TITLE: GCN CIRCULAR NUMBER: 42085 SUBJECT: GRB 251003A: Kilonova-Catcher optical afterglow detection DATE: 25/10/03 10:33:41 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com> M. Freeberg (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 251003A detected by Fermi/GBM (Fermi GBM team, GCN 42069) and Swift/BAT (Beardmore et al., GCN 42070) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL operated by M. Freeberg. Our observations started at TGRB+1.2hr. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart reported by OSN (Aceituno et al., GCN 42072), COLIBRI (Moreno Méndez et al., GCN 42073), LCO-1m (Strausbaugh et al., GCN 42074). We report our follow-up results in the table below +---------------+-----------+--------+----------------+------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+========+================+============+ | 1.71 | 20 x 180s | r (AB) | 21.07 +/- 0.37 | TEC160FL | | 3.58 | 25 x 180s | i (AB) | 19.14 +/- 0.18 | TEC160FL | +---------------+-----------+--------+----------------+------------+ As also pointed out by (Moreno Méndez et al., GCN 42073, Strausbaugh et al., GCN 42074), the r-i color index we measure indicates a very red afterglow and further observations at infrared wavelengths and spectroscopic observations are encouraged to disentangle whether this burst is highly extinguished or localized at a moderately high redshift. 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/42085. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...