TITLE:   GCN CIRCULAR
NUMBER:  35673
SUBJECT: GRB 240204A: optical afterglow detection with LCOGT 1m telescopes at Sutherland and Teide Observatories
DATE:    24/02/05 02:47:44 GMT
FROM:    Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>

I. Pérez-Fournon and F. Poidevin (IAC and ULL) report

We observed the field of GRB 240204A, detected by FERMI GBM (Fermi GBM team, GCN 35664) and by Swift XRT (Cenko et al., GCN 35666), centred at the enhanced Swift-XRT position reported by Beardmore et al. (GCN 35671) with LCOGT 1m telescopes at Sutherland and Teide Observatories. We detect a source, not visible in PanSTARRS imaging, at the position RA (J2000) = 06:56:43.367, Dec (J2000) = +01:01:38.06 (+/- 0.5" in both coordinates). We measure the following magnitudes in SDSS filters: r' = 21.10 +/- 0.15 on 2024-02-04 20:37:30 UT (Sutherland Observatory) and i' = 20.79 +/- 0.15  on 2024-02-04 21:29:56 UT (Teide Observatory), calibrated using the Gaia DR3 synthetic photometry catalog generated from the Gaia BP/RP mean spectra (Gaia Collaboration, 2022), uncorrected for interstellar extinction.

The reported position agrees within the errors with the enhanced Swift-XRT position and with the positions of the optical source detected by Pozanenko et al. (GCN 35670) and Leonini et al. (GCN 35672). 

The flux is clearly decreasing in the red bands.