GRB 261029A
GCN Circular 46117
Subject
GRB 261029A: SVOM/ECLAIRs refined analysis
Date
2026-10-30T21:20:44Z (2 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Brunet, O. Godet, J.-L. Atteia (IRAP), A. Coleiro (APC), Y. Liang (PMO), Z. Liu (GZNU) report on behalf of the SVOM/ECLAIRs team
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 261029A (SVOM burst-id sb29102901 – Goto et al., GCN 261029A, trigger time T0 = 2026-10-29T01:27:07 UTC), which was also detected by Fermi/GBM (Fermi GBM team, GCN 46071, and Scotton et al., GCN 46098), Fermi/LAT (Longo et al., GCN 46085), AstroSat/CZTI (Salunke et al., GCN 46089), CALET Gamma Ray Burst Monitor (Marrocchesi et al. GCN 46095), SVOM/GRM (Yu et al., GCN 46096), NuSTAR (Waratkar et al., GCN 46100), GECAM-B (Yu et al., GCN 46108) and Glowbug (Cheung et al., GCN 46112).
The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = 47.5 +1.0/-0.9 s in the 4-120 keV energy band.
The refined burst localization is RA, Dec = 8.827, 34.533 degrees :
RA (J2000) = 00h35m18.5s
Dec (J2000) = 34d31m58.8s
with a 90% C.L. radius of 2.31 arcmin (including systematic error of 2 arcmin added in quadrature).
This position is 2.01 arcmin from the afterglow position determined by GOTO (O’Neill et al., GCN 46073).
The time-averaged spectrum from T0-0.15s s to T0+47.34s s in the 5-120 keV energy range is best fitted by a powerlaw + blackbody model (chi²/dof = 40/26 ). The photon index is alpha = -1.10 +/-0.03 and the blackbody temperature is 1.42 +/-0.17 keV. With this model, the 4-120 keV fluence is (2.34+/-0.04)e-5 erg/cm^2 and the 4-120 keV photon flux is 10.4 +/- 0.1 ph/cm^2/s.
Using a simple powerlaw does not give a good fit (chi²/dof = 83.8/28).
All the quoted errors are at the 68% confidence level.
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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC.
The SVOM/ECLAIRs point of contact for this burst is: M. Brunet (IRAP) (marius.brunet at utoulouse.fr)
GCN Circular 46113
Subject
GRB 261029A / AT 2026ahaw: Optical upper limits from the PKU 60cm Telescope
Date
2026-10-30T15:02:52Z (2 days ago)
From
Y.C. Kang at Peking University <yckang@stu.pku.edu.cn>
Via
Web form
Yacheng Kang (PKU), Fengkai Wan (PKU), Xinmiao Zhao (PKU), and Fangzhou Ren (PKU) report on behalf of the PKU HiTF (High-energy Transients Follow-up) group:
We observed the field of GRB 261029A, triggered by Fermi/GBM (Fermi GBM team, GCN 46071; T0 = 2026-10-29T01:27:03) and SVOM/ECLAIRs (Goto et al., GCN 46072), using the PKU 60cm telescope at Xinglong Observatory, NAOC. Observations in the r and i bands were obtained approximately 1.4 days after the Fermi/GBM trigger.
No significant optical counterpart is detected in the stacked r- and i-band images at the reported position of the optical/infrared counterpart (O'Neill et al., GCN 46073; He et al., GCN 46078; Wang et al. GCN 46079; De et al., GCN 46080; Cotter et al., GCN 46081; Álvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090; Ma et al., GCN 46092; De et al., GCN 46093; Novotny et al., GCN 46097; Zhao et al., GCN 46099; Dimple et al., GCN 46101; Novotny et al., GCN 46102; Rodríguez-Torres et al., GCN 46103; Hua et al., GCN 46104; Yin et al., GCN 46109). We derive 3-sigma upper limits of r > 22.14 mag and i > 21.48 mag. Preliminary photometry was calibrated against nearby Pan-STARRS field stars. The reported limits are approximate AB magnitudes and have not been corrected for Galactic extinction.
The observation log is summarized below following the time sequence:
| Date | Start_UT | T_mid - T0 (days) | Filter | Exposure (s) | 3-sigma Upper Limit |
|---|---|---|---|---|---|
| 2026-10-30 | 10:50:60 | 1.43 | r | 9 * 600 | > 22.14 |
| 2026-10-30 | 12:36:48 | 1.50 | i | 9 * 600 | > 21.48 |
Further optical follow-up observations are encouraged.
The PKU 60cm Telescope is operated by the Department of Astronomy, Peking University. The PKU HiTF group is dedicated to rapid follow-up observations of high-energy transients.
GCN Circular 46112
Subject
GRB 261029A: Glowbug gamma-ray detection
Date
2026-10-30T14:45:24Z (2 days ago)
From
C.C. Cheung at Naval Research Lab <Teddy.Cheung@nrl.navy.mil>
Via
Web form
C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:
The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, confirms the detection of GRB 261029A, which was detected by Fermi/GBM (GCN 46071, 46098), SVOM (GCN 46072, 46096), Fermi/LAT (GCN 46085), AstroSat/CZTI (GCN 46089), CALET (GCN 46095), NuSTAR (GCN 46100), and GECAM-B (GCN 46108).
Taking the CALET (GCN 46095) trigger time, T0 = 2026-10-29 01:27:33.19, Glowbug detects the bright multi-peaked emission from ~T0+2s to +10s. The detection occurred during a time of high background as Glowbug was in the northern radiation belt. Earlier emission may be present at lower significances.
The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.
Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC.
[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular 46109
Subject
GRB 261029A : SVOM/GWAC-F60 observations
Date
2026-10-30T09:02:16Z (2 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
S.J. Yin (GXU), C. Wu, L.P. Xin, X.H. Han, P.P. Zhang, J.L. Wang (NAOC), Y.Y. Shi, Y.X. Guan, E.W. Liang, X.G. Wang(GXU) report on behalf of the SVOM follow-up team:
We observed the field of GRB261029A detected by SVOM/ECLAIRs (Goto et al., GCN 46072), with the GWAC-F60 at Xinglong Observatory, China. F60 started observing at 2026-10-29T10:41:58.75 UTC in R-band.
The optical counterpart (O'Neill et al., GCN 46073; He et al., GCN 46078; Wang et al., GCN 46079; De et al., GCN 46080; Cotter et al., GCN 46081; Sanchez Alvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090; Ma et al., GCN 46092; De et al., GCN 46093; Novotny et al., GCN 46097; Zhao et al., GCN 46099; Dimple et al., GCN 46101; and Novotny et al., GCN 46102; Rodríguez-Torres et al., GCN 46103;Hua et al., GCN 46104) is detected in our images by F60A. We measure the following magnitudes calibrated against the NOMAD catalog, and not corrected for Galactic extinction:
R = 19.67+/- 0.2 mag (mid-time 9.32 hr after the trigger);
Two 60cm GWAC-F60(A/B) are operated by Guangxi University and NAOC, CAS, at Xinglong Observatory, China. The field of view is 19*19 arcmin.
GCN Circular 46108
Subject
GRB 261029A: GECAM-B detection of a bright burst
Date
2026-10-30T08:00:02Z (2 days ago)
From
yzh807926@163.com
Via
Web form
Zheng-Hang Yu, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by a burst GRB 261029A at 2026-10-29T01:27:04.300 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #46071), SVOM/ECLAIRs (Hatsune Goto et al., GCN #46072), CALET (P. S. Marrocchesi., GCN #46095) and SVOM/GRM (Yu et al., GCN #46096). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 40.0 +/-0.6 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn/gcn/2026/10/gecambgrb261029A.png
The time-averaged spectrum from T0-5.0 to T0+50.0 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is 1.05 +0.04/-0.05 and the cutoff energy, parameterized as Epeak, is 914 +88/-81 keV. The event fluence (10-1000 keV) in this time interval is (1.09 +/-0.01) E-04 erg/cm^2.
With the measured redshift z=3.27 (L. Cotter et al., GCN 46081), we calculate the isotropic energy Eiso is about 3.6E54 erg. Thus GRB 261029A is well consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn/gcn/2026/10/gecambgrb261029A_amati.png
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN Circular 46104
Subject
GRB 261029A: WFST optical observations
Date
2026-10-30T02:41:48Z (3 days ago)
From
ylhua@pmo.ac.cn
Via
Web form
Yan-Long Hua, Jin-Jun Geng, Tian-Rui Sun, Bin-Yang Liu, Ye Li, Yi-Fang Liang, Ding-Fang Hu, Yuan-Tai Yang, Ji-An Jiang, and Xue-Feng Wu report on behalf of the WFST team:
Following the detection of GRB261029A by Fermi GBM (Fermi GBM Team
, GCN 46071) and SVOM/ECLAIRs (Goto et al., GCN 46072), we performed follow-up observations using the Wide Field Survey Telescope (WFST Collaboration; arXiv:2306.07590) at the Lenghu Astronomical Observation Base in Qinghai Province, China. Observations in the g/i/r bands began at 2026-10-29T12:26:03, approximately 10.98 hours after the trigger.
We clearly detect the optical counterpart (O'Neill et al. GCN 46073; He et al. GCN 46078; Wang et al. GCN 46079; Cotter et al. GCN 46081; Álvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090; Ma et al., GCN 46092.; De et al., GCN 46093) in the images. The g-band photometry result is presented in the following :
MJD | exposure time (s) | band | mag (AB)
-------------|-------------------|------|---------------
61342.56469907407 | 120 | g | 20.73+/-0.02
We thank the WFST staff for supporting these observations.
GCN Circular 46103
Subject
GRB 261029A: ULL-ASTRO-MASTER observations with LCO 1-m telescope at Siding Spring Observatory
Date
2026-10-30T00:09:44Z (3 days ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
L. Rodríguez-Torres, S. Abad Gómez, K.N. Alvez Báez, G. de la Mata Núñez, J. Díaz-Miguel Font, A. Fernández-Roselló, L. García Rodríguez, S. M. Holtham, R. Jiménez Rioja, H. Morín-González, L. Ortega-Barcenilla, C. Pasamontes-Duarte, M. Ríos-Jiménez, S.J. Riquelme-Salinas, A. Rosendo Pato, E. Ruiz-Laguna, I. Ruiz-Pérez, D. Zazo-Callejas (all ULL), S. R. Berlanas (IAC and ULL), and I. Pérez-Fournon (IAC and ULL)
We report on observations of the long GRB 261029A detected by Fermi GBM (Fermi GBM team, GCN 46071; and Scotton et al., GCN 46098), SVOM/ECLAIRs (Goto et al., GCN 46072), Fermi-LAT (Longo et al., GCN 46085), EP-FXT (Kan et al., GCN 46086), AstroSat CZTI (Salunke et al., GCN 46089), the CALET Gamma-ray Burst Monitor (Marrocchesi et al., GCN 46095), and NuSTAR (Waratkar et al., GCN 46100) at a redshift of z = 3.27 (Cotter et al., GCN 46081).
We observed the field of GRB 261029A with a Las Cumbres Observatory (LCO) 1-m telescope, equipped with a Sinistro camera, at the LCO node at Siding Spring Observatory, New South Wales, Australia. The observations consisted of 300-sec exposures in each of the SDSS r', i' and g' filters that were obtained at a large airmass. The r´-band observation began on 2026-10-29 at 10:23:26 UT (about 8.94 hr after the Fermi trigger). The optical counterpart first reported by GOTO (O'Neill et al., GCN 46073; AT 2026ahaw, O'Neill et al., TNS Astronomical Transient Report No. 330168 ) is clearly detected in the three images. We measure the following AB magnitudes, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction:
Date (UT, mid-time) | filter | mag | error |
------------------------------------------------------
2026-10-29 10:25:56 r' 19.61 0.05
2026-10-29 10:56:32 i' 19.33 0.07
2026-10-29 11:32:06 g' 20.78 0.10
These results are consistent with other optical and near-IR detections (O'Neill et al., GCN 46073; He et al., GCN 46078; Wang et al., GCN 46079; De et al., GCN 46080; Cotter et al., GCN 46081; Sanchez Alvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090; Ma et al., GCN 46092; De et al., GCN 46093; Novotny et al., GCN 46097; Zhao et al., GCN 46099; Dimple et al., GCN 46101; and Novotny et al., GCN 46102).
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026B-010).
These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain).
This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).
GCN Circular 46102
Subject
GRB 261029A: Ondrejov D50 optical observations, possible rebrightening
Date
2026-10-29T23:20:31Z (3 days ago)
From
Filip Novotný at Masaryk University <filip.novotny@talentovani.cz>
Via
Web form
F. Novotny, J. Strobl, M. Jelinek and R. Hudec (ASU CAS Ondrejov) report:
We observed the field of GRB 261029A (Fermi GBM team, GCN 46071;
Goto et al., GCN 46072) with the D50 robotic telescope of the
Astronomical Institute Ondrejov, near Prague, Czech Republic.
We obtained a long series of 60s Sloan i'-band exposures between
starting at 16:42UT on 2026 October 29 (T0+15.3h or 0.64d);
observations are continuing.
The photometry of combined images (15x60s) suggests there has been a
rebrightening or a flat phase, and that the afterglow reached i~19.6
at 0.75 day post-burst, at which point it starts to be compatible with a
decay again.
Photometry is calibrated in Sloan i' (AB system) against
ATLAS-RefCat2 field stars, not corrected for Galactic extinction
(E(B-V)=0.081 mag).
GCN Circular 46101
Subject
GRB 261029A: Liverpool Telescope observations
Date
2026-10-29T22:44:59Z (3 days ago)
From
Dimple at University of Birmingham <dimplepanchal96@gmail.com>
Via
Web form
Dimple (U. Birmingham), D. O’Neill (U. Birmingham), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud) and B. P. Gompertz (U. Birmingham) report on behalf of a larger collaboration:
We have conducted observations of GRB 261029A, detected by SVOM/ECLAIRs (Goto et al., GCN 46072), with the IO:O optical camera on the 2-m robotic Liverpool Telescope in the u, g, r, i, and z filters starting on 2026-10-29 at 20:11:47 UT (0.790 days after the burst).
We clearly detected the afterglow (O'Neill et al., GCN 46073; He et al., GCN 46078; Wang et al., GCN 46079; De et al., GCN 46080; Cotter et al., GCN 46081; Sanchez Alvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090; Ma et al., GCN 46092; De et al., GCN 46093; Zhao et al., GCN 46099) with magnitude 20.37+/- 0.06 in r-band.
Comparing our r-band magnitude with the previous observations, we estimate a temporal decay index of alpha ~ 1.4. The value is consistent with the late-time decay reported by Novotny et al. (GCN 46097).
Magnitudes are calibrated against nearby Pan-STARRS stars and are not corrected for Galactic extinction.
GCN Circular 46100
Subject
GRB 261029A: NuSTAR detection of bright prompt emission
Date
2026-10-29T18:20:35Z (3 days ago)
From
Gaurav Waratkar at Caltech <gauravwaratkar@iitb.ac.in>
Via
Web form
G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group:
The NuSTAR SINGS working group reports the detection of bright prompt emission from the long-duration GRB 261029A in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper.
The NuSTAR SINGS algorithm triggered at 2026-10-29T01:27:03.81 UTC shows a detection of GRB 261029A, also detected by Fermi-GBM (GCN 46071), SVOM (GCN 46072), Fermi-LAT (GCN 46085), AstroSat-CZTI (GCN 46089), and CALET-GBM (GCN 46095).
The NuSTAR CsI shield data are recorded at 1 Hz. We detect a double-peaked burst lasting for about 40-s. The peak count rate is ~4000-cps with a baseline rate of ~1000-cps during this time period. We also see clear evidence in the signal above 100 keV in the CZT detectors.
The optical counterpart (GCN 46073) at RA = 8.817988, Dec = 34.500138 implies an offset from the NuSTAR boresight of 95-deg and an offset from the geocenter of 71-deg.
Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/261029A
Information on NuSTAR SINGS can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/
NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington.
GCN Circular 46099
Subject
GRB 261029A: Optical detection with 60cm Panzhihua Telescope
Date
2026-10-29T17:36:17Z (3 days ago)
From
Jiewei Zhao at SWIFAR, YNU <meow.jiewei.zhao@gmail.com>
Via
Web form
Jiewei Zhao, Xinchao Wang, Brajesh Kumar, Wenyu Li, Guowang Du, Yuanpei Yang (SWIFAR, YNU), Bin-Bin Zhang, Kamil Nadaf (NJU), Kai Liao, Xinyu Wang, Xing Yao, Yang Zeng and Chunlai Zhang (SSO) report on behalf of a larger collaboration:
We observed the GRB 261029A field detected by Fermi/GBM (Fermi GBM Team, GCN 46071) and SVOM/ECLAIRs (Goto et al., GCN 46072). The observations were initiated at 2026-10-29T13:38:33.40 (~12.19 hours after the trigger) with the 60cm Panzhihua Telescope located at the Sichuan South Observatory (SSO), China. A total of 10 frames with 300s exposure each were acquired in L band.
We clearly detect the optical counterpart (O'Neill et al. GCN 46073; He et al. GCN 46078; Wang et al. GCN 46079; Cotter et al. GCN 46081; Álvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090; Ma et al., GCN 46092.; De et al., GCN 46093) in the stacked image. The L-band photometry result is presented in the following table:
MJD (Exp_Start) MAG FILTER
61342.56844 20.23 +/- 0.15 L
Note that the expected Galactic extinction is not applied in our estimates.
GCN Circular 46098
Subject
GRB 261029A: Fermi GBM Observation
Date
2026-10-29T17:16:12Z (3 days ago)
From
Lorenzo Scotton at UAH <lscottongcn@outlook.com>
Via
Web form
L. Scotton (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 01:27:03.81 UT on 29 October 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 261029A (trigger 814930028/261029060), which was also detected by SVOM (Goto et al. 2026, GCN 46072), Fermi-LAT (Longo et al. 2026, GCN 46085), EP-FXT (Kan et al. 2026, GCN 46086), SVOM/C-GFT (Shi et al. 2026, GCN 46088), AstroSat CZTI (Salunke et al. 2026, GCN 46089), CALET Gamma-Ray Burst Monitor (Marrocchesi et al. 2026, GCN 46095), SVOM/GRM (Yu et al. 2026, GCN 46096).
An optical counterpart is identified by GOTO (ONeill et al. 2026, GCN 46073), TRT (He et al. 2026, GCN 46078), KAIT (Wang et al. 2026, GCN 46079), MDM/MIRAGE (De et al. 2026, GCN 46080), NOT imaging and (Cotter et al. 2026, GCN 46081), LCO (Yin et al. 2026, GCN 46082), SVOM/COLIBRÍ (FM-GFT) (Álvarez et al. 2026, GCN 46083), LCO (Yin et al. 2026, GCN 46084), the PKU 60cm (Kang et al. 2026, GCN 46090), SVOM/VT (Ma et al. 2026, GCN 46092), MDM/MIRAGE (De et al. 2026, GCN 46093).
The redshift of the source is measured to be z = 3.27, NOT imaging and (Cotter et al. 2026, GCN 46081).
The Fermi GBM real-time localization (GCN 46071) is consistent with the SVOM position.
The angle from the Fermi LAT boresight is 69 degrees.
The GBM light curve consists of two emission episodes with a duration (T90) of about 43.8 s (50-300 keV). The time-averaged spectrum from T0-5.9 to T0+86.9 s is best fit by a Band function with Epeak = 621 +/- 7 keV, alpha = -0.85 +/- 0.01, and beta = -2.23 +/- 0.02.
The event fluence (10-1000 keV) in this time interval is (1.100 +/- 0.009)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+39.2 s in the 10-1000 keV band is 34.6 +/- 0.4 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular 46097
Subject
GRB 261029A: FRAM-ORM and FRAM-Auger optical afterglow light curve
Date
2026-10-29T17:15:07Z (3 days ago)
From
Filip Novotný at Masaryk University <filip.novotny@talentovani.cz>
Via
Web form
Filip Novotny, Martin Jelinek and Jan Strobl
(ASU CAS Ondrejov, CZ),
Martin Masek, Sergey Karpov, Petr Janecek, Jakub Jurysek,
Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza
(Institute of Physics, Prague, CZ)
report:
The 25 cm robotic telescope FRAM-ORM at La Palma (Spain) reacted
robotically to the SVOM/ECLAIRs alert of GRB 261029A (Goto et al.,
GCN 46072; Fermi GBM Team, GCN 46071), obtaining a series of
120 x 60 s unfiltered images between 01:38:35 and 03:55:27 UT,
i.e. from ~11.5 min to ~148 min post trigger.
We clearly detect the optical afterglow (O'Neill et al., GCN 46073;
He et al., GCN 46078; Wang et al., GCN 46079; De et al., GCN 46080;
Cotter et al., GCN 46081; Sanchez Alvarez et al., GCN 46083; Yin et
al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090; Ma et
al., GCN 46092) in single images up to ~T0+42 min and in combined
frames thereafter. Forced aperture photometry at the GOTO position
yields, for the first image and the last combined frame:
T-T0[mid] Images Filter Mag (AB)
12.0 min 1 x 60 s CR 13.30 +/- 0.03
138.0 min 18 x 60 s CR 17.42 +/- 0.10
CR denotes unfiltered magnitudes calibrated to the r band.
The 30 cm robotic telescope FRAM-Auger at the Pierre Auger
Observatory (Malargue, Argentina) also reacted to the alert. The
images obtained before 02:53 UT are not usable due to a technical
problem. Combining 14 x 60 s R-band images obtained between 02:57:57
and 03:15:44 UT at an elevation of ~20 deg, we detect the afterglow
with R(Vega) = 16.34 +/- 0.10 at T0+99 min.
A preliminary fit suggests a steeper decay before ~T0+50 min,
followed by a shallower power-law decline, F ~ t^-alpha, with
alpha ~ 1.3. Our late-time magnitudes are consistent with those
reported by NOT, LCO and TRT (Cotter et al., GCN 46081; Yin et al.,
GCN 46084; He et al., GCN 46078).
The photometry was reduced with the PyRT pipeline and is calibrated
against the ATLAS-REFCAT2 catalogue (Tonry et al. 2018, ApJ, 867,
105). It is not corrected for Galactic extinction.
GCN Circular 46096
Subject
GRB 261029A: SVOM/GRM observation of a bright burst
Date
2026-10-29T16:20:14Z (3 days ago)
From
yzh807926@163.com
Via
Web form
SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong(IHEP)
SVOM/ECLAIRs team: Marius Brunet (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 261029A (SVOM trigger reference: sb26102901) at 2026-10-29T01:27:04.500 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #46071), and SVOM/ECLAIRs (Hatsune Goto et al., GCN#46072).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-episodes with a T90 of 43.50 +/-0.60 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn/gcn/2026/10/svgrb261029A.png
In addition, the localization of this burst, as determined by GOTO (RA = 8.817988, Dec = 34.500138, GCN #46073), is located at about 45 degrees from the SVOM optical axis.
With this localization, the time-averaged spectrum from T0-3 to T0+60 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is 0.94 +/-0.02 and the cutoff energy, parameterized as Epeak, is 897 +55/-52 keV. The event fluence (10-1000 keV) in this time interval is (1.15 +/-0.01)E-04 erg/cm^2.
The 1s peak spectrum, measured from T0+38.5 to T0+39.5 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is 0.79 +/-0.03 and the cutoff energy, parameterized as Epeak, is 838 +56/-50 keV. The flux (10-1000 keV) in this time interval is (1.04 +/-0.18)E-05 erg/cm^2/s.
With the measured redshift z=3.275 (L. Cotter et al., GCN 46081), we calculate the isotropic energy Eiso is about 3.84E54 erg. Thus GRB 261029A is well consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn/gcn/2026/10/svgrb261029A_amati.png
The localization of GRB 261029A in the 'Yonetoku' relation diagram is shown at:
https://www.bursthub.cn/gcn/2026/10/svgrb261029A_yonetoku.png
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM/GRM point of contact for this burst is: Zheng-Hang Yu (IHEP) (zhyu@ihep.ac.cn)
GCN Circular 46095
Subject
GRB 261029A: CALET Gamma-Ray Burst Monitor detection
Date
2026-10-29T16:07:41Z (3 days ago)
From
Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>
Via
Web form
P. S. Marrocchesi (U of Siena), A. Yoshida, T. Sakamoto, S. Sugita,
Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA),
Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu,
T. Tamura (Kanagawa U), N. Cannady (GSFC), M. L. Cherry (LSU),
S. Ricciarini (U of Florence),
and the CALET collaboration:
The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 261029A
at 01:27:33.19 UTC on 29 October 2026 (trigger #1477272361;
https://cgbm.calet.jp/cgbm_trigger/flight/1477272361/index.html).
A CGBM Notice was distributed in near real time.
This event was also reported by Fermi GBM (Fermi GBM team, GCN #46071), SVOM (Goto et al., GCN #46072), Fermi-LAT (Longo et al., GCN #46085), AstroSat CZTI (Salunke et al., GCN #46089).
The burst signal was seen by all CGBM detectors.
The burst light curve shows a multi-peaked structure starting
at T-28.9 s, peaking at T+10.1 s, and ending at T+ 11.9 s.
The T90 and T50 durations measured with the SGM data are 32.2 +/- 1.0 s
and 17.6 +/- 0.3 s in the 40-1000 keV band, respectively.
The ground-processed light curve is available at:
https://cgbm.calet.jp/cgbm_trigger/ground/1477272361/
The CALET data used in this analysis were provided by
the Waseda CALET Operation Center located at Waseda University.
GCN Circular 46093
Subject
GRB261029A: Infrared fading detected with MDM/MIRAGE
Date
2026-10-29T15:08:32Z (3 days ago)
From
Kishalay De at Columbia University <kd3038@columbia.edu>
Via
Web form
K. De (Columbia U), S. Manyan (Columbia U), G. Mo (Caltech/Carnegie), V. Karambelkar (Columbia U), D. Schiminovich (Columbia U) report:
We performed a second infrared observation of the field of GRB 261029A detected by Fermi GBM (Fermi GBM Team, GCN 46071), SVOM (Goto et al., GCN 46072), Fermi/LAT (Longo et al., GCN 46085) and AstroSat CZTI (Salunke et al., GCN 46089) in the near-infrared J and Hs band with the MDM InfraRed Astronomy inGaas Experiment (MIRAGE) instrument on the MDM 1.3m telescope.
Optical observations have been reported in O'Neill et al. GCN 46073; He et al. GCN 46078; Wang et al. GCN 46079; Cotter et al. GCN 46081; Álvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090 and Ma et al. GCN 46092.
The second epoch of infrared observations began at 2026-10-27T09:08 (7.5 hours after GRB trigger) in the J band lasting 1080 s, and in the Hs band lasting 1590 s. We clearly detect an infrared source at the reported optical position with J = 18.52 +/- 0.08 AB mag and Hs = 18.76 +/- 0.20 AB mag. Compared to our previous infrared observation at at 1.5 hours after GRB trigger (De et al. GCN 46080), our measurements indicate rapid infrared fading of ~ 2.2 mag in 6 hours.
MIRAGE is a new robotic YJHs-band near infrared imager for the MDM 1.3 m telescope. We thank the Mt Cuba astronomical foundation for supporting development of MIRAGE and MDM Observatory staff for supporting the observations.
GCN Circular 46092
Subject
GRB 261029A: SVOM/VT optical observation
Date
2026-10-29T14:15:17Z (3 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, J. R. Xu, L. J. Chen, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Y. F. Liang (PMO), Z. Y. Liu (GZNU) report on behalf of the SVOM/VT team.
SVOM/VT performed an automatic slew on the burst GRB 261029A (sb26102901) triggered by SVOM/ECLAIRs and SVOM/GRM (Goto et al., GCN 46072). This burst was also detected by Fermi/GBM (Fermi GBM Team, GCN 46071), Fermi/LAT (Longo et al., GCN 46085) and AstroSat CZTI (Salunke et al., GCN 46089). SVOM/VT began observing the field at 2026-10-29T02:12:58 UTC, 45.859 minutes after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X-band data available, the optical counterpart (O'Neill et al. GCN 46073; He et al. GCN 46078; Wang et al. GCN 46079; De et al. GCN 46080; Cotter et al. GCN 46081; Álvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090) within EP/FXT error box (Kan et al., GCN 46086) was detected in both VT_B and VT_R bands. The AB magnitudes are:
mid time (h) | exposure time (s) | band | mag (AB)
-------------|-------------------|------|---------------
0.77 | 50 | VT_B | 16.21+/-0.01
0.77 | 50 | VT_R | 15.41+/-0.01
7.94 | 100 | VT_B | 19.93+/-0.04
7.94 | 100 | VT_R | 19.11+/-0.03
Our photometry was not corrected for Galactic extinction.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 46090
Subject
GRB 261029A / AT2026ahaw: r- and i-band optical follow-up with the PKU 60cm Telescope
Date
2026-10-29T13:32:54Z (3 days ago)
From
Y.C. Kang at Peking University <yckang@stu.pku.edu.cn>
Via
Web form
Yacheng Kang (PKU), Xinmiao Zhao (PKU), and Fangzhou Ren (PKU) report on behalf of the PKU HiTF (High-energy Transients Follow-up) group:
We observed the field of GRB 261029A, triggered by Fermi/GBM (Fermi GBM team, GCN 46071; T0 = 2026-10-29T01:27:03) and SVOM/ECLAIRs (Goto et al., GCN 46072), using the PKU 60cm telescope at Xinglong Observatory, NAOC. Observations were conducted in the r and i bands at approximately 10 hr after the Fermi/GBM trigger.
In the stacked r- and i-band images, we clearly detect the optical counterpart in the difference images at a position consistent with previous GCN reports (O'Neill et al., GCN 46073; He et al., GCN 46078; Wang et al. GCN 46079; De et al., GCN 46080; Cotter et al., GCN 46081; Álvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088). Preliminary photometry is calibrated against nearby Pan-STARRS field stars and reported in the AB magnitude system, without correction for Galactic extinction.
The observation log is summarized below following the time sequence:
| Date | Start_UT | T_mid - T0 (days) | Filter | Exposure (s) | Magnitude (AB) |
|---|---|---|---|---|---|
| 2026-10-29 | 10:57:38.04 | 0.42 | r | 6 * 600 | 19.74 +/- 0.07 |
| 2026-10-29 | 12:02:02.32 | 0.46 | i | 6 * 600 | 19.74 +/- 0.19 |
Further optical follow-up observations are encouraged.
The PKU 60cm Telescope is operated by the Department of Astronomy, Peking University. The PKU HiTF group is dedicated to rapid follow-up observations of high-energy transients.
GCN Circular 46089
Subject
GRB 261029A : AstroSat CZTI detection
Date
2026-10-29T13:26:02Z (3 days ago)
From
ABHINAV GOYAL at Indian Institute of Technology Bombay <abhigoyale2003@gmail.com>
Via
Web form
S. Salunke (IUCAA), Harsha K. H. (IUCAA), A. Goyal (IITB), A. Arya (IITB), S. Puri (IITB), G. Waratkar (Caltech/IITB), V. Bhalerao (IITB), A. Vibhute (IUCAA), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a GRB 261029A which was also detected by Fermi (Fermi GBM team, GCN Circ. 46071), SVOM (Goto et. al., GCN Circ. 46072) and Fermi LAT (Gupta et. al., GCN Circ. 46085).
The source was detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-10-29 01:27:42.65 UTC. The measured peak count rate associated with the burst is 775 (+53, -54) counts/s above the background in the combined data of all four quadrants, with a total of 8463 (+365, -387) counts. The local mean background count rate was 275 (+2, -3) counts/s. We measure a T90 of 38 (+1, -1) s from the cumulative CZT light curve.
The source was also detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.The light curve showed multiple peaks of emission with the strongest peak at 2026-10-29 01:27:42.98 UTC. The measured peak count rate associated with the burst 2526 (+89, -89) counts/s above the background in the combined data of all four quadrants, with a total of 27187 (+557, -595) counts. The local mean background count rate was 624 (+4, -4) counts/s. We measure a T90 of 37 (+1, -1) s from the cumulative Veto light curve.
In the preliminary analysis, we find 1151 Compton events associated with this event.
CZTI data products like interactive and downloadable light curves for this GRB can be found at:
https://astrosat.iucaa.in/cift/cift_products/ET20261029T012733/ET20261029T012733_details.html
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 46088
Subject
GRB 261029A: SVOM/C-GFT optical observations
Date
2026-10-29T12:59:21Z (3 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Y.Y. Shi(GXU), Z. Kang (CHO), 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), Yifang Liang (PMO), Zhiyong Liu (GZNU) report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 261029A detected by SVOM/ECLAIRs (Goto et al., GCN 46072) with LATIOS on SVOM/C-GFT. Observations started at 2026-10-29T10:14:32 UTC, ~8.79 h after the trigger.
The optical counterpart (O'Neill et al. GCN 46073, He et al. GCN 46078, Wang et al. GCN 46079, De et al. GCN 46080, Cotter et al. GCN 46081, Álvarez et al. GCN46083, Yin et al. GCN 46084) was detected in our images of band g, r and i. The magnitude is:
| [date-obs(mid-time)] | Mid_t-T0(h) | exposure time (s) | band | mag (AB) | mag_err |
|---|---|---|---|---|---|
| 2026-10-29T11:03:05 | 9.60 | 4528s | g | 20.86 | +/- 0.33 |
| 2026-10-29T11:13:55 | 9.78 | 4529s | r | 19.44 | +/- 0.12 |
| 2026-10-29T10:52:16 | 9.42 | 4528s | i | 19.41 | +/- 0.11 |
The photometry was calibrated against Pan-STARRS DR1 catalogue and no correction for Galactic dust extinction was applied.
We thank the observation assistants C.-L. Guo and Y.-H. Hao 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 46086
Subject
GRB 261029A: EP-FXT follow-up observation
Date
2026-10-29T09:33:51Z (3 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
C. K. Kan (HKU), D. F. Hu, Y. L. Hua (PMO,CAS), H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of GRB 261029A, detected by SVOM/ECLAIRs (Goto
et al., GCN 46072), at 2026-10-29 02:14:00 (UTC), about 47 minutes after the SVOM/ECLAIRs trigger, with an exposure time of 1936 s.
On-ground analysis of the EP-FXT data identified an uncataloged X-ray source located 4.95 arcmin from the SVOM/ECLAIRs position (Goto et al., GCN 46072), but only 1.67 arcsec from the GOTO optical counterpart candidate (O'Neill et al., GCN 46073). The preliminary results for the X-ray source are as follows:
Source name: EPF_J003516.3+342959
R.A., Decl. (J2000) = 8.8178, 34.4997 deg
Localization error radius = 10 arcsec
0.5-10 keV flux = 2.822e-11 erg/cm^ 2/s
Flux error = 1.28e-12 erg/cm^2/s (1 sigma)
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 46085
Subject
GRB 261029A: Fermi-LAT detection
Date
2026-10-29T08:20:47Z (3 days ago)
From
Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>
Via
Web form
F. Longo (Univ. and INFN, Trieste), T. Nymark (KTH), A. Holzmann Airasca (UniTrento and INFN Bari), and R. Gupta (NASA/GSFC) report on behalf of the Fermi-LAT collaboration:
At 01:27:03 UT on October 29th, 2026, Fermi-LAT detected high-energy emission from GRB 261029A, which was also detected by Fermi-GBM (trigger 814930028/261029060, GCN #46071) and SVOM (GCN #46072). Its optical counterpart was found by GOTO (GCN #46073) at a redshift of z = 3.27 using the NOT (GCN #46081).
The best LAT on-ground location is found to be
RA, Dec = 9.69, 35.52 (J2000)
with an error radius of 0.57 deg (90 % containment, statistical error only).
This was 67 deg from the LAT boresight at the time of the trigger.
The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance.
The photon flux above 100 MeV in the time interval 0 - 120 s after the GBM trigger is (9.4 ± 1.1)E-4 ph/cm2/s. The estimated photon index above 100 MeV is -2.80 ± 0.17. The highest energy photon has an energy of 2.5 GeV and occurs at 44 s after trigger time.
The Fermi-LAT point of contact for this burst is Riccardo Martinelli (riccardo.martinelli@phd.units.it).
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular 46084
Subject
GRB 261029A: LCO optical observations (correction to GCN 46082)
Date
2026-10-29T07:10:42Z (4 days ago)
Edited On
2026-10-29T14:05:56Z (3 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
S.J. Yin(GXU), C. Wu (NAOC), A. Saccardi (CEA/Irfu), L.P. Xin, X.H. Han (NAOC),Hatsune Goto (RIKEN/CEA), Hanrui He (PMO), Clara Plasse (HKU), W.J. Xie (NAOC), Y.F. Liang (PMO), Z.Y. Liu (GZNU), Y.Y. Shi, Y.X. Guan(GXU) report on behalf of the SVOM mission team:
We observed the field of the SVOM/ECLAIRs GRB 261029A (Goto et al., GCN 46072) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument.
Our observation started on 2026-10-29 at 03:34:23.407 UT and we obtained 2x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters.
The optical counterpart (O'Neill et al. GCN 46073, He et al. GCN 46078, Wang et al. GCN 46079, De et al. GCN 46080, Cotter et al. GCN 46081) is detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:
r = 17.25 +/- 0.02 AB (mid-time 2.17 hr after the trigger);
z = 17.34 +/- 0.04 AB (mid-time 2.83 hr after the trigger).
This project is funded by the SVOM collaboration.
GCN Circular 46083
Subject
GRB 261029A: SVOM/COLIBRÍ (FM-GFT) optical observations
Date
2026-10-29T06:40:42Z (4 days ago)
From
Stephane Basa at UAR Pytheas/OHP, LAM <stephane.basa@lam.fr>
Via
Web form
Fredd Sánchez Álvarez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Diego López-Cámara (UNAM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Y.F. Liang (PMO) and Z.Y. Liu (GZNU) report:
We imaged the field of the SVOM GRB 261029A (Fermi GBM team, GCN Circ. 46071, and Goto et al., GCN Circ. 46072) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-10-29 01:45:00.61 to 2026-10-29 05:19:50.52 UTC (from 0.2989 to 3.8794 hours after the trigger) and obtained 24 minutes of exposure in the r filter.
The data were reduced and coadded with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
The source reported by O'Neill et al. (GCN Circ. 46073), He et al. (GCN Circ. 46078), Wang et al. (GCN Circ. 46079), De et al. (GCN Circ. 46080), Cotter et al. (GCN Circ. 46081), Yin et al. (GCN Circ. 46082) is very clearly detected and shows fading.
The preliminary magnitude measured in the first observation, obtained 0.3072 hours after the trigger, is:
r = 14.41 +/- 0.01
Further observations are ongoing.
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 46082
Subject
GRB 261029A: LCO optical observations
Date
2026-10-29T05:57:13Z (4 days ago)
Edited On
2026-10-29T14:06:05Z (3 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
S.J. Yin(GXU), C. Wu (NAOC), A. Saccardi (CEA/Irfu), L.P. Xin X.H. Han (NAOC),Hatsune Goto (RIKEN/CEA), Hanrui He (PMO), Clara Plasse (HKU), W.J. Xie (NAOC), Y.F. Liang (PMO), Z.Y. Liu (GZNU), Y.Y. Shi, Y.X. Guan(GXU) report on behalf of the SVOM mission team:
We observed the field of the SVOM/ECLAIRs GRB 261029A (Goto et al., GCN 46072) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument.
Our observation started on 2026-10-29 at 03:34:23.407 UT and we obtained 3x200 s exposures in the SDSS r and 2x200 s exposures in the Pan-STARRS z filters.
The optical counterpart (O'Neill et al. GCN 46073, He et al. GCN 46078, Wang et al. GCN 46079, De et al. GCN 46080, Cotter et al. GCN 46081) is detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:
r = 17.25 +/- 0.02 AB (mid-time 2.17 hr after the trigger);
z = 17.34 +/- 0.04 AB (mid-time 2.83 hr after the trigger).
This project is funded by the SVOM collaboration.
GCN Circular 46081
Subject
GRB 261029A: NOT imaging and spectroscopic redshift z = 3.27
Date
2026-10-29T05:41:22Z (4 days ago)
Edited On
2026-10-29T14:06:18Z (3 days ago)
From
Laura Cotter at Cornell <laura.cotter@ucdconnect.ie>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Laura Cotter at Cornell <laura.cotter@ucdconnect.ie>
Via
Web form
L. Cotter (Cornell), L. B. He (NAOC), D. O’Neill (Birmingham), D. Xu (NAOC), N. R. Tanvir (Leicester), D. B. Malesani (DAWN/NBI and Radboud), J. An (NAOC) and K. Jhass (Birmingham) report on behalf of a larger collaboration:
We observed the optical and near-infrared counterpart (O’Neill et al., GCN 46073; He et al., GCN 46078; Wang et al., GCN 46079; De et al., GCN 46080) of the Fermi and SVOM GRB 261029A (Fermi GBM team, GCN 46071; Goto et al., GCN 46072) using the Nordic Telescope (NOT) equipped with the ALFOSC imager. Observations began on 2026-10-29 at 02:52:39 UT, approximately 86 min post-trigger. We obtained 3x300 s exposures in the SDSS-r band and 5x200 s exposures in the SDSS-z band. The optical counterpart candidate is well detected in our images; photometry yields the following preliminary magnitudes:
r: 16.61 +/- 0.01 AB at a mid time of 93.5 min post trigger;
z: 16.62 +/- 0.01 AB at a mid time of 114 min post trigger.
Photometry was calibrated against Pan-STARRS DR2 catalog stars and is not corrected for Galactic extinction.
Spectroscopic observations began at 03:53:31 UT consisting of 4x1200 s exposures using grism 4, which covers the wavelength range between 3200 and 9600 Å. Based on a preliminary reduction of the spectra using IRAF, we observe a number of absorption features matching well Lyman delta, gamma, beta, alpha, Si II, O I, C II, Si IV, C IV, Al II, all at a common redshift of z = 3.27, which we consider to be the redshift of GRB 261029A.
GCN Circular 46080
Subject
GRB261029A: Early infrared detection with MDM/MIRAGE
Date
2026-10-29T05:34:18Z (4 days ago)
From
Kishalay De at Columbia University <kd3038@columbia.edu>
Via
Web form
K. De (Columbia U), S. Manyan (Columbia U), G. Mo (Caltech/Carnegie), V. Karambelkar (Columbia U), D. Schiminovich (Columbia U) report:
We observed the field of GRB 261029A detected by Fermi (Fermi GBM Team, GCN 46071) and SVOM (Goto et al., GCN 46072), with a reported optical counterpart candidate from GOTO (O'Neill et al. GCN 46073, He et al. GCN 46078, Wang et al. GCN 46079) in the near-infrared J and Hs band with the MDM InfraRed Astronomy inGaas Experiment (MIRAGE) instrument on the MDM 1.3m telescope.
Observations began at 2026-10-27T03:08 (1.5 hours after GRB trigger) in the J band lasting 1080 s, and in the Hs band lasting 1590 s. We clearly detect a bright infrared source at the reported optical position with J = 16.32 +/- 0.01 AB mag and Hs = 16.45 +/- 0.02 AB mag.
MIRAGE is a new robotic YJHs-band near infrared imager for the MDM 1.3 m telescope. We thank the Mt Cuba astronomical foundation for supporting development of MIRAGE and MDM Observatory staff for supporting the observations.
GCN Circular 46079
Subject
GRB 261029A: KAIT optical observations
Date
2026-10-29T05:03:21Z (4 days ago)
From
wangyun@berkeley.edu
Via
Web form
Yun Wang (UCB), WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of GRB 261029A (Goto et al., GCN 46072; Fermi GBM team, GCN 46071), using the optical counterpart candidate coordinates reported by GOTO (O'Neill et al., GCN 46073), starting at 03:40:13 UT on 2026 October 29, about 2.2 hours after the trigger. We clearly detected the source with a magnitude of 17.15 +/- 0.09 mag in the first 60 s clear (roughly R) filter image, consistent with the observation reported by TRT (He et al., GCN 46078). The object continued fading in our follow-up observations and observations are ongoing.
GCN Circular 46078
Subject
GRB 261029A: TRT optical observations
Date
2026-10-29T04:24:56Z (4 days 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(NAOC), S.Y. Fu(HUST), S.Q. Jiang(NAOC), L. Lei(HUST), X. Liu, D. Xu, Z.P. Zhu (NAOC) report:
We observed the field of GRB 261029A detected by Fermi (Fermi GBM Team, GCN 46071) and potentially also by SVOM (Goto et al., GCN 46072), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT). A series of Johnson R-band frames were obtained.
The previously reported optical counterpart (O'Neill et al., GCN 46073) is clearly detected in our first image with a brightness of R = 17.41 +/- 0.14 at a median time of 2.30 hrs since the Fermi trigger, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction.
Observations are still ongoing.
GCN Circular 46073
Subject
GRB 261029A: GOTO optical counterpart candidate
Date
2026-10-29T02:20:34Z (4 days ago)
Edited On
2026-10-29T14:06:37Z (3 days ago)
From
d.s.oneill@bham.ac.uk
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of d.s.oneill@bham.ac.uk
Via
Web form
D. O'Neill, R. Starling, B. Gompertz, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar, M. Pursiainen, 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 Fermi/GBM alert GRB 261029A (Fermi GBM team, GCN #46071, SVOM/ECLAIRS, Goto et al. GCN #46072).
Observations covering the localisation area began at 2026-10-29 01:32:25 UT, (+0.09h post trigger) and continued through to 2026-10-29 01:46:56 UT (+0.33h post trigger). 23 images were taken, across 3 unique pointings, covering 91.3 sq. deg within the 90% localisation contour. ~40.5% of the total 2D localisation probability was covered, with an average 5-sigma depth of 19.8 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.
A new optical source GOTO26llt/AT2026ahaw is identified within the GBM 90% localisation region with co-ordinates:
RA,DEC (J2000) = 8.817988, 34.500138,
00:35:16.32, +34:30:00.50
This position is 295” from the SVOM position. The source was detected with L = 13.69 ± 0.01 AB mag at 01:39:12 (+0.20h) and faded to L = 14.85±0.01 AB mag at 01:50:10 UTC (+0.386h) . We find no evidence of the source prior to the GRB trigger time in previous GOTO observations 2026-10-28 23:49:04 (-1.63h) down to a depth of >19.34 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 46072
Subject
GRB 261029A: SVOM detection of a burst
Date
2026-10-29T02:02:11Z (4 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Hatsune Goto (RIKEN/CEA), Hanrui He (PMO), Clara Plasse (HKU), Wenjin Xie (NAOC), Yifang Liang (PMO), Zhiyong Liu (GZNU) report on behalf of the SVOM mission team:
At 2026-10-29T01:27:07 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 261029A (SVOM burst-id sb26102901).
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 19 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 58.13 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2026-10-29T01:27:04.
The localization of the best alert is R.A., Dec. 8.8858, 34.5603 degrees:
R.A. (J2000) = 0h35m32.60s
Dec. (J2000) = 34d33m37.05s
with a 90% confidence level (C.L.) radius of 2.40 arcmin (including systematic error of 2 arcmin added in quadrature).
This burst also triggered SVOM/GRM at 2026-10-29T01:27:04.
Detailed analysis results will be reported in future.
This burst is consistent in time and position with Fermi/GBM detection at 01:27:03 UTC (GCN #46071).
SVOM slewed to the burst. At the time of the trigger, MXT was in Earth occultation. Observations performed by SVOM/MXT and SVOM/VT will be reported 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 Yifang Liang: yfliang@pmo.ac.cn.
Please contact the BA by email if you require additional information.
GCN Circular 46071
Subject
GRB 261029A: Fermi GBM Final Real-time Localization
Date
2026-10-29T01:37:40Z (4 days 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 LONG GRB
At 01:27:03 UT on 29 Oct 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 261029A (trigger 814930028.806162 / 261029060).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 12.2, Dec = 32.3 (J2000 degrees, equivalent to J2000 00h 48m, 32d 17'), with a statistical uncertainty of 3.6 degrees.
The angle from the Fermi LAT boresight is 71.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn261029060/quicklook/glg_skymap_all_bn261029060.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/bn261029060/quicklook/glg_healpix_all_bn261029060.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn261029060/quicklook/glg_lc_medres34_bn261029060.gif