{
  "circularId": 41331,
  "eventId": "GRB 250812A",
  "submitter": "Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>",
  "format": "text/plain",
  "body": "M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), M. Pillas (ULiege), M. Molham (NRIAG), M. Mašek (Institute of Physics, Prague, FZU, CZ), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration:\n\nWe observed the field of GRB 250812A (Xin et al., GCN 41322) detected by SVOM/ECLAIRs with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope T72 telescope operated by M. Freeberg. Our observations started at T0+1.8hr. \n\nIn our stacked frames, subtracted from the Legacy Survey DR10 template image, we detect an uncatalogued optical source at a position consistent with the TRT (He et al., GCN 41324), SVOM/VT (Xin et al., GCN 41326) and SVOM/COLIBRÍ (FM-GFT) (Rakotondrainibe\n et al., GCN 41328) optical afterglow candidate as well as the Swift/XRT (Sbarrato et al., GCN41325) x-ray afterglow candidate .\n\nWe report our follow-up results in the table below:\n+---------------+-----------+-----------+----------------+------------+\n| Tmid-TGRB (hr)| Exp (s)   | Filter    | Magnitude      | Instrument |\n+===============+===========+===========+================+============+\n| 2.3           | 10 x 300s | Rc (Vega) | 18.60 +/- 0.06 | iT72       | \n| 12.4          | 20 x 180s | Rc (Vega) | 19.12 +/- 0.11 | iT72       | \n+---------------+-----------+-----------+----------------+------------+\n\nOur observations clearly show a fading behavior as also shown by the TRT and SVOM/VT observations (He et al., GCN 41324; Xin et al., GCN 41326). Thus we also suggest this source to be the afterglow of GRB 250812A.\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",
  "subject": "GRB 250812A: Kilonova-Catcher optical afterglow detection",
  "bibcode": "2025GCN.41331....1F",
  "createdOn": 1755019959937,
  "submittedHow": "web"
}