GRB 261011A
GCN Circular 45915
R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, K.-X. Lu and B. Wang (YNAO, CAS) report:
We observed the field of GRB 261011A (Huang et al., GCN 45895; Cenko et al., GCN 45896; T0 at 2026-10-11T13:46:41) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2026-10-11T16:41:50, about 2.92 hours after the trigger.
The optical counterpart reported by Swift-UVOT (Cenko et al., GCN 45896) and by other facilities (O'Neill et al., GCN 45897; Fu et al., GCN 45898; Izzo et al., GCN 45899; Wu et al., GCN 45900; Yin et al., GCN 45901; Shi et al., GCN 45903; Aryan et al., GCN 45904; Arya et al., GCN 45907; Izzo et al., GCN 45909; Huang et al., GCN 45913; Bochenek et al., GCN 45914) was detected in was detected in an r-band image.
The preliminary analysis results are shown as follows:
| Start time [UTC] | Exposure [s] | Tmid-T0 [h] | Filter | AB Magnitude | 5-sigma U.L. |
|---|---|---|---|---|---|
| 2026-10-11 16:41:50.018 | 300 | 2.961 | r | 20.46 ± 0.04 | 22.2 |
The given magnitudes are derived based on calibration against Legacy Survey DR10 field stars, and are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.019 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011).
GCN Circular 45914
A. Bochenek, D. A. Perley (LJMU), report:
We observed the field of GRB 261011A (Huang et al., GCN 45895; Cenko et al., GCN 45896) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x100s exposures in SDSS gr filters, starting at 2026-10-11 23:08:04 UT, approximately 9.36 hours after Swift trigger.
We detect a counterpart in the stacked images, at a position consistent with that reported by Cenko et al. (GCN 45896). Photometry is given below; the g-band detection is tentative.
| MJD (mid) | T_mid-T_0 | Filter | Mag. (AB) |
| ------------ | ------------ | --------- | ------------ |
| 61324.97054 | 9.51 h | g | 22.46 ± 0.29 |
| 61324.98405 | 9.84 h | r | 21.98 ± 0.16 |
The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction.
GCN Circular 45913
Si-Rui Huang, Jin-Ji Li, Zhong-Nan Dong, Jia-Qi Lin, Pu Lin, Yun Shi, Jian-Hong Cao, Hao-Nan Yang, Rui-Chen Gao, Jing-Kai Sun, Hao-Ran Zhang, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team:
We observed the field of GRB 261011A, detected by SVOM/ECLAIRs (Huang et al., GCN 45895) and Swift/BAT (Cenko et al., GCN 45896), using the Sun Yat-sen University (SYSU) 80cm infrared telescope. Our observations were carried out on 2026 Oct 11 from 16:27:30 to 17:07:28 UT, approximately 2.68–3.35 hours after the Swift/BAT trigger, using stacked images in the J band.
We clearly detect the near-infrared afterglow at the position of the previously reported optical counterpart (Cenko et al., GCN 45896; O'Neill et al., GCN 45897). The photometric results are listed below (times refer to the midpoints of the observations):
* **16:37:14 UT (T0 + 2.84 hr):** 58 x 20 s (1160 s total exposure), J = 18.07 +/- 0.07 mag (Vega).
* **16:57:34 UT (T0 + 3.18 hr):** 59 x 20 s (1180 s total exposure), J = 18.65 +/- 0.14 mag (Vega).
The source shows a decline of approximately 0.58 mag between the two epochs.
The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction.
An additional approximately one hour of J-band observations was obtained, and the data are currently being processed.
The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University.
GCN Circular 45909
L. Izzo (INAF-OACn and DARK/NBI) reports on behalf of a larger collaboration:
We continued to observe the afterglow of GRB261011A (Huang et al., GCN #45895; Cenko et al., GCN #45896) with the Sinistro instrument mounted on the 1-m telescope of the LCO network, located at the Sutherland Observatory, South Africa. Observations started on 2026 October 11 at 18:56 UT (5.17 hr after the GRB trigger). We obtained a single image of 300s in the SDSS-g and SDSS-r filters.
The optical counterpart reported by Swift-UVOT (Cenko et al., GCN #45896) and by other ground-based facilities (O'Neill et al., GCN #45897, Fu et al., GCN #45898, Izzo et al., GCN #45899, Wu et al., GCN #45900, Yin et al., GCN #45901, Shi et al., GCN #45903, Aryan et al., GCN #45904, Arya et al., GCN #45907) is faintly detected in both images. We measure preliminary magnitudes of g = 21.91 +/- 0.17 mag and r = 21.09 +/- 0.14 (AB), calibrated against nearby stars from the Pan-STARRS catalog.
This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 101004719.
GCN Circular 45907
R. Arya (IITB), Harshita (IITB), V. Vijaykumar (IITB), S. Patil (IITB), A.P. Saikia (IITB), V. Swain (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of GRB 261011A detected by SWIFT (Cenko et al., GCN 45896), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-10-11 17:11:43 UT, i.e., 3.329 hours after the trigger, and obtained multiple exposures in the SDSS r' filter. We detect the optical counterpart in our images at the position reported by SWIFT-UVOT. The photometric results are as follows:
| MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Magnitude (AB) | Limiting Magnitude (5-sigma) |
|---|---|---|---|---|---|
| 61324.720 | r' | 3.565 | 3x300 | 20.93 +/- 0.10 | 21.15 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
Our results are consistent with other optical observations (O'Neill et al., GCN 45897, Fu et al., GCN 45898, Izzo et al., GCN 45899, Wu et al., GCN 45900, Yin et al., GCN 45901, Shi et al., GCN 45903, and Aryan et al., GCN 45904)
The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.
GCN Circular 45906
Chenxi Bao (PKU), Yacheng Kang (PKU), Xinmiao Zhao (PKU), and Zhuokai Liu (PKU) report on behalf of the Interestar Collaboration and the PKU HiTF (High-energy Transients Follow-up) group:
We observed the field of GRB 261011A, detected by Swift/BAT (Cenko et al., GCN 45896; T0 = 2026-10-11T13:46:41) and SVOM/ECLAIRs (Huang et al, GCN 45895), using a 28cm optical telescope located in Chengde, Hebei, China. The observation began on 2026-10-11 at 14:33:32 UT, approximately 0.78 hr after the Swift/BAT trigger.
We obtained the Luminance-band image with a total exposure time of 1800 s. No significant source is detected at the position of the reported optical counterpart (Cenko et al., GCN 45896; O'Neill et al., GCN 45897; Fu et al., GCN 45898; Izzo et al., GCN 45899; Wu et al., GCN 45900; Yin et al., GCN 45901; Shi et al., GCN 45903; Aryan et al., GCN 45904; Buckley et al., GCN 45905). We derive a 5-sigma upper limit of L > 19.65 mag.
Preliminary photometric calibration was performed using nearby catalogued field stars. The reported limit is an approximate AB-equivalent magnitude and has not been corrected for Galactic extinction. Our non-detection is consistent with the reported fading behavior of the optical counterpart. Further optical follow-up observations are encouraged.
The 28cm optical telescope is operated by the Interestar Collaboration, which contributes to the rapid follow-up of high-energy transients as part of the PKU HiTF group.
GCN Circular 45905
D.Buckley (SAAO),
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya..Kechin, V.Senik, A.Chasovnikov, K.Labsina (Lomonosov MSU)
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
A.Sosnovskij (Lomonosov MSU)
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory)
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
R.Rebolo (The Instituto de Astrofisica de Canarias)
O.Gress, N.Budnev(ISU)
M. Segura, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA)
MASTER-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 261011A ( S. B. Cenko et al., GCN 45896) errorbox 13536 sec after notice time and 13752 sec after trigger time at 2026-10-11 17:35:53 UT, with upper limit up to 18.0 mag. Observations started at twilight. The observations began at zenith distance = 67 deg. The sun altitude is -11.5 deg.
The galactic latitude b = -79 deg., longitude l = 181 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3524824
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
13842 | MASTER-SAAO | C | 180 | 18.0 |
13842 | MASTER-SAAO | C | 180 | 17.8 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html
GCN Circular 45904
A. Aryan, Z.-Y. Chen, T.-W. Chen, W.-J. Hou, Y.-H. Lee (all NCU), A. K. H. Kong (NTHU), S. Yang (HNAS), S. J. Smartt, J. H. Gillanders (both Oxford), A. Sankar.K, K. N.-T. Ho, A. Dutta, M.-H. Lee, C.-S. Lin, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), K. W. Smith, H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report:
As part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86,doi:10.3847/1538-4357/adb428), we conducted multi-band optical follow-up observations of GRB 261011A, detected by SVOM (Huang et al., GCN 45895) and Swift (Cenko et al., GCN 45896).
Imaging was acquired in the g-band using the 1m Lulin One-meter Telescope (LOT), and in the r- and i-bands using the 40cm Seisi Lulin Telescope (SLT). Our observations started at MJD 61324.6155, approximately 0.99 hr after the Swift/BAT trigger.
The optical counterpart reported by Swift/UVOT (Cenko et al., GCN 45896), GOTO (O'Neill et al., GCN 45897), and more instruments (Fu et al., GCN 45898; Izzo et al., GCN 45899; Wu et al., GCN 45900; Yin et al., GCN 45901; Shi et al., GCN 45902) was clearly detected in all three bands.
We used AutoPhOT (Brennan & Fraser 2022, A&A, 667, A62) to perform PSF photometry. Preliminary measurements are as follows:
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude
LOT | g | 61324.6155 | 0.99 | 60 * 1 | 20.47 +/- 0.10
SLT | r | 61324.6157 | 1.04 | 300 * 1 | 19.91 +/- 0.07
SLT | i | 61324.6194 | 1.09 | 300 * 1 | 19.69 +/- 0.07
Using the nearly simultaneous g- and r-band measurements at approximately 1.04 hr after the trigger, and correcting for Galactic foreground extinction, we obtain (g-r) = 0.64 +/- 0.11 mag. Using the earliest r- and i-band measurements, we obtain (r-i) = 0.20 +/- 0.10 mag. Thus, the source shows a relatively red (g-r) colour while remaining considerably flatter between r and i.
The presented magnitudes are calibrated using field stars from the ATLAS-RefCat2 catalog from MAST (Tonry et al. 2018, ApJ, 867, 105) and are not corrected for Galactic foreground extinction of A_g = 0.07, A_r = 0.05 and A_i = 0.04 mag in the direction of the transient (Schlafly & Finkbeiner 2011).
The methodology, details on the Lulin Observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69.
GCN Circular 45903
Y.Y. Shi(GXU), Z. Kang (CHO),S.J. Yin (GXU), C. Wu (NAOC), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC), Massimiliano Lincetto (CPPM), Damien Dornic (CPPM) report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 261011A detected by SVOM/ECLAIRs (Huang et al., GCN 45895) with LATIOS on SVOM/C-GFT. Observations started at 2026-10-11T13:52:56 UTC, ~3.87 min after the trigger.
The optical candidate (Cenko et al., GCN 45896; O'Neill et al., GCN 45897; Fu et al., GCN 45898; Izzo et al., GCN 45899; Wu et al., GCN 45900; Yin et al., GCN 45901) was detected in our images of band i. The magnitude is:
| [date-obs(mid-time)] | Mid_t-T0(min) | exposure time (s) | band | mag (AB) | mag_err |
|---|---|---|---|---|---|
| 2026-10-11T13:53:01 | 3.95 | 10s | i | 15.25 | +/- 0.06 |
The photometry was calibrated against DESI Legacy Imaging Surveys DR10 catalogue and no correction for Galactic dust extinction was applied.
We thank the observation assistants B.-W. Li and H.-X. Xue at Jilin observatory for their excellent support.
The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcmin x 21 arcmin FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.
GCN Circular 45901
S.J. Yin(GXU),J.G. Ducoin(CPPM),D. B. Malesani (DAWN/NBI and Radboud), C. Wu (NAOC), A. Saccardi (CEA/Irfu), L.P. Xin, X.H. Han, P.P. Zhang (NAOC),Y.Y .Shi, Y.X. Guan(GXU), Massimiliano Lincetto (CPPM), Damien Dornic (CPPM) report on behalf of the SVOM mission team:
We observed the field of the SVOM/ECLAIRs GRB 261011A (Huang et al., GCN 45895) with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument.
Our observation started on 2026-10-11 at 14:04:15.8 UT and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters.
The optical counterpart (Cenko et al., GCN 45896, Neill et al., CGN 45897, Fu et al., GCN 45898, Izzo et al., GCN 45899, Wuet al., GCN 45900) is detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:
r = 19.87 +/- 0.02 AB (mid-time 0.96 hr after the trigger);
z = 17.52 +/- 0.02 AB (mid-time 0.34 hr after the trigger).
This project is funded by the SVOM collaboration.
GCN Circular 45900
C. Wu (NAOC), L. P. Xin, Y. L. Qiu (NAOC), J. T. Palmerio (CEA/Irfu), Massimiliano Lincetto (CPPM), Damien Dornic (CPPM), on behalf of the SVOM/VT team.
After the trigger by SVOM/ECLAIRs (sb26101102) at 2026-10-11T13:49:04 UTC(T0), SVOM performed an automatic slew on the burst location ( Huang et al., GCN 45895).
From a preliminary analysis of the 1-bit subimage and source list downloaded via the VHF network, the candidate reported by Swift/UVOT (Cenko et al., GCN 45896), Neill et al. (GCN 45897), Fu et al. (GCN 45898), Izzo et al. (GCN 45899) was clearly detected in VT VHF data. Details are presented below.
This candidate was detected in both VT_R and VT_B. Its magnitudes are:
| date-obs (UTC) | mid-time (t-T0) | exposure | VT_B mag(AB) | VT_R mag(AB) |
|---|---|---|---|---|
| 2026-10-11T13:56:30 | 7.4 min | 6x50 s | 17.27 ± 0.10 | 16.260 ± 0.008 |
| 2026-10-11T14:02:20 | 13.3 min | 6x50 s | 18.13 ± 0.10 | 17.17 ± 0.10 |
Magnitudes were not corrected for Galactic reddening.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 45899
L. Izzo (INAF-OACn and DARK/NBI) reports on behalf of a larger collaboration:
We observed the field of GRB261011A (Cenko et al., GCN #45896) with the Sinistro instrument mounted on the 1-m telescope of the LCO network, located at Siding Spring, Australia. Observations started on 2026 October 11 at 14:25 UT (0.65 hr after the GRB trigger). We obtained a single image of 300s in the SDSS-g and SDSS-r filters.
We detect a bright source consistent with the position of the optical afterglow reported by Swift-UVOT (Cenko et al., GCN #45896) and by other ground-based facilities (O'Neill et al., GCN #45897; Fu et al., GCN #45898). We measure preliminary magnitudes of g = 20.01 +/- 0.02 mag and r = 19.47 +/- 0.02 (AB), calibrated against nearby stars from the Pan-STARRS catalog.
This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 101004719. We also acknowledge the use of the ECSnoopy package by E. Cappellaro.
GCN Circular 45898
S.Y. Fu (HUST), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), J. An, L.B. He, S.Q. Jiang, X. Liu, D. Xu, Z.P. Zhu (NAOC), L. Lei (HUST) report:
We observed the field of GRB 261011A detected by SVOM (Huang et al., GCN 45895) and Swift (Cenko et al., GCN 45896) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT). A series of Sloan r-band frames were obtained.
The optical afterglow is detected at the Swift/UVOT position (Cenko et al., GCN 45896) with r ~ 19.1 at a median time of 37.6 mins after the Swift trigger.
Observations are ongoing.
GCN Circular 45897
D. O'Neill,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 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 the Swift/BAT (Cenko et al. GCN 45896 and SVOM ECLIARS (Huang et al, GCN 45895) alerts for GRB 261011A.
Observations covering the localisation area began at 2026-10-11 13:53:16 UT, (+0.11h post trigger) with an average 5-sigma depth of 21.2 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 (Lyman et al. 2026).
We detect the counterpart reported in Cenko et al. GCN 45896.The source was detected with L = 16.32 ± 0.01 AB mag (+0.11h). We find no evidence of the source prior to the GRB trigger time in previous GOTO observations taken at 2026-10-11 13:40:24 (-0.1h) down to a depth of >20.57 AB mag, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021).
GCN Circular 45896
S. B. Cenko (GSFC), S. D. Barthelmy (GSFC), S. Dichiara (PSU),
R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa),
M. J. Moss (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL),
and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 13:46:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 261011A (trigger=1516664). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 21.925, -21.529 which is
RA(J2000) = 01h 27m 42s
Dec(J2000) = -21d 31' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a broad soft pulse
from T0 to T0+130 sec and a shoulder extending out to T0+260 sec for a total
duration of about 260 sec. The peak count rate was ~8000 counts/sec
(15-350 keV), at ~95 sec after the trigger.
The XRT began observing the field at 13:51:57.1 UT, 315.8 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. We are waiting for the full dataset to detect and localise the
XRT counterpart.
UVOT took a finding chart exposure of nominal 150.000 seconds with the White
filter starting 321 seconds after the BAT trigger. There is a candidate
afterglow in the list of sources generated on-board at
RA(J2000) = 01:27:35.39 = 21.89746
DEC(J2000) = -21:33:37.2 = -21.56032
with a 90%-confidence error radius of about 1.10 arc sec. This position is
145.7 arc sec. from the center of the BAT error circle. The estimated magnitude
is 17.78. No correction has been made for extinction.
The BAT lightcurve is very unusual in that it combines a 260 second long
low energy emission mostly below 50 keV, with a ~5 second short peak
structure around T+95 seconds visible at all energies up the to 100-350 keV band.
Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)
GCN Circular 45895
Yiming Huang (APC), Massimiliano Lincetto (CPPM), Damien Dornic (CPPM), Hui Yang (IRAP), Pierre Maggi (ObAS) report on behalf of the SVOM mission team:
At 2026-10-11T13:49:04 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 261011A (SVOM burst-id sb26101102).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 22 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 90.76 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2026-10-11T13:49:04.
The localization of the best alert is R.A., Dec. 21.9017, -21.5422 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.17 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs light curve showed a multiple peak structure with a T90 duration of about 66.77 (-1.48 +1.35) s.
This burst also triggered SVOM/GRM at 2026-10-11T13:49:07 on a timescale of 1 seconds with an SNR of 7. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 63.09 (-0.74 +0.67) s.
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2026-10-11T13:56:38 UTC, 454 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 21.9074, -21.5577 degrees:
R.A. (J2000) = 1h27m37.79s
Dec. (J2000) = -21d33m27.83s
with a 90% C.L. radius of 60.42 arcseconds.
This location is 0.99 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.
VT began observing the field after the slew. The analysis of the data will be published in a future circular.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.
The Burst Advocate (BA) on shift for this alert is Yiming HUANG: huangym@ihep.ac.cn.
Please contact the BA by email if you require additional information.