- vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 41323] GRB 251221A: Swift-BAT refined analysis
by GCN Circulars 25 Dec '25

25 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43234 SUBJECT: GRB 251221A: Swift-BAT refined analysis DATE: 25/12/25 05:09:07 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> A. Y. Lien (U Tampa), E. Ambrosi (INAF-IASFPA), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), 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-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251221A (trigger #1426088) (Ambrosi, et al., GCN Circ. 43166). The BAT ground-calculated position is RA, Dec = 101.422, 0.738 deg which is RA(J2000) = 06h 45m 41.4s Dec(J2000) = +00d 44' 15.8" with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 42%. The mask-weighted light curves displays a complicated multi-pulsed light curve. The T90 (15-350 keV) is 56.86 +- 7.05 sec (estimated error including systematics). The time-averaged spectrum from T-38.10 to T+27.74 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.25 +- 0.13. The fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+2.91 sec in the 15-150 keV band is 1.1 +- 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/1426088 View this GCN Circular online at https://gcn.nasa.gov/circulars/43234. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41322] GRB 251222A/EP251222b: FTW optical and NIR observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43233 SUBJECT: GRB 251222A/EP251222b: FTW optical and NIR observations DATE: 25/12/24 14:24:34 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43233. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41321] EP251222a: FTW optical and NIR observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43232 SUBJECT: EP251222a: FTW optical and NIR observations DATE: 25/12/24 14:24:05 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> 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 EP251222a (Huang et al. GCN 43200, Li et al. GCN 43205, Guo et al. GCN 43216) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J-band simultaneously for 10 x 180 s starting at 2025-12-23T21:27:09 UT (1.26 days after the trigger). We detect the counterpart in all bands. Using a template from the DESI Legacy Surveys, we measure an r-band magnitude of r = 21.64 +/- 0.06 AB mag. Our measurements are consistent with the reports by Li et al. (GCN 43205), Kumar et al. (GCN 43210), Malesani et al. (GCN 43211), and Lipunov et al. (GCN 43219). 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43232. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41320] GRB 251205A: Kilonova-Catcher optical afterglow detection
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43231 SUBJECT: GRB 251205A: Kilonova-Catcher optical afterglow detection DATE: 25/12/24 12:30:36 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> 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 251205A detected by Swift/BAT (Lanava et al., GCN 43005), Fermi/GBM (Fermi GBM team, GCN 43059) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+10.6h and were taken with sdss r and i filters. In our stacked frames, subtracted from the Pan STARRS DR2 template image, we detect the optical counterpart reported by Swift/UVOT (Lanava et al., GCN 43005, Klingler et al., GCN 43016), MASTER (Lipunov et al., GCN 43006), GTC/OSIRIS (de Ugarte Postigo et al., GCN 43008), NOT (Malesani et al., GCN 43009), GOTO (O'Neill et al., GCN 43010), COLIBRÍ (Mandarakas et al., GCN 43011) and Zeiss-1000 Koshka observatory (Pankov et al., GCN 43012), Liverpool telescope (Bochenek et al., GCN 43015, GCN 43024, GCN 43038), GROWTH (Patil et al., GCN 43019), ZTF and ATLAS (Pérez-Fournon et al., GCN 43020), FTW (Busmann et al., GCN 43026), MITSuME (Hagio et al., GCN 43029), WINTER (Mo et al., GCN 43044), 1.3m DFOT (Gupta et al., GCN 43067). We report our follow-up results in the table below: +---------------+-----------+------------+----------------+--------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+============+================+==============+ | 10.86 | 10 x 180s | sdssr (AB) | 18.35 +/- 0.09 | TEC160FL | | 12.51 | 22 x 180s | sdssi (AB) | 18.56 +/- 0.09 | TEC160FL | | 35.63 | 20 x 180s | sdssr (AB) | 19.79 +/- 0.15 | TEC160FL | | 36.72 | 19 x 180s | sdssi (AB) | 19.91 +/- 0.30 | TEC160FL | +---------------+-----------+------------+----------------+--------------+ 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. 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/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43231. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41319] GRB 251222A: AbAO optical observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43230 SUBJECT: GRB 251222A: AbAO optical observations DATE: 25/12/24 11:20:29 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43230. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41318] GRB 251222A / EP251222b: Kilonova-Catcher optical afterglow detection
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43229 SUBJECT: GRB 251222A / EP251222b: Kilonova-Catcher optical afterglow detection DATE: 25/12/24 11:03:12 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> 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/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43229. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41317] GRB 251129A / EP251129a: VLA detection of a radio counterpart
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43228 SUBJECT: GRB 251129A / EP251129a: VLA detection of a radio counterpart DATE: 25/12/24 10:46:36 GMT FROM: Tao An at SHAO, CAS <antao(a)shao.ac.cn> Tao An (SHAO), Ailing Wang (IHEP), Zigao Dai (USTC), and collaborators report on VLA observations of GRB 251129A. We observed GRB 251129A, also reported as EP251129a (e.g., GCNs 42877, 42879, 42880, 42882, 42884, 42887, 42888, 42891, 42897, 42900, 42902, 42959, 42972, 42985), with the Karl G. Jansky Very Large Array (VLA) under program VLA/25B-403 (AA627) on 2025 December 15 UT, approximately 16.0 days after the burst (relative to the SVOM/ECLAIRs trigger at 2025 Nov 29 02:32:05 UT). Observations were obtained in C band (4–8 GHz). A significant radio source is detected at the GRB position. Using standard wideband imaging, we measure: - Position (J2000): RA = 14:57:18.867 ± 0.044 s Dec = +79:17:34.74 ± 0.09″ - Peak flux density: 75.1 ± 8.4 μJy beam⁻¹ at 5 GHz 62.2 ± 9.4 μJy beam⁻¹ at 7 GHz The implied in-band spectral index across 5–7 GHz is consistent with being flat within uncertainties. The VLA position is consistent with the reported optical afterglow position (e.g., GCN 42883) and is also consistent with the X-ray localizations reported by SVOM/MXT, Swift/XRT, and Einstein Probe (e.g., GCN 42877, 42884, 42891), supporting the association of this radio source with GRB 251129A. This VLA detection provides an important radio counterpart to the unusual multi-wavelength behaviour of GRB 251129A reported in earlier GCNs, including its ultra-long high-energy emission and peculiar X-ray temporal and spectral evolution. We note that our eMERLIN observations reported in GCN 43040 resulted in a non-detection at C band between 2025 December 3-5, placing a 3σ upper limit of 0.066 mJy beam⁻¹ on the flux density. The new VLA detection therefore indicates a rising or previously sub-threshold radio afterglow component emerging on week timescales. More radio observations are encouraged to measure the temporal decay and spectral evolution and to distinguish between internal-engine and external-shock interpretations of this event. We thank the VLA Time Allocation Committee for approving these observations and the NRAO VLA operations and scheduling teams for the rapid execution and support that made this time-critical observation possible. View this GCN Circular online at https://gcn.nasa.gov/circulars/43228. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41316] EP251222a: VLT/FORS2 spectroscopic redshift z = 0.505
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43227 SUBJECT: EP251222a: VLT/FORS2 spectroscopic redshift z = 0.505 DATE: 25/12/24 09:47:04 GMT FROM: Laura Cotter at University College Dublin <laura.cotter(a)ucdconnect.ie> J. An (NAOC), L. Izzo (INAF/OACn & DARK/NBI), A. Saccardi (CEA/Irfu), L. Cotter (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. L. Thakur (INAF-IAPS), D. Xu (NAOC), report on behalf of the Stargate collaboration: We observed the optical counterpart (Li et al., GCN 43205; Malesani et al., GCN 43211) of EP251222a (Huang et al., GCN 43200; Guo et al., GCN 43216) with the ESO VLT UT1 (Antu) equipped with the FORS2 spectrograph. Our observations began on 2025 December 24 at 02:21:56 UT, 1.46 days post trigger. A spectrum covering the wavelength range 3600-8600 AA was secured using grism 300V (with no order-sorting filter), with a total exposure time of 4x600 s. In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. From the detection of multiple absorption lines, which we interpret as the Mg II doublet (2796, 2804) and Fe II (2587, 2600), we infer a redshift of z = 0.505. At a consistent redshift, we also detect emission lines due to the [O II] 3726,3729 doublet and [O III] 5007 from the host galaxy. We acknowledge expert support from the observing staff in Paranal, in particular Elyar Sedaghati. View this GCN Circular online at https://gcn.nasa.gov/circulars/43227. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41315] GRB 251222A: ZTSH BVRI optical observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43226 SUBJECT: GRB 251222A: ZTSH BVRI optical observations DATE: 25/12/24 08:57:11 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43226. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41314] GRB 251222A: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 24 Dec '25

24 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43225 SUBJECT: GRB 251222A: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 25/12/24 08:20:51 GMT FROM: globus(a)astro.unam.mx 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43225. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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