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.