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

[vsnet-grb-info 41374] SVOM GRB251231.57: Global MASTER-Net observations report
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43283 SUBJECT: SVOM GRB251231.57: Global MASTER-Net observations report DATE: 25/12/31 23:56:31 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> 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) started inspect of the SVOM GRB251231.57 (trigger No 1767188879,18h 28m 56.90s , +11d 21m 52.2s, R=1) errorbox 33399 sec after notice time and 33434 sec after trigger time at 2025-12-31 23:05:13 UT, with upper limit up to 16.6 mag. The observations began at zenith distance = 80 deg. The sun altitude is -18.4 deg. The galactic latitude b = 10 deg., longitude l = 41 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3091965 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 33464 | 2025-12-31 23:05:13 | MASTER-Tunka | (18h 28m 26.18s , +10d 59m 08.2s) | C | 60 | 16.6 | 33464 | 2025-12-31 23:05:13 | MASTER-Tunka | (18h 28m 44.47s , +10d 53m 07.2s) | 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/43283. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41373] GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43282 SUBJECT: GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit DATE: 25/12/31 17:00:53 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 conducted continued observations 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; Wang et al., GCN 43272; Sbarrato et al., GCN 43275). The magnitudes of the optical afterglow (Li et al., GCN 43255; Lipunov et al., GCN 43256; Busmann et al., GCN 43258; Masi, 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; Gupta et al., GCN 43277; Sankar.K et al., GCN 43279; He et al., GCN 43280; Antier et al., GCN 43281) are: mid time (h) | exposure time (s) | band | mag (AB) -------------|-------------------|------|---------- 16.51 | 37*50 | VT_B | 23.0+-0.3 29.48 | 41*50 | VT_B | >23.4 16.51 | 37*50 | VT_R | 22.5+-0.2 29.46 | 39*50 | VT_R | >23.1 Our photometry was not corrected for Galactic extinction. Further analysis is ongoing. 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. Happy New Year to everyone ! ! ! View this GCN Circular online at https://gcn.nasa.gov/circulars/43282. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41372] GRB 251230A: GRANDMA/TAROT Early Detection
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43281 SUBJECT: GRB 251230A: GRANDMA/TAROT Early Detection DATE: 25/12/31 14:25:21 GMT FROM: Dalya Akl at New York University Abu Dhabi <dka2010(a)nyu.edu> S. Antier (IJCLAB), A. Klotz (IRAP), D. Akl (NYUAD), C. Limonta (OCA), A. Dupin (OCA), Q. André (OCA), M. Coughlin (UNM), R. Strausbaugh (EIU), Z. Maksut (NU), E. Abdikamalov (NU), P. Hello (IJCLAB), S. Karpov (FZU), M. Pillas (IAP), C. Douzet (IJCLAB), Z. Wang (BNU), N. Kochiashvili (AbAO), A. Iskandar (XAO) on behalf of GRANDMA: We observed the field of the fast X-ray transient GRB 251230A/EP251230a (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263; Wang et al., GCN 43272; Sbarrato et al., GCN 43275) using TAROT/TCA with no filter. The observations started at 01:22:07 UTC on the 30th of December 2025, 36s post Swift trigger time, and lasted for 3 hours. We detected the optical afterglow candidate in the first (earliest) measurement with TAROT/TCA (60s exposure time), and we measured on 2025-12-30 01:23:19, r = 13.1 +/- 0.05 mag, after color correction. The data were reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022), using the PS1 catalogue for reference. Part of the light curve is public here on Skyportal/ICARE (https://skyportal-icare.ijclab.in2p3.fr) and also accessible in the public-report group of Skyportal: https://skyportal-icare.ijclab.in2p3.fr/public/sources/GRB-251230_012141/ve… We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). The results are consistent with other measurements reported. 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/43281. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41371] GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43280 SUBJECT: GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening DATE: 25/12/31 12:31:28 GMT FROM: luca.izzo(a)inaf.it L. He (NAOC), L. Izzo (INAF/OACN and DARK/NBI), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), K. Valeckas (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; Starling et al., GCN 43267; He et al., GCN 43269; Breeveld et al., GCN 43271; Sankar et al., GCN 43279) 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. A series of 10 x 150s exposures was taken in the i band starting on 2025 Dec 31 at 04:46:27 (1.14 days after the Swift trigger). The afterglow is detected in the final stacked images with an AB magnitude of i = 22.93 +/- 0.09 mag, at a mid-time of 1.15 days after the trigger. Our photometry was calibrated using nearby stars from the Pan-STARRS catalog and is not corrected for Galactic extinction. This new epoch suggests that the fading of the optical afterglow has slowed down considerably from the decay index reported by He et al. GCN 43269. We note that, based on the colour measured in our earlier epoch, the r-band upper limit reported by Sankar et al. GCN 43279 suggests a possible rebrightening. Happy New Year to everyone!!! View this GCN Circular online at https://gcn.nasa.gov/circulars/43280. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41370] GRB 251230A/EP251230a: Optical upper limit with Kinder observations
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43279 SUBJECT: GRB 251230A/EP251230a: Optical upper limit with Kinder observations DATE: 25/12/31 10:29:09 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Sankar.K, A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, M.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, W.-J. Hou, H.-Y. Hsiao, 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 fast X-ray transient GRB 251230A/EP251230a (Lanava et al., GCN#43252; Wang et al., GCN#43259; Osborne et al., GCN#43263; Wang et al., GCN#43272; Sbarrato et al., GCN#43275) 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 18:17 UTC on the 30th of December 2025 (MJD 61039.762), 16.91 hr after the Swift/BAT trigger. 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 frame, we did not detect the proposed optical counterpart candidate (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; Breeveld et al., GCN#43271), which has a tentative redshift upper limit of z < 2.2 (He et al., GCN#43269). Moreover, we utilized AutoPhOT to perform the PSF photometry. The details of the observations and the measured 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 61039.762 | 16.91 | 300 * 24 | >22.5 | 2".10 | 1.17 Utilizing the rigorous Lulin Observatory optical follow-up of the Einstein-Probe-discovered FXTs within the first year of the mission's operation, we investigated the possible connection between FXTs and GRBs, as reported in Aryan et al. (2025), ApJS, 281, 20. Our upper limits are the deepest and latest among those reported (Starling et al., GCN#43267; Tak et al., GCN#43270). The presented upper limit is calibrated using the field stars from the PanSTARRs DR2 and is not corrected for the expected Galactic foreground extinction of A_r = 0.05 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43279. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41369] EP251229a: Optical upper limit with Kinder observations
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43278 SUBJECT: EP251229a: Optical upper limit with Kinder observations DATE: 25/12/31 10:27:16 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Sankar.K, A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, M.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, W.-J. Hou, H.-Y. Hsiao, 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 fast X-ray transient EP251229a (Wang et al., GCN#43253) 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 20:18 UTC on the 29th of December 2025 (MJD 61038.846), 0.32 hr after the EP-WXT trigger. 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. Moreover, we utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al., 2019, AJ 157, 168) DR10 image using the 'sfft' (Hu et al., 2022, ApJ, 936, 157) algorithm. We did not detect any new and uncataloged source within the EP-FXT localization circle with a radius of 20", either in the stacked or difference image. Moreover, we further utilized AutoPhOT to perform the PSF photometry. The details of the observations and the measured 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 61038.846 | 0.32 | 300 * 12 | >22.4 | 2".01 | 1.35 Our non-detection is deeper than Lipunov et al. (GCN#43254), consistent with Martin-Carrillo et al. (GCN#43266) and Perez-Garcia et al. (GCN#43268). The absence of any associated optical counterpart down to 22.4 mag with the optical observations starting at 0.32 hours of its X-ray discovery aligns well with the 'Dark' nature of FXTs (Aryan et al., 2025, ApJS, 281, 20). The presented upper limit is calibrated using the field stars from the PanSTARRs DR2 and is not corrected for the expected Galactic foreground extinction of A_r = 0.14 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43278. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41368] GRB 251230A: 1.3m DFOT optical upper limit
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43277 SUBJECT: GRB 251230A: 1.3m DFOT optical upper limit DATE: 25/12/31 09:38:27 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kuntal Misra, Pankaj Pawar, Dhruv Jain, Debalina Kar (ARIES) report: We observed the field of GRB 251230A detected by Swift (Lanava et al. 2025, GCN 43252) 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 began on 2025-12-30 at 21:36:37 UT, ~ 20.24 hours after the Swift trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We could not detect the optical emission in our stacked image within the error box of Swift/UVOT (Breeveld et al. 2025, GCN 43271). We obtain the following 3-sigma upper limit in the stacked image: Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude =============================================================== 2025-12-30 21:36:37 ~20.24 R 300s*6 >22.3 The non-detection of the burst is consistent with Li et al. 2025, (GCN 43255); Lipunov et al. 2025, (GCN 43256); Busmann et al. 2025, (GCN 43258); Masi et al. 2025, (GCN 43260); Ghosh et al. 2025, (GCN 43262); Ma et al. 2025, (GCN 43265); Starling et al. 2025, (GCN 43267); He et al. 2025, (GCN 43269); Breeveld et al. 2025, (GCN 43271). 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43277. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41367] Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43276 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB DATE: 25/12/31 02:32:09 GMT FROM: Glowbug DEV <boyan.a.hristov(a)nasa.gov> B. Hristov (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 788833547/251231018 at 00:25:42.73 UT on 31 December 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to a Solar flare." View this GCN Circular online at https://gcn.nasa.gov/circulars/43276. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41366] GRB 251230A: Swift-XRT refined Analysis
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43275 SUBJECT: GRB 251230A: Swift-XRT refined Analysis DATE: 25/12/31 01:48:14 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.6 ks of XRT data for GRB 251230A, from 92 s to 50.9 ks after the trigger. The data comprise 329 s in Windowed Timing (WT) mode (the first 6 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=7.1 (+/-0.5). At T+129 s the decay flattens to an alpha of 0.2 (+0.3, -1.1) before breaking again at T+194 s to a final decay with index alpha=1.51 (+/-0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+/-0.06). The best-fitting absorption column is 4.4 (+1.3, -1.2) x 10^20 cm^-2, in excess of the Galactic value of 1.9 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.82 (+/-0.14) and a best-fitting absorption column of 5.7 (+3.6, -3.2) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.7 (+3.6, -3.2) x 10^20 cm^-2 Galactic foreground: 1.9 x 10^20 cm^-2 Excess significance: 2.0 sigma Photon index: 1.82 (+/-0.14) If the light curve continues to decay with a power-law decay index of 1.51, the count rate at T+24 hours will be 2.3 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x 10^-14 (9.4 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01429020. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43275. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41365] GRB 251231A: Fermi GBM Final Real-time Localization
by GCN Circulars 31 Dec '25

31 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43274 SUBJECT: GRB 251231A: Fermi GBM Final Real-time Localization DATE: 25/12/31 00:36:41 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely SHORT GRB At 00:25:42 UT on 31 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251231A (trigger 788833547.728264 / 251231018). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 312.1, Dec = -46.0 (J2000 degrees, equivalent to J2000 20h 48m, -46d 00'), with a statistical uncertainty of 16.4 degrees. The angle from the Fermi LAT boresight is 12.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251231018/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251231018/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251231018/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43274. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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