GCN Circular 43863
Subject
GRB 260223A: 7DT detection and Medium-band SED of Afterglow
Event
Date
2026-02-27T12:05:22Z (13 days ago)
From
YoungPyo Hong at Seoul National University <evan77333@gmail.com>
Via
Web form
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:
We report optical follow-up observations of GRB26023A (GCN 43808; GCN 43809), conducted with the 7-Dimensional Telescope (7DT), located in Chile.
The 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.
Initial observations were made with 15, units in 19 medium-band filters as well as r-band filters (20 filters in total).
The following table summarizes the observations and the derived 5-sigma upper limits:
Filter Mag Mag_err Exposure Date Time
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r 19.05 0.08 300.0 2026-02-23T04:49:44.000
m400 >19.02 N/A 300.0 2026-02-23T04:44:14.000
m425 19.28 0.16 300.0 2026-02-23T04:44:31.667
m450 19.48 0.24 300.0 2026-02-23T04:44:16.667
m475 18.97 0.12 300.0 2026-02-23T04:44:15.000
m500 19.62 0.27 300.0 2026-02-23T04:44:20.667
m525 19.48 0.24 300.0 2026-02-23T04:44:23.000
m550 >19.29 N/A 300.0 2026-02-23T04:49:38.000
m575 18.95 0.14 300.0 2026-02-23T04:51:58.000
m600 18.92 0.20 300.0 2026-02-23T04:49:39.333
m625 18.79 0.22 300.0 2026-02-23T04:49:37.000
m650 18.66 0.22 300.0 2026-02-23T04:44:38.000
m675 >18.95 N/A 300.0 2026-02-23T04:44:23.000
m700 18.13 0.18 300.0 2026-02-23T04:44:18.000
m725 >18.46 N/A 300.0 2026-02-23T04:44:23.000
m750 18.23 0.22 300.0 2026-02-23T04:44:20.667
m775 17.99 0.31 300.0 2026-02-23T04:44:43.333
m800 >17.52 N/A 300.0 2026-02-23T04:44:21.667
m825 >17.41 N/A 300.0 2026-02-23T04:44:21.333
m850 >17.05 N/A 300.0 2026-02-23T04:44:21.000
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* Upper limits (marked with '>') are 5-sigma limits
The optical counterpart was detected in most filters.
Photometric 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.
The 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/.