TITLE: GCN CIRCULAR NUMBER: 41087 SUBJECT: GRB 250706B/C: 7DT Follow-up Observations DATE: 25/07/14 06:58:11 GMT FROM: Mankeun Jeong jmk5040@gmail.com
Mankeun Jeong (SNU/SNUARC), Myungshin Im (SNU/SNUARC), Hyeonho Choi (SNU/SNUARC), and Seo-Won Chang (SNU/SNUARC) report on behalf of the 7-Dimensional Telescope collaboration
We observed the field of GRB 250706B/C (Palmerio et al., GCN 40989; Zhu et al., GCN 40991; Frederiks et al., GCN 41013; Longo et al., GCN 41019) using the 7-Dimensional Telescope (7DT). Observations were conducted on 2025 July 8 in multiple broadband and medium-band filters.
We performed forced photometry at the position of the UVOT optical counterpart (GCN 41015; RA = 02:44:53.43, Dec = −50:03:40.2, J2000), using a coadded image from all filters for source detection. Photometric calibration was performed using Gaia XP synthetic photometry (Gaia Collaboration et al. 2022).
We report a marginal detection only in the i-band, with a magnitude of i = 19.68±0.38 AB mag at T-T0 ≈ 1.84 days. The following table lists our photometric measurements (AB magnitudes). For non-detections, we provide 5σ upper limits:
Filter Mag (AB) Exp(s) UT Date-Obs T−T₀ (days) ----------------------------------------------------------------------- g >19.90 300 2025-07-08 07:21:36 1.842 r >19.88 300 2025-07-08 07:26:58 1.846 i 19.68 ± 0.38 1200 2025-07-08 07:38:17 1.841 m400 >18.19 300 2025-07-08 07:27:01 1.846 m450 >18.85 300 2025-07-08 07:21:33 1.842 m475 >18.94 300 2025-07-08 07:26:58 1.846 m550 >18.65 300 2025-07-08 07:21:40 1.842 m575 >18.69 300 2025-07-08 07:27:08 1.846 m600 >18.71 300 2025-07-08 07:21:41 1.842 m625 >18.56 300 2025-07-08 07:27:15 1.846 m650 >18.81 300 2025-07-08 07:21:34 1.842 m675 >18.78 300 2025-07-08 07:26:57 1.846 m700 >18.62 300 2025-07-08 07:21:29 1.841 m725 >18.46 300 2025-07-08 07:26:50 1.846 m750 >18.31 300 2025-07-08 07:21:36 1.842 m775 >17.94 300 2025-07-08 07:26:59 1.846 m800 >17.70 300 2025-07-08 07:21:43 1.842 m825 >17.63 300 2025-07-08 07:27:13 1.846 m850 >17.06 300 2025-07-08 07:21:31 1.842 m875 >16.84 300 2025-07-08 07:21:37 1.842
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