Long GRB 260511B detected by Fermi/GBM and SVOM with optical counterpart at z=2.006

AI Summary

A long-duration gamma-ray burst (GRB 260511B) was detected on 2026-05-11 at 11:00:31 UTC by Fermi/GBM (trigger 800190036) and SVOM/ECLAIRs, with a T90 duration of ~41 seconds and peak energy of 209 keV. The burst exhibited two distinct emission episodes with fluence of 2.48×10⁻⁵ erg/cm² (Konus-Wind). An optical counterpart was rapidly identified at RA=192.57°, Dec=4.06° with redshift z=2.006, showing initial magnitude r≈15.56 and fading to r≈21.33 by 34 hours post-trigger. Multi-wavelength follow-up observations from ground and space-based facilities (NuSTAR, AstroSat CZTI, Einstein Probe, and numerous optical telescopes) confirmed the afterglow with consistent decay properties (α≈-1.3).

Measurements

Notices (1)

Fermi GBM — GRB · Mon, 11 May 2026 11:00:31 GMT

GCN Circulars (29)

GCN-44618 — GRB 260511B · Fri, 15 May 2026 16:42:48 GMT
The optical counterpart of GRB 260511B was observed using the Nordic Optical Telescope, with a detected magnitude of r = 21.33 AB at 34.337 hours after the trigger. The observations were calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction.

GCN-44615 — GRB 260511B · Fri, 15 May 2026 04:58:07 GMT
The GMG-2.4m telescope at the Lijiang Observatory observed the field of GRB 260511B approximately 73.74 hours after its detection, but did not detect an optical counterpart. The observation, conducted in the r-band, set a 5-sigma upper limit magnitude of 21.6.

GCN-44610 — GRB 260511B · Thu, 14 May 2026 15:51:44 GMT
The Mephisto telescope conducted multi-band optical observations of GRB 260511B, detecting the optical counterpart approximately 1.2 days after the SVOM/ECLAIRs trigger. The preliminary photometry results are consistent with previous observations, providing valuable data for understanding the afterglow of this gamma-ray burst.

GCN-44600 — GRB 260511B · Wed, 13 May 2026 22:29:56 GMT
The GRB 260511B, initially detected by multiple observatories including Fermi and SVOM, was observed using the Zeiss-1000 telescope at SAO RAS. The optical transient associated with the GRB was detected with a brightness of 21.49 in the Rc band on May 13, 2026, providing further data for analysis.

GCN-44597 — GRB 260511B · Wed, 13 May 2026 12:12:06 GMT
The Konus-Wind instrument detected the long-duration gamma-ray burst GRB 260511B, which exhibited two distinct multipeaked episodes and a total duration of approximately 43.4 seconds. The burst's spectrum and energy release parameters were analyzed, confirming its alignment with known GRB relations.

GCN-44593 — GRB 260511B · Wed, 13 May 2026 02:15:50 GMT
The SYSU 80 cm infrared telescope detected the afterglow of GRB 260511B in the J-band, with a redshift of z=2.006. Observations were conducted over several hours, providing photometric data calibrated against nearby stars from the 2MASS catalog.

GCN-44592 — GRB 260511B · Wed, 13 May 2026 00:24:14 GMT
The Calapai Observatory in Massa S. Giorgio, Italy, detected the optical transient (OT) of GRB 260511B approximately 10.40 hours after the burst using a 14-inch Schmidt-Cassegrain telescope. The OT was observed at a magnitude of 18.85 with clear skies and good visibility conditions, consistent with other reported observations.

GCN-44582 — GRB 260511B · Tue, 12 May 2026 15:32:19 GMT
The GRB 260511B was observed by multiple telescopes, including the Zeiss-1000 and 1m telescope of the SAO RAS, starting approximately 8.14 hours after the initial trigger. The optical transient (OT) was detected in various filters (B, V, Rc, Ic) with measured magnitudes ranging from 18.50 to 19.56, providing preliminary photometry based on nearby SDSS stars.

GCN-44580 — GRB 260511B · Tue, 12 May 2026 13:59:31 GMT
The optical afterglow of GRB 260511B was detected by the FRAM robotic telescope at the Observatorio del Roque de los Muchachos, La Palma, Spain, from T+9.6 hr to T+17.4 hr, showing a fading magnitude from CR = 18.89 +/- 0.10. The observations confirmed a power-law decay consistent with earlier reports, with alpha = 1.39 +/- 0.29.

GCN-44578 — GRB 260511B · Tue, 12 May 2026 12:55:37 GMT
The Einstein Probe (EP) performed a follow-up observation of GRB 260511B, detecting an uncatalogued fading source consistent with optical counterparts reported by SVOM/C-GFT and MITSuME. The source's spectrum was fitted with an absorbed power-law model, revealing significant X-ray emission.

GCN-44577 — GRB 260511B · Tue, 12 May 2026 12:22:26 GMT
The Las Cumbres Observatory (LCO) detected the optical counterpart of the long gamma-ray burst GRB 260511B, which was initially detected by multiple observatories including Fermi GBM, SVOM ECLAIRs, MXT, NuSTAR, and AstroSat. The optical counterpart was observed in SDSS r', g', and i' filters, with magnitudes consistent with other detections, confirming the afterglow of the burst.

GCN-44574 — GRB 260511B · Tue, 12 May 2026 09:48:43 GMT
The SVOM/ECLAIRs GRB 260511B was observed using the LCO 1m telescope at Cerro Tololo Observatory, detecting an optical counterpart with magnitudes r = 19.68 +/- 0.02 AB and z = 19.71 +/- 0.09 AB. This observation, part of a follow-up study, confirms the detection of the gamma-ray burst by multiple facilities including Fermi/GBM, NuSTAR, and AstroSat.

GCN-44573 — GRB 260511B · Tue, 12 May 2026 09:05:55 GMT
Spectroscopic observations of the optical counterpart of GRB 260511B were conducted using the T193cm telescope at Observatoire de Haute-Provence, detecting the host environment at a redshift of z=2.007. The observations confirmed the presence of FeII lines at a consistent redshift, providing valuable data on the host galaxy of the gamma-ray burst.

GCN-44572 — GRB 260511B · Tue, 12 May 2026 08:15:30 GMT
The Gravitational-wave Optical Transient Observer (GOTO) detected the optical counterpart of GRB 260511B, confirming previous reports with a magnitude of 19.45 in the L-band. Observations were conducted in response to triggers from Fermi/GBM and SVOM/ECLAIRs, starting approximately 10.13 hours post-trigger.

GCN-44571 — GRB 260511B · Tue, 12 May 2026 07:55:07 GMT
The optical counterpart of GRB 260511B was observed using the NAOC 2.16m telescope at Xinglong observatory, confirming a redshift of approximately 2.006 through absorption features of multiple ions. An additional feature at a redshift of 1.435 was identified, possibly due to an intervening system.

GCN-44568 — GRB 260511B · Tue, 12 May 2026 04:28:34 GMT
The SVOM/VT telescope detected the afterglow of GRB 260511B in both VT_B and VT_R bands, with measurements taken approximately 3.45 and 10.159 hours post-trigger, showing a fading slope of about -1.3. The afterglow was also detected by multiple other observatories, including Fermi-GBM, AstroSat, and NuSTAR.

GCN-44567 — GRB 260511B · Tue, 12 May 2026 04:22:36 GMT
The SVOM/COLIBRÍ telescope detected an optical counterpart to GRB 260511B, with preliminary magnitudes of r = 19.99 and z = 19.67, approximately 16 hours after the initial trigger. The source showed an optical decay temporal index of alpha ≈ -1.3, indicating a significant decrease in brightness over time.

GCN-44565 — GRB 260511B · Mon, 11 May 2026 23:06:28 GMT
The optical counterpart of GRB 260511B was observed using the Gran Telescopio Canarias (GTC) with the OSIRIS+ instrument, revealing a redshift of 2.006. The spectrum showed multiple metal absorption features, indicating the presence of various elements at this redshift.

GCN-44561 — GRB 260511B · Mon, 11 May 2026 17:39:26 GMT
The GROWTH-India Telescope observed the optical counterpart of GRB 260511B, detected by Fermi, in the SDSS r', g', and i' filters approximately 5.32 hours after the trigger. The observations, calibrated against PanSTARRS DR1, detected the optical transient with magnitudes of 18.27 +/- 0.05 in r', 18.54 +/- 0.06 in g', and 18.10 +/- 0.10 in i', consistent with other reported observations.

GCN-44560 — GRB 260511B · Mon, 11 May 2026 17:32:28 GMT
A long gamma-ray burst, GRB 260511B, was detected by AstroSat CZTI and confirmed by multiple other observatories including Fermi/GBM, SVOM/ECLAIRs, and NuSTAR. The burst showed multiple emission peaks with significant count rates in both the 20-200 keV and 100-500 keV energy ranges.

GCN-44557 — GRB 260511B · Mon, 11 May 2026 16:10:48 GMT
The SYSU 80 cm infrared telescope detected GRB 260511B in the J-band, measuring a magnitude of 16.02 Vega mag. The observations, starting 2.9 hours after the GRB trigger, were calibrated against nearby stars from the 2MASS catalog.

GCN-44556 — GRB 260511B · Mon, 11 May 2026 16:08:21 GMT
The NuSTAR SINGS working group detected prompt emission from the long-duration GRB 260511B, which was also observed by Fermi/GBM and SVOM. The detection includes an initial faint burst followed by a 20-second brighter burst, with a peak count rate of approximately 2500 counts per second.

GCN-44554 — GRB 260511B · Mon, 11 May 2026 15:37:39 GMT
On May 11, 2026, the Fermi Gamma-ray Burst Monitor (GBM) detected GRB 260511B, a gamma-ray burst with a duration of 41 seconds and significant emission episodes. The event was also detected by SVOM/ECLAIRs, MXT, and C-GFT, with preliminary spectral analysis indicating a peak energy of 209 keV.

GCN-44552 — GRB 260511B · Mon, 11 May 2026 15:08:48 GMT
The SVOM satellite detected a gamma-ray burst (GRB 260511B) on May 11, 2026, and captured optical images using the SVOM/VT instrument. The optical transient was clearly detected with a magnitude of 17.83 in the VT_B filter, providing valuable data for further analysis.

GCN-44551 — GRB 260511B · Mon, 11 May 2026 14:21:35 GMT
The field of GRB 260511B, detected by SVOM and Fermi, was observed using the 0.7-m telescope of the Thai Robotic Telescope network in Australia, revealing an optical counterpart with a brightness of R = 16.82 at 1.875 hours post-burst. The detection was calibrated with Pan-STARRS DR2 stars and not corrected for Galactic extinction.

GCN-44549 — GRB 260511B · Mon, 11 May 2026 13:40:52 GMT
The MITSuME 50-cm telescope Akeno detected an optical afterglow candidate for GRB 260511B, observed 11.4 minutes after the trigger, with preliminary magnitudes reported in g', Rc, and Ic bands. The detection is near the position reported by SVOM/ECLAIRs, providing crucial data for further analysis of the gamma-ray burst event.

GCN-44547 — GRB 260511B · Mon, 11 May 2026 13:03:12 GMT
An optical counterpart to GRB 260511B was detected by the SVOM/C-GFT telescope approximately 0.48 hours after the initial burst. The source, located at R.A. 12h50m17.63s and Dec. +04d03m18.4s, has a magnitude of 15.56 in the r-band and is proposed as the optical counterpart of the gamma-ray burst.

GCN-44543 — GRB 260511B · Mon, 11 May 2026 11:25:44 GMT
The SVOM mission detected a gamma-ray burst, GRB 260511B, on May 11, 2026, at 11:00:32 UTC. The burst was also detected by Fermi/GM and exhibited a multiple peak structure with a T90 duration of about 41.2 seconds. The SVOM/MXT instrument identified an uncatalogued X-ray source associated with the burst.

GCN-44542 — GRB 260511B · Mon, 11 May 2026 11:10:56 GMT
On May 11, 2026, the Fermi Gamma-ray Burst Monitor detected a likely long gamma-ray burst (GRB 260511B) at 11:00:31 UT. The event was localized to RA = 192.2, Dec = 5.0 with a statistical uncertainty of 1.4 degrees.