Gamma-ray Burst 251116B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #42702
M. Pillas (IAP), M.G. Bernardini (INAF-OAB, LUPM), M. Brunet (IRAP), report on behalf of the SVOM mission team:
At 2025-11-16T15:32:36 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251116B (SVOM burst-id sb25111604).
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 Count-Rate Trigger (CRT), which produced a sequence of 1 alert. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 6.67 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2025-11-16T15:32:26.
The localization of the best alert is R.A., Dec. 18.8320, -41.0854 degrees:
```
R.A. (J2000) = 1h15m19.68s
Dec. (J2000) = -41d05m07.42s
```
with a 90% confidence level (C.L.) radius of 11.72 arcmin (including systematic error of 2 arcmin added in quadrature).
Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst. Further observations by SVOM/VT are currently scheduled.
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 Marion Pillas: marion.pillas@iap.fr. Please contact the BA by email if you require additional information.
GCN Circular #42706
D. Turpin, A. Saccardi, J. T. Palmerio (CEA/Irfu), L. P. Xin, C. Wu (NAOC), B. Cordier (CEA/Irfu), M. Pillas (IAP), M.G. Bernardini (INAF-OAB, LUPM), report on behalf of the SVOM mission team:
We observed the field of GRB 251116B (Pillas et al., GCN 42702) with the LCO 1m telescope at the South African Astronomical Observatory (SAAO) equipped with the Sinistro instrument.
Our observation started at 2025-11-16T18:42:46, about 3.1 hours after the SVOM/ECLAIRs trigger time. We obtained 3x200 s exposures in the SDSS r and the Pan-STARRS z filters. No uncatalogued source was identified in our stacked frames after subtraction against the Legacy Survey DR10 catalog image.
We measure the following upper limits (5 sigma) calibrated against the SkyMapper DR4 catalog, and not corrected for Galactic extinction:
```
r = 22.1  (AB) T_mid - T0 = 3.26 hr
z = 20.1 (AB) T_mid - T0 = 3.98 hr
```
This project is funded by the SVOM collaboration.

GCN Circular #42709
D.Y. Li, G. J. Yang, C. L. Guo (NAO, CAS), D. Z. Du (ZJU), R. X. Hu (WHU), Q. J. Huang(PMO, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 251116B (SVOM/sb25111604, Pillas et al., GCN #42702) at 2025-11-16 17:13:25 (UTC), about 1.7 hours after the SVOM/ECLAIRs trigger, with an exposure time of 5832s. Six 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_J011551.9-410700
RA (J2000): 18.9664
Dec (J2000): -41.1167
Flux: 5.54 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 1.68 x 10^-14 erg/s/cm2 (1 sigma)

EPF_J011518.5-405816
RA (J2000): 18.8272
Dec (J2000): -40.971
Flux: 1.35 x 10^-13 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 4.97 x 10^-14 erg/s/cm2 (1 sigma)

EPF_J011442.3-410511
RA (J2000): 18.6761
Dec (J2000): -41.0863 
Flux: 4.54 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 1.58 x 10^-14 erg/s/cm2 (1 sigma)

EPF_J011604.1-410246
RA (J2000): 19.0172
Dec (J2000): -41.0461
Flux: 6.74 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 1.73 x 10^-14 erg/s/cm2 (1 sigma)

EPF_J011523.3-410250
RA (J2000): 18.8471
Dec (J2000): -41.0471
Flux: 6.72 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 2.29 x 10^-14 erg/s/cm2 (1 sigma)

EPF_J011535.7-410502
RA (J2000): 18.8988
Dec (J2000): -41.0839
Flux: 7.66 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 1.59x 10^-14 erg/s/cm2 (1 sigma)

GCN Circular #42723
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Y. N. Ma, Z. H. Yao, Y. Xu, X. H. Han, 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), M. Pillas (IAP), M.G. Bernardini (INAF-OAB, LUPM) report on behalf of the SVOM/VT team.
SVOM/VT performed ToO observation on GRB 251116B (SVOM burst-id sb25111604, Pillas et al., GCN 42702). The observation started on 2025-11-17T01:05:38 UT (i.e. 9.55 hour post trigger) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously.
Inside the error box of SVOM/ECL (Pillas et al., GCN 42702) and the 6 sources reported by EP-FXT (Li et al., GCN 42709), we did not detect any new uncatalogued sources. Also no significant variation was found for the catalogued sources within EP-FXT's error circles. The 3 sigma upper limit magnitudes are derived as below:
Mid time | Band | Exposure Time | 3 sigma upper limit
```
10.0 hour   VT_B        19*70 sec       >23.3 mag    
10.0 hour   VT_R        22*70 sec       >23.3 mag
```
Our result is consistent with the LCO's observation (Turpin et al., GCN 42706).
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 #42741
M. Brunet, O. Godet (IRAP), M. Pillas (IAP), M.G. Bernardini (INAF-OAB, LUPM),
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 251116B (SVOM burst-id sb25111604, GCN 42702) detected at T0 = 2025-11-16T15:32:36.
The burst that triggered ECLAIRs consists of a single peak lightcurve, lasting about 10 s in the 4-120 keV energy band.
The time-averaged spectrum from T0-10 s to T0+0.25s in the 5-120 keV energy range is best fitted by a power-law model with a photon index of 1.49 +/-0.28. With this model, the total 4-120 keV fluence is (3.2 +0.2/-1.7)e-07 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: Marius Brunet (IRAP) (marius.brunet at irap.omp.eu)

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Jochen Greiner, last update: 18-Nov-2025 [Disclaimer]