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[vsnet-grb-info 41203] GRB 251209A: GECAM-B observation of a long burst
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43122 SUBJECT: GRB 251209A: GECAM-B observation of a long burst DATE: 25/12/15 13:57:46 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Sheng-Lun Xie, Yang-Zhao Ren, Peng Zhang, Yue Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a long burst GRB 251209A at 2025-12-09T13:24:22.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43048 and GCN #43068), Global MASTER-Net (V.Lipunov et al., GCN#43053), AstroSat CZTI (M. Tembhurnikar et al., GCN#42996), NuSTAR (G. Waratkar et al., GCN #43078) and Insight-HXMT (Hao-Xuan Guo et al., GCN #43119). 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 40.5 +/-1.7 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb251209A.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). View this GCN Circular online at https://gcn.nasa.gov/circulars/43122. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41202] GRB 251214D: GECAM-B observation of a long burst
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43121 SUBJECT: GRB 251214D: GECAM-B observation of a long burst DATE: 25/12/15 13:47:03 GMT FROM: Xinghao Luo at SVOM/GRM <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 251214D, at 2025-12-14T21:24:17.950 UTC (denoted as T0), which is also detected by AstroSat/CZTI (A. Arya et.al., GCN #43109). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 28.5 +6.5/-5.0 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251214D.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). View this GCN Circular online at https://gcn.nasa.gov/circulars/43121. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41201] GRB 251214B: Fermi GBM Observation
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43120 SUBJECT: GRB 251214B: Fermi GBM Observation DATE: 25/12/15 13:26:50 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova (MUNI) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 09:02:18.03 UT on 14 December 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251214B (trigger 787395743/251214377), which was also detected by Swift BAT (R. A. J. Eyles-Ferris et al. 2025, GCN 43089) and GECAM-B (X. H. Luo et al. 2025, GCN 43113). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 97 degrees. The GBM light curve consists of a double-peaked emission with a duration (T90) of about 15 s (50-300 keV). The time-averaged spectrum from T0-0.6 to T0+9.9 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.81 +/- 0.05 and the cutoff energy, parameterized as Epeak, is 1280 +/- 80 keV. The event fluence (10-1000 keV) in this time interval is (1.3 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.58 s in the 10-1000 keV band is 3.3 +/- 0.3 ph/s/cm^2. 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/" View this GCN Circular online at https://gcn.nasa.gov/circulars/43120. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41200] GRB 251209A: Insight-HXMT/HE detection
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43119 SUBJECT: GRB 251209A: Insight-HXMT/HE detection DATE: 25/12/15 13:24:01 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2025-12-09T13:24:31.000 (T0), Insight-HXMT/HE detected a long burst, GRB 251209A, which is also detected by Fermi/GBM (Fermi GBM team, GCN #43048 and GCN #43068), Global MASTER-Net (V.Lipunov et al., GCN#43053), AstroSat CZTI (M. Tembhurnikar et al., GCN#42996) and NuSTAR (G. Waratkar et al., GCN #43078). The Insight-HXMT/HE light curve mainly consists of multiple pulses with T90 of 43.0 +13.5/-10.0 s. The 1s peak rate, measured from T0+0.25 s, is 822 cnts/sec. Insight-HXMT/HE detected a total of 12,343 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251209A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the Low-Gain mode with the energy range of about 300-3000 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org View this GCN Circular online at https://gcn.nasa.gov/circulars/43119. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41199] GRB 251215A: Swift ToO observations
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43118 SUBJECT: GRB 251215A: Swift ToO observations DATE: 25/12/15 13:10:55 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Swift/BAT-detected event GRB 251215A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021894 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 Swift/BAT 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43118. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41198] EP trigger 01709250023: LCO optical limits
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43117 SUBJECT: EP trigger 01709250023: LCO optical limits DATE: 25/12/15 12:43:14 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> R. A. J. Eyles-Ferris (Leicester), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of the EP/EXT trigger 01709250023 (trigger time 2025-12-14T07:20:22.899 UT), using the Sinistro instrument at the 1m telescope in Siding Springs, Australia, part of the LCO network. Observations were carried out in the r (3x300 s) and z (6x300 s) bands, at mean epochs of 2025 Dec 14.658 and 14.687 UT, respectively (8.395 and 9.076 hr after trigger). After subtracting from our stacks archival templates from the Pan-STARRS survey, we detect no new sources in either bands within the EP/WXT error circle, down to 3-sigma limiting AB magnitudes r > 22.4 and z > 21.6 (photometry calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction). The two sources detected by Swift/XRT outside the EP/WXT error circle (https://www.swift.ac.uk/EP/EP_FIELD00087/) have stellar counterparts in Pan-STARRS. This further confirms that they are unlikely to be related to the EP transient. Furthermore, XRT source #1 matches an AGN from the C75 WISE AGN catalog (Assef et al. 2018; doi:10.3847/1538-4365/aaa00a), and is thus possibly an AGN. The lack of detection is consistent with the results by COLIBRÍ (Basa et al., GCN 43090) and Swift/XRT. View this GCN Circular online at https://gcn.nasa.gov/circulars/43117. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41197] GRID detection of GRB 251213A
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43116 SUBJECT: GRID detection of GRB 251213A DATE: 25/12/15 11:47:12 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Long-Hao Li, Chen-Yu Wang, Zi-Rui Yang report on behalf of the GRID Collaboration: GRID reports the detection of GRB 251213A, a long-duration gamma-ray burst, which was also detected by GECAM-B (GCN Circ.43106), SVOM/GRM and AstroSat CZTI (GCN Circ. 43108). The event triggered GRID-11B at T0 = 2025-12-13 12:30:04 UTC. The measured burst duration is T90 = 34.6 ± 2.8 s in the 30–2000 keV energy range. The GRID light curve for this event is available at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB251213A/GRID_GRB…. GRID is a student-led project to monitor the transient gamma-ray sky with multiple detectors onboard different nanosatellites in the era of multi-messenger astronomy. For more information about GRID, please refer to the following references: https://doi.org/10.1007/s10686-019-09636-w and https://doi.org/10.1007/s10686-021-09819-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/43116. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41196] GRB 251203B: AbAO optical observations
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43115 SUBJECT: GRB 251203B: AbAO optical observations DATE: 25/12/15 11:12:25 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. A. Volnova (IKI), R. Ya. Inasaridze (AbAO), A. S. Pozanenko (IKI), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN: We observed the field of the SWOM trigger sb25120304 (Brunet et al. GCN 42973) with the AS-32 0.7m telescope of Abastumani Observatory (AbAO) taking several frames in R-band. The observations started on Dec. 3 at 21:00 UT, i.e., ~ 3 hours after the SWOM trigger. In the stacked image, we do not detect any new source within the MXT error circle. The star Gaia DR3 2534635509050352256 reported previously (Palmerio et al., GCB 42978; Malesani et al., GCN 42979; Perez-Garcia et al., GCN 42982) is consistent with two USNO-B1.0 sources 0900-0013627 (RA(J2000) = 01:13:26.6548920, Dec(J2000) = +00:01:08.382180; R1 = 13.31) and 0900-0013628 (RA(J2000) = 01:13:26.8108752, Dec(J2000) = +00:01:08.040144; R2 = 13.83) and is clearly detected in the stacked frame. Its R-magnitude is brighter ~0.2 mag than the catalogue USNO-B1.0 R1 value, that supports the nature of the trigger as a star flare. Photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2025-12-03 21:00:00 0.15311 60*20 R 13.13 0.02 19.5 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/43115. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41195] GRB 251215A: Swift/BAT-GUANO arcminute localization of a burst
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43114 SUBJECT: GRB 251215A: Swift/BAT-GUANO arcminute localization of a burst DATE: 25/12/15 10:28:41 GMT FROM: Samuele Ronchini at PSU <sjs8171(a)psu.edu> Samuele Ronchini (GSSI), James DeLaunay (PSU), Aaron Tohuvavohu (Cosmic Frontier), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251215A onboard (T0: 2025-12-15T04:21:21.57 UTC, Fermi GCN 43104). The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The position is found with the newly developed pipeline BAT-GLIMPSE: Gamma-ray Localization using Imaging and Mosaic techniques for Pointing and Slew Epochs (Ronchini et. al, in prep). The pipeline makes use of the tools from BatAnalysis ([Parsotan et al. 2025](https://iopscience.iop.org/article/10.3847/1538-4357/ade240)) The source was detected with an SNR = 6.5 in a 16.384 s analysis time bin starting at t0 - 4.096 s. Independently, the BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), confirms the detection of the burst in a 16.384 s analysis time bin starting at T0 - 4.096 s with a sqrt(TS) of 14.6. An arcminute localization is found with DeltaLLHOut of 63.97 and a DeltaLLHPeak of 36.66. See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut. The NITRATES and BAT-GLIMPSE positions are compatible. Moreover, at T0: 2025-12-15T04:23:36.28 UTC, also a CALET trigger (trig number 1449807236) activated GUANO. A signal is found by BAT-GLIMPSE during Swift slew using a mosaic technique. The source is found with an SNR = 27.1. The position is compatible with the one found by BAT-GLIMPSE and NITRATES for the Fermi-GBM trigger. Hence we conclude that the two signals are associated to the same GRB. The BAT position is: RA, Dec = 122.6526, -36.7395 deg which is RA(J2000) = 08h 10m 36.62s Dec(J2000) = -36d 44’ 22.2″ with an estimated uncertainty of 3 arcmin radius. More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=787465318 XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars. GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/43114. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41194] GRB 251214B: GECAM-B observation of a long burst
by GCN Circulars 15 Dec '25

15 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43113 SUBJECT: GRB 251214B: GECAM-B observation of a long burst DATE: 25/12/15 09:50:28 GMT FROM: Xinghao Luo at SVOM/GRN <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 251214B, at 2025-12-14T09:02:19.10 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43088). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 17.7 +1.8/-1.2 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251214B.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). View this GCN Circular online at https://gcn.nasa.gov/circulars/43113. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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