GRB 260607A
GCN Circular 44876
Subject
GRB 260607A: AT2026ong (GOTO26fqf) is a type-Ia SN
Date
2026-06-08T18:46:23Z (3 hours ago)
From
Daniele Bj ørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
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.
GCN Circular 44875
Subject
GRB 260607A / GOTO26fqf / AT2026ong: COLIBRÍ optical observations
Date
2026-06-08T18:24:05Z (3 hours ago)
From
Massimiliano Lincetto at Aix Marseille Univ, CNRS/IN2P3, CPPM <lincetto@cppm.in2p3.fr>
Via
Web form
Massimiliano Lincetto (CPPM), Leonardo García García (UNAM), Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM) and Antonio de Ugarte Postigo (LAM) report:
We imaged the candidate optical counterpart GOTO26fqf / AT2026ong (Gompertz et al., GCN Circ. 44864) of the Fermi GRB 260607A (Fermi GBM, GCN Circ. 44855) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-08 09:42 to 09:58 UTC (23 hours after the trigger) and obtained 840 seconds of simultaneous exposure in the r/z filters.
The data were reduced and coadded with the COLIBRÍ ASU pipeline and analysed in STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
After subtracting template Pan-STARRS images, we detected the optical counterpart reported by Gompertz et al., GCN Circ. 44864, at preliminary magnitudes of:
r = 19.72 +/- 0.01
z = 20.05 +/- 0.04
The measurement is consistent with a no-evolution scenario with reference to the GOTO measurement taken 14.7h after the trigger. The color r-z = -0.33 indicates a blue object, not consistent with typical GRB afterglows.
We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 44866
Subject
GRB 260607A: TRT optical observations
Date
2026-06-08T10:34:45Z (11 hours ago)
From
L. B. He at NAOC <helb@bao.ac.cn>
Via
Web form
L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), J. An, X. Liu, Z.P. Zhu, S.Q. Jiang, L.B. He, D. Xu (NAOC), S.Y. Fu (HUST) report:
We observed the optical counterpart candidate, AT2026ong, (Gompertz et. al., GCN 44864) of GRB 260607A detected by Fermi GBM (Fermi GBM Team, GCN 44855), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO). A series of frames in the R-band were obtained.
AT2026ong is clearly detected in our stacked image with a brightness of R = 19.2 +/- 0.2 at a median time of ~20.5 hrs post-trigger, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. There is no decay between the GOTO and TRT observations.
The previously reported potential host galaxy of AT2026ong (Gompertz et. al., GCN 44864) has a redshift of z ~ 0.126 from the REGALADE catalog (Tranin et al., 2026).
GCN Circular 44864
Subject
GRB 260607A: GOTO tentative optical counterpart candidate GOTO26fqf / AT2026ong
Date
2026-06-08T09:15:55Z (12 hours ago)
From
Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk>
Via
email
B. P. Gompertz, M. Shrestha, R. Starling, A. Kumar, G. Ramsay, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, D. O'Neill and M. Pursiainen report on behalf of GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to short GRB 260607A (Fermi GBM Team, GCN 44855).
Targeted observations from GOTO-N covering the localisation area began at 2026-06-07 23:38:04 UT, (+10.81h post trigger) and continued through to 2026-06-08 03:49:33 UT (+15.0h post trigger). 260 images were taken, across 11 unique pointings, covering 417.3 sq. deg within the 90% localisation contour. ~82.7% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.5 mag.
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.
We identify one candidate optical counterpart contained within the 90% probability contour:
+--------------------------------------------------------------------------+
| Internal name | IAU name | RA (J2000) | dec (J2000) | AB mag |
+--------------------------------------------------------------------------+
| GOTO26fqf | AT2026ong | 314.468601 | 34.277287 | 19.54 ± 0.10 |
+--------------------------------------------------------------------------+
We find no evidence of this source prior to the GRB trigger time in the previous GOTO epoch, taken at 04:13:23 UT on 2026-06-07 (t0 - 8.6h) to a 3-sigma limiting magnitude of L > 20.1 (AB). We also find no evidence for the source prior to the GRB in the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). Its position is on the 63% probability contour of the GBM localisation map.
GOTO26fqf / AT2026ong was detected in 3 epochs with magnitudes of L = 19.54 ± 0.10 (t0 + 12.1h), L = 19.83 ± 0.14 (t0 + 13.4h) and L = 19.84 ± 0.14 (t0 + 14.7h), which is consistent with a power-law temporal decay with an index of t^[-1.60 ± 0.64]. However, we caution that epochs 2 and 3 are consistent with no evolution. The candidate counterpart is spatially coincident with an extended object in PanSTARRS archival imaging, which we suggest is the host galaxy of the unidentified transient. We are unable to robustly relate GOTO26fqf / AT2026ong to GRB 260607A based on available observations but further follow-up, especially spectroscopic classification, is encouraged.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for 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).
GCN Circular 44856
Subject
GRB 260607A: Fermi GBM Final Real-time Localization (duplicate submission)
Date
2026-06-07T13:01:39Z (a day ago)
Edited On
2026-06-07T13:19:24Z (a day ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>
Via
email
GCN Circular 44855
Subject
GRB 260607A: Fermi GBM Final Real-time Localization
Date
2026-06-07T13:00:13Z (a day ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely SHORT GRB
At 12:49:18 UT on 7 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260607A (trigger 802529363.702736 / 260607534).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 304.2, Dec = 36.5 (J2000 degrees, equivalent to J2000 20h 16m, 36d 30'), with a statistical uncertainty of 7.3 degrees.
The angle from the Fermi LAT boresight is 57.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/quicklook/glg_skymap_all_bn260607534.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/quicklook/glg_healpix_all_bn260607534.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/quicklook/glg_lc_medres34_bn260607534.gif