Long GRB 260604C detected by SVOM/ECLAIRs with bright optical afterglow and late rebrightening

AI Summary

SVOM/ECLAIRs detected a long-duration gamma-ray burst (GRB 260604C) on 2026-06-04 at 20:21:59 UTC with SNR 8.23 in the 5-20 keV band, also confirmed by Fermi/GBM, GECAM-B, Konus-Wind, and AstroSat/CZTI. The burst showed a multiple-peak light curve with ~255 s duration and peak energy ~551 keV. A bright optical counterpart was rapidly identified by MASTER, LAST, and other ground-based telescopes, with initial magnitude ~16.4 AB and subsequent decay. Notably, multi-wavelength follow-up observations revealed a late rebrightening episode ~30 hours post-trigger lasting ~30 hours, confirmed by GRANDMA and CFHT/MegaCam observations through 2026-06-10.

Measurements

Notices (1)

SVOM — GRB · Thu, 04 Jun 2026 20:20:37 GMT

GCN Circulars (28)

GCN-44952 — GRB 260604C · Tue, 16 Jun 2026 13:14:53 GMT
Astronomers conducted follow-up observations of the Gamma-Ray Burst GRB 260604C using the Canada-France-Hawaii Telescope, confirming the end of a rebrightening episode on 2026-06-10. The data, aligned with previous GRANDMA measurements, was made publicly available on the Skyportal/ICARE platform.

GCN-44887 — GRB 260604C · Tue, 09 Jun 2026 16:52:29 GMT
The Konus-Wind satellite detected a long-duration gamma-ray burst (GRB 260604C) on June 4, 2026, at 20:18:48.568 UT. The burst had a single pulse lasting approximately 8.5 seconds and was observed up to 4 MeV, with significant fluence and peak flux measurements recorded.

GCN-44885 — GRB 260604C · Tue, 09 Jun 2026 13:26:28 GMT
AstroSat's CZTI detector has identified a long gamma-ray burst (GRB 260604C) on June 4, 2026, which was also detected by Fermi/GBM and SVOM/ECLAIRs. The burst was observed in the 20-200 keV and 100-500 keV energy ranges with peak count rates of 1274 counts/s and 3712 counts/s, respectively.

GCN-44883 — GRB 260604C · Tue, 09 Jun 2026 11:58:07 GMT
The SVOM/ECLAIRs team reported a refined analysis of GRB 260604C, a gamma-ray burst with a multiple peak lightcurve and a duration of 255 seconds. The burst was also detected by Fermi/GBM and GECAM-B, and its localization is consistent with the afterglow detected by MASTER OT.

GCN-44877 — GRB 260604C · Mon, 08 Jun 2026 22:27:43 GMT
The optical transient (OT) associated with the long gamma-ray burst GRB 260604C was observed using the Zeiss-1000 1-m telescope at SAO RAS, detecting a brightness of 23.08 +/- 0.18 in the Rc band. This observation is part of a broader follow-up effort involving multiple telescopes and institutions, including Fermi, SVOM, and GECAM-B.

GCN-44873 — GRB 260604C · Mon, 08 Jun 2026 15:49:40 GMT
The GRB 260604C event showed significant reddening between two observation epochs, indicating a change in the source's color over time. Additionally, a late rebrightening phase was confirmed, starting approximately 30 hours after the initial trigger and lasting about 30 hours.

GCN-44872 — GRB 260604C · Mon, 08 Jun 2026 15:20:05 GMT
The SVOM/C-GFT team observed the field of GRB 260604C approximately 19.54 hours after the trigger but did not detect an optical counterpart, setting an upper limit of g > 21.1 AB at a 3-sigma confidence level. The observations were calibrated against the Pan-STARRS1 DR1 catalog without correction for Galactic dust extinction.

GCN-44865 — GRB 260604C · Mon, 08 Jun 2026 09:38:41 GMT
Further observations of GRB 260604C by the GRANDMA network have detected a possible re-brightening in multiple filters, confirmed by various telescopes and aligned with previous reports. The observations are part of the P7 campaign to monitor fast transients.

GCN-44862 — GRB 260604C · Mon, 08 Jun 2026 09:03:44 GMT
Observations of GRB 260604C using the AZT-33IK 1.6-m telescope at the Sayan Solar Observatory revealed a possible brightening of the optical afterglow approximately 2.86 days after the initial gamma-ray burst. The afterglow was detected with a magnitude of 21.18 in the R-band, showing evidence of increased brightness compared to earlier observations.

GCN-44858 — GRB 260604C · Sun, 07 Jun 2026 19:31:45 GMT
The optical afterglow of GRB 260604C was observed using the Zeiss-1000 1-m telescope at the Simeiz Observatory on June 5 and June 6, 2026. The afterglow was detected with magnitudes of 21.35 and 21.53 on these dates, respectively, using an R-filter. The photometry was based on nearby SDSS stars and was not corrected for Galactic extinction.

GCN-44857 — GRB 260604C · Sun, 07 Jun 2026 13:35:13 GMT
The GRANDMA collaboration reported follow-up observations of GRB 260604C using the OPD1.6m telescope, detecting the source in Sloan bands with measured magnitudes ranging from 21.44 to 22.09. The observations were part of the P7 campaign to monitor alerts from explosive fast transients.

GCN-44854 — GRB 260604C · Sun, 07 Jun 2026 12:57:24 GMT
The GECAM-B satellite detected GRB 260604C, a gamma-ray burst with a single pulse lasting approximately 7 seconds, which was also observed by Fermi/GBM and SVOM/ECLAIRs. The burst's position was determined by SVOM/ECLAIRs, and its spectrum was best fitted by a power law with an exponential high-energy cutoff, indicating significant high-energy emission.

GCN-44853 — GRB 260604C · Sun, 07 Jun 2026 10:22:39 GMT
The Very Large Array (VLA) observed the field of GRB 260604C at 6 GHz, 38 hours after it was detected by Fermi-GBM and SVOM, but no radio source was found at the optical transient position. Further observations are planned to continue monitoring the event.

GCN-44851 — GRB 260604C · Sat, 06 Jun 2026 17:16:35 GMT
GRANDMA conducted follow-up observations of GRB 260604C, detecting its optical afterglow at multiple epochs. The data, corrected for Galactic extinction, is available on the Skyportal/ICARE public site, confirming previous reports and contributing to multi-messenger astrophysics studies.

GCN-44844 — GRB 260604C · Fri, 05 Jun 2026 21:22:48 GMT
The SVOM mission team observed the field of GRB 260604C using the LCO 1m telescope at the South African Astronomical Observatory but did not detect an optical counterpart, setting an upper limit of r > 21.8 AB magnitude.

GCN-44843 — GRB 260604C · Fri, 05 Jun 2026 14:01:06 GMT
The Liverpool Telescope detected the optical counterpart of GRB 260604C approximately 3.92 hours after the burst, measuring an AB magnitude of r = 18.60 ± 0.05 in the SDSS r filter. The observations were calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction.

GCN-44837 — GRB 260604C · Fri, 05 Jun 2026 09:47:43 GMT
The Gravitational-wave Optical Transient Observer (GOTO) detected the optical afterglow of GRB 260604C, initially discovered by Fermi/GBM and SVOM, with observations taken in the GOTO-L filter. The optical counterpart was detected in three epochs, with magnitudes calibrated using ATLAS-REFCAT2.

GCN-44836 — GRB 260604C · Fri, 05 Jun 2026 08:46:15 GMT
The GRB 260604C alert issued a correction to previously reported photometry data, which was listed in reverse order. The corrected photometry data shows the optical counterpart candidate's magnitude increasing over time.

GCN-44835 — GRB 260604C · Fri, 05 Jun 2026 08:27:06 GMT
The GRANDMA/Kilonova-Catcher collaboration detected the optical afterglow of GRB 260604C using telescopes in Chile and the USA, confirming the presence of an optical counterpart to the gamma-ray burst. Observations were conducted with CDK17 telescopes and various filters, providing crucial data for understanding the event's characteristics.

GCN-44834 — GRB 260604C · Fri, 05 Jun 2026 04:19:38 GMT
The optical counterpart of GRB 260604C was observed using the COLIBRÍ telescope, revealing preliminary magnitudes in various filters and a temporal decay index of -1.2. The data suggest a low-redshift event, with further analysis ongoing to confirm the nature of the burst.

GCN-44832 — GRB 260604C · Fri, 05 Jun 2026 02:52:57 GMT
Astronomical alert: GRB 260604C: Jinshan optical observations

GCN-44831 — GRB 260604C · Fri, 05 Jun 2026 02:49:32 GMT
Astronomical alert: GRB 260604C: Fermi GBM Observation

GCN-44828 — GRB 260604C · Thu, 04 Jun 2026 23:52:38 GMT
The Large Array Survey Telescope (LAST) detected an optical counterpart candidate for GRB 260604C, which was initially detected by Fermi-GBM and SVOM. The transient, identified as AT 2026ofi, showed rapid decay consistent with afterglow emission, and observations were conducted over four epochs with clear band filters.

GCN-44827 — GRB 260604C · Thu, 04 Jun 2026 22:45:21 GMT
Astronomical alert: GRB 260604C: MASTER OT J145749.59+284903.0 optical counterpart discovery

GCN-44826 — GRB 260604C · Thu, 04 Jun 2026 21:20:24 GMT
The Fermi GRB 260604C was detected and observed by the MASTER-Tavrida and MASTER-Kislovodsk robotic telescopes, with the former starting observations 68 seconds after the notice time and the latter 2607 seconds later. The observations provided upper limits on the magnitude of the event, with the highest upper limit being 19.9 mag.

GCN-44825 — GRB 260604C · Thu, 04 Jun 2026 21:18:02 GMT
The MASTER-Net telescopes in Russia began observing the error box of the Fermi GRB 260604C within minutes of the trigger, with the MASTER-Tavrida telescope starting 68 seconds after the notice and the MASTER-Kislovodsk telescope starting 2607 seconds after the notice. The observations did not detect any optical transient, setting upper limits on the magnitude.

GCN-44823 — GRB 260604C · Thu, 04 Jun 2026 20:43:09 GMT
The SVOM mission detected a long gamma-ray burst, GRB 260604C, on June 4, 2026, at 20:21:59 UTC. The burst was located at R.A. 14h57m23s and Dec. 28d39m20s with a 90% confidence level radius of 9.6 arcmin, and was also detected by Fermi/GBM. The burst was significant with a signal-to-noise ratio of 8.23 in the 5-20 keV energy band over 163.84 seconds.

GCN-44822 — GRB 260604C · Thu, 04 Jun 2026 20:31:01 GMT
The Fermi Gamma-ray Burst Monitor (GBM) detected a likely long gamma-ray burst (GRB 260604C) on June 4, 2026, at 20:18:44 UT. The event was located at RA = 220.5, Dec = 33.4 (J2000) with a statistical uncertainty of 1.0 degrees.