GCN Circular 44914
Subject
GRB 260610B: optical counterpart shows spectroscopic redshift of z=0.473
Event
Date
2026-06-11T13:44:50Z (2 days ago)
From
Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk>
Via
email
D. O'Neill, J. Mills, M. Pursiainen, T. Killestein, D. B. Malesani, B. P. Gompertz, J. Lyman, R. Starling, K. Ackley, M. Dyer, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson and A. Kumar report on behalf of the GOTO collaboration.
We observed GOTO26fua/AT2026owq (O'Neill et al., GCN Circ. 44903, Watson et al., GCN Circ. 44905, Zhu et al. GCN Circ 44909, Gillanders et al. GCN Circ 44910, Akl et al. GCN Circ 44911), the optical counterpart of GRB 260610B (Fermi GBM team, GCN Circ. 44891), with the Alhambra Faint Object Spectrograph (ALFOSC) mounted on the Nordic Optical Telescope (NOT) as part of the GOTO Fast Analysis and Spectroscopy of Transients program (GOTO-FAST; Godson et al., AstroNote 2023-224).
We obtained spectroscopy with ALFOSC, 2x900s total with grism #4, starting at 2026-06-10 02:10:00 (+2.5h post-trigger). We identify Mg II and Ca II absorption features at a common redshift of z=0.473, which we suggest to be the redshift of GRB 260610B.
We also obtained multi-colour photometry starting at 2026-06-11 02:35 (+2.8h post-trigger)
| MJD | T - T0 (hours) | Filter | AB mag |
|------------ |---------------- |---------- |-------- |
| 61202.1079 | 2.81 | g | 18.85 |
| 61202.1090 | 2.84 | r | 18.40 |
| 61202.1100 | 2.87 | i | 18.14 |
| 61202.1111 | 2.90 | z | 17.92 |
| 61202.1264 | 3.27 | g | 19.00 |
| 61202.1275 | 3.29 | r | 18.49 |
| 61202.1285 | 3.31 | i | 18.25 |
| 61202.1296 | 3.34 | z | 18.04 |
Magnitudes are reported in the AB system, calibrated against SDSS DR16 photometry, and are not corrected for foreground Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).