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GRB 251214B

GCN Circular 43141

Subject
GRB 251214B: Mondy optical upper limit
Date
2025-12-16T13:49:15Z (5 hours ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. A. Volnova (IKI), E. Klunko (ISTP), A. S. Pozanenko (IKI), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN:

We observed the field of the long GRB 251214B detected by Fermi (Fermi team, GCN 43088), Swift (Eyles-Ferris et al., GCN 43089; Evans et al., GCN 43098; Kuin and Eyles-Ferris, GCN 43105; Burrows et al., GCN 43112; Laha et al., GCN 43129), and GECAM-B (Luo et al., GCN 43113) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) taking several 120-second expositions in R-band starting on Dec.15 UT 11:36:28. In the stacked image we do not detect the optical counterpart reported previously (Eyles-Ferris et al., GCN 43089; Kang et al., GCN 43093; Gress et al., GCN 43095; Fu et al., GCN 43097; Gupta et al., GCN 43100; Watson et al., GCN 43103; Kuin and Eyles-Ferris, GCN 43105; Pérez-Fournon et al., GCN 43123; Volnova et al., GCN 43124; de Ugarte Postigo et al., GCN 43131; Pankov et al., GCN 43132; Lin et al., GCN 43134). Preliminary photometry and observational details are the following:

Date        UT start  t-T0       Exp.    Filter  Obj.  Err.  UL       Site/Telescope
                     (mid,days)  (n*s)                      (3sigma)
2025-12-15  11:36:28  1.12792    30*120  R       n/d   n/d   22.6     Mondy/AZT-33IK


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

GCN Circular 43134

Subject
GRB 251214B: 1.6m Mephisto observations with newly installed mosaic cameras
Date
2025-12-16T04:17:28Z (15 hours ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Weikang Lin, Guowang Du, Ziwei Li, Brajesh Kumar, Jiayu Qi, Donglin Gao, Yu Pan, Yuan Fang, Xinlei Chen, Xingzhu Zou, Xufeng Zhu, Tao Wang, Jinghua Zhang, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:

We performed simultaneous multi-band photometric observations of GRB 251214B (Fermi GBM Team, GCN Circ. 43088; Eyles-Ferris et al., GCN Circ. 43089) with the newly installed three mosaic cameras on the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at the Lijiang Observatory. The observations were initiated at 11:31:54UTC2025-12-14 (~2.5 hours after the Swift/BAT trigger). Multiple frames were obtained in uvgriz - bands. The optical counterpart is detected in the stacked images of g, r bands and single frames of i, z bands, but there is no detection in the u and v band stacked images. The preliminary photometric magnitudes and 3-sigma upper limits are listed below. These magnitudes are not corrected for the Galactic extinction in the direction of the burst.

UT Start             |Band | Exposure(s)| mag/LimMag (AB) 
---------------------|-----|------------|----------------
2025-12-14T11:49:07  | u   |  300.0*2   |  >22.68
2025-12-14T11:31:54  | v   |  300.0*2   |  >22.47 
2025-12-14T11:49:09  | g   |  300.0*2   |  21.08 (+/-0.12)
2025-12-14T11:31:56  | r   |  300.0*2   |  20.64 (+/-0.08)
2025-12-14T11:49:09  | i   |  300.0     |  19.50 (+/-0.07)
2025-12-14T11:31:56  | z   |  300.0     |  18.60 (+/-0.14)

The optical detection of the burst is consistent with Eyles-Ferris et al. 2025 (GCN 43089); Kang et al. 2025 (GCN 43093); Gress et al. 2025 (GCN 43095); Fu et al. 2025 (GCN 43097); Gupta et al. 2025 (GCN 43100); Watson et al. (GCN 43103); Kuin et al. (GCN 43105); Pérez-Fournon (GCN 43123); Volnova et al. (GCN 43124); Postigo et al. (GCN 43131). 

-------------------------------------------------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025, and these are currently in the commissioning phase. Here, we note that the current data processing pipeline is still at a preliminary stage, with flux calibration precision in each band at the level of about 5% or even higher.
-------------------------------------------------------------------------------------------------

GCN Circular 43132

Subject
GRB 251214B: UAFO optical upper limit
Date
2025-12-15T18:11:38Z (a day ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
N. S. Pankov (HSE, IKI), A. Kochergin (UAFO IAA), A. A. Volnova (IKI), A. S. Pozanenko (IKI)  report on behalf of IKI-GRB-FuN:

We observed the field of the long GRB 251214B detected by Fermi (Fermi team, GCN 43088), Swift (Eyles-Ferris et al., GCN 43089; Evans et al., GCN 43098; Kuin and Eyles-Ferris, GCN 43105; Burrows et al., GCN 43112; Laha et al., GCN 43129), and GECAM-B (Luo et al., GCN 43113) with the RC-500 (0.5m) telescope of Ussuriysk Astrophysical Observatory (UAFO) taking several frames in R-band. The observations started on Dec. 14 at 10:44 UT, i.e., ~ 1.5 hours after the Swift/BAT trigger. In the stacked image we do not detect the optical counterpart reported previously (Eyles-Ferris et al., GCN 43089; Kang et al., GCN 43093; Gress et al., GCN 43095; Fu et al., GCN 43097; Gupta et al., GCN 43100; Watson et al., GCN 43103; Kuin and Eyles-Ferris, GCN 43105; Pérez-Fournon et al., GCN 43123; Volnova et al., GCN 43124; de Ugarte Postigo et al., GCN 43131). Photometry and observational details are the following:

Date        UT start  t-T0       Exp.    Filter   Obj.   Err.  UL         Site/Telescope
                     (mid,days)  (n*s)                         (3sigma)
2025-12-14  10:44:26  0.09073    57*60   R        n/d    n/d   19.4       UAFO/RC500

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

GCN Circular 43131

Subject
GRB 251214B: VLT/X-shooter observations
Date
2025-12-15T17:56:34Z (a day ago)
From
Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>
Via
email
A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud), M. Garnichey (LUX-Paris Obs.), J. An (NAOC), G. Corcoran (UCD), L. Izzo (INAF/OACn & DARK/NBI), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF/IAPS), A. Torralba (ISTA) and Y. Ma (Princeton U.) report on behalf of the Stargate collaboration:

We observed the optical counterpart of GRB 251214B detected by Fermi (Fermi GBM team, GCN 43088), Swift (Eyles-Ferris et al., GCN 43089) and GECAM-B (Luo et al., GCN 43113) with X-shooter mounted on the UT3 (Melipal) of ESO’s Very Large Telescope (Paranal Observatory, Chile). Observations were conducted in twilight and at large airmass.

The acquisition images, which started at 00:46:54 UT of 15 Dec 2025 (15.74 hr after the burst onset) show the counterpart with the following photometry (AB magnitudes), as compared to field stars from the SDSS catalogue:

g = 23.15 +/- 0.06
r = 22.19 +/- 0.04
z = 20.76 +/- 0.05

A 2x600 s spectrum followed, covering the spectral range between 3000 and 21000 AA. 
The spectrum shows a red continuum, consistent with the photometry, only detectable above 6000 AA, and more prominent at infrared wavelengths. We do not detect clear emission features from the underlying host galaxy (mentioned by Gress et al., GCN 43095 and Watson et al., GCN 43103), which prevents us from measuring its redshift. We note that the Legacy Survey reveals that the source underlying the afterglow is composed of two blobs, a fainter one right under the GRB and a brighter one towards the North East, at a distance of 1". The slight difference between our photometry and the one of COLIBRÍ (Watson et al., GCN 43103) could be due to the different contribution of these underlying sources within the photometric aperture.

We acknowledge expert support from the ESO observing staff in Paranal, in particular Claudia Paladini, Célia Desgrange, Cecila Bustos, and Ana Jimenez-Gallardo.

GCN Circular 43129

Subject
GRB 251214B: Swift-BAT refined analysis
Date
2025-12-15T16:41:36Z (a day ago)
From
Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>
Via
Web form
S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), 
R. A. J. Eyles-Ferris (U Leicester), R. Gupta (GSFC),
H. A. Krimm (NSF), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. J. Moss (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC),
D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 251214B (trigger #1423875)
(Eyles-Ferris, et al., GCN Circ. 43089).  The BAT ground-calculated position is
RA, Dec = 330.222, -9.155 deg which is 
   RA(J2000)  =  22h 00m 53.4s 
   Dec(J2000) = -09d 09' 17.3" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 99%.
 
The mask-weighted BAT light curve shows a double-peaked structure with a duration of about 10 sec
T90 (15-350 keV) is 9.38 +- 0.73 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.19 to T+9.97 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.79 +- 0.12.  The fluence in the 15-150 keV band is 5.0 +- 0.4 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T-0.13 sec in the 15-150 keV band
is 2.0 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1423875

GCN Circular 43124

Subject
GRB 251214B: AbAO optical observations
Date
2025-12-15T14:54:17Z (a day ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. A. Volnova (IKI), R. Ya. Inasaridze (AbAO), A. S. Pozanenko (IKI), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN:

We observed the field of the long GRB 251214B detected by Fermi (Fermi team, GCN 43088), Swift (Eyles-Ferris et al., GCN 43089; Evans et al., GCN 43098; Kuin and Eyles-Ferris, GCN 43105; Burrows et al., GCN 43112), and  GECAM-B (Luo et al., GCN 43113) with the AS-32 0.7m telescope of Abastumani Observatory (AbAO) taking several frames in R-band. The observations started on Dec. 14 at 15:00 UT, i.e., ~ 6 hours after the Swift/BAT trigger. In the stacked image we detect the optical afterglow reported previously (Eyles-Ferris et al., GCN 43089; Kang et al., GCN 43093; Gress et al., GCN 43095; Fu et al., GCN 43097; Gupta et al., GCN 43100; Watson et al., GCN 43103; Kuin and Eyles-Ferris, GCN 43105; Pérez-Fournon et al., GCN 43123). Preliminary photometry and observational details are the following:

Date        UT start  t-T0       Exp.    Filter   Obj.   Err.  UL         Site/Telescope
                     (mid,days)  (n*s)                         (3sigma)
2025-12-14  15:00:25  0.27325    51*60   R        20.6   0.2   20.7       AbAO/AS-32

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

GCN Circular 43123

Subject
GRB 251214B: LCO detection of the optical counterpart
Date
2025-12-15T14:21:49Z (a day ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), and A. López-Oramas (IAC and ULL)

Following the detection of the long GRB 251214B, detected by Fermi GBM (Fermi GBM team, GCN #43088), Swift BAT, XRT, and UVOT (Eyles-Ferris et al., GCN #43089; Evans et al., GCN #43098; Kuin and Eyles-Ferris, GCN #43105; and Burrows et al., GCN #43112), and  GECAM-B (Luo et al., GCN #43113), we observed the field with one of the two Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Siding Spring Observatory near Coonabarabran, New South Wales, Australia. The observation, a single exposure of 60 sec in the SDSS r' filter, started on 2025-12-14 at 10:26:57 UT, about 1.41 hours after the Fermi, Swift, and GECAM-B triggers. The optical counterpart first detected by Swift UVOT (Eyles-Ferris et al., GCN #43089) is clearly detected in our image with a preliminary magnitude of r' = 19.18 +/- 0.10, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. Our result is consistent with other optical and UV detections (Eyles-Ferris et al., GCN  43089; Kang et al., GCN #43093; Gress et al., GCN #43095; Fu et al., GCN #43097; Gupta et al., GCN #43100; Watson et al., GCN #43103; and Kuin and Eyles-Ferris, GCN #43105). 

Our preliminary photometry is not corrected for the light of the likely host galaxy discussed by Gress et al. (GCN #43095), and Watson et al. (GCN #43103) at a photometric redshift of z = 0.709 +/- 0.078 (Duncan, 2022).

This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2025B-008, SGLF and Superluminous Supernovae surveys).

This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).

GCN Circular 43120

Subject
GRB 251214B: Fermi GBM Observation
Date
2025-12-15T13:26:50Z (a day ago)
From
Marianna Dafčíková at Masaryk University <500025@mail.muni.cz>
Via
Web form
M. Dafcikova (MUNI) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 09:02:18.03 UT on 14 December 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251214B (trigger 787395743/251214377),
which was also detected by Swift BAT (R. A. J. Eyles-Ferris et al. 2025, GCN 43089)
and GECAM-B (X. H. Luo et al. 2025, GCN 43113).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 97 degrees.

The GBM light curve consists of a double-peaked emission with a duration (T90)
of about 15 s (50-300 keV). The time-averaged spectrum
from T0-0.6 to T0+9.9 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.81 +/- 0.05 and the cutoff energy,
parameterized as Epeak, is 1280 +/- 80 keV.

The event fluence (10-1000 keV) in this time interval is
(1.3 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.58 s in the 10-1000 keV band is 3.3 +/- 0.3 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 43113

Subject
GRB 251214B: GECAM-B observation of a long burst
Date
2025-12-15T09:50:28Z (a day ago)
From
Xinghao Luo at SVOM/GRN <2952704891@qq.com>
Via
Web form
Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered in-flight by GRB 251214B, at 2025-12-14T09:02:19.10 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43088).

According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of  17.7 +1.8/-1.2 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb251214B.png

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).

GCN Circular 43112

Subject
GRB 251214B: Swift-XRT refined Analysis
Date
2025-12-15T09:28:13Z (a day ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana
(INAF-OAB), S. Lanava (PSU), S. Dichiara (PSU) and P.A. Evans report on
behalf of the Swift-XRT team:

We have analysed 5.9 ks of XRT data for GRB 251214B, from 46 s to 28.7
ks after the   trigger. The data comprise 8 s in Windowed Timing (WT)
mode (taken while Swift was slewing), with the remainder in Photon
Counting (PC) mode. 

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.72 (+0.14, -0.17), followed by a break at T+418 s to
an alpha of 1.33 (+0.10, -0.08).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.82 (+0.19, -0.18). The
best-fitting absorption column is  1.6 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 4.0 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 3.9 x 10^-11 (4.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 4.0 x 10^20 cm^-2
Excess significance: 3.5 sigma
Photon index:	     1.82 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
1.33, the count rate at T+24 hours will be 1.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x
10^-14 (7.8 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01423875.

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

GCN Circular 43105

Subject
GRB 251214B: Swift/UVOT Detection
Date
2025-12-15T05:01:50Z (2 days ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
Via
email
N.P.M. Kuin (MSSL/UCL) and R. Eyles-Ferris (U. Leicester) report on behalf
of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251214B  64 s
after the BAT trigger (Eyles-Ferris et al., GCN Circ. 43089).  A source
consistent with the XRT position Evans et al.  GCN Circ. 43098) is detected
in the initial UVOT exposures.

There were early reports of the optical afterglow from Zhe Kang et al. (GCN
Circ. 43093) and S.Y. Fu et al. (GCN Circ. 43097).

The preliminary UVOT position is:
    RA  (J2000) =  22:00:50.53 = 330.21053 (deg.)
    Dec (J2000) = -09:09:46.4  =  -9.16290 (deg.)
with an estimated uncertainty of 0.43 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

white               64          214          147         17.21 +/- 0.03
v                  606          800           39         17.09 +/- 0.17
b                  532          724           39         18.08 +/- 0.17
u                  277          527          246         17.76 +/- 0.08
w1                 655         1472           97        >18.9
m2                 630         1447           97        >20.3
w2                 582         5213          136        >19.6

The magnitudes in the table are not corrected for the Galactic extinction due
to the reddening of E(B-V) = 0.039 in the direction of the burst  (Schlegel
et al. 1998).

GCN Circular 43103

Subject
GRB 251214B: COLIBRÍ observations of the afterglow
Date
2025-12-15T04:27:56Z (2 days ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Alan M. Watson (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), Camila Angulo (UNAM), 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), Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM) report:

We imaged the field of the Fermi/Swift GRB 251214B (Fermi GBM Team, GCN Circ. 43088; Eyles-Ferris et al., GCN Circ. 43089) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-15 01:33 to 03:22 UTC (from 16.52 to 18.34 hours after the Swift/BAT trigger) and obtained 28, 28, 28, and 84 minutes of simultaneous exposure in the g, r, i, and z filters, respectively.

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.

In our stacked images, at the position of the afterglow (Eyles-Ferris et al., GCN Circ. 43089; Kang et al., GCN Circ. 43093; Gress et al., GCN Circ. 43095; Fu et al., GCN Circ. 43097; and Gupta et al., GCN Circ 43100) we detect the a source with preliminary magnitudes of:

g = 22.97 +/- 0.21
r = 22.05 +/- 0.12
i = 21.52 +/- 0.12
z = 20.97 +/- 0.08

We note the presence of a bright galaxy coincident with the afterglow in Legacy Survey observations (Dey et al. 2019) with g = 23.70 +/- 0.11, r = 22.37 +/- 0.06, i = 21.62 +/- 0.06, z = 21.12 +/- 0.04, and a photometric redshift of z = 0.70 +/- 0.07. We suggest this might be the host galaxy. Its low redshift is consistent with the detection of the afterglow in g by Kang et al. (GCN Circ. 43093) and in our observations.

Our observations include light from both the afterglow and this galaxy, and the afterglow is only clearly detected above the galaxy in g. The fading in g between the observations of Kang et al. (GCN Circ. 43093) and our observations implies a temporal power-law index of 1.08 or steeper.

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 43100

Subject
GRB 251214B: 1.3m DFOT optical detection
Date
2025-12-14T20:36:58Z (2 days ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Dhruv Jain, Pankaj Pawar, Debalina Kar, and Kuntal Misra (ARIES) report:

We observed the field of GRB 251214B detected by Fermi/GBM (Fermi GBM team, GCN 43088) and Swift/BAT (Eyles-Ferris et al. 2025, GCN 43089) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on  2025-12-14 at 12:59:37  UT, i.e., ~ 3.95 hours after the Fermi/GBM trigger. We have taken multiple frames with an exposure time of 300s in the I filter. We stacked the images after the alignment. We 
detect an optical afterglow in our stacked image within the error box of Swift/UVOT (Eyles-Ferris et al. 2025, GCN 43089). We obtain the following preliminary magnitude in the stacked image:

Date Start_UT T_start-T0 (hour) Filter  Exp time (s)  Magnitude
===============================================================
2025-12-14  12:59:37    ~3.95   I     300s*18     20.03 +/-0.03


The optical detection of the burst is consistent with Eyles-Ferris et al. 2025 (GCN 43089); Lipunov et al. 2025 (GCN 43091); Kang et al. 2025 (GCN 43093); Gress et al. 2025 (GCN 43095); and Fu et al. 2025 (GCN 43097).

The magnitude is not corrected for the Galactic extinction in the direction of the burst.
Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue.

GCN Circular 43098

Subject
GRB 251214B: Enhanced Swift-XRT position
Date
2025-12-14T17:09:40Z (2 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1446 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 251214B, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 330.21069, -9.16291 which is equivalent
to:

RA (J2000): 22h 00m 50.57s
Dec (J2000): -09d 09' 46.5"

with an uncertainty of 2.1 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at https://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

GCN Circular 43097

Subject
GRB 251214B: Xinglong-2.16m optical observation
Date
2025-12-14T13:15:50Z (2 days ago)
From
syfu@nao.cas.cn
Via
Web form
S.Y. Fu(HUST), D. Xu, Y.N. Zhu, P.L. Du, J.J. Jin, Z. Fan, X. Liu, L.B. He, J. An, S.Q. Jiang, Z.P. Zhu, J.J. Jia(NAOC)

We observed the field of GRB 251214B detected by Swift (Eyles-Ferris et al., GCN 43089) using the Xinglong-2.16m telescope equipped with the BFOSC camera. Observations started at 10:26:38 UT on 2025-12-14 (i.e., 1.41 h after the trigger), and a series of r- / g-band frames have been obtained.

The optical afterglow (Eyles-Ferris et al., GCN 43089; Kang et al., GCN 43093; Gress et al., GCN 43095) was clearly detected in our stacked frame with a magnitude of r = 19.40 +- 0.03 at a mid-time of 1.53 hr and g = 20.63 +- 0.09 at a mid-time of 1.88 hr, respectively, calibrated with Pan-STARRS1 DR2 catalog and not corrected for Galactic extinction.

We thank the staff at Xinglong observatory for their excellent support.

GCN Circular 43095

Subject
GRB 251214B : MASTER optical afterglow detection
Date
2025-12-14T12:55:36Z (2 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
O.A.Gress, N.M.Budnev (ISU),
V.M.Lipunov, P.Balanutsa, I.Panchenko, A.Kuznetsov, E.Gorbovskoy, G.Antipov,
N. Tiurina, Ya.Kechin,A.Chasovnikov, D.Vlasenko, V.Shumkov, I.Ionov, Yu.Tselik(Lomonosov MSU, SAI, Moscow),
R.Mirgazov, A.Diachok, O.Ershova (Irkutsk State University),
R. Podesta, C.Francile,  F. Podesta, E. Gonzalez (OAFA, San JuanUni.,Argentina);
D.Buckley (SAAO),
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 OT J220050.55-090945.8 detection

MASTER-Tunka  robotic telescope of MASTER Global Robotic Net (Lipunov et al. [1-4], http://observ.pereplet.ru ),
started Fermi (GCN 43088) and Swift (GCN 43089) GRB 251214B error-box observations
after sunset at 2025-12-14 10:20:46 UT (Lipunov et al. GCN 43091, cover map https://master.sai.msu.ru/site/master2/event.php?id=3070779 )

MASTER auto-detection system found optical afterglow at summary images
MASTER OT J220050.55-090945.8 , discovered by Swift (Eyles-Ferris et al. GCN 430089) and also observed by SVOM (Zhe Kang et al. GCN 43093)
 with unfiltered m_OT=19.5m at 2025-12-14 10:49:16UT.

There is SDSS galaxy (poss.host) in 0.067" in VIZIER database with z_phot=0.6634

Observation and reduction will continue.

[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 43093

Subject
GRB 251214B: SVOM/C-GFT optical observations
Date
2025-12-14T11:59:55Z (2 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form

Zhe Kang (CHO), Chao WU (NAOC), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), report on behalf of the SVOM/C-GFT team:

We observed the field of GRB 251214B detected by Fermi/GBM (Fermi GBM team, GCN 43088

Loading...
 
 
) and Swift/BAT (Eyles-Ferris et al., GCN 43089) with LATIOS on SVOM/C-GFT. Observations started at 2025-12-14T09:12:24 UTC, ~10.12 min after the trigger.

The optical counterpart (Eyles-Ferris et al., GCN 43089

Loading...
 
 
) was clearly detected in our stacked images of band g, r , and i. The magnitudes are:

[date-obs(mid-time)]Mid_t-T0(min)exposure time (s)bandmag (AB)mag_err
2025-12-14T09:12:4210.753x10i16.560.070
2025-12-14T09:26:5524.645x30g18.560.090
2025-12-14T09:40:0337.776x30r18.330.050

The photometry was calibrated against UCAC4 catalogue and no correction for Galactic dust extinction was applied.

We thank the observation assistants Chun-Lei Guo and Yin-Huai Hao at Jilin observatory for their excellent support.

The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.

GCN Circular 43091

Subject
Swift GRB 251214B: Global MASTER-Net observations report
Date
2025-12-14T10:37:41Z (2 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-Tunka robotic telescope  [1]  located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the Swift GRB 251214B ( R. A. J. Eyles-Ferris et al., GCN 43089) errorbox  4148 sec after notice time and 4708 sec after trigger time at 2025-12-14 10:20:46 UT, with upper limit up to  17.4 mag. Observations started at twilight.  The observations began at zenith distance = 61 deg. The sun  altitude  is -11.8 deg. 

The galactic latitude b = -46 deg., longitude l = 50 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3070785

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

    4739 |        MASTER-Tunka |   C |    60 | 16.3 |        
    4799 |        MASTER-Tunka |   C |   180 | 17.4 |  Coadd 
    4739 |        MASTER-Tunka |   C |    60 | 15.9 |        
    4814 |        MASTER-Tunka |   C |    60 | 16.8 |        
    4814 |        MASTER-Tunka |   C |    60 | 16.4 |        
    4886 |        MASTER-Tunka |   C |    60 | 16.7 |        
    4886 |        MASTER-Tunka |   C |    60 | 17.0 |        
    4963 |        MASTER-Tunka |   C |    60 | 17.1 |        
    4963 |        MASTER-Tunka |   C |    60 | 16.8 |        
    5036 |        MASTER-Tunka |   C |    60 | 16.8 |        
    5036 |        MASTER-Tunka |   C |    60 | 16.5 |        
    5111 |        MASTER-Tunka |   C |    60 | 15.5 |        
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 43089

Subject
GRB 251214B: Swift detection of a burst with an optical counterpart
Date
2025-12-14T09:28:08Z (2 days ago)
From
K.L. Page at U Leicester <klp5@leicester.ac.uk>
Via
email
R. A. J. Eyles-Ferris (U Leicester), J. J. DeLaunay (PSU),
R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
T. M. Parsotan (GSFC) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 09:02:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 251214B (trigger=1423875).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 330.217, -9.167 which is 
   RA(J2000) = 22h 00m 52s
   Dec(J2000) = -09d 10' 00"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 09:03:18.2 UT, 60.7 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 330.21095,
-9.16335 which is equivalent to:
   RA(J2000)  = 22h 00m 50.63s
   Dec(J2000) = -09d 09' 48.1"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 25 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at https://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (4.01 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.2
(+2.80/-2.44) x 10^21 cm^-2 (90% confidence).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 63 seconds after the BAT trigger. There is a candidate afterglow in
the list of sources generated on-board at
  RA(J2000)  =	22:00:50.52 = 330.21052
  DEC(J2000) = -09:09:46.7  =  -9.16296
with a 90%-confidence error radius of about 1.10 arc sec. This position is 3.6
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.47. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.039.

Burst Advocate for this burst is R. A. J. Eyles-Ferris (raje1 AT leicester.ac.uk).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)

GCN Circular 43088

Subject
GRB 251214B: Fermi GBM Final Real-time Localization
Date
2025-12-14T09:13:00Z (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 09:02:18 UT on 14 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251214B (trigger 787395743.028482 / 251214377).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 329.6, Dec = -18.5 (J2000 degrees, equivalent to J2000 21h 58m, -18d 30'), with a statistical uncertainty of 9.3 degrees.

The angle from the Fermi LAT boresight is 91.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251214377/quicklook/glg_skymap_all_bn251214377.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/bn251214377/quicklook/glg_healpix_all_bn251214377.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251214377/quicklook/glg_lc_medres34_bn251214377.gif
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