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GCN Circular 39129

Subject
GRB 250129A: 7DT Detection and Medium-band SED of Afterglow
Date
2025-02-03T06:14:53Z (8 days ago)
From
Gregory Paek at Seoul National University <gregorypaek94@gmail.com>
Via
Web form
Gregory S.H. Paek (IfA, SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Hyeonho Choi (SNU ARC/SNU), Donggeun Tak (SNU ARC/SNU), Seo-Won Chang (SNU ARC/SNU), and Ji Hoon Kim (SNU ARC/SNU) report on behalf of the 7-Dimensional Telescope collaboration

We detected the optical counterpart of GRB 250129A using the 7-Dimensional Telescopes (7DT). Approximately 1 hour and 14 minutes following the initial detection by Swift (Swift team, Beardmore et al., GCN #39066Loading...
 
 ), we targeted the localization center provided by Swift/UVOT at RA, Dec = 198.67673 deg, +5.03063 deg with an uncertainty of 1.10 arcseconds. Observations were made with eleven 7DT units in r-band and nineteen medium-band filters, denoted as m400, m425, then through m875, in which the numeric values indicate their central wavelengths in nanometers. Each medium-band filter has a bandwidth of 25nm.

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. The optical counterpart was detected in most filters. However, only marginal detection was observed in m800, m825, m850, and m875. This is based on preliminary photometry, and no extinction correction has been applied. The 5-sigma upper limits (AB) and detections in relevant filters are summarized below.
------
Filter Mag  Mag_err Date-obs[UT]        Exp.time[s] Depth(5sigma) Note
m425   17.3 0.0     2025-01-29T05:59:21 300         19.9
m450   17.2 0.0     2025-01-29T05:53:51 300         19.2
m475   17.2 0.0     2025-01-29T05:59:21 300         19.5
m500   17.2 0.0     2025-01-29T05:53:51 300         20.0
m525   17.2 0.0     2025-01-29T05:59:20 300         20.1
m550   17.0 0.1     2025-01-29T05:53:52 300         18.6
m575   17.0 0.0     2025-01-29T05:59:19 300         18.8
m600   16.9 0.0     2025-01-29T05:53:58 300         19.7
m625   16.9 0.0     2025-01-29T05:59:36 300         19.4
m650   16.9 0.0     2025-01-29T05:53:56 300         19.4
m675   17.1 0.1     2025-01-29T05:59:22 300         19.4
m700   16.9 0.0     2025-01-29T05:53:49 300         19.2
m725   17.0 0.0     2025-01-29T05:59:17 300         18.9
m750   17.0 0.1     2025-01-29T05:53:54 300         18.8
m775   17.0 0.1     2025-01-29T05:59:22 300         18.3
m800                2025-01-29T05:53:59 300         17.8          n/d
m825                2025-01-29T05:59:32 300         17.6          n/d
m850                2025-01-29T05:53:54 300         17.2          n/d
m875                2025-01-29T05:59:15 300         17.1          n/d
r      17.0 0.0     2025-01-29T05:59:07 600         20.9

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 http://gwuniverse.snu.ac.kr/.