GRB 251202A
GCN Circular 42966
Subject
GRB 251202A / EP251202a: SVOM/VT optical observation
Date
2025-12-03T05:27:52Z (9 hours ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, Y. L. Qiu, C. Wu, H. L. Li, L. P. Xin, Z. H. Yao, X. H. Han, Y. Xu, 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), J. X. Cao, X. Tian (GXU), Y. Wang (PMO) report on behalf of the SVOM/VT team.
SVOM/VT performed Target of Opportunity observations of GRB 251202A / EP251202a triggered by Fermi/GBM (Fermi GBM team, GCN 42933; Bala et al., GCN 42957) and EP/WXT (Zhang et al., GCN 42937; Liang et al., GCN 42946). The observation began at 2025-12-02T06:43:31 UTC, 4.905 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X-band data available, the optical counterpart (Li et al., GCN 42934; Zhu et al., GCN 42939; O’Neill et al., GCN 42947; Quirola-Vasquez et al., GCN 42948; Kuin & Moss, GCN 42956; Zheng et al., GCN 42964) was clearly detected within EP/FXT and Swift/XRT's errorbox (Zhang et al., GCN 42937; Sbarufatti et al., GCN 42943) in both VT_B and VT_R bands. The measurements in AB magnitude are as below:
mid time (h) | exposure time (s) | band | mag (AB) | mag err
-------------|-------------------|------|----------|--------
5.307 | 22*50 | VT_B | 19.29 | 0.03
5.300 | 24*50 | VT_R | 18.86 | 0.03
16.816 | 24*50 | VT_B | 20.40 | 0.06
16.726 | 22*50 | VT_R | 19.75 | 0.04
Our photometry was not corrected for Galactic extinction.
In the VT_R stacked images, we can clearly see an extended source (g=24.37, r=22.77, z=21.99) at the position 3 arcseconds away from the optical counterpart, compared to Legacy Survey DR10 catalogue, as mentioned by Li et al. (GCN 42934).
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 42957
Subject
GRB 251202A: Fermi GBM Observation
Date
2025-12-02T16:57:29Z (21 hours ago)
From
Suman Bala at USRA <sumanbala2210@gmail.com>
Via
Web form
S. Bala (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 01:50:52.31 UT on 02 December 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251202A (GCN trigger 786333057/251202077),
which was also detected by Einstein Probe (Y. J. Zhang et al. 2025, GCN 42937),
Swift XRT (B. Sbarufatti et al. 2025, GCN 42943), Swift UVOT (N.P.M. Kuin et al. 2025, GCN 42956)
GOTO (D. O’Neill et al. 2025, GCN 42947) and LCO (J. Quirola-Vasquez et al. 2025, GCN 42948).
The spectroscopic redshift of GRB 251202A is found to be 2.785 by NOT (Z.P. Zhu et al. 2025, GCN 42939).
The Fermi GBM Final Real-time Localization (GCN 42933) is consistent with the position reported by other instruments.
The angle from the Fermi LAT boresight is 73 degrees.
The GBM light curve consists of a single emission episode with a duration (T90)
of about 43 s (50-300 keV). The time-averaged spectrum
from T0-10 to T0+55 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.07 +/- 0.06 and the cutoff energy,
parameterized as Epeak, is 350 +/- 50 keV.
The event fluence (10-1000 keV) in this time interval is
(9.9 +/- 0.6)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+8.8 s in the 10-1000 keV band is 4.2 +/- 0.2 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular 42956
Subject
GRB 251202A: Swift/UVOT Detection
Date
2025-12-02T16:35:43Z (a day ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
Via
email
N.P.M. Kuin (UCL-MSSL) and M. J. Moss (GSFC) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began settled observations of the field of EP251202a/GRB
251202A 17,500s after the EP trigger (Zhang et al., GCN Circ. No 42937).
A source consistent with Li et al. (GCN Circ No 42934) and the XRT
position (Sbarufatti
et al. GCN Circ. No. 42943) is detected in the initial UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 08:08:27.5 = 122.11420 (deg.)
Dec (J2000) = 40:36:45.3 = 40.61244 (deg.)
with an estimated uncertainty of 0.48 arc sec. (radius, 90% confidence).
Preliminary detections and 3-sigma upper limits using the UVOT photometric
system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures
are:
Filter T_start(s) T_stop(s) Exp(s) Mag
u 17500 18104 509 19.80 +/- 0.20
u 23697 24044 342 20.26 +/- 0.39
u 28710 28841 129 20.06 +/- 0.53
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.043 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 42947
Subject
GRB 251202A: GOTO optical afterglow detection
Date
2025-12-02T13:55:02Z (a day ago)
From
d.s.oneill@bham.ac.uk
Via
Web form
D. O’Neill, S. Moran, G. Ramsay, R. Starling, B. P. Gompertz, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar and M. Pursiainen report on behalf of GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the GRB 251202A (Fermi GBM team, GCN 42923; Einstein Probe, GCN 42937).
Targeted observations were performed beginning at 2025-12-02 03:00:49 UT, (+1.19h post trigger). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations.
We detect the counterpart (Moss et al., GCN 42924; Osborne et al., GCN 42927; Goyal et al., GCN 42925; Li et al., GCN 42931; Sbarufatti et al. GCN 42943) with magnitude L = 17.92 ± 0.04 AB mag (+1.71h), before fading to L = 18.83 ± 0.07 AB mag (+4.3h).
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 42943
Subject
GRB 251202A: Swift-XRT afterglow detection
Date
2025-12-02T11:00:16Z (a day ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
B. Sbarufatti (INAF-OAB), 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), C. Salvaggio (INAF-OAB), M. Ferro
(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 251202A. We
searched for X-ray sources in 759 s of Photon Counting (PC) mode data.
The total exposure at the position of the afterglow (see below) is 759
s, obtained between T0+2.4 ks and T0+24.0 ks.
An uncatalogued X-ray source are clearly detected within the Einstein
Probe/WXT error region. Using 411 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 =
122.11512, +40.61228 which is equivalent to:
RA (J2000): 08h 08m 27.63s
Dec(J2000): +40d 36' 44.2"
with an uncertainty of 2.4 arcsec (radius, 90% confidence). This
position is 10.3 arcsec from the EP/FXT position (Zhang et al., GCN
Circ. 42937) and 2.2 arcsec from the optical counterpart reported by Li
et al. (GCN 42934).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.08 (+0.33, -0.24).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.93 (+0.45, -0.22). The
best-fitting absorption column is consistent with the Galactic value
of 6.5 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 3.4 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Galactic foreground: 6.5 x 10^20 cm^-2
Intrinsic column: 6 (+/-166) x 10^20 cm^-2 at z=2.785
Photon index: 1.93 (+0.45, -0.22)
If the light curve continues to decay with a power-law decay index of
1.08, the count rate at T+24 hours will be 0.018 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x
10^-13 (7.2 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/03000226.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/EP/EP_FIELD00086.
This circular is an official product of the Swift-XRT team.
GCN Circular 42938
Subject
Fermi GRB 251202A: Global MASTER-Net observations report
Date
2025-12-02T03:30:34Z (a day 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-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 251202A ( Fermi GBM team, GCN 42933) errorbox 570 sec after notice time and 604 sec after trigger time at 2025-12-02 02:00:56 UT, with upper limit up to 18.8 mag. Observations started at twilight. The observations began at zenith distance = 76 deg. The sun altitude is -15.8 deg.
The galactic latitude b = 31 deg., longitude l = 177 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3057770
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
634 | 2025-12-02 02:00:56 | MASTER-SAAO | (07h 56m 46.47s , +43d 37m 13.0s) | C | 60 | 17.7 |
694 | 2025-12-02 02:00:56 | MASTER-SAAO | (07h 56m 46.46s , +43d 37m 13.0s) | C | 180 | 18.6 | Coadd
634 | 2025-12-02 02:00:56 | MASTER-SAAO | (07h 59m 07.79s , +43d 21m 09.1s) | C | 60 | 18.0 |
694 | 2025-12-02 02:00:56 | MASTER-SAAO | (07h 59m 07.80s , +43d 21m 09.1s) | C | 180 | 18.8 | Coadd
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 42933
Subject
GRB 251202A: Fermi GBM Final Real-time Localization
Date
2025-12-02T02:01:27Z (2 days ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 01:50:52 UT on 2 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251202A (trigger 786333057.306028 / 251202077).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 120.3, Dec = 43.5 (J2000 degrees, equivalent to J2000 08h 01m, 43d 30'), with a statistical uncertainty of 2.8 degrees.
The angle from the Fermi LAT boresight is 70.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251202077/quicklook/glg_skymap_all_bn251202077.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251202077/quicklook/glg_healpix_all_bn251202077.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251202077/quicklook/glg_lc_medres34_bn251202077.gif