sb26021801
GCN Circular 43821
H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, 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), W. J. TAN (IHEP) report on behalf of the SVOM/VT team.
SVOM/VT performed ToO osbervation on the long faint X-ray transient sb26021801 reported by SVOM/Eclairs (Tan et al., GCN 43778). The observation started at about 7.75 hours after trigger in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously.
No credible sources are detected in single or stacked images within error box of SVOM/Eclairs (Tan et al., GCN 43778) with the 3 sigma limit magnitudes of VT_B ~ 23.8 mag and VT_R ~ 23.5 mag at 9.42 hours post trigger.
Our non-detection is consistent with the reports from LCO (Wu et al., GCN 43792), COLIBRÍ (Fortin et al., GCN 43783), LAST (Konno et al., GCN 43784) and C-GFT (Wu et al, GCN 43819).
Our photometry was in AB magnitude and 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 43819
C. Wu (NAOC), Z. Kang (CHO), 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), Wenjin TAN (IHEP) report on behalf of the SVOM/C-GFT team:
We observed the field of sb26021801 detected by SVOM/ECLAIRs (Tan et al., GCN 43778) with LATIOS on SVOM/C-GFT. Observations started at 2026-02-18T16:23:38 UTC, ~11.14 hr after the trigger.
We obtained g, r, and i-band follow-up imaging. After preliminary analysis, no credible candidate was detected within the error box provided by SVOM/ECLAIRs (Tan et al., GCN 43778) in our images. The 5-sigma upper limits are:
| Mid_t - T0 (hr) | Exposure Time (s) | Band | Upper Limit (AB) |
|---|---|---|---|
| 11.67 | 20×90 | i | 20.7 |
| 11.95 | 20×90 | g | 20.7 |
| 12.23 | 20×90 | r | 20.9 |
The photometry was calibrated against nearby Pan-STARRS1 stars and no correction for Galactic dust extinction was applied.
This result is consistent with Fortin et al.(GCN 43783), Konno et al.(GCN 43784), and Wu et al. (GCN 43792).
We thank the observation assistants Yin-Huai Hao and Chun-Lei Guo 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 arcsec x 21 arcsec 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 43792
C. Wu (NAOC), A. Saccardi (CEA/Irfu), D. Turpin (CEA/Irfu), L.P. Xin (NAOC), and X.H. Han (NAOC) report on behalf of the SVOM mission team:
We observed the field of sb26021801 (TAN et al., GCN 43778) with the LCO 1-m telescope, equipped with the Sinistro instrument, at both the Cerro Tololo Interamerican Observatory and the Teide Observatory (Tenerife).
Our observation started on 2026-02-18 at 06:33:39 UT (about 78.35 min after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box, in agreement with Fortin et al. (GCN 43783) and Konno et al.(GCN 43784).
We measure the following upper limit calibrated against the PanSTARSS DR1 catalog, and not corrected for Galactic extinction:
r > 22.1 AB (5-sigma, mid-time 83.35 min after the trigger)
z > 20.2 AB (5-sigma, mid-time 85.38 min after the trigger).
This project is funded by the SVOM collaboration.
GCN Circular 43784
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 the X-ray transient alert sb26021801, reported by SVOM (Tan et al., GCN 43778). 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).
Observations of sb26021801 were taken over 11 sequential epochs in clear band (similar to the Gaia Bp band). The first epoch began at 2026-02-18 23:06:13 UTC (T-T0 = 0.76d). Each epoch consists of 20x20s exposures.
We coadd a total of 160x20s 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 21.5 (AB) within the error region reported in Tan et al., GCN 43778. See also Fortin et al. GCN 43783 for further optical limits.
LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/).
GCN Circular 43783
Francis Fortin (IRAP), Noémie Globus (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (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), 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), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Wenjin TAN (IHEP) and Chao WU (NAOC) report:
We imaged the field of the SVOM trigger sb26021801 (Tan et al., GCN Circ. 43778) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-02-19T08:46:59.976 to 2026-02-19T09:30:49.700 UTC (from 1.16 to 1.19 days after the trigger) and obtained 32 minutes of exposure in the r and z filters.
The data were reduced, coadded and analysed with the COLIBRÍ 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.
In the stacked image, we do not detect any new source at the ECLAIRs source position (Tan et al., GCN Circ. 43778) down to the following 5-sigma limit:
r > 22.50
z > 21.36
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 43778
Wenjin TAN (IHEP), Chao WU (NAOC), Wenjin XIE (NAOC), Hatsune GOTO (Kanazawa Univ.), Pierre MAGGI (ObAS) , report on behalf of the SVOM mission team:
At 2026-02-18T05:15:18 UTC (T0), SVOM/ECLAIRs triggered and located an X-ray transient (SVOM burst-id sb26021801).
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 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.29 in the 5-20 keV energy band over a time window of 1310.72 seconds starting at 2026-02-18T04:53:28.
The localization of the best alert is R.A., Dec. 194.8408, 27.9434 degrees:
R.A. (J2000) = 12h59m21.80s
Dec. (J2000) = 27d56m36.21s
with a 90% confidence level (C.L.) radius of 9.50 arcmin (including systematic error of 2 arcmin added in quadrature).
The Coma Cluster (ACO 1656) and its Brightest Central Galaxy NGC 4874 are within the trigger error circle and may be the source triggering the ECLAIRs telescope.
Due to the detection significance being below the slew threshold, 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 Wenjun Tan: tanwj@ihep.ac.cn.
Please contact the BA by email if you require additional information.