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[vsnet-grb-info 42714] GRB 260511A: Glowbug gamma-ray detection
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44586 SUBJECT: GRB 260511A: Glowbug gamma-ray detection DATE: 26/05/12 17:03:10 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 260511A, which was also detected by Fermi GBM (GCN 44529), SVOM (GCN 44532), NuSTAR (GCN 44555), and Konus–Wind (GCN 44585). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-11 06:13:28.904 with a duration of 11.3 s and a total significance of about 41.6 sigma. The light curve comprises three primary peaks from T0 to ~T0+11s. 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/44586. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42713] Konus-Wind detection of GRB 260511A
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44585 SUBJECT: Konus-Wind detection of GRB 260511A DATE: 26/05/12 16:55:02 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260511A (Fermi-GBM detection: Fermi GBM team, GCN 44529; Roberts et al., GCN 44548; BALROG localization: Preis & Greiner, GCN 44531; SVOM detection: Godet et al., GCN 44532; NuSTAR detection: Waratkar et al., GCN 44555) triggered Konus-Wind at T0=22416.401 s UT (06:13:36.401). The burst light curve shows a multipeaked structure which starts at ~T0-4.6 s and has a total duration of ~20.5 s. The emission is seen up to ~6 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260511_T22416/ As observed by Konus-Wind, the burst had a fluence of 1.72(-0.05,+0.05)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.482 s, of 6.96(-0.71,+0.71)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+16.640 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.79(-0.08,+0.09) and Ep = 187(-8,+8) keV (chi2 = 107/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.1 (chi2 = 107/98 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.66(-0.08,+0.08) and Ep = 187(-6,+7) keV (chi2 = 88/86 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.9 (chi2 = 87/85 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44585. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42712] MASS-Cube (GRID 2.0) detection of GRB 260511A
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44584 SUBJECT: MASS-Cube (GRID 2.0) detection of GRB 260511A DATE: 26/05/12 16:35:13 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Jiahuan Zhu, Chenyu Wang, Xutao Zheng, Hao Chang, Zirui Yang report on behalf of the MASS-Cube Collaboration: MASS-Cube reports the detection of the long-duration GRB 260511A, which was also observed by Fermi/GBM (GCN #44548, #44548), SVOM (GCN #44532) and GRID. The optical counterpart was detected by TRT (GCN #44533). The event was triggered by MASS-Cube on 2026-05-11 at 06:13:29.2 UTC. The measured burst duration (T90) in the 50-10000 keV range is approximately 9.7 +/- 2.3 seconds. The second peak is not clearly detected by MASS-Cube due to its limited sensitivity. The MASS-Cube light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260511A/MASS_Cub…. MASS-Cube is a pathfinder for a 3D position-sensitive Compton telescope in space, currently considered the next generation of the GRID constellation in the era of multi-messenger astronomy. For more information about MASS-Cube, please refer to the following reference: https://doi.org/10.1007/s10686-024-09920-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/44584. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42711] MASS-Cube (GRID 2.0) detection of GRB 260507A
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44583 SUBJECT: MASS-Cube (GRID 2.0) detection of GRB 260507A DATE: 26/05/12 16:33:06 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Jiahuan Zhu, Chenyu Wang, Xutao Zheng, Hao Chang, Zirui Yang report on behalf of the MASS-Cube Collaboration: MASS-Cube reports the detection of the long-duration GRB 260507A, which was also detected by Fermi/GBM (GCN Circular 44493) and GRID-09. The event was triggered by MASS-Cube on 2026-05-07 at 20:27:59.7 UTC. The measured burst duration (T90) in the 50-10000 keV range is approximately 19.3 +/- 3.2 seconds. The MASS-Cube light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260507A/MASS_Cub…. MASS-Cube is a pathfinder for a 3D position-sensitive Compton telescope in space, currently considered the next generation of the GRID constellation in the era of multi-messenger astronomy. For more information about MASS-Cube, please refer to the following reference: https://doi.org/10.1007/s10686-024-09920-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/44583. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42710] GRB 260511B: SAO RAS optical observations
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44582 SUBJECT: GRB 260511B: SAO RAS optical observations DATE: 26/05/12 15:32:19 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS) and A. Pozanenko (IKI), report on behalf of GRB the follow-up team. We observed the field of the GRB 260511B discovered by Fermi (The Fermi GBM team, GCN 44542; Roberts, GCN 44554), SVOM (Godet et al., GCN 44543), NuSTAR (Waratkar and Grefenstette, GCN 44556), AstroSat CZTI (Arya et al., GCN 44560); EP-FXT (Fu et al., GCN 44578) with the Zeiss-1000, 1m telescope of the SAO RAS equipped with the CCD photometer. Observations were performed in B, V, Rc, Ic filters and started on May 11, 19:08:40 UT (8.14 hours after the trigger). The OT (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Vijaykumar et al., GCN 44561; de Ugarte Postigo et al., GCN 44565; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573; Saccardi et al., GCN 44574; Rajabov et al., GCN 44576; Pérez-Fournon et al., GCN 44577; Novotný et al., GCN 44580; also detected in NIR by Li et al., GCN 44557) is clearly detected in all frames with the following brightness. Date T_start T_end t_mid-T0, exp, s filter mag +/- err UT hours 2026-05-11T19:14:19--19:54:19 8.56306 3*300 B 19.56 +/- 0.03 2026-05-11T19:20:15--19:40:09 8.49444 2*120 V 19.09 +/- 0.04 2026-05-11T19:08:40--19:43:12 8.42333 3*120 Rc 18.75 +/- 0.02 2026-05-11T19:11:24--19:51:31 8.51542 5*120 Ic 18.50 +/- 0.05 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44582. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42709] GRB 260510D: Glowbug gamma-ray detection of a likely short burst
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44581 SUBJECT: GRB 260510D: Glowbug gamma-ray detection of a likely short burst DATE: 26/05/12 14:39:43 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 the likely short burst GRB 260510D, which was detected by Fermi/GBM (GCN 44523). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-10 20:38:07.656 with a duration of 0.13 s and a total significance of about 9.7 sigma. The lightcurve comprises a single peak. 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/44581. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42708] GRB 260511B: FRAM-ORM optical detection
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44580 SUBJECT: GRB 260511B: FRAM-ORM optical detection DATE: 26/05/12 13:59:31 GMT FROM: Filip Novotný at Masaryk University <filip.novotny(a)talentovani.cz> Filip Novotný, Martin Jelínek, Jan Štrobl (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Mašek, Petr Janeček, Jakub Juryšek, Jan Ebr, Ronan Cunniffe, Petr Travníček and Michael Prouza (Institute of Physics, Prague, CZ) report: We observed the field of GRB 260511B detected by Fermi/GBM (Fermi GBM Team, GCN 44542) and SVOM/ECLAIRs (Godet et al., GCN 44543) with the FRAM robotic telescope at the Observatorio del Roque de los Muchachos (ORM), La Palma, Spain. Observations were carried out in the clear filter from T+9.6 hr to T+17.4 hr with 60-second exposures stacked per epoch. The optical afterglow(Wu et al., GCN 44547 ; Sasada et al., GCN 44549 ; Jiang et al., GCN 44551 ; Wu et al., GCN 44552 ; Li et al., GCN 44557 ; Vijaykumar et al., GCN 44561 ; de Ugarte Postigo et al., GCN 44565 ; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572) of GRB 260511B (FERMI team, GCN 44542 ; Godet et al., GCN 44543; Roberts et al., GCN 44554; Waratkar et al., GCN 44556; Arya et al., GCN 44560) is clearly detected throughout the night, fading from CR = 18.89 +/- 0.10 at T+9.8 hr till about T+16 hr, when the target terminated due to dawn. Magnitudes were reduced using the PyRT pipeline and calibrated to r-band AB magnitudes against the ATLAS catalog. No correction for Galactic extinction has been applied. Fitting a power law F(t) ~ t^(-alpha) to our data yields alpha = 1.39 +/- 0.29, consistent with the power-law decay reported by earlier observers (GCN 44547, 44549, 44551, 44561). View this GCN Circular online at https://gcn.nasa.gov/circulars/44580. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42707] GRB 260511A: EP-FXT follow-up observation
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44579 SUBJECT: GRB 260511A: EP-FXT follow-up observation DATE: 26/05/12 13:12:09 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.-Y. Fu (HUST), X. Tian (GXU), H.-N. Yang, Z.-X. Ling (NAOC, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260511A (SVOM/sb26051101, Godet et al., GCN 44532), which also triggered Fermi-GBM (Fermi GBM team, GCN 44529). The follow-up obervation started at 2026-05-11T07:00:13 UTC, approximately 46.7 minutes after the SVOM trigger, with a total exposure time of 2.2ks. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 197.8992, -33.8042 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic) near the ECLAIRs error circle. This position is consistent with the optical counterpart reported by TRT (Jiang et al., GCN 44533) and FM-GFT (Akl et al. GCN 44534). The average FXT 0.3-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value, adittional hydrogen column density of 5.9 (+-1.3) ×10^20 cm^-2, and a photon index of 1.93 +- 0.05. The derived average unabsorbed flux in the 0.3-10 keV band is 6.33 (+-0.18)×10^-11 erg s^-1 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/44579. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42706] GRB 260511B: EP-FXT follow-up observation
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44578 SUBJECT: GRB 260511B: EP-FXT follow-up observation DATE: 26/05/12 12:55:37 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.-Y. Fu (HUST), X. Tian (GXU), H.-N. Yang, Z.-X. Ling (NAOC, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of GRB 260511B detected by Fermi/GBM (the Fermi GBM team, GCN 44542) and SVOM/ECLAIRs (SVOM/sb26051102, Godet et al., GCN 44543). The follow-up obervation started at 2026-05-11T11:41:41 UTC, approximately 40.7 minutes after the SVOM trigger, with a total exposure time of 5.9 ks. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 192.574, 4.0549 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic) near the ECLAIRs error circle. This position is consistent with the optical counterpart reported by SVOM/C-GFT (Wu et al., GCN 44547) and MITSuME (Sasada et al. GCN 44549). The average FXT 0.3-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value, intrinsic hydrogen column density of 3.8 (+-0.10) ×10^21 cm^-2, and a photon index of 2.10 +- 0.04. The derived average unabsorbed flux in the 0.3-10 keV band is 2.07 (+-0.05)×10^-11 erg s^-1 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/44578. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42705] GRB 260511B: LCO optical counterpart detection
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44577 SUBJECT: GRB 260511B: LCO optical counterpart detection DATE: 26/05/12 12:22:26 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) We report on Las Cumbres Observatory (LCO) observations of the long GRB 260511B, detected by Fermi GBM (Fermi GBM team, GCN circ. 44542; Roberts et al., GCN circ. 44554), SVOM ECLAIRs and MXT (Godet et al., GCN circ. 44543), NuSTAR (Waratkar and Grefenstette, GCN circ. 44556), and AstroSat (Arya et al., GCN circ. 44560). We observed the field of GRB 260511B with one of the two LCO 1-m telescopes equipped with Sinistro cameras located at the LCO node at McDonald Observatory, Texas, in the SDSS r´ (300 sec), g' (200 sec), and i' (200 sec) filters. The first observation, in the SDSS r' filter, started on 2026-05-12 at 03:00:47 UT, 16.00 hours after the Fermi and SVOM trigger. The optical conterpart, first reported by Wu et al. (GCN circ. 44547), at a redshift of z = 2.006 (de Ugarte Postigo et al., GCN circ. 44565; Wang et al., GCN circ. 44571; and Adami et al., GCN circ. 44573), is clearly detected in our LCO images. The AB magnitudes, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction are: r' = 19.81 +/- 0.06 (mid-time 16.05 hours after the trigger) g' = 20.21 +/- 0.06 (mid-time 16.67 hours after the trigger) i' = 19.71 +/- 0.07 (mid-time 16.73 hours after the trigger) These results are consistent with other optical and near-IR detections of the afterglow (Wu et al., GCN circ. 44547; Sasada et al., GCN circ. 44549; Jiang et al., GCN circ. 44551; Wu et al., GCN circ. 44552; Li et al., GCN circ. 44557; Vijaykumar et al., GCN circ. 44561; de Ugarte Postigo et al., GCN circ. 44565; Lee et al., GCN circ. 44567; Li et al., GCN circ. 44568; Wang et al., GCN circ. 44571; Belkin et al., GCN circ. 44572; Adami et al., GCN circ. 44573; Saccardi et al., GCN circ. 44574); and Rajabov et al., GCN circ. 44576). 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/44577. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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