GCN Circular 38658

Gregory S.H. Paek (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Hyeonho Choi (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 searched for the optical counterpart of the GRB, GRB241113A (Siegel et al., GCN #38194
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 ) using the 7-Dimensional Telescopes (7DT). Approximately 18.8 hours following the initial detection (2024-11-13T07:48:13 UTC), we targeted the localization center provided by the Swift UVOT at RA, Dec = 16.56518 deg, -22.67177 deg with an uncertainty of 0.7 arcsecs. Observations were made with eleven 7DT units in twenty 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. 

No significant transient event was identified in the preliminary result. Photometric flux calibration was performed using synthetic photometries derived from the Gaia DR3 XP catalog (Gaia Collaboration et al. 2022) within the AB magnitude system. The 5-sigma upper limits (AB) range from 16.8 to 19.0 mag in the medium-band filters. To improve the depth for detection, we combined all images taken with the medium-band filters from m400 to m875. The combined image was treated as an r-band equivalent, and photometric measurements were performed. This approach yielded a 5-sigma upper limit of 19.7 AB magnitudes. Despite the increased depth, no significant transient detection was identified. Observations were conducted under suboptimal conditions, potentially limiting our search sensitivity.
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Filter Date-obs[UT] Exp.time[s] Depth(5sigma)
m400 2024-11-14T02:42:18 300 18.526
m425 2024-11-14T02:42:16 300 18.738
m450 2024-11-14T02:36:44 300 18.467
m475 2024-11-14T02:42:15 300 18.638
m500 2024-11-14T02:36:43 300 18.849
m525 2024-11-14T02:42:11 300 18.995
m550 2024-11-14T02:36:47 300 18.534
m575 2024-11-14T02:42:16 300 18.614
m600 2024-11-14T02:36:50 300 18.560
m625 2024-11-14T02:42:26 300 18.515
m650 2024-11-14T02:36:47 300 18.248
m675 2024-11-14T02:42:15 300 18.171
m700 2024-11-14T02:36:46 300 18.075
m725 2024-11-14T02:42:15 300 17.918
m750 2024-11-14T02:36:45 300 17.930
m775 2024-11-14T02:42:16 300 17.723
m800 2024-11-14T02:35:00 600 17.669
m825 2024-11-14T02:40:32 600 17.552
m850 2024-11-14T02:36:47 300 16.957
m875 2024-11-14T02:36:47 300 16.841

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/.