GRB 251222A, EP251222b
GCN Circular 43273
Subject
GRB 251222A: Mondy Optical Observations
Date
2025-12-30T17:23:31Z (10 days ago)
From
Nicolai Pankov at IKI <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 251222A (The Fermi GBM team, GCN 43186; Yang et. al, GCN 43188; Preis & Greiner, GCN 43190; Evans, GCN 43191; Beardmore et. al, GCN 43213; Frederiks et. al, GCN 43214; Guo et. al, GCN 43218; Neights et. al, GCN 43222) at z = 3.171 (Saccardi et. al, GCN 43204) in the R filter using the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations began on 2025-12-25 at 14:32 UT, i.e. ~2.91 days since trigger. The optical counterpart (Palmerio et. al, GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Gupta et al., GCN 43224; Globus et al., GCN 43225; Freeberg et al., GCN 43229; Volnova et al., GCN 43230; Busmann et al., GCN 43233; Lee et al., GCN 43236; Maksut et al., GCN 43237; Kumar et al., GCN 43250) is detected in the co-add image of 30x120 sec.
The observation details and preliminary photometry are presented in the table below:
Date UT start t-T0 Exp. Filter OT Err. UL
(mid, days) (s) (3sigma)
2025-12-25 14:32:35 2.91441 30*120 R 21.66 0.12 22.9
The photometry was calibrated using nearby stars from USNO-B1.0 and not corrected for the Galactic extinction.
GCN Circular 43250
Subject
GRB 251222A/EP251222b: 1.6m Mephisto optical followup
Date
2025-12-29T11:31:46Z (11 days ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Brajesh Kumar, Shiyan Zhong, Guowang Du, Hongguang Li, Dan Zhu, Yu Pan, Yuan Fang, Xingzhu Zou, Xinlei Chen, Xufeng Zhu, Tao Wang, Jinghua Zhang, Yehao Cheng, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:
We observed GRB 251222A/EP251222b (SVOM burst-id sb25122206, Yang et al. GCN 43188; Fermi/GBM, GCN 43186; EP-WXT, Guo et al., GCN 43201) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at the Lijiang Observatory. Multi-band (ugi and vrz) simultaneous observations were acquired in two sets using the newly installed three mosaic cameras. The first set (in ugi bands) and the second set (in vrz and ugi bands) of observations were started from 17:11:08T2025-12-22 (~5 min after the SVOM trigger) and 17:48:08T2025-12-22, respectively. These observations were continued till 2025-12-22T19:23:19.
The optical counterpart reported previously (Palmerio et al., GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207 GCN 43224; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Globus et al., GCN 43225; Pankov et al., GCN 43226; Freeberg et al., GCN 43229; Volnova et al., GCN 43230; Busmann et al., GCN 43233; Lee et al., GCN 43236; Maksut et al., GCN 43237) was clearly detected in our vgriz bands but not in u band. Although our first set of observations is limited, the overall preliminary light curves indicate a decay trend during ~300 - 2500 sec and a rise afterward. The preliminary photometric magnitudes of initial frames are listed below. These magnitudes are not corrected for the Galactic extinction in the direction of the burst.
------------------------------------------------------------------
Start_Time(UT) |Band | Exp(s)| Mag/LimMag (AB)
---------------------|------|-------|-----------------------------
2025-12-22T17:11:08 | u | 45*2 | >20.85
2025-12-22T17:48:08 | v | 60*3 | 21.41 +/- 0.32
2025-12-22T17:11:11 | g | 45 | 18.28 +/- 0.05
2025-12-22T17:48:10 | r | 60 | 19.18 +/- 0.08
2025-12-22T17:11:11 | i | 45 | 17.60 +/- 0.03
2025-12-22T17:48:10 | z | 60 | 19.02 +/- 0.23
------------------------------------------------------------------
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. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. 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 presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. 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 43237
Subject
GRB 251222A: NUTTelA-TAO Early Measurements
Date
2025-12-25T13:23:54Z (15 days ago)
From
Zhanat Maksut at Nazarbayev University <zhanat.maksut@nu.edu.kz>
Via
Web form
Z. Maksut (NU), B. Grossan (UCB, NU), T. Komesh (NU), D. Berdikhan (NU), E. Abdikamalov (NU), M. Krugov (FAI), K. Baigarin (NU), M. Coughlin (UNM), P. Hello (IJCLAB), S. Antier (IJCLAB), and S. Karpov (FZU) on behalf of the GRANDMA/NUTTelA-TAO:
The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB 251222A on receipt of an automated SVOM/ECLAIRs position alert. Observations started at 17:07:10 UT on 2025-12-22, 84 s after the SVOM/ECLAIRs trigger (Yang et al., GCN 43188). We observe in Sloan g' and i' bands simultaneously with the Burst Simultaneous Three-Channel Imager (Grossan, Kumar & Smoot 2019, JHEA, 32, 14). A new optical counterpart reported previously (Palmerio et al., GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Gupta et al., GCN 43224; Globus et al., GCN 43225; Pankov et al., GCN 43226; Freeberg et al., GCN 43229) was detected. We observe a rapid decay during the first ∼100 s, followed by a gradual rise leading to the first bump at around 500 s. The light curve then exhibits a decay until ∼4000 s, after which it rises again, reaching a second bump at around 10 ks. The total duration of the observations was about 4.5 hours. We report the following preliminary, uncorrected, selected photometric values:
tc-t0(s) t_exp i'(mag) err(mag) g’(mag) err(mag)
-------- ------ ------- --------
85.5 3.0 16.2 0.08 17.02 0.09
117 30.0 17.58 0.07 19.45 0.09
519 30.0 17.32 0.08 18.22 0.07
3161 180.0 19.3 0.09 19.95 0.08
tc-t0 = trigger time minus image center time. Calibration was done with 5 bright Pan-STARRS catalog stars (see Komesh, T. et al. 2023, MNRAS 520, 6104). We caution that these are preliminary results, without color or other corrections.
This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazakhstan. GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular 43236
Subject
GRB 251222A/EP251222b: Optical detection with Kinder observations
Date
2025-12-25T09:54:37Z (15 days ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
M.-H. Lee, A. Aryan, T.-W. Chen, W.-J. Hou, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
We observed the field of the GRB/fast X-ray transient GRB 251222A/EP251222ba (Fermi/GBM team, GCN#43186; Yang et al., GCN#43188; Guo et al., GCN#43201; Shi et al., GCN#43215; Neights et al., GCN#43222) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations started at 10:39 UTC on the 23rd of December 2025 (MJD 61032.444), 17.55 hr after the Fermi/GBM detection.
We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked image, we clearly detected the optical counterpart candidate proposed by Palmerio et al. (GCN#43189) at a spectroscopic redshift of z = 3.171 (Saccardi et al., GCN#43204). The optical counterpart candidate was confirmed by several observations, including An et al. (GCN#43194); Calapai et al. (GCN#43195); Durbak et al. (NIR detection, GCN#43197); Li et al. (optical rebrightening, GCN#43203); Gupta et al. (GCN#43207, GCN#43224); Saccardi et al. (GCN#43208); Kumar et al. (GCN#43209); Pérez-Fournon et al. (GCN#43212); Globus et al. (GCN#43225); Pankov et al. (GCN#43226); Freeberg et al. (GCN#43229); Volnova et al. (GCN#43230) and Busmann et al. (GCN#43233).
Moreover, we further utilized AutoPhOT to perform the PSF photometry. The details of the observations and the measured magnitude (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude. | avg. Seeing | med. Airmass
SLT | i | 61032.444 | 17.55 | 300 * 12 | 19.48 +/- 0.07 | 3".7 | 2.27
The BALROG localization of the transient was reported by Preis et al. (GCN#43190), the Swift/XRT counterpart candidate was reported by Beardmore et al. (GCN#43213), and Frederiks et al. (GCN#43214) reported the Konus-Wind detection.
The presented magnitude is calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry et al., 2018, ApJ, 867, 105) and is not corrected for the expected Galactic foreground extinction of A_i = 0.17 mag in the direction of the transient (Schlafly & Finkbeiner, 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al., 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69.
GCN Circular 43233
Subject
GRB 251222A/EP251222b: FTW optical and NIR observations
Date
2025-12-24T14:24:34Z (16 days ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Via
Web form
Malte Busmann (LMU), Xander J. Hall (CMU), Mitra Maleki (LMU), Brendan O'Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report:
We observed the counterpart of GRB 251222A/EP251222b (Fermi GBM team et al. GCN 43186, Yang et al. GCN 43188, Palmerio et al. GCN 43189, Guo et al. GCN 43201, Huang et al. GCN 43215) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J-band simultaneously for 5 x 180 s starting at 2025-12-23T22:12:24 UT (1.21 days after the trigger). We detect the counterpart in all bands and measure an r-band magnitude of
r = 20.68 +/- 0.02 AB mag.
Our measurements are consistent with the reports by Lupinov et al. (GCN 43187), Palmerio et al. (GCN 43189), An et al. (GCN 43194), Calapai et al. (GCN 43195), Durbak et al. (GCN 43197), Li et al. (GCN 43203), Saccardi et al. (GCN 43204), Gupta et al. (GCN 43207), Saccardi et al. (CGN 43208), Kumar et al. (GCN 43209), Pérez-Fournon et al. (GCN 43212) Gupta et al. (GCN 43224), Glubus et al. (GCN 43225), Pankov et al. (GCN 43226), Freeberg et al. (GCN43229), and Volnova et al. (GCN 43230).
The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction.
We thank Michael Schmidt from the Wendelstein Observatory for obtaining these observations.
GCN Circular 43230
Subject
GRB 251222A: AbAO optical observations
Date
2025-12-24T11:20:29Z (16 days ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. A. Volnova (IKI), R. Ya. Inasaridze (AbAO), N. S. Pankov (HSE, IKI), A. S. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 251222A (The Fermi GBM team, GCN 43186; Yang et. al, GCN 43188; Preis & Greiner, GCN 43190; Evans, GCN 43191; Beardmore et. al, GCN 43213; Frederiks et. al, GCN 43214; Guo et. al, GCN 43218; Neights et. al, GCN 43222) at z = 3.171 (Saccardi et. al, GCN 43204) with the AS-32 0.7m telescope of Abastumani Observatory (AbAO) taking several 60-second frames in R-band. The observations started on Dec. 23 at UT 18:16:00, i.e., ~ 1 day after the trigger. In the stacked image we detect the optical counterpart reported previously (Palmerio et. al, GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Gupta et al., GCN 43224; Globus et al., GCN 43225; Pankov et al., GCN 43226; Freeberg et al., GCN 43229). 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)
2025-12-23 18:16:00 1.07935 72*60 R 20.46 0.18 21.3 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 43229
Subject
GRB 251222A / EP251222b: Kilonova-Catcher optical afterglow detection
Date
2025-12-24T11:03:12Z (16 days ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 251222A / EP251222b detected by Fermi/GBM (Fermi GBM team, GCN 43186), SVOM (Yang et al., GCN 43188; Wang et al. GCN 43202), Einstein Probe (Guo et al., GCN 43201), Konus-WIND (Frederiks et al. GCN 43214) and Gecam-B (Guo et al., GCN 43218) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope 72 located in Chile and the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+7.9h and were taken with Rc and sdss r and i filters.
In our stacked frames, subtracted from the Pan STARRS DR2 template image, we detect the optical counterpart reported by SVOM/VT (Palmerio et al., GCN 43189, Li et al., GCN 43203), NOT (An et al., GCN 43194), Calapai Astronomical Observatory (Calapai et al., GCN 43195), PRIME (Durbak et al., GCN 43197), VLT/Xshooter (Saccardi et al., GCN 43204), DFOT (Gupta et al., GCN 43207, GCN 43224), LCO/1m (Saccardi et al., GCN 43208; Pérez-Fournon et al., GCN 43212), GOTO (Kumar et al., GCN 43209), SVOM/COLIBRÍ (FM-GFT) (Globus et al., GCN 43225) and ZTSH (Pankov et al., GCN 43226).
We report our follow-up results in the table below:
+---------------+-----------+------------+----------------+-------------+
| Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument |
+===============+===========+============+================+=============+
| 8.36 | 9 x 300s | Rc (Vega) | 19.28 +/- 0.03 | iT72 |
| 9.95 | 15 x 180s | sdssr (AB) | 19.55 +/- 0.10 | TEC160FL |
| 10.77 | 15 x 180s | sdssi (AB) | 19.45 +/- 0.17 | TEC160FL |
| 32.8 | 12 x 300s | Rc (Vega) | 20.71 +/- 0.08 | iT72 |
+---------------+-----------+------------+----------------+-------------+
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-Cousins filters were calibrated using the GAIA DR3 Synphot catalog.
We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023).
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular 43226
Subject
GRB 251222A: ZTSH BVRI optical observations
Date
2025-12-24T08:57:11Z (16 days ago)
From
Nicolai Pankov at IKI <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), V. Rumyantsev (CrAO), A. Pozanenko (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of GRB 251222A (The Fermi GBM team, GCN 43186; Yang et. al, GCN 43188; Preis & Greiner, GCN 43190; Evans, GCN 43191; Beardmore et. al, GCN 43213; Frederiks et. al, GCN 43214; Guo et. al, GCN 43218; Neights et. al, GCN 43222) at z = 3.171 (Saccardi et. al, GCN 43204) in the BVRI filters using the 2.6-meter ZTSh telescope of CrAO. The observations began in the I-filter on 2025-12-22 at 21:15 UT, i.e. 0.173 days since trigger. The optical counterpart (Palmerio et. al, GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Gupta et al., GCN 43224; Globus et al., GCN 43225) is detected in the majority of individual V,R images.
The observation properties and the preliminary photometry of a V,R-filter image pair are presented in the table below:
Date UT start t-T0 Exp. Filter OT Err. UL
(mid, days) (s) (3sigma)
2025-12-22 21:36:41 0.188142 120 V 19.14 0.08 20.8
2025-12-22 21:38:48 0.189615 120 R 18.77 0.04 21.4
The photometry was calibrated using nearby stars from USNO-B1.0 and not corrected for the Galactic extinction. A power law fit to the R-filter light curve gives a temporal index of -0.64 +- 0.08.
GCN Circular 43225
Subject
GRB 251222A: SVOM/COLIBRÍ (FM-GFT) optical observations
Date
2025-12-24T08:20:51Z (16 days ago)
From
globus@astro.unam.mx
Via
Web form
Noémie Globus (UNAM), Camila Angulo (UNAM), 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), Nikos Mandarakas (LAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Hui Yang (IRAP) report:
We imaged the field of GRB 251222A (Fermi GBM team, GCN Circ. 43186; Yang et al., GCN Circ. 43188; Guo et al., GCN Circ. 43201; Frederiks et al., GCN Circ. 43214; Guo et al. GCN Circ 43218) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-12-23 04:28 UTC to 08:22 UTC (from 11.37 to 15.27 hours after the trigger) and obtained 78 and 103 minutes of exposure in the r and z filters, respectively. We observed in poor weather conditions with variable transparency.
The data were reduced, coadded, calibrated, 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 detected the optical counterpart discovered by Palmerio et al. (GCN Circ. 43189), and subsequently observed by An et al. (GCN Circ. 43194), Calapai (GCN Circ. 43195), Durbak et al. (GCN Circ, 43197), Li et al. (GCN Circ. 43203), Saccardi et al. (GCN Circ. 43204), Gupta et al. (GCN Cric. 43207), Saccardi et al. (GCN Circ. 43208), Kumar et al. (GCN Circ 43209), Pérez-Fournon et al. (GCN Circ. 43212) and Gupta et al. (GCN Circ. 43224), at preliminary magnitudes of:
r = 19.83 +/- 0.01,
z = 19.39 +/- 0.01.
During our observations, the afterglow fades smoothly, with no evidence for further rebrightenings like the one reported by Li et al. (GCN Circ. 43203).
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 43224
Subject
GRB 251222A: Continued 1.3m DFOT optical observation
Date
2025-12-24T07:40:06Z (16 days ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Kuntal Misra, Pankaj Pawar, Dhruv Jain, and Debalina Kar (ARIES) report:
We observed the field of GRB 251222A detected by Fermi/GBM (Fermi GBM team, GCN 43186) and SVOM (Yang et al. 2025, GCN 43188) 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 2025-12-23 at 18:56:19 UT, i.e., ~ 25.84 hours after the Fermi/GBM trigger. We have taken multiple frames with an exposure time
of 200s 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 SVOM (Palmerio et al. 2025, GCN 43189). We obtain the following preliminary magnitude in the stacked image:
Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude
===============================================================
2025-12-23 18:56:19 ~25.84 I 200s*8 19.55 +/-0.02
The optical detection of the burst is consistent with Palmerio et al. 2025, (GCN 43189); An et al. 2025 (GCN 43194); Calapai et al. 2025 (GCN 43195); Durbak et al. 2025 (GCN 43197); Li et al. 2025 (GCN 43203); Saccardi et al. 2025 (GCN 43204); Gupta et al. 2025 (GCN 43207); Saccardi et al. 2025 (GCN 43208); Kumar et al. 2025 (GCN 43209); Pérez-Fournon et al. 2025 (GCN 43212).
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 43222
Subject
GRB 251222A: Fermi GBM Observation
Date
2025-12-23T18:39:59Z (17 days ago)
From
eliza.neights@gmail.com
Via
Web form
Eliza Neights (GWU, NASA GSFC) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 17:05:51.27 UT on 22 December 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251222A (trigger 788115956/251222712).
which was also detected by SVOM ECLAIRs, GRM, and MXT (H. Yang et al. 2025, GCN 43188),
SVOM VT (J. T. Palmerio et al. 2025, GCN 43189), NOT (J. An et al. 2025, GCN 43194),
Calapai Observatory (G. Calapai et al. 2025, GCN 43195), PRIME (J. Durbak et al. 2025, GCN 43197),
EP WXT (C.-L. Guo et al. 2025, GCN 43201), DFOT (A. Gupta et al. 2025, GCN 43207),
LCO (A. Saccardi et al. 2025, GCN 43208; I. Pérez-Fournon et al. 2025, GCN 43212),
GOTO (A. Kumar et al. 2025, GCN 43209), Swift XRT (A.P. Beardmore et al. 2025, GCN 43213),
and Konus Wind (D. Frederiks et al. 2025, GCN 43214).
The spectroscopic redshift of GRB 251222A is found to be 3.171 by VLT/X-shooter (A. Saccardi et al. 2025, GCN 43204).
The Fermi GBM on-ground location is consistent with the position reported by other instruments.
The angle from the Fermi LAT boresight is 83 degrees.
The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 83 s (50-300 keV). The time-averaged spectrum
from T0-2.2 to T0+91.7 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.26 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 118 +/- 1 keV.
The event fluence (10-1000 keV) in this time interval is
(1.09 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+54 s in the 10-1000 keV band is 9.5 +/- 0.3 ph/s/cm^2.
A Band function fits the spectrum equally well
with Epeak= 64.9 +/- 0.8 keV, alpha = -0.84 +/- 0.01 and beta = -2.0 +/- 0.02.
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 43218
Subject
GRB 251222A / EP251222b: GECAM-B observation
Date
2025-12-23T15:23:20Z (17 days ago)
From
guohx@ihep.ac.cn
Via
Web form
Hao-Xuan Guo, Chen-Wei Wang, Yue Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by a long burst GRB 251222A at 2025-12-22T17:05:52.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43186), SVOM (H. Yang et al., GCN #43188, Chen-Wei Wang et al., GCN #43202), Einstein Probe (C.-L. Guo et al., GCN #43201) and Konus-Wind (D. Frederiks et al., GCN #43214). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses main emission with a duration (T90) of 55.8 +1.4/-9.6 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb251222A.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 43215
Subject
EP251222b/GRB 251222A: refined analysis of the EP-WXT and EP-FXT observations
Date
2025-12-23T14:13:35Z (17 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
R.Shi, Q. J. Huang (PMO, CAS), C. L. Guo, X. Mao, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP251222b triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Guo et al., GCN 43201), which is associated with GRB 251222A (Yang et al., GCN 43188), and followed by several telescopes (Palmerio et al., GCN 43189, Evans et al., GCN 43191, An et al., GCN 43194, Li et al., GCN 43203, Saccardi et al., GCN 43204, Gupta et al., GCN 43207, Saccardi et al., GCN 43208, Kumar et al., GCN 43209, Pérez-Fournon et al., GCN 43212, Beardmore et al., GCN 43213). The refined analysis of the WXT data shows that the event started at T0=2025-12-22T17:04:52 (UTC) and lasted for ~350 s with the peak flux of 1.4e-8 erg/s/cm^2. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 9.81e20 cm^-2 and a photon index of 1.1 (-/+0.15). The derived average unabsorbed 0.5-4 keV flux is 2.8 (-0.2/+0.3) x 10^(-9) erg/s/cm^2.
The observation by the Follow-up X-ray Telescope (FXT) was performed at 2025-12-23T05:11:10 (UTC), about 12.11 hours after T0. The exposure time of this observation is 1884 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 77.1954, -7.2139 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 9.81e20 cm^-2 and a photon index of 1.86 (-0.25/+0.26). The derived average unabsorbed 0.5-10 keV flux is 1.8 (-0.3/+0.4) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
Further observations are encouraged.
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 43214
Subject
Konus-Wind detection of GRB 251222A / EP251222b
Date
2025-12-23T12:47:21Z (17 days ago)
Edited On
2025-12-23T16:20:21Z (17 days ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Dmitry Frederiks at Ioffe Institute <ddfrederiks@gmail.com>
Via
email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 251222A (Fermi-GBM detection:
The Fermi GBM team, GCN 43186; SVOM detection:
Yang et al., GCN 43188, Wang et al., GCN 43202),
associated with the Einstein Probe X-ray transient
EP251222b (Guo et al., GCN 43201),
triggered Konus-Wind (KW) at T0=61605.670 s UT (17:06:45.670).
The burst shows multiple emission pulses in the interval from
T0-50 s to T0+33 s and has a total duration of ~83 s.
The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/
As observed by Konus-Wind, the burst had
the fluence of (9.92 ± 0.94)x10^-6 erg/cm^2 and
the 64-ms peak energy flux, measured from T0 + 4.864 s,
of (2.51 ± 0.32)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the brightest part of the burst
(measured from T0 to T0+33.024 s) is best fit in the 20 keV - 15 MeV range
by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.45 (-0.21, + 0.24)
and Ep = 102(-16,+17) keV, chi^2 = 94/98 dof.
The spectrum near the peak count rate (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range by a CPL model
with alpha = -1.23 (-0.20, + 0.23)and Ep = 131(-14,+18) keV, chi^2 = 69/83 dof.
Assuming the redshift z=3.171 (Saccardi et al., GCN 43204)
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the burst isotropic energy release E_iso to (2.21 ± 0.21)x10^53 erg,
the isotropic peak luminosity L_iso to (2.33 ± 0.30)x10^53 erg/s,
the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (425 ± 69) keV,
and the rest-frame peak energy at the peak of the emission Ep,p,z to (546 ± 68) keV.
With the obtained estimates, GRB 251222A is consistent with 68% prediction bands
of both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs
with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021),
see http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/GRB251222A_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 43213
Subject
GRB 251222A: Swift-XRT afterglow detection
Date
2025-12-23T11:12:39Z (17 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAR), T. Sbarrato
(INAF-OAB), P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows
(PSU), S. Lanava (PSU), 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 251222A. We searched for X-ray sources
in 2.0 ks of Photon Counting (PC) mode data. The total exposure at the
position of the afterglow (see below) is 2.0 ks, obtained between
T0+10.7 ks and T0+17.4 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 1130 s of PC mode data and 2 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 = 77.19502, -7.21354
which is equivalent to:
RA (J2000): 05h 08m 46.81s
Dec(J2000): -07d 12' 48.7"
with an uncertainty of 2.5 arcsec (radius, 90% confidence). This
position is 36 arcsec from the SVOM/ECLAIRs position.
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.9 (+0.8, -0.7).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.92 (+0.31, -0.20). The
best-fitting absorption column is 1.05 (+0.91, -0.12) x 10^21 cm^-2,
consistent with the Galactic value of 9.3 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 3.6 x 10^-11 (4.3 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.05 (+0.91, -0.12) x 10^21 cm^-2
Galactic foreground: 9.3 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.92 (+0.31, -0.20)
If the light curve continues to decay with a power-law decay index of
1.9, the count rate at T+24 hours will be 4.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-13 (2.0 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis of the likely afterglow
are at https://www.swift.ac.uk/ToO_GRBs/00021895/Source1.php.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021895.
This circular is an official product of the Swift-XRT team.
GCN Circular 43212
Subject
GRB 251222A / EP251222b: LCO detection of the optical counterpart
Date
2025-12-23T10:34:06Z (17 days 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 251222A / EP251222b detected by Fermi/GBM (The Fermi GBM team, GCN #43186; and Preis and Greiner, GCN #43190), SVOM ECLAIRs, GRM, and MXT (Yang et al., GCN #43188), EP/WXT (Guo et al., GCN #43201), SVOM/GRM (Wang et al., GCN 43202) and Swift-XRT (Evans, GCN #43191, source 1 of https://www.swift.ac.uk/ToO_GRBs/00021895/), we observed the field with one of the three Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Sutherland Observatory, South Africa. The observation, a single exposure of 300 sec in the SDSS r' filter, started on 2025-12-22 at 18:48:07 UT, about 1.7 hours after the SVOM and Fermi triggers.
The optical counterpart detected by SVOM/VT (Palmerio et al., GCN #43189; and Li et al., GCN #43203) is clearly detected in our image with a magnitude of r' = 18.55 +/- 0.03 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. Our result is consistent with other optical and near-IR detections (Palmerio et al., GCN #43189; An et al., GCN #43194; Calapai et al., GCN #43195; Durbak et al., GCN #43197; Li et al., GCN #43203; Saccardi et al., GCN #43204; Gupta et al., GCN #43207; Saccardi et al., GCN #43208; and Kumar et al., GCN #43209). We notice a minimum in the light curve at the time of our LCO r'-band and the Calapai Observatory (Calapai et al., GCN #43195) observations.
Saccardi et al. (GCN #43204) have reported a spectroscopic redshift of z = 3.171.
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 43209
Subject
GRB 251222A / EP251222b: GOTO optical counterpart detection
Date
2025-12-23T07:19:23Z (17 days ago)
From
Amit Kumar at The Open University, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar, G. Ramsay, D. O’Neill, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration:
We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) that serendipitously covered the field of GRB 251222A / EP251222b, detected by Fermi/GBM (The Fermi GBM team, GCN 43186), SVOM/ECLAIRs (Yang et al., GCN 43188), EP/WXT (Guo et al., GCN 43201) and SVOM/GRM (Wang et al., GCN 43202). Targeted observations were performed by GOTO-North at 2025-12-22 23:02:47 UT (5.95 hours post-trigger). The observation consisted of 4x45s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings.
The optical afterglow (Palmerio et al., GCN 43189; An et al., GCN 43194; Calapai et al., GCN 43195; Durbak et al., GCN 43197; Li et al., GCN 43203; Saccardi et al., GCN 43204; Gupta et al., GCN 43207; Saccardi et al., GCN 43208) detected with an L-band magnitude of 19.51 ± 0.11 (AB).
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing.
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 43208
Subject
GRB 251222A / EP251222b: LCO optical observations
Date
2025-12-23T07:17:11Z (17 days ago)
Edited On
2025-12-23T16:20:28Z (17 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
A. Saccardi, J. T. Palmerio (CEA/Irfu), C. Wu, L.P. Xin (NAOC), H. Yang, S. Guillot (IRAP) report on behalf of the SVOM mission team:
We observed the field of GRB 251222A (Yang et al., GCN 43188; Fermi GBM team, GCN 43186; Wang et al., GCN 43202; Guo et al., GCN 43201) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument.
Our observation started at 2025-12-22T19:31:31 (about 2.43 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical counterpart reported by Palmerio et al. (GCN 43189) is clearly detected in our images.
We measure the following magnitudes, calibrated against the Pan-STARRS1 catalog, and not corrected for Galactic extinction:
r = 18.55 +/- 0.01 AB (mid-time of 3.04 hr after the trigger);
z = 18.17 +/- 0.01 AB (mid-time of 2.59 hr after the trigger).
This result is consistent with the reports (An et al., GCN 43194; Durbak et al., GCN 43197, Li et al., GCN 43203).
This project is funded by the SVOM collaboration.
GCN Circular 43207
Subject
GRB 251222A: 1.3m DFOT optical detection
Date
2025-12-23T07:11:28Z (17 days ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Kuntal Misra, Samrat Ghosh, Pankaj Pawar, Debalina Kar, and Dhruv Jain (ARIES) report:
We observed the field of GRB 251222A detected by Fermi/GBM (Fermi GBM team, GCN 43186) and SVOM (Yang et al. 2025, GCN 43188) 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 2025-12-22 at 20:28:35 UT, i.e., ~ 3.38 hours after the Fermi/GBM trigger. We have taken multiple frames with an exposure time
of 300s in the R filter. We stacked the images after the alignment. We detect an optical afterglow in our stacked image within the error box of SVOM (Palmerio et al. 2025, GCN 43189). We obtain the following preliminary magnitude in the stacked image:
Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude
===============================================================
2025-12-22 20:28:35 ~3.38 R 300s*5 18.39 +/-0.01
The optical detection of the burst is consistent with Palmerio et al. 2025 (GCN 43189); An et al. 2025 (GCN 43194); Calapai et al. 2025 (GCN 43195); Durbak et al. 2025 (GCN 43197); Li et al. 2025 (GCN 43203); Saccardi et al. 2025 (GCN 43204).
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 43204
Subject
GRB 251222A / EP251222b: VLT/X-shooter spectroscopic redshift z = 3.171
Date
2025-12-23T05:41:55Z (18 days ago)
From
Andrea Saccardi at CEA/Irfu <andrea.saccardi@cea.fr>
Via
Web form
A. Saccardi (CEA/Irfu), A. L. Thakur (INAF-IAPS), Z.P. Zhu, J. An (NAOC), D. B. Malesani (DAWN/NBI and Radboud), L. Cotter, A. Martin-Carrillo (UCD), report on behalf of the Stargate collaboration:
We observed the optical/NIR counterpart (Palmerio et al., GCN 43189; An et al., GCN 43194; Calapai et al., GCN 43195; Durbak et al., GCN 43197; Li et al., GCN 43203) of the GRB 251222A / EP251222b detected by Fermi/GBM (Fermi GBM team, GCN 43186), SVOM/ECLAIRs (Yang et al., GCN 43188), EP/WXT (Guo et al., GCN 43201) and SVOM/GRM (Wang et al., GCN 43202) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph.
Our spectra cover the wavelength range 3000-21000 AA and consist of 2 exposures of 600 s each. Observations started on 2025 December 23 at 03:38:43 UT (10.55 hr after the burst).
In a 15-s acquisition image secured in the r band (10.45 hr after trigger), we measure r = 19.91 +/- 0.04 (AB), calibrated against nearby stars from Pan-STARRS.
In a preliminary reduction of the spectra, we clearly detect a continuum over the entire wavelength range and a trough due to Lya absorption visible at ~5070 AA. From the detection of multiple absorption features, including S II, Si II, Si II*, O I, O I*, Ni II, Si IV, C IV, Fe II, Fe II*, Al II, Al III, Cr II, Ni II*, Mg II, and Mg I we infer a redshift of z = 3.171. At the same redshift we also detect absorption features consistent with Ly-beta, Ly-gamma, and the Lyman-limit.
We acknowledge the excellent support of the ESO observing staff in Paranal. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
GCN Circular 43203
Subject
GRB 251222A / EP251222b: SVOM/VT optical rebrightening
Date
2025-12-23T05:39:41Z (18 days ago)
From
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, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) , H. Yang, S. Guillot (IRAP) report on behalf of the SVOM/VT team.
SVOM/VT performed an automatic slew on the burst GRB 251222A (SVOM trigger reference:sb25061207) triggered by SVOM/ECLAIRs (Zhang et al., GCN 40697) and also detected by SVOM/GRM (Wang et al., GCN 43202), and Fermi/GBM (Fermi GBM team, GCN 43186), which is likely associated with EP251202b (Guo et al., GCN 43201). The observation began at 2025-12-22T17:09:44 UTC, i.e. 238 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With the data received, the optical counterpart (Palmerio et al., GCN 43819; An et al., GCN 43194; Durbak et al., GCN 43197) was rising at early time to the peak of VT_R~17.37+/-0.02 mag at 389 sec and then fading in both channels with the slope of -0.92. At around 10000 seconds, the brightness was VT_R ~ 18.09+/-0.02 mag confirming a rebrightening between the epoch, and then decayed with the slope of -0.84. The result would be be refined with more data received. The measurements are derived in AB magnitude as follows:
mid-time | exposure time | band | mag (AB)
------------|----------------- |-------------------
263 sec | 50 sec | VT_B | 18.27+/-0.03
263 sec | 50 sec | VT_R | 17.57+/-0.02
5.242 hour | 100 sec | VT_B | 19.28+/-0.04
5.242 hour | 100 sec | VT_R | 18.56+/-0.03
Our photometry was not corrected for Galactic extinction.
More VT follow ups are scheduled.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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 43202
Subject
EP251222b/GRB 251222A: SVOM/GRM observation
Date
2025-12-23T04:07:28Z (18 days ago)
Edited On
2025-12-24T23:35:47Z (16 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Hui Yang, Sebastien Guillot(IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a burst GRB 251222A (SVOM trigger reference: sb25122207) at 2025-12-22T17:05:52.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#43186), SVOM/ECLAIRs (Yang et al., GCN#43188) and EP (Guo et al., GCN#43201).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 85.5 +3.0/-3.5 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb251222A.png
In addition, the position of this burst, as determined by SVOM/ECLAIRs (RA= 77.202 deg, DEC= -7.206 deg, ERR=29 arcsec), is located at about 34 degrees from the SVOM optical axis.
With this localization, the time-averaged spectrum from T0-20 to T0+100 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.49 +0.12/-0.12 and the cutoff energy, parameterized as Epeak, is 221 +233/-60 keV. The event fluence (10-1000 keV) in this time interval is (1.37 +0.17/-0.14)E-05 erg/cm^2.
The 1s peak spectrum, measured from T0+53 to T0+54 s, is also best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.95 +0.12/-0.12 and the cutoff energy, parameterized as Epeak, is 209 +40/-28 keV. The flux (10-1000 keV) in this time interval is (1.05 +0.09/-0.08)E-06 erg/cm^2/s.
The localization of GRB 251222A in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb251222A_amati.png
And the localization in the 'Yonetoku' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb251222A_yonetoku.png
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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)
GCN Circular 43201
Subject
EP251222b/GRB 251222A: Einstein Probe detection of an X-ray transient
Date
2025-12-23T03:35:23Z (18 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
C.-L. Guo (NAO, CAS), R. Shi (PMO, CAS), Q.-J. Huang (PMO,CAS), X. Mao (NAO, CAS), and 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 EP251222b. The transient triggered EP-WXT (ID: 01709250454) at 2025-12-22 17:05:34 (UTC). The WXT position of the source is R.A. = 77.207 deg, DEC = -7.208 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). EP251222b is located 0.8 arcmin away from GRB 251222A (GCN 43189), and the trigger time is differ by only 12 seconds. Thus EP251222b is possibly associated with GRB 251222A.
Further information will be updated when the telemetry data are 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 43197
Subject
GRB 251222A: PRIME near-infrared detection
Date
2025-12-23T01:48:17Z (18 days ago)
From
Joe Durbak at UMD <gcn.joedurbak@gmail.com>
Via
Web form
J. Durbak (UMD), N. Passaleva (U Rome), O. Guiffreda (UMD), M. El Kabir (U Rome), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC)
Following the Fermi GBM detection (GCN 43186) and SVOM (Yang et al., GCN 43188), we observed the transient field in Y, J and H filters with PRIME ~2 hours after Fermi and SVOM detections.
At the position of the optical counterpart reported by SVOM/VT (Palmerio et al., GCN 43189), we detect an uncatalogued source in J band. Using nearby VISTA Hemispherical Survey (VHS) stars for preliminary calibration we derive the following magnitudes, not corrected for Galactic extinction:
Filter | Mag(AB) |
-------|----------------|
J | 18.04 +/- 0.02 |
Further observations are planned.
PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024, Sumi et al. 2025).
We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations.
GCN Circular 43195
Subject
GRB 251222A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
Date
2025-12-23T01:14:18Z (18 days ago)
From
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai@tiscali.it>
Via
Web form
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy
Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani.
Report:
We observed the field of GRB 251222A detected by SVOM/ECLAIRs (Yang et al., GCN 43188) and Fermi Gamma-ray Burst Monitor (GCN 43186) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3.
The observations were started at 2025-12-22 18:27:54 UT (approximately 1.37 hours after burst) stacking a sets of unfiltered CCD image. The observations were carried out with clear skies, good visibility conditions and light gusts of wind.
The OT was detected at the following position:
RA (J2000.0) 05h 08m 46.7s
Decl. (J2000.0) -07° 12' 48.4"
Photometry was obtained using nearby PanSTARRS stars as follows:
Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Mag. err.
2025-12-22 18:56:55 UT 1.85 30x60s CR 18.70 +/- 0.09
Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations.
No correction for galactic dust extinction was applied.
Our observations are consistent with other already reported Palmerio et al. (GCN 43189); An et al. (GCN 43194).
The message may be cited.
GCN Circular 43194
Subject
GRB 251222A: NOT optical observations
Date
2025-12-22T23:07:49Z (18 days ago)
From
Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>
Via
Web form
J. An (NAOC), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), B. Schneider (LAM), A. Saccardi (CEA/Irfu), L. Cotter (UCD), M. A. Diaz Teodori, A. Nitindala (University of Turku), report on behalf of a larger collaboration:
We observed the optical counterpart (Palmerio et al., GCN 43189) of GRB 251222A (Yang et al., GCN 43188; Fermi GBM team, GCN 43186) using the Nordic Optical Telescope equipped with the Standby Camera (StanCam). A series of 3 x 300s exposures were taken in the R band starting at 2025-12-22T21:34:54.
The afterglow is well detected in the individual images with an AB magnitude of R = 18.96 +/- 0.02 at a mid-time of 4.53 hr after the trigger. Our photometry was calibrated using nearby stars from the Pan-STARRS catalog and is not corrected for Galactic extinction.
GCN Circular 43191
Subject
GRB 251222A: Swift ToO observations
Date
2025-12-22T20:09:26Z (18 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 251222A. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021895
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 43190
Subject
GRB 251222A: BALROG localization (Fermi Trigger / GRB 251222712)
Date
2025-12-22T18:24:42Z (18 days ago)
From
Jochen Greiner at MPE <jcgrog@mpe.mpg.de>
Via
email
T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
at 17:05:51 on 22 Dec. 2025 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).
The best-fit position is:
RA(2000.0) = 76.6 deg
Decl.(2000.0) = -7.7 deg
The 1 sigma statistical error radius is 2.5 deg.
We estimate an additional systematic error of 1 deg.
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB251222712/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB251222712/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB251222712/json
GCN Circular 43189
Subject
GRB 251222A: SVOM/VT optical candidate
Date
2025-12-22T17:48:55Z (18 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
J. T. Palmerio (CEA/Irfu), Y. L. Qiu, C. Wu, L. P. Xin (NAOC) on behalf of the SVOM/VT team.
After the trigger by SVOM/ECLAIRs at 2025-12-22T17:05:46 UTC (T0), SVOM performed an automatic slew on the burst location (Yang et al., GCN 43188). SVOM/VT began observing the field at 2025-12-22T17:10:47, 300.27 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below.
VT_ID 117:
This bright candidate was flagged as an uncatalogued fading source. The position of this candidate is R.A., Dec. 77.1948558, -7.2135525 degrees, corresponding to:
R.A. (J2000) = 05h08m46.8s
Dec. (J2000) = -07d12m48.8s
with an uncertainty of 0.5 arcsec. This location is within the R90 uncertainty region of the SVOM/MXT onboard localization. The source was detected in both VT_R and VT_B. The candidate's magnitudes are:
| date-obs (UTC) | mid-time | exposure | band | mag(AB) |
| -------------------- | ----------- | --------- | ----- | ------------- |
| 2025-10-13T17:44:04 | 7.5 min | 6*50 sec | VT_B | 18.70 ± 0.01 |
| 2025-10-13T17:44:04 | 7.5 min | 6*50 sec | VT_R | 17.89 ± 0.01 |
Magnitudes were not corrected for dust extinction.
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 43188
Subject
GRB 251222A: SVOM detection of a long burst
Date
2025-12-22T17:37:38Z (18 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
H. Yang, S. Guillot (IRAP), D. Götz (CEA), Y. Huang (IHEP) report on behalf of the SVOM mission team:
At 2025-12-22T17:05:46 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251222A (SVOM burst-id sb25122206). The burst was also detected by Fermi/GBM (GCN # 43186).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 9 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 26.30 in the [8-50] keV energy band over a time window of 20.40 seconds starting at 2025-12-22T17:05:51.
The localization of the best alert is R.A., Dec. 77.2146, -7.2161 degrees (J2000) with a 90% confidence level (C.L.) radius of 3.55 arcmin (including systematic error of 2 arcmin added in quadrature).
This burst also triggered SVOM/GRM at 2025-12-22T17:05:52. SVOM slewed to the burst.
SVOM/MXT began observing the field at 2025-12-22T17:08:42 UTC, 176 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at
R.A., Dec. 77.202, -7.206 degrees:
R.A. (J2000) = 5h08m48.5s
Dec. (J2000) = -7d12m21.6s
with a 90% C.L. radius of 29 arcseconds (including systematics).
This location is 1 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 Hui Yang: hyang@irap.omp.eu.
Please contact the BA by email if you require additional information.
GCN Circular 43187
Subject
SVOM GRB251222A: Global MASTER-Net observations report
Date
2025-12-22T17:28:28Z (18 days ago)
Edited On
2025-12-23T16:20:38Z (17 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Vladimir Lipunov at Lomonosov Moscow State University <lipunov@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 SVOM GRB251222.71 (trigger No 1766423142,05h 08m 53.93s , -07d 11m 56.4s, R=0.0699) errorbox 607 sec after notice time and 841 sec after trigger time at 2025-12-22 17:19:43 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 60 deg. The sun altitude is -62.3 deg.
The galactic latitude b = -25 deg., longitude l = 208 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3081133
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
872 | 2025-12-22 17:19:43 | MASTER-Tunka | (05h 08m 48.67s , -06d 53m 37.5s) | C | 60 | 16.5 |
872 | 2025-12-22 17:19:43 | MASTER-Tunka | (05h 08m 26.69s , -06d 47m 23.2s) | C | 60 | 16.2 |
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 43186
Subject
GRB 251222A: Fermi GBM Final Real-time Localization
Date
2025-12-22T17:16:31Z (18 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 17:05:51 UT on 22 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251222A (trigger 788115956.26632 / 251222712).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 75.7, Dec = -5.3 (J2000 degrees, equivalent to J2000 05h 02m, -5d 17'), with a statistical uncertainty of 2.0 degrees.
The angle from the Fermi LAT boresight is 81.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251222712/quicklook/glg_skymap_all_bn251222712.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/bn251222712/quicklook/glg_healpix_all_bn251222712.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251222712/quicklook/glg_lc_medres34_bn251222712.gif