Gamma-ray Burst 260211A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #43705
D. Gotz, D. ADRIEN, D. Turpin , S. Schanne (CEA), T. Maiolino (LUPM), report on behalf of the SVOM mission team:
At 2026-02-11T19:24:33 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260211A (SVOM burst-id sb26021102).
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 22 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 14.48 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2026-02-11T19:24:28.
The localization of the best alert is R.A., Dec. 86.9994, -0.4306 degrees:
```
R.A. (J2000) = 5h47m59.85s
Dec. (J2000) = -0d25m50.14s
```
with a 90% confidence level (C.L.) radius of 5.68 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs light curve showed a single/multiple broad/narrow peak structure with a T90 duration of about 15.15 (-1.54/+1.27) (5-120 keV).
This burst was also detected by SVOM/GRM with a significance of 12.50. The SVOM/GRM light curve showed a single/multiple broad/narrow peak structure with a T90 duration of about 27.45(-8.13/+6.72) (4-550 keV).
Due to satellite constraints, no immediate slew was performed on this burst. No X-ray observation could be performed by SVOM/MXT for the time being.No optical observation could be performed by SVOM/VT for the time being.
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 Diego Gotz: diego.gotz@cea.fr. Please contact the BA by email if you require additional information.
GCN Circular #43707
Noémie Globus (UNAM), Damien Dornic (CPPM), Alan M. Watson (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), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Diego Gotz (CEA/Irfu) report:
We imaged the field of GRB 260211A (Gotz et al., GCN Circ. 43705) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-02-12 04:19 UTC to 05:20 UTC (from 8.9 to 9.9 hours after the trigger) and obtained 30 minutes of simultaneous exposure in the r and z filters.
The data were reduced and analyzed with the COLIBRÍ 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.
WIthin the 5.7 arcmin error circle (Gotz et al., GCN Circ. 43705), and comparing to the PS1 catalog and images, we do not detect any new sources to preliminary 5-sigma limiting magnitudes of:
```
r > 23.0,
z > 21.6.
```
Further observations are ongoing.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
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 #43709
C. Wu (NAOC), A. Saccardi (CEA/Irfu), D. Turpin (CEA/Irfu), D. Gotz (CEA/Irfu), D. Adrien (CEA/Irfu), report on behalf of the SVOM mission team:
We observed the field of GRB 260211A (Gotz et al., GCN 43705) with the LCO 1-m telescope at Cerro Tololo Interamerican Observatory equipped with the Sinistro instrument.
Our observation started on 2026-02-12 at 02:37:50 UT (about 7.22 hr 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, in agreement with Globus et al. (GCN 43707).
We measure the following upper limit calibrated against the UCAC4 catalog, and not corrected for Galactic extinction:
r > 22.2 AB (5-sigma, mid-time 7.28 hr after the trigger).
This project is funded by the SVOM collaboration.
GCN Circular #43713
R. Hamburg (USRA) reports on behalf of the Fermi-GBM Team:
SVOM/ECLAIRs detected GRB 260211A on 2026-02-11 at 19:24:33 UTC (GCN 43705). There was no Fermi-GBM onboard trigger around this time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates.
The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient starting 0.8 seconds after the ECLAIRs trigger time, most significantly on the 16 s timescale and with a false alarm rate of 4.3e-05 Hz. The Fermi-MET of this transient is 792530678.844 s. The Targeted Search localization is consistent with the ECLAIRs location.
Additionally, the GBM Targeted Search transient was found with highest significance using a soft spectral template (i.e., Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7).
[1] Goldstein et al. 2019 arXiv:1903.1259
GCN Circular #43715
R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) report on behalf of the LAST Collaboration.
We report observations of GRB 260211A, detected by SVOM (Gotz et al., GCN 43705). Observations were conducted with the Large Array Survey Telescope (LAST; Ofek et al. 2023, PASP 135, 5001; Ben-Ami et al. 2023, PASP 135, 5002).
We observed the field of GRB 260211A using 4 divergent telescopes (each with a 7.4 deg^2 FoV) in clear band (similar to the Gaia Bp band) over 18 sequential epochs. Each epoch consists of 20x20s exposures.
We began observations at 2026-02-11 19:27:31 UTC (T-T0 = 178 s). We coadd a total of 220x20s exposure images and perform image subtraction using a reference image of the field. We do not detect any new optical source up to a limiting magnitude of 20.12 (AB) within the error region reported in Gotz et al., GCN 43705.
LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/).
GCN Circular #43718
S. Belkin, I. Worssam, A. Kumar, D. O’Neill, G. Ramsay, B. P. Gompertz, R. Starling, M. Wortley, M. Kennedy, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, 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 SVOM detected GRB 260211A (Gotz et al., GCN 43705). Two epochs of observations covering the localisation area were taken at 2026-02-11 20:08:30 UT (+44min post trigger) and 2026-02-11 21:16:33 UT (+1.87h post trigger) utilising GOTO-North. Each observation consisted of 4x90 s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations.
No new transients that could be credibly associated with GRB 260211A were detected down to an average 5-sigma depth of 20.6 mag (AB), see also Globus et al., GCN 43707; Wu et al., GCN 43709; Konno et al., GCN 43715.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular #43720
H. L. Li, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, L. P. Xin, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), R. C. Chen (NJU), A. Li (BNU), W. K. Zheng (UCB) report on behalf of the SVOM/VT team.
SVOM/VT performed ToO observation to GRB260211A detected by SVOM/Eclairs (sb26021102, Gotz et al., GCN 43705) and Fermi GBM (Hamburg et al., GCN 43713). The observation started at 2026-02-11T20:48:38 UTC, i.e., 1.41 hours post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
SVOM/VT performed ToO observation to GRB260211A detected by SVOM/Eclairs (sb26021102, Gotz et al., GCN 43705) and Fermi GBM (Hamburg et al., GCN 43713). The observation started at 2026-02-11T20:48:38 UTC, i.e., 1.41 hours post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
Following EP-FXT's detections, two optical candidates were detected only in VT_R images compared to the PanSTARRS catalogue:
```
Source1 : R.A., Dec. (2000)= 86.978758, -0.450528     4.7 arcsecs   from the center of FXT src-1   
Source2 : R.A., Dec. (2000)= 86.977490, -0.453334    17.9 arcsecs   from the center of FXT src-1 
```
The positions are given with an uncertainty of 0.5 arcsec.
The measurements in AB magnitudes are given below:
```
    ID.          Mid time.        Band        Exposure Time     Magnitude (AB)
   Source1.      2.35 hour        VT_R           16*70 sec       22.5+/-0.3 mag
                 5.63 hour        VT_R           12*70 sec       >22.6 mag    
                 1.52 hour        VT_B           16*70 sec       >23.0 mag
                 5.95 hour        VT_B            6*70 sec       >22.5 mag

   Source2.      2.35 hour        VT_R           16*70 sec       21.9+/-0.2 mag
 	         5.63 hour        VT_R		 12*70 sec       21.9+/-0.2 mag
                 1.52 hour        VT_B           16*70 sec       >23.0 mag
	         5.95 hour.       VT_B            6*70 sec       >22.5 mag
```
Our photometry was not corrected for Galactic extinction.
For source2, we notice that there is a faint source in the PanSTARRS image. More followup observation is encouraged to confirm the nature of the sources.
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 #43721
R.D. Liang, M. J. Liu (NAOC), H. Z. Wu (HUST), H. Sun (NAOC) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260211A (SVOM/sb26021102, Gotz et al., GCN 43705) at 2026-02-11 21:16:34 (UTC), about 52 minutes after the SVOM/ECLAIRs trigger, with an exposure time of 4569 s. Two uncataloged sources are detected within the ECLAIRs error circle. Preliminary analysis on these sources is automatically conducted, and the details are listed as follows.
```
EPF_J054755.7-002705
RA (J2000): 86.9816
Dec (J2000):  -0.4505
Flux: 1.2432 x 10^-12 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 2.2401 x 10^-13 erg/s/cm2 (1 sigma)

EPF_J054802.6-002834
RA (J2000): 87.0127
Dec (J2000): -0.4750
Flux: 3.1645 x 10^-13 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 4.0267x 10^-14 erg/s/cm2 (1 sigma)
```
Note that the position of the second candidate is consistent with a known X-ray source 1eRASS J054803.1-002833.
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 #43724
T. Maiolino (LUPM), D. Götz, D. Adrien (CEA/Irfu), M. Brunet (IRAP), F. Piron (LUPM) on behalf of the ECLAIRs team.
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 260211A (SVOM burst-id 26021102), which was also detected by Fermi/GBM sub-threshold event (GCN #43713).
The burst that triggered ECLAIRs onboard (GCN #43705) consists of a double-peaked pulse with a duration of T90 = 21.6 +9.2/-2.8 s in the 4-120 keV energy band.
The time-averaged spectrum from T0-7.54 s to T0+13.12 s (T0 = 2026-02-11T19:24:33 UTC) in the energy range 5-120 keV is best fitted by a powerlaw model with a photon index of -1.71 +0.06/-0.07. With this model, the total 4-120 keV fluence is (1.08 ± 0.06)*E-6 erg/cm^2.
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: Tais Maiolino (LUPM) (tais.maiolino at lupm.in2p3.fr)
GCN Circular #43748
H. L. Li, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, L. P. Xin, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), R. C. Chen (NJU), A. Li (BNU), W. K. Zheng (UCB) report on behalf of the SVOM/VT team.
SVOM/VT performed further ToO observations to GRB260211A detected by SVOM/Eclairs (sb26021102, Gotz et al., GCN 43705) and Fermi GBM (Hamburg et al., GCN 43713). The observation started at 2026-02-14T11:37:39 UTC, i.e., 2.676 days post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The source 1 reported in Li et al. (GCN 43720) with coordinations R.A., Dec. (2000)= 86.978758, -0.450528 degrees was fading from 22.5+/-0.3 mag at 2.35 hours to 23.5 +/-0.3 mag at 2.79 days in VT_R channel. The temporal slope is roughly -0.27. Given that the VT source 1 was fading and located within the error box of EP-FXT EPF_J054755.7-002705 (Liang et al., GCN 43721), we propose it is the optical counterpart of the burst.
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 #43923
H. L. Li, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, L. P. Xin, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team.
SVOM/VT performed further ToO observations of GRB 260211A detected by SVOM/Eclairs and SVOM/GRM (sb26021102, Gotz et al., GCN 43705). Also there was a sub-threshold detection by Fermi GBM (Hamburg et al., GCN 43713). The observations were performed on 2026-03-03 and 2026-03-05 in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.
The optical counterpart (Li et al., GCN 43720, GCN 43748) was measured to have a brightness of VT_R=22.91+/-0.25 mag at 19.36 days post trigger and VT_R=22.85+/-0.25 mag at 21.31 days respectively. These measurements show that the counterpart is rebrightening, relative to the reported brightness (Li et al. GCN 43748).
We suggest that it is likely the supernova associated with the burst.
Further follow-up observations are encouraged. Our photometry was in AB magnitude and 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 #43938
G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), S. Bijavara Seshashayana (NOT and Malmo Univ.) report on behalf of a larger collaboration:
We observed the optical counterpart (Li et al., GCN 43748) of GRB 260211A (Gotz et al., GCN 43705; Hamburg, GCN 43713) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. Observations (3x300 s) were conducted in the SDSS i band, in order to reduce the effect of the large Galactic extinction towards this line of sight (A_V = 2.1 mag). Our image quality was unfortunately degraded by poor seeing (2.1").
The optical counterpart is detected in our images (mid time 23.1 days after the SVOM trigger). We measure a magnitude i = 22.5 +/- 0.2 AB, calibrated against nearby objects from the Pan-STARRS catalog, and not corrected for Galactic extinction.
The source is also detected in archival imaging from the DELVE survey (Drlica-Wagner et al., 2022, doi:10.3847/1538-4365/ac78eb), for which we find a consistent magnitude to within 0.2 mag. Imagine subtraction between the two data sets yields an upper limit of i > 22.9 for any excess component at the afterglow location.
Li et al. (GCN 43923) report a rebrightening of this source between 2.7 and 19.4 days after trigger, possibly suggesting the emergence of a SN. Our data cannot confirm this trend, though the different filters and the large extinction may introduce a systematic difference.

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