Gamma-ray Burst 251116C

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #42703
M. Pillas (IAP), M.G. Bernardini (INAF-OAB, LUPM), M. Brunet (IRAP), A. Saccardi (CEA/Irfu), report on behalf of the SVOM mission team:
At 2025-11-16T15:57:41 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251116C (SVOM burst-id sb25111605).
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 3 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 12.47 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2025-11-16T15:57:36.
The localization of the best alert is R.A., Dec. 335.3182, -10.4239 degrees:
```
R.A. (J2000) = 22h21m16.37s
Dec. (J2000) = -10d25m26.01s
```
with a 90% confidence level (C.L.) radius of 6.49 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the 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 Marion Pillas: marion.pillas@iap.fr. Please contact the BA by email if you require additional information.
GCN Circular #42705
D. Turpin, A. Saccardi, J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), 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 251116C (Pillas et al., GCN 42703) with the LCO 1m telescope at the South African Astronomical Observatory (SAAO) equipped with the Sinistro instrument.
Our observation started at 2025-11-16T18:45:47 about 2.8 hours after the SVOM/ECLAIRs trigger time. We obtained 3x200 s exposures in the SDSS r and 3x200s exposures in the PanSTARRS z filters. No any uncatalogued source was identified in our stacked frames.
We measure the following upper limits (5 sigma) calibrated against the PanSTARRS DR1 catalog, and not corrected for Galactic extinction:
```
r = 21.5  (AB) T_mid - T0 = 3.1 hr
z = 19.9 (AB) T_mid - T0 = 2.9 hr
```
This project is funded by the SVOM collaboration.
GCN Circular #42712
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 an automatic slew on GRB 251116C (SVOM burst-id sb25111605, Pillas et al., GCN 42703). The observation started on 2025-11-16T17:04:52 UT (i.e. 1.1 hour post trigger) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No uncatalogued sources are detected in single or stacked images within ECL's error box (Pillas et al., GCN 42703) and the Swift/XRT source #1 and source #2's error box (https://www.swift.ac.uk/SVOM/SVOM_FIELD00051/). The 3 sigma limit magnitudes are derived as below:
Mid time | Band | Exposure Time | 3 sigma limit magnitude
```
1.4 hour   VT_B     23*50 sec           >23.3 mag    
1.4 hour   VT_R     28*50 sec           >23.4 mag
```
Our result is consistent with the LCO's observation (Turpin et al., GCN 42705).
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 #42721
P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 251116C, collecting 1.7 ks of Photon Counting (PC) mode data between T0+10 ks and T0+26 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows:
```
  * 0 likely counterparts
  * 0 candidate counterparts
  * 2 uncatalogued X-ray sources
  * 0 known X-ray sources
```
Uncatalogued X-ray sources
--------------------------
Source 1 (SWIFT J222122.5-102045):
==================================
```
    RA (J2000.0):   335.3441  =  22 21 22.58
    Dec (J2000.0):  -10.3459  =  -10 20 45.2
    Error:	    6.9 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    6.1 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    (7.3 [+3.1, -2.5])e-3 ct s^-1
    Mean flux:	    (4.4 [+1.9, -1.5])e-13 erg cm^-2 s^-1
    Peak rate:	    (7.3 [+3.1, -2.5])e-3 ct s^-1
    Peak flux:	    (4.4 [+1.9, -1.5])e-13 erg cm^-2 s^-1
    ECF:	    6.06e-11 erg cm^-2 ct^-1
		      assuming NH=4.81e+20 cm^-2, gamma=0.94
		      determined from a spectral fit.
    XMM UL:	    4.1e-12 erg cm^-2 s^-1, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.
    There is 1 2MASS object within the source's 3-sigma error radius.
```
Source 2 (SWIFT J222052.1-102849):
==================================
```
    RA (J2000.0):   335.2172  =  22 20 52.13
    Dec (J2000.0):  -10.4803  =  -10 28 49.1
    Error:	    5.8 (arcsec, radius, 90% confidence).
    Detect flag:    POOR
    Distance:	    5.1 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    (-1.0 +/- -1.0)e0 ct s^-1
    Mean flux:	    (-4.3 +/- -4.3)e-11 erg cm^-2 s^-1
    Peak rate:	    (2.4 [+1.9, -1.3])e-3 ct s^-1
    Peak flux:	    (1.03 [+0.80, -0.57])e-13 erg cm^-2 s^-1
    XMM UL:	    4.7e-12 erg cm^-2 s^-1, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.
```
All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.
The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00051.
This circular is an official product of the Swift-XRT team.
GCN Circular #42726
James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Cosmic Frontier), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 251116C onboard (T0: 2025-11-16T15:57:41 UTC, SVOM/ECLAIRS GCN 42703).
In a ground search of BAT survey data, the GRB was detected at a S/N of 7.2 in a single 300 s image (14 - 80 keV) starting at ~T0 - 192 s.
The BAT position is RA, Dec = 335.3327, -10.3401 deg which is
```
   RA(J2000)  = 22h 21m 19.9s
   Dec(J2000) = -10d 20′ 24.4″
```
with an estimated uncertainty of 3 arcmin radius.
Source X1 detected by Swift/XRT (GCN 42721) falls inside this error circle.
GCN Circular #42742
M. Brunet, O. Godet (IRAP), W. Xie (NAOC), 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 251116C (SVOM burst-id sb25111605, GCN 42703) detected at T0 = 2025-11-16T15:57:41, which was also detected by Swift/BAT (GCN 42726).
The burst that triggered ECLAIRs consists of a single peak lightcurve, lasting about 60 s in the 4-120 keV energy band. We note that the burst occurred close to the Earth limb and that it was quickly hidden behind the Earth after the trigger so that part of the emission might have been missed by ECLAIRs.
The time-averaged spectrum from T0-15 s to T0+39 s in the 5-120 keV energy range is best fitted by a power-law model with a photon index of 1.95 +/-0.10. With this model, the total 4-120 keV fluence is (1.2 +/-0.1) e-06 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)
GCN Circular #42772
G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), L. Fuglsang (NOT) report on behalf of a larger collaboration:
We observed the location of the SVOM/ECLAIRs (Pillas et al., GCN 42703; Brunet et al., GCN 42703) and Swift/BAT (DeLaunay et al., GCN 42726) GRB 251116C, using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera.
Our observation covers ~90% of the 3'-radius BAT error circle (including XRT source #1; Evans et al., GCN 42721), and consists of six 300-s images in the r band, taken at a mean epoch of 2025 Nov 17.910 UT (1.245 days after the trigger).
Inside or in close proximity of XRT source #1, four objects (3 point-like) are detected in both the NOT and Legacy Survey images. Their photometry does not show significant variation by more than ~0.1 mag.
Image subtraction was performed using the Legacy Survey as reference template. No new sources are detected within the covered fraction of the BAT error circle, down to a 3 sigma limiting magnitude of r > 24.4. Our non-detection is consistent with the earlier reports by LCO (Turpin et al., GCN 42705) and SVOM/VT (Li et al., GCN 42712).
GCN Circular #42815
M. Ferro, M. G. Bernardini, B. Sbarufatti, C. Salvaggio, R. Brivio, A. Mei (INAF-OAB) report on behalf of the Swift-XRT team:
Swift-XRT has conducted further observations of the field of the SVOM/ECLAIRs-detected burst GRB 251116C (Pillas et al., GCN 42703). The observations now extend from T0+10 ks to T0+452 ks and have a total exposure time of 6.1 ks.
The previously-reported "Source 1" (Evans et al., GCN 42721), is now found to be fading with ~3-sigma significance, and is therefore likely the GRB afterglow.
The results of the XRT-team automatic analysis of the source are available at https://www.swift.ac.uk/SVOM/team/SVOM_FIELD00051/Source1.php. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00051/.
This circular is an official product of the Swift-XRT team.

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Jochen Greiner, last update: 24-Nov-2025 [Disclaimer]