03:13:37.8 UT, corresponding to ~1.16 and ~1.18 days post-trigger, respectively. Each band consisted of 3 × 600 s exposures.

We do not detect the optical afterglow of GRB 250813B (Jelinek et al., GCN 41355; de Ugarte Postigo et al., GCN 41356; Schneider et al., GCN 41363; Xin et al., GCN 41369; Corcoran et al., GCN 41370) down to limiting magnitudes of r >22.0 and z >20.6.

Photometric calibration was performed using Pan-STARRS stars. The quoted magnitudes are not corrected for Galactic extinction in the direction of the GRB.