GRB 260917B
GCN Circular 45681
Subject
GRB 260917B:: SVOM/ECLAIRs refined analysis
Date
2026-09-21T14:58:07Z (7 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
H. Yang, M. Brunet, O. Godet (IRAP), N. Dagoneau (CEA), K. Liu (USTC), C. Wu (NAOC)
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 260917B (SVOM burst-id sb26091701 – GCN 45606, trigger time T0 = 2026-09-17T03:52:21 UTC).
The burst that triggered ECLAIRs onboard shows a broad bump from T0 - 18 s to T0 + 17 s. The burst duration estimated through the imaging technique is T90 = 35 +/- 6 s in the 4-120 keV energy band.
The time-averaged spectrum from T0 - 18 s to T0 + 17 s in the 5-120 keV energy range is best fitted by a powerlaw model, with alpha = -1.4 +/- 0.1. With this model, the 4-120 keV fluence is (7.4 +/- 0.8)e-7 erg/cm^2 and the 4-120 keV photon flux is (5.7 +/- 0.5)e-1 ph/cm^2/s.
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: Hui Yang (hui.yang at cnrs.fr)
GCN Circular 45631
Subject
GRB 260917B: Mondy optical upper limit
Date
2026-09-18T13:51:45Z (10 days ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. Volnova (IKI), E. Klunko (ISTP), A. Pozanenko (IKI), A. Moskvitin (SAO), N. Pankov (IKI) report on behalf of IKI-GRB-FuN:
We observed the field of the GRB 260917B detected by SVOM/ECLAIRs (sb26091701; He et al., GCN 45606) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting on 17 Sep, 2026, at 19:39 UT (i.e., ~16h after the trigger).
The optical counterpart reported previously by SVOM/COLIBRÍ (Dornic et al., GCN 45607) and observed by other facilities (Ma et al., GCN 45610; Yin et al., GCN 45608; Mohan et al., GCN 45611; Jelinek et al., GCN 45617) is not detected in the stacked frame.
Preliminary photometry and observational details are the following:
Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope
(mid,days) (n*s) (3sigma)
2026-09-17 19:39:51 0.67396 21*120 R n/d n/d 21.5 Mondy/AZT-33IK
The photometry (Vega) is based on several nearby PS1-DR2 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction.
GCN Circular 45625
Subject
GRB 260917B: EP-FXT follow-up observation
Date
2026-09-18T10:20:25Z (11 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Q. J. Huang (PMO, CAS), K. R. Ni (CCNU), T. Wu (AHNU), H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of GRB 260917B, detected by SVOM/ECLAIRs (sb26091701; He et al., GCN 45606), which was also observed in optical by SVOM/COLIBRÍ (Dornic et al., GCN 45607), SVOM/VT (Ma et al., GCN 45610), LCO ( Yin et al., GCN 45608), WINTER (Mohan et al., GCN 45611) and FRAM-Auger (Jelinek et al., GCN 45617). The observation started at 2026-09-17 07:43:08 (UTC), about 3.85 hours after the SVOM/ECLAIRs trigger, with an exposure time of 2985 s.
On-ground analysis of the EP-FXT data found six uncataloged X-ray sources within the SVOM/ECLAIRs error region (He et al., GCN 45606). The position of Source 6 is consistent with that of the optical counterpart candidate (Dornic et al., GCN 45607), and its X-ray flux shows a declining trend. The preliminary results for the X-ray sources are as follows:
Source 1: EPF_J030731.7+252560
R.A., Decl. (J2000) = 46.8822, 25.4332 deg
Localization error radius = 10 arcsec
0.5-10 keV flux = 7.56e-14 erg/cm^ 2/s
Flux error = 2.67e-14 erg/cm^2/s (1 sigma)
Separation = 3.17 arcmin
Source 2: EPF_J030721.6+252434
R.A., Decl. (J2000) = 46.8399, 25.4095 deg
Localization error radius = 10 arcsec
0.5-10 keV flux = 5.91e-14 erg/cm^ 2/s
Flux error = 2.39e-14 erg/cm^2/s (1 sigma)
Separation = 4.64 arcmin
Source 3: EPF_J030705.6+252807
R.A., Decl. (J2000) = 46.7734, 25.4687 deg
Localization error radius = 10 arcsec
0.5-10 keV flux = 5.03e-14 erg/cm^ 2/s
Flux error = 1.58e-14 erg/cm^2/s (1 sigma)
Separation = 5.02 arcmin
Source 4: EPF_J030738.5+252413
R.A., Decl. (J2000) = 46.9105, 25.4035 deg
Localization error radius = 10 arcsec
0.5-10 keV flux = 1.97e-13 erg/cm^ 2/s
Flux error = 4.29e-14 erg/cm^2/s (1 sigma)
Separation = 5.41 arcmin
Source 5: EPF_J030758.4+253204
R.A., Decl. (J2000) = 46.9934, 25.5343 deg
Localization error radius = 10 arcsec
0.5-10 keV flux = 8.03e-14 erg/cm^ 2/s
Flux error = 2.21e-14erg/cm^2/s (1 sigma)
Separation = 7.61 arcmin
Source 6: EPF_J030755.8+253327
R.A., Decl. (J2000) = 46.9823, 25.5576 deg
Localization error radius = 10 arcsec
0.5-10 keV flux = 6.96e-13 erg/cm^ 2/s
Flux error = 1.83e-13 erg/cm^2/s (1 sigma)
Separation = 7.77 arcmin
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 45617
Subject
GRB 260917B: FRAM-Auger optical limits
Date
2026-09-17T23:15:49Z (11 days ago)
From
Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>
Via
email
Martin Jelinek, Jan Strobl and Filip Novotny
(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 30cm robotic telescope FRAM-Auger at the Pierre Auger
Observatory (Cerro Los Leones, Malargue, Argentina) reacted
robotically to the alert of GRB 260917B (He et al., GCN
45606), obtaining a series of R-band images starting at
04:04:32 UT, i.e. ~12 min post trigger, at an elevation of
only 7-9 deg. A second series was obtained about two hours
after the trigger, when the field had risen higher.
We do not detect the optical counterpart reported by Dornic
et al. (GCN 45607), Yin et al. (GCN 45608), Ma et al. (GCN
45610) and Mohan et al. (GCN 45611), neither in single
images nor in the combined frames, with the following
limits:
T-T0[mid] Images Span[s] Limit (Vega)
~17 min 9 630 R_C > 17.0
~116 min 11 767 R_C > 17.9
The photometry is calibrated against the Atlas-REFCAT2
catalogue (Tonry et al. 2018, ApJ, 867, 105) and is not
corrected for Galactic extinction. The early limit implies
that this faint burst was not accompanied by a bright
optical flash or strong flaring activity.
GCN Circular 45611
Subject
GRB 260917B: WINTER J-band observations
Date
2026-09-17T10:21:46Z (12 days ago)
From
tanishk.mohan@iitb.ac.in
Via
Web form
Tanishk Mohan (IITB), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of GRB 260917B (He et al., GCN 45606) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations began on 2026-09-17 at 06:18:01.556 UTC in the J band (2.43 hr after the SVOM/ECLAIRs trigger), consisting of 15*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).
We detect a faint source present at the optical counterpart position (Dornic et al., GCN 45607; Yin et al., GCN 45608; Ma et al., GCN 45610) in our stacked image. We obtain the following magnitude: J = 19.02 +- 0.23 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
GCN Circular 45610
Subject
GRB 260917B: SVOM/VT optical observations
Date
2026-09-17T09:05:04Z (12 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), K. Liu (USTC) report on behalf of the SVOM/VT team.
SVOM/VT performed an automatic slew on the burst GRB 260917B (sb26091701) triggered by SVOM/ECLAIRs (He et al., GCN 45606). SVOM/VT began observing the field at 2026-09-17T05:27:45 UTC, 1.59 hours after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X-band data available, the SVOM/COLIBRÍ optical candidate (Dornic et al., GCN 45607; Yin et al., GCN 45608) was detected in both VT_B and VT_R bands and showed a power law decay with the index of 1.0 during our observation. The AB magnitudes are:
mid time | exposure time | band | mag (AB)
-----------|----------------|------|------------
2.83 h | 22*100 s | VT_B | 22.7+/-0.2
2.85 h | 22*100 s | VT_R | 20.8+/-0.1
Our photometry was not corrected for Galactic extinction.
Given the red VT color (VT_B-VT_R~1.9) of this burst, it is likely at medium redshift (Wang et al., 2020).
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 45608
Subject
GRB 260917B: LCO optical observation
Date
2026-09-17T08:36:34Z (12 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
S. J. Yin (GXU), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), C. Wu (NAOC), Y.X. Guan, Y.Y. Shi(GXU), K. Liu (GXU), report on behalf of the SVOM mission team:
We observed the field of GRB 260917B detected by SVOM/ECLAIRs (He et al., GCN 45606) with the LCO 1m telescope at Teide Observatory equipped with the Sinistro instrument.
Our observation started on 2026-09-17 at 04:53:16 UT (about 1.02 hr after the trigger) and we obtained 6x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters.
The optical candidate (Dornic et al., GCN 45607) is detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:
r = 21.34 +/- 0.11 AB (mid-time 1.24 hr after the trigger).
z = 20.16 +/- 0.14 AB (mid-time 1.16 hr after the trigger).
This project is funded by the SVOM collaboration.
GCN Circular 45607
Subject
GRB 260917B: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
Date
2026-09-17T08:10:04Z (12 days ago)
From
damien dornic <damiendornic@gmail.com>
Via
Web form
Damien Dornic (CPPM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), 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), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Hanrui He (PMO), and Wenjin Xie (NAOC) report:
We imaged the field of the SVOM GRB 260917B (He et al., GCN Circ. 45606) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-09-17 05:24:09 to 2026-09-17 05:33:40 UTC (from 1.53 to 1.69 hours after the trigger) and obtained 16 minutes of simultaneous exposure in the r/z filters.
The data were reduced, coadded and analyzed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1, is in the AB system, and is not corrected for Galactic extinction.
We detect an uncatalogued and fading source consistent with the ECLAIRs 8.84 arcmin error circle (He et al., GCN Circ. 45606) at:
RA(J2000) = 03:07:56.12 = 46.98383 degrees
Dec(J2000) = +25:33:24.4 = 25.55678 degrees
with an uncertainty of 0.5 arcsec.
The preliminary magnitude derived for that source is:
r = 21.29 +/- 0.06
z = 19.84 +/- 0.06
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 45606
Subject
GRB 260917B: SVOM detection of a faint burst
Date
2026-09-17T04:33:30Z (12 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Hanrui He (PMO), Wenjin Xie (NAOC), Chao Wu (NAOC), Kuan Liu (USTC), Clara Plasse (HKU) , Hatsune Goto (RIKEN, CEA), Stephane Schanne (CEA) report on behalf of the SVOM mission team:
At 2026-09-17T03:52:21 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260917B (SVOM burst-id sb26091701). 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 8 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.95 in the [8-120] keV energy band over a time window of 20.40 seconds starting at 2026-09-17T03:52:11.
The localization of the best alert is R.A., Dec. 46.8646, 25.4836 degrees:
R.A. (J2000) = 3h07m27.50s
Dec. (J2000) = 25d29m00.99s
with a 90% confidence level (C.L.) radius of 8.84 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the burst. MXT and 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 Chao Wu: cwu@bao.ac.cn
Please contact the BA by email if you require additional information.