TITLE: GCN CIRCULAR NUMBER: 41442 SUBJECT: GRB 250818B: Liverpool Telescope optical detections DATE: 25/08/20 11:30:44 GMT FROM: Dimple at University of Birmingham dimplepanchal96@gmail.com

Dimple (U. Birmingham), B. P. Gompertz (U. Birmingham), and A. Kumar (RHUL) report on behalf of a larger collaboration:

We conducted follow-up observations of GRB 250818B (Wang et al., GCN Circ. 41405) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 03:46:39 UT on 2025-08-20, ~2 days after the SVOM/ECLAIRs trigger, and consisted of 5 x 240 s exposures in each of the SDSS g, r, i, and z filters.

We detect the optical afterglow (Kumar et al., GCN Circ. 41406; Yao et al., GCN Circ. 41409; Zheng et al., GCN Circ. 41417; Bendtsen et al., GCN Circ. 41426; Moskvitin et al., GCN Circ. 41428; An et al., GCN Circ. 41430; Kumar et al., GCN Circ. 41431) in all filters, and measure an AB magnitude of r = 22.14 ± 0.10 (mid-time t0+2.03 days).

Magnitudes are calibrated against nearby Pan-STARRS stars and are not corrected for Galactic extinction.

View this GCN Circular online at https://gcn.nasa.gov/circulars/41442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...