GRB 260909A
GCN Circular 45704
Subject
ATCA observations of GRB 260909A
Date
2026-09-23T14:06:52Z (3 days ago)
From
Lauren Rhodes at McGill <lauren.rhodes@mcgill.ca>
Via
Web form
L. Rhodes (TSI/McGill), G. E. Anderson (CSIRO), A. J. van der Horst (GWU), J. K. Leung (UofT/HUJI), S. Chastain (TTU), A. Gulati (Utah), J. Chauhan (ULeicester) on behalf of the PanRadio GRB collaboration
We observed GRB 260909A (Saccardi et al., GCN 45534) starting at 18-Sep-2026 14:56UT for 4 hours with the Australia Telescope Compact Array (ATCA), as part of the "PanRadio GRB" Large ATCA follow-up programme C3542 (PI. Anderson).
We report a preliminary detection of a radio counterpart at coordinates consistent with those reported in de Ugarte Postigo et al., (GCN 45597):
7.2GHz 59+/-9uJy
9.1GHz 62+/-8uJy
11.0GHz 86+/-9uJy
The positive spectral index indicates that the spectral peak of the afterglow is above the ATCA observing band. More observations are ongoing.
We thank the CSIRO Space and Astronomy staff for supporting these observations.
We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.
GCN Circular 45597
Subject
GRB 260909A: NOEMA detection
Date
2026-09-16T18:28:12Z (10 days ago)
From
Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>
Via
email
A. de Ugarte Postigo (LAM), M. Bremer (IRAM), C. C. Thoene (AbAO), S. Basa (LAM), S. Geier (GTC), L. Izzo (INAF/OACN and DARK/NBI), A. Martin-Carrillo (UCD), M. Michalowski (AOI-AMU), D. A. Perley (LJMU), D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), N.R. Tanvir (U. Leicester), L. Resmi (IIST), K. Misra (ARIES) report:
We observed the field of GRB 260909A (Saccardi et al. GCN 45534, Wang et al. GCN 45538, Brunet et al. GCN 45553) with the NOEMA interferometer, located at Plateau de Bure (France). Observations started on the 14th September 2026 at 22:55 UT (5.48 days after the GRB) at 81 and 96 GHz simultaneously. An object is clearly detected consistent with the position of the X-ray afterglow (Mao et al., GCN 45543), at a combined flux density of ~0.4 mJy. . The spectral slope between our two observing bands is beta ~ -1.3 +/- 0.6 (where F_nu is proportional to nu^beta). Although this is a rather steep value for this observing time, the large uncertainties make it compatible with a normal spectral slope of a GRB afterglow, where the peak frequency falls at lower frequencies.
The best coordinates of the source are (J2000):
R.A. = 00:52:08.462
Dec. = +24:11:47.12
With an uncertainty of ~ 0.2 "
We acknowledge excellent support from the IRAM staff. Based on observations carried out under project number S26DT with the IRAM NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).
GCN Circular 45593
Subject
GRB 260909A: Swift-XRT observations
Date
2026-09-16T11:20:41Z (10 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
S. Dichiara (PSU), M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR),
V. D'Elia (SSDC & INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU),
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans
(U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the
SVOM/ECLAIRs-detected burst GRB 260909A, collecting 2.9 ks of Photon
Counting (PC) mode data between T0+137.7 ks and T0+264.7 ks.
No X-ray sources have been detected within the estimated 90% SVOM/MXT
error region (64 arcsec; Saccardi et al. GCN 45534) or at the position
of the EP candidate (Mao et al. GCN 45543). The 3-sigma upper limit in
the field ranges from ~0.003 to ~0.005 ct s^-1, corresponding to a
0.3-10 keV observed flux of 1.1e-13 to 1.8e-13 erg cm^-2 s^-1 (assuming
a typical GRB spectrum).
Four uncatalogued sources were detected too far from the GRB position
to be likely afterglow candidates.
The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021911.
This circular is an official product of the Swift-XRT team.
GCN Circular 45556
Subject
GRB 260909A: OSN 1.5m, CAHA 2.2m and GTC 10.4m optical upper limits
Date
2026-09-12T21:03:53Z (14 days ago)
From
I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg@iaa.es>
Via
Web form
I. Perez-Garcia, J. Rodrigo, M.D. Caballero-Garcia, M. Gritsevich, S.-Y. Wu, S. Guziy (IAA-CSIC), Y.-D. Hu (GXU), G. Gomez-Velarde (IAC, GRANTECAN), F. Tinaut-Ruano (CAHA) and A.J. Castro-Tirado (IAA-CSIC), on behalf of a larger collaboration
Following the detection of GRB 260909A by SVOM/ECLAIRs (Saccardi et al. GCN 45534), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). Images were gathered starting on Sep. 10 00:07 UT (i.e. ~12.8 hours after the trigger) in the Sloan i, Sloan z and clear bands, covering the SVOM/MXT (Saccardi et al. GCN 45534) and EP/FXT (Mao et al. GCN 45543) error circles. No optical transient is detected in the co-added images (900 s per band) down to 3-sigma limits of z = 21.13, i = 22.25 and clear = 22.43 mag.
The field was also observed with the 1.5m telescope at the Sierra Nevada Observatory (OSN, Granada, Spain). A 300 s I-band image was obtained on Sep. 10 starting at 01:49 UT (i.e. ~14.5 hours after the trigger). No optical transient is detected within the above-mentioned error boxes down to I = 20.61 mag (3-sigma).
Later on we also triggered the 10.4m GTC telescope equipped with OSIRIS in La Palma (Spain). Sloan z-band images were gathered on Sep. 10 starting at 05:33 UT (mid-time ~18.5 hours after the trigger). No optical transient is detected on the co-added image (900 s) down to z = 24.55 mag (3-sigma).
A second GTC/OSIRIS epoch in the Sloan z band was obtained on Sep. 12 (mid-time Sep. 12 03:16 UT, i.e. ~2.7 days after the trigger; 1020 s in total) under worse seeing conditions. No optical transient is detected down to z = 24.17 mag (3-sigma), and no variable source is found between both GTC epochs.
Magnitudes are in the AB system (Vega for the I band), calibrated against ATLAS-REFCAT2 (the clear band against Gaia G and the I band through the Lupton 2005 transformations), and not corrected for Galactic extinction.
These non-detections are consistent with the reports from SVOM/C-GFT (Guan et al. GCN 45535), Xinglong 2.16m (Ma et al. GCN 45536), SVOM/VT (Li et al. GCN 45539), VLT (Saccardi et al. GCN 45545), OHP/T193 (Amram et al. GCN 45546), KAIT (Zheng et al. GCN 45549) and CrAO/AbAO (Pankov et al. GCN 45554).
We thank the staff at GTC, Calar Alto and Sierra Nevada observatories for their excellent support.
GCN Circular 45554
Subject
GRB 260909A: CrAO and AbAO optical upper limits
Date
2026-09-11T20:58:57Z (15 days ago)
From
Nicolai Pankov at IKI <colinsergesen@gmail.com>
Via
Web form
N. Pankov (IKI), V. Rumyantsev (CrAO), R. Ya. Inasaridze (AbAO), M. Zhuzhunadze (AbAO),
A. Pozanenko (IKI), A. Volnova (IKI), A. Moskvitin (SAO RAS) and E. Klunko (ISTP) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 260909A (discovered by SVOM, Saccardi et al., GCN 45534) in the optical R-band with the Shajn 2.6-meter telescope (ZTSh) of CrAO and the AS-32 0.7-meter telescope of AbAO. The observations started at both telescopes ~0.53 days since trigger. We do not detect any new optical sources in the EP-FXT localization circle (Mao et al., GCN 45543) in the co-add images from both telescopes.
The suggested source (Pankov et al., GCN 45537) is no longer considered as a candidate for the optical counterpart of GRB 260909A.
The observation details and preliminary upper limits are as follows:
Date UTstart t-T0 Exp. Filter UL Site/Telescope
(mid,d) (n*s) (3-sigma)
2026-09-09 22:44:16 0.53128 82*120 R 24.5 CrAO/ZTSh
2026-09-09 23:30:39 0.53744 89*60 R 21.2 AbAO/AS-32
The preliminary photometry (Vega) is based on nearby USNO-B1.0 stars
and not corrected for the Galactic extinction.
The result is an agreement with upper limits obtained by SVOM/C-GFT (Guan et al., GCN 45535),
Xinglong/2.16m (Ma et al., GCN 45536), Mondy/AZT-33IK (Pankov et al., GCN 45537),
SVOM/VT (Li et al., GCN 45539), ESO/VLT (Saccardi et al., GCN 45545),
OHP/T193 (Amram et al., GCN 45546), and LO/KAIT (Zheng et al., GCN 45549).
GCN Circular 45553
Subject
GRB 260909A: SVOM/ECLAIRs refined analysis
Date
2026-09-11T14:27:15Z (15 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Brunet, O. Godet (IRAP) , W.-J. Xie (NAOC), A. Saccardi, S. Schanne (CEA/Irfu), C. Plasse (HKU), A. Li (BNU), 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 260909A (SVOM burst-id sb26090910 – GCN 45534, trigger time T0 = 2026-09-09T11:18:01 UTC).
The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration estimated through the imaging technique is T90 = 47 +2/-3 s in the 4-120 keV energy band.
The time-averaged spectrum from T0-16 s to T0+31 s in the 5-120 keV energy range is best fitted by a powerlaw model, with alpha = -1.23 +/-0.07. With this model, the 4-120 keV fluence is (9.4 +/-0.8)e-6 erg/cm^2 and the 4-120 keV photon flux is 4.5 +/-0.3 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: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr)
GCN Circular 45551
Subject
GRB 260909A: Swift ToO observations
Date
2026-09-11T07:04:33Z (15 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the SVOM/ECLAIRs-detected event
GRB 260909A. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021911
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the SVOM/ECLAIRs event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a
GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular 45549
Subject
GRB 260909A: KAIT optical upper limit
Date
2026-09-10T17:35:32Z (16 days ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
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, automatically responded to the SVOM GRB
260909A (Saccardi et al., GCN 45534) starting at 11:32:08, 14.1 min
after the burst. Observations were performed in 3 x 3 tiling mode,
and a set of clear (roughly R) filter images were obtained. In one
of the field coving the EP-FXT uncataloged fading X-ray source (Mao
et al., GCN 45543), we did not detect any new source in our clear
coadd images with a limiting mag of ~20.5 at a mid time of 31.5 min
after the burst.
GCN Circular 45546
Subject
GRB 260909A: OHP/T193 z-band upper limit
Date
2026-09-10T09:27:50Z (16 days ago)
From
Christophe Adami at LAM <christophe.adami@lam.fr>
Via
Web form
P. Amram (LAM/Pytheas/AMU), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Saccardi (CEA/Irfu), F. Schüssler (CEA/DPhP), S. Basa (LAM/OHP/Pytheas/AMU), D. Russeil (LAM/Pytheas/AMU), report on behalf of a larger collaboration:
We observed the field of the SVOM/ECLAIRs GRB 260909A (Saccardi et al., GCN 45534; see also Mao et al., GCN 45543; Guan et al., GCN 45535; Ma et al., GCN 45536; Pankov et al., GCN 45537; Wang et al., GCN 45538; Li et al., GCN 45539; Saccardi et al., GCN 45545) with the 1.93-m T193 telescope at the Observatoire de Haute-Provence (France), equipped with the MISTRAL spectro-imager.
We obtained 52 individual exposures in the z band for a total integration time of 5.68 h. The observations started on 2026 September 9 at 20:36:43 UT (T-T_0 = 9.3 h), with a mean time on September 10 at 00:10:48 UT (T-T_0 = 13.9 h).
The stacked image reaches a 3 sigma limiting magnitude of z = 23.25.
A faint source with a magnitude of z = 23.5 +/- 0.5 is barely detected within the error region reported by Mao et al. (GCN 45543). This source is also present in the Legacy Survey and has a consistent archival magnitude of z = 23.21. Its presence at a similar brightness level in pre-existing data therefore suggests that it is unlikely to be the GRB afterglow.
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025).
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular J. Balcaen.
GCN Circular 45545
Subject
GRB 260909A: VLT optical and near-infrared upper limits
Date
2026-09-10T08:23:43Z (16 days ago)
From
Andrea Saccardi at CEA/Irfu <andrea.saccardi@cea.fr>
Via
Web form
A. Saccardi (CEA/Irfu), B. Schneider (LAM), J. An (NAOC), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), S. D. Vergani (LUX-Paris Obs.), A. J. Levan (Radboud and Warwick), N. R. Tanvir (U. Leicester), A. L. Thakur (INAF/IAPS), report on behalf of the Stargate collaboration:
In light of the early optical upper limits reported by Li et al. (GCN 45539), we observed the field of the SVOM GRB 260909A (Saccardi et al., GCN 45534; Wang et al., GCN 45538) using the ESO VLT UT1 (Antu) equipped with the FORS2 imager and the ESO VLT UT4 (Keyen) equipped with the HAWK-I near-infrared imager.
We obtained a multi-filter observation in the z-band and in the near-infrared YJHK bands. A preliminary analysis reveals no new sources consistent with the EP/FXT position (Mao et al., GCN 45543), down to the following 3-sigma limiting magnitudes (calibrated against Pan-STARRS and 2MASS for the optical and near-infrared bands, respectively):
| Band | Mid time (UT) | T-T0 (hr) | Exposure time (min) | Instrument | Magnitude (AB) |
|---|---|---|---|---|---|
| z | 2026 Sep 10.21 | 17.65 | 20 | VLT/FORS2 | > 24.3 |
| Y | 2026 Sep 10.19 | 17.35 | 10 | VLT/HAWK-I | > 23.9 |
| J | 2026 Sep 10.20 | 17.56 | 8 | VLT/HAWK-I | > 23.6 |
| H | 2026 Sep 10.21 | 17.76 | 8 | VLT/HAWK-I | > 23.1 |
The K-band integration was curtailed, and analysis of the frames obtained is ongoing.
We acknowledge the excellent support from the observing staff in Paranal.
GCN Circular 45543
Subject
GRB 260909A: EP-FXT follow-up observation
Date
2026-09-10T01:38:50Z (17 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
X. Mao, Q. H. Lao (NAO, CAS), M. Y. Wang (XMU), L. N. Xu (USTC), S. Y. Fu, A. D. Zhu (HUST), H. H. Zhang (NJU), M. Nie (YNAO, CAS), X. H. Tang (THU), C. C. Jin (NAO,CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of GRB 260909A, detected by SVOM/ECLAIRs (sb26090910; Saccardi et al., GCN 45534), SVOM/MXT (Saccardi et al., GCN 45534) and SVOM/GRM (Wang et al., GCN 45538), and observed in optical by COLIBRI (Guan et al., GCN 45535), Xinglong (Ma et al., GCN 45536), Mondy (Pankov et al., GCN 45537), SVOM/VT (Li et al. GCN 45539). The observation started at 2026-09-09 12:49:58 (UTC), about 1.53 hours after the SVOM/ECLAIRs trigger, with an exposure time of 6002 s.
On-ground analysis of the EP-FXT data found an uncataloged fading X-ray source within the SVOM/MXT error region (Pankov et al., GCN 45537). The preliminary results for the X-ray source are as follows:
Source name: EPF_J005208.3+241147
R.A., Decl. (J2000) = 13.0345, 24.1964 deg
Localization error radius = 10 arcsec
0.5-10 keV flux = 4.07e-12 erg/cm^ 2/s
Flux error = 2.48e-13 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 45539
Subject
GRB 260909A: SVOM/VT optical upper limits
Date
2026-09-09T17:02:11Z (17 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, Y. N. Ma, C. Wu, L. P. Xin, Y. L. Qiu, Z. H. Yao, J. R. Xu, L. J. Chen, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu), C. Plasse (HKU) and A. Li (BNU) report on behalf of the SVOM/VT team.
SVOM/VT performed an automatic slew on the burst GRB 260909A detected by SVOM/ECLAIRs (sb26090910, Saccardi et al., GCN 45534), SVOM/MXT (Saccardi et al., GCN 45534) and SVOM/GRM (Wang et al., GCN 45538). The observation started at 2026-09-09T11:22:16 UTC, i.e. 255 sec in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X band downlinked data, no credible candidates were identified in our single or stacked images within the error box of MXT (Saccardi et al., GCN 45534) compared to the Legacy Survey.
The following measurements are in the AB magnitude and are not corrected for Galactic extinction:
Mid time | Band | Exposure Time | 3-sigma upper limit
9.6 min VT_B 12*50 sec > 23.0 mag
9.3 min VT_R 13*50 sec > 22.8 mag
1.5 hr VT_B 50*50 sec > 23.3 mag
1.5 hr VT_R 50*50 sec > 23.2 mag
Our results are consistent with the non-detections from SVOM/C-GFT (Guan et al., GCN 45535) and Xinglong 2.16m telescope (Ma et al., GCN 45536).
Deeper optical and near-infrared follow-ups are encouraged.
For the Mondy candidate (Pankov et al., GCN 45537), we notice that there is a catalog source at this position in the Legacy Survey with magnitudes g=22.51, r=21.72, i=21.41, z=21.33.
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 45538
Subject
GRB 260909A: SVOM/GRM observation
Date
2026-09-09T16:19:04Z (17 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Yang-Zhao Ren, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Cyril Lachaud (APC)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 260909A (SVOM trigger reference: sb26090910) at 2026-09-09T11:18:02.000 (T0), which was also detected by SVOM/ECLAIRs (A. Saccardi et al, GCN 45534).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-peaks structure with a T90 of 26.6 +2.6/-2.2 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn/gcn/2026/svgrb260909A.png
With the localization from SVOM/ECLAIRs, the time-averaged spectrum from T0-25 s to T0+20 s is best fitted a power law function with an exponential high-energy cutoff. The power law index is -1.45 +0.25/-0.24 and the cutoff energy, parameterized as Epeak, is 37 +5/-7 keV. The event fluence (10-1000 keV) in this time interval is (4.85 +0.27/−0.26)E-06 erg/cm^2.
The localization of GRB 260909A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn/gcn/2026/svgrb260909A_amati.png
The localization of GRB 260909A in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn/gcn/2026/svgrb260909A_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: Chen-Wei Wang (IHEP) (cwwang@ihep.ac.cn)
GCN Circular 45537
Subject
GRB 260909A: Mondy optical observations and afterglow candidate
Date
2026-09-09T16:14:01Z (17 days ago)
From
Nicolai Pankov at IKI <colinsergesen@gmail.com>
Via
Web form
N. Pankov (IKI), E. Klunko (ISTP), A. Pozanenko (IKI),
A. Volnova (IKI), A. Moskvitin (SAO RAS) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 260909A discovered by SVOM
(Saccardi et al., GCN 45534), and observed in optical by COLIBRI
(Guan et al., GCN 45535) and Xinglong (Ma et al., GCN 45536), which resulted in upper limits. The observations were carried out using the 1.6-meter AZT-33IK telescope of Sayan Solar Observatory (Mondy) equipped with a CMOS photometer. A set of 38x120 sec images in the R band was obtained starting on 2026-09-09 at 13:44 UT (i.e. 2.446 hours since trigger).
In the coadd image we detect an uncatalogued object at coordinates (J2000) RA=00 52 08.462, Dec=+24 11 30.93 with a statistical uncertainty of 0.37 arcsec (66.7%).
The observation details and preliminary photometry is as follows:
Date, UTstart t-T0 Exp. Filter Mag Err. UL
(mid,d) (n*s) (3-sigma)
2026-09-09 13:44:47 0.12831 38*120 R 21.6 0.1 22.7
The preliminary photometry (Vega) is based on nearby USNO-B1.0 stars
and not corrected for the Galactic extinction. We suggest
this uncatalogued source to be the GRB 260909A afterglow. We
encourage further photometric follow-up of the SVOM/MXT field to verify
this candidate source.
GCN Circular 45536
Subject
GRB 260909A: Xinglong 2.16m optical upper limit
Date
2026-09-09T15:59:21Z (17 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, L. J. Chen, L. P. Xin, Y. L. Qiu, C. Wu, J. Wang, X. H. Han, P. P. Zhang, H. L. Li, J. Wang, J. Zheng, J. Y. Wei (NAOC), C. Plasse (HKU), A. Li (BNU) report on behalf of SVOM follow-up team:
We observed the field of GRB 260909A triggered by SVOM/ECLAIRs (Saccardi et al., GCN 45534) using the 2.16m telescope located at Xinglong observatory, China, equipped with the BFOSC camera. We obtained 3*60s frames in R-band, starting at 13:09:25 UT on 2026-09-09, about 1.86 hours after the trigger.
No uncatalogued source was detected in our stacked images compared to the Pan-STARRS catalog within the error box provided by SVOM/MXT (Saccardi et al., GCN 45534) down to 3-sigma upper limit of about 20.6 mag.
Our result is consistent with SVOM/C-GFT (Guan et al., GCN 45535).
We thank the staff at Xinglong observatory for their excellent support.
GCN Circular 45535
Subject
GRB 260909A: SVOM/C-GFT optical upper limit
Date
2026-09-09T15:17:49Z (17 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
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Y.X. Guan, S.J. Yin(GXU), Z. Kang (CHO), C. Wu , 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), C. Plasse (HKU), A. Li (BNU), report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 260909A detected by SVOM/ ECLAIRs (Saccardi et al., GCN 45534) with LATIOS on SVOM/C-GFT. Observations started at 2026-09-09T11:39:37.644827 UTC, ~ 21.61min after the trigger.
We obtained i-band follow-up imaging. After preliminary analysis, no credible candidate was detected within the error box provided by SVOM/MXT (Saccardi et al., GCN 45534) in our images. We measure the following upper limit calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:
i > 20.1 AB (3-sigma, mid-time 28.3 min after the trigger).
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 45534
Subject
GRB 260909A: SVOM detection of a burst
Date
2026-09-09T11:52:24Z (17 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
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A. Saccardi, S. Schanne (CEA/Irfu), Y.-H. I. Yin, C. Plasse (HKU), Y. Huang (APC), B. Cordier, J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM mission team:
At 2026-09-09T11:18:01 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260909A (SVOM burst-id sb26090910).
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 7 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 12.10 in the [8-50] keV energy band over a time window of 20.40 seconds starting at 2026-09-09T11:17:45 (Tb).
The localization of the best alert is R.A., Dec. 13.0009, 24.2188 degrees (J2000) with a 90% confidence level (C.L.) radius of 6.67 arcmin (including systematic error of 2 arcmin added in quadrature).
This burst also triggered SVOM/GRM at 2026-09-09T11:18:01 on a timescale of 1 seconds with an SNR of 7.30.
The SVOM/GRM light curve showed a single peak structure with a duration of about 30 s.
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2026-09-09T11:21:14 UTC, 193 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 13.0346, 24.1956 degrees:
R.A. (J2000) = 0h52m08s
Dec. (J2000) = 24d11m44s
with a 90% C.L. radius of 64 arcseconds.
This location is 2.31 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 Clara Plasse: cplasse@hku.hk
Please contact the BA by email if you require additional information.