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[vsnet-grb-info 40609] GRB 251025C: SVOM/GRM observation
by GCN Circulars 30 Oct '25

30 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42524 SUBJECT: GRB 251025C: SVOM/GRM observation DATE: 25/10/30 17:03:31 GMT FROM: tanwj(a)ihep.ac.cn SVOM/GRM team: Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Sebastien Guillot (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 251025C (SVOM burst-id sb25102505) at 2025-10-25T23:08:41.000 (T0), which is also detected by Fermi/GBM (Fermi/GBM team, GCN # 42449), CALET (S. Torii, et al. GCN # 42467), AstroSat CZTI (A. Arya, et al. GCN # 42469) and Glowbug (R. Woolf, et al. GCN # 42490). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a significant peak followed by weak emission with a T90 of 30.4 +13.2/-12.6 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251025C.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 170.7, Dec = 54.9 , GCN #42449), is located at about 89 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization given by Fermi/GBM, the time-averaged spectrum from T0-2 to T0+30 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.97 +0.16/-0.14 and the cutoff energy, parameterized as Epeak, is 1450 +680/-440 keV. The event fluence (10-1000 keV) in this time interval is (1.06 +0.09/-0.27)E-05 erg/cm^2. The localization of GRB 251025C in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251025C_amati.png 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 point of contact for this burst is: Wen-Jun Tan (IHEP)(tanwj(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42524. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40608] GRB 251028A: GECAM-B detection
by GCN Circulars 30 Oct '25

30 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42523 SUBJECT: GRB 251028A: GECAM-B detection DATE: 25/10/30 15:46:39 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a long burst, GRB 251028A, at 2025-10-28T03:26:40.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42497, GCN#42499), MAXI/GSC (MAXI team, GCN#42498), Glowbug (C.C. Cheung et al., GCN#42506) and SVOM/GRM (SVOM/GRM team, SVOM/ECLAIRs team, GCN#42522). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 38 +4/-5 s. shi The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251028A.png The time-averaged spectrum from T0-10 s to T0+45 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.05 +0.11/-0.11 and the cutoff energy, parameterized as Epeak, is 259 +38/-25 keV. The event fluence (10-1000 keV) in this time interval is (3.12 +0.20/-0.17)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 251028A is shown at: https://www.bursthub.cn//admin/static/gecambgrb251028A_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/42523. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40607] GRB 251028A: SVOM/GRM observation
by GCN Circulars 30 Oct '25

30 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42522 SUBJECT: GRB 251028A: SVOM/GRM observation DATE: 25/10/30 13:47:16 GMT FROM: Haoxuan Guo <skyairsama(a)gmail.com> SVOM/GRM team: Hao-Xuan Guo, Chen-Wei Wang, Zheng-Hang Yu, Chao Zheng,, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)SVOM/ECLAIRs team: Report on behalf of the SVOM team: SVOM/ECLAIRs team: Sebastien Guillot (IRAP) SVOM/GRM was triggered in-flight by a burst GRB 251028A (SVOM trigger reference: sb25102801) at 2025-10-28T03:26:37.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42497, GCN#42499), MAXI/GSC (MAXI team, GCN#42498) and Glowbug (C.C. Cheung et al., GCN#42506). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple peaks with a T90 of 31.0 +6.5/-3.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251028A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 149.5, DEC= 20.2, GCN#42497), is located at about 157 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst still clearly detected by ECLAIRs due to the reflection of the Earth atmosphere. With this localization, the time-averaged spectrum from T0-10 to T0+45 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.31 +0.14/-0.16 and the cutoff energy, parameterized as Epeak, is 345 +107/-64 keV. The event fluence (10-1000 keV) in this time interval is (4.56 +0.24/-0.27)E-5 erg/cm^2. The localization of GRB 251028A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251028A_amati.png 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 point of contact for this burst is: Hao-Xuan Guo (IHEP)(guohx(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42522. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40606] IceCube-251025A: Two Transient Candidates from the Zwicky Transient Facility
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42521 SUBJECT: IceCube-251025A: Two Transient Candidates from the Zwicky Transient Facility DATE: 25/10/29 23:11:01 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Akshay Eranhalodi (DESY), Robert Stein (JSI), Jannis Necker (Leiden University) and Anna Franckowiak (Ruhr University Bochum) report: On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-251025A (Zegarelli et. al, GCN 42436) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2025-10-26 11:02 UTC, approximately 21.2 hours after event time. We covered 98.9% (2.1 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019) . We are left with the following high-significance transient candidates by our pipeline, all lying within the 90.0% localization of the skymap. ±–––––––––––––––––––––––––––––––––––––––-+ | ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr | ±–––––––––––––––––––––––––––––––––––––––-+ | ZTF25acammho | AT 2025abwy | 144.8380039 | +15.6961873 | g | 21.13 | 0.21 | | ZTF25acamsai | AT 2025abtz | 146.0869065 | +14.6023944 | r | 20.75 | 0.12 | ±–––––––––––––––––––––––––––––––––––––––-+ Amongst our candidates, we find two unclassified transients of potential interest. ZTF25acammho/AT 2025abwy was inititally detected on 2025-10-03 in r-band, and was then redetected in our ToO observations three weeks later. The source appears to be hostless, with a current magnitude of 21.13. ZTF25acamsai/AT 2025abtz was first detected on 2025-10-22, and appears coincident with a host galaxy of photometric redshift z=0.2. This would imply a magnitude of M=-19.5. The source appears to be blue. We encourage spectrscopic observations to confirm the nature of these two transients. In addition, we also recover one known supernova, ZTF25abvepyj/SN2025zno. The source was first detected by ZTF on 2025-10-02, and is classified as Type Ia Supernova at a redshift of 0.064. Type Ia supernovae are not predicted to be significant neutrino emitters, so we conclude that this source is unrelated to the neutrino. We further find one likely AGN (ZTF19aaixfxw) with W1-W2=0.8. This source does not display any evidence of flaring coincident with the neutrino, and we see no reason to associate it with IC251025A. The neutrino localisation was also observed by DDOTI (Becerra et al., GCN 42457) who report no uncatalogued source with w > 20. These observations are consistent with our observations reported here. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA; WIS, Israel; OKC, Sweden; JSI/UMd, USA; DESY, Germany; TANGO, Taiwan; UW Milwaukee, USA; LANL, USA; TCD, Ireland; IN2P3, France. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). View this GCN Circular online at https://gcn.nasa.gov/circulars/42521. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40605] GRB 251028A: Fermi GBM Observation
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42520 SUBJECT: GRB 251028A: Fermi GBM Observation DATE: 25/10/29 20:08:12 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 03:26:31.86 UT on 28 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251028A (trigger 783314796/251028143) which was also detected by MAXI (Negoro et al. 2025, GCN 42498) and Glowbug (Cheung et al. 2025, GCN 42506). The Fermi GBM on-ground location is consistent with the MAXI position. The angle from the Fermi LAT boresight is 50 degrees. The GBM light curve consists of multiple overlapping pulses with a duration (T90) of about 30 s (50-300 keV). The time-averaged spectrum from T0 to T0+39.9 s is best fit by a Band function with Epeak = 244 +/- 14 keV, alpha = -0.91 +/- 0.03, and beta = -2.4 +/- 0.1. The event fluence (10-1000 keV) in this time interval is (3.13 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+24 s in the 10-1000 keV band is 10.8 +/- 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/42520. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40604] GRB 251026B: SOAR Classification of GOTO25jgl/SN2025absf as a Type Ia supernova
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42519 SUBJECT: GRB 251026B: SOAR Classification of GOTO25jgl/SN2025absf as a Type Ia supernova DATE: 25/10/29 20:04:03 GMT FROM: jcarney(a)unc.edu Jonathan Carney (UNC), Xander J. Hall (CMU), Igor Andreoni (UNC), Brendan O’Connor (CMU), Malte Busmann (LMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the source SN 2025absf reported by Belkin et al. (GCN 42470), a possible counterpart to short GRB 251026B (GCN 42455), with the Goodman High Throughput Spectrograph (GHTS; Clemens 2004) on the Southern Astrophysical Telescope (SOAR). We used a grating of 400 lines/mm and a 1.0'' wide slit mask in the M1 spectroscopic setup (hereafter 400M1) with 2x2 binning using the GHTS Red Camera. The 400M1 spectra cover a wavelength range of 3800 -- 7040 Å. The spectra were reduced using Pypeit (Prochaska 2020), using arcs taken immediately after target observation and calibration images from the same night. Flux calibration was performed using observations of HR7596 taken on the same night as the observations with an identical 400M1 setup and 2x2 binning. Using SNID (Blondin et al. 2011) and NGSF (AstroNote 2022-191), we find good template matches to a Ia-norm SN at z ~ 0.044. Thus, we classify SN 2025absf as a type Ia supernova. We therefore conclude that SN 2025absf is not the optical counterpart to GRB 251026B. We thank the CTIO and NOIRLab staff for supporting these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40603] GRB 251022A: Swift-XRT confirmation of fading
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42518 SUBJECT: GRB 251022A: Swift-XRT confirmation of fading DATE: 25/10/29 19:49:57 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has conducted further observations of the field of the Fermi/LAT-detected burst GRB 251022A. The observations now extend from T0+38.6 ks to T0+575.9 ks and have a total exposure time of 6.6 ks. . The previously-reported "Source 4" (Burrows et al., GCN Circ. 42417), coincident with GOTO25iym, is now found to be fading with >3-sigma significance, and is therefore likely the GRB afterglow. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/00021864. The results of the full analysis of the tiled XRT observations are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00139. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42518. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40602] GRB 251026B: LBT near-infrared observations
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42517 SUBJECT: GRB 251026B: LBT near-infrared observations DATE: 25/10/29 17:44:10 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang, Eleonora Troja, Massine El Kabir, Muskan Yadav (U Rome) report on behalf of the ERC BHianca team: Following the detection of GRB 251026B by Fermi/GBM (Dafčíková et al., GCN 42455), we observed the candidate optical counterpart GOTO25jgl/AT2025absf (Belkin et al., GCN 42470) in the J filter with the LUCI near-infrared imager mounted on the Large Binocular Telescope (LBT). Observations started at 2025-10-29T11:28:17 (~ 3.2 d after the GBM trigger) with an average airmass of 1.5. We detect the source previously reported as a candidate from GOTO (Belkin et al., GCN 42470) with a preliminary magnitude of J ~ 19.2 AB mag, calibrated using nearby stars from the 2MASS catalog (Skrutskie et al. 2006), uncorrected for Galactic extinction. Our measurement is consistent with the near-infrared upper limit derived by PRIME (Kabir et al. GCN 42501). Compared to the predicted optical magnitude L~19.3 at the same epoch using the magnitudes and decay trend reported by GOTO (Belkin et al., GCN 42470), we find no evidence for a red color excess. Based on the lack of X-ray emission (Osborne et al. GCN 42491) and blue color, the properties of GOTO25jgl do not appear consistent with standard afterglow or kilonova emission, therefore its association with GRB 251026B cannot be confirmed. We acknowledge excellent support from the LBTO and LBT-INAF staff, particularly Ester Marini. View this GCN Circular online at https://gcn.nasa.gov/circulars/42517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40601] GRB 250926B: VZLUSAT-2 detection
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42516 SUBJECT: GRB 250926B: VZLUSAT-2 detection DATE: 25/10/29 16:40:33 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250926B (Fermi/GBM detection: GCN 42012) was detected by the GRB detector on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/) The data acquisition was performed by the GRB detector unit no. 0. The detection was confirmed at the peak time 2025-09-26 19:50:31 UTC. The T90 duration is 26 s and the significance during T90 reaches 5.4 sigma. The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250926B_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/42516. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40600] GRB 250926A: VZLUSAT-2 detection
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42515 SUBJECT: GRB 250926A: VZLUSAT-2 detection DATE: 25/10/29 16:39:53 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250926A (Fermi/GBM detection: GCN 41993; AstroSat/CZTI detection: GCN 42008; INSIGHT-HXMT/HE detection: GCN 42013; CALET/CGBM detection: GCN 42027; Wind/Konus detection trigger at 2025-09-26 00:21:25.489 UTC) was detected by the GRB detectors on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/) The data acquisition was performed by the GRB detector units no. 0 and no. 1. The detection was confirmed at the peak time 2025-09-26 00:21:23 UTC. The T90 duration is 1 s (2 s) and the significance during T90 reaches 5 sigma (17 sigma) for detector unit no. 0 (no. 1). The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250926A_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/42515. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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