TITLE: GCN CIRCULAR NUMBER: 44993 SUBJECT: GRB 260610B/AT2026owq: 1.3m DFOT optical rebrightening detection DATE: 26/06/19 10:18:21 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180@gmail.com> Anshika Gupta, Divyanshu Janghel, Debalina kar, Pankaj Pawar, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of GRB 260610B/AT 2026owq discovered by Fermi (The Fermi GBM team, GCN 44901; Godwin and Meegan; GCN 44931; Yu et al., GCN 44944)) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2026-06-15 at 16:53:40 UT, i.e., ~ 4.71 days after the Fermi trigger (GCN 44901). We have taken multiple frames with an exposure time of 300 s in the R and I filter. We stacked the images after the alignment. We detect a optical afterglow in our stacked image. We obtain the following preliminary magnitude in the stacked image: Date Mid_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================= 2026-06-15 17:24:09.406 ~4.73 R 300s*12 20.88 +/-0.05 The optical detection of the burst is consistent with O'Neill et al., GCN 44903; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCN 44910; Akl et al., GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918; Jackson-Horne et al., GCN 44919; Izzo, GCN 44920; Li et al., GCN 44921; Bochenek and Perley, GCN 44927; Moskvitin et al., GCN 44929; Akl et al., GCN 44930; Bochenek & Perley, GCN 44932; Pankov et al., GCN 44946; Gillanders et al., GCN 44955; Angulo et al., GCN 44958; Dimple et al., GCN 44959; Moskvitin et al., GCN 44963; Pankov et al., GCN 44977; Gassert et al., GCN 44981. The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the Gaia DR3 Synphot catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/44993. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...