TITLE: GCN CIRCULAR NUMBER: 35690 SUBJECT: GRB 240204A : OHP/T193/T120 optical afterglow fading detection DATE: 24/02/06 05:05:24 GMT FROM: Christophe Adami at LAM <christophe.adami@lam.fr> C. Adami, D. Russeil, H. LeCoroller (Pythéas/LAM), E. Abdo, M. Carta, T. Chehab, M. Colliaux, A. Gharibi-Ziarati, E. Pouyer, A. Jacquet, F. Malaval, S. Aftis (AMU), J. Balcaen, Y. Degot-Longhi, (OHP/Pythéas), E. Le Floc'h, D. Götz, F. Schüssler (CEA Paris-Saclay), B. Schneider (MIT), S. Basa (Pytheas/OHP/LAM), A. Saccardi, S. D. Vergani (GEPI, Obs. de Paris), M. Dennefeld (IAP), report on behalf of a larger collaboration We observed the field of GRB 240204A (Fermi-GBM team GCN 35664, Cenko et al. GCN 35666, Pozanenko et al. GCN 35670, Leonini et al. GCN 35672, Pérez-Fournon et al. GCN 35673, Dainotti et al. GCN 35677, Bochenek et al. GCN 35678) using the T193cm telescope equiped with the MISTRAL instrument and with the T120cm telescope at Observatoire de Haute-Provence (France). On the night of 04 February 2024, we made 9 sets of observations with MISTRAL in r band (30min each) and two sets of observations with the T120 telescope (V and i bands: 135min each). On the night of 05 February 2024, we made an additional single set of observations with MISTRAL in r band during 97.5min. Details are given in the table below. All magnitudes were calibrated against the PanStarrs catalog (mean Kron magnitudes), extracted in a radius of 1arcmin around the GRB position. Magnitudes were not corrected for galactic extinction. Our results in r-band show a fading behaviour of typically 0.09+/-0.03 mag/hour over the 10 first hours and of 0.06+/-0.01 mag/hours over the 31 first hours. ----------------------------------------------- T-T0 (in hours) | mag | filter | Telescope ----------------------------------------------- +4.09 | 21.82+/-0.21 | r | MISTRAL@T193 +4.70 | 21.88+/-0.15 | r | MISTRAL@T193 +5.29 | 21.86+/-0.11 | r | MISTRAL@T193 +5.89 | 21.92+/-0.12 | r | MISTRAL@T193 +6.64 | 21.77+/-0.10 | r | MISTRAL@T193 +7.22 | 21.98+/-0.10 | r | MISTRAL@T193 +7.99 | 21.88+/-0.12 | r | MISTRAL@T193 +8.69 | 22.10+/-0.13 | r | MISTRAL@T193 +9.32 | 22.51+/-0.31 | r | MISTRAL@T193 +30.72 | 23.37+/-0.31 | r | MISTRAL@T193 +6.02 | 22.69+/-0.17 | g | T120 +6.02 | 20.33+/-0.13 | i | T120 We acknowledge OHP staff for its excellent support during the AMU M2-Physics 2024 observationnal internship. This work received support from the French government under the France2030 investment plan, as part of the initiative d’Excellence d’Aix-Marseille Universit´e- A*MIDEX (AMX-19-IET-008). We were also supported by the IPhU Graduate School program at Aix-Marseille University. We also acknowledge the support by Master Erasmus Mundus Europhotonics (599098-EPP-1-2018-1-FR-EPPKA1-JMD-MOB) financed by EACEA (European Education and Culture Executive Agency). View this GCN Circular online at https://gcn.nasa.gov/circulars/35690. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...