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[vsnet-grb-info 43701] EP260830a: EP-WXT detection of a fast X-ray transient
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45480 SUBJECT: EP260830a: EP-WXT detection of a fast X-ray transient DATE: 26/09/01 06:21:48 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. Mao (NAO, CAS), Y. F. Liang, J. Y. Liu (PMO), Q. H. Lao, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient, designated EP260830a (notice ID: 01709295827), by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient was identified in the telemetry data. The transient started about 2026-08-30T15:30:23(UTC) and lasted for about 500s. The position of the transient is R.A. = 2.055 deg, Dec. = 16.919 (J2000), with an uncertainty radius of 2.4 arcmin in radius (90% confidence level, including both statistical and systematic uncertainties). There are no known X-ray sources in the WXT error circle. The average WXT 0.5-4 keV spectrum can be fitted by an absorbed power-law model with a fixed Galactic hydrogen column density of 4.21×10^20 cm^-2 and a photon index of 1.03 (-0.92/+1.02). The derived average unabsorbed 0.5-4 keV flux is 3.69 (-1.65/+2.93) x 10^(-11) erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters. Follow-up observations by EP-FXT will be arranged. Launched on 2024 January 9, Einstein Probe is a space-based X-ray observatory designed to monitor the dynamic X-ray sky and perform rapid follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/45480. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43700] GRB 260827A: SVOM/GRM observation
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45479 SUBJECT: GRB 260827A: SVOM/GRM observation DATE: 26/09/01 06:14:46 GMT FROM: yzh807926(a)163.com SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Yue Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260827A at 2026-08-27T10:43:00.700 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #45453). 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 1.7 +0.6/-0.3 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn/gcn/2026/svgrb260827A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 247.9, Dec = -53.5, Error = 2.4 degrees, GCN #45453), is located at about 105 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. Nevertheless, ECLAIRs detected the GRB through the shield above 50 keV. With this localization, the time-averaged spectrum from T0-1 to T0+2 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.49 +0.24/-0.27 and the cutoff energy, parameterized as Epeak, is 431 +91/-64 keV. The event fluence (10-1000 keV) in this time interval is (4.61 +0.32/−0.34)E-06 erg/cm^2. The localization of GRB 260827A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn/gcn/2026/svgrb260827A_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/GRM point of contact for this burst is: Zheng-Hang Yu (IHEP) (zhyu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/45479. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43699] NuSTAR 260828: a 1100s hard X-ray transient
by GCN Circulars 31 Aug '26

31 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45478 SUBJECT: NuSTAR 260828: a 1100s hard X-ray transient DATE: 26/08/31 22:36:44 GMT FROM: Murray Brightman at Caltech <murray(a)srl.caltech.edu> Murray Brightman (Caltech) on behalf of the NuSTAR Science Operations Center: We report on the detection of NuSTAR 260828, a 1100s hard X-ray transient found at 2026-08-28 18:39:29.6 (UTC, MJD=61280.7) with a position of RA=91.9004 deg, -8.49441 deg (~10 arcsec uncertainty). The spectrum can be described by a power-law with spectral index, Gamma=1.7^+2.0_-1.9 with a 3--79 keV flux of 2.9 +/- 2.2 x10^-12 erg cm^-2 s^-1, which extrapolates to 1.1^+3.1_-0.9 x10^-12 erg cm^-2 s^-1 in the 0.2--10 keV band. No X-ray source has been catalogued at the position of the NuSTAR source, despite multiple Swift observations of the region. With the soft, albeit unconstrained spectrum, and position close to the Galactic plane, a flare star cannot be ruled out. We encourage follow-up observations at other wavelengths in order to determine the nature of this X-ray transient. More information about previously detected fast X-ray transients in the NuSTAR archive can be found in this paper: [https://ui.adsabs.harvard.edu/#abs/2026ApJ...999...75B/abstract] NuSTAR is a NASA small explorer mission operated at Caltech. It was launched in June 2012 into low-Earth orbit and operates in the 3--79 keV energy band. It was the first focusing hard X-ray (>10 keV) observatory in orbit and is currently the most sensitive X-ray telescope above 10 keV of any operating mission. View this GCN Circular online at https://gcn.nasa.gov/circulars/45478. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43698] GRB 260831B: SVOM detection of a possible burst
by GCN Circulars 31 Aug '26

31 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45477 SUBJECT: GRB 260831B: SVOM detection of a possible burst DATE: 26/08/31 19:20:03 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> O. Godet (IRAP), C. Guepin (LUPM), S. Guillot (IRAP) report on behalf of the SVOM mission team: At 2026-08-31T18:36:12 UTC (T0), SVOM/ECLAIRs triggered and located the possible gamma-ray burst GRB 260831B (SVOM burst-id sb26083106). 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 5 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.11 in the [8-50] keV energy band over a time window of 655.36 seconds starting at 2026-08-31T18:32:07. The localization of the best alert is R.A., Dec. 52.977, 43.971 degrees: R.A. (J2000) = 3h31m54.41s Dec. (J2000) = 43d58m15.22s with a 90% confidence level (C.L.) radius of 8.69 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve is featureless. SVOM slewed to the burst. SVOM/MXT began observing the field about 10 minutes after T0. Using onboard processed data, no source was detected during a > 10 min exposure. The SVOM/MXT team is waiting for the full dataset to detect and localise the possible SVOM/MXT counterpart. VT began observing the field after the slew. The analysis of the data will be published in a future circular. We note that the classical nova V* GK Per that triggered ECLAIRs in the past few weeks is within the ECLAIRs error circle. 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 Claire Guepin: claire.guepin at lupm.in2p3.fr Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/45477. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43697] IPN triangulation of GRB 260829A
by GCN Circulars 31 Aug '26

31 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45476 SUBJECT: IPN triangulation of GRB 260829A DATE: 26/08/31 19:15:43 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(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, A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, 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, 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 260829A (Fermi-GBM detection: Fermi GBM team, GCN 45464; Malacaria et al., GCN 45467; BALROG localization: Preis & Greiner, GCN 45465; GECAM-B detection: Zao et al., GCN 45470) was detected by Fermi (GBM trigger 809676494), Konus-Wind, GECAM-B, and Mars-Odyssey (HEND) at about 22089 s UT (06:08:09). We have triangulated it to the 3 sigma localization region whose area is 5.2 sq. deg, and its maximum dimension is 31 deg (the minimum one is 10 arcmin). This localization may be improved. A triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB260829_T22110/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/45476. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43696] GRB 260827A: Glowbug gamma-ray detection
by GCN Circulars 31 Aug '26

31 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45475 SUBJECT: GRB 260827A: Glowbug gamma-ray detection DATE: 26/08/31 16:07:18 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 260827A, which was also detected by Fermi/GBM (GCN 45453). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-08-27 10:42:58.640 with a duration of 2.6 s and a total significance of about 11.3 sigma. The light curve 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/45475. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43695] EP260727a: ATCA 10 GHz detection
by GCN Circulars 31 Aug '26

31 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45474 SUBJECT: EP260727a: ATCA 10 GHz detection DATE: 26/08/31 14:44:51 GMT FROM: Giulia Gianfagna at INAF-IAPS <giulia.gianfagna(a)inaf.it> G. Bruni, A. L. Thakur, M. Fanelli., G. Gianfagna, L. Piro (INAF-IAPS) report: We observed the Fast X-ray Transient EP260727a (Hu et al., GCN 45235; Wu et al., GCN 45244) with the Australian Telescope Compact Array (ATCA). Observations were performed on August 28 2026 (at a mean epoch of 31.76 days after the EP trigger) for a total of 6.5 hours at 4 cm under program C3638 (PI Gianfagna). Data were reduced and imaged with standard CASA procedures. The final 10 GHz image has an rms of ~8 uJy/beam. We detect radio emission at a flux density of ~0.1 mJy at a position consistent with the optical counterpart (He et al., GCN 45234; Maksut et al., GCN 45238; Eyles-Ferris et al., GCN 45239; Adami et al., GCN 45243; Guziy et al., GCN 45245; Moskvitin et al., GCN 45252; Schneider et al., GCN 45256). Further ATCA observations are planned. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (grid.421683.a), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. View this GCN Circular online at https://gcn.nasa.gov/circulars/45474. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43694] GRB 260831A: Fermi GBM Final Real-time Localization
by GCN Circulars 30 Aug '26

30 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45473 SUBJECT: GRB 260831A: Fermi GBM Final Real-time Localization DATE: 26/08/31 04:17:21 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 04:09:00 UT on 31 Aug 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260831A (trigger 809842145.925584 / 260831173). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 220.0, Dec = -7.2 (J2000 degrees, equivalent to J2000 14h 39m, -7d 12'), with a statistical uncertainty of 6.5 degrees. The angle from the Fermi LAT boresight is 84.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260831173/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260831173/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260831173/… View this GCN Circular online at https://gcn.nasa.gov/circulars/45473. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43693] Fermi-LAT Gamma-ray Observations of IceCube-260827A
by GCN Circulars 30 Aug '26

30 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45472 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260827A DATE: 26/08/30 16:23:13 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa(a)weizmann.ac.il> S. Garrappa (Weizmann Institute of Science), L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and C. Bartolini (INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260827A neutrino event (GCN 45455) 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 2026-08-27 at 15:35:36.97 UTC (T0) with J2000 position RA = 86.31 (+0.65, -0.47) deg, Decl. = 8.12 (+0.42, -0.41) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260827A localization error (FL16Y, The Fermi-LAT 16 Year Source List, The Fermi-LAT collaboration 2026, arXiv:2602.22148). 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 IC260827A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260827A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.0e-10 ph cm^-2 s^-1 for ~18-years (2008-08-04 / T0), <9.5e-09 (<1.6e-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 S. Garrappa (simone.garrappa at weizmann.ac.il). 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/45472. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43692] Fermi-LAT Gamma-ray Observations of IceCube-260825A
by GCN Circulars 30 Aug '26

30 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45471 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260825A DATE: 26/08/30 16:21:25 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa(a)weizmann.ac.il> S. Garrappa (Weizmann Institute of Science), L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and C. Bartolini (INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260825A neutrino event (GCN 45438) 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 2026-08-25 at 10:53:33.63 UTC (T0) with J2000 position RA = 91.95 (+0.75, -0.74) deg, Decl. = 45.73 (+0.52, -0.51) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260825A localization error (FL16Y, The Fermi-LAT 16 Year Source List, The Fermi-LAT collaboration 2026, arXiv:2602.22148). 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 IC260825A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260825A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.8e-10 ph cm^-2 s^-1 for ~18-years (2008-08-04 / T0), <5.2e-09 (<1.1e-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 S. Garrappa (simone.garrappa at weizmann.ac.il). 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/45471. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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