TITLE: GCN CIRCULAR NUMBER: 41247 SUBJECT: GRB 250806A: Kilonova-Catcher optical upper limits DATE: 25/08/06 13:12:51 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com> M. Freeberg, R. Hellot (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), M. Pillas (ULiege), A. Simon, D. Zazubyk (ASPD TShNU of Kyiv), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250806A (Xie et al., GCN 41243) detected by SVOM/ECLAIRs with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope T72 and TEC160FL telescopes operated by M. Freeberg and the CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot. Our observations started at T0+43min. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we do not detect any optical counterpart inside the SVOM/MXT position (Xie et al., GCN 41243). We report our follow-up results in the table below: +---------------+-----------+------------+---------------------+--------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+============+=====================+==============+ | 1.39 | 5 x 600s | sdssr (AB) | 20.4 (U.L., 5 sigma) | CDK17-AITP | | 1.46 | 16 x 180s | Rc (Vega) | 21.0 (U.L., 5 sigma) | iT72 | | 2.27 | 18 x 300s | sdssr (AB) | 21.3 (U.L., 5 sigma) | TEC160FL | +---------------+-----------+------------+----------------------+-------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/41247. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...