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

[vsnet-grb-info 41274] GRB 251222A: SVOM/VT optical candidate
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43189 SUBJECT: GRB 251222A: SVOM/VT optical candidate DATE: 25/12/22 17:48:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43189. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41273] GRB 251222A: SVOM detection of a long burst
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43188 SUBJECT: GRB 251222A: SVOM detection of a long burst DATE: 25/12/22 17:37:38 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> 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(a)irap.omp.eu. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43188. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41272] SVOM GRB251222.71: Global MASTER-Net observations report
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43187 SUBJECT: SVOM GRB251222.71: Global MASTER-Net observations report DATE: 25/12/22 17:28:28 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) 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/43187. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41271] GRB 251222A: Fermi GBM Final Real-time Localization
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43186 SUBJECT: GRB 251222A: Fermi GBM Final Real-time Localization DATE: 25/12/22 17:16:31 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 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/… 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/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251222712/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43186. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41270] EP251220a: PRIME upper limit
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43185 SUBJECT: EP251220a: PRIME upper limit DATE: 25/12/22 16:55:31 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> N. Passaleva (U Rome), O. Guiffreda (UMD), M. El Kabir (U Rome), J. Durbak (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) We observed the field of the optical counterpart (Sánchez Álvarez et al. GCN 43167) of the fast X-ray transient EP251220a (Liu et al., GCN 43162) in J filter with PRIME. Observations started ~35h after the trigger. Using Two Micron All Sky Survey (2MASS) nearby stars for preliminary calibration we do not detect any uncatalogued source down to J>20.5 AB (3-sigma) not corrected for galactic extinction at the position of the candidate reported by Sánchez Álvarez et al. (GCN 43167), Kumar et al. (GCN 43169), Busmann et al. (GCN 43181), van Hoof et al. (GCN 43182), An et al. (GCN 43184). 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). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43185. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41269] EP251220a: VLT/FORS2 spectroscopic redshift z = 2.375
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43184 SUBJECT: EP251220a: VLT/FORS2 spectroscopic redshift z = 2.375 DATE: 25/12/22 16:47:08 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome <aishth(a)outlook.com> J. An (NAOC), A. Saccardi (CEA/Irfu), R. A. J. Eyles-Ferris (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), M. Ferro (INAF-OABr), A. P. C. van Hoof (Radboud), A. L. Thakur (INAF-IAPS), D. Xu (NAOC), report on behalf of the Stargate collaboration: We observed the optical counterpart of EP251220a (Sánchez Álvarez et al., GCN 43167; Rakotondrainibe et al., GCN 43170; Busmann et al., GCN 43181; van Hoof et al., GCN 43182) detected by the Einstein Probe (Liu et al., GCN 43162) using the ESO VLT UT1 (Antu) equipped with the FORS2 spectrograph. Our observation started at 01:02:04 UT on 2025 December 22 (40.6 hr after the EP trigger). A series of spectra was obtained with the 300V grism covering the range 3500-6500 AA and consisted of 4 exposures of 600 s each. In the acquisition image (40.46 hr after trigger), we measure for the transient a magnitude r = 21.80 +- 0.05 (AB), calibrated against nearby stars from the Pan-STARRS catalogue, and not corrected for Galactic extinction. This value indicates little decay compared to the other reported optical observations. In a preliminary reduction of the data, we identify multiple absorption features, including Lyα broad trough likely due to H I, as well as Si II, C II, and Al II, at a common redshift of 2.375, which we thus suggest to be the redshift for this transient. The COLIBRÍ redshift upper limit (Sánchez Álvarez et al., GCN 43167) is thus fully consistent with our spectroscopic measurement. We acknowledge expert support from the ESO observing staff in Paranal, particularly Juan Carlos Olivares and Maria Jose Rain. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/43184. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41268] GRB 251221A: PRIME near-infrared observation
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43183 SUBJECT: GRB 251221A: PRIME near-infrared observation DATE: 25/12/22 16:02:42 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> N. Passaleva (U Rome), O. Guiffreda (UMD), M. El Kabir (U Rome), J. Durbak (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the Fermi/Swift (Fermi GBM team, GCN 43164; Ambrosi et al., GCN 43166) detection, we observed the transient field in J and H filter with PRIME. Observations started ~15.5 hours after the initial trigger. Using Two Micron All Sky Survey (2MASS) nearby stars for preliminary calibration we detect an uncatalogued source at the position reported by Rakotondrainibe et al. (GCN 43168) and Volnova et al. (GCN 43180). We derived the following magnitudes not corrected for galactic extinction: J = 20.27 ± 0.09 H = 19.52 ± 0.04 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). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43183. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41267] EP251220a: NOT optical observations
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43182 SUBJECT: EP251220a: NOT optical observations DATE: 25/12/22 14:18:06 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. P. C. van Hoof (Radboud), G. Corcoran (UCD), J. An (NAOC), R. A. J. Eyles-Ferris (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), D. Xu (NAOC), J. Sanchez-Sierras (Radboud), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), A. Kadela (NOT and NBI), report on behalf of a larger collaboration: We observed the optical counterpart (Álvarez et al., GCN 43167; Kumar et al., GCN 43169; Rakotondrainibe et al., GCN 43170; Busmann et al., GCN 43181) of EP251220a (Liu et al., GCNs 43162, 43172) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A sequence of 4x300 s exposures were taken in SDSS r-band starting on 2025-12-21 at 19:37:19.906 UT (~35.18 hr since the EP trigger). The source is well detected in the stacked image with a preliminary photometry of r = 21.79 +/- 0.05 (AB), calibrated against nearby stars from the Pan-STARRS catalog and not corrected for Galactic extinction. Our photometry is consistent with the temporal index found by Rakotondrainibe et al. (GCN 43170). View this GCN Circular online at https://gcn.nasa.gov/circulars/43182. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41266] EP251220a: FTW optical and NIR observations
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43181 SUBJECT: EP251220a: FTW optical and NIR observations DATE: 25/12/22 13:41:22 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Xander J. Hall (CMU), Julius Gassert (LMU/CMU), Brendan O'Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the counterpart of EP251220a (Liu et al. GCN 43162, Sánchez Álvarez et al. GCN 43167, Liu et al. GCN 43172) 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 2025-12-21T18:45:36 UT (1.43 days after the trigger). We detect the counterpart in the r and i-band and measure an r-band magnitude of r = 21.94 +/- 0.12 AB mag. Our measurements are consistent with the reports by Lipunov et al. (GCN 43163), Sánchez Álvarez et al. (GCN 43167), Kumar et al. (GCN 43169), and Rakotondrainibe et al. (GCN 43170). 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/43181. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41265] GRB 251221A: UAFO and Mondy optical upper limit
by GCN Circulars 22 Dec '25

22 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43180 SUBJECT: GRB 251221A: UAFO and Mondy optical upper limit DATE: 25/12/22 12:03:11 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. A. Volnova (IKI), A. Kochergin (UAFO IAA), E. Klunko (ISTP), A. S. Pozanenko (IKI), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 251221A (Fermi GBM team, GCN 43164; Ambrosi et al., GCN 43166) with the RC-500 (0.5m) telescope of Ussuriysk Astrophysical Observatory (UAFO) and with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) taking several frames in R-band. The observations started on Dec. 21 at UT 15:18:04 with RC-500 and at UT 17:25:26, i.e., ~ 0.4-0.5 days after the Swift/BAT trigger. In the stacked images in the Swift/XRT error circle (Goad et al., GCN 43175) we do not detect the optical counterpart reported previously by Rakotondrainibe et al. (GCN 43168). Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope fwhm" (mid,days) (n*s) (3sigma) 2025-12-21 15:18:04 0.42900 60*60 R n/d n/d 19.7 UAFO/RC-500 2.7 2025-12-21 17:25:26 0.51314 18*120 R n/d n/d 22.1 Mondy/AZT-33IK 2.6 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/43180. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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