{
  "submittedHow": "web",
  "submitter": "Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>",
  "format": "text/plain",
  "eventId": "GRB 250920C",
  "subject": "GRB 250920C: Kilonova-Catcher optical afterglow detection",
  "bibcode": "2025GCN.41967....1F",
  "createdOn": 1758724642151,
  "body": "M. Freeberg (KNC), C. Andrade(UMN), D. Turpin (CEA-Saclay/Irfu), S. Antier (OCA/IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration:\n\nWe observed the field of GRB 250920C detected by Fermi/GBM (Fermi GBM team, GCN 41903), Swift/BAT (Gupta et al., GCN 41904), SVOM/GRM (Wang et al., GCN 41929) and Konus-WIND (Panteleeva et al., GCN 41957) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope T30 telescope operated by M. Freeberg. Our observations started at TGRB+3.3hr. \n\nIn our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical/IR counterpart reported by GOTO (Wortley et al., GCN 41907) and further confirmed by many other teams (Strausbaugh et al.,GCN 41911; Ghosh et al., GCN 41913; Kuin et al., GCN 41920; Mohan et al., GCN 41925; Sanchez-Ramirez et al., GCN 41928; Guiffreda et al., GCN 41943; Mo et al., GCN 41947; de Ugarte Postigo et al., GCN 41951; de Wet et al., GCN 41952; Izzo et al., GCN 41955; Zheng et al., GCN 41956; Zhu et al., GCN 41965)\n\nWe report some of our first image follow-up results in the table below \n+---------------+----------+-----------+----------------+--------------+\n| Tmid-TGRB (hr)| Exp (s)  | Filter    | Magnitude      | Instrument   |\n+===============+==========+===========+================+==============+\n| 3.49          | 3 x 300s | Rc (Vega) | 18.93 +/- 0.07 | iT30         | \n+---------------+----------+-----------+----------------+--------------+\n\nAll 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. \n\nWe use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). \n\nGRANDMA 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/).\n",
  "circularId": 41967
}