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GCN Circular 35690

GRB 240204A : OHP/T193/T120 optical afterglow fading detection
2024-02-06T05:05:24Z (4 months ago)
Christophe Adami at LAM <>
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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). 
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