{
  "eventId": "GRB 260223A",
  "body": "YoungPyo Hong (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Donggeun Tak (SNU ARC/SNU), Hyeonho Choi (SNU ARC/SNU), Donghwan Hyun (SNU ARC/SNU), Gregory S.H. Paek (IfA, SNU ARC/SNU), Seo-Won Chang (SNU ARC/SNU), Ji Hoon Kim (SNU ARC/SNU), and Won-Hyeong Lee (SNU ARC/SNU), report on behalf of the 7 Dimensional Telescope (7DT) team:\n \nWe report optical follow-up observations of GRB26023A (GCN 43808; GCN 43809), conducted with the 7-Dimensional Telescope (7DT), located in Chile.\n \nThe 7DT follow-up began at 04:44:14 UTC on 2026-02-23, corresponding to T0 + 33 minutes, pointing to a region covering the target localization provided by Fermi (GCN 43808) at RA, DEC = 110.5 deg,  -29.4 deg with an uncertainty of 1.7 degree.\n \nInitial observations were made with 15, units in 19 medium-band filters as well as r-band filters (20 filters in total).\n \nThe following table summarizes the observations and the derived 5-sigma upper limits:\nFilter       Mag          Mag_err      Exposure        Date Time                     \n----------------------------------------------------------------------------------------------------\nr            19.05        0.08         300.0           2026-02-23T04:49:44.000       \nm400         >19.02       N/A          300.0           2026-02-23T04:44:14.000       \nm425         19.28        0.16         300.0           2026-02-23T04:44:31.667       \nm450         19.48        0.24         300.0           2026-02-23T04:44:16.667       \nm475         18.97        0.12         300.0           2026-02-23T04:44:15.000       \nm500         19.62        0.27         300.0           2026-02-23T04:44:20.667       \nm525         19.48        0.24         300.0           2026-02-23T04:44:23.000       \nm550         >19.29       N/A          300.0           2026-02-23T04:49:38.000       \nm575         18.95        0.14         300.0           2026-02-23T04:51:58.000       \nm600         18.92        0.20         300.0           2026-02-23T04:49:39.333       \nm625         18.79        0.22         300.0           2026-02-23T04:49:37.000       \nm650         18.66        0.22         300.0           2026-02-23T04:44:38.000       \nm675         >18.95       N/A          300.0           2026-02-23T04:44:23.000       \nm700         18.13        0.18         300.0           2026-02-23T04:44:18.000       \nm725         >18.46       N/A          300.0           2026-02-23T04:44:23.000       \nm750         18.23        0.22         300.0           2026-02-23T04:44:20.667       \nm775         17.99        0.31         300.0           2026-02-23T04:44:43.333       \nm800         >17.52       N/A          300.0           2026-02-23T04:44:21.667       \nm825         >17.41       N/A          300.0           2026-02-23T04:44:21.333       \nm850         >17.05       N/A          300.0           2026-02-23T04:44:21.000       \n----------------------------------------------------------------------------------------------------\n* Upper limits (marked with '>') are 5-sigma limits\n \nThe optical counterpart was detected in most filters.\n \nPhotometric flux calibration was performed using synthetic photometry based on the Gaia DR3 XP catalog (Gaia Collaboration et al. 2022) within the AB magnitude system. Note that no extinction correction has been applied.\n \nThe 7-Dimensional Telescope (7DT), located in Chile and comprising 20 wide-field telescopes equipped with 40 medium-bandwidth (~25nm) filters, aims to detect optical counterparts of GW sources and conduct the 7-Dimensional Sky Survey (7DS) of the Southern Hemisphere. Further information about the 7DT is available at https://7ds.snu.ac.kr/ and http://gwuniverse.snu.ac.kr/.",
  "subject": "GRB 260223A: 7DT detection and Medium-band SED of Afterglow",
  "createdOn": 1772193922519,
  "format": "text/plain",
  "bibcode": "2026GCN.43863....1H",
  "circularId": 43863,
  "submittedHow": "web",
  "submitter": "YoungPyo Hong at Seoul National University <evan77333@gmail.com>"
}