GRB 261011A: Long-duration gamma-ray burst at z=2.407 with bright optical afterglow

AI Summary

SVOM/ECLAIRs detected a long-duration gamma-ray burst (GRB 261011A) on 2026-10-11 at 13:49:04 UTC with T90~67 seconds, also confirmed by Swift/BAT, GECAM-B, and Konus-Wind. The burst was localized to RA=21.90°, Dec=-21.54° with a bright optical counterpart detected by multiple ground-based facilities within minutes. Spectroscopic observations with the Gran Telescopio Canarias determined a redshift of z=2.407, placing the source at cosmological distance. The optical afterglow showed rapid fading from r~19.5 mag at ~0.65 hours post-trigger to non-detection at J>19.6 mag by ~28 hours, consistent with standard GRB afterglow decay.

Measurements

Notices (1)

SVOM — GRB · Sun, 11 Oct 2026 13:56:38 GMT

GCN Circulars (28)

GCN-45942 — GRB 261011A · Tue, 13 Oct 2026 13:41:51 GMT
The Sun Yat-sen University 80 cm infrared telescope conducted J-band observations of GRB 261011A and did not detect the source at the position of the counterpart, setting a 5-sigma upper limit of J > 19.6 mag (Vega). This observation was made 27.85–29.91 hours after the Swift/BAT trigger, providing later-epoch data on the gamma-ray burst.

GCN-45939 — GRB 261011A · Tue, 13 Oct 2026 12:29:42 GMT
The GECAM-B satellite detected a gamma-ray burst, GRB 261011A, on October 11, 2026, at 13:49:15.250 UTC, which was also observed by other satellites including SVOM/ECLAIRs, Swift/BAT, and Konus-Wind. The burst exhibited multiple pulses with a duration of approximately 40 seconds.

GCN-45934 — GRB 261011A · Tue, 13 Oct 2026 07:14:45 GMT
The Swift-XRT team has refined the analysis of GRB 261011A, providing a precise position and detailed light curve modeling. The event shows a series of power-law decays with significant absorption, indicating a complex afterglow behavior.

GCN-45933 — GRB 261011A · Tue, 13 Oct 2026 07:11:07 GMT
The Swift-XRT team has reported an enhanced position for the gamma-ray burst GRB 261011A, with coordinates RA (J2000): 01 27 35.33, Dec (J2000): -21 33 37.9 and an uncertainty of 2.9 arcsec. This position is based on 1938 seconds of XRT Photon Counting mode data and 4 UVOT images, and may be further refined with additional data.

GCN-45931 — GRB 261011A · Tue, 13 Oct 2026 05:21:34 GMT
The optical afterglow of GRB 261011A was observed using the Gran Telescopio Canarias, revealing a spectroscopic redshift of z = 2.407. This confirms the tentative redshift derived from previous observations and identifies a likely host galaxy candidate.

GCN-45930 — GRB 261011A · Tue, 13 Oct 2026 00:39:46 GMT
The Swift-BAT team has refined the analysis of GRB 261011A, determining its position at RA, Dec = 21.911, -21.550 deg with a 1.0 arcmin uncertainty. The event showed a multi-peaked light curve and was best fit by a simple power-law model, with a fluence of 6.3 +- 0.3 x 10^-06 erg/cm2 in the 15-150 keV band.

GCN-45926 — GRB 261011A · Mon, 12 Oct 2026 17:05:52 GMT
The REM 60 cm robotic telescope at the ESO observatory of La Silla observed the field of GRB 261011A, detected by Swift/BAT and SVOM/ECLAIRs, but did not detect the optical/NIR counterpart down to 3-sigma limits of r > 20.6 (AB) and K > 14.2 (Vega). Observations began approximately 11.7 hours after the burst and lasted for about 2 hours.

GCN-45924 — GRB 261011A · Mon, 12 Oct 2026 15:15:46 GMT
The Konus-Wind spacecraft detected a long-duration gamma-ray burst, GRB 261011A, on October 12, 2026, at 13:49:07 UT. The burst showed a significant increase in count rate and was also detected by SVOM and Swift spacecraft, with a total fluence of 1.30 x 10^-5 erg/cm^2 and a peak energy flux of 4.63 x 10^-7 erg/cm^2/s.

GCN-45922 — GRB 261011A · Mon, 12 Oct 2026 12:56:33 GMT
The SOAR telescope observed the afterglow of GRB 261011A approximately 17 hours after the initial detection by Swift/BAT, refining its position and measuring its brightness in g, r, and z filters. The afterglow was detected at RA, Dec (J2000) = 01:27:35.40, -21:33:37.7 with magnitudes g = 23.93, r = 22.75, and z = 22.43.

GCN-45920 — GRB 261011A · Mon, 12 Oct 2026 07:37:55 GMT
Observations of GRB 261011A using the X-Shooter spectrograph on the ESO VLT UT3 telescope detected a faint continuum emission, setting a redshift upper limit of z<3.7 and suggesting a tentative redshift of z=2.405. This redshift information is crucial for understanding the distance and environment of the gamma-ray burst.

GCN-45917 — GRB 261011A · Mon, 12 Oct 2026 03:31:32 GMT
An optical afterglow candidate for the gamma-ray burst GRB 261011A was detected by the MITSuME 50-cm telescope Akeno, with preliminary magnitudes of Rc=16.5 and Ic=16.2, observed 580 seconds after the Swift/BAT trigger. This detection is significant as it provides crucial data for studying the afterglow properties of the gamma-ray burst.

GCN-45916 — GRB 261011A · Mon, 12 Oct 2026 03:09:29 GMT
The Sichuan South Observatory (SSO) in China detected the optical counterpart of Gamma-Ray Burst (GRB) 261011A using a 60cm telescope, confirming previous observations by Swift-UVOT and other facilities. The preliminary photometry in the L band showed a fading optical transient with magnitudes ranging from 19.67 to 20.66 over approximately 2.40 hours.

GCN-45915 — GRB 261011A · Mon, 12 Oct 2026 01:58:20 GMT
The GMG-2.4m telescope at the Lijiang Observatory detected the optical counterpart of GRB 261011A in the r-band with a magnitude of 20.46 ± 0.04, approximately 2.92 hours after the initial trigger. This observation confirms the detection reported by Swift-UVOT and other facilities, providing additional data for the study of this gamma-ray burst.

GCN-45914 — GRB 261011A · Mon, 12 Oct 2026 00:58:10 GMT
The Liverpool Telescope detected an optical counterpart to the gamma-ray burst GRB 261011A approximately 9.36 hours after the initial Swift trigger, with tentative g-band and confirmed r-band detections. The photometry measurements provide insights into the afterglow of the gamma-ray burst, aiding in the study of these high-energy astrophysical events.

GCN-45913 — GRB 261011A · Mon, 12 Oct 2026 00:22:24 GMT
The SYSU 80cm infrared telescope detected the near-infrared afterglow of GRB 261011A in the J-band, approximately 2.68–3.35 hours after the Swift/BAT trigger, showing a decline of 0.58 mag between two observation epochs. This detection confirms the presence of an optical counterpart and provides valuable data for studying the afterglow of this gamma-ray burst.

GCN-45909 — GRB 261011A · Sun, 11 Oct 2026 20:09:17 GMT
The afterglow of GRB261011A was observed using the Sinistro instrument on the 1-m telescope of the LCO network, detecting a faint optical counterpart with preliminary magnitudes of g = 21.91 +/- 0.17 mag and r = 21.09 +/- 0.14 (AB). This observation is part of a larger collaborative effort to study the afterglow of the gamma-ray burst.

GCN-45907 — GRB 261011A · Sun, 11 Oct 2026 19:15:24 GMT
The GROWTH-India Telescope detected the optical counterpart of GRB 261011A, a gamma-ray burst initially detected by SWIFT, with a magnitude of 20.93 in the SDSS r' filter. The observation, consistent with other optical detections, was made 3.565 hours after the burst and calibrated against PanSTARRS DR1.

GCN-45906 — GRB 261011A · Sun, 11 Oct 2026 18:53:04 GMT
A 28cm optical telescope in Chengde, China, observed the field of GRB 261011A approximately 0.78 hours after its detection by Swift/BAT and SVOM/ECLAIRs, finding no significant source at the reported optical counterpart position, with a 5-sigma upper limit of L > 19.65 mag. This non-detection is consistent with the reported fading behavior of the optical counterpart.

GCN-45905 — GRB 261011A · Sun, 11 Oct 2026 17:46:58 GMT
The MASTER-SAAO robotic telescope in South Africa observed the error box of the Swift GRB 261011A 13,752 seconds after the trigger, with an upper limit magnitude of 18.0 in the clear filter. The observations began at twilight with a zenith distance of 67 degrees and a sun altitude of -11.5 degrees, and the galactic coordinates were b = -79 degrees and l = 181 degrees.

GCN-45904 — GRB 261011A · Sun, 11 Oct 2026 16:42:15 GMT
The Kinder collaboration conducted multi-band optical follow-up observations of GRB 261011A, detected by SVOM and Swift, using the 1m Lulin One-meter Telescope and the 40cm Seisi Lulin Telescope. The optical counterpart was clearly detected in g-, r-, and i-bands, with preliminary measurements indicating a relatively red (g-r) color but a flatter (r-i) color.

GCN-45903 — GRB 261011A · Sun, 11 Oct 2026 16:07:29 GMT
The SVOM/C-GFT telescope detected an optical candidate for GRB 261011A approximately 3.87 minutes after the initial trigger, with a magnitude of 15.25 in the i-band. This detection was part of a coordinated effort involving multiple observatories and instruments, contributing to the ongoing study of gamma-ray bursts.

GCN-45901 — GRB 261011A · Sun, 11 Oct 2026 15:53:31 GMT
The SVOM/ECLAIRs GRB 261011A was observed using the LCO 1m telescope at Siding Spring Observatory, detecting an optical counterpart with magnitudes r = 19.87 and z = 17.52 AB. These observations provide crucial data for understanding the afterglow and properties of the gamma-ray burst.

GCN-45900 — GRB 261011A · Sun, 11 Oct 2026 15:46:41 GMT
The SVOM satellite detected a gamma-ray burst (GRB 261011A) and performed an automatic slew to observe the event. The SVOM/VT instrument confirmed the detection of an optical counterpart, providing preliminary magnitude measurements in both VT_R and VT_B filters.

GCN-45899 — GRB 261011A · Sun, 11 Oct 2026 15:39:30 GMT
The field of GRB 261011A was observed with the Sinistro instrument on the 1-m telescope of the LCO network, detecting a bright optical afterglow with preliminary magnitudes of g = 20.01 +/- 0.02 mag and r = 19.47 +/- 0.02 (AB). This detection is consistent with previous reports from Swift-UVOT and other ground-based facilities.

GCN-45898 — GRB 261011A · Sun, 11 Oct 2026 14:55:20 GMT
The optical afterglow of GRB 261011A was detected by the Thai Robotic Telescope network (TRT) at a magnitude of approximately 19.1 in the Sloan r-band, 37.6 minutes after the Swift trigger. This detection follows the initial identification of the gamma-ray burst by SVOM and Swift.

GCN-45897 — GRB 261011A · Sun, 11 Oct 2026 14:26:21 GMT
The GOTO collaboration detected an optical counterpart to the gamma-ray burst GRB 261011A, with a magnitude of 16.32 AB mag, approximately 0.11 hours post-trigger. No pre-trigger detection was found, confirming the transient nature of the event.

GCN-45896 — GRB 261011A · Sun, 11 Oct 2026 14:20:50 GMT
The Swift Burst Alert Telescope (BAT) detected an unusual gamma-ray burst, GRB 261011A, with a broad soft pulse and a short peak structure, lasting approximately 260 seconds. The burst was detected at RA, Dec 21.925, -21.529 with a candidate afterglow identified by the UVOT.

GCN-45895 — GRB 261011A · Sun, 11 Oct 2026 14:20:12 GMT
The SVOM mission detected a long, bright gamma-ray burst, GRB 261011A, on October 11, 2026, at 13:49:04 UTC. The burst, which had a T90 duration of approximately 66.77 seconds, was observed by multiple instruments onboard the SVOM satellite, including ECLAIRs and GRM, and an X-ray source was identified by the MXT instrument.