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[vsnet-grb-info 41113] GRB 251208B: Swift/BAT-GUANO arcminute localization of a burst
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43033 SUBJECT: GRB 251208B: Swift/BAT-GUANO arcminute localization of a burst DATE: 25/12/08 18:03:30 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Aaron Tohuvavohu (Cosmic Frontier), Samuele Ronchini (GSSI), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251208B onboard (T0: 2025-12-08T10:17:17.29 UTC, Fermi Trig 786881842). 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 BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), detects the burst in a 8.192 s analysis time bin starting at T0 - 2.048 s with a sqrt(TS) of 17.6. An arcminute localization is found with DeltaLLHOut of 43 and a DeltaLLHPeak of 30.0. 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 BAT position is RA, Dec = 228.453, 29.044 deg which is RA(J2000) = 15h 13m 48.72s Dec(J2000) = 29d 02’ 38.4″ with an estimated uncertainty of 5 arcmin radius. More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=786881874 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/43033. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41112] GRB 251208D: SVOM possible detection of a faint burst
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43032 SUBJECT: GRB 251208D: SVOM possible detection of a faint burst DATE: 25/12/08 17:25:54 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z.-Y. Lin, F. Cangemi (APC), D. Turpin, S. Schanne (CEA/Irfu), F. Daigne (IAP) At 2025-12-08T16:51:43 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251208D (SVOM burst-id sb25120806). 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 Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 6.64 in the [8-120] keV energy band over a time window of 81.92 seconds starting at 2025-12-08T16:50:21. The localization of the best alert is R.A., Dec. 337.5347, -0.3918 degrees: R.A. (J2000) = 22h30m08.33s Dec. (J2000) = -0d23m30.32s with a 90% confidence level (C.L.) radius of 11.77 arcmin (including systematic error of 2 arcmin added in quadrature). Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst. A SVOM ToO has been requested. MXT and VT ToO observation results will be reported in dedicated GCN Circulars. 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 Zhe-Yu Lin: zheyu.lin(a)apc.in2p3.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43032. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41111] GRB 251206A: SVOM detection of a burst through offline search
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43031 SUBJECT: GRB 251206A: SVOM detection of a burst through offline search DATE: 25/12/08 16:55:31 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, J.-L. Atteia (IRAP), N. Dagoneau (CEA), report on behalf of the SVOM team: The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 251206A, starting at 2025-12-06T20:48:20.92 UTC (T0), through an offline search with the event-by-event data downloaded through the X-band ground station. The burst was detected within several energy ranges and timescales. The best detection is obtained by the Image Trigger (IMT) with a signal-to-noise ratio of 8.5 within 4-20 keV over a time window of 20.48 seconds starting at T0-20.48s. The lightcurve shows an asymmetric double-peaked structure, with a minor peak followed by a major peak, lasting around 20 s. The localization of the source is RA, Dec = 1.843, -4.404 degrees: RA (J2000) = 00h07m22.32s Dec (J2000) = -04d24m16.85s with a 90% C.L. radius of 10.9 arcmin (including systematic error of 6 arcmin added in quadrature). We note that no bright catalogued X-ray sources are found in the error box. The time-averaged spectrum from T0 to T0+20.48s in the energy range 5-120 keV is best fitted by a power law. The powerlaw index is -1.96 -0.15/+0.17. With this model, the total fluence in 4-120 keV is (3.56 +0.28/-0.57)e-7 erg/cm^2. All quoted errors are at the 68% confidence level. The Space 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. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP. The SVOM point of contact for this event is : Marius Brunet : marius.brunet at irap.omp.eu Please contact him by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/43031. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41110] GRB 251208C: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43030 SUBJECT: GRB 251208C: Fermi GBM Final Real-time Localization DATE: 25/12/08 13:03:09 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 12:52:32 UT on 8 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251208C (trigger 786891157.548312 / 251208536). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 312.8, Dec = -30.7 (J2000 degrees, equivalent to J2000 20h 51m, -30d 41'), with a statistical uncertainty of 4.8 degrees. The angle from the Fermi LAT boresight is 84.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208536/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208536/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208536/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43030. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41109] GRB 251205A : MITSuME Akeno optical afterglow candidate detection
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43029 SUBJECT: GRB 251205A : MITSuME Akeno optical afterglow candidate detection DATE: 25/12/08 10:54:40 GMT FROM: hagio.h.ffca(a)m.isct.ac.jp H. Hagio, Y. Kubo, I. Takahashi, M. Sasada, H. Seki, A. Ochi, R. Kato, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 251205A detected by Swift (Lanava et al., GCN 43005) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2025-12-06 16:56:58 UT (16.3 hr after the trigger). We stacked the images taken under good conditions. We detected a point source in the Rc- and Ic-band images at a position of the reported optical candidate (Lipunov et al., GCN 43004; Lanava et al., GCN 43005; Lipunov et al., GCN 43006; Malesani et al., GCN 43009; O'Neill et al., GCN 43010; Mandarakas et al., GCN 43011; Pankov et al., GCN 43012; Bochenek et al., GCN 43015; Klingler et al., GCN 43016; Patil et al., GCN 43019; Pérez-Fournon et al., GCN 43020; Bochenek et al., GCN 43024; Busmann et al., GCN 43026 ). Our photometric results can be contaminated by the flux from the nearby galaxy. Here we report the preliminary magnitudes of the source as follows. T0+[sec] | MID-UT | T-EXP[sec] | magnitudes --------------------------------------------------------------------------------------------------------------- 68759 | 2025-12-06 18:45:46 | 4860 | Rc=19.1+/-0.2, Ic=18.8+/-0.2 --------------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the trigger T-EXP: Total exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire) View this GCN Circular online at https://gcn.nasa.gov/circulars/43029. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41108] GRB 251208B: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43028 SUBJECT: GRB 251208B: Fermi GBM Final Real-time Localization DATE: 25/12/08 10:27:53 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 10:17:17 UT on 8 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251208B (trigger 786881842.294214 / 251208429). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 212.3, Dec = 30.1 (J2000 degrees, equivalent to J2000 14h 09m, 30d 06'), with a statistical uncertainty of 5.8 degrees. The angle from the Fermi LAT boresight is 25.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208429/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208429/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208429/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43028. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41107] GRB 251208A: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43027 SUBJECT: GRB 251208A: Fermi GBM Final Real-time Localization DATE: 25/12/08 09:36:35 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 09:25:57 UT on 8 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251208A (trigger 786878762.38767 / 251208393). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 32.8, Dec = -66.7 (J2000 degrees, equivalent to J2000 02h 11m, -66d 42'), with a statistical uncertainty of 3.9 degrees. The angle from the Fermi LAT boresight is 56.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208393/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208393/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208393/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43027. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41106] GRB 251205A: FTW optical and NIR observations
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43026 SUBJECT: GRB 251205A: FTW optical and NIR observations DATE: 25/12/07 23:06:48 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Xander J. Hall (CMU), Jule Augustin (LMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the counterpart of GRB 251205A (Lavana et al. GCN 43005) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, z, J, and Ks bands. We detect the counterpart across all bands. | Start Time | t - t0 (days) | Filter | Exposures | Magnitude (AB) | |---------------------|---------------|--------|-----------------------|----------------| | 2025-12-06T03:25:42 | 0.157 | r' | 5 x 150 s + 5 x 180 s | 18.09 +/- 0.05 | | 2025-12-06T03:25:42 | 0.157 | i' | 5 x 150 s | 18.10 +/- 0.05 | | 2025-12-06T03:41:46 | 0.168 | z' | 5 x 180 s | 17.74 +/- 0.05 | | 2025-12-06T03:42:00 | 0.168 | J | 5 x 180 s | 17.46 +/- 0.05 | | 2025-12-06T03:25:55 | 0.157 | Ks | 10 x 60 s | 17.13 +/- 0.05 | These measurements are consistent with the magnitudes reported by Lavana et al. (GCN 43005), Lipunov et al. (GCN 43006), Malesani et al. (GCN 43009), O’Neill et al. (GCN 43010), Mandarakas et al. (GCN 43011), Bochenek & Perley (GCN 43015), Klinger et al. (GCN 43016), Patil et al. (GCN 43019), Pérez-Fournon et al. (GCN 43020), and Bochenek et al. (GCN 13024). The r, i, and z-band magnitudes are calibrated against the PS1 catalog, and the J and Ks-band magnitudes are calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are 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/43026. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41105] EP-WXT trigger 01709249380: KAIT confirmation of a stellar flare
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43025 SUBJECT: EP-WXT trigger 01709249380: KAIT confirmation of a stellar flare DATE: 25/12/07 22:39:57 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, automatically responded to the EP-WXT trigger 01709249380 (Li et al. GCN 43021) starting at 09:30 UT, about 11 minutes after the trigger. A set of clear (roughly R) filter images were obtained and lasted for ~2 hours. We performed the photometry on the suggested flare star 2MASS J05100460-0428037 and see its brightness decreased from ~10.8 mag to ~11.2 mag in about 15 minutes, then remained ~11.2 mag afterward, thus confirming the EP X-ray trigger is related to the stellar flare. Our result also confirms the observations from Perez-Garcia et al. (GCN 43022) who reported similar decrease in mag from the flare star. View this GCN Circular online at https://gcn.nasa.gov/circulars/43025. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41104] GRB 251205A: Liverpool Telescope further optical follow-up observations
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43024 SUBJECT: GRB 251205A: Liverpool Telescope further optical follow-up observations DATE: 25/12/07 16:36:22 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of GRB 251205A (Lanava et al., GCN 43005) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures the SDSS i and r filters starting at 2025-12-07 04:57:54 UT, approximately 29.3 hours after trigger. Some exposures were affected by telescope wobble or poor seeing and had to be discarded before stacking. We report detections in both filters, at the position first reported by Lanava et al., GCN 43005: MJD (mid) T_mid-T_0 Filter Mag. (AB) 61016.21035 29.4 h i 19.57 ± 0.06 61016.21529 29.5 h r 19.72 ± 0.07 The photometry is consistent with measurements by Lanava et al. GCN 43005; Lipunov et al. GCN 43006; de Ugarte Postigo et al. GCN 43008; Malesani et al. GCN 43009; O’Neill et al., GCN 43010; Mandarakas et al. GCN 43011; Pankov et al., GCN 43012; Bochenek and Perley, GCN 43015; Klingler et al., GCN 43016; Patil et al., GCN 43019; and Pérez-Fournon et al., GCN 43020. The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43024. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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