March 2026 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 42280] Fermi GBM Sub-Threshold Detection of GRB 260330B
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44159 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 260330B DATE: 26/03/30 19:48:13 GMT FROM: atrigg2(a)lsu.edu A.C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi-GBM Team: SVOM/ECLAIRs detected GRB 260330B on 2026-03-30 at 14:19:57 UTC (GCN 44157). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates. The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient approximately 16 s after the ECLAIRs best image SNR time of 2026-03-30T14:19:31. The Targeted Search candidate was found most significantly on the 32 s timescale using the "soft" spectral template (i.e., Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) and has a false alarm rate of 1.0-04 Hz. The Fermi-MET of this transient is 796573176.806 s. The Targeted Search localization is spatially consistent with the ECLAIRs location. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/44159. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42279] GRB 260330B: LCO optical upper limits
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44158 SUBJECT: GRB 260330B: LCO optical upper limits DATE: 26/03/30 18:58:32 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), G. X. Lan (IRAP), S. Guillot (IRAP), report on behalf of the SVOM mission team: We observed the field of GRB 260330B detected by SVOM (Lan et al., GCN 44157) with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument. Our observation started on 2026-03-30 at 17:05:41 UT (about 2.76 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 SVOM/ECLAIRs error box. We measure the following upper limit calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r > 20.4 AB (5-sigma, mid-time 2.85 hr after the trigger); z > 19.2 AB (5-sigma, mid-time 2.86 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44158. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42278] GRB 260330B: SVOM detection of a burst
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44157 SUBJECT: GRB 260330B: SVOM detection of a burst DATE: 26/03/30 14:50:52 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> G. X. Lan, S. Guillot, H. Yang, O. Godet (IRAP), report on behalf of the SVOM mission team: At 2026-03-30T14:19:57 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260330B (SVOM burst-id sb26033003). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 9 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 12.13 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2026-03-30T14:19:31. The localization of the best alert is R.A., Dec. 252.555, 36.862 degrees: R.A. (J2000) = 16h50m13s Dec. (J2000) = 36d51m44s with a 90% confidence level (C.L.) radius of 6.66 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed multiple broad peak structures with a T90 duration of about 20.844 (-3.025 / +7.55) s. This burst was also detected by SVOM/GRM with a significance of 9.10. SVOM slewed to the burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. 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 Guangxuan Lan: glan(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/44157. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42277] EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44156 SUBJECT: EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope DATE: 26/03/30 13:44:34 GMT FROM: Y.C. Kang at Peking University <yckang(a)stu.pku.edu.cn> Yacheng Kang, Zexuan Wu, Qiang Wang, Ruize Shi, Xinmiao Zhao, Zhuokai Liu, Chenxi Bao, Yiming Dong, Ziming Wang, Fangzhou Ren, Lijing Shao, Zhuo Li, Subo Dong, Xian Chen (PKU) report on behalf of the PKU HiTF (High-energy Transients Follow-up) group: We observed the field of EP260324a (Wu et al., ATel 17728; T0 = 2026-03-24T07:04:20) using the PKU 60cm telescope at Xinglong Observatory, NAOC. Observations began on 2026 Mar 27, corresponding to ~ 3.4 days after the EP-WXT detection, and spanned two epochs. In the stacked g- and r-band images, we detect the optical counterpart in the difference image at a position consistent with that of ZTF26aapviim / AT2026hir (Anumarlapudi et al., GCN 44120; Mohan et al., GCN 44128). Preliminary photometry is calibrated against nearby Pan-STARRS field stars and reported in the AB magnitude system, without correction for Galactic extinction. The observation log is summarized below: | Date | Start_UT | T_mid − T0 (days) | Filter | Exposure (s) | Magnitude (AB) | | :--------: | :---------: | :---------------: | :----: | :----------: | :------------: | | 2026-03-27 | 16:33:34.32 | 3.41 | g | 4 * 600 | 17.88 +/- 0.02 | | 2026-03-27 | 17:16:14.28 | 3.44 | r | 4 * 600 | 18.22 +/- 0.03 | Further analysis and follow-up observations are ongoing. The PKU 60cm Telescope is operated by the Department of Astronomy, Peking University. The PKU HiTF group is dedicated to rapid follow-up observations of high-energy transients. View this GCN Circular online at https://gcn.nasa.gov/circulars/44156. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42276] EP260329b: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44155 SUBJECT: EP260329b: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/03/30 13:25:23 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> The fast X-ray transient EP260329b triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Song et al., GCN 44142) , and followed by several optical telescopes (Li et al., GCN 44139, Zhu et al., GCN 44140, Eyles-Ferris et al., GCN 44144, Magnani et al., GCN 44146, Aryan et al., GCN 44147, Lipunov et al., GCN 44150). The refined analysis of the WXT data shows that the event started at T0=2026-03-29T10:35:25 (UTC) and lasted for 35 s with a single pulse, before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.51 x 10^20 cm^-2 and a photon index of 1.42 +/- 0.65. The derived average unabsorbed 0.5-4 keV flux is 1.07 (-0.37/+0.56) x 10^(-9) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-03-29T10:38:50.16 (UTC), about 3 minutes after T0. The exposure time of this observation is 4388 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 181.3131, 4.3505 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT detected a sharp pulse lasting about 200 s. About 400 s after the end of the pulse, the light curve started to rise again. The rising phase was slower than that of the initial pulse and lasted for roughly 800 s, until the observation was interrupted due to Earth occultation. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 1.51 x 10^20 cm^-2 and a photon index of 1.91 +/-0.04. The derived average unabsorbed 0.5-10 keV flux is 1.54 +/-0.05 x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44155. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42275] EP260329a: COLIBRÍ optical upper limit
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44154 SUBJECT: EP260329a: COLIBRÍ optical upper limit DATE: 26/03/30 07:26:18 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260329a (Yang et al., GCN Circ. 44141) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-29 11:41:47 to 12:23:53 UTC (from 8.19 to 8.89 hours after the trigger, starting 1.3 hours after the notice) and obtained 29 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the position of the two EP/FXT sources (assuming a 10″ error) reported by Yang et al. (GCN Circ. 44153), as well as at the position of the optical counterpart reported by NOT (He et al., GCN Circ. 44152), down to the following 3-sigma limit: r > 22.45 z > 21.06 Our non-detection, together with the FXT observation, is consistent with the candidate reported by NOT (He et al., GCN Circ. 44152) being a plausible optical counterpart of EP260329A. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44154. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42274] EP260329a: EP-FXT follow up observation
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44153 SUBJECT: EP260329a: EP-FXT follow up observation DATE: 26/03/30 06:40:23 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Guojiong Yang (NAO, CAS), F.-F. Song (YNAO, CAS), Wei Chen, Yuan Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260329a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Yang et al., GCN 44141). Early optical follow-up observations reported only upper limits (Sankar et al., GCN 44145). A possible uncatalogued optical counterpart was reported by later optical observations (He et al., GCN 44152). EP-FXT performed a follow-up observation starting at 2026-03-29T14:47:27 UTC, approximately 11.3 hours after the WXT trigger, with a total exposure time of 5934 s. Two uncataloged sources are detected within the WXT error circle. Preliminary analysis on these sources is automatically conducted, and the details are listed as follows. EPF_J002151.2+822924 RA (J2000): 5.4918, Dec (J2000): 82.4881 Flux: 4.9e-14 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 1.3e-14 erg/s/cm^2 (1 sigma) EPF_J002212.3+823200 RA (J2000): 5.5758 Dec (J2000): 82.5335 Flux: 5.3e-14 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 1.5e-14 erg/s/cm^2 (1 sigma) We note that the position of EPF_J002151.2+822924 is consistent with the optical uncatalogued counterpart reported by GCN 44152 (He et al.) Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44153. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42273] EP260329a: NOT optical counterpart candidate
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44152 SUBJECT: EP260329a: NOT optical counterpart candidate DATE: 26/03/30 06:09:01 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, S.Q. Jiang, Z.P. Zhu, J. An, X. Liu, D. Xu (NAOC), S.Y. Fu (HUST), J. P. U. Fynbo (DAWN/NBI), K. Valeckas (NOT) report: We observed the field of EP260329a detected by Einstein Probe (EP), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 3 x 300 s frames in the Sloan r-band. An uncatalogued optical source is detected within the EP-WXT error circle (Yang et al., GCN 44141) at coordinates R.A. (J2000) = 5.4770 (deg) Dec. (J2000) = 82.4894 (deg) with an uncertainty of ~ 0.5 arcsec. The source has r ~ 21.6 mag (AB) at a median time of 45 mins after the EP trigger, calibrated with nearby PanSTARRS1-dr2 catalog and not corrected for Galactic extinction. No source is present at the above position in PanSTARRS down to a 5-sigma limit of r ~22.3 mag. No NEO object would be at the above position at the NOT observational time by checking MPC. We thus think the source could be the optical counterpart of EP260329a. View this GCN Circular online at https://gcn.nasa.gov/circulars/44152. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42272] GRB 260330A: Fermi GBM Final Real-time Localization
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44151 SUBJECT: GRB 260330A: Fermi GBM Final Real-time Localization DATE: 26/03/30 03:48:27 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 03:40:19 UT on 30 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260330A (trigger 796534824.63566 / 260330153). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 93.6, Dec = -44.6 (J2000 degrees, equivalent to J2000 06h 14m, -44d 36'), with a statistical uncertainty of 2.8 degrees. The angle from the Fermi LAT boresight is 63.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260330153/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260330153/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260330153/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44151. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42271] EP260329b: Global MASTER-Net observations report
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44150 SUBJECT: EP260329b: Global MASTER-Net observations report DATE: 26/03/29 23:45:30 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-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260329b ( EP Team et al., GCN 44142) errorbox 41172 sec after notice time and 46747 sec after trigger time at 2026-03-29 23:35:07 UT, with upper limit up to 17.2 mag. Observations started at twilight. The observations began at zenith distance = 75 deg. The sun altitude is -13.8 deg. The galactic latitude b = 65 deg., longitude l = 277 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3219325 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 46777 | 2026-03-29 23:35:07 | MASTER-OAFA | (12h 05m 25.47s , +04d 20m 43.8s) | C | 60 | 16.4 | 46837 | 2026-03-29 23:35:07 | MASTER-OAFA | (12h 05m 25.47s , +04d 20m 43.7s) | C | 180 | 17.2 | Coadd 46852 | 2026-03-29 23:36:21 | MASTER-OAFA | (12h 05m 25.71s , +04d 21m 49.7s) | C | 60 | 16.6 | 46927 | 2026-03-29 23:37:36 | MASTER-OAFA | (12h 05m 33.10s , +04d 20m 55.0s) | C | 60 | 16.7 | 47124 | 2026-03-29 23:40:54 | MASTER-OAFA | (12h 05m 30.36s , +04d 21m 51.8s) | C | 60 | 16.9 | 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/44150. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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