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[vsnet-grb-info 41950] GCN Announcement: Passing of Scott Barthelmy, GCN Founder
by GCN Announcements 25 Feb '26

25 Feb '26

With heavy hearts, we report that our colleague and mentor Scott Barthelmy passed away on February 25, 2026. Scott was the founder, architect, and tireless maintainer of GCN from its inception in 1993 until his retirement (see history of GCN; https://gcn.nasa.gov/docs/about/history) Scott was supportive of the development of the new GCN, and we have always aimed to honor his legacy and service to our community. As PI of the Swift-BAT and Swift Project Scientist, he had exceptional impacts on our field. For more details on this new feature and an archive of GCN news and announcements, see https://gcn.nasa.gov/news. For questions, issues, or bug reports, please contact us via: - Contact form: https://gcn.nasa.gov/contact - GitHub issue tracker: https://github.com/nasa-gcn/gcn.nasa.gov/issues --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41949] GRB 260225C: Fermi GBM Final Real-time Localization
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43836 SUBJECT: GRB 260225C: Fermi GBM Final Real-time Localization DATE: 26/02/25 19:08:07 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 18:55:39 UT on 25 Feb 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260225C (trigger 793738544.90425 / 260225789). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 102.6, Dec = 69.3 (J2000 degrees, equivalent to J2000 06h 50m, 69d 17'), with a statistical uncertainty of 15.2 degrees. The angle from the Fermi LAT boresight is 54.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260225789/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260225789/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260225789/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43836. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41948] GRB 260223A: Fermi GBM Observation
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43835 SUBJECT: GRB 260223A: Fermi GBM Observation DATE: 26/02/25 17:16:57 GMT FROM: Peter Veres at University of Alabama in Huntsville <veresp(a)gmail.com> P. Veres (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 04:11:09.81 UT on 23 February 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260223A (trigger 793512674/260223174), which was also detected by DDOTI (Becerra et al. 2026, GCN 43811), COLIBRI (de Ugarte Postigo et al. 2026, GCNs 43812, 43814 & 43820), SVOM/GRM (Wang et al. 2026, GCN 43815), SVOM/VT (Li et al. 2026, GCN 43816) and Glowbug (Woolf et al. 2026, GCN 43824). The Fermi GBM on-ground location (GCN 43808) is consistent with the DDOTI position. The angle from the Fermi LAT boresight is 33 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 39 s (50-300 keV). The time-averaged spectrum from T0-9.2 to T0+51.2 s is best fit by a Band function with Epeak = 70 +/- 6 keV, alpha = -0.76 +/- 0.09, and beta = -1.91 +/- 0.02. The event fluence (10-1000 keV) in this time interval is (2.16 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+18 s in the 10-1000 keV band is 10.4 +/- 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/43835. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41947] GRB 260225A: SVOM/VT optical upper limits
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43834 SUBJECT: GRB 260225A: SVOM/VT optical upper limits DATE: 26/02/25 16:35:56 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, Y. N. Ma, Z. H. Yao, Y. L. Qiu, L. P. Xin, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) and L. Zhang (IHEP) report on behalf of the SVOM/VT team. SVOM/VT performed observation with auto slew to the field of GRB 260226A triggered by SVOM/ECLAIRs (sb26022501, Ma et al., GCN 43829). The observation started at 2026-02-25T09:38:31 UTC, i.e. about 47.68 minutes post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No bright uncatalogued sources were detected within the error box of ECLAIRs (Ma et al., GCN 43829), compared to the Legacy survey catalog, down to the 3 sigma limit of VT_R ~ 22.0 mag. This non-detection is consistent with the result from COLIBRÍ (Basa et al., GCN 43830). More detailed analysis is still on going. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. 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/43834. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41946] GRB 260225B: Fermi GBM Final Real-time Localization
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43833 SUBJECT: GRB 260225B: Fermi GBM Final Real-time Localization DATE: 26/02/25 15:24:47 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 15:14:07 UT on 25 Feb 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260225B (trigger 793725252.479854 / 260225635). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 326.4, Dec = 0.9 (J2000 degrees, equivalent to J2000 21h 45m, 0d 54'), with a statistical uncertainty of 1.8 degrees. The angle from the Fermi LAT boresight is 66.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260225635/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260225635/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260225635/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43833. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41945] EP260126a: VLA 6 GHz detection
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43832 SUBJECT: EP260126a: VLA 6 GHz detection DATE: 26/02/25 15:06:53 GMT FROM: Roberto Ricci at INAF-IRA <ricci(a)ira.inaf.it> R. Ricci, M. Yadav, E. Troja, N. Passaleva and Y.-H. Yang (U Rome) report: We observed the Einstein Probe event detected by EP/WXT (S.F. Fu et al. GCN 43520) with Very Large Array in C-band at the centre frequency of 6 GHz with a bandwidth of 4 GHz in two epochs on Jan 29th 2026 (3.3 days after the trigger) and Feb 19th 2026 (24.1 days after the trigger). Within the EP/FXT localization (S.F Fu et al., GCN 43526), we detect two radio sources, however only one shows a significant rebrightening between the two epochs. We therefore propose that this source, located at RA, DEC(J2000) = 06:55:01.01, +37:42:18.68, is the radio counterpart of EP260126A. At this position, Legacy Survey DR10 (Dey et al. 2019) images show a faint object (r~24 AB mag), which we suggest as the putative host galaxy of the EP transient. Further observations are planned. We thank the VLA staff for executing the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43832. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41944] EP260223a: Liverpool Telescope upper limits
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43831 SUBJECT: EP260223a: Liverpool Telescope upper limits DATE: 26/02/25 14:09:47 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris and N. Habeeb (Leicester) report on behalf of a larger collaboration: We observed the field of EP260223a (Liu et al., GCN 43817) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 8x200s exposures in the SDSS r’ and 9x200s exposures in the SDSS z’ filters starting at 2026-02-24 21:07:44 UT, approximately 33.8 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Within the EP/WXT localisation (Liu et al., GCN 43817), we detect no new sources in our stacked images consistent with the results of Álvarez et al. (GCN 43818) and Zhu et al. (GCN 43826). This is also consistent with the fast fading X-ray emission implied by Liu et al. (GCN 43822). We derive 3-sigma upper limits of r’ > 22.9 and z’ > 22.6 for our stacked images. View this GCN Circular online at https://gcn.nasa.gov/circulars/43831. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41943] GRB 260225A: SVOM/COLIBRÍ (FM-GFT) optical upper limits
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43830 SUBJECT: GRB 260225A: SVOM/COLIBRÍ (FM-GFT) optical upper limits DATE: 26/02/25 13:15:27 GMT FROM: Stephane Basa at UAR Pytheas/OHP, LAM <stephane.basa(a)lam.fr> Stéphane Basa (UAR Pytheas), Diego López-Cámara (UNAM), Benjamin Schneider (LAM), Damien Dornic (CPPM), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), and L. Zhang (IHEP) report: We imaged the field of GRB 260225A (Ma et al., GCN Circ. 43829) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-02-25 09:02 UTC to 10:24 UTC (from 0.18 to 1.57 hours after the trigger) and obtained 64 minutes of simultaneous exposure in the r and z filters. The data were reduced and analyzed with the COLIBRÍ ASU pipeline, and also analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the Pan-STARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. Within the ECLAIRs 5.1 arcmin error circle and in comparison to the corresponding LS catalog and images, we do not detect any new sources to preliminary 5-sigma limiting magnitudes of: r > 24.1 z > 22.5. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. 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/43830. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41942] GRB 260225A: SVOM detection of a burst
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43829 SUBJECT: GRB 260225A: SVOM detection of a burst DATE: 26/02/25 09:40:51 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Yinuo Ma (NAOC), Li Zhang (IHEP), Nicolas Dagoneau (CEA), Frédéric Daigne (IAP), Pierre Maggi (ObAS), report on behalf of the SVOM mission team: At 2026-02-25T08:51:15 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260225A (SVOM burst-id sb26022501). 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 11 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 16.32 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2026-02-25T08:50:57. The localization of the best alert is R.A., Dec. 204.6748, 44.6546 degrees: R.A. (J2000) = 13h38m41.95s Dec. (J2000) = 44d39m16.67s with a 90% confidence level (C.L.) radius of 5.13 arcmin (including systematic error of 2 arcmin added in quadrature). This burst was also detected by SVOM/GRM with a significance of 4.90. SVOM slewed to the burst. No X-ray observation could be performed by SVOM/MXT for the time being, due to Earth occultation. SVOM/VT observations will be reported in 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 zhangli: zhangli(a)ihep.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43829. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41941] EP260224a: Einstein Probe detection of an X-ray transient
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43828 SUBJECT: EP260224a: Einstein Probe detection of an X-ray transient DATE: 26/02/25 09:01:39 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Guojiong Yang(NAO, CAS), Jiaying Cao(IHEP), Wenfeng Wen(SZTU) and Haiwu Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260224a. The transient triggered EP-WXT at 2026-02-24T17:03:42 (UTC). The WXT position of the source is R.A. = 175.200 deg, DEC = -41.415 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) started at 2026-02-25T06:21:59 (UTC), approximately 13 hours after the WXT trigger. No onboard alert was generated by FXT during this observation. Further follow-up observations are encouraged. 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/43828. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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