TITLE: GCN CIRCULAR NUMBER: 35678 SUBJECT: GRB 240204a: Liverpool Telescope optical afterglow detection DATE: 24/02/05 20:01:51 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk> A. Bochenek, J. Wise, D. A. Perley (LJMU) report: We observed the field of GRB 240204A (Fermi-GBM team, GCN 35664; Cenko et al., GCN 35666; Pozanenko et al., GCN 35670) with the IO:O optical camera on the 2m robotic Liverpool Telescope. We conducted two sets of observations, the first starting at 2024-02-04 22:39:16 UT (approx. 7.5h after the burst), and the second starting at 2024-02-04 23:57:25 UT (approx. 9h after the burst). Both consisted of 2x60s exposures in the SDSS g, r, i, and z filters. Conditions were generally good throughout. The afterglow is detected in the i and z bands in both epochs, and in the r-band in the first epoch. We measure the following magnitudes: MJD Time since burst Filter Mag. (AB) 60344.94386 7.52 hours g > 22.72 60344.94585 7.57 hours r 21.37 ± 0.20 60344.94783 7.62 hours i 20.98 ± 0.21 60344.94981 7.66 hours z 20.74 ± 0.20 60344.99812 8.82 hours g > 22.29 60345.00012 8.87 hours r > 22.08 60345.00210 8.92 hours i 20.85 ± 0.12 60345.00408 8.97 hours z 20.34 ± 0.13 The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction. The source was detected at a position consistent with previous detections. View this GCN Circular online at https://gcn.nasa.gov/circulars/35678. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...