GCN Circular 43270
Subject
GRB251230A: 7DT optical upper limits
Event
Date
2025-12-30T13:38:44Z (a day ago)
From
Donggeun Tak <donggeun.tak@gmail.com>
Via
Web form
Donggeun Tak (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), YoungPyo Hong (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), and Ji Hoon Kim (SNU ARC/SNU) report on behalf of the 7 Dimensional Telescope (7DT) team:
We report optical follow-up observations of GRB251230A (GCN 43252; GCN 43263), conducted with the 7-Dimensional Telescope (7DT), located in Chile.
The 7DT follow-up began at 06:52:54 UTC on 2025-12-30, corresponding to T0 + 5.5 hours, pointing to a region covering the target localization provided by Swift (GCN 43252) at RA, DEC = 179.89760 deg, 11.43870 deg.
Initial observations were made with 12 units in 20 medium-band filters as well as g-, r-, and i-band filters (23 filters in total).
The following table summarizes the derived 5-sigma upper limits:
Filter Mag Mag_err Exposure Date Time
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g >20.04 N/A 300s 2025-12-30T06:49:06.000
r >19.42 N/A 300s 2025-12-30T06:54:28.333
i >18.34 N/A 300s 2025-12-30T06:49:04.000
m400 >18.32 N/A 300s 2025-12-30T06:54:34.667
m425 >18.89 N/A 300s 2025-12-30T06:54:20.000
m450 >18.95 N/A 300s 2025-12-30T06:49:02.667
m475 >19.00 N/A 300s 2025-12-30T06:54:26.000
m500 >19.04 N/A 300s 2025-12-30T06:49:10.667
m525 >18.93 N/A 300s 2025-12-30T06:54:29.000
m550 >18.60 N/A 300s 2025-12-30T06:54:34.000
m575 >18.79 N/A 300s 2025-12-30T06:49:09.667
m600 >18.60 N/A 300s 2025-12-30T06:49:08.667
m625 >18.21 N/A 300s 2025-12-30T06:54:42.667
m650 >18.25 N/A 300s 2025-12-30T06:49:03.000
m675 >18.28 N/A 300s 2025-12-30T06:54:38.333
m700 >18.16 N/A 300s 2025-12-30T06:49:07.000
m725 >17.72 N/A 300s 2025-12-30T06:54:36.333
m750 >17.56 N/A 600s 2025-12-30T06:51:49.833
m775 >17.04 N/A 300s 2025-12-30T06:54:24.667
m800 >16.81 N/A 300s 2025-12-30T06:49:05.667
m825 >16.65 N/A 300s 2025-12-30T06:54:29.667
m850 >16.44 N/A 300s 2025-12-30T06:48:59.000
m875 >15.91 N/A 300s 2025-12-30T06:49:08.000
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No significant transient event was identified in the preliminary result. Preliminary analysis yields 5σ limiting magnitudes in the range of 15.91–20.04 mag depending on sky brightness and airmass.
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/.