December 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 41364] GRB 251222A: Mondy Optical Observations
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43273 SUBJECT: GRB 251222A: Mondy Optical Observations DATE: 25/12/30 17:23:31 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43273. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41363] EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43272 SUBJECT: EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/12/30 14:21:51 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B.T. Wang (YNAO, CAS), J.P. Chen (SYSU), D. Zhu, K.J. Zhang (YNU), and Z.X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP251230a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 43259) and Swift/BAT as GRB 251230A (Lanava et al., GCN 43252, Osborne et al., GCN 43263), and was followed by several optical telescopes (Li et al., GCN 43255, Lipunov et al., GCN 43256, Busmann et al., GCN 43258, Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265, Starling et al., GCN 43267, He et al., GCN 43269, Tak et al., GCN 43270, Breeveld et al., GCN 43271). The refined analysis of the WXT data shows that the event started at T0=2025-12-30T01:21:31 (UTC) and lasted for 72 s with a single pulse. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.21(-0.48/+0.59) x 10^22 cm^-2 and a photon index of 2.16 (-0.82/+0.89). The derived average unabsorbed 0.5-4 keV flux is 6.56 (-2.40, +2.80) x 10^(-9) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2025-12-30T01:24:36 (UTC), about 3 minutes after T0. The exposure time of this observation is 1859 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 179.8974, 11.4382 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 2.0 x 10^20 cm^-2 and a photon index of 1.83 (-0.04/+0.04). The derived average unabsorbed 0.5-10 keV flux is 4.02 (-0.13/+0.13) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/43272. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41362] GRB 251230A: Swift/UVOT detection
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43271 SUBJECT: GRB 251230A: Swift/UVOT detection DATE: 25/12/30 13:45:04 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk> A.A. Breeveld (UCL-MSSL), N.P.M. Kuin (UCL-MSSL), S. Lanava (PSU) and M. De Pasquale (U. Messina) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251230A 76s after the BAT trigger (Lanava et al., GCN Circ. 43252). A bright, fading source consistent with the enhanced XRT position (Osborne et al., GCN Circ. 43263) and optical detections (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265, He et al., GCN 43269) is detected in the initial UVOT exposures in the white, v, b, u and uvw1 filters. The burst is also detected in the UV grism and, while there is some contamination from other zeroth orders, we obtain a tentative redshift of z=1.73. The preliminary UVOT position is: RA (J2000) = 11:59:35.41 = 179.89756 (deg.) Dec (J2000) = +11:26:19.2 = 11.43867 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the finding chart (FC) and other early settled exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 76 226 147 13.61 ± 0.03 white 868 1017 286 15.63 ± 0.02 v 619 638 19 14.69 ± 0.07 b 545 564 20 14.78 ± 0.05 u_FC 288 538 246 13.77 ± 0.02 uvw1 668 687 19 15.2 ± 0.1 uvm2 643 1775 136 >18.8 uvw2 594 614 19 >17.7 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.024 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/43271. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41361] GRB251230A: 7DT optical upper limits
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43270 SUBJECT: GRB251230A: 7DT optical upper limits DATE: 25/12/30 13:38:44 GMT FROM: Donggeun Tak <donggeun.tak(a)gmail.com> Donggeun Tak (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), YoungPyo Hong (SNU ARC/SNU), Hyeonho Choi (SNU ARC/SNU), Donghwan Hyun (SNU ARC/SNU), Gregory S.H. Paek (IfA, SNU ARC/SNU), Seo-Won Chang (SNU ARC/SNU), and Ji Hoon Kim (SNU ARC/SNU) report on behalf of the 7 Dimensional Telescope (7DT) team: We report optical follow-up observations of GRB251230A (GCN 43252; GCN 43263), conducted with the 7-Dimensional Telescope (7DT), located in Chile. The 7DT follow-up began at 06:52:54 UTC on 2025-12-30, corresponding to T0 + 5.5 hours, pointing to a region covering the target localization provided by Swift (GCN 43252) at RA, DEC = 179.89760 deg, 11.43870 deg. Initial observations were made with 12 units in 20 medium-band filters as well as g-, r-, and i-band filters (23 filters in total). The following table summarizes the derived 5-sigma upper limits: Filter Mag Mag_err Exposure Date Time ---------------------------------------------------------------------------------------------------- g >20.04 N/A 300s 2025-12-30T06:49:06.000 r >19.42 N/A 300s 2025-12-30T06:54:28.333 i >18.34 N/A 300s 2025-12-30T06:49:04.000 m400 >18.32 N/A 300s 2025-12-30T06:54:34.667 m425 >18.89 N/A 300s 2025-12-30T06:54:20.000 m450 >18.95 N/A 300s 2025-12-30T06:49:02.667 m475 >19.00 N/A 300s 2025-12-30T06:54:26.000 m500 >19.04 N/A 300s 2025-12-30T06:49:10.667 m525 >18.93 N/A 300s 2025-12-30T06:54:29.000 m550 >18.60 N/A 300s 2025-12-30T06:54:34.000 m575 >18.79 N/A 300s 2025-12-30T06:49:09.667 m600 >18.60 N/A 300s 2025-12-30T06:49:08.667 m625 >18.21 N/A 300s 2025-12-30T06:54:42.667 m650 >18.25 N/A 300s 2025-12-30T06:49:03.000 m675 >18.28 N/A 300s 2025-12-30T06:54:38.333 m700 >18.16 N/A 300s 2025-12-30T06:49:07.000 m725 >17.72 N/A 300s 2025-12-30T06:54:36.333 m750 >17.56 N/A 600s 2025-12-30T06:51:49.833 m775 >17.04 N/A 300s 2025-12-30T06:54:24.667 m800 >16.81 N/A 300s 2025-12-30T06:49:05.667 m825 >16.65 N/A 300s 2025-12-30T06:54:29.667 m850 >16.44 N/A 300s 2025-12-30T06:48:59.000 m875 >15.91 N/A 300s 2025-12-30T06:49:08.000 ---------------------------------------------------------------------------------------------------- No significant transient event was identified in the preliminary result. Preliminary analysis yields 5σ limiting magnitudes in the range of 15.91–20.04 mag depending on sky brightness and airmass. Photometric flux calibration was performed using synthetic photometry based on the Gaia DR3 XP catalog (Gaia Collaboration et al. 2022) within the AB magnitude system. Note that no extinction correction has been applied. The 7-Dimensional Telescope (7DT), located in Chile and comprising 20 wide-field telescopes equipped with 40 medium-bandwidth (~25nm) filters, aims to detect optical counterparts of GW sources and conduct the 7-Dimensional Sky Survey (7DS) of the Southern Hemisphere. Further information about the 7DT is available at https://7ds.snu.ac.kr/ and http://gwuniverse.snu.ac.kr/. View this GCN Circular online at https://gcn.nasa.gov/circulars/43270. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41360] GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43269 SUBJECT: GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2 DATE: 25/12/30 13:23:01 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> L. He (NAOC), L. Izzo (INAF/OACN and DARK/NBI), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), J. An (NAOC), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Kadela (NOT & NBI) report on behalf of a larger collaboration: We observed the optical counterpart (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi, GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265) of GRB 251230A / EP251230a (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263), using the Nordic Optical Telescope (NOT), equipped with the ALFOSC camera and spectrograph. We obtained three exposures of 300 s in the r-band starting on 2025 Dec 30 at 06:30:20 UT (5.144 hr after the Swift trigger). The afterglow is clearly detected with an AB magnitude of r = 20.75 +/- 0.02 mag, calibrated against nearby stars from the Pan-STARRS catalogue and not corrected for Galactic extinction. Compared to previous measurements, our photometry suggests rapid optical decay with power-law index ~1.95. A sequence of 4 spectra of 1200 s each was acquired, covering the wavelength range 3700-9600 AA. In a preliminary reduction of the spectra, we detect a continuum over the entire covered wavelength range. From detection in the blue down to ~3900 AA, and the lack of hydrogen absorption, we set a redshift upper limit z < 2.2. We do not identify clear metal absorption features. Further analysis is ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/43269. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41359] EP251229a: BOOTES-2 early optical upper limit
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43268 SUBJECT: EP251229a: BOOTES-2 early optical upper limit DATE: 25/12/30 12:07:44 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, M.D. Caballero-Garcia, E. J. Fernandez-Garcia, R. Sanchez-Ramirez, S.-Y. Wu, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), Y.-D. Hu (GXU), C. Perez del Pulgar and A. Reina (Univ. of Malaga), M. Gritsevich (Univ. of Helsinki), R. Fernandez-Munoz (IHSM/UMA-CSIC), D. R. Xiong (Yunnan Observatories of CAS), and M. Jelinek (ASU-CAS, Ondrejov Obs.), on behalf of a larger collaboration, report: Following the detection of the X-ray transient EP251229a by Einstein Probe (Wang et al. GCN 43253), the 0.6m BOOTES-2/TELMA robotic telescope at IHSM UMA “La Mayora” (Malaga, Spain) automatically responded to this high-energy event starting on Dec 29, 20:11:10 UT (i.e. 12 min after detection). On a coadd image (14 x 60sec) at 20:50:40 UT (mid exposure time; i.e. 51 min after detection), nothing is detected down to 19.3 mag (clear filter) within the FXT error region (Wang et al. GCN 43264), in agreement with the deeper observations taken later on (Martin-Carrillo et al. GCN 43266). We would like to thank the staff at IHSM-/UMA-CSIC “La Mayora” for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/43268. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41358] GRB 251230A: GOTO optical upper limit
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43267 SUBJECT: GRB 251230A: GOTO optical upper limit DATE: 25/12/30 11:26:15 GMT FROM: Rhaana Starling at U of Leicester <rlcs1(a)leicester.ac.uk> R. Starling, A. Kumar, G. Ramsay, D. O’Neill, B. P. Gompertz, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, 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 251230A detected by Swift (Lanava et al., GCN 43252; Osborne et al., GCN 43263) and likely coincident with an Einstein Probe trigger (Wang et al., GCN 43259). Two sets of observations were performed by GOTO-North at 2025-12-30 06:01:45 UT and 2025-12-30 06:16:08 UT. Each observation consisted of 4x45 s exposures in the GOTO L-band (400-700 nm). Images were processed using the GOTO pipeline. We do not detect the optical counterpart (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265) down to 3-sigma limiting magnitudes of L >20.8 (AB) and L >20.6 (AB) at 4.7 hours and 4.9 hours post-trigger, respectively. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/43267. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41357] EP251229a: NOT optical upper limits
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43266 SUBJECT: EP251229a: NOT optical upper limits DATE: 25/12/30 10:31:06 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> A. Martin-Carrillo (UCD), J. Chacón (PUC), Z.P. Zhu, D. Xu (NAOC), G. Corcoran (UCD), F. E. Bauer (SSI and UTA), P.G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP251229a (Wang et al., GCN 43253) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the SDSS i and z bands consisting of 5x200 s exposures, starting on 2025-12-29 at 23:36:08 UTC (3.622 hours after the WXT trigger). No new source is detected within or at the border of the EP/FXT uncertainty region (Wang et al., GCN 43253). From the stacked images we obtain the following 3-sigma upper limits:  i > 24.0 z > 23.1 These upper limits are in AB magnitudes and were calibrated using nearby stars from the Pan-STARRS catalog and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43266. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41356] GRB 251230A / EP251230a: SVOM/VT optical observation
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43265 SUBJECT: GRB 251230A / EP251230a: SVOM/VT optical observation DATE: 25/12/30 09:58:05 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), J. X. Cao (GXU), W. L. Zhang (PMO) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of GRB 251230A / EP251230a detected by Swift/BAT and EP/WXT (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263). SVOM/VT began observing the field at 2025-12-30T03:13:20 UTC, 1.861 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Li et al., GCN 43255; Busmann et al., GCN 43258; Masi, GCN 43260; Ghosh et al., GCN 43262) was clearly detected in both VT_B and VT_R bands. The magnitudes are: mid time (s) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 6874 | 50 | VT_B | 19.11 | 0.04 8174 | 50 | VT_B | 19.53 | 0.05 6874 | 50 | VT_R | 18.57 | 0.03 8174 | 50 | VT_R | 19.07 | 0.05 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/43265. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41355] EP251229a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 30 Dec '25

30 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43264 SUBJECT: EP251229a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/12/30 09:05:29 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B.T. Wang (YNAO, CAS), J.P. Chen (SYSU), D. Zhu, K.J. Zhang (YNU), and Z.X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP251229a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 43253) and followed by an optical telescope (Lipunov et al., GCN 43254). The refined analysis of the WXT data shows that the event started at T0=2025-12-29T19:54:09 (UTC) and lasted for 173 s with a single pulse. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 5.3 (-2.2/+2.6) x 10^21 cm^-2 and a photon index of 2.3 (-0.68/+0.77). The derived average unabsorbed 0.5-4 keV flux is 1.62 (-0.41/+0.87) x 10^(-9) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2025-12-29T20:01:28 (UTC), about 7 minutes after T0. The exposure time of this observation is 855 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 124.1027, 37.2068 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 6.0 x 10^20 cm^-2 and a photon index of 1.89 (-0.13/+0.13). The derived average unabsorbed 0.5-10 keV flux is 3.46 (-0.37/+0.40) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/43264. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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