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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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[vsnet-grb-info 41969] GRB 260226A : GROWTH-India Telescope optical observations
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43853 SUBJECT: GRB 260226A : GROWTH-India Telescope optical observations DATE: 26/02/26 19:55:15 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> A.P. Saikia, V. Vijaykumar, T. Mohan, A. Devaraj, S. Patil, V. Swain, 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 Fermi GRB 260226A (Fermi GBM team, GCN 43840) also detected by Fermi LAT (Depalo et al., GCN 43844, 43850), with 0.7m GROWTH-India Telescope (GIT). The observations started at 2026-02-26 14:33:34 UT, i.e 3.9 hours after the GBM trigger. We tiled the LAT localization region, observed the field at a position angle of approximately 45 degrees, and covered about 74% of the localization area. No new transients were detected within the observed region. Each exposure was taken in the r′ filter with an exposure time of 300 seconds. The photometric results are summarized below: Tile Number | Tmid - T0 (hours) | RA (deg) | Dec (deg) |Upper limit (5 sigma)(AB) | | ------------ | ------ | --------------- | ------------------------- | -------------- | | 1 | 3.95 | 42.05 | 8.033 | 19.7 | | 2 | 4.03 | 41.83 | 7.713 | 19.6 | | 3 | 4.12 | 41.83 | 7.873 | 19.9 | | 4 | 4.21 | 41.83 | 8.033 | 19.8 | | 5 | 4.30 | 41.83 | 8.193 | 19.6 | | 6 | 4.39 | 41.83 | 8.353 | 19.7 | | 7 | 4.47 | 41.94 | 7.713 | 19.6 | | 8 | 4.56 | 41.94 | 7.873 | 19.7 | | 9 | 4.65 | 41.94 | 8.033 | 19.6 | | 10 | 4.75 | 41.94 | 8.193 | 19.5 | | 11 | 4.84 | 41.94 | 8.353 | 19.6 | | 12 | 4.93 | 42.05 | 7.713 | 19.4 | | 13 | 5.02 | 42.05 | 7.873 | 19.2 | | 14 | 5.10 | 42.05 | 8.193 | 19.3 | | 15 | 5.19 | 42.05 | 8.353 | 19.2 | | 16 | 5.28 | 42.16 | 7.873 | 19.0 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our results are consistent with other optical non-detections (Lipunov et al., GCN 43847,43848, Konno et al., 43852) The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 8' x 11' 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/43853. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41968] GRB 260226A: LAST optical upper limit
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43852 SUBJECT: GRB 260226A: LAST optical upper limit DATE: 26/02/26 19:42:00 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 GRB 260226A, reported by Fermi-GBM (Fermi GBM Team, GCN 43840), as well as by Fermi-LAT (Depalo et al, GCN 43844) and AstroSat CZTI (Harsha et al, GCN 43846). 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 GRB 260226A were taken over 10 sequential epochs in clear band (similar to the Gaia Bp band) with 4 telescopes simultaneously. The first epoch began at 2026-02-26 16:30:51UTC (T-T0 = 5.88 h). Each epoch consists of 20x20s exposures per telescope. We coadd a total of 4x120x20s (mid. T-T0=6.67 h) exposure images and perform image subtraction using a reference image of the field. We do not detect any clear new optical source up to a 5-sigma limiting magnitude of 20.15 (AB) within the error region reported in Bissaldi et al., GCN 43851. Performing image subtraction between the latest (mid. T-T0 = 7.31 h) and earliest (mid. T-T0 = 5.94 h) 20x20s exposure images also shows no source brighter than 19.4 mag decaying by more than 0.5 mag. Our results are consistent with other optical non-detections (Lipunov et al., GCN 43847,43848). 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/43852. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41967] GRB 260226A: Fermi GBM observation
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43851 SUBJECT: GRB 260226A: Fermi GBM observation DATE: 26/02/26 16:21:05 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi(a)ba.infn.it> E. Bissaldi (Politecnico and INFN Bari), O.J. Roberts (Uni. of Galway, Ireland), P. Veres (UAH) and A. von Kienlin (MPE) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 10:39:05 UT on 26 February 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260226A (trigger 793795080/260226443), which was also detected by Fermi-LAT (Depalo et al. 2026, GCN 43844 and 43850) and AstroSat CZTI (Harsha et al. 2026, GCN 43846). The Fermi GBM on-ground location (GCN 43840) is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 26 degrees. The GBM light curve consists of a very bright and structured emission episode with a duration (T90) of about 82 s (50-300 keV). The time-averaged spectrum from T0 to T0+81 s is best fit by a Band function with Epeak = 723 +/- 8 keV, alpha = -0.95 +/- 0.01, and beta = -2.47 +/- 0.02. The event fluence (10-1000 keV) in this time interval is (4.54 +/- 0.01)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+19.3 s in the 10-1000 keV band is 166 +/- 2 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/43851. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41966] GRB 260226A: Fermi-LAT refined analysis
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43850 SUBJECT: GRB 260226A: Fermi-LAT refined analysis DATE: 26/02/26 16:15:30 GMT FROM: Davide Depalo at Politecnico and INFN Bari <davide.depalo(a)ba.infn.it> D. Depalo (Politecnico and INFN Bari), E. Bissaldi (Politecnico and INFN Bari), A. Holzmann Airasca (UniTrento and INFN Bari), R. Gupta (NASA/GSFC), F. Longo (University and INFN, Trieste), S. Lopez (CNRS / IN2P3), R. Martinelli (University and INFN, Trieste), and J. L. Racusin (NASA/GSFC) report on behalf of the Fermi-LAT team: At 10:38:18.84 UT on Feb 26th, 2026 Fermi-LAT triggered and detected high-energy emission from GRB 260226A (Depalo et al., GCN Circular 43844), which was also detected by Fermi-GBM (trigger 793795080 / 260226443, GCN Circular 43840) and Astrosat (Harsha et al., GCN Circular 43846). The best LAT on-ground location is found to be RA, Dec = 41.93, 7.73 (J2000) with an error radius of 0.11 deg (90 % containment, statistical error only). This was 26 deg from the LAT boresight at the time of the trigger. The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 0 - 1.5 ks after the GBM trigger is (1.50 ± 0.06)E-4 ph/cm2/s. The estimated photon index above 100 MeV is -3.25 ± 0.08. The highest energy photon has an energy of 1.1 GeV and occurs at 420 s after trigger time. The Fermi-LAT point of contact for this burst is Niccolò Di Lalla (niccolo.dilalla(a)stanford.edu) 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/43850. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41965] The EP-WXT trigger 01709258652 is likely a flaring star
by GCN Circulars 26 Feb '26

26 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43849 SUBJECT: The EP-WXT trigger 01709258652 is likely a flaring star DATE: 26/02/26 16:09:54 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Guojiong Yang, Tong Zhao(Nao, CAS), Zecheng Zou(NJU) and Wenda Zhang(Nao, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709258652 at the time of 2026-02-26T13:49:59(UTC), is likely a stellar flare associated with LP 435-538. The WXT position of the source is R.A. = 190.202 deg, DEC = 19.917 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). 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 2.071e+31 erg/s. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. An onboard alert was generated by FXT during this observation and the FXT position is R.A. = 190.1724 deg, DEC = 19.9231 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). The FXT position is consistent with the star LP 435-538. 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/43849. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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