GRB 260808B
GCN Circular 45449
A. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI),
A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team
We observed the field of the GRB 260808B discovered by the SVOM
(Bouchet et al., GCN 45316; Brunet et al., GCN 45333), and also
detected by EP-FXT (Wang et al., GCN 45322) with the Zeiss-1000,
SAO RAS telescope + CCD photometer. A set of 7 x 300 sec images
in Rc band were obtained on August 12, 22:44:17 -- August 13,
00:05:06 UT.
The OT (Turpin et al., GCNs 45317; 45318; Li et al. GCN 45320;
Adami et al., GCN 45323; Saccardi et al., GCN 45328; Schneider et al.,
GCN 45329; Bochenek and Perley, GCN 45330; Basa et al., GCN 45341;
Burkhonov et al., GCN 45352; Li et al. GCN 45359; Moskvitin et al.,
GCN 45360; Guelfand et al., GCN 45364; de Ugarte Postigo et al.
GCN 45379; Bochenek and Perley, GCN 45380) is clearly detected
in our stacked image. Details of the observation are the following.
Date, UTstart, t-T0, Exp., Filter, Mag, Err., UL
(mid,d) (n*s) (3-sigma)
2026-08-12 22:44:17 4.37759 7*300 Rc 21.52 +/- 0.06 23.6
In comparison with our first epoch of observations (~0.42 days,
see Moskvitin et al., GCN 45360) OT became 0.9 mag brighter.
We can confirm rebrightening reported by Li et al. GCN 45359 and
Guelfand et al., GCN 45364.
The preliminary photometry (Vega) is based on nearby SDSS stars
(Lupton 2005 transformation) and not corrected for Galactic extinction.
GCN Circular 45380
A. Bochenek, D. A. Perley (LJMU), report:
We observed the field of GRB 260808B (Bouchet et al., GCN 45316) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x120s exposures in SDSS griz filters, starting at 2026-08-13 01:30:02 UT, approximately 4.5 days after SVOM/ECLAIRS trigger.
We detect a source in the stacked images, with the photometry given below, at the counterpart position reported by Turpin et al. (GCN 45318), Li et al. (GCN 45320), also observed by Wang et al. (GCN 45322), Adami et al. (GCN 45323), Saccardi et al. (GCN 45328), Schneider et al. (GCN 45329), Bochenek et al., (GCN 45330), with re-brightening reported by Li et al. (GCN 45359) and Guelfand et al. (GCN 45364).
MJD (mid) T_mid-T_0 Filter Mag. (AB)
61265.06782 4.47 d g 22.19 ± 0.09
61265.08202 4.48 d r 21.77 ± 0.06
The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction.
GCN Circular 45379
A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud), S. Geier (GTC), M. A. Aloy (UV), C. C. Thoene (AbAO), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), L. Izzo (INAF/OACN and DARK/NBI), G. Lombardi (GTC), A. Martin-Carrillo (UCD), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), A. Cabrera-Lavers (GTC), A. M. Garcia Rodriguez (GTC) report:
We observed the optical counterpart (Turpin et al., GCN 45318; Li et al., GCN 45320), recently reported to be brightening (Li et al., GCN 45359; Guelfand et al., GCN 45364) of GRB 260808B (Bouchet et al., GCN 45316; Brunet et al., GCN 45333) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument.
In a 30-s acquisition image (beginning on 2026-08-13 at 02:07:19 UT, that is 4.49 days after trigger), the optical afterglow is well detected with a magnitude of 21.70 +- 0.10 (AB), calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction. Our measurement confirms the rebrightening (Li et al., GCN 45359; Guelfand et al., GCN 45364).
A total of 3 spectra of 1200 s were secured, starting on 2025-08-13 at 02:10:52 UT (mid time 4.51 days after trigger), using grism R1000B. Continuum is visible over the wavelength range 3620-7800 AA. A number of metal absorption features are detected, which we interpret as due to Fe II, Mg II and Mg I, all at a common redshift z = 1.295, which we suggest to be the redshift of GRB 260808B.
This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774).
GCN Circular 45364
Marion Guelfand (CPPM), Fredd Sánchez Álvarez (UNAM), Noémie Globus (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), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM) and Michela Maria Dinatolo (U. Milano) report:
We continued imaging the field of the SVOM GRB 260808B (Bouchet et al., GCN 45316) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-08-12 09:54:12 to 10:07:40 UTC (from 91.5 to 91.8 hours after the trigger) and obtained 720 seconds of simultaneous exposure in the r and z filters.
The data were reduced, coadded and analyzed with the ASU COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1r catalog, is in the AB system, and is not corrected for Galactic extinction.
Compared to our previous observation (Basa et al., GCN 45341), where we measured z = 22.21 ± 0.08 at 40.6–42.4 hours after the trigger, we find that the optical counterpart (Turpin et al., GCN 45318; Li et al., GCN 45320; Saccardi et al., GCN 45328; Schneider et al., GCN 45329; Bochenek et al., GCN 45330) has significantly rebrightened, as also reported by Li et al. (GCN 45359). We measure the following preliminary magnitudes:
r = 21.68 ± 0.04,
z = 21.36 ± 0.11.
Further observations are planned.
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 45360
A. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI),
A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team
We observed the field of the GRB 260808B discovered by the SVOM
(Bouchet et al., GCN 45316; Brunet et al., GCN 45333), also detected
by EP-FXT (Wang et al., GCN 45322) with the Zeiss-1000, SAO RAS 1-m
telescope + CCD photometer. The observations were carried out on August 9,
00:11:49--00:38:47 UT. We obtained 5 x 300 sec images in Rc band.
The OT (Turpin et al., GCNs 45317; 45318; Li et al. GCN 45320;
Adami et al., GCN 45323; Saccardi et al., GCN 45328; Schneider et al.,
GCN 45329; Bochenek and Perley, GCN 45330; Basa et al., GCN 45341;
Burkhonov et al., GCN 45352; Li et al. GCN 45359) is clearly detected
in our stacked image. Details of the observation are the following.
Date, UTstart, t-T0, Exp., Filter, Mag, Err., UL
(mid,d) (n*s) (3-sigma)
2026-08-09 00:11:49 0.41968 5*300 Rc 22.44 +/- 0.13 23.2
This preliminary photometry (Vega) is based on nearby SDSS stars
(Lupton 2005 transformation) and not corrected for Galactic extinction.
GCN Circular 45359
H. L. Li, C. Wu, L. P. Xin, Y. L. Qiu, Y. N. Ma, 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), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team.
SVOM/VT performed further ToO observations of GRB 260808B (sb26080812; Bouchet et al., GCN 45316; Brunet et al., GCN 45333) on 10 and 11 August 2026. The two epochs correspond to mid-times of 1.45 d and 2.94 d post-trigger, with simultaneous exposures acquired in the VT_B (400–650 nm) and VT_R (650–1000 nm) channels.
The afterglow (Turpin et al., GCN 45318; Li et al., GCN 45320; Wang et al., GCN 45322; Adami et al., GCN 45323; Saccardi et al., GCN 45328; Schneider et al., GCN 45329; Bochenek et al., GCN 45330; Mohan et al., GCN 45334; Basa et al., GCN 45341; Burkhonov et al., GCN 45352) was still detected at these two epochs and exhibited rebrightening in both channels on 11 August 2026.
The following measurements are in the AB magnitude and are not corrected for Galactic extinction:
Mid time | Band | Exposure Time | Brightness
2.94 d VT_B 78*80 s 21.9 +/- 0.2 mag
2.94 d VT_R 80*70 s 21.3 +/- 0.2 mag
More observations for this burst are encouraged.
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 45352
O. Burkhonov, Y. Rajabov, B.Abidkhanov, S. Ehgamberdiev, Y. Tillayev (UBAI), A. Shaymanov, T. Boyqobilov (Maidanak Observatory/UBAI), M. Coughlin (UMN), P. Hello (IJCLAB), S. Antier (IJCLAB), M. Pillas (IAP), and S. Karpov (FZU) report on behalf of UBAI team and GRANDMA collaboration.
We observed the field of GRB 260808B detected by SVOM (Bouchet et al., GCN 45316) with the AZT-22 1.5m telescope of the Maidanak Observatory (MAO) starting on 2026-08-10 at 21:07:04 UT, i.e, ~2.2932 days after the SVOM/ECLAIRs trigger. In total we obtained 6x300 s exposures in the R-band using 4kx4k CCD SNUCAM camera (Im et al., 2010).
We detect the optical counterpart reported by many teams (Turpin et al., GCN 45318; Li et al., GCN 45320; Adami et al., GCN 45323; Saccardi et al., GCN 45328; Schneider et al., GCN 45329; Bochenek et al., GCN 45330; Basa et. al., GCN 45341).
Preliminary photometry is as follows:
Date UTstart Exptime t-T0 Filter OT Err. UL SNR Site/Telescope
(nxs) (mid, days)
2026-08-10 21:07:04 6x300 2.29327 R 21.51 0.05 23.10 18 MAO/AZT-22
All the data have been reduced by a single data processing pipeline, STDWeb (Karpov 2025). Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog. Our measurements in Vega magnitude system and the data has not corrected for the Galactic extinction.
Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/).
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). Astrophysics Center for Multimessenger studies in Europe is supported Skyportal/ICARE (contact camille.douzet@ijclab.in2p3.fr, skyportal.io).
GCN Circular 45341
Stéphane Basa (UAR Pytheas), Noémie Globus (UNAM), 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), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), 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), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM) and Michela Maria Dinatolo (U. Milano) report:
We imaged the field of the SVOM GRB 260808B (Bouchet et al., GCN 45316) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-08-10 07:02:08 to 08:48:29 UTC (from 40.6 to 42.4 hours after the trigger) and obtained 48x60 seconds 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 DR1r catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, we detect the optical counterpart (Turpin et al., GCN 45318; Li et al., GCN 45320; Saccardi et al., GCN 45328; Schneider et al., GCN 45329; Bochenek et al., GCN 45330) at a preliminary magnitude of:
z = 22.21 +/- 0.08
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 45334
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 260808B (Bouchet et al., GCN 45316) 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 at 2026-08-09T04:57:29.690 UTC in the J band (14.61 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 do not detect the optical counterpart (Turpin et al., GCN 45318; Li et al., GCN 45320; Saccardi et al., GCN 45328; Schneider et al., GCN 45329; Bochenek et al., GCN 45330; and also Wang et al., GCN 45322) in our stacked image. We obtain the following 5-sigma upper limit: J = 18.82 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 45333
Authors: M. Brunet, L. Bouchet, S. Guillot (IRAP), Michela Dinatolo (U. Milano)
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 260808B (SVOM burst-id sb26080812 – GCN 45316, trigger time T0 = 2026-08-08T14:20:58 UTC).
The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve with a possible precursor at T0-84.5 s lasting around 2 s. The burst duration is T90 = 178 +12/-8 s in the 4-120 keV energy band.
The time-averaged spectrum before the slew, from T0-45s to T0+43s in the 5-120 keV energy range is best fitted by a powerlaw model with alpha = -1.96 +0.14/-0.16. With this model, the 4-120 keV fluence is 6.4 +/-0.9 e-7 erg/cm^2 and the 4-120 keV photon flux is 0.32 +/-0.03 ph/cm^2/s.
The possible precursor is too faint to extract any significant spectral parameters.
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: L. Bouchet (IRAP) (laurent.bouchet at utoulouse.fr)
GCN Circular 45330
A. Bochenek, D. A. Perley (LJMU), report:
We observed the field of GRB 260808B (Bouchet et al., GCN 45316) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x120s exposures in SDSS griz filters, starting at 2026-08-09 00:32:11 UT, approximately 10.17 hours after SVOM/ECLAIRS trigger.
We detect a source in the stacked images at the counterpart position reported by Turpin et al. (GCN 45318), Li et al. (GCN 45320), also observed by Wang et al. (GCN 45322), Adami et al. (GCN 45323), Saccardi et al. (GCN 45328), and Schneider et al. (GCN 45329), with preliminary photometry given below:
MJD (mid) T_mid-T_0 Filter Mag. (AB)
61261.02909 10.35 h i 22.50 ± 0.23
61261.04320 10.88 h z 21.96 ± 0.28
61261.05760 11.03 h g 22.95 ± 0.25
61261.07154 11.37 h r 22.74 ± 0.19
The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction.
GCN Circular 45329
B. Schneider (LAM), L. Izzo (INAF/OACN and DARK/NBI), A. Saccardi (CEA/Irfu), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), D. O’Neill (U. Birmingham), report on behalf of a larger collaboration:
We observed the field of GRB 260808B detected by SVOM/ECLAIRs (Bouchet et al., GCN 45316; see also Wang et al., GCN 45322), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 3x300 s exposures in the SDSS r-band and 5x200s in the SDSS z-band at mid time 2026 Aug 09.1158 UT (12.43 hr after the trigger).
In the stacked images, we clearly detect the optical afterglow (Turpin et al., GCN 45318; Li et al., GCN 45320; Adami et al., GCN 45323; Saccardi et al., GCN 45328). We measure a preliminary AB magnitude of r = 22.72 +/- 0.17 mag, and z = 22.19 +/- 0.24 mag, calibrated against nearby stars from the Pan-STARRS catalog, and not corrected for Galactic extinction.
GCN Circular 45328
A. Saccardi (CEA/Irfu), S. J. Yin (GXU), C. Wu (NAOC), D. Turpin (CEA/Irfu), M. Dinatolo (U. Milano), report on behalf of the SVOM mission team:
We observed the field of GRB 260808B detected by SVOM/ECLAIRs (Bouchet et al., GCN 45316; see also Wang et al., GCN 45322) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument.
Our observation started on 2026-08-08 at 20:29:25 UT (about 6.14 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters.
The optical counterpart (Turpin et al., GCN 45318; Li et al., GCN 45320; Adami et al., GCN 45323) is detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction:
r = 22.13 +/- 0.23 AB (5-sigma, mid-time 6.23 hr after the trigger).
z > 20.74 AB (3-sigma, mid-time 7.44 hr after the trigger).
This project is funded by the SVOM collaboration.
GCN Circular 45323
C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), B. Schneider (LAM), A. Saccardi (CEA/Irfu), S. Basa (LAM/OHP/Pytheas/AMU) report on behalf of a larger collaboration:
We observed the field of GRB 260808B (Bouchet et al., GCN45316; see also Wang et al., GCN45322) using the T193cm telescope at Observatoire de Haute-Provence (France) with the MISTRAL spectro-imager. We obtained 7x10 + 1x5 minutes of exposure in the i-band and 6x20minutes in the Y-band under a 2.3arcsec seeing, starting at 20260808_223518UT (~8.3 hr after the Bouchet et al. trigger) and ending at 20260809_021419UT (~11.9 hr after the Bouchet et al. trigger).
In the preliminary stacked images, we detect in i’ band the afterglow at the position of Turpin et al. (GCN 45318) and Li et al. (GCN 45320) at a preliminar magnitude of:
i = 22.63 +/- 0.13 mag
We do not detect the source in our Y-band image. This image has a preliminar estimated limiting magnitude of Y=21.8 (3sigma).
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction.
We acknowledge the excellent support from Observatoire de Haute-Provence and in particular Stephane Favard.
GCN Circular 45322
Y. Wang (PMO, CAS; UCB), H. C. Ding (AHNU), R. X. Hu (WHU), Z. X. Li (IHEP, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of GRB 260808B detected by SVOM/ECLAIRs (Bouchet et al., GCN 45316). The observation started at 2026-08-08 15:55:38 (UTC), about 1.6 hr after the SVOM trigger, with a total exposure time of around 4 ks.
On-ground analysis of the FXT data found a source EPF_J230056.0+082842 at R.A. = 345.2350 deg and Dec. = 8.4771 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The source position is consistent with the optical afterglow confirmed by SVOM/VT (Li et al., GCN 45320). The observed flux is approximately 1.6 × 10^-13 erg s^-1 cm^-2.
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 45320
H. L. Li, C. Wu, L. P. Xin, Y. L. Qiu, Y. N. Ma, 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), J. T. Palmerio (CEA/Irfu), M. Dinatolo (U. Milano) report on behalf of the SVOM/VT team.
SVOM/VT performed observations with automatic slew for GRB 260808B triggered by SVOM/ECLAIRs (sb26080812, Bouchet et al., GCN 45316) and detected by SVOM/MXT (Bouchet et al., GCN 45316). The observation started at 2026-08-08T14:24:26 UTC, i.e., 208 seconds post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.
The optical candidate (Turpin et al., GCN 45318) was detected in both channels. The position is at R.A., Dec. = 345.233538, 8.478528 degrees, equivalent to:
R.A. (J2000) = 23:00:56.05
Dec. (J2000) = +8:28:42.70
with an uncertainty of 0.5 arcsec.
The following measurements are in the AB magnitude and are not corrected for Galactic extinction:
Mid time | Band | Exposure Time | Brightness
233 s VT_B 50 s 20.9 +/- 0.2 mag
233 s VT_R 50 s 20.3 +/- 0.1 mag
1.51 h VT_B 16*50 s 22.8 +/- 0.2 mag
1.51 h VT_R 16*50 s 22.0 +/- 0.2 mag
The source faded rapidly with a temporal decay slope of -1.9 in both channels during our early observations taken within 400 seconds post trigger.
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 45318
D. Turpin (CEA/Irfu), C. Wu (NAOC), A. Saccardi (CEA/Irfu), L. P. Xin (NAOC), M. Dinatolo (U. Milano), report on behalf of the SVOM/VT team:
After the trigger by SVOM/ECLAIRs at 2026-08-08T14:20:58 UTC (T0), SVOM performed an automatic slew on the burst location (sb26080812, Bouchet et al., GCN 45316). SVOM/VT began observing the field in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
From a preliminary analysis of the source list and 1-bit subimage downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below.
VT_ID 40: The position of this candidate is R.A., Dec. 345.23359 8.47848 degrees, corresponding to:
R.A. (J2000) = 23:00:56.06
Dec. (J2000) = +08:28:42.5
with an uncertainty of 0.5 arcsec.
This candidate was detected in both VT_R and VT_B in the first sequence of images and no longer detected in the following ones. No minor planet objects were found at the position of the candidate and within a 1 arcmin radius. No catalogue source was found in the Legacy DR10 catalog. The candidate's magnitudes are:
| date-obs (UTC) | mid-time（sec） | exposure | VT_B mag(AB) | VT_R mag(AB) |
|---|---|---|---|---|
| 2026-08-08T14:25:16.000 | 408 | 6x50s | 21.72 ± 0.10 | 21.02 ± 0.08 |
Magnitudes were not corrected for Galactic reddening.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
The Burst Advocate (BA) on shift for this alert is Michela Maria Dinatolo: michela.dinatolo@unimi.it. Please contact the BA by email if you require additional information
GCN Circular 45317
D. Turpin (CEA/Irfu), C. Wu (NAOC), A. Saccardi (CEA/Irfu), L. P. Xin (NAOC), M. Dinatolo (U. Milano), report on behalf of the SVOM/VT team:
After the trigger by SVOM/ECLAIRs at 2026-08-08T14:20:58 UTC (T0), SVOM performed an automatic slew on the burst location (sb26080812, Bouchet et al., GCN 45316). SVOM/VT began observing the field in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
From a preliminary analysis of the source list and 1-bit subimage downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below.
VT_ID 40: The position of this candidate is R.A., Dec. 345.23359 8.47848 degrees, corresponding to:
R.A. (J2000) = 23:00:56.06 Dec. (J2000) = +08:28:42.5
with an uncertainty of 0.5 arcsec.
This candidate was detected in both VT_R and VT_B in the first sequence of images and no longer detected in the following ones. No minor planet objects were found at the position of the candidate and within a 1 arcmin radius. No catalogue source was found in the Legacy DR10 catalog. The candidate's magnitudes are:
| date-obs (UTC) | mid-time（sec） | exposure | VT_B mag(AB) | VT_R mag(AB) |
|---|---|---|---|---|
| 2026-08-08T14:25:16.000 | 408 | 6x50s | 21.72 ± 0.10 | 21.02 ± 0.08 |
Magnitudes were not corrected for Galactic reddening.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
The Burst Advocate (BA) on shift for this alert is Michela Maria Dinatolo: michela.dinatolo@unimi.it. Please contact the BA by email if you require additional information.
GCN Circular 45316
Laurent Bouchet (IRAP), Sebastien Guillot (IRAP), Michela Dinatolo (U. Milano), Diego Götz (CEA) report on behalf of the SVOM mission team:
At 2026-08-08T14:20:58 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260808# (SVOM burst-id sb26080812).
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 Image Trigger (IMT), which produced a sequence of 5 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 7.52 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2026-08-08T14:20:18.
The localization of the best alert is R.A., Dec. 345.2202, 8.4310 degrees (J2000) with a 90% confidence level (C.L.) radius of 10.44 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2026-08-08T14:23:30 UTC, 152 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 345.239, 8.467 degrees:
R.A. (J2000) = 23h00m57.38s
Dec. (J2000) = 8d28m00.34s
with a 90% C.L. radius of 48 arcseconds.
This location is 2.42 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 Michela Maria Dinatolo: michela.dinatolo@unimi.it.
Please contact the BA by email if you require additional information.