GCN 45276: GRB 260802A / EP J223759.5+531421: SVOM/VT optical upper limit
2026-08-02T16:50:27.208Z | rev 0
L. P. Xin, H. L. Li, C. Wu, Y. N. Ma, Y. L. Qiu, Z. H. Yao, J. R. Xu, 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), and J. T. Palmerio (CEA/Irfu), Wenjin Xie(NAOC), and Runchao Chen (NJU) report on behalf of the SVOM/VT team.
VT performed observations with automatic slew of GRB 260802A triggered by SVOM/ECLAIRs (sb26080210, Feng et al., GCN 45270). The observation started at 2026-08-02T09:28:46.00 UTC, about 6.0 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.
With X band data, no uncatalogued optical transient is detected in the stacked image at the position of the possible associate SGR EP J223759.5+531421 (Feng et al., GCN 45270; Postigo et al., GCN 45272; Shi et al., GCN 45274; Wu et al., GCN 45275).
The following measurements are in AB magnitudes and are not corrected for Galactic extinction:
Mid time (hr) | Exposure Time (s) | Band | Brightness (mag)
0.36 | 50*26 | VT_R | > 23.0
0.34 | 50*36 | VT_B | > 23.0
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 45275: GRB 260802A: SVOM/VT optical upper limits from VHF data
2026-08-02T13:53:21.819Z | rev 0
C. Wu, L. P. Xin, Y.L. Qiu (NAOC), J. T. Palmerio (CEA/Irfu), Wenjin Xie (NAOC), Runchao CHEN (NJU) report on behalf of the SVOM/VT team.
After the trigger by SVOM/ECLAIRs at 2026-08-02T09:23:10 UTC (T0), SVOM performed an automatic slew on the burst location (Feng et al., GCN 45270). SVOM/VT took images of the field in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
From a preliminary analysis of the 1-bit subimage and source list downloaded via the VHF network, no uncatalogued optical source was detected within the MXT localization region (Feng et al., GCN 45270) in our three sequence images, compared to the Legacy Survey DR10. The suggested position of the magnetar EP J223759.5+531421 (Rea et al. ATel 17870; Coti Zelati et al. ATel 17909) falls within the subimage coverage. No optical counterpart was detected at this position. The 5-sigma upper limits are:
| Mid time (min) | Band | Exposure (s) | 5-sigma upper limit (mag) |
| :--- | :--- | :--- | :--- |
| 6.43 | VT_B | 6 * 50 | > 21.5 |
| 6.43 | VT_R | 6 * 50 | > 21.5 |
| 100.32 | VT_R | 6 * 50 | > 21.5 |
We note that the 1-bit subimage and source list do not fully cover the entire MXT uncertainty region. Radio or infrared follow-up observations are encouraged to further investigate the association with the magnetar candidate EP J223759.5+531421.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe.
SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN 45274: GRB 260802A: LCO optical upper limits
2026-08-02T13:15:26.897Z | rev 0
Y.Y. Shi (GXU), C. Wu, L.P. Xin (NAOC), A. Saccardi, D. Turpin (CEA/Irfu), R.C. Chen, W.J. Xie (BA-F), report on behalf of the SVOM mission team:
We observed the field of GRB 260802A (SVOM burst-id sb26080210) detected by SVOM (Feng et al., GCN 45270) with the LCO 1m telescope at McDonald Observatory equipped with the Sinistro instrument.
Our observation started on 2026-08-02 at 10:21:46 UT (about 58.6 min after the trigger) and we obtained 3x200 s exposures in the SDSS r filter.
In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limit calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:
r > 20.96 AB (5-sigma, mid-time 1.07 hr after the trigger).
This project is funded by the SVOM collaboration.
GCN 45272: GRB 260802A / EP J223759.5+531421: SVOM/COLIBRÍ (FM-GFT) optical upper limit
2026-08-02T11:23:07.854Z | rev 0
Antonio de Ugarte Postigo (LAM), Asuka Kuwata (UNAM), 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), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Alan M. Watson (UNAM), Wenjin Xie(NAOC), and Runchao Chen (NJU) report:
We imaged the field of the SVOM GRB 260802A (Feng et al., GCN Circ. 45270) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-08-02 09:26:49 to 10:36:51 UTC (from 0.0188 1.2025 hours after the trigger) and obtained 61 minutes of exposure in the z band.
The data were reduced, coadded and analyzed with the ASU and CPPM COLIBRÍ pipelines. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, we do not detect any new source at the ECLAIRs source position (Feng et al., GCN Circ. 45270) down to the following 5-sigma limit:
z > 22.6
We note that the ECLAIRs coordinates are coincident with the EP J223759.5+531421 magnetar (Rea et al. ATel 17870) and that inspection of the most precise localisation, provided by XMM (Coti Zelati et al. ATel 17909) also shows no new counterpart down to a 3-sigma limit of:
z > 23.1
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 45270: GRB 260802A/EP J223759.5+531421: SVOM detection of a possible magnetar burst
2026-08-02T10:09:19.994Z | rev 2
Xin Feng (GXU), Hatsune Goto (RIKEN, CEA), Donghua Zhao (NAOC), Weinjin Xie (NAOC), Runchao CHEN (NJU), Feliu Lacreu (IAP), Diego Götz (CEA), report on behalf of the SVOM mission team:
At 2026-08-02T09:23:10 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260802A (SVOM burst-id sb26080210).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 3 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.09 in the [5-20] keV energy band starting at 2026-08-02T09:23:10.
The localization of the best alert is R.A., Dec. 339.4431, 53.2195 degrees (J2000) with a 90% confidence level (C.L.) radius of 9.72 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs showed a single peak structure lasting about 0.2 seconds.
We note that the magnetar EP J223759.5+531421(Atel #17859) is located in ECLAIRs error box, and given the short and soft nature of the burst, we suggest it is associated with this newly discovered magnetar.
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2026-08-02T09:25:42 UTC, 151 seconds after T0. Using onboard processed data we found a possible uncatalogued X-ray source with a low SNR, located at R.A., Dec. 339.439, 53.234 degrees:
R.A. (J2000) = 22h37m45s
Dec. (J2000) = 53d14m02s
with a 90% C.L. radius of 161 arcseconds.
This location is 0.89 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 Wenjin Xie: xiewj@bao.ac.cn.
Please contact the BA by email if you require additional information.
GCN 45270: GRB 260802A/EP J223759.5+531421: SVOM detection of a possible magnetar burst
2026-08-02T10:09:19.994Z | rev 2
Xin Feng (GXU), Hatsune Goto (RIKEN, CEA), Donghua Zhao (NAOC), Weinjin Xie (NAOC), Runchao CHEN (NJU), Feliu Lacreu (IAP), Diego Götz (CEA), report on behalf of the SVOM mission team:
At 2026-08-02T09:23:10 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260802A (SVOM burst-id sb26080210).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 3 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.09 in the [5-20] keV energy band starting at 2026-08-02T09:23:10.
The localization of the best alert is R.A., Dec. 339.4431, 53.2195 degrees (J2000) with a 90% confidence level (C.L.) radius of 9.72 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs showed a single peak structure lasting about 0.2 seconds.
We note that the magnetar EP J223759.5+531421(Atel #17859) is located in ECLAIRs error box, and given the short and soft nature of the burst, we suggest it is associated with this newly discovered magnetar.
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2026-08-02T09:25:42 UTC, 151 seconds after T0. Using onboard processed data we found a possible uncatalogued X-ray source with a low SNR, located at R.A., Dec. 339.439, 53.234 degrees:
R.A. (J2000) = 22h37m45s
Dec. (J2000) = 53d14m02s
with a 90% C.L. radius of 161 arcseconds.
This location is 0.89 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 Wenjin Xie: xiewj@bao.ac.cn.
Please contact the BA by email if you require additional information.