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[vsnet-grb-info 41118] GRB 251205A: Liverpool Telescope further optical follow-up observations
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43038 SUBJECT: GRB 251205A: Liverpool Telescope further optical follow-up observations DATE: 25/12/08 21:58:15 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 in the SDSS i and r filters starting at 2025-12-08 05:21:03 UT, approximately 2.24 days after trigger. We report detections in the stacked images of both filters, at the position first reported by Lanava et al., GCN 43005: MJD (mid) T_mid-T_0 Filter Mag. (AB) 61017.22543 53.8 h i 21.02 ± 0.19 61017.23156 53.9 h r 21.14 ± 0.26 The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction. The photometry is consistent with late-time optical measurements by Mandarakas et al., GCN 43011; Pérez-Fournon et al., GCN 43020; Bochenek & Perley, GCN 43024; and Hagio et al., GCN 43029. View this GCN Circular online at https://gcn.nasa.gov/circulars/43038. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41117] GRB 251208D: LCO optical upper limits
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43037 SUBJECT: GRB 251208D: LCO optical upper limits DATE: 25/12/08 20:27:36 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin, A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), Z.-Y. Lin, F. Cangemi (APC), report on behalf of the SVOM mission team: We observed the field of the SVOM GRB 251208D (Lin et al., GCN 43032) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2025-12-08 at 19:02:27 UT (about 2.18 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. In the stacked image, we do not detect any new source within the ECLAIRs error circle. We measure the following upper limits calibrated against the PanSTARRS DR1 catalog, and not corrected for Galactic extinction: r > 21.6 AB (mid-time 2.27 hr after the trigger); z > 19.7 AB (mid-time 2.65 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/43037. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41116] SVOM GRB251208.70: Global MASTER-Net observations report
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43036 SUBJECT: SVOM GRB251208.70: Global MASTER-Net observations report DATE: 25/12/08 19:28:32 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-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the SVOM GRB251208.70 (trigger No 1765212621,22h 30m 08.33s , -00d 23m 30.5s, R=0.1962) errorbox 6047 sec after notice time and 7322 sec after trigger time at 2025-12-08 18:52:23 UT, with upper limit up to 13.3 mag. The observations began at zenith distance = 73 deg. The sun altitude is -56.3 deg. MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) was pointed to the SVOM GRB251208.70 errorbox 7366 sec after notice time and 8641 sec after trigger time at 2025-12-08 19:14:22 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 56 deg. The sun altitude is -17.9 deg. The galactic latitude b = -47 deg., longitude l = 66 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3064681 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 7382 | 2025-12-08 18:52:23 | MASTER-Kislovodsk | (22h 29m 37.06s , -00d 21m 55.6s) | C | 120 | 12.6 | 7382 | 2025-12-08 18:52:23 | MASTER-Kislovodsk | (22h 29m 37.94s , -00d 00m 13.8s) | C | 120 | 13.2 | 8671 | 2025-12-08 19:14:22 | MASTER-SAAO | (22h 28m 00.88s , -00d 37m 02.0s) | C | 60 | 18.9 | 8671 | 2025-12-08 19:14:22 | MASTER-SAAO | (22h 26m 18.28s , -00d 21m 13.1s) | C | 60 | 18.5 | 8764 | 2025-12-08 19:15:54 | MASTER-SAAO | (22h 27m 55.90s , -00d 37m 31.3s) | C | 60 | 19.0 | 8764 | 2025-12-08 19:15:54 | MASTER-SAAO | (22h 26m 13.40s , -00d 21m 40.9s) | C | 60 | 18.6 | 8867 | 2025-12-08 19:17:38 | MASTER-SAAO | (22h 26m 12.54s , -00d 20m 34.9s) | C | 60 | 18.5 | 8892 | 2025-12-08 19:18:03 | MASTER-Kislovodsk | (22h 29m 36.09s , -00d 22m 32.0s) | C | 60 | 12.2 | 8892 | 2025-12-08 19:18:03 | MASTER-Kislovodsk | (22h 29m 39.94s , -00d 01m 05.5s) | C | 60 | 13.2 | 8972 | 2025-12-08 19:19:22 | MASTER-Kislovodsk | (22h 29m 33.23s , -00d 02m 12.0s) | C | 60 | 13.3 | 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/43036. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41115] GRB 251208B: Swift ToO observations
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43035 SUBJECT: GRB 251208B: Swift ToO observations DATE: 25/12/08 19:26:56 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 Fermi/LAT-detected event GRB 251208B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021893 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 Fermi/LAT 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/43035. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41114] GRB 251208B: Fermi-LAT detection
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43034 SUBJECT: GRB 251208B: Fermi-LAT detection DATE: 25/12/08 18:51:48 GMT FROM: chiara.bartolini-1(a)unitn.it E. Bissaldi (Politecnico and INFN Bari), N. Di Lalla (Stanford University), R. Gupta (NASA/GSFC), A. Holzmann Airasca (UniTrento and INFN Bari), C. Bartolini (UniTrento and INFN Bari) and F. Longo (University and INFN, Trieste) report on behalf of the Fermi-LAT team: At 10:17:17.29 UT on December, 08, 2025 Fermi-LAT detected high-energy emission from GRB 251208B, which was also detected by Fermi-GBM (trigger 786881842 / 251208429, GCN #43028) and Swift/BAT-GUANO (GCN #43033). The best LAT on-ground location is found to be RA, Dec = 228.48, 29.07 (J2000) with an error radius of 0.07 deg (90 % containment, statistical error only), which is consistent with the Swift/BAT-GUANO localization. This was 39 deg from the LAT boresight at the time of the trigger. The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 0 - 1 ks after the GBM trigger is (3.13 ± 0.09)E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.01 ± 0.23. The highest-energy photon is a 17 GeV event which is observed 419 seconds after the GBM trigger. A Swift ToO has been approved for this burst. The Fermi-LAT point of contact for this burst is Chiara Bartolini (chiara.bartolini(a)ba.infn.it). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/43034. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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