- GCN Circular #41769
Yinuo MA, Donghua ZHAO, Wenjin XIE (NAOC), Li ZHANG (IHEP), Charlotte VAN HOVE(IJCLab) report on behalf of the SVOM mission team:
At 2025-09-10T03:16:30 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250910A (SVOM burst-id sb25091001).
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 8 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.02 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2025-09-10T03:16:10.
The localization of the best alert is R.A., Dec. 39.7665, -39.6758 degrees:
R.A. (J2000) = 2h39m03.96s
Dec. (J2000) = -39d40m32.94s
with a 90% confidence level (C.L.) radius of 9.80 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM/GRM had no significant detection.
SVOM slewed to the burst. SVOM/MXT and SVOM/VT were occulted by the Earth.
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 Yinuo Ma: mayn@bao.ac.cn.
Please contact the BA by email if you require additional information.
- GCN Circular #41770
D. Götz (CEA), C. Van Hove (IJCLab), M. Moita (CEA) F. Robinet (IJCLab), P. Maggi (ObAS), H. Goto (Kanazawa Univ./CEA), C. Plasse (CEA) , report of behalf of the SVOM/MXT Team:
GRB 250910A (Ma et al. GCN# 41769) was observed by SVOM/MXT after an automatic SVOM slew, but due to Earth constraints the observation started at 2025-09-10T05:37:38, about 88 minutes after Tb. Using the on board automatic detection software, MXT detects a faint source at the coordinates
R.A. (J2000) = 02h39m18s,
Dec (J2000) = -39d39m39s
with a 90% C.L. radius of 2.5 arc min (including 25 arc sec systematic error added in quadrature). This position is at 2.8 arc min from the ECLAIRs position. At this time we cannot evaluate the variability of the source. We hence encourage follow-up with other X-ray facilities.
The Space 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. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE.
The Burst Advocate (BA) on shift for this alert is Yinuo Ma: mayn@bao.ac.cn. Please contact the BA by email if you require additional information.
- GCN Circular #41772
C. Wu (NAOC), A. Saccardi (CEA/Irfu), L. P. Xin (NAOC), J. T. Palmerio (CEA/Irfu), B.
Cordier (CEA/Irfu), Y. N. Ma (NAOC), D. Zhao (NAOC) report on behalf of the SVOM mission team:
We observed the field of the GRB 250910A detected by SVOM/ECLAIRs (Ma et al., GCN 41769) with the LCO 1m telescope at Cerro Tololo Interamerican Observatory equipped with the Sinistro instrument.
Our observation started on 2025-09-10 at 05:03:46 UT (~1.79 hr after the trigger) and we obtained 3x200 s exposures using the SDSS r filter.
In the stacked image, we did not detect any new optical source at the SVOM/MXT position (Götz et al., GCN 41770). We derived the following upper limit r > 20.8 mag (5-sigma) calibrated using nearby stars from the UCAC4 catalog and not corrected for Galactic extinction.
This project is funded by the SVOM collaboration.
- GCN Circular #41774
H. L. Li, Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei, D. H. Zhao (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.
SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Ma et al., GCN 41769). SVOM/VT began observing the field at 2025-09-10T04:00:48 UTC, 0.739 hours after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No credible candidate was detected in our single or stacked images at the SVOM/MXT position (Götz et al., GCN 41770), the three sigma limits are:
mid-time | exposure time (s) | band | upper limit (AB)
---------|-------------------|------|-----------------
1.08h | 16*50 | VT_B | 22.8
1.08h | 16*50 | VT_R | 23.3
Our results are consistent with LCO (Wu et al., GCN 41772).
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 #41776
Q. C. Liu (THU), H. N. Yang, H. W. Pan (NAO,CAS) on behalf of the Einstein Probe team:
We report on the detection of a fast X-ray transient, designated EP250910a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2025-09-10T03:16:04 (UTC). The position of the source is R.A. = 39.797 deg, DEC = -39.686 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic). The trigger time and position of this X-ray transient are consistent with that of GRB 250910A (GCN 41769, GCN 41770). The 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.74 x 10^20 cm^-2 and a photon index of 0.8 (+0.3/-0.3) during the flare. The estimated unabsorbed 0.5-4 keV flux of the flare is 1.2 (+0.3/-0.2) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
The transient event lasts for 160 seconds. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 39.8048 deg, DEC = -39.6966 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
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 #41777
M. Garnichey (LUX-Paris Obs.), V. D'Elia (ASI-SSDC), B. Schneider (LAM), A. J. Levan (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF-IAPS), S. D. Vergani (LUX-Paris Obs.) report on behalf the Stargate collaboration:
We observed the field of GRB 250910A / EP250910a (Ma et al., GCN 41769; Götz et al. GCN 41770; Wu et al., GCN 41772; Li et al., GCN 41774; Liu et al., GCN 41776) using the ESO VLT UT4 (Yepun) equipped with the HAWK-I NIR camera. We obtained 15 min imaging in the J band, beginning on 2025-09-10 at 08:28 UT (5.2 hr post-trigger).
Within the 20"-radius EP/FXT error circle (Liu et al., GCN 41776), several objects are visible in the stack of our data. All have an archival optical counterpart in the Legacy Survey (and they are thus not high-redshift candidates). Any of these sources could in principle contain an afterglow contribution, but a new template image is required to isolate any transient flux that might be present in our image. Further observations are planned with HAWK-I.
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Julien Drevon.
- GCN Circular #41794
B. Schneider (LAM), A. Martin-Carrillo (UCD), M. Garnichey (LUX-Paris Obs.), V. D'Elia (ASI-SSDC), A. J. Levan (Radboud U.), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF-IAPS), S. D. Vergani (LUX-Paris Obs.) report on behalf of the Stargate collaboration:
We observed again the field of GRB 250910A / EP250910a (Ma et al., GCN 41769; Götz et al. GCN 41770; Wu et al., GCN 41772; Li et al., GCN 41774; Liu et al., GCN 41776) using the ESO VLT UT4 (Yepun) equipped with the HAWK-I NIR camera. We obtained 15 min imaging in the J band, beginning on 2025-09-11 at 09:36:48 UT (1.26 days post-trigger).
Carrying out image subtraction with HOTPANTS between our new and previous (Garnichey et al., GCN 41777) images, a clear transient source is detected at coordinates (0.5" error):
RA(J2000) = 02:39:12.56
Dec(J2000) = -39:41:40.9
These coordinates are consistent with the EP/FXT X-ray location (Liu et al., GCN 41776) and Swift/XRT X-ray detection (https://www.swift.ac.uk/SVOM/SVOM_FIELD00036/). We measure for the transient a magnitude J = 22.73 +/- 0.08 (AB, at 5.2 hr post trigger), calibrated against nearby 2MASS stars and not corrected for Galactic extinction. We caution that strictly this is a lower limit to the source brightness, as it is possible that residual transient light was present in our second observation.
The spatial association with the X-ray afterglow and its fading behavior indicate that this object is the NIR afterglow of GRB 250910A / EP250910a.
We note that at this location, an extended optical source can be seen in the Legacy Survey (magnitudes g = 24.56, r = 23.80, i = 23.38, z = 23.66), likely being the host galaxy of this source.
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Juan Carlos Olivares and Robert De Rosa.
- GCN Circular #41798
H.L. Li (NAOC), Y.N. Ma, L.P. Xin, Y. L. Qiu, C. Wu, Z.H. Yao, 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), D. H. Zhao, J. Palmerio (CEA) report on behalf of the SVOM/VT team.
SVOM/VT performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Ma et al., GCN 41769) and EP-WXT (Liu et al., GCN 41776). The observation with good image quality began at 2025-09-10T04:00:48 UTC, ie. 44 min post trigger in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
A second ToO observation was performed to the field (Wu et al., GCN 41772; Li et al., GCN 41774; Garnichey et al., GCN 41777; Lipunov et al., GCN 41789), which stared at 2025-09-11T09:10:42 UTC, i.e., 1.24 day post trigger.
The NIR counterpart reported by VLT (Schneider et al., GCN 41794) in the errorbox of SVOM/MXT (Götz et al., GCN 41770), EP-FXT (Liu et al., GCN 41776) and Swift/XRT (https://www.swift.ac.uk/SVOM/SVOM_FIELD00036/) was detected in our stacked images in both channels. It was fading from our earliest observation at about 22.7+/-0.3 mag to 23.6+/-0.4 mag (1.27 days) in VT_R band.
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 #41799
S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M.
Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti
(INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:
Swift-XRT has performed follow-up observations of GRB 250910A. We
searched for X-ray sources in 1.2 ks of Photon Counting (PC) mode
data. The total exposure at the position of the afterglow (see below)
is 1.2 ks, obtained between T0+29.5 ks and T0+30.7 ks.
An uncatalogued X-ray source is detected and is believed to be the
afterglow. Using 1195 s of PC mode data and 1 UVOT image, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 39.80164, -39.69498
which is equivalent to:
RA (J2000): 02h 39m 12.39s
Dec(J2000): -39d 41' 41.9"
with an uncertainty of 8.4 arcsec (radius, 90% confidence). This source
is consistent with the position reported by EP/FXT (Liu et al., GCN
41776) and with the optical/NIR source detected with VLT (Schneider et
al., GCN 41794) and SVOM/VT (Li et al., GCN 41798). We cannot determine
at the present time whether the source is fading.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/03000083.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/SVOM/SVOM_FIELD00036.
This circular is an official product of the Swift-XRT team.
- GCN Circular #41842
Baptiste Hubert, Nicolas Dagoneau, Stéphane Schanne (CEA), Jean-Luc Atteia (IRAP), Frédéric Piron (LUPM), Yinuo Ma, Donghua Zhao, Wenjin Xie (NAOC)
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250910A (SVOM burst-id sb25091001).
The burst that triggered ECLAIRs (GCN 41769) consists of a broad structure with a duration of T90 = 22 -2/+3 s in the 4-20 keV energy band.
The time-averaged spectrum from T0-15.5 s to T0+6.7 s (T0 = 2025-09-10T03:16:30) in the energy range 4-120 keV is best fitted by a power-law model with photon index 1.7 +/-0.2. With this model, the 4-120 keV flux is (2.2 -0.4/+0.2)e-08 erg/cm^2/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: Nicolas Dagoneau (CEA) (nicolas.dagoneau at cea.fr)
- GCN Circular #42031
A. Saccardi (CEA/Irfu), N. Habeeb (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), N. R. Tanvir (Leicester), report on behalf of the Stargate collaboration:
We observed the object visible in the Legacy Survey underlying the position of the optical/NIR afterglow (Schneider et al., GCN 41794; Li et al., GCN41798) of GRB 250910A / EP250910a (Ma et al., GCN 41769; Liu et al., GCN 41776; Hubert et al., GCN 41842) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph.
A spectrum covering the wavelength range 3000-21000 AA was secured, with a total exposure time 2x1440 s in each of the UVB, VIS, and NIR arms. Our observation started at 03:01:23 UT on 2025 September 30, i.e. about 20 days after the SVOM trigger.
Emission lines are detected in the visible and near-infrared arms, which we identify as H-alpha, the [O III] 4959, 5007 doublet, H-beta, and the [O II] 3726, 3729 doublet, all at a common redshift of z = 0.592. We suggest this to be the redshift of the host galaxy of GRB 250910A / EP250910a.
We acknowledge excellent support from the ESO staff in Paranal, in particular Elisa Rita Garro, Rodrigo Romero and Jonathan Smoker.
- GCN Circular #42036
N. Habeeb (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), B. Rayson (U. Leicester), N. R. Tanvir (U. Leicester), report on behalf of the Stargate collaboration:
We obtained late-time imaging of the GRB 250910A / EP250910a field (Schneider et al., GCN 41794; Li et al., GCN 41798; see also Ma et al., GCN 41769; Liu et al., GCN 41776; Hubert et al., GCN 41842) at z = 0.592 (Saccardi et al., GCN 42031) with the ESO VLT equipped with FORS2. Observations were carried out on 2025 Oct 1.16 UT, i.e. ~21 days after the trigger, in the z and R bands.
At the position of the reported afterglow/NIR counterpart we detect a source in both filters. From photometry we measure z = 23.19 ± 0.11 (AB) and r = 23.97 ± 0.10 (AB) calibrated against nearby SkyMapper stars and not corrected for Galactic extinction (which is small, A_V = 0.05 mag). We note that a source is clearly visible at this location in the Legacy Survey images with magnitudes of z = 23.10 ± 0.20 and r = 23.73 ± 0.10 (both in AB).
Within the present uncertainties and allowing for filter differences, the fluxes are consistent with the pre-existing host-galaxy brightness. Using SN1998bw as the canonical GRB-SN template, the expected associated SN would have a magnitude of z ~ 22.8 at this epoch, implying a total host+SN flux of z ~ 22.2, which is not observed in this case. We therefore find no evidence for an optically bright SN associated with GRB 250910A / EP250910a at ~21 days post-burst (~13 days in the rest frame). The lack of an additional component on top of the host galaxy suggests that the expected SN emission would need to have approximately z < 24.1, corresponding to a SN ~3x fainter than SN1998bw. Without additional epochs for accurate template subtraction, at this moment, we cannot confirm if GRB 250910A / EP250910a truly lacks an associated SN component or if it simply suffers from some extinction.
We acknowledge excellent support from the ESO staff in Paranal, in particular Abel de Burgo Sierra and Cecilia Bustos.
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