TITLE: GCN CIRCULAR NUMBER: 44876 SUBJECT: GRB 260607A: AT2026ong (GOTO26fqf) is a type-Ia SN DATE: 26/06/08 18:46:23 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk> G. Corcoran (UCD), L. Izzo (INAF/OAC and DARK/NBI), B. Schneider (LAM), J. An (NAOC), B. P. Gompertz (Birmingham), V. Abril-Melgarejo (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of the Stargate collaboration: We observed the transient AT2026ong (GOTO26fqf; Gompertz et al., GCN 44864; He et al., GCN 44866; Lincetto et al., GCN 44875), proposed to be associated with the Fermi GBM GRB 260607A (Fermi GBM team, GCN 44855) using the ESO Very Large Telescope (VLT) UT3 (Melipal) equipped with the X-shooter telescope. Our spectra cover the wavelength range 3000-25000 AA, and consist of 2 exposures of 600 s each. The observation mid time was 2026 Jun 8.40 UT (20.87 hr after the GRB). In the acquisition image, we measure an AB magnitude r = 19.49 +- 0.03 (calibrated against Pan-STARRS, not corrected for Galactic extinction). The slit also covers the galaxy just east of the transient (Gompertz et al., GCN 44864), its likely host galaxy. From detection of multiple emission (Halpha, [N II], [S II]) and absorption (Ca II, G band) features, we measure for the galaxy a redshift of z = 0.111. The spectrum of the transient reveals a clear continuum with broad undulations across the entire optical range, markedly different from GRB afterglow spectra. Template matching via SNID-SAGE (Stoppa et al. 2026, doi:10.48550/arXiv.2603.28741) indicates a good agreement with a type-Ia SN, at a redshift consistent with the galaxy redshift. GOTO26fqf is thus not related to GRB 260607A and has been now named SN 2026ong. The UVB and VIS spectra of the transient are available via TNS at https://www.wis-tns.org/object/2026ong. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange and Francisco Caceres, for rapidly executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44876. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...