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

[vsnet-grb-info 41979] EP260214a: VLT/FORS2 optical observations
by GCN Circulars 27 Feb '26

27 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43862 SUBJECT: EP260214a: VLT/FORS2 optical observations DATE: 26/02/27 09:53:25 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> N. Passaleva, H. Waseem, Yu-Han Yang, and Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of EP260214a (Li et al., GCN 43742) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began 11.3 days after the EP/WXT trigger and were carried out at an average airmass ~1.3 and with an average seeing ~0.45 arcsec in the R filter. At the position of the candidate radio counterpart reported by Ricci et al. (GCN 43845) we detect a faint source (r~26 AB mag). Assuming our observations are dominated by the host galaxy light, we compute a chance alignment of Pcc~1%. 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/43862. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41978] GRB 260225A: WINTER J-band upper limit
by GCN Circulars 27 Feb '26

27 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43861 SUBJECT: GRB 260225A: WINTER J-band upper limit DATE: 26/02/27 09:35:03 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of the SVOM GRB 260225A (Ma et al., GCN Circ. 43829) in the near-infrared with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations started on 2026-02-25 at 09:09:10 UT (17.92 min after the trigger) and consisted of 15 exposures of 120 s in the J-band. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) and analysed with STDWeb/STDPipe (Karpov 2025). The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitude is not corrected for Galactic extinction. In the stacked image, the optical counterpart reported by Ducoin et al., GCN Circ. 43839 and Li et al., GCN Circ. 43838, consistent with the uncatalogued X-ray source detected by EP/FXT position (Yang et al., GCN 43839), is not detected down to the following 3-sigma AB magnitude: J > 19.5 WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/43861. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41977] GRB 260225A: WINTER J-band upper limit
by GCN Circulars 27 Feb '26

27 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43861 SUBJECT: GRB 260225A: WINTER J-band upper limit DATE: 26/02/27 09:35:03 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of the SVOM GRB 260225A (Ma et al., GCN Circ. 43829) in the near-infrared with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations started on 2026-02-25 at 09:09:10 UT (17.92 min after the trigger) and consisted of 15 exposures of 120 s in the J-band. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) and analysed with STDWeb/STDPipe (Karpov 2025). The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitude is not corrected for Galactic extinction. In the stacked image, the optical counterpart reported by Ducoin et al., GCN Circ. 43839 and Li et al., GCN Circ. 43838, consistent with the uncatalogued X-ray source detected by EP/FXT position (Yang et al., GCN 43839), is not detected down to the following 3-sigma AB magnitude: J > 19.5 WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/43861. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41976] GRB 260226A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 27 Feb '26

27 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43860 SUBJECT: GRB 260226A: CALET Gamma-Ray Burst Monitor detection DATE: 26/02/27 08:55:16 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> K. Kobayashi (Waseda U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 260226A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 43840; BALROG localization: Preis et al., GCN Circ 43843; Fermi-LAT detection: Depalo et al., GCN Circ 43844; AstroSat CZTI detection: Harsha et al., GCN Circ 43846; Fermi-LAT refined analysis: Depalo et al., GCN Circ 43850; Fermi GBM observation: Bissaldi et al., GCN Circ 43851; NuSTAR detection: Waratkar et al., GCN Circ 43854; Glowbug gamma-ray detection: Woolf et al., GCN Circ 43855) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 10:38:04.46 UTC on 26 February 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1456137494/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T-3.9 sec, peaks at T+11.1 sec, and ends at T+37.0 sec. The T90 and T50 durations measured by the SGM data are 16.0 +/- 0.3 sec and 8.2 +/- 0.1 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1456137494/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/43860. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41975] GRB 260226A: COLIBRÍ optical upper limits
by GCN Circulars 27 Feb '26

27 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43859 SUBJECT: GRB 260226A: COLIBRÍ optical upper limits DATE: 26/02/27 06:16:42 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Camila Angulo (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), 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), 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 the Fermi GRB 260226A (Fermi GBM Team, GCN Circ. 43840, Fermi LAT, GCN Circ. 43844) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-27 02:54:20 to 03:52:25 UTC (from 16.27 to 17.25 hours after the trigger) and obtained 45 minutes of simultaneous exposures in the r and z filters. The data were reduced and coadded with the ASU pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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, comparing to LS (Dey et al. 2019), we do not detect any new source at the LAT source position (Depalo et al., GCN Circ. 43850) down to the following 5-sigma limits: r > 22.86 z > 21.99 These upper limits are consistent with the ones reported by Lipunov et al. (GCN Circ. 43847, 43848), Konno et al. (GCN Circ. 43852), Saikia et al. (GCN Circ. 43853), and Strausbaugh et al. (GCN Circ. 43858). 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/43859. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41974] GRB 260226A: LCOGT Optical Upper Limit
by GCN Circulars 27 Feb '26

27 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43858 SUBJECT: GRB 260226A: LCOGT Optical Upper Limit DATE: 26/02/27 03:17:12 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the Fermi GRB 260226A field (Fermi GBM Team, GCN 43840) with the LCOGT 1-meter Sinistro instrument at the McDonald Observatory, USA site, on February 27, from 01:46 to 02:18 UT (corresponding to 15.15 to 15.68 hours after the GRB trigger time) with the SDSS r and i filters. We performed a series of 3x300s exposures in i-band and r-band. We do not detect any uncatalogued sources within the Fermi LAT error region (Depalo et al., GCN 43850) in either band. The following 5-sigma upper limits are calculated using the PanSTARRS catalog as reference: r > 21.6 i > 21.1 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43858. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41973] EP-WXT trigger 01709258652: SVOM/C-GFT confirmation of a stellar flare
by GCN Circulars 27 Feb '26

27 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43857 SUBJECT: EP-WXT trigger 01709258652: SVOM/C-GFT confirmation of a stellar flare DATE: 26/02/27 02:06:29 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) report on behalf of the SVOM/C-GFT team: We observed the field of trigger 01709258652 detected by EP/WXT (Yang et al., GCN 43849) with LATIOS on SVOM/C-GFT. Observations started at 2026-02-26T13:56:46 UTC, ~6.77 min after the trigger. A sequence of g-, r-, and i-band images was obtained over ~110 min. Photometry of the suggested flare star LP 435-538 (High Proper Motion Star; Yang et al., GCN 43849) shows a decline from ~13.8 to ~15.4 mag in g-band over ~110 min. The fading was initially fast, then slowed, and was flatter in the r and i bands. This confirms the EP X-ray trigger is associated with a stellar flare. The photometry was calibrated against nearby Pan-STARRS1 stars and no correction for Galactic dust extinction was applied. We thank the observation assistants Hong-Xv Xue and Bo-Wen Li at Jilin ob-servatory 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/43857. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41972] GRB 260225D: Glowbug gamma-ray detection of a likely short burst
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43856 SUBJECT: GRB 260225D: Glowbug gamma-ray detection of a likely short burst DATE: 26/02/26 20:53:48 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, 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 260225D, which was also detected by Konus-Wind (Trig_Time 19:51:32.84) and SVOM/GRM (sb26022503). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-02-25 19:51:28.768 with a duration of 1.98 s and a total significance of about 62 sigma. The light curve comprises two primary peaks at ~T0+0.2s and +1.6s. The best-fit localization is RA, Dec. (J2000, deg) = 94.7, 13.8 with a radius of 7.0 deg (95% confidence), with a highly uncertain systematic uncertainty. 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/43856. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41971] GRB 260226A: Glowbug gamma-ray detection
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43855 SUBJECT: GRB 260226A: Glowbug gamma-ray detection DATE: 26/02/26 20:34:03 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 260226A, which was also detected by Fermi GBM (GCN 43840), Fermi LAT (GCN 43844), AstroSat CZTI (GCN 43846), NuSTAR (GCN 43854), and CALET (Trigger 1456137494). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-02-26 10:38:07.336 with a duration of 18.6s and a total significance of about 61.8 sigma. The light curve comprises three primary peaks at ~T0+6s, T0+7.5s and T0+10.5s, followed by three lesser peaks at ~T0+14s, T0+16s and T0+18s. Note that data from ~T0+9.5s to T0+11s suffered from deadtime in various detectors. Additionally, CLLB inorganic scintillation detectors [2], internal to the Glowbug shielded chassis, registered counts above background that are coincidence in time with the main Glowbug 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/43855. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41970] GRB 260226A: NuSTAR detection of bright prompt emission
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43854 SUBJECT: GRB 260226A: NuSTAR detection of bright prompt emission DATE: 26/02/26 20:10:43 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of bright prompt emission from the long-duration GRB 260226A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-02-26 10:38:05.0, shows a detection of GRB 260226A consistent with the detections by Fermi/GBM (Fermi GBM Team, GCN Circ. 43840) and AstroSat/CZTI (Harsha et al., GCN Circ. 43846). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single bright peak lasting for ~20-s, consistent with the bright episode from the lightcurve of Fermi/GBM. The peak count rate is ~14000-cps with a baseline rate of ~1000-cps during this time period. We also see clear evidence above 100 keV in the CdZnTe detectors, lasting for ~20-s. The Fermi/LAT localization (Depalo et al., GCN Circ. 43844) at RA = 42.05, Dec = 8.033 implies an offset from the NuSTAR boresight of 91-deg (i.e. from the side of the instrument) and an offset from the geocenter of 68-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260226A Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/43854. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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