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EP251129a, GRB 251129A

GCN Circular 43040

Subject
GRB 251129A: e-MERLIN C-band observations
Date
2025-12-09T00:50:36Z (8 hours ago)
From
Tao An at SHAO, CAS <antao@shao.ac.cn>
Via
Web form

Tao An (SHAO), Ailing Wang (IHEP), Emmanuel Bempong-Manful (UoM), Zigao Dai (USTC), and collaborators report on e-MERLIN observations of GRB 251129A.

We observed GRB 251129A (GCN 42877

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, 42879, 42880, 42882, 42884, 42887, 42888, 42891, 42897, 42900, 42902, 42959, 42972, 42985) with the e-MERLIN array in the C band between 2025 December 3, 17:40 UT and December 5, 04:19 UT (project RR20009). Four antennas, Pickmere (Pi), Darnhall (Da), Knockin (Kn), and Cambridge (Cm), participated in the observation.

Observing setup:

  • Frequency coverage: 4.82–5.33 GHz (C band), total bandwidth 512 MHz
  • Antennas: Pi, Da, Kn, Cm
  • Polarizations: Right and left circular
  • Spectral setup: 4 × 128 MHz spectral windows, 128 × 1 MHz channels per window (post-averaging)
  • Observation span: 2025-12-03 17:40 UT to 2025-12-05 04:19 UT

The data were processed using the standard e-MERLIN pipeline followed by calibration and imaging in CASA.

No significant radio emission was detected at the position of GRB 251129A. We place a 3σ upper limit of 0.066 mJy beam⁻¹ on the flux density.

We encourage coordinated and continued radio follow-up to further constrain the flux density and probe potential variability at C band and complementary frequencies. We thank the e-MERLIN TAG and operations teams for their support.

GCN Circular 42985

Subject
GRB 251129A/EP251129a : SVOM/ECLAIRs refined analysis
Date
2025-12-04T09:35:09Z (5 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
H. Yang, M. Brunet, O. Godet, J.-L. Atteia (IRAP), W. J. Xie (NAOC), W. J. Tan (IHEP), D. F. Kong (GXU) 

Using the event-by-event data downloaded through the X-band ground stations, we report further analysis of ECLAIRs observations of GRB 251129A/EP251129a (SVOM burst-id sb25112901, GCN 42877) detected at T0 = 2025-11-29T02:32:05 UT, which was also detected by EP/WXT (GCN 42884). 

The burst that triggered ECLAIRs shows a featureless light curve, and is detected from T0-41 s to T0+3200 s in the 4-120 keV energy band, indicating that it may be an ultra-long GRB or a very bright afterglow or a combination of both. The peculiar multi-wavelength temporal behavior of this event makes it a burst of great interest.    

ECLAIRs observations of GRB 251129A/EP251129a were interrupted by a slew and by a pass through the SAA, which divides the data into three time intervals for the time-averaged spectra analysis. 

The time-averaged spectrum from T0-41 s to T0+77 s (before the slew) in the 4-120 keV is well fitted by a power-law model with a photon index of 1.7+/-0.1 and a corresponding 4-120 keV flux of (1.5+/-0.2)e-8 erg/cm^2/s. 

The spectrum from T0+190 s to T0+585 s (after the slew and before the SAA transit) in the 4-120 keV is well fitted by a power-law model with a photon index of 2.1+/-0.1, with a 4-120 keV flux of (3.9+0.5-0.4)e-9 erg/cm^2/s. 

The spectrum from T0+1600 s to T0+3200 s (after the SAA transit) in the 4-120 keV is well fitted by a power-law model with a photon index of 2.0+/-0.1, with a 4-120 keV flux of (1.5+0.1-0.3)e-9 erg/cm^2/s. 

Overall, the ECLAIRs spectral analysis shows that GRB 251129A/EP251129a is decreasing in fluxes, and shows no significant spectral evolution from T0+190 s to T0+3200 s. The photon index measured from T0+190 s to T0+3200 s is consistent with that measured from EP/FXT at T0+2643 s (GCN 42902). The long-lasting emission seen by ECLAIRs matches the X-ray emission of the uncatalogued source seen by SVOM/MXT (GCN 42877).     
 
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: Hui Yang (IRAP) (hui.yang@irap.omp.eu)

GCN Circular 42972

Subject
GRB 251129A / EP251129a: SVOM/VT optical color bluer
Date
2025-12-03T15:51:33Z (6 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, J. Wang, Y. Xu, 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)  report on behalf of the SVOM/VT team.

SVOM/VT performed further ToO observations for GRB 251129A / EP251129a triggered by SVOM/ECLAIRs (sb25112901, Tan et al., GCN 42877, GCN 42879) and Einstein Probe (Wu et al., GCN 42884). 

The observations showed the color of the afterglow (Evans, GCN 42888; Angulo et al., GCN 42880; Watson, GCN 42883; Wu et al., GCN 42882; Masi, GCN 42885; Li et al., GCN 42887; Page et al., GCN 42891; Lipunov et al., GCN 42892; Moskvitin et al., GCN 42897; Guziy et al., GCN 42899; Sanchez-Ramirez et al., GCN 42900; Jiang et al., GCN 42902; Yaqup et al., GCN 42942; Kuin et al., GCN 42959) was changed from VT_B-VT_R~0.30+/-0.03 mag at 0.5 hours to VT_B-VT_R~0+/-0.05 mag at around 4 to 50 hours post burst.

The latest measurements are 21.8+/-0.1 mag in both channels at the mid time of 49.83 hours post burst with the exposure time of 47*70 sec. 

Our photometry was in AB magnitude and not corrected for Galactic extinction.

More 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 42959

Subject
GRB251129A/EP251129a: Swift UVOT detection
Date
2025-12-02T18:31:14Z (7 days ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
Via
email
N.P.M. Kuin (UCL-MSSL) and B. Cenko (NASA/GSFC) report on behalf of the
Swift/UVOT team:

The Swift/UVOT began observations of the field of GRB 251129A  16.8 ks
after the SVOM  trigger (Tan et al., GCN Circ. 42877). GRB251129A was
also  detected
by the EP (Wu et al, GCN Circ. 16828).
The optical afterglow consistent with the  SVOM/COLIBRI position (Angulo et
al. GCN Circ. 42880; Watson, GCN Circ. 42883)  is detected in the initial
UVOT exposures.

Preliminary 3-sigma upper limits using the UVOT photometric system  (Breeveld
et al. 2011, AIP Conf. Proc. 1358, 373) are::

Filter   T_start(s)  T_stop(s)  Exp(s)     Mag

white    16828         17147     315    19.63 +/- 0.07
white    27564        28089     502    19.69 +/- 0.12
white   111007       117142    1044    20.22 +/- 0.12
white   227072       234439    2745    20.92 +/- 0.17
u        16503                   16823           315          20.06  +/-
0.30

The magnitudes in the table are not corrected for the Galactic extinction due
to the reddening of E(B-V) = 0.025 in the direction of the burst (Schlegel
et al. 1998).

GCN Circular 42942

Subject
EP251129a/GRB 251129A: NOWT Detection
Date
2025-12-02T08:20:32Z (7 days ago)
From
Abdusamatjan Iskandar at XAO,CAS <abudu@xao.ac.cn>
Via
Web form
Shahidin Yaqup, Abdusamatjan Iskandar, Jinzhong Liu, report on behalf of optical group of the XAO:

We imaged the field of the GRB 251129A/EP 251129a (GCN Circ. 42877, 42880, 42884 ) using the Nanshan One-meter Wide-field Telescope (NOWT) at Nanshan Station of Xinjiang Astronomical Observatory (XAO). We observed from 2025-11-29 20:08:26 to 20:32:43 UTC and obtained 6 x 300 s exposure in the V filter. The stack image photometry was calibrated using nearby stars from the GAIA synthesis catalog, without correction for Galactic extinction.

We detect a source at the position (RA, DEC(J2000) = 14:57:18.88, +79:17:34.8) reported by GCN Circ.42880, with preliminary magnitude of V = 21.74+-0.64 mag.

GCN Circular 42902

Subject
EP251129a/GRB 251129A: EP-FXT follow-up observations
Date
2025-11-30T06:51:00Z (9 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. H. Jiang, Y. Wu, C. Y. Dai (NJU), Y. Wang (PMO), H. C. Ding, T. Wu (AHNU), W. J. Zhang, Y. Liu (NAO, CAS), on behalf of the Einstein Probe (EP) team:

A follow-up observation of EP251129a / GRB 251129A (Wu et al., GCN 42884, Tan et al., GCN 42877) with the Follow-up X-ray Telescope (FXT) was performed automatically at 2025-11-29T03:16:08 (UTC),  i.e. T0+2643 s, where T0 is reported by SVOM (Tan et al., GCN 42877) , with an exposure time of 5,003 s. The average FXT 0.5-10 keV spectrum of the observation can be fitted with an absorbed power law, with a fixed Galactic hydrogen column density of 2.94 x 10^20 cm^-2, an intrinsic hydrogen column density of 1.40 (-0.05/+0.05) x 10^22 cm^-2, and a photon index of 1.98 (-0.02/+0.02) . The derived average unabsorbed 0.5-10 keV flux is 1.74 (-0.02/+0.02) x 10^(-9) erg/s/cm^2.

We performed two target-of-opportunity (ToO) follow-up observations with FXT at 2025-11-29T05:26:09 (UTC, T0+10,444 s) and 2025-11-29T12:34:30 (UTC, T0+36,145 s), with an exposure time of 2,786 s and 3,091 s, respectively.

The average FXT 0.5-10 keV spectrum of the first ToO observation can be fitted with an absorbed power law, with a fixed Galactic hydrogen column density of 2.94 x 10^20 cm^-2, an intrinsic hydrogen column density of 1.04 (-0.11/+0.11) x 10^22 cm^-2, and a photon index of 2.45 (-0.05/+0.05) . The derived average unabsorbed 0.5-10 keV flux is 1.56 (-0.04/+0.04) x 10^(-10) erg/s/cm^2.

The average FXT 0.5-10 keV spectrum of the second ToO observation can be fitted with an absorbed power law, with a fixed Galactic hydrogen column density of 2.94 x 10^20 cm^-2, an intrinsic hydrogen column density of 1.49 (-0.46/+0.46) x 10^22 cm^-2, and a photon index of 3.49 (-0.23/+0.23). The derived average unabsorbed 0.5-10 keV flux is 9.20 (-0.75/+0.82) x 10^(-13) erg/s/cm^2.

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 42900

Subject
GRB 251129A / EP251129a: GTC/OSIRIS+ spectroscopic redshift z = 1.460
Date
2025-11-29T20:56:25Z (9 days ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
Via
email
R. Sanchez-Ramirez, A. J. Castro-Tirado, S. Guziy, M.D. Caballero-Garcia, I. Perez-Garcia, E. Fernandez-Garcia and S. Wu (IAA-CSIC), A.M. Garcia Rodriguez (IAC), D. Gonzalez (GTC), C. Hernandez (GTC), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXI) and L. Piro (INAF), on behalf of a larger collaboration, report:

Following the detection of GRB 251129A by SVOM/ECLAIRs (Tan et al., GCN 42877, GCN 42879), Einstein Probe (EP Team et al., GCN 42884), and by additional Swift ToO observations (Evans, GCN 42888), we observed the optical afterglow detected by Angulo et al. (GCN 42880) and further reported (Watson, GCN 42883, Wu et al., GCN 42882, Masi, GCN 42885, Li et al., GCN 42887, Lipunov et al.  GCN 42892, Moskvitin et al., GCN 42897 and Guziy et al., GCN 42899), with the 10.4m GTC telescope, at the Spanish Roque de los Muchachos Observatory, on the island of La Palma, equipped with the OSIRIS+ instrument.

The spectroscopic data consisted of 900s exposures using grisms R1000B and R2500I, covering the spectral range between 3,600 and 10,000 A. The observations started on Nov 29, 05:32 UT (i.e. 3.01 h after the burst trigger), and were carried out at high airmass (X~2). From a preliminary reduction, we find a highly absorbed continuum, showing several metal absorption with complex velocity structure. We interpret these lines as coming from CrII, FeII, FeII*, MgII, NiII, SiII, ZnII, all at z=1.460. The detection of iron fine structure lines links this system to the GRB.

GCN Circular 42899

Subject
GRB 251129A / EP251129a: OSN and CAHA optical follow-up
Date
2025-11-29T20:25:20Z (10 days ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
Via
email
S. Guziy, A. Sota, M.D. Caballero-Garcia, R. Sanchez-Ramirez, I. Olivares, I. Perez-Garcia, E. Fernandez-Garcia, S. Wu and A.J. Castro-Tirado (IAA-CSIC), J.I. Vico Linares, A. Fernandez-Martin and J. Flores-Martin (CAHA), E. Gomez, B. Rodriguez, J.P. Lopez, N. Morant Juan, I. Castillo, A. Lozano-Fernandez, F. Lopez-Martinez, M. Salah-Martinez and R. Ardon-Leon (VIU, Valencia), M. Gritsevich (Univ. of Helsinki) and Y.-D. Hu (GXI), on behalf of a larger collaboration, report:

Following the detection of GRB 251129A/EP251129a by SVOM (Tan et al. GCNC 42879) and EP (Wu et al. GCNC 42884) we imaged the gamma-ray burst error box with both the 0.9 and 1.5m telescopes at Sierra Nevada Observatory. In addition to them, we also used the 1.23m and 2.2m telescopes at the nearby Calar Alto Observatory.

We clearly detect the optical afterglow discovered by Angulo et al. (GCNC 42880), also reported by Wu et al. (GCNC 42882), Masi (GCNC 42885), Li et al. (GCNC 42887), Lipunov et al. (GCNC 42892) and Moskvitin et al. (GCNC 42897). At both Sierra Nevada and Calar Alto observatories we measure R = 19.8 +/- 0.2 and i = 19.9 +/- 0.3 respectively (2.47 h and 2.90 h after the burst onset time).

This preliminary photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and SDSS and is not corrected for the Galactic extinction.

GCN Circular 42897

Subject
GRB 251129A / EP251129a: SAO RAS optical observations
Date
2025-11-29T17:59:49Z (10 days ago)
From
Alexander Moskvitin at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin and O. I. Spiridonova (SAO RAS) 
report on behalf of GRB follow-up team.

We observed the field of the SVOM GRB 251129A (Tan et al., GCN 42877)
also detected by Einstein Probe as EP251129a (Wu et al., GCN 42884)
and Swift (Evans, GCN 42888; Page et al., GCN 42891) 
with the Zeiss-1000 1m telescope of the SAO RAS on November 29, 
15:27:01--16:00:22 UT (t_mid - T0 = 0.54973 days). We obtained 
6 * 300 sec images in Rc band.

The optical afterglow (Angulo et al., GCN 42880; Wu et al., GCN 42882; 
Watson, GCN 42883; Masi, GCN 42885; Li et al., GCN 42887; 
Lipunov et al., GCN 42892) is clearly detected in the stacked frame 
with the following brightness.

Date        UT start  t-T0       Exp.    Filter  OT     Err.  UL      
                     (mid,days)  (n*s)                       (3sigma)

2025-11-29  15:27:01  0.54973    6*300   Rc      21.00  0.07  22.8

This preliminary photometry is based on nearby stars from the USNO-B1 
catalogue (R2 magnitudes) and is not corrected for the Galactic 
extinction.

GCN Circular 42892

Subject
SVOM GRB 251129A : MASTER optical counterpart detection
Date
2025-11-29T14:26:34Z (10 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.M. Lipunov, A.Kuznetsov, I.Panchenko, E.Gorbovskoy, G.Antipov, P.Balanutsa, V.Senik, N. Tiurina, K.Zhirkov, Ya.Kechin, A.Chasovnikov, D.Vlasenko, Yu. Tselik(Lomonosov MSU, SAI, Moscow),
O.A.Gress, N.M.Budnev, O.Ershova (Irkutsk State University),
R. Podesta, C.Francile,  F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina);
D. Buckley (SAAO, South Africa),
A. Sosnovskij (CrAO RAS),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino, J.Martinez, A.R.Corella,L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico)
V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias,Spain),

MASTER-Kislovodsk robotic telescope  (Global MASTER-Net [1-4], http://observ.pereplet.ru)
started inspect (Lipunov et al. GCN 42878) of SVOM GRB 251129A ( GCN 42877)
9 sec after notice time (997 sec after trigger time) at 2025-11-29 02:48:01 UT

There is optical counterpart with unfiltered m_OT=18.7(auto-detection) at 2025-11-25 02:48:01UT,
that was discovered by SVOM/COLIBRÍ (Angulo et al. GCN 42880)
at 2025-11-29 02:51:22UT and also observed by SVOM/VT (Wu et al. GCN 42882, Li et al. GCN 42887), VT (Maxi et al. GCN 42885).


Real time updated cover map and OT  position are available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3054567

[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 V., Kornilov V., Gorbovskoy E., Tiurina N., Kuznetsov A. 2023,
Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp.
http://www.pereplet.ru/lipunov/625.html#625

GCN Circular 42891

Subject
GRB 251129A: Swift-XRT afterglow detection
Date
2025-11-29T12:29:18Z (10 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
K.L. Page (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti
(INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU),
A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester) and P.A.
Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
SVOM/ECLAIRs-detected burst GRB 251129A. We searched for X-ray sources
in  732 s of Photon Counting (PC) mode data. The total exposure at the
position of the afterglow (see below) is 2.3 ks, obtained between
T0+16.5 ks and T0+28.5 ks.

An uncatalogued X-ray source is detected within the estimated 3-sigma
SVOM/ECLAIRs error region (49 arcsec) and is above the RASS 3-sigma
upper limit at this position, and is therefore likely the GRB
afterglow. Using 2336 s of PC mode data and 4 UVOT images, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 224.33074, +79.29312
which is equivalent to:

RA (J2000): 14h 57m 19.38s
Dec(J2000): +79d 17' 35.2"

with an uncertainty of 2.1 arcsec (radius, 90% confidence). This
position is 26 arcsec from the SVOM/ECLAIRs position. The position is
consistent with the optical afterglow (GCNs 42880, 42882, 42883, 42885,
42887) and the EP X-ray transient (GCN 42884).

The light curve can be modelled can be modelled with a power-law decay
with a decay index of alpha=6.23 (+0.32, -0.29).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.71 (+0.22, -0.20). The
best-fitting absorption column is  7.3 (+3.7, -3.3) x 10^20 cm^-2, in
excess of the Galactic value of 2.9 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 2.6 x 10^-11 (3.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.3 (+3.7, -3.3) x 10^20 cm^-2
Galactic foreground: 2.9 x 10^20 cm^-2
Excess significance: 2.2 sigma
Photon index:	     2.71 (+0.22, -0.20)

If the light curve continues to decay with a power-law decay index of
6.2, the count rate at T+24 hours will be 1.1 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x
10^-15 (4.2 x 10^-15) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/00021892.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021892.

This circular is an official product of the Swift-XRT team.

GCN Circular 42888

Subject
GRB 251129A: Swift ToO observations
Date
2025-11-29T07:05:48Z (10 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a ToO observation of the SVOM/ECLAIRs-detected event
GRB 251129A. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021892
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the SVOM/ECLAIRs event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a 
GCN Circular after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

This circular is an official product of the Swift-XRT team.

GCN Circular 42887

Subject
GRB 251129A / EP251129a: SVOM/VT optical fading
Date
2025-11-29T05:41:54Z (10 days ago)
Edited On
2025-12-01T04:53:50Z (8 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li ,  L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), W. J. Tan (IHEP), D. F. Kong (GXU) report on behalf of the SVOM/VT team.

SVOM/VT performed an automatic slew to GRB 251129A/EP251129a triggered by SVOM/ECL (sb25112901, Tan et al., GCN 42879). The burst was also triggered by EP (Wu et al., GCN 42884). SVOM/VT began the observation at 2025-11-29T02:43:03 UTC, i.e., 658 seconds post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. 
 
With the downloaded early X band data, the optical counterpart (Angulo et al. GCN 42880; Watson, GCN 42883; Wu et al., GCN 42882; Masi et al. GCN 42885) was clearly detected in both channels. The measurements are given below:

  Mid_time        Band        Exposure Time       Magnitude (AB)
12.43 min         VT_B            50 sec         18.16+/-0.03 mag                      
12.43 min         VT_R            50 sec         17.89+/-0.03 mag 
44.96 min         VT_B            50 sec         19.11+/-0.04 mag                      
44.96 min         VT_R            50 sec         18.80+/-0.03 mag 

It was fading with a slope of about 0.7 with a single power law.

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 42886

Subject
EP251129a: Global MASTER-Net observations report
Date
2025-11-29T05:36:20Z (10 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, 
G.Antipov,  A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez  (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 

MASTER-Kislovodsk robotic telescope  [1]  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP251129a ( EP Team et al., GCN 42884) errorbox 107 sec after trigger time at 2025-11-29 03:16:10 UT, with upper limit up to  17.6 mag. Observations started at twilight.  The observations began at zenith distance = 44 deg. The sun  altitude  is -11.4 deg. 

The galactic latitude b = 36 deg., longitude l = 116 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3054702

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

     167 | 2025-11-29 03:16:10 |   MASTER-Kislovodsk | (14h 59m 24.03s , +79d 38m 56.6s) |   C |   120 | 17.2 |        
     287 | 2025-11-29 03:16:10 |   MASTER-Kislovodsk | (14h 59m 24.03s , +79d 38m 56.6s) |   C |   360 | 17.6 |  Coadd 
     167 | 2025-11-29 03:16:10 |   MASTER-Kislovodsk | (15h 21m 34.38s , +79d 11m 04.2s) |   C |   120 | 17.4 |        
     307 | 2025-11-29 03:18:30 |   MASTER-Kislovodsk | (14h 59m 22.72s , +79d 39m 05.4s) |   C |   120 | 17.0 |        
     307 | 2025-11-29 03:18:30 |   MASTER-Kislovodsk | (15h 21m 33.89s , +79d 11m 14.4s) |   C |   120 | 17.1 |        
     447 | 2025-11-29 03:20:49 |   MASTER-Kislovodsk | (14h 59m 21.42s , +79d 39m 14.1s) |   C |   120 | 16.6 |        
     447 | 2025-11-29 03:20:49 |   MASTER-Kislovodsk | (15h 21m 32.90s , +79d 11m 24.4s) |   C |   120 | 16.7 |        
     587 | 2025-11-29 03:23:09 |   MASTER-Kislovodsk | (14h 59m 20.23s , +79d 39m 22.9s) |   C |   120 | 16.4 |        
     707 | 2025-11-29 03:23:09 |   MASTER-Kislovodsk | (14h 59m 20.29s , +79d 39m 22.8s) |   C |   360 | 17.0 |  Coadd 
     587 | 2025-11-29 03:23:09 |   MASTER-Kislovodsk | (15h 21m 29.63s , +79d 11m 35.4s) |   C |   120 | 14.6 |        
     727 | 2025-11-29 03:25:29 |   MASTER-Kislovodsk | (14h 59m 19.13s , +79d 39m 30.8s) |   C |   120 | 16.3 |        
     867 | 2025-11-29 03:27:49 |   MASTER-Kislovodsk | (14h 59m 17.67s , +79d 39m 36.8s) |   C |   120 | 16.1 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023,  Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html

GCN Circular 42885

Subject
GRB 251129A: Optical Observations via Virtual Telescope Project, Italy
Date
2025-11-29T05:27:43Z (10 days ago)
From
Gianluca Masi at Virtual Telescope Project <gianluca@bellatrixobservatory.org>
Via
Web form
Gianluca Masi, Virtual Telescope Project (Italy), reports:

We attempted to observe the optical counterpart of GRB 251129A (Wenjun et al., GCN 42877) with the 14” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-3200E based CCD camera, its QE peaking (90%) in the red part of the spectrum.

We collected five, 300-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 29 Nov., 04:54:23 UTC, that is about 2.4 hours after the burst.

We detected a bright object at the following position (J2000.0):

R.A.: 14 57 18.81
Decl.: +79 17 34.6
mean residuals < 0.1” on both axes
R= 19.5 (assuming R-mags from Gaia DR2 for the reference stars).

This position is consistent with Angulo et al. (GCN 42880). The source is not present in the PanSTARRS DR1 dataset.

GCN Circular 42884

Subject
EP251129a/GRB 251129A : Einstein Probe detection of an X-ray transient
Date
2025-11-29T05:21:00Z (10 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form

Y. Wu, Y. H. Jiang, C. Y. Dai (NJU), Y. Wang (PMO), H. C. Ding, T. Wu (AHNU), W. J. Zhang, Y. Liu (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 EP251129a. The transient triggered EP-WXT (ID: 01709248891) at 2025-11-29T03:14:23 (UTC). The WXT position of the source is R.A. = 224.294 deg, DEC = 79.301 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).

A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 224.3331 deg, DEC = 79.2903 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). The position of FXT is 36 arcsec from SVOM/MXT detection of GRB 251129A (Tan et al., GCN 42877

Loading...
 
 
), and 10 arcsec from its optical counterpart (Angulo et al., GCN 42883). 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 42883

Subject
GRB 251129A: Correction to the position of the optical counterpar
Date
2025-11-29T04:48:59Z (10 days ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Alan Watson (UNAM) reports:

The position of the optical counterpart given by Angulo et al. (GCN 42880) was not given completely correctly. The position was given correctly in sexagesimal but not in degrees. The correct position is:

RA(J2000) = 14:57:18.88 =  224.3286 degrees
Dec(J2000) = +79:17:34.8 =  79.2930 degrees

We apologize for this error. We thank Huali Li for bringing this mistake to our attention.

GCN Circular 42882

Subject
GRB 251129A: SVOM/VT optical counterpart confirmation with VHF data
Date
2025-11-29T04:12:26Z (10 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
C. Wu, H. L. Li, L.P. Xin, Y. L. Qiu (NAOC), J. T. Palmerio (CEA), W. J. Tan (IHEP), D. F. Kong (GXU)  report on behalf of the SVOM team.

After the trigger by SVOM/ECLAIRs at 2025-11-29T02:32:05 UTC (T0), SVOM/VT performed an automatic slew to the burst GRB 251129A (sb25112901, Tan et al., GCN 42879). The observation began at 2025-11-29T02:43:03, 658 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.

The optical counterpart reported (Angulo et al., GCN 42880) was clearly detected  in the 1-bit subimages and source lists downloaded via VHF network in both channels. 
The magnitudes are :
 Mid_time     Band    Magnitude (AB)
  808 sec     VT_B   18.63+/-0.01 mag                      
  808 sec     VT_R   18.02+/-0.01 mag 

Our photometry was derived in AB magnitude and not corrected for Galactic extinction.

Given the VT color, it is likely a low redshift GRB. 

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/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.

GCN Circular 42880

Subject
GRB 251129A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
Date
2025-11-29T03:38:10Z (10 days ago)
From
Camila Angulo Valdez at UNAM <camiangulo@astro.unam.mx>
Via
Web form
Camila Angulo (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP),  Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Wenjun Tan (IHEP), Defeng Kong (GXU), Wenjin Xie (NAOC), Donghua Zhao (NAOC), Hatsune Goto (Kanazawa Univ.) report:

We imaged the field of the SVOM GRB 251129A (Tan et al., GCN Circ. 42877) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-11-29 02:51:22 to 02:57:11 UTC (from 20.0 to 25.8 minutes after the trigger) and obtained 5 minutes of simultaneous exposure in the r and z filters.

The data were reduced, coadded, and analyzed with the ASU 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.

We detect an uncatalogued source just outside the MXT error circle at: 

RA(J2000) = 14:57:18.88 = 224.2949 degrees
Dec(J2000) = +79:17:34.8= 79.3050 degrees
with an uncertainty of 0.5 arcsec.

The preliminary magnitude derived for that source is:

r = 18.30 +/-  0.01
z = 18.03 +/-  0.01


Further observations are ongoing.

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 42879

Subject
GRB 251129A: SVOM detection of a burst
Date
2025-11-29T03:15:27Z (10 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Wenjun Tan (IHEP), Defeng Kong (GXU), Wenjin Xie, Donghua Zhao (NAOC), Hatsune Goto (Kanazawa Univ.) report on behalf of the SVOM mission team:

At 2025-11-29T02:32:05 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251129A (SVOM burst-id sb25112901).

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 5 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.82 in the [8-50] keV energy band over a time window of 81.92 seconds starting at 2025-11-29T02:31:24.

The localization of the best alert is R.A., Dec. 224.5380, 79.4287 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.96 arcmin (including systematic error of 2 arcmin added in quadrature).

SVOM slewed to the burst.

SVOM/MXT began observing the field at 2025-11-29T02:45:53 UTC, 828 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 224.3258, 79.3004 degrees:
R.A. (J2000) = 14h57m01.94s
Dec. (J2000) = 79d18m32.94s

with a 90% C.L. radius of 25.08 arcseconds.

This location is 7.82 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.

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@ihep.ac.cn
Please contact the BA by email if you require additional information.

GCN Circular 42878

Subject
SVOM GRB251129A: Global MASTER-Net observations report
Date
2025-11-29T03:14:31Z (10 days ago)
Edited On
2025-12-01T14:36:50Z (8 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, 
G.Antipov,  A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez  (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 

MASTER-Kislovodsk robotic telescope  [1]  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the SVOM GRB251129.11 (trigger No 1764383485,14h 58m 09.12s , +79d 25m 43.3s, R=0.1493) errorbox  9 sec after notice time and 997 sec after trigger time at 2025-11-29 02:48:01 UT, with upper limit up to  18.9 mag. Observations started at twilight.  The observations began at zenith distance = 45 deg. The sun  altitude  is -16.3 deg. 

The galactic latitude b = 36 deg., longitude l = 116 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3054567

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

    1057 | 2025-11-29 02:48:01 |   MASTER-Kislovodsk | (14h 59m 33.58s , +79d 37m 30.3s) |   C |   120 | 18.3 |        
    1177 | 2025-11-29 02:48:01 |   MASTER-Kislovodsk | (14h 59m 33.58s , +79d 37m 30.3s) |   C |   360 | 18.9 |  Coadd 
    1057 | 2025-11-29 02:48:01 |   MASTER-Kislovodsk | (15h 21m 37.07s , +79d 09m 16.3s) |   C |   120 | 18.4 |        
    1197 | 2025-11-29 02:50:21 |   MASTER-Kislovodsk | (14h 59m 33.13s , +79d 37m 36.2s) |   C |   120 | 18.0 |        
    1197 | 2025-11-29 02:50:21 |   MASTER-Kislovodsk | (15h 21m 37.81s , +79d 09m 22.5s) |   C |   120 | 18.2 |        
    1337 | 2025-11-29 02:52:41 |   MASTER-Kislovodsk | (14h 59m 32.62s , +79d 37m 42.8s) |   C |   120 | 18.0 |        
    1337 | 2025-11-29 02:52:41 |   MASTER-Kislovodsk | (15h 21m 38.00s , +79d 09m 30.4s) |   C |   120 | 18.0 |        
    1487 | 2025-11-29 02:55:11 |   MASTER-Kislovodsk | (14h 59m 32.17s , +79d 37m 50.0s) |   C |   120 | 17.8 |        
    1607 | 2025-11-29 02:55:11 |   MASTER-Kislovodsk | (14h 59m 32.18s , +79d 37m 50.0s) |   C |   360 | 18.3 |  Coadd 
    1487 | 2025-11-29 02:55:11 |   MASTER-Kislovodsk | (15h 21m 37.94s , +79d 09m 39.5s) |   C |   120 | 18.0 |        
    1627 | 2025-11-29 02:57:31 |   MASTER-Kislovodsk | (14h 59m 31.42s , +79d 37m 57.4s) |   C |   120 | 17.6 |        
    1627 | 2025-11-29 02:57:31 |   MASTER-Kislovodsk | (15h 21m 37.84s , +79d 09m 49.2s) |   C |   120 | 17.7 |        
    1766 | 2025-11-29 02:59:50 |   MASTER-Kislovodsk | (14h 59m 30.65s , +79d 38m 04.2s) |   C |   120 | 17.5 |        
    1766 | 2025-11-29 02:59:50 |   MASTER-Kislovodsk | (15h 21m 37.58s , +79d 09m 57.9s) |   C |   120 | 17.8 |        
    1906 | 2025-11-29 03:02:10 |   MASTER-Kislovodsk | (14h 59m 29.69s , +79d 38m 11.3s) |   C |   120 | 17.6 |        
    1906 | 2025-11-29 03:02:10 |   MASTER-Kislovodsk | (15h 21m 37.28s , +79d 10m 06.9s) |   C |   120 | 17.9 |        
    2046 | 2025-11-29 03:04:31 |   MASTER-Kislovodsk | (14h 59m 28.84s , +79d 38m 19.5s) |   C |   120 | 17.7 |        
    2046 | 2025-11-29 03:04:31 |   MASTER-Kislovodsk | (15h 21m 37.01s , +79d 10m 17.3s) |   C |   120 | 17.9 |        
    2186 | 2025-11-29 03:06:50 |   MASTER-Kislovodsk | (14h 59m 27.87s , +79d 38m 27.5s) |   C |   120 | 17.7 |        
    2186 | 2025-11-29 03:06:50 |   MASTER-Kislovodsk | (15h 21m 36.63s , +79d 10m 27.4s) |   C |   120 | 17.9 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023,  Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html

GCN Circular 42877

Subject
GRB 251129A: SVOM detection of a burst
Date
2025-11-29T03:14:08Z (10 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form

Wenjun Tan (IHEP), Defeng Kong (GXU), Wenjin Xie, Donghua Zhao (NAOC), Hatsune Goto (Kanazawa univ.) report on behalf of the SVOM mission team:

At 2025-11-29T02:32:05 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251129A (SVOM burst-id sb25112901).

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 5 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.82 in the [8-50] keV energy band over a time window of 81.92 seconds starting at 2025-11-29T02:31:24.

The localization of the best alert is R.A., Dec. 224.5380, 79.4287 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.96 arcmin (including systematic error of 2 arcmin added in quadrature).

SVOM slewed to the burst.

SVOM/MXT began observing the field at 2025-11-29T02:45:53 UTC, 828 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 224.3258, 79.3004 degrees:
R.A. (J2000) = 14h57m01.94s
Dec. (J2000) = 79d18m32.94s

with a 90% C.L. radius of 25.08 arcseconds.

This location is 7.82 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.

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@ihep.ac.cn
Please contact the BA by email if you require additional information.
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