TITLE: GCN CIRCULAR NUMBER: 44248 SUBJECT: GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification DATE: 26/04/09 13:57:11 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com> M. Freeberg, M. Serrau (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 have continued to observe the field of GRB 260310A detected by Fermi/GBM (Fermi GBM team, GCN 43951) and AstroSat CZTI (Salunke et al., GCN 43958) with the GRANDMA citizen science project Kilonova-catcher (KNC) over the past days mainly in Rc and sdssr filters. Our last night observations were performed with a TEC180FL telescope operated by M. Freeberg. Our observations started at TGRB+29.9 days and were taken with Rc filters. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we still detect the optical counterpart at Rc = 20.39+/-0.18 at a midtime T-TGRB = 29.97 days. Despite the moderate Signal-to-Noise ratio (SNR) in our image series, we tentatively identified the supernova peak brightness at Rc = 19.9+/-0.1 around T-TGRB = 21.8 days. At z = 0.153 (de Ugarte Postigo et al., GCN 43984), such a brightness and peak time seem in good agreement with the expected peak brightness and time of the redshifted canonical GRB/SNe SN 1998bw. The KNC members will keep monitoring the source as long as it stays detectable. 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/44248. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...