TITLE: GCN CIRCULAR NUMBER: 38620 SUBJECT: GRB 241218A: REM optical upper limit DATE: 24/12/18 13:54:03 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it> R. Brivio, M. Ferro, P. D’Avanzo (INAF-OAB), D. B. Malesani (DAWN/NBI and Radboud Univ.) S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 241218A detected by Swift (Williams et al., GCN 38601) with the REM 60cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z bands, starting on 2024 December 18 at 08:05:53 UT (i.e. 8.0 hours after the Swift trigger), and lasting for about 1 hour. From preliminary photometry we do not detect any optical counterpart at the XRT enhanced position (Beardmore et al., GCN 38604) down to the following 3sigma magnitude upper limits: r > 19.2 (AB; calibrated against the Pan-STARRS catalogue) at a mid-time of t - t0 = 8.4 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/38620. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...