TITLE: GCN CIRCULAR NUMBER: 45127 SUBJECT: GRB 260708A: Kilonova-Catcher optical afterglow detection DATE: 26/07/09 17:01:32 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com> M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (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 260708A detected by Fermi/GBM (Fermi GBM team, GCN 45115; GCN 45124) and Fermi/LAT (Holzmann Airasca et al., GCN 45117) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a iTtelescope T30 located at Siding Spring Observatory operated by M. Freeberg. Our observations started at TGRB+1.17 days and were taken with the Johnson/Cousins R filter. In our stacked frames, we clearly detect the optical counterpart reported by MASTER (Shilova et al., GCN 45123). We report part of our follow-up results in the table below : | Tmid-TGRB (days) | Exp (s) | Filter | Magnitude | Instrument | | ------------ | ------------ |------------ |------------ |------------ | | 1.18 | 3 x 300s | R (Vega) | 18.93 +/- 0.14 | iT30 | Given the significant fading behavior compared to the previous MASTER epoch, we considered this optical candidate is the optical afterglow of the energetic burst GRB 260708A. Further observations are ongoing. All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). 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/45127. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...