TITLE: GCN CIRCULAR NUMBER: 44930 SUBJECT: GRB 260610B / AT2026owq: GRANDMA optical observations DATE: 26/06/13 13:50:34 GMT FROM: Dalya Akl at New York University Abu Dhabi <dka2010@nyu.edu> D. Akl (NYUAD), M. Mašek (FZU), R. Hanna (IJCLAB), P. Putsathan (KKU), Y. Rajabov (UBAI), S. Antier (IJCLAB), P. Hello (IJCLAB), M. Coughlin (UNM), S. Karpov (FZU), M. Pillas (IAP), C. Douzet (IJCLAB), A. Simon (TShNU of Kyiv), D. Rusanova (TShNU of Kyiv), V. Vasylenko (NC JASU), O. Burkhonov (UBAI), S. Ehgamberdiev (UBAI), Y. Tillayev (UBAI), P. Put (NARIT), K. Noysena (NARIT), M. Tanasan (CMU/NARIT), D. Turpin (CEA-Saclay/Irfu), M. Freeberg (KNC), A. Klotz (IRAP), C. Limonta (OCA), A. Dupin (OCA), Q. André (OCA), M. Molham (NRIAG), E. Elhosseiny (NRIAG), A. Takey (NRIAG), N. Kochiashvili (AbAO), R. Inasaridze (AbAO), V. Zhuzhunadze (AbAO) on behalf of the GRANDMA collaboration: We observed the field of the Fermi Long GRB 260610B (Fermi GBM team, GCN 44901). The observations started at 16:29:50 UTC on the 11 of June 2026, 0.7 days post the Fermi Trigger. We detected the optical afterglow candidate, reported by GOTO (O'Neill et al, GCN 44903), in several epochs, using TRT-SRO in California state, UBAI-NT60, UBAI-AZT-22 at Madainak Observatory, AZT-8 at Lisnyky Observatory, KAO-1.88m at Kottamia Astronomical Observatory, TAROT-TCA/TCH at Calern and La Silla, and Kilonova Catcher. A subset of the photometry corrected for Galactic extinction is reported in the public ACME service Skyportal/ICARE https://skyportal-icare.ijclab.in2p3.fr/source/2026owq. To access, one simply needs to create an account using your ORCID ID. The data were reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-Cousins filters were calibrated using the Gaia DR3 Synphot catalog. The observations are performed under the P7 campaign of GRANDMA to monitor SVOM alerts and LSST alerts from explosive fast transients filtered by BOOM/Babamul and FINK. The results are consistent with other measurements reported (Zhu et al., GCN 44909; Akl et al., GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918; Jackson-Horne et al., GCN 44919; Li et al., GCN 44921; Bochenek and Perley, GCN 44927; Moskvitin et al., GCN 44929) GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/44930. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...