TITLE: GCN CIRCULAR NUMBER: 44402 SUBJECT: GRB 260421B: Kilonova-Catcher optical afterglow detection DATE: 26/04/23 15:46:39 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com> M. Freeberg, R. Hellot, M. Serrau (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 260421B detected by Fermi/GBM (Fermi GBM team, GCN 44360) and SVOM (Zhao et al., GCN 44362; Guo et al., GCN 44389) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot and the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+1.9 hours and were taken with sdss-r filter. In our stacked frames, subtracted from the Legacy Survey DR10 template image, we marginally detect the optical counterpart (He et al., GCN 44363; Álvarez et al., GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366; Lipunov et al., GCN 44367; Schneider et al., GCN 44368; Li et al., GCN 44377; Pérez-Fournon et al., GCN 44383; Mo et al., GCN 44384; and Shi et al., GCN 44388, Pawar et al., GCN 44396). We report our follow-up results in the table below: | Tmid-TGRB (hrs) | Exp (s) | Filter | Magnitude | Instrument | | ------------ | ------------ |------------ |------------ |------------ | | 2.48 | 20 x 180s | r (AB) | 21.12 +/- 0.30 | TEC160FL | | 3.87 | 9 x 300s | r (AB) | 20.94 (3 sig U.L.) | CDK17 | 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. 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/44402. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...