GRB 260402A, EP260402a
GCN Circular 44236
Subject
GRB 260402A: SVOM/ECLAIRs refined analysis
Date
2026-04-08T13:04:28Z (8 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Brunet, O.Godet (IRAP), W.-J. Xie (NAOC), W. Tan, R. Li (IHEP), 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 260402A(SVOM burst-id sb26040203– GCN 44181, trigger time T0 = 2026-04-02T10:30:17 UTC), which was also detected by EP/WXT (GCN 44186).
The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = (15.2 -3.9/+3.1) s in the 4-120 keV energy band. However, some emission is seen for 41 s from T0 up to T0 + 41 s in the 4-20 keV energy band through imaging.
The time-averaged spectrum from T0 to T0+41s in the energy range 5-120 keV is best fitted by a powerlaw model with a photon index of -2.18 +0.09/-0.10. With this model, the 4-120 keV fluence is (5.40 +0.33/-0.57)e-7 erg/cm^2 and the 4-120 keV photon flux is 0.67 +0.03/-0.04 ph/cm^2/s.
This GRB shows some spectral evolution.
The spectrum from T0 to T0 + 1 s in the 5-120 keV energy range is best fitted by a power-law model with a photon index of -1.37 +/-0.12. With this model, the 4-120 keV flux is (8.9 +0.6/-1.7)e-8 erg/cm²/s.
The spectrum from T0 + 1 s to T0 + 5 s in the 5-120 keV energy range is best fitted by a broken power-law model with the second photon index fixed at -3, which gives a first photon index of -0.85 +0.23/-0.20 and a break energy of 17.3 +2.0/-1.6 keV. With this model, the 4-120 keV flux is (4.6 +0.1/-1.1)e-8 erg/cm²/s.
The spectrum from T0 + 5 s to T0 + 10 s in the 5-120 keV energy range is best fitted by a broken power-law model with the first photon index fixed at -0.85 and the second one fixed at -3, which gives a break energy of 8.6 +1.2/-0.8 keV. With this model, the 4-120 keV flux is (2.3 +0.1/-0.2)e-8 erg/cm²/s.
The spectrum from T0 + 10 s to T0 + 41 s in the 5-50 keV energy range is best fitted by a power-law model with a photon index of -2.9 +0.3/-0.4. With this model, the 4-120 keV flux is (4.8 +0.3/-2.0)e-9 erg/cm²/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) (mbrunet at utoulouse.fr)
GCN Circular 44233
Subject
EP260402a / GRB 260402A: Mephisto optical upper limits
Date
2026-04-07T15:20:03Z (9 days ago)
Edited On
2026-04-07T15:48:47Z (9 days ago)
From
Chenxu Liu at Mephisto Team <cxliu@ynu.edu.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Chenxu Liu at Mephisto Team <cxliu@ynu.edu.cn>
Via
Web form
Chenxi Shang, Chenxu Liu, Guowang Du (SWIFAR, YNU), Jinghang Xue (NJU), Yuhui Zhang, Jialei Zheng, Tao Wang, Brajesh Kumar, Xueling Du, Xufeng Zhu, Yu Pan, Xingzhu Zou, Xinlei Chen, Yuan Fang, Jinghua Zhang (SWIFAR, YNU), Chao Wu (NAOC), Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:
The 1.6-m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory, was triggered at 2026-04-02 19:52:10 UT (~9.4 hours after the Einstein Probe/WXT trigger; Zhao et al., GCN 44186) to observe the field of EP260402a. The observations were acquired in relatively poor seeing conditions (FWHM >2.5 arcsec). Two frames of simultaneous multi-band (u, g, v, r, i, z) were collected with individual exposure times of 45 s. The images in each band were later stacked for analysis. In our stacked images, no uncatalogued optical source is detected at the FXT position or within its error circle (radius ~10–20 arcsec). The 5-sigma limiting magnitudes (AB system, not corrected for Galactic extinction) are listed below:
----------------------------------------------------------------------------------------------
Start Time (UT) | Band | Exposure (s) | Mag / Limiting Mag
----------------------------------------------------------------------------------------------
2026-04-02T19:52:10 | u | 45.0*2 | >19.77
2026-04-02T19:54:55 | v | 45.0*2 | >18.81
2026-04-02T19:52:23 | g | 45.0*2 | >20.21
2026-04-02T19:55:08 | r | 45.0*2 | >20.33
2026-04-02T19:52:13 | i | 45.0*2 | >20.23
2026-04-02T19:54:58 | z | 45.0*2 | >19.48
----------------------------------------------------------------------------------------------
Our non-detection is consistent with previous optical and near-infrared upper limits reported by SVOM/COLIBRÍ (Antier et al., GCN 44183), MASTER (Carrasco et al., GCN 44184), Kilonova-Catcher (Freeberg et al., GCN 44185), SVOM/C-GFT (Wu et al., GCN 44189), SVOM/VT (Li et al., GCN 44190), GIT (Vijaykumar et al. GCN 44191), WINTER (Schneider et al., GCN 44192) and Jinshan (He et al., GCN 44199).
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025 and presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. We note that the current data-processing pipeline is still at a preliminary stage, with flux calibration precision of about 2% in the u and v bands, about 1% in the g and r bands, and better than 1% in the i and z bands.
GCN Circular 44230
Subject
EP260402a/GRB 260402A: Xinglong optical upper limit
Date
2026-04-07T15:05:38Z (9 days ago)
Edited On
2026-04-10T14:29:34Z (6 days ago)
From
Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Via
Web form
Min-He (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Junjun-Jia (NAOC), Yuguang-Sun (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration:
Following the detection of EP260402a (Zhao et al., GCN 44186), we observed the field of EP260402a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s clear-band frames by using 2.16-m with a median time of 2026-04-07T13:19:08, 5 days after the EP trigger.
No uncatalogued optical transient is detected in the stacked images within the 10 arcsec EP/FXT error circle (Zhao et al., GCN 44186), down to 3-sigma limiting magnitudes of Clear-band ~22.13 mag for for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle.
GCN Circular 44201
Subject
EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
Date
2026-04-03T09:03:27Z (13 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. Q. Zhao (USTC,PRIC), C. L. Guo, J. W. Hu, C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP260402a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (GCN #44186), and temporally and spatially consistent with GRB 260402A (GCN #44181). The telemetry WXT data show that the flare started at 2026-04-02T10:29:33 (UTC) and exhibits a double-peaked burst lasting about 200 s. The average WXT 0.5-4 keV spectrum of the burst period can be fitted with an absorbed power law with a hydrogen column density of 0.76（-0.36/+0.41）×10^22 cm^-2 and a photon index of 2.09(-0.77/+0.84). The derived average unabsorbed 0.5-4 keV flux is 2.68 (-0.83/+1.97) ×10^(-9) erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP observed this source at 2026-04-02T12:55:33 (UTC, T0+8760 s). The exposure time of this observation is 3.0ks. On-ground analysis of the FXT data found an uncatalogued source at R.A., Dec. = 170.9607, 63.6128 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 0.40 (-0.13/+0.14) × 10^22 cm^-2 and a photon index of 3.20 (-0.51/+0.55). The derived average unabsorbed 0.5-10 keV flux is 2.91 (-0.73/+1.46) × 10^(-12) erg/s/cm^2.
The optical and near-infrared follow-up observations were performed by Antier et al. (GCN 44183), Carrasco et al. (GCN 44184), Freeberg et al. (GCN 44185), Wu et al. (GCN 44189), Li et al. (GCN 44190), Vijaykumar et al. (GCN 44191), Schneider et al. (GCN 44192) and He et al. (GCN 44199).
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 44199
Subject
EP260402a/GRB 260402A: Jinshan near-infrared upper limit
Date
2026-04-03T08:06:20Z (13 days ago)
From
L. B. He at NAOC <helb@bao.ac.cn>
Via
Web form
L. B. He, X. Liu (NAOC), S.Y. Fu, A.D. Zhu, L. Lei, H.Z. Wu, W.H. Lei, Y.C. Zou (HUST), J. An, S.Q. Jiang, Z.P. Zhu, D. Xu (NAOC), J.Z. Liu (XAO), Z.N. Dong, B. Ma (SYU) report:
We observed the field of EP260402a/GRB 260402A detected by EP (Zhao et al., GCN 44186) and SVOM (Tan et al., GCN 44181; Gotz et al., GCN 44182), using the JinShan 100C telescope located at Altay, Xinjiang, China. Observation started at 2026-04-02 14:51:48 UT, i.e., 4.36 hrs post-burst, and a series of J-band frames were obtained.
No new source is detected in the stacked image within the EP/FXT error circle, down to a 5-sigma limiting magnitude of J ~ 17.3 (Vega), calibrated with 2MASS stars in the field. This upper limit is consistent with that reported at WINTER (Schneider et al., GCN 44192).
We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations.
GCN Circular 44192
Subject
GRB 260402A: WINTER J-band upper limit
Date
2026-04-02T18:08:21Z (13 days ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
Benjamin Schneider (LAM), Geoffrey Mo (Caltech/Carnegie), Robert Stein (UMD), Viraj Karambelkar (Columbia), Tomas Ahumada (NOIRLab), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of GRB 260402A detected by SVOM/ECLAIRs (Tan et al., GCN 44181) and EP/WXT (Zhao et al., GCN Circ. 44186) in the near-infrared with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations started on 2026-04-02 at 10:58:52 UT (28.58 min after the trigger) and consisted of 30 exposures of 120 s in the J-band.
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). The photometric calibration was performed using nearby stars from the 2MASS catalog. The magnitude 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 FXT position (Zhao et al., GCN Circ. 44186) or MXT position (Gotz et al., GCN Circ. 44182) and derive the following 5-sigma upper limit:
J > 18.9
Our upper limit is consistent with previously reported optical upper limits from Antier et al. (GCN Circ. 44183), Carrasco et al. (GCN Circ. 44184), Freeberg et al. (GCN Circ. 44185), Wu et al. (GCN Circ. 44189), Li et al. (GCN Circ. 44190), and Vijaykumar et al. (GCN Circ. 44191).
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 44191
Subject
GRB260402A: GROWTH-India Telescope optical upper limit
Date
2026-04-02T17:45:27Z (13 days ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form
V. Vijaykumar, A. Khade, R. Arya, V. Swain, S. Patil, A.P. Saikia, T. Mohan, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team:
We observed the field of GRB260402A detected by SVOM/ECLAIRs (SVOM, GCN 44181), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-04-02 14:10:35 (UTC), i.e., 3.65 hours after the trigger, and obtained multiple exposures in the r' filter. We do not detect any transient in our image within the uncertainty region of source position reported by ECLAIRs and MXT (Tan et al., GCN Circ. 44181, Gotz et al., GCN Circ.44182). The photometric upper limit is as follows:
| MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Magnitude (AB) |
|---|---|---|---|---|
| 61132.590 | r' | 3.92 | 5x360 | 20.5 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
Our magnitude for the optical counterpart is consistent with other optical observations (GCN 44190 Li et al.; GCN 44189 Wu et al.; GCN 44185 Freeberg et al.; GCN 44184 Carrasco et al.; GCN 44183 Antier et al.)
The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.
GCN Circular 44190
Subject
GRB 260402A / EP260402a: SVOM/VT optical upper limits
Date
2026-04-02T16:30:34Z (13 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, C. Wu, Y. L. Qiu, L. P. Xin, 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, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), W. Tan (IHEP) and R. Li (YNAO) report on behalf of the SVOM/VT team.
SVOM/VT performed observations with automatic slew to the field of GRB 260402A triggered by SVOM/ECLAIRs (sb26032123, Tan et al., GCN 44181), SVOM/GRM (Tan et al., GCN 44181) and Einstein Probe (EP260402a, Zhao et al., GCN 44186). The observation started at 2026-04-02T10:44:07 UTC, approximately 13.8 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.
No uncatalogued sources are detected in single or stacked images within the error box of SVOM/MXT (Gotz et al., GCN 44182) or EP-FXT (Zhao et al., GCN 44186), compared to the Legacy Survey. The 3-sigma limit magnitudes are VT_B ~ 23.1 mag and VT_R ~ 23.0 mag at 31.3 minutes post trigger.
Our result is consistent with the non-detection reports from SVOM/COLIBRÍ (Antier et al., GCN 44183), MASTER (Carrasco et al., GCN 44184), Kilonova-Catcher (Freeberg et al., GCN 44185) and SVOM/C-GFT (Wu et al., GCN 44189).
Given the early optical non-detection, near-infrared follow-up observations 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 44189
Subject
EP260402a/GRB 260402A: SVOM/C-GFT upper limit
Date
2026-04-02T15:30:47Z (14 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
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) , W. Tan, R. Li (IHEP) report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 260402A (SVOM burst-id sb26040203) detected by SVOM/ECLAIRs (Tan et al., GCN 44181) with LATIOS on SVOM/C-GFT. Observations started at 2026-04-02T12:50:51 UTC, ~2.34 hr 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 (Gotz et al., GCN 44182) and EP/MXT (Zhao et al., GCN 44186) in our stacked image. The 3-sigma upper limit is:
| Mid_t - T0 (hr) | Exposure Time (s) | Band | Upper Limit (AB) |
|---|---|---|---|
| 2.69 | 30×30 | i | 19.0 |
The photometry was calibrated against Pan-STARRS1 stars and no correction for Galactic dust extinction was applied.
This result is consistent with Antier et al. (GCN 44183) and Freeberg et al.(GCN 44185).
We thank the observation assistants Ying-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 44186
Subject
EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
Date
2026-04-02T14:16:37Z (14 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. Q. Zhao (USTC,PRIC), C. L. Guo, J. W. Hu, C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260402a. The transient triggered EP-WXT (ID: 01709259488) at 2026-04-02T10:30:41 (UTC). The WXT position of the source is R.A. = 170.994 deg, DEC = 63.604 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). EP260402a is temporally and spatially consistent with GRB 260402A (GCN #44181).
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically triggered by SVOM GRB detection, began at 2026-04-02T12:55:33Z. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 170.9607 deg, DEC = 63.6128 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
Further information will be updated when the telemetry data is received.
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 44185
Subject
GRB 260402A: Kilonova-Catcher optical upper limit
Date
2026-04-02T13:09:54Z (14 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 260402A detected by SVOM/ECLAIRs (Tan et al., GCN 44181) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+20.8 min and were taken with the sdssr filter.
In our stacked frames, subtracted from the PanSTARRS DR2 template image, we do not detect any optical counterpart in the SVOM/ECLAIRs error radius.
We report our follow-up results in the table below:
+----------------+----------+---------+---------------+--------------+
| Tmid-TGRB (min)| Exp (s) | Filter | Magnitude | Instrument |
+================+==========+=========+===============+==============+
| 29.97 | 5 x 180s | r (AB) | 19.5 (5 sigma)| TEC160FL |
+----------------+----------+---------+---------------+--------------+
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Sloan filters were calibrated using the PanSTARRS DR1 catalog.
We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023).
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/).
GCN Circular 44184
Subject
GRB 260402A: MASTER optical observations
Date
2026-04-02T12:22:04Z (14 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez, A.R.Corella,
J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
V.Lipunov, A.Kuznetsov, I.Panchenko, P.Balanutsa, G.Antipov, E.Gorbovskoy, N.Tiurina,
V.Senik, A.Chasovnikov, Ya.Kechin, V.Topolev, D.Vlasenko, A.Sankovich,Yu.Tselik (Lomonosov MSU),
M.J. Segura, C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
N.Budnev, O.Gress (ISU),
A.Sosnovskij (CrAO),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
MASTER-OAGH robotic telescope of MASTER Global Robotic Net [1-4]
started SVOM GRB 260302A (Tan et al. GCN 44181, Gotz et al. GCN 44182 Ttrigger=2026-04-02 10:30:17UT)
at 2026-04-02 10:55:46UT (25min after trigger time) with m_lim=19.1m(unfiltered) at 1st image. We didn't find new object inside error-box at single images.Observations and reduction will be continued.
Error-box altitude was 34deg, the sun_alt=-28deg, the FULL moon (0.99) alt=27deg (in 75 deg from erro-box) Cover map is available here
https://master.sai.msu.ru/site/master2/event.php?id=3227188
[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271
[3] Lipunov et a. 2019, ARep, vol.63, 293
[4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel
Astrophysics,Lomonosov MSU PRESS, 591pp.
http://www.pereplet.ru/lipunov/625.html#625
GCN Circular 44183
Subject
GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
Date
2026-04-02T12:17:52Z (14 days ago)
From
antier@ijclab.in2p3.fr
Via
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Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), 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), 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), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), 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), W. Tan (IHEP), R. Li (IHEP) report:
We imaged the field of the SVOM GRB 260402A (Tan et al., GCN Circ. 44181) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-04-02 10:37:04 to 11:52:05 UTC (from 7 minutes after the trigger) and obtained about 45 min of exposure in the r/z filters.
The data were reduced and coadded with the ASU and Colibri 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 and MXT source position (Tan et al., GCN Circ. 44181, Gotz et al., GCN Circ.44182) and down to the following 3-sigma limit:
r > 22.6
z > 22.0
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 44182
Subject
GRB 260402A: SVOM/MXT candidate X-ray afterglow
Date
2026-04-02T11:12:18Z (14 days ago)
From
Diego Gotz at CEA <diego.gotz@cea.fr>
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D. Gotz (CEA Saclay) on behalf of the SVOM MXT team reports:
MXT observed the field of GRB 260402A at 10:53:24 U.T., about 23 minutes after the ECLAIRs trigger.
The automatic on board software detects a faint source at
R.A.= 170.806 deg (J2000)
Dec.= +63.627 deg (J2000)
with a R90 uncertainty (incdluding systematics) of 114 arc sec.
This position is at 4.7 arc min from the ECLAIRs position reported by Tan et al. (GCN 44181).
Further data will be needed to confirm the afterglow nature of this candidate source.
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 at ihep.ac.cn.
Please contact the BA by email if you require additional information.
GCN Circular 44181
Subject
GRB 260402A: SVOM detection of a burst
Date
2026-04-02T10:51:18Z (14 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
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W. Tan, R. Li (IHEP), M. Brunet, O. Godet (IRAP), D. Gotz (CEA), report on behalf of the SVOM mission team:
At 2026-04-02T10:30:17 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260402A (SVOM burst-id sb26040203).
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 17 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 18.74 in the [5-20] keV energy band over a time window of 10.20 seconds starting at 2026-04-02T10:30:17.
The localization of the best alert is R.A., Dec. 170.982, 63.622 degrees:
R.A. (J2000) = 11h23m55s
Dec. (J2000) = 63d37m18s
with a 90% confidence level (C.L.) radius of 4.57 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs light curve showed a broad peak structure with a T90 duration of 15.17 (-1.27 / +5.86) s in the 5-120 keV energy band.
This burst was also detected by SVOM/GRM with a significance of 7.20.
SVOM slewed to the burst.
No prompt X-ray observation could be performed by SVOM/MXT for the time being.
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 Wenjun Tan: tanwj at ihep.ac.cn.
Please contact the BA by email if you require additional information.