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[vsnet-grb-info 41957] GRB 260226A???: BALROG localization (Fermi Trigger 793795080 / GRB 260226443)
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43843 SUBJECT: GRB 260226A???: BALROG localization (Fermi Trigger 793795080 / GRB 260226443) DATE: 26/02/26 13:23:46 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 793795080 at 10:37:55 on 26 Feb. 2026 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 43.6 deg Decl.(2000.0) = 9.6 deg The 1 sigma statistical error radius is 0.2 deg. We estimate an additional systematic error of 2 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260226443/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260226443/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260226443/json View this GCN Circular online at https://gcn.nasa.gov/circulars/43843. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41956] EP260224a: LCO optical upper limits
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43842 SUBJECT: EP260224a: LCO optical upper limits DATE: 26/02/26 12:00:50 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), A. van Hoof (Radboud), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), and A. J. Levan (Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260224a (Yang et al., GCN 43828) using LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) and the South African Astronomical Observatory (South Africa) equipped with the SINISTRO instrument. A series of 6x300 s exposures were taken in each of the SDSS-r and SDSS-z filters, starting at 2026-02-26 03:25:00 UT (32.4 hr after the trigger) and 2026-02-25 23:23:55 UT (30.3 hr after the trigger) respectively. We performed subtractions on our stacked images using a template image from the KMTNet Synoptic Survey of the Southern Sky (Kim et al. 2016, doi:10.5303/JKAS.2016.49.1.37) and compared the stacks and template manually. No new source is detected within or at the border of the EP/WXT uncertainty region (Yang et al., GCN 43828). From the stacked images, we obtain the following 3-sigma upper limits:  r > 23.6 z > 21.6 These upper limits are in AB magnitudes, calibrated using nearby stars from the SkyMapper catalog, and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43842. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41955] GRB260225A: SVOM/ECLAIRs refined position
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43841 SUBJECT: GRB260225A: SVOM/ECLAIRs refined position DATE: 26/02/26 11:19:51 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP), on behalf of the ECLAIRs team report: Using the event-by-event data downloaded through the X-band ground station, we were able to improve the ECLAIRs position of GRB 260204A (SVOM burst-id sb26022501, Ma et al., GCN 43829) as: R.A., Dec.: 204.7191, 44.6194 degrees: R.A. (J2000) = 13h38m52.58s Dec. (J2000) = 44d37m09.84s with a 90% confidence level (C.L.) radius of 7.1 arcmin. Within this refined position, a counterpart has been detected in optical by SVOM/COLIBRÍ (Ducoin et al., GCN 43837) and SVOM/VT (Li et al., GCN 43838) as well as in X-rays by EP/FXT (Yang et al., GCN 43839). 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. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. ECLAIRs was developed jointly by CNES, IRAP, APC and CEA. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/43841. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41954] GRB 260226A: Fermi GBM Final Real-time Localization
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43840 SUBJECT: GRB 260226A: Fermi GBM Final Real-time Localization DATE: 26/02/26 10:48:46 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 10:37:55 UT on 26 Feb 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260226A (trigger 793795080.95811 / 260226443). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 45.3, Dec = 15.7 (J2000 degrees, equivalent to J2000 03h 01m, 15d 41'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 17.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260226443/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260226443/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260226443/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43840. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41953] GRB 260225A: EP-FXT follow-up observation
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43839 SUBJECT: GRB 260225A: EP-FXT follow-up observation DATE: 26/02/26 04:07:27 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: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260225A (SVOM/sb26022501; Ma et al., GCN 43829) starting at 2026-02-25T09:26:28 UTC, approximately 35 minutes after the SVOM trigger, with a total exposure time of 6090 s. At the optical position reported by Basa et al. (GCN Circ. 43837), an uncatalogued X-ray source (EPF_J133924.5+443450; RA, Dec = 204.852, 44.5806, J2000) is detected, with a 90% confidence positional uncertainty of 2.1 arcsec (statistical only). The spectrum can be well fitted with an absorbed power-law model, with the Galactic hydrogen column density. The best-fit photon index is about 1.56. The corresponding unabsorbed flux in the 0.5–10 keV band is 1.89×10^-12 erg cm^-2 s^-1 Flux_err: 2.3 × 10^-13 erg cm^-2 s^-1 (1σ) 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/43839. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41952] GRB 260225A: SVOM/VT optical observation
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43838 SUBJECT: GRB 260225A: SVOM/VT optical observation DATE: 26/02/26 03:29:53 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, 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), D. Turpin (CEA) and L. Zhang (IHEP) report on behalf of the SVOM/VT team. Following the report of the optical counterpart (Ducoin et al., GCN 43837) by SVOM/COLIBRÍ (Basa et al., GCN 43830), we reanalyzed SVOM/VT Xband data (Li et al., GCN 43834) for GRB 260225A (Ma et al., GCN 43829). The source was detected by SVOM/VT in both channels. The measurements in AB magnitude are derived as follows: Mid time | Band | Exposure Time | Magnitude 1.13 hours VT_B 52*50 sec 22.09 +/- 0.16 mag 1.07 hours VT_R 41*50 sec 22.00 +/- 0.20 mag Our photometry was not corrected for Galactic extinction. 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/43838. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41951] GRB 260225A: SVOM/COLIBRÍ (FM-GFT) Detection of an Optical Counterpart Candidate
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43837 SUBJECT: GRB 260225A: SVOM/COLIBRÍ (FM-GFT) Detection of an Optical Counterpart Candidate DATE: 26/02/26 00:08:25 GMT FROM: Stephane Basa at UAR Pytheas/OHP, LAM <stephane.basa(a)lam.fr> Jean-Grégoire Ducoin (CPPM), 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), 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: The data reported in the GCN by Basa et al. (GCN Circ. 43830) have been reanalyzed following an improved localization provided by ECLAIRs (private communication). The images have been acquired by 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 exposure. The data were reduced and analyzed with the COLIBRÍ 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. We detect an uncatalogued source revealed by image subtraction using Legacy Survey as template and consistent with the new ECLAIRs localization at: RA(J2000) = 13:39:24.56 = 204.852333 degrees Dec(J2000) = 44:34:51.0 = 44.580833 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitude derived for that source is: r = 21.55 Further observations and analysis are ongoing. 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/43837. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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[vsnet-grb-info 41940] EP 260225.148: COLIBRÍ Confirmation of flaring star
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43827 SUBJECT: EP 260225.148: COLIBRÍ Confirmation of flaring star DATE: 26/02/25 06:39:13 GMT FROM: Stephane Basa at UAR Pytheas/OHP, LAM <stephane.basa(a)lam.fr> Diego López-Cámara (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), 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), Asuka Kuwata (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), 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 automatically observed the field of EP-WXT trigger 01709258631 (Lui et al., GCN Circ. 43817) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-25 04:42 to 05:54 UTC (from 1.16 to 2.36 hours after the trigger) and obtained 55 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. We used STDWeb (Karpov 2025) to perform image subtraction against Legacy Survey DR10 templates (Dey et al. 2019). We do not detect any new source in the WXT uncertainty region down to the following 5-sigma limits: r > 23.4 z > 22.4 Our observation supports that EP-WXT trigger 01709258631 is very probably due to a flaring star as announced by Cao et al. (GCN Circ. 4382517). 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/43827. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41939] EP260223a: Xinglong optical upper limit
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43826 SUBJECT: EP260223a: Xinglong optical upper limit DATE: 26/02/25 06:29:12 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Yinan-Zhu (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Yuguang-Sun (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP260223a (GCN Circular 43817), we observed the field of EP260223a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s N-band frames by using 2.16-m with a median time of 2026-02-24 10:56:45 (UT), 4 hrs after the EP trigger and 3x300s clear-band frames by using 2.16-m with a median time of 2026-02-21T19:09:10, 8 hrs after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 20 arcsec EP/FXT error circle (GCN Circular 43817), down to 3-sigma limiting magnitudes of N-band ~19.11 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/43826. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41938] The EP-WXT trigger 01709258631 is likely a flaring star
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43825 SUBJECT: The EP-WXT trigger 01709258631 is likely a flaring star DATE: 26/02/25 06:09:06 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> JiaYing Cao(IHEP), WenFeng Wen(SZTU), Guojiong Yang and Haiwu Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709258631 at 2026-02-25T03:33:22 is likely a stellar flare associated with RX J1220.4+1226. The estimated flux of the flare is around 4e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4e+31 erg/s. 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/43825. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41937] GRB 260223A: Glowbug gamma-ray detection
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43824 SUBJECT: GRB 260223A: Glowbug gamma-ray detection DATE: 26/02/25 05:26:59 GMT FROM: Richard S. Woolf at US Naval Research Laboratory <richard.s.woolf.civ(a)us.navy.mil> R. Woolf, C.C. Cheung, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260223A, which was also detected by Fermi GBM (GCN 43808) and SVOM/GRM (GCN 43815). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-02-23 04:11:09.520 with a duration of 20.5 s and a total significance of about 48.4 sigma. Following the initial event onset, the light curve comprises two main peaks at ~T0+11s and +18s. Note that data from ~T0+15s to T0+17s suffered from deadtime in various detectors. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/43824. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41936] EP260213a: Mephisto optical upper limits
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43823 SUBJECT: EP260213a: Mephisto optical upper limits DATE: 26/02/25 04:33:50 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Guowang Du, Ziwei Li, Zhenfei Qin, Jialong Zhou, Yu Pan, Xingzhu Zou, Xinlei Chen, Brajesh Kumar, Yuan Fang, Jinghua Zhang, Xufeng Zhu, Tao Wang, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: The 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory, was triggered at 2026-02-13T20:05:57 (~7.2 min after the EP/WXT trigger) to observe the field of EP260213a (Yang et al., GCN 43729; Li et al., GCN 43730). A set of simultaneous multi-band (ugi and vrz) images was collected. In our stacked frames, no new candidate was detected within the EP/FXT localization (Li et al., GCN 43730) and the upper limits (3 sigma) are listed below. These results are consistent with previously reported non-detection by Cotter et al. (GCN 43728), Wu et al. (GCN 43731), Maksut et al. (GCN 43732), Pankov et al. (GCN 43733), Li et al. (GCN 43734), Aryan et al. (GCN 43735), Fortin et al. (GCN 43737), Lipunov et al. (GCN 43738) and Eyles-Ferris et al. (GCN 43739). --------------------------------------------------- Start_Time(UT) | Band | Exp(s) | LimMag (AB) --------------------------------------------------- 2026-02-13T20:11:30 | u | 45.0*8 | >22.68 2026-02-13T20:05:57 | v | 45.0*5 | >22.62 2026-02-13T20:11:33 | g | 45.0*8 | >23.51 2026-02-13T20:05:59 | r | 45.0*5 | >23.41 2026-02-13T20:13:07 | i | 45.0*8 | >22.84 2026-02-13T20:05:59 | z | 45.0*5 | >21.85 --------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025 and presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. Here, we note that the current data processing pipeline is still at a preliminary stage, with flux calibration precision in each band at the level of about 5% or even higher. View this GCN Circular online at https://gcn.nasa.gov/circulars/43823. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41935] EP260223a: EP-FXT follow-up observation
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43822 SUBJECT: EP260223a: EP-FXT follow-up observation DATE: 26/02/25 04:06:11 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), J. W. Hu and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: We performed one follow-up observation of the X-ray transient EP260223a (Liu et al., GCN 43817, and followed by Álvarez et al., GCN 43818) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2026-02-24 04:45:40 (UTC), about 17.42 hours after the WXT detection, with an exposure of ~5.2 ks. No source was detected within the WXT error circle. The 0.5-10 keV flux upper limit is about 6e-14 erg/s/cm^2 (90% C. L.). 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/43822. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41934] sb26021801: SVOM/VT optical upper limits
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43821 SUBJECT: sb26021801: SVOM/VT optical upper limits DATE: 26/02/25 03:59:02 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, 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), W. J. TAN (IHEP) report on behalf of the SVOM/VT team. SVOM/VT performed ToO osbervation on the long faint X-ray transient sb26021801 reported by SVOM/Eclairs (Tan et al., GCN 43778). The observation started at about 7.75 hours after trigger in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. No credible sources are detected in single or stacked images within error box of SVOM/Eclairs (Tan et al., GCN 43778) with the 3 sigma limit magnitudes of VT_B ~ 23.8 mag and VT_R ~ 23.5 mag at 9.42 hours post trigger. Our non-detection is consistent with the reports from LCO (Wu et al., GCN 43792), COLIBRÍ (Fortin et al., GCN 43783), LAST (Konno et al., GCN 43784) and C-GFT (Wu et al, GCN 43819). Our photometry was in AB magnitude and not corrected for Galactic extinction. 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/43821. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41933] GRB 260223A: COLIBRÍ optical afterglow decay confirmation
by GCN Circulars 24 Feb '26

24 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43820 SUBJECT: GRB 260223A: COLIBRÍ optical afterglow decay confirmation DATE: 26/02/24 09:24:20 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Fredd Sánchez Álvarez (UNAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), 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), Asuka Kuwata (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Benjamin Schneider (LAM) report: We continued to observe the field of the Fermi GRB 260223A (Fermi GBM team et al., GCN Circ. 43808) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed in two epochs between 2026-02-24 02:23:16 and 07:15:39 UTC (between 22.20 and 27.07 hours after the trigger) obtaining images in the grizy filters on the first and rz on the second. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR2, is in the AB system, and is not corrected for Galactic extinction. The optical counterpart reported by Becerra et al. (GCN Circ. 43811) and confirmed by our earlier observations (de Ugarte Postigo et al. GCN Circ 43812) has decayed after the early rebrightnening (de Ugarte Postigo et al. GCN Circ 43814). On our latest stack, we detect the afterglow of GRB 260223A at r = 20.93 +/- 0.07 mag. Between our last observation obtained yesterday and today’s observations, we measure a decay slope of alpha ~ -1.1 (where F_nu ~ t ^ alpha). This is consistent with the observations obtained by SVOM/VT a few hours before (Li et al. GCN Circ. 43816) and serves to confirm that this object is indeed the afterglow of GRB 260223A. 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/43820. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41932] sb26021801: SVOM/C-GFT upper limit
by GCN Circulars 24 Feb '26

24 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43819 SUBJECT: sb26021801: SVOM/C-GFT upper limit DATE: 26/02/24 08:27:40 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), Z. Kang (CHO), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC), Wenjin TAN (IHEP) report on behalf of the SVOM/C-GFT team: We observed the field of sb26021801 detected by SVOM/ECLAIRs (Tan et al., GCN 43778) with LATIOS on SVOM/C-GFT. Observations started at 2026-02-18T16:23:38 UTC, ~11.14 hr after the trigger. We obtained g, r, and i-band follow-up imaging. After preliminary analysis, no credible candidate was detected within the error box provided by SVOM/ECLAIRs (Tan et al., GCN 43778) in our images. The 5-sigma upper limits are: | Mid_t - T0 (hr)| Exposure Time (s) | Band | Upper Limit (AB) | |----------------|-------------------|------|------------------| | 11.67 | 20×90 | i | 20.7 | | 11.95 | 20×90 | g | 20.7 | | 12.23 | 20×90 | r | 20.9 | The photometry was calibrated against nearby Pan-STARRS1 stars and no correction for Galactic dust extinction was applied. This result is consistent with Fortin et al.(GCN 43783), Konno et al.(GCN 43784), and Wu et al. (GCN 43792). We thank the observation assistants Yin-Huai Hao and Chun-Lei Guo at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/43819. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41931] EP260223a: COLIBRÍ optical upper limits
by GCN Circulars 24 Feb '26

24 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43818 SUBJECT: EP260223a: COLIBRÍ optical upper limits DATE: 26/02/24 06:15:59 GMT FROM: freddalvarez(a)astro.unam.mx Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), 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), Asuka Kuwata (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Benjamin Schneider (LAM) report: We observed the field of the EP260223a (Liu et al., GCN Circ. 43817) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-24 04:07 to 05:22 UTC (from 16.79 to 18.03 hours after the trigger and 17 minutes after the GCN Circular) and obtained 57 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. We used STDWeb (Karpov 2025) to perform image subtraction against Legacy Survey DR10 templates (Dey et al. 2019). We do not detect any new source in the WXT uncertainty region (Liu et al., GCN Circ. 43817) down to the following 5-sigma limits: r > 23.7 z > 22.9 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/43818. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41930] EP260223a: Einstein Probe detection of an X-ray transient
by GCN Circulars 24 Feb '26

24 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43817 SUBJECT: EP260223a: Einstein Probe detection of an X-ray transient DATE: 26/02/24 03:53:43 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), J. W. Hu and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260223a. The transient did not trigger the WXT onboard unit due to the limited number of counts. The WXT position of the source is R.A. = 92.774 deg, DEC = 56.577 deg (J2000) with an uncertainty of 2.7 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the event started at T0=2026-02-23T11:20:27 (UTC), and lasted for approximately 130 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.7×10^21 cm^-2 and a photon index of 2.6 (+1.1/-0.9). The derived average unabsorbed 0.5-4 keV flux is 4.1 (+1.7/-1.3) x 10^-10 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT follow-up observations have been arranged. 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/43817. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41929] GRB 260223A: SVOM/VT optical observation
by GCN Circulars 24 Feb '26

24 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43816 SUBJECT: GRB 260223A: SVOM/VT optical observation DATE: 26/02/24 03:00:50 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, 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) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of GRB 260223A detected by Fermi (Fermi GBM team et al., GCN 43808; Preis et al., GCN 43810) and SVOM/GRM (sb26022301, Wang et al., GCN 43815). The observation started on 2026-02-23T15:26:24 UTC, i.e. about 11.26 hours after the trigger time of GBM, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (Becerra et al., GCN 43811; Postigo et al., GCN 43812; Postigo et al., GCN 43814) were detected in both channels. The measurements in AB magnitude are derived as follows: Mid time | Band | Exposure Time | Magnitude (AB) 14.893 hours VT_R 27*70 sec 19.66 +/- 0.06 mag 14.864 hours VT_B 28*70 sec 20.50 +/- 0.08 mag The counterpart showed a power-law decay with the index of -1.1 during our observation from 11.40 hours to 15.14 hours. Our photometry was not corrected for Galactic extinction. 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/43816. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41928] GRB 260223A: SVOM/GRM observation
by GCN Circulars 23 Feb '26

23 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43815 SUBJECT: GRB 260223A: SVOM/GRM observation DATE: 26/02/23 17:10:56 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260223A (SVOM trigger reference: sb26022301) at 2026-02-23T04:11:28.000 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43808). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 26 +8/-4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260223A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 110.5, Dec = -29.4, Error = 1.7, GCN #43808), is located at about 96 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. ECLAIRs was not collecting data at the time of this burst. With this localization, the time-averaged spectrum from T0-23 to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.29 +0.10/-0.11 and the cutoff energy, parameterized as Epeak, is 194 +33/-25 keV. The event fluence (10-1000 keV) in this time interval is (2.27 +0.13/-0.13)E-05 erg/cm^2. The 1s peak spectrum, measured from T0-0 to T0+1 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.39 +0.10/-0.11 and the cutoff energy, parameterized as Epeak, is 741 +456/-228 keV. The flux (10-1000 keV) in this time interval is (3.03 +0.18/-0.18)E-06 erg/cm^2/s. The localization of GRB 260223A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260223A_amati.png The localization of GRB 260223A in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260223A_yonetoku.png The SVOM/VT ToO has been performed. 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/43815. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41927] GRB 260223A: COLIBRÍ further optical observations and a brightening
by GCN Circulars 23 Feb '26

23 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43814 SUBJECT: GRB 260223A: COLIBRÍ further optical observations and a brightening DATE: 26/02/23 14:15:07 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Antonio de Ugarte Postigo (LAM), Leonardo García García (UNAM), Rosa L. Becerra (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), 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), and Benjamin Schneider (LAM) report: We continued to observe the field of the Fermi GRB 260223A (Fermi GBM team et al., GCN Circ. 43808) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-23 06:16 to 07:48 UTC (from 2.08 to 3.67 hours after the trigger) and obtained near-continuous, alternating 60-second exposures in the grizy filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR2, is in the AB system, and is not corrected for Galactic extinction (A_V = 0.68, Schlafly et al. 2011). The optical counterpart reported by Becerra et al. (GCN Circ. 43811) and confirmed by our earlier observations (de Ugarte Postiga et al. GCN Circ 43812) is observed to brighten continuously during our extended observations, rising from i = 18.55 at the start of our observations to i = 18.15 at the end. Similar behaviour is seen in the other bands. 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/43814. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41926] EP260221a: Optical upper limit with Kinder observations
by GCN Circulars 23 Feb '26

23 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43813 SUBJECT: EP260221a: Optical upper limit with Kinder observations DATE: 26/02/23 09:42:06 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> Y.-H. Lee, A. Aryan, H.-Y. Hsiao, T.-W. Chen (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), A. Sankar.K, M.-H. Lee, C.-H. Lai, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz, and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260221a (Zhang et al., GCN 43791 and Liu et al., GCN 43802) using the 40cm SLT at the Lulin observatory, as part of the Kinder collaboration (Chen & Yang et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations in r-band started at 13:51 UTC on 21st of February 2026 (MJD 61092.577), 2.13 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Neither in the stacked frame nor in the difference image do we detect the optical counterpart candidate proposed by Watson et al. (GCN 43806) and confirmed by Eyles-Ferris et al. (GCN 43807). Clearly, our non-detection is attributable to the shallower detection limits in our observations. Moreover, we used AutoPhOT to perform PSF photometry. The details of the observations and the measured 3-sigma upper limits (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 61092.577 | 2.13 | 300 * 24 | >20.7 | 3".42 | 2.11 The non-detection in our observations is consistent with the reports by Mandarakas et al. (GCN 43793), Kumar et al. (GCN 43794), and Min-He et al. (GCN 43798). The presented magnitude is calibrated using the field stars from the ATLAS-refcat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105) and is not corrected for the expected Galactic foreground extinction of A_r = 0.075 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/43813. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41925] GRB 260223A: COLIBRÍ optical observations
by GCN Circulars 23 Feb '26

23 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43812 SUBJECT: GRB 260223A: COLIBRÍ optical observations DATE: 26/02/23 08:22:07 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Leonardo García García (UNAM), Rosa L. Becerra (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), 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), and Benjamin Schneider (LAM) report: We imaged the field of the Fermi GRB 260223A (Fermi GBM team et al., GCN Circ. 43808) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-23 06:16:02 to 06:26:30 UTC (from 2.081 to 2.256 hours after the trigger) and obtained 3x60 s of simultaneous exposure in the grizy filters. The data were reduced, coadded and analysed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR2, is in the AB system, and is not corrected for Galactic extinction (A_V = 0.68, Schlafly et al. 2011). We detected the optical counterpart reported by Becerra et al., GCN Circ. 43811, at preliminary magnitudes of: g = 19.44 +/- 0.06 r = 18.92 +/- 0.04 i = 18.52 +/- 0.05 z = 18.27 +/- 0.04 y = 18.23 +/- 0.07 Further observations are ongoing. 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/43812. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41924] GRB 260223A: DDOTI Optical Candidate
by GCN Circulars 23 Feb '26

23 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43811 SUBJECT: GRB 260223A: DDOTI Optical Candidate DATE: 26/02/23 05:44:22 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observe the field of GRB 260223A (Fermi Team, GCN Circ. 43808) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2026-02-23 UTC. DDOTI observed from 04:26 UTC to 04:36 UTC (T+14.9 minutes to T+25.3 minutes after the trigger), with a total exposure time of 8 minutes. Comparing our observations with the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect an uncatalogued fading source at: RA = 07:24:21.20 (111.0883 deg) DEC = -29:25:04.4 (-29.4179 deg) at a preliminary AB magnitude of: w = 18.30 +/- 0.13 at T + 14.9 minutes. From our observations, we estimate a temporal decay of approximately −0.6. We suggest that this source is the optical counterpart of GRB 260223A and encourage follow-up observations. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/43811. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41923] GRB 260223A: BALROG localization (Fermi Trigger 793512674 / GRB 260223174)
by GCN Circulars 23 Feb '26

23 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43810 SUBJECT: GRB 260223A: BALROG localization (Fermi Trigger 793512674 / GRB 260223174) DATE: 26/02/23 05:37:50 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 793512674 at 04:11:09 on 23 Feb. 2026 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 109.5 deg Decl.(2000.0) = -28.9 deg The 1 sigma statistical error radius is 1.7 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260223174/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260223174/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260223174/json View this GCN Circular online at https://gcn.nasa.gov/circulars/43810. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41922] Fermi GRB 260223A: Global MASTER-Net observations report
by GCN Circulars 23 Feb '26

23 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43809 SUBJECT: Fermi GRB 260223A: Global MASTER-Net observations report DATE: 26/02/23 05:15:25 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) started inspect of the Fermi GRB 260223A ( Fermi GBM team, GCN 43808) errorbox 123 sec after notice time and 154 sec after trigger time at 2026-02-23 04:13:44 UT, with upper limit up to 19.8 mag. The observations began at zenith distance = 32 deg. The sun altitude is -48.2 deg. The galactic latitude b = -7 deg., longitude l = 243 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3152151 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 170 | 2026-02-23 04:13:44 | MASTER-OAFA | (07h 21m 14.73s , -29d 00m 58.9s) | C | 30 | 19.3 | 210 | 2026-02-23 04:14:20 | MASTER-OAFA | (07h 21m 14.73s , -29d 00m 58.0s) | C | 40 | 19.5 | 262 | 2026-02-23 04:15:07 | MASTER-OAFA | (07h 21m 14.77s , -29d 00m 57.4s) | C | 50 | 19.6 | 324 | 2026-02-23 04:16:03 | MASTER-OAFA | (07h 21m 14.79s , -29d 00m 56.9s) | C | 60 | 18.9 | 395 | 2026-02-23 04:17:09 | MASTER-OAFA | (07h 21m 14.83s , -29d 00m 56.3s) | C | 70 | 19.8 | 603 | 2026-02-23 04:20:17 | MASTER-OAFA | (07h 22m 38.12s , -29d 04m 33.0s) | C | 110 | 19.3 | 730 | 2026-02-23 04:22:15 | MASTER-OAFA | (07h 22m 38.17s , -29d 04m 33.2s) | C | 130 | 19.4 | 882 | 2026-02-23 04:24:31 | MASTER-OAFA | (07h 22m 38.28s , -29d 04m 33.1s) | C | 160 | 19.5 | 998 | 2026-02-23 04:27:17 | MASTER-OAFA | (07h 22m 38.38s , -29d 04m 32.8s) | C | 60 | 18.9 | 1063 | 2026-02-23 04:28:23 | MASTER-OAFA | (07h 22m 38.43s , -29d 04m 32.7s) | C | 60 | 19.2 | 1129 | 2026-02-23 04:29:29 | MASTER-OAFA | (07h 22m 38.49s , -29d 04m 32.7s) | C | 60 | 19.1 | 1196 | 2026-02-23 04:30:35 | MASTER-OAFA | (07h 22m 38.53s , -29d 04m 32.7s) | C | 60 | 19.1 | 1261 | 2026-02-23 04:31:40 | MASTER-OAFA | (07h 22m 38.57s , -29d 04m 32.8s) | C | 60 | 18.9 | 1326 | 2026-02-23 04:32:46 | MASTER-OAFA | (07h 22m 38.61s , -29d 04m 33.1s) | C | 60 | 18.9 | 1393 | 2026-02-23 04:33:52 | MASTER-OAFA | (07h 22m 38.66s , -29d 04m 33.1s) | C | 60 | 19.0 | 1458 | 2026-02-23 04:34:58 | MASTER-OAFA | (07h 22m 38.71s , -29d 04m 33.0s) | C | 60 | 18.8 | 1524 | 2026-02-23 04:36:04 | MASTER-OAFA | (07h 22m 38.76s , -29d 04m 33.3s) | C | 60 | 19.2 | 1591 | 2026-02-23 04:37:10 | MASTER-OAFA | (07h 22m 38.81s , -29d 04m 33.5s) | C | 60 | 19.2 | 1656 | 2026-02-23 04:38:15 | MASTER-OAFA | (07h 22m 38.85s , -29d 04m 33.5s) | C | 60 | 19.2 | 1721 | 2026-02-23 04:39:21 | MASTER-OAFA | (07h 22m 38.89s , -29d 04m 33.7s) | C | 60 | 19.1 | 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/43809. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41921] GRB 260223A: Fermi GBM Final Real-time Localization
by GCN Circulars 23 Feb '26

23 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43808 SUBJECT: GRB 260223A: Fermi GBM Final Real-time Localization DATE: 26/02/23 04:20:24 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 04:11:09 UT on 23 Feb 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260223A (trigger 793512674.810552 / 260223174). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 110.5, Dec = -29.4 (J2000 degrees, equivalent to J2000 07h 21m, -29d 23'), with a statistical uncertainty of 1.7 degrees. The angle from the Fermi LAT boresight is 33.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260223174/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260223174/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260223174/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43808. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41920] EP260221a: COLIBRÍ optical counterpart candidate
by GCN Circulars 23 Feb '26

23 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43806 SUBJECT: EP260221a: COLIBRÍ optical counterpart candidate DATE: 26/02/22 17:22:21 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Antonio de Ugarte Postigo (LAM), Rosa L. Becerra (UNAM), Benjamin Schneider (LAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Fredd Sánchez Álvarez (UNAM) report: We reobserved the field of the EP260221a (Zhang et al., GCN Circ. 43791) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-22 05:55 to 10:54 UTC (from 18.20 to 23.20 hours after the trigger) and obtained 71 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. When we subtract the r-band image from our second epoch from the one from our first (Mandarakas et al., GCN Circ. 43793), we detect a residual source with a SNR of about 5 at: RA (J2000) = 11:55:01.22 = 178.7551 deg Dec (J2000) = -20:58:57.6 = -20.9827 deg The uncertainty on this position is 0.5 arcsec. The source is also seen in subtractions against PS1 images, but at a lower significance, and lies within the enhanced FXT uncertainty region (Liu et al., GCN Circ. 43802). We suggest it is the optical counterpart of the EP source. We notice that these coordinates are consistent with the position of a galaxy present in the Legacy Survey catalog (Dey et al., 2019) with magnitudes g = 23.68 +/- 0.17, r = 23.29 +/- 0.18, i = 22.41 +/- 0.12, and z = 21.90 +/- 0.15 and with a photo-z = 1.22 +/- 0.55. In the r band, the total magnitude of the galaxy and the candidate counterpart faded from 22.54 +/- 0.08 in our first epoch to 23.39 +/- 0.15 in our second epoch (a difference of 0.85 +/- 0.17) and in the z band it faded from 22.03 +/- 0.17 to 22.69 +/- 0.16 (a difference of 0.66 +/- 0.23). These fadings have significances of 5.0- and 2.8-sigma, respectively. The detection of this candidate in r as well as z is consistent with the photo-z of the coincident galaxy Therefore, we suggest that this galaxy might be the host. The non-detection of this source in deep imaging by Levan et al. (GCN Circ. 43805) suggests that it faded very quickly. This is perhaps consistent with temporal decay estimated from the two values reported in X-rays by (Liu et al., GCN Circ. 43802) alpha of approximately 2.2 and suggests the presence of an early jet break. 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/43806. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41919] EP260221a: Liverpool Telescope detection of COLIBRÍ counterpart candidate
by GCN Circulars 22 Feb '26

22 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43807 SUBJECT: EP260221a: Liverpool Telescope detection of COLIBRÍ counterpart candidate DATE: 26/02/22 19:53:08 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris and P. T. O’Brien (Leicester) report on behalf of a larger collaboration: We observed the field of EP260221a (Zhang et al., GCN 43791; Liu et al., GCN 43802) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x200s exposures in the SDSS i’ and 8x200s exposures in the SDSS z’ filters starting at 2026-02-22 00:47:58 UT, approximately 14.1 hours after the X-ray detection. Within the EP/FXT localisation (Liu et al., GCN 43802), we detect no new sources in our stacked images consistent with the results of Mandarakas et al. (GCN 43793), Kumar et al. (GCN 43794), He et al. (GCN 43798), Lipunov et al. (GCN 43803), and Levan et al. (GCN 43805). At the position of the candidate counterpart identified by Watson et al. (GCN 43806), we measure i’ = 22.21 +/- 0.12 and z’ = 22.29 +/- 0.18 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. As pointed out by Watson et al. (GCN 43806), this is significantly brighter than the magnitudes catalogued in Legacy DR10 and suggests this could indeed be the counterpart of EP260221a. We derive 3-sigma upper limits of i’ > 23.4 and z’ > 23.0 for our stacked images. View this GCN Circular online at https://gcn.nasa.gov/circulars/43807. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41918] EP260221a: COLIBRÍ optical counterpart candidate
by GCN Circulars 22 Feb '26

22 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43806 SUBJECT: EP260221a: COLIBRÍ optical counterpart candidate DATE: 26/02/22 17:22:21 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Antonio de Ugarte Postigo (LAM), Rosa L. Becerra (UNAM), Benjamin Schneider (LAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Fredd Sánchez Álvarez (UNAM) report: We reobserved the field of the EP260221a (Zhang et al., GCN Circ. 43791) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-22 05:55 to 10:54 UTC (from 18.20 to 23.20 hours after the trigger) and obtained 71 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. When we subtract the r-band image from our second epoch from the one from our first (Mandarakas et al., GCN Circ. 43793), we detect a residual source with a SNR of about 5 at: RA (J2000) = 11:55:01.22 = 178.7551 deg Dec (J2000) = -20:58:57.6 = -20.9827 deg The uncertainty on this position is 0.5 arcsec. The source is also seen in subtractions against PS1 images, but at a lower significance, and lies within the enhanced FXT uncertainty region (Liu et al., GCN Circ. 43802). We suggest it is the optical counterpart of the EP source. We notice that these coordinates are consistent with the position of a galaxy present in the Legacy Survey catalog (Dey et al., 2019) with magnitudes g = 23.78 +/- 0.13, r = 23.68 +/- 0.14, i = 23.86 +/- 0.27 and z = 23.56 +/- 0.37 and with a photo-z = 1.22 +/- 0.55. In the r band, the total magnitude of the galaxy and the candidate counterpart faded from 22.54 +/- 0.08 in our first epoch to 23.39 +/- 0.15 in our second epoch (a difference of 0.85 +/- 0.17) and in the z band it faded from 22.03 +/- 0.17 to 22.69 +/- 0.16 (a difference of 0.66 +/- 0.23). These fadings have significances of 5.0- and 2.8-sigma, respectively. The detection of this candidate in r as well as z is consistent with the photo-z of the coincident galaxy Therefore, we suggest that this galaxy might be the host. The non-detection of this source in deep imaging by Levan et al. (GCN Circ. 43805) suggests that it faded very quickly. This is perhaps consistent with temporal decay estimated from the two values reported in X-rays by (Liu et al., GCN Circ. 43802) alpha of approximately 2.2 and suggests the presence of an early jet break. 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/43806. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41917] EP260221a: Gemini South z-band upper limit
by GCN Circulars 22 Feb '26

22 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43805 SUBJECT: EP260221a: Gemini South z-band upper limit DATE: 26/02/22 11:42:57 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> Andrew J. Levan (Radboud), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), J. A. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), J. Sanchez-Sierras (Radboud), D. Xu (NAOAC), report on behalf of a larger collaboration We observed the field of the fast X-ray transient EP260221a (Zhang et al., GCN 43791; Liu et al., GCN 43802) using the GMOS-S instrument mounted on the Gemini South telescope (Cerro Pachon, Chile). A single 300 s z-band observation was secured starting on 2026 Feb 22 at 08:20 UT (20.62 hr after trigger). No new source is detected within the EP/FXT error circle, down to a limiting magnitude z = 24.8 (AB, calibrated against nearby sources from the Pan-STARRS catalog, and not corrected for Galactic extinction). A number of faint sources are visible consistent with the EP/FXT position, but they are all present in archival imaging from the Legacy survey and from DECam. Our results are consistent with other non-detection reports (Mandarakas et al., GCN 43793; Kumar et al., GCN 43794; He et al., GCN 43798; Lipunov et al., GCN 43803). We thank excellent support from the Gemini staff, in particular Lindsay Magill. View this GCN Circular online at https://gcn.nasa.gov/circulars/43805. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41916] GRB 260222A: Fermi GBM Final Real-time Localization
by GCN Circulars 22 Feb '26

22 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43804 SUBJECT: GRB 260222A: Fermi GBM Final Real-time Localization DATE: 26/02/22 10:20:22 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 10:09:38 UT on 22 Feb 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260222A (trigger 793447783.750804 / 260222423). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 336.2, Dec = 61.7 (J2000 degrees, equivalent to J2000 22h 24m, 61d 42'), with a statistical uncertainty of 4.4 degrees. The angle from the Fermi LAT boresight is 36.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260222423/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260222423/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260222423/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43804. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41915] EP260221a: Global MASTER-Net observations report
by GCN Circulars 22 Feb '26

22 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43803 SUBJECT: EP260221a: Global MASTER-Net observations report DATE: 26/02/22 08:54:25 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 EP260221a ( EP Team et al., GCN 43791) errorbox 44530 sec after notice time and 51263 sec after trigger time at 2026-02-22 01:57:37 UT, with upper limit up to 13.5 mag. The observations began at zenith distance = 76 deg. The sun altitude is -22.8 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260221a errorbox 53402 sec after notice time and 60136 sec after trigger time at 2026-02-22 04:25:30 UT, with upper limit up to 20.7 mag. The observations began at zenith distance = 27 deg. The sun altitude is -48.3 deg. The galactic latitude b = 40 deg., longitude l = 286 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3149283 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 51354 | 2026-02-22 01:57:37 | MASTER-Kislovodsk | (11h 54m 51.01s , -20d 28m 04.3s) | C | 180 | 13.5 | 60167 | 2026-02-22 04:25:30 | MASTER-OAFA | (11h 50m 53.67s , -20d 40m 02.3s) | C | 60 | 20.3 | 60227 | 2026-02-22 04:25:30 | MASTER-OAFA | (11h 50m 53.67s , -20d 40m 02.4s) | C | 180 | 20.5 | Coadd 60243 | 2026-02-22 04:26:46 | MASTER-OAFA | (11h 50m 48.37s , -20d 40m 39.3s) | C | 60 | 20.3 | 60317 | 2026-02-22 04:28:00 | MASTER-OAFA | (11h 50m 49.21s , -20d 39m 36.9s) | C | 60 | 18.6 | 60395 | 2026-02-22 04:29:18 | MASTER-OAFA | (11h 59m 28.08s , -20d 41m 19.6s) | C | 60 | 19.8 | 60455 | 2026-02-22 04:29:18 | MASTER-OAFA | (11h 59m 28.07s , -20d 41m 19.6s) | C | 180 | 20.7 | Coadd 60474 | 2026-02-22 04:30:37 | MASTER-OAFA | (11h 59m 24.96s , -20d 40m 07.1s) | C | 60 | 20.2 | 60551 | 2026-02-22 04:31:54 | MASTER-OAFA | (11h 59m 25.03s , -20d 41m 43.3s) | C | 60 | 20.2 | 75471 | 2026-02-22 08:39:34 | MASTER- | (11h 56m 08.31s , -21d 31m 03.3s) | C | 180 | 19.7 | 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/43803. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41914] EP260221a: EP-FXT follow-up observation
by GCN Circulars 22 Feb '26

22 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43802 SUBJECT: EP260221a: EP-FXT follow-up observation DATE: 26/02/22 05:03:51 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Tian-Yu Liu, X. X. Sun, M.-H. Zhang, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260221a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 43791). The optical upper limits were reported by COLIBRI telescope, GOTO and the 2.16m Xinglong Telescope (GCN 43793, GCN 43794, GCN 43798). The refined analysis of the WXT data shows that the event started at T0=2026-02-21T11:39:48 (UTC) and lasted for 550 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.5 x 10^20 cm^-2 and a photon index of 2.9 (-0.3/+0.4). The derived average unabsorbed 0.5-4 keV flux is 3.1 (-0.7/+0.5) x 10^(-10)erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source at 2026-02-21T12:44:34 (UTC), about 1 hour 5 minutes after T0. The exposure time of this observation is 5997s. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 178.7560, DEC = -20.9819 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.5 x 10^20 cm^-2 and a photon index of 1.36 (-0.22/+0.22). The derived average unabsorbed 0.5-10 keV flux is 6.9 (-1.6/+2.0) x 10^(-13)erg/s/cm^2. 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/43802. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41913] Fermi GRB 260221B: Global MASTER-Net observations report
by GCN Circulars 22 Feb '26

22 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43801 SUBJECT: Fermi GRB 260221B: Global MASTER-Net observations report DATE: 26/02/22 02:30:42 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) started inspect of the Fermi GRB 260221B ( Fermi GBM team, GCN 43800) errorbox 9789 sec after notice time and 9824 sec after trigger time at 2026-02-22 02:02:07 UT, with upper limit up to 15.3 mag. The observations began at zenith distance = 52 deg. The sun altitude is -22.0 deg. The galactic latitude b = 16 deg., longitude l = 112 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3150150 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 9855 | 2026-02-22 02:02:07 | MASTER-Kislovodsk | (21h 49m 42.78s , +74d 56m 55.5s) | C | 60 | 12.5 | 9970 | 2026-02-22 02:04:03 | MASTER-Kislovodsk | (21h 29m 11.14s , +73d 03m 13.8s) | C | 60 | 15.3 | 10074 | 2026-02-22 02:05:47 | MASTER-Kislovodsk | (21h 30m 08.15s , +73d 03m 12.4s) | C | 60 | 12.1 | 10227 | 2026-02-22 02:08:19 | MASTER-Kislovodsk | (21h 23m 43.72s , +76d 53m 40.4s) | C | 60 | 14.2 | 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/43801. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41912] GRB 260221B: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43800 SUBJECT: GRB 260221B: Fermi GBM Final Real-time Localization DATE: 26/02/21 23:29:14 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 23:18:22 UT on 21 Feb 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260221B (trigger 793408707.776836 / 260221971). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 328.4, Dec = 75.0 (J2000 degrees, equivalent to J2000 21h 53m, 75d 00'), with a statistical uncertainty of 8.4 degrees. The angle from the Fermi LAT boresight is 12.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260221971/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260221971/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260221971/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43800. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41911] EP-WXT01709258519: Xinglong optical upper limit
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43799 SUBJECT: EP-WXT01709258519: Xinglong optical upper limit DATE: 26/02/21 21:25:15 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Min-He (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP-WXT01709258519, we observed the field of EP-WXT01709258519 ( +11:05:00.96 +38:12:32.40 ) using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s clear-band frames with a median time of 2026-02-21T19:28:39, 11 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (WXT01709258519), down to 3-sigma limiting magnitudes of 21.01 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/43799. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41910] EP-WXT01709258519: Xinglong optical upper limit
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43799 SUBJECT: EP-WXT01709258519: Xinglong optical upper limit DATE: 26/02/21 21:25:15 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Min-He (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP-WXT01709258519, we observed the field of EP-WXT01709258519 ( +11:05:00.96 +38:12:32.40 ) using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s clear-band frames with a median time of 2026-02-21T19:28:39, 11 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (WXT01709258519), down to 3-sigma limiting magnitudes of 21.01 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/43799. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41909] EP-WXT01709258519: Xinglong optical upper limit
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43799 SUBJECT: EP-WXT01709258519: Xinglong optical upper limit DATE: 26/02/21 21:25:15 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Min-He (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP-WXT01709258519, we observed the field of EP-WXT01709258519 ( +11:05:00.96 +38:12:32.40 ) using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s clear-band frames with a median time of 2026-02-21T19:28:39, 11 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (WXT01709258519), down to 3-sigma limiting magnitudes of 21.01 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/43799. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41908] EP260221a: Xinglong optical upper limit
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43798 SUBJECT: EP260221a: Xinglong optical upper limit DATE: 26/02/21 20:39:37 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Min-He (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Yuguang-Sun (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP260221a (WXT01709258521; Zhang et al., GCN 43791), we observed the field of EP260221a using the 0.8-m and 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x600s g-band frames by using 0.8-m with a median time of 2026-02-21T17:18:37.349, 4 hrs after the EP trigger and 3x600s clear-band frames by using 2.16-m with a median time of 2026-02-21T19:09:10, 6 hrs after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 20 arcsec EP/FXT error circle (Zhang et al., GCN 43791), down to 3-sigma limiting magnitudes of g-band ~15.48 mag for 0.8-m and clear-band 20.71 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/43798. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41907] Fermi GRB 260221A: Global MASTER-Net observations report
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43797 SUBJECT: Fermi GRB 260221A: Global MASTER-Net observations report DATE: 26/02/21 19:00:32 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) started inspect of the Fermi GRB 260221A ( Fermi GBM team, GCN 43795) errorbox 1055 sec after notice time and 1088 sec after trigger time at 2026-02-21 16:41:00 UT, with upper limit up to 12.4 mag. The observations began at zenith distance = 74 deg. The sun altitude is -21.2 deg. MASTER-Tunka robotic telescope located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 260221A errorbox 5336 sec after notice time and 5369 sec after trigger time at 2026-02-21 17:52:21 UT, with upper limit up to 16.0 mag. The observations began at zenith distance = 30 deg. The sun altitude is -49.0 deg. The galactic latitude b = 61 deg., longitude l = 96 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3149550 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 1118 | 2026-02-21 16:41:00 | MASTER-Kislovodsk | (13h 44m 40.23s , +50d 10m 34.6s) | C | 60 | 12.4 | 1657 | 2026-02-21 16:49:59 | MASTER-Kislovodsk | (13h 49m 30.45s , +48d 15m 50.3s) | C | 60 | 12.0 | 5399 | 2026-02-21 17:52:21 | MASTER-Tunka | (14h 07m 03.52s , +53d 13m 43.3s) | C | 60 | 15.9 | 5399 | 2026-02-21 17:52:21 | MASTER-Tunka | (14h 07m 59.88s , +53d 08m 17.6s) | C | 60 | 16.0 | 5473 | 2026-02-21 17:53:35 | MASTER-Tunka | (14h 20m 10.09s , +51d 18m 47.8s) | C | 60 | 15.9 | 5473 | 2026-02-21 17:53:35 | MASTER-Tunka | (14h 21m 02.69s , +51d 13m 17.9s) | C | 60 | 15.9 | 5547 | 2026-02-21 17:54:48 | MASTER-Tunka | (14h 19m 45.21s , +55d 07m 57.6s) | C | 60 | 15.6 | 5547 | 2026-02-21 17:54:48 | MASTER-Tunka | (14h 20m 44.18s , +55d 02m 30.8s) | C | 60 | 15.5 | 5621 | 2026-02-21 17:56:03 | MASTER-Tunka | (14h 10m 13.14s , +49d 24m 43.5s) | C | 60 | 15.2 | 5621 | 2026-02-21 17:56:03 | MASTER-Tunka | (14h 11m 03.71s , +49d 19m 11.0s) | C | 60 | 15.1 | 5695 | 2026-02-21 17:57:17 | MASTER-Tunka | (14h 32m 57.97s , +53d 06m 17.2s) | C | 60 | 14.4 | 5696 | 2026-02-21 17:57:17 | MASTER-Tunka | (14h 32m 03.19s , +53d 11m 49.2s) | C | 60 | 14.5 | 5770 | 2026-02-21 17:58:31 | MASTER-Tunka | (13h 56m 11.18s , +51d 17m 55.4s) | C | 60 | 15.6 | 5770 | 2026-02-21 17:58:31 | MASTER-Tunka | (13h 57m 05.52s , +51d 12m 26.1s) | C | 60 | 15.5 | 5844 | 2026-02-21 17:59:46 | MASTER-Tunka | (13h 53m 32.03s , +55d 08m 06.5s) | C | 60 | 15.3 | 5844 | 2026-02-21 17:59:46 | MASTER-Tunka | (13h 54m 33.24s , +55d 02m 18.8s) | C | 60 | 15.2 | 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/43797. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41906] ZTF26aaglqak/AT2026dbl: COLIBRÍ Optical Observations
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43796 SUBJECT: ZTF26aaglqak/AT2026dbl: COLIBRÍ Optical Observations DATE: 26/02/21 17:13:45 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Nikos Mandarakas (LAM), Asuka Kuwata (UNAM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), 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), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM) report: We observed the field of AT2026dbl discovered by ZTF (Pérez-Fournon et al., TNSTR No. 291251) and identified as a LFBOT candidate by Einstein Probe (Jayaraman et al., TNSAN No. 2026-38) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. We observed from 2026-02-21 06:00:34 to 07:13:21 UTC (from 6.90 to 6.95 days after discovery date) and obtained 20, 20, 19 and 60 minutes of exposure time in the g, r, i and z filters, respectively. The data were reduced, calibrated and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and was not corrected for Galactic extinction. In our images, we detect AT2026dbl at the position reported by Pérez-Fournon et al. (TNSTR No. 291251) about 2” away from a bright galaxy (with reported magnitudes of g = 21.11 +/- 0.03, r = 20.52 +/- 0.04, i= 20.37 +/- 0.04, z = 20.31 +/- 0.05 in the Legacy Survey DR10; Dey et al. 2019). At the reported redshift of z = 0.19 (Wise et al., TNSCR No. 22993), this corresponds to an offset of about 6 kpc from the center of the galaxy. Subsequently, after the subtraction against PanSTARRS images, we measure preliminary magnitudes of: g = 20.62 +/ - 0.03 r = 20.96 +/ - 0.03 i = 21.21 +/ - 0.06 z = 21.41 +/ - 0.16 Considering the redshift (z=0.19) reported by Wise et al. (TNSCR No. 22993), we find that these magnitudes are brighter than expected for the prototypical LFBOT AT2018cow at this redshift. Further observations are planned. 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/43796. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41905] GRB 260221A: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43795 SUBJECT: GRB 260221A: Fermi GBM Final Real-time Localization DATE: 26/02/21 16:33:30 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 16:22:52 UT on 21 Feb 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260221A (trigger 793383777.240036 / 260221683). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 213.3, Dec = 51.9 (J2000 degrees, equivalent to J2000 14h 13m, 51d 53'), with a statistical uncertainty of 6.6 degrees. The angle from the Fermi LAT boresight is 128.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260221683/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260221683/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260221683/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43795. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41904] EP260221a: GOTO optical upper limit
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43794 SUBJECT: EP260221a: GOTO optical upper limit DATE: 26/02/21 14:41:25 GMT FROM: Amit Kumar at The Open University, UK <amitkundu515(a)gmail.com> A. Kumar, G. Ramsay, D. O’Neill, K. Ulaczyk, S. Moran, B. P. Gompertz, R. Starling, M. Wortley, M. Kennedy, K. Ackley, M. Dyer, J. Lyman, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, M. Pursiainen, on behalf of GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) that serendipitously covered the field of EP/WXT detected EP260221a (WXT01709258521; Zhang et al., GCN 43791). Observations covering the localisation area were taken at 2026-02-21 13:15:35 UT (+1.54h post trigger) utilising GOTO-South. Each observation consisted of 4x45s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. No new transients that could be credibly associated with EP260221a were detected down to a 3-sigma depth of 20.9 mag (AB); see also Mandarakas et al., GCN 43793. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/43794. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41903] EP260221a: COLIBRÍ optical upper limit
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43793 SUBJECT: EP260221a: COLIBRÍ optical upper limit DATE: 26/02/21 14:25:23 GMT FROM: nikos.mandarakas(a)lam.fr EP260221a: COLIBRÍ optical upper limit Nikos Mandarakas (LAM), Asuka Kuwata (UNAM), Benjamin Schneider (LAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (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), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260221a (Zhang et al., GCN Circ. 43791) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-21T12:22:07 to 2026-02-21T13:05:02 UTC (from 38.87 to 81.80 minutes after the trigger, 30 seconds after the GCN notice) and obtained 32 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the Pan-STARRS-DR2 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 FXT source position (Zhang et al., GCN Circ. 43791) down to the following 5-sigma limit: r > 23.1 z > 21.8 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/43793. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41902] SVOM alert sb26021801: LCO optical upper limit
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43792 SUBJECT: SVOM alert sb26021801: LCO optical upper limit DATE: 26/02/21 14:13:23 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), A. Saccardi (CEA/Irfu), D. Turpin (CEA/Irfu), L.P. Xin (NAOC), and X.H. Han (NAOC) report on behalf of the SVOM mission team: We observed the field of sb26021801 (TAN et al., GCN 43778) with the LCO 1-m telescope, equipped with the Sinistro instrument, at both the Cerro Tololo Interamerican Observatory and the Teide Observatory (Tenerife). Our observation started on 2026-02-18 at 06:33:39 UT (about 78.35 min 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, in agreement with Fortin et al. (GCN 43783) and Konno et al.(GCN 43784). We measure the following upper limit calibrated against the PanSTARSS DR1 catalog, and not corrected for Galactic extinction: r > 22.1 AB (5-sigma, mid-time 83.35 min after the trigger) z > 20.2 AB (5-sigma, mid-time 85.38 min after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/43792. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41901] EP260221a: Einstein Probe detection of an X-ray transient
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43791 SUBJECT: EP260221a: Einstein Probe detection of an X-ray transient DATE: 26/02/21 13:34:01 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M.-H. Zhang, X. X. Sun, Tian-Yu Liu, Y. Liu (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 EP260221a. The transient triggered EP-WXT (ID: 01709258521) at 2026-02-21T11:43:14 (UTC). The WXT position of the source is R.A. = 178.749 deg, DEC = -20.978 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) was performed at 2026-02-21T12:44:34 (UTC). Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 178.7568 deg, DEC = -20.9847 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). 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/43791. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41900] The EP-WXT trigger 01709258519 is likely caused by Mrk 421
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43790 SUBJECT: The EP-WXT trigger 01709258519 is likely caused by Mrk 421 DATE: 26/02/21 10:01:16 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M.-H. Zhang, X. X. Sun, Tian-Yu Liu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709258519 at the time of 2026-02-21T08:28:55 is likely associated with the known source Mrk 421. 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/43790. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41899] GRB 260219A: AstroSat CZTI detection
by GCN Circulars 21 Feb '26

21 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43789 SUBJECT: GRB 260219A: AstroSat CZTI detection DATE: 26/02/21 09:34:45 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long,faint GRB 260219A which was also detected by Fermi GBM (Fermi GBM Team., GCN Circ. 43785), and GECAM-B (Jin-Peng Zhang et al., GCN Circ. 43787). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-02-19 14:04:53.66 UTC. The measured peak count rate associated with the burst is 345 (+63, -68) counts/s above the background in the combined data of all quadrants, with a total of 974 (+218, -254) counts. The local mean background count rate was 1127 (+7, -7) counts/s. We measure a T90 of 6.8 (+1.6, -1.3) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/43789. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41898] IceCube-260217A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 20 Feb '26

20 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43788 SUBJECT: IceCube-260217A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/02/20 22:37:41 GMT FROM: syan079(a)icecube.wisc.edu The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-260217A (https://gcn.nasa.gov/circulars/43768) in a time range of 1000 seconds centered on the alert event time (2026-02-17 05:47:04.510 UTC to 2026-02-17 06:03:44.510 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-260217A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.4e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260217A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 1e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-02-16 05:55:24.510 UTC to 2026-02-18 05:55:24.510 UTC). In this case, we report a p-value of 0.014, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260217A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/43788. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41897] GRB 260219A: GECAM-B observation of a long burst
by GCN Circulars 20 Feb '26

20 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43787 SUBJECT: GRB 260219A: GECAM-B observation of a long burst DATE: 26/02/20 11:47:59 GMT FROM: zhangjinpeng(a)ihep.ac.cn Jin-Peng Zhang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260219A, at 2026-02-19T14:04:54.600 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43785). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of one pulse, with a duration (T90) of 13 +/- 4 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260219A.png The time-averaged spectrum from T0 - 1.0 to T0 + 13.0 s (photon energy > 70 keV) is fitted by a power law function. The power law index is -2.16 +0.14/-0.16. The event fluence (10-1000 keV) in this time interval is (7.7 +0.9/-1.1)E-06 erg/cm^2. 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/43787. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41896] Fermi GRB 260219A: Global MASTER-Net observations report
by GCN Circulars 19 Feb '26

19 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43786 SUBJECT: Fermi GRB 260219A: Global MASTER-Net observations report DATE: 26/02/19 18:36:32 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-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 260219A ( Fermi GBM team, GCN 43785) errorbox 8595 sec after notice time and 8760 sec after trigger time at 2026-02-19 16:30:53 UT, with upper limit up to 19.8 mag. The observations began at zenith distance = 44 deg. The sun altitude is -49.0 deg. The galactic latitude b = 61 deg., longitude l = 245 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3145377 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 8790 | 2026-02-19 16:30:53 | MASTER-Tunka | (11h 07m 54.97s , +13d 08m 20.3s) | C | 60 | 19.0 | 8790 | 2026-02-19 16:30:53 | MASTER-Tunka | (11h 07m 34.84s , +13d 15m 31.6s) | C | 60 | 19.0 | 9759 | 2026-02-19 16:47:02 | MASTER-Tunka | (11h 03m 29.25s , +11d 14m 56.3s) | C | 60 | 19.4 | 9759 | 2026-02-19 16:47:02 | MASTER-Tunka | (11h 03m 09.30s , +11d 21m 54.5s) | C | 60 | 19.3 | 10877 | 2026-02-19 17:05:40 | MASTER-Tunka | (11h 18m 34.85s , +11d 21m 16.4s) | C | 60 | 19.7 | 10877 | 2026-02-19 17:05:40 | MASTER-Tunka | (11h 18m 55.04s , +11d 14m 26.8s) | C | 60 | 19.8 | 12397 | 2026-02-19 17:31:00 | MASTER-Tunka | (11h 15m 03.51s , +09d 19m 24.2s) | C | 60 | 17.4 | 12397 | 2026-02-19 17:31:00 | MASTER-Tunka | (11h 14m 42.55s , +09d 26m 02.0s) | C | 60 | 17.4 | 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/43786. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41895] GRB 260219A: Fermi GBM Final Real-time Localization
by GCN Circulars 19 Feb '26

19 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43785 SUBJECT: GRB 260219A: Fermi GBM Final Real-time Localization DATE: 26/02/19 14:18:05 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 14:04:53 UT on 19 Feb 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260219A (trigger 793202698.807012 / 260219587). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 167.4, Dec = 9.6 (J2000 degrees, equivalent to J2000 11h 09m, 9d 35'), with a statistical uncertainty of 2.7 degrees. The angle from the Fermi LAT boresight is 97.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260219587/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260219587/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260219587/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43785. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41894] SVOM alert sb26021801: LAST optical upper limit
by GCN Circulars 19 Feb '26

19 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43784 SUBJECT: SVOM alert sb26021801: LAST optical upper limit DATE: 26/02/19 13:17:44 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) report on behalf of the LAST Collaboration. We report observations of the X-ray transient alert sb26021801, reported by SVOM (Tan et al., GCN 43778). Observations were conducted with the Large Array Survey Telescope (LAST; Ofek et al. 2023, PASP 135, 5001; Ben-Ami et al. 2023, PASP 135, 5002). Observations of sb26021801 were taken over 11 sequential epochs in clear band (similar to the Gaia Bp band). The first epoch began at 2026-02-18 23:06:13 UTC (T-T0 = 0.76d). Each epoch consists of 20x20s exposures. We coadd a total of 160x20s exposure images and perform image subtraction using a reference image of the field. We do not detect any new optical source up to a limiting magnitude of 21.5 (AB) within the error region reported in Tan et al., GCN 43778. See also Fortin et al. GCN 43783 for further optical limits. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43784. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41893] sb26021801: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 19 Feb '26

19 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43783 SUBJECT: sb26021801: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 26/02/19 10:40:16 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Noémie Globus (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (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), Damien Dornic (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), 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), Antonio de Ugarte Postigo (LAM), Wenjin TAN (IHEP) and Chao WU (NAOC) report: We imaged the field of the SVOM trigger sb26021801 (Tan et al., GCN Circ. 43778) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-02-19T08:46:59.976 to 2026-02-19T09:30:49.700 UTC (from 1.16 to 1.19 days after the trigger) and obtained 32 minutes of exposure in the r and z filters. The data were reduced, coadded and analysed with the COLIBRÍ 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 ECLAIRs source position (Tan et al., GCN Circ. 43778) down to the following 5-sigma limit: r > 22.50 z > 21.36 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/43783. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41892] IceCube Alert 260217A: Global MASTER-Net observations report
by GCN Circulars 19 Feb '26

19 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43782 SUBJECT: IceCube Alert 260217A: Global MASTER-Net observations report DATE: 26/02/19 02:52:48 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 IceCube Alert 260217A (trigger No 80851825,05h 03m 33.60s , +14d 37m 48.0s, R=0.68) errorbox 16 sec after notice time and 1 days 73773 sec after trigger time at 2026-02-19 02:24:58 UT, with upper limit up to 20.1 mag. The observations began at zenith distance = 60 deg. The sun altitude is -35.3 deg. The galactic latitude b = -15 deg., longitude l = 187 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3144643 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 160204 | 2026-02-19 02:24:58 | MASTER-OAFA | (05h 03m 45.23s , +14d 51m 29.0s) | C | 60 | 19.8 | 160264 | 2026-02-19 02:24:58 | MASTER-OAFA | (05h 03m 45.23s , +14d 51m 29.0s) | C | 180 | 20.1 | Coadd 160264 | 2026-02-19 02:24:58 | MASTER- | (05h 04m 46.08s , +13d 52m 00.1s) | C | 180 | 18.5 | 160264 | 2026-02-19 02:24:58 | MASTER- | (05h 03m 26.64s , +14d 25m 36.7s) | C | 180 | 17.8 | 160269 | 2026-02-19 02:26:03 | MASTER-OAFA | (05h 03m 45.21s , +14d 51m 29.3s) | C | 60 | 19.8 | 160335 | 2026-02-19 02:27:09 | MASTER-OAFA | (05h 03m 45.18s , +14d 51m 29.4s) | C | 60 | 19.8 | 160453 | 2026-02-19 02:28:07 | MASTER- | (05h 04m 43.62s , +13d 53m 35.3s) | C | 180 | 18.6 | 160453 | 2026-02-19 02:28:07 | MASTER- | (05h 03m 24.11s , +14d 27m 11.9s) | C | 180 | 17.9 | 160461 | 2026-02-19 02:28:15 | MASTER-OAFA | (05h 03m 45.15s , +14d 51m 29.9s) | C | 180 | 20.1 | Coadd 160641 | 2026-02-19 02:31:15 | MASTER- | (05h 04m 43.75s , +13d 51m 54.5s) | C | 180 | 18.5 | 160641 | 2026-02-19 02:31:15 | MASTER- | (05h 03m 24.24s , +14d 25m 30.5s) | C | 180 | 18.1 | 160830 | 2026-02-19 02:34:24 | MASTER- | (05h 04m 46.70s , +13d 53m 29.4s) | C | 180 | 18.4 | 160830 | 2026-02-19 02:34:24 | MASTER- | (05h 03m 27.15s , +14d 27m 05.6s) | C | 180 | 17.9 | 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/43782. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41891] Fermi-LAT Gamma-ray Observations of IceCube-260217A
by GCN Circulars 18 Feb '26

18 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43781 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260217A DATE: 26/02/18 21:17:41 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260217A neutrino event (GCN 43768) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 26-02-17 at 05:55:24.52 UTC (T0) with J2000 position RA = 75.89 (+0.52, -0.56) deg, Decl. = 14.63 (+0.45, -0.43 ) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260217A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC260217A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260217A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.0e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <5.5e-09 (<1.7e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). 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/43781. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41890] GRB 260217A: Fermi GBM Final Localization
by GCN Circulars 18 Feb '26

18 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43780 SUBJECT: GRB 260217A: Fermi GBM Final Localization DATE: 26/02/18 11:43:01 GMT FROM: Cuán de Barra at UCD <cuan.debarra(a)ucdconnect.ie> The Fermi GBM team reports the detection of a likely LONG GRB At 09:18:12.01 UT on 17 February 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260217A (trigger 793012697/260217388). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 278.43, Dec = -5.30 (J2000 degrees, equivalent to J2000 18h 34m, -5d 18'), with a statistical uncertainty of 11.59 degrees. The angle from the Fermi LAT boresight is 91 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260217388/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260217388/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260217388/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43780. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41889] GRB 260214B/EP260214b: SVOM/ECLAIRs detection through targeted search
by GCN Circulars 18 Feb '26

18 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43779 SUBJECT: GRB 260214B/EP260214b: SVOM/ECLAIRs detection through targeted search DATE: 26/02/18 09:25:40 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. Yang, M. Brunet, O. Godet, J.-L. Atteia (IRAP) report on behalf of the SVOM team: The SVOM/ECLAIRs telescope detected GRB 260214B/EP260214b (EP team, GCN 43744), starting at 2026-02-14T22:03:41.16 UTC (T0), through an offline targeted search with the event-by-event data downloaded through the X-band ground station. The burst was detected within several timescales and energy ranges. The best detection is obtained by the image trigger with a signal-to-noise ratio (SNR) of 7.06 within 4-90 keV over a time window of 6 seconds starting at T0. This event was not detected onboard because it was too faint. The localization of the source is RA, Dec = 191.147, 23.990 degrees: RA (J2000) = 12h44m35s Dec (J2000) = 23d59m24s with a 90% C.L. radius of 12.5 arcmin (including systematic error of 6 arcmin added in quadrature). This position is consistent with that measured by EP/WXT, with an angular separation of 10 arcmin. The time-averaged spectrum from T0 to T0+6 s in the energy range 4-90 keV is best fitted by a broken powerlaw, with a break energy of 8.2+/-0.9 keV, a second photon index of 1.9+0.4/-0.3, while the first photon index is not well constrained. If the first photon index is fixed to 0.7, as measured by EP/WXT, the fit yields a break energy of 10+3/-2 keV and a second photon index of 1.7+0.4/-0.3. With this model, the total energy flux in the 4-120 keV is (2.6+/-0.8)e-8 erg/cm^2/s. Assuming a redshift of z=1.208 (E. Le Floch et al., GCN 43749) and a standard cosmology with H_0 = 67.3 km/s/Mpc and Omega_M = 0.315 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is (2.7+/-0.8)e51 erg, and the rest-frame peak energy of the time-averaged spectrum Ep,z is 22+7/-4 keV. With these estimates, GRB 260214B/EP260214b is consistent with the distribution of Type II (long) GRBs on the Amati relation reported by Willingale et al. 2017, although it lies toward the lower end of the Ep,z and E_iso ranges. 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/ECLAIRs point of contact for this event is : Hui Yang (hui.yang(a)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/43779. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41888] sb26021801: SVOM detection of a long faint X-ray transient
by GCN Circulars 18 Feb '26

18 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43778 SUBJECT: sb26021801: SVOM detection of a long faint X-ray transient DATE: 26/02/18 07:15:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Wenjin TAN (IHEP), Chao WU (NAOC), Wenjin XIE (NAOC), Hatsune GOTO (Kanazawa Univ.), Pierre MAGGI (ObAS) , report on behalf of the SVOM mission team: At 2026-02-18T05:15:18 UTC (T0), SVOM/ECLAIRs triggered and located an X-ray transient (SVOM burst-id sb26021801). 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 8.29 in the 5-20 keV energy band over a time window of 1310.72 seconds starting at 2026-02-18T04:53:28. The localization of the best alert is R.A., Dec. 194.8408, 27.9434 degrees: R.A. (J2000) = 12h59m21.80s Dec. (J2000) = 27d56m36.21s with a 90% confidence level (C.L.) radius of 9.50 arcmin (including systematic error of 2 arcmin added in quadrature). The Coma Cluster (ACO 1656) and its Brightest Central Galaxy NGC 4874 are within the trigger error circle and may be the source triggering the ECLAIRs telescope. Due to the detection significance being below the slew threshold, no immediate slew was performed on this 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 Wenjun Tan: tanwj(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/43778. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41887] The EP-WXT trigger 01709258455 is likely a flaring star
by GCN Circulars 18 Feb '26

18 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43777 SUBJECT: The EP-WXT trigger 01709258455 is likely a flaring star DATE: 26/02/18 02:52:19 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. X. Sun (NAO, CAS), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC), Y.Q. Zhao(USTC,PRIC), and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709258455 at the time of 2026-02-17T21:46:05, is likely a stellar flare associated with RX J0920.0+3052. The estimated flux of the flare is around 8e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 5.2e30 erg/s. 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/43777. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41886] EP-WXT 01709258455: NOT optical upper limits
by GCN Circulars 18 Feb '26

18 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43776 SUBJECT: EP-WXT 01709258455: NOT optical upper limits DATE: 26/02/18 00:20:32 GMT FROM: javisansie(a)gmail.com J. Quirola-Vasquez (Radboud), G. Corcoran (UCD), J. Sanchez-Sierras (Radboud), A. Martin-Carrillo (UCD) and P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of the Einstein Probe trigger WXT 01709258455, using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were triggered using the recently implemented automatic “rapid response mode” (RRM) and were obtained in the SDSS r (5x180 s) and z (9x150 s) bands, starting on 2026-02-17 at 21:56:02 UT (9.94 min after the WXT trigger). We carried out subtraction in both bands using Pan-STARRS archival images as templates. The subtractions were performed using the ZOGY algorithm (Zackay et al. 2016), as implemented in PyZOGY (Guevel et al. 2021). We do not find any new, uncatalogued sources within the EP-WXT uncertainty region. From the stacked images we obtain the following 3-sigma upper limits: r > 23.8 z > 22.0 These limits are in the AB system, were calibrated using nearby stars from the Pan-STARRS catalog and are not corrected for Galactic extinction. We note the presence of an M-class dwarf with ROSAT X-ray emission within the error region. We cannot discard whether this trigger can be attributed to a stellar flare, because we cannot measure its brightness due to the source being saturated in our images. View this GCN Circular online at https://gcn.nasa.gov/circulars/43776. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41885] EP260214b: Mondy optical observations
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43775 SUBJECT: EP260214b: Mondy optical observations DATE: 26/02/17 17:29:43 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP260214b (Yang et al., GCNs 43744, 43760) with the AZT-33IK 1.5m telescope of the Mondy observatory starting on 2026-02-16 (UT) 19:44:56 and taking several 120-seconds frames in the R band. The optical counterpart (He et al., GCN 43745; Watson et al., GCN 43747; Pérez-Fournon et al., GCN 43750; Russeil et al., GCN 43752; Li et al., GCN 43755; Vijaykumar et al., GCN 43757; Becerra et al., GCN 43758; Aryan et al., GCN 43762; Bochenek & Perley, GCN 43764; Kar et al., GCN 43774) at a redshift z = 1.208 (Le Floch et al., GCN 43749) is detected in the stacked frame. Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-02-16 19:44:56 1.93455 45*120 R 21.67 0.16 23.0 Mondy/AZT-33IK The photometry is based on nearby SDSS stars (R-magnitudes obtained using the 2005 Lupton transformation equations) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43775. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41884] EP260214b: 1.3m DFOT optical upper limit
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43774 SUBJECT: EP260214b: 1.3m DFOT optical upper limit DATE: 26/02/17 17:26:03 GMT FROM: Debalina Kar at ARIES <kardebalina2000(a)gmail.com> Debalina Kar, Pankaj Pawar, Anshika Gupta, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of EP260214b detected by EP/WXT (Yang et al., GCN 43744) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-02-17 at 00:15:22 UT, approximately 50.82 hours after the trigger. We obtained multiple exposures of 300 s each in the R filter. A total of 15 frames were aligned and stacked to improve the signal-to-noise ratio. In the stacked frame we do not detect any optical counterpart within the error box of EP/WXT (Yang et al., GCN 43760) as reported by He et al. (GCN 43745). This is consistent with the non-detection reported by Aryan et al. (GCN 43762). We derive the following 3-sigma upper limit from the stacked image: Date (UT) Start Time T_start–T0 (hr) Filter Exposure Magnitude ---------------------------------------------------------------------------------- 2026-02-17 00:15:22 ~50.82 R 300 s × 15 > 22.40 The non-detection is consistent with the detection and fading behavior reported by Watson et al. (GCN 43747), Floch et al. (GCN 43749), Pérez-Fournon et al. (GCN 43750), Russeil et al. (GCN 43752), Li et al. (GCN 43755), Becerra et al. (GCN 43758), as well as with the upper limit reported by Vijaykumar et al. (GCN 43757). The reported magnitude is not corrected for Galactic extinction. Photometric calibration was performed using standard stars from the Pan-Starrs catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43774. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41883] EP260210a: Mondy optical upper limits
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43773 SUBJECT: EP260210a: Mondy optical upper limits DATE: 26/02/17 15:04:00 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), E. Klunko (ISTP), N. Pankov (IKI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP260210a (Shi et al. GCN 43681) with the AZT-33IK 1.5m telescope of the Mondy observatory on Feb. 10 and 14 taking several 120-seconds frames in the R band. In the refined EP-FXT error circle (Yang et al., GCN 43696) we do not detect any new optical source in the stacked frames of our data. All catalogued sources located inside the refined EP-FXT error circle are detected in our stacked frames and do not exhibit any significant variations between the two epochs. In particular, the only one galaxy is presented within the refined EP-FXT error circle at coordinates of (J2000) 11:19:19.81 +45:23:43.8 in the SDSS catalogue. Preliminary photometry of the galaxy and observational details are the following: Date UT start t-T0 Exp. Filter SDSS_galaxy UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-02-10 15:18:13 0.22584 30*120 R 20.29+/-0.05 22.7 Mondy/AZT-33IK 2026-02-14 20:08:59 4.42816 30*120 R 20.31+/-0.06 22.4 Mondy/AZT-33IK The photometry is based on nearby SDSS stars (R-magnitudes obtained using the 2005 Lupton transformation equations) and is not corrected for Galactic extinction. Our results are consistent with other published observations (Kang et al., GCN 43683; Fortin et al., GCN 43684; Li et al., GCN 43687; Aryan et al., GCN 43692; Lipunov et al., GCN 43697). View this GCN Circular online at https://gcn.nasa.gov/circulars/43773. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41882] Konus-Wind detection of GRB 260212A
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43772 SUBJECT: Konus-Wind detection of GRB 260212A DATE: 26/02/17 14:55:21 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260212A (Fermi-GBM detection: The Fermi GBM team, GCN 43716; Neights and Meegan GCN 43740; Glowbug detection: Cheung et al., GCN 43719; SVOM-GRM detection: Zhang et al., GCN 43727; GECAM-B detection: Zhang et al., GCN 43736; AstroSat-CZTI detection: Salunke et al., GCN 43741; IPN triangulation: Kozyrev et al., GCN 43769) triggered Konus-Wind (KW) at T0=64149.637 s UT (17:49:09.637). The burst light curve shows multiple emission pulses in the interval from ~T0-0.5 s to ~T0+11 s. The emission is seen up to ~2 MeV. We also note a much weaker emission bump around T0+25 s, which is visible only below 80 keV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260212_T64149/ As observed by Konus-Wind, the burst had the fluence of (6.81 ± 0.55)x10^-6 erg/cm^2 and the 64-ms peak energy flux, measured from T0 + 0.640 s, of (4.98 ± 0.40)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+16.640 s) is best fitted in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.16 (-0.10, + 0.10) and Ep = 115(-7,+9) keV, chi^2 = 97/93 dof. Fitting this spectrum by a Band GRB function yields the same values of alpha and Ep, and only an upper limit on the high energy photon index beta of -2.7 The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fitted in the 20 keV - 15 MeV range by a CPL model with alpha = -0.86 (-0.11, + 0.12)and Ep = 108(-8,+10) keV, chi^2 = 94/78 dof. Fitting this spectrum by a Band function yields the same values of alpha and Ep, and only an upper limit on the high energy photon index beta of -3.2 All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary View this GCN Circular online at https://gcn.nasa.gov/circulars/43772. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41881] GRB 260208A: AbAO and Terskol optical upper limits
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43771 SUBJECT: GRB 260208A: AbAO and Terskol optical upper limits DATE: 26/02/17 14:19:08 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), R. Ya. Inasaridze (AbAO), I. Sokolov (INASAN, KIAM), A. Pozanenko (IKI), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 260208A (Fermi GBM team, GCN 43635; Sonawane et al. 2026, GCN 43642; Longo et al. 2026, GCN 43645; Dichiara et al. 2026, GCN 43652; Luo et al. 2026, GCN 43658; Mukherjee & Meegan, GCN 43673; Waratkar & Grefenstette, GCN 43674; Cheung et al., GCN 43675) at z = 2.36 (Dimple et al., GCN 43662) with the 0.7-meter AS-32 telescope of Abastumani Observatory (AbAO) and with the 2-meter Zeiss-2000 telescope of the Terskol observatory on Feb. 10 taking several R-filter exposures. We do not detect the optical counterpart (Lipunov et al., GCN 43640; Wortley et al., GCN 43641; Dichiara et al., GCN 43652; Ma et al., GCN 43655; Ahumada et al., GCN 43657; Dimple et al., GCN 43661; Magnani et al., GCN 43664; Gupta et al., GCN 43665; Volnova et al., GCN 43666, 43770; Pérez-Fournon et al., GCN 43694; Kuin & Cenko, GCN 43702) in the stacked frames of both telescopes. Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-02-10 21:58:14 2.77172 65*120 R n/d n/d 20.4 AbAO/AS-32 2026-02-10 23:52:31 2.81612 21*150 R n/d n/d 21.2 Terskol/Zeiss-2000 The photometry is based on nearby SDSS stars (R-magnitudes obtained using the 2005 Lupton transformation equations) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43771. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41880] GRB 260208A: continued Mondy optical observations
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43770 SUBJECT: GRB 260208A: continued Mondy optical observations DATE: 26/02/17 14:07:31 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), E. Klunko (ISTP), N. Pankov (IKI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 260208A (Fermi GBM team, GCN 43635; Sonawane et al. 2026, GCN 43642; Longo et al. 2026, GCN 43645; Dichiara et al. 2026, GCN 43652; Luo et al. 2026, GCN 43658; Mukherjee & Meegan, GCN 43673; Waratkar & Grefenstette, GCN 43674; Cheung et al., GCN 43675) at z = 2.36 (Dimple et al., GCN 43662) with the AZT-33IK 1.5m telescope of the Mondy observatory on Feb. 9 and 10 taking several 120-seconds frames in the R band. The optical counterpart (Lipunov et al., GCN 43640; Wortley et al., GCN 43641; Dichiara et al., GCN 43652; Ma et al., GCN 43655; Ahumada et al., GCN 43657; Dimple et al., GCN 43661; Magnani et al., GCN 43664; Gupta et al., GCN 43665; Volnova et al., GCN 43666; Pérez-Fournon et al., GCN 43694; Kuin & Cenko, GCN 43702) is detected in the stacked frame from Feb. 09, and is not detected on the next day. Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-02-09 17:00:51 1.51973 35*120 R 21.58 0.10 22.6 Mondy/AZT-33IK 2026-02-10 17:58:12 2.55608 30*120 R n/d n/d 22.6 Mondy/AZT-33IK The photometry is based on nearby SDSS stars (R-magnitudes obtained using the 2005 Lupton transformation equations) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43770. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41879] IPN triangulation of GRB 260212A
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43769 SUBJECT: IPN triangulation of GRB 260212A DATE: 26/02/17 12:10:47 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, A. Tohuvavohu, and J. DeLaunay on behalf of the Swift-BAT team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The long-duration GRB 260212A (Ferm-GBM detection: The Fermi GBM team, GCN 43716; Neights and Meegan GCN 43740; Glowbug detection: Cheung et al., GCN 43719; SVOM-GRM detection: Zhang et al., GCN 43727; GECAM-B detection: Zhang et al., GCN 43736; AstroSat-CZTI detection: Salunke et al., GCN 43741) was detected by Fermi (GBM trigger 792611353), Swift (BAT), Konus-Wind, Glowbug, SVOM (GRM), GECAM-B, Astrosat (CZTI), and Mars-Odyssey (HEND) at about 64148 s UT (17:49:08) The burst was outside the coded field of view of the BAT. We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 224.837 (14h 59m 21s) +74.800 (+74d 47' 59") Corners: 225.022 (15h 00m 05s) +76.212 (+76d 12' 45") 224.790 (14h 59m 09s) +73.505 (+73d 30' 18") 224.644 (14h 58m 35s) +73.384 (+73d 23' 04") 224.855 (14h 59m 25s) +76.092 (+76d 05' 30") --------------------------------------------- The error box area is 372 sq. arcmin, and its maximum dimension is 2.830 deg (the minimum one is 2.3 arcmin). The Sun distance was 106 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB260212_T64149/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/43769. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41878] IceCube-260217A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43768 SUBJECT: IceCube-260217A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/02/17 11:46:06 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-02-17 at 05:55:24.52 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 2.768 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert, more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-02-17 Time: 05:55:24.52 UT RA: 75.89 (+0.52/-0.56 deg 90% PSF containment) J2000 Dec: 14.63 (+0.45/-0.43 deg 90% PSF containment) J2000 No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of this event. As announced in GCN Circular 43419, IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. Additional information is available at https://gcn.nasa.gov/missions/icecube. The initial automated alert was not distributed through the classical GCN notice system, and the cause is currently under investigation. Meanwhile, the Kafka notification was streamed with an approximate delay of 30 minutes due to a temporary technical issue. As a result, the initial GCN schema (“record_number” = 0) streamed via Kafka contains some errors (this is not the case for the GCN schema (“record_number” = 1), corresponding to the updated reconstruction, which is sent along with this circular). Specifically: The fields “ra_dec_error” and “far” were sent as strings instead of numerical values. record_number was sent as 1, but it should have been 0. The field “p_astro” was sent as a percentage (30.722) instead of a decimal fraction; the correct value is 0.31. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/43768. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41877] GRB 260213A: GECAM-B observation of a short burst
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43767 SUBJECT: GRB 260213A: GECAM-B observation of a short burst DATE: 26/02/17 08:42:41 GMT FROM: Xinghao Luo at IHEP <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 260213A, at 2026-02-13T08:23:49.800 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43722). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 1.5 +/-0.7 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260213A.png The 'Amati' relation diagram of GRB 260213A is shown at: https://www.bursthub.cn//admin/static/gecambgrb260213A_amati.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/43767. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41876] GRB 260216A: Fermi Gamma-ray Burst Monitor trigger 792969362/260216886 is not a GRB
by GCN Circulars 17 Feb '26

17 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43766 SUBJECT: GRB 260216A: Fermi Gamma-ray Burst Monitor trigger 792969362/260216886 is not a GRB DATE: 26/02/17 04:23:20 GMT FROM: Boyan A. Hristov at UAH <boyan.a.hristov(a)nasa.gov> B. Hristov (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 792969362/260216886 at 21:15:57.07 UT on 16 February 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to distant particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/43766. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41875] GRB 260216A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 Feb '26

16 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43765 SUBJECT: GRB 260216A: Fermi GBM Final Real-time Localization DATE: 26/02/16 21:26:38 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 21:15:57 UT on 16 Feb 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260216A (trigger 792969362.07265 / 260216886). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 292.5, Dec = -25.0 (J2000 degrees, equivalent to J2000 19h 30m, -25d 00'), with a statistical uncertainty of 12.6 degrees. The angle from the Fermi LAT boresight is 127.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260216886/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260216886/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260216886/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43765. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41874] EP260214b: Liverpool Telescope optical observations
by GCN Circulars 16 Feb '26

16 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43764 SUBJECT: EP260214b: Liverpool Telescope optical observations DATE: 26/02/16 14:12:34 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 EP 260214b (Yang et al., GCN 43744; Yang et al., GCN 43760) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x100s exposures in SDSS g filter and 6x100s in SDSS r and i, starting at 2026-02-16 02:51:39.908 UT, approximately 28.8 hours after trigger. Some exposures were discarded prior to stacking due to poor seeing. They were subtracted from PanSTARRS reference images using PSF matching with the use of PSFEx. We report detections in stacked images in all filters at the position first reported by He et al., GCN 43745 and Watson et al., GCN 43747. MJD (mid) T_mid-T_0 Filter Mag. (AB) 61087.12195 28.86 h g 22.45 ± 0.27 61087.13116 29.08 h r 22.22 ± 0.33 61087.13913 29.27 h i 21.75 ± 0.24 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/43764. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41873] GRB 260206A: probable hard X-ray burst from 4U 0513-40
by GCN Circulars 16 Feb '26

16 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43763 SUBJECT: GRB 260206A: probable hard X-ray burst from 4U 0513-40 DATE: 26/02/16 11:32:52 GMT FROM: Hitoshi Negoro at Nihon University/MAXI team <negoro.hitoshi(a)nihon-u.ac.jp> H. Negoro, M. Nakajima (Nihon U.), J.A. Kennea (PSU), T. Mihara (RIKEN) This is a cross-posting of ATel 17682. In Swift-XRT followup observations of GRB 260206A detected with the MAXI-GSC (GCN Circ. 43624), the XRT marginally detected a faint, uncatalogued X-ray source near the center of the MAXI error region (Lenava et al. GCN Circ. 43630). The XRT also detected a bright known X-ray source, LSXPS J051406.5-400237, of which a count rate was 7.3 +/- 0.3 cts/s, approximately 70% higher than the mean count rate (Source 1: Evans et al. GCN Circ. 43625). We analyzed the GSC energy spectrum of the burst, and found that a power-law model gave a better fit to the spectrum than a blackbody model. This is because many hard X-ray photons were detected above 10 keV. We fixed the equivalent hydrogen column density to 3.84e20 (obtained with the nH Calculator at NASA/HEASARC for the direction of 4U 0513-40), and obtained a photon index of 1.7 (+0.7, -0.6 at 90% confidence interval) and a blackbody temperature of 1.5 (+0.6, - 0.4) keV in each fit. The burst exhibited a double-peaked-like structure with an e-folding decay time of 5.8 +/- 1.0 sec at 2-20 keV without any collimator response correction. The peak X-ray flux is around 1.22e-8 erg/cm2/s at 2-10 keV, which corresponds to 2.2e38 erg/s if the source is in the globular cluster NGC 1851 hosting 4U 0513-40 (aka X0512-401) (12.2 kpc away). MAXI detected more than ten X-ray bursts with a variety of time profiles originating from the direction of NGC 1851. These strongly suggest that this hard energetic burst also came from 4U 0513-40 (or ABK A, see Homer et al. 2001, ApJ, L155), within the error circle of LSXPS J051406.5-400237, though 4U 0513-40 is just outside the MAXI error box if we take account of the systematic uncertainty of the localization, 0.1 deg (GCN Circ. 43624). View this GCN Circular online at https://gcn.nasa.gov/circulars/43763. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41872] EP260214b: Optical upper limit with Kinder observations
by GCN Circulars 16 Feb '26

16 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43762 SUBJECT: EP260214b: Optical upper limit with Kinder observations DATE: 26/02/16 10:28:20 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, C.-S. Lin, T.-W. Chen (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, M.-H. Lee, C.-H. Lai, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz, and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260214b (Yang et al., GCN 43744 & GCN 43760) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen & Yang et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in r-band started at 14:34 UTC on the 15th of February 2026 (MJD 61086.607), 16.50 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We used the Python-based AutoPhOT package (Brennan & Fraser 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. In the stacked frame or the difference image, we did not detect the proposed optical counterpart reported by He et al. (GCN 43745). Moreover, we used AutoPhOT to perform PSF photometry. The details of the observations and the measured 3-sigma upper limits (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 61086.607 | 16.50 | 300 * 6 | >22.2 | 1".76 | 1.85 The non-detection in our observations is consistent with (detection) reports by Watson et al. (GCN 43747), Floch et al. (GCN 43749), Pérez-Fournon et al. (GCN 43750), Russeil et al. (GCN 43752), Li et al. (GCN 43755), Becerra et al. (GCN 43758), and also with the upper limit reported by Vijaykumar et al. (GCN 43757). The presented magnitude is calibrated using the field stars from the Pan-Starrs catalog and is not corrected for the expected Galactic foreground extinction of A_r = 0.04 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/43762. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41871] EP260214a: Optical upper limits with Kinder observations
by GCN Circulars 16 Feb '26

16 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43761 SUBJECT: EP260214a: Optical upper limits with Kinder observations DATE: 26/02/16 10:22:14 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, C.-S. Lin, T.-W. Chen (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, M.-H. Lee, C.-H. Lai, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz, and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260214a (Li et al., GCN 43742 & GCN 43751) using the 40cm SLT at the Lulin observatory, as part of the Kinder collaboration (Chen & Yang et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The FXT was found to be coincident with GRB 260214A (Ravasio et al., GCN 43759). The first SLT epoch of observations in r-band started at 20:46 UTC on 14th of February 2026 (MJD 61085.865), 0.13 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We used the Python-based AutoPhOT package (Brennan & Fraser 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Either in the stacked frame or in the difference image, we do not detect any new or uncataloged sources within the 10" refined EP-FXT localization circle (Li et al. GCN 43751). Moreover, we used AutoPhOT to perform PSF photometry. The details of the observations and the measured 3-sigma upper limits (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 61085.865 | 0.13 | 300 * 6 | >20.6 | 2".62 | 1.79 The non-detection in our observations is consistent with those reported by Lipunov et al. (GCN 43743), Li et al. (GCN 43746), Watson et al. (GCN 43753), and He et al. (GCN 43754). The presented magnitude is calibrated using the field stars from the Pan-Starrs catalog and is not corrected for the expected Galactic foreground extinction of A_r = 0.16 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/43761. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41870] EP260214b: EP-FXT follow-up observation
by GCN Circulars 16 Feb '26

16 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43760 SUBJECT: EP260214b: EP-FXT follow-up observation DATE: 26/02/16 05:59:28 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), A. Li (BNU), Y. H. Jiang (NJU), Y. Liu (NAOC) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260214b was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Yang et al., GCN 43744), whose optical counterpart was detected by several optical telescopes (He et al., GCN 43745, Watson et al., GCN 43747, Pérez-Fournon et al., GCN 43750, Russeil et al., GCN 43752, Li et al., GCN 43755, Becerra et al., GCN 43758) at a resdhift z = 1.208 (Le Floch et al., GCN 43749). EP-FXT performed a follow-up observation of EP260214b about 5.8 hours after the WXT detection, with an exposure time of 2.8 ks. The FXT telemetry data shows that an uncatalogued source was detected within the WXT error circle at R.A. = 191.2581, DEC = 23.8529 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 1.57 x 10^20 cm^-2 and a photon index of 2.2 (+0.3/-0.3). The derived unabsorbed 0.5-10 keV flux is approximately 2.8 (+0.7/-0.5) x 10^-13 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/43760. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41869] EP260214a / GRB 260214A: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43759 SUBJECT: EP260214a / GRB 260214A: Fermi-GBM Sub-Threshold Detection DATE: 26/02/15 20:20:37 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), P.G. Jonker (Radboud Univ.) and E. Burns (LSU), R. Hamburg (USRA) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP260214a detected by EP-WXT (Li et al., GCN 43742, Li et al., GCN 43751). There was no Fermi-GBM onboard trigger around the EP refined starting time T0=2026-02-14T20:37:00 (UTC). The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from the EP T0. A weak transient signal was found most significantly at ~T0+35 s on a 16 s timescale, with a false alarm rate of 2.27e-04 Hz. The localisation is consistent with the EP one, with a spatial association probability of 87.4%. Among the three spectral templates tested, the transient was best-fit with a "soft" spectrum (i.e., a Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/43759. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41868] EP260214b: DDOTI Optical Detection
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43758 SUBJECT: EP260214b: DDOTI Optical Detection DATE: 26/02/15 20:17:14 GMT FROM: Rosa L. Becerra at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observe the field of EP260214b (Yang et al., GCN Circ. 43744) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2026-02-15 UTC. DDOTI observed from 05:32 UTC to 13:08 UTC (T+8.9 h to T+16.5 h after the trigger), with a total exposure time of 3.7 hours. These observations were interleaved with other scientific programs. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect the optical counterpart reported by He et al. (GCN Circ. 43745), at preliminary AB magnitude of: w = 21.08 +/- 0.23. This value is consistent with previous observations reported (He et al., GCN Circ. 43745; Watson et al., GCN Circ. 43747; Pérez-Fournon et al., GCN Circ. 43750; Russeil et al., GCN Circ. 43752; Li et al., GCN Circ. 43755; Vijaykumar et al., GCN Circ. 43757) and is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/43758. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41867] EP260214b: GROWTH-India Telescope optical upper limit
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43757 SUBJECT: EP260214b: GROWTH-India Telescope optical upper limit DATE: 26/02/15 18:57:19 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Vijaykumar, A. Khade, V. Swain, S. Patil, A.P. Saikia, T. Mohan, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of EP260214b detected by the Einstein Probe (EP) mission (EP mission, GCN 43744), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-02-15 16:28:03 (UTC), i.e., 18.40 hours after the trigger and obtained a single exposure in r' filter. We did not detect any transient in our image. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | --------------- | ------------------- | ---------------- | | 61086.68614 | r' | 18.40 | 650 | 20.9 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our magnitude is consistent with other optical observations (He. et al., GCN 43745; Watson et.al., GCN 43747; Pérez-Fournon et.al GCN 43750; Russeil et.al GCN 43752; Li et.al GCN 43755). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/43757. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41866] EP250214a: VLT near-infrared observation
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43756 SUBJECT: EP250214a: VLT near-infrared observation DATE: 26/02/15 18:04:57 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> Niccolò Passaleva, Massine El Kabir, Narges Shahamat, Eleonora Troja (U Rome) on behalf of the ERC BHianca team: We observed the field of EP260214a (Li et al., GCN 43742) with the HAWKI imager on the ESO VLT UT4 (Yepun). Observations began at ~11.9 hr after the EP/WXT trigger and were carried out at an average airmass of about 1.0 in the J filter. Several extended sources are visible close to or within the EP/FXT error region (Li et al., GCN 43751), however no uncatalogued source is clearly identified in our observations down to a 3 sigma limiting magnitude J~25 AB mag calibrated using nearby stars in the 2MASS Catalogue (Skrutskie et al. 2006) and not corrected for Galactic extinction. We thank the staff at the VLT, for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43756. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41865] EP250214a: VLT near-infrared observation
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43756 SUBJECT: EP250214a: VLT near-infrared observation DATE: 26/02/15 18:04:57 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> Niccolò Passaleva, Massine El Kabir, Narges Shahamat, Eleonora Troja (U Rome) on behalf of the ERC BHianca team: We observed the field of EP260214a (Li et al., GCN 43742) with the HAWKI imager on the ESO VLT UT4 (Yepun). Observations began at ~11.9 hr after the EP/WXT trigger and were carried out at an average airmass of about 1.0 in the J filter. Several extended sources are visible close to or within the EP/FXT error region (Li et al., GCN 43751), however no uncatalogued source is clearly identified in our observations down to a 3 sigma limiting magnitude J~25 AB mag calibrated using nearby stars in the 2MASS Catalogue (Skrutskie et al. 2006) and not corrected for Galactic extinction. We thank the staff at the VLT, for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43756. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41864] EP260214b: SVOM/VT optical observation
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43755 SUBJECT: EP260214b: SVOM/VT optical observation DATE: 26/02/15 16:46:31 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, 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) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of EP260214b detected by Einstein Probe (Yang et al., GCN 43744). The observation started on 2026-02-15T03:52:22 UTC, i.e. 5.81 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (He et al., GCN 43745; Watson et al., GCN 43747; Le Floch et al., GCN 43749; Pérez-Fournon et al., GCN 43750; Russeil et al., GCN 43752) were detected in both channels. The measurements in AB magnitude are derived as follows: Mid time | Band | Exposure Time | 3 sigma limit magnitude 6.93 hours VT_B 80*50 sec 21.29 +/-0.08 mag 6.94 hours VT_R 67*50 sec 20.84 +/- 0.07 mag The counterpart show no significant variation during our observation from 5.81 hours to 8.08 hours. Our photometry was not corrected for Galactic extinction. 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/43755. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41863] EP260214a: NOT optical upper limits
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43754 SUBJECT: EP260214a: NOT optical upper limits DATE: 26/02/15 15:07:18 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He (NAOC), S.Y. Fu (HUST), J. An, X. Liu, S.Q. Jiang, Z.P. Zhu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), K. Valeckas (NOT) report on behalf of a large collaboration: We observed the field of EP260214a (Li et al., GCN 43742) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 03:39:29.978 UT on 2026-02-15, i.e., 7.02 hrs after the EP trigger, and we obtained 3x300 s frames in the Sloan r-band and 5 x 200 s frames in the Sloan z- band. No new optical source is detected within the EP/FXT error circle (Li et al., GCN 43751), down to 5-sigma upper limits of r ~ 23.1 and z ~ 21.8, calibrated with nearby Pan-STARRS stars and not corrected for Galactic extinction. These upper limits are consistent with the ones previously reported (Li et al., GCN 43746; Watson et al. GCN 43753). View this GCN Circular online at https://gcn.nasa.gov/circulars/43754. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41862] EP260214a: COLIBRÍ optical upper limits
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43753 SUBJECT: EP260214a: COLIBRÍ optical upper limits DATE: 26/02/15 14:43:58 GMT FROM: Rosa L. Becerra at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Alan M. Watson (UNAM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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), 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 EP260214a (Li et al., GCN Circ. 43742) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-15 10:20 to 11:32 UTC (from 13.70 to 14.92 hours after the trigger) and obtained 53 minutes of exposure, in r and z filters. The data were reduced, calibrated, and analysed with the COLIBRÍ 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 images, we do not detect any new source at the refined FXT position (Li et al., GCN Circ. 43751) down to the following 3-sigma limits: r > 23.6 z > 22.2 These upper limits are consistent with the ones reported by SVOM/VT (Li et al. GCN Circ. 43746). 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/43753. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41861] EP260214b: OHP/T120 optical observations
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43752 SUBJECT: EP260214b: OHP/T120 optical observations DATE: 26/02/15 14:06:52 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> D. Russeil (LAM/AMU), C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), B. Schneider (LAM), J. Balcaen (Pytheas/OHP), Y. Degot-Longhi (Pytheas/OHP), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), P. Araigi-hayek (AMU), J. Bourges (AMU), N. Hatchodourian (AMU), E. Lefevre-forjan (AMU), O. Maegey (AMU), P. Montaigne (AMU), C. Rey (AMU), M. Rousse (AMU), B. Sevilla (AMU), H. Subra (AMU), L. Valliccioni (AMU), H. LeCoroller (LAM), M. Ould-elhkim (LAM) report on behalf of a larger collaboration: We observed the field of the EP260214b (Yang et al., GCN 43744) using the T120cm telescope at Observatoire de Haute-Provence (France). We obtained 40 minutes of exposure in the r-band starting at 01:37:37.6 UT on 2026-02-15 (~3.6 hr after the trigger). In the stacked image, the optical counterpart detected by He et al.(GCN 43745), Watson et al. (GCN 43747), and Perez-Fournon et al. (GCN 43750), and measured at a redshift of 1.208 (LeFloch et al., GCN 43749) is visible with a preliminar magnitude of: r = 21.22 +/- 0.13 mag (AB) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction. We acknowledge the excellent support from Observatoire de Haute-Provence. View this GCN Circular online at https://gcn.nasa.gov/circulars/43752. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41860] EP260214a: refined analysis of the EP-FXT observation
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43751 SUBJECT: EP260214a: refined analysis of the EP-FXT observation DATE: 26/02/15 13:22:15 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li (BNU), J. Yang (ZZU), Y. H. Jiang (NJU), Y. Liu (NAOC) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260214a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Li et al., GCN 43742). It was followed by Global MASTER-Net (Lipunov et al., GCN 43743) and SVOM-VT (Li et al., GCN 43746). The refined analysis of the WXT data shows that the event started at T0=2026-02-14T20:37:00 (UTC), and lasted for approximately 60 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 4.6×10^20 cm^-2 and a photon index of 0.8 (-0.6/+0.7). The derived average unabsorbed 0.5-4 keV flux is 9.7 (-0.3/+0.4) × 10^(-11) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-02-14T20:39:31 (UTC), 2.5 minutes after T0. The effective exposure time of the observation is around 3.3 ks. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 201.2305, DEC = -29.0431 (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.6 × 10^20 cm^-2, and a photon index of 2.3 (-0.3/+0.3). The derived average unabsorbed 0.5-10 keV flux is 1.4 (-0.1/+0.2) ×10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT follow-up observations have been arranged. 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/43751. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41859] EP260214b: LCO optical counterpart detection
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43750 SUBJECT: EP260214b: LCO optical counterpart detection DATE: 26/02/15 11:37:27 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), A. López-Oramas (IAC and ULL), and D. Aguado (IAC and ULL) Following the detection of the fast X-ray transient EP260214b (Yang et al., GCN #43744), we observed the field with one of the two Las Cumbres Observatory (LCO) 1-m telescopes located at the LCO node at McDonald Observatory, Texas. The observation consisted of a single exposure of 500 sec in the SDSS r' filter, that started on 2026-02-15 at 09:24:15 UT, about 11.34 hours after the EP trigger. The optical counterpart detected by He et al. (GCN #43745) and Watson et al. (GCN #43747) at a resdhift z = 1.208 (Le Floch et al., GCN #43749) is clearly detected in our image with an AB magnitude of r' = 21.28 +/- 0.09, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026A-011, SGLF and Superluminous Supernovae surveys). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/43750. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41858] EP260214b: VLT/X-shooter spectroscopic redshift z = 1.208
by GCN Circulars 15 Feb '26

15 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43749 SUBJECT: EP260214b: VLT/X-shooter spectroscopic redshift z = 1.208 DATE: 26/02/15 10:06:03 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome <aishth(a)outlook.com> E. Le Floch (CEA/Irfu), J. An (NAOC), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF-IAPS), D. Xu (NAOC), L. Cotter (UCD), D. Malesani (DAWN/NBI and Radboud), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration We observed the optical counterpart (He et al. GCN 43745; Watson et al. GCN 43747) of EP260214b (Yang et al. GCN 43744) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 Å and consist of 4 exposures of 600 s each. Observations started on 2026 February 15 at 06:24:46 UT (at 8.35 hr post-trigger). In a preliminary reduction of the spectra, we detect continuum over the entire wavelength range. From the detection of multiple absorption lines, which we interpret as the Al II, Fe II, Mg II, we infer a redshift of z = 1.208. Additionally, at a consistent redshift (z = 1.207) we note the presence of several emission lines due to the [O II] doublet, Ne III, the [O III] doublet, and the Balmer lines from the GRB host galaxy. We acknowledge the excellent support of the ESO observing staff in Paranal, in particular Celia Desgrange, Mar Carretero Castrillo, Diego Parraguez and Fuyan Bian. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/43749. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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