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[vsnet-grb-info 43254] Fermi GBM trigger 804010507/260624677 is not a GRB
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45039 SUBJECT: Fermi GBM trigger 804010507/260624677 is not a GRB DATE: 26/06/24 17:44:48 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA) reports report on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 804010507/260624677 at 16:15:02.91 UT on 24 June 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to particle activity." View this GCN Circular online at https://gcn.nasa.gov/circulars/45039. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43253] Konus-Wind detection of GRB 260618B
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45038 SUBJECT: Konus-Wind detection of GRB 260618B DATE: 26/06/24 17:14:43 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 260618B (Fermi-GBM detection: Fermi GBM team, GCN 44979; Veres & Meegan, GCN 45010; Fermi-LAT detection: Gupta et al., GCN 44983) triggered Konus-Wind at T0=60907.637 s UT (16:55:07.637). The burst light curve shows a multipeaked structure which starts at ~T0-1.6 s and has a total duration of ~61.2 s. The emission is seen up to ~4 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260618_T60907/ As observed by Konus-Wind, the burst had the total fluence of 2.26(-0.34,+0.43)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+0.378 s, of 4.90(-0.98,+1.01)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+57.600 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 = -0.83(-0.16,+0.19) and Ep = 1066(-241,+365) keV (chi2 = 94/98 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.7 (chi2 = 94/97 dof). The spectrum near the maximum count rate (measured from T0 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 = -0.39(-0.14,+0.15) and Ep = 817(-97,+119) keV (chi2 = 96/88 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.2 (chi2 = 96/87 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/45038. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43252] GRB 260624A: Fermi GBM Final Real-time Localization
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45037 SUBJECT: GRB 260624A: Fermi GBM Final Real-time Localization DATE: 26/06/24 16:09:12 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 15:54:14 UT on 24 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260624A (trigger 804009259.148196 / 260624663). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 54.1, Dec = -21.0 (J2000 degrees, equivalent to J2000 03h 36m, -21d 00'), with a statistical uncertainty of 4.4 degrees. The angle from the Fermi LAT boresight is 73.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… View this GCN Circular online at https://gcn.nasa.gov/circulars/45037. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43251] GRB 260624A: Fermi GBM Final Real-time Localization
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45036 SUBJECT: GRB 260624A: Fermi GBM Final Real-time Localization DATE: 26/06/24 16:06:42 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 15:54:14 UT on 24 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260624A (trigger 804009259.148196 / 260624663). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 54.1, Dec = -21.0 (J2000 degrees, equivalent to J2000 03h 36m, -21d 00'), with a statistical uncertainty of 4.4 degrees. The angle from the Fermi LAT boresight is 73.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… View this GCN Circular online at https://gcn.nasa.gov/circulars/45036. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43250] EP260623a:refined analysis of the EP-WXT and EP-FXT observation
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45035 SUBJECT: EP260623a:refined analysis of the EP-WXT and EP-FXT observation DATE: 26/06/24 09:06:30 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B.T. Wang (YNAO, CAS), Y. L. Hua (PMO, CAS) and C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260623a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 45020) and followed by several optical telescopes (Li et al., GCN 45021; Angulo et al., GCN 45024; Brivio et al., GCN 45025; Jiang et al., GCN 45026; Li et al., GCN 45027; Jelinek et al., GCN 45029; Lee et al., GCN 45030; Saikia et al., GCN 45034) with the redshift confirmed at z=0.703 (Izzo et al., GCN 45022). The refined analysis of the WXT data shows that the event started at T0=2026-06-23T02:52:27Z (UTC) and lasted for 103 s before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model (tbabs*ztbabs*powerlaw) with a fixed Galactic hydrogen column density of 8.1 × 10^20 cm^-2 and a fixed redshift of z = 0.703. The best-fit photon index is 1.83 (-0.56/+0.63), and the intrinsic hydrogen column density is 2.25 (-0.97/+1.21) × 10^22 cm^-2. The derived average unabsorbed 0.5–4 keV flux is 3.17 (-0.74/+1.39) × 10^-9 erg/s/cm^2. The estimated peak flux is 1.0 × 10^-8 erg/s/cm^2, corresponding to a peak luminosity of 2.2 × 10^49 erg/s. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-06-23T02:56:08 (UTC), about 3.7 minutes after T0. The exposure time of this observation is 3211 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 328.2698, 12.7938 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT light curve displays two pulses structure lasting for around 210 s. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 8.1 × 10^20 cm^-2 and a photon index of 1.96 (-/+ 0.03), and the intrinsic hydrogen column density is 0.94 (-/+ 0.04) × 10^22 cm^-2. The derived average unabsorbed 0.5-10 keV flux is 7.33 (-/+ 0.10) × 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/45035. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43249] EP260623a: WINTER J-band observations
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45034 SUBJECT: EP260623a: WINTER J-band observations DATE: 26/06/23 22:37:06 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Aditya Pawan Saikia (IITB), Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (NOIRLab), Benjamin Schneider (LAM), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of EP260623a (Wang et al., GCN 45020) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-06-23T07:00:29 UTC in the J band (4.1 hr after the EP trigger), consisting of 30*120 sec exposures. 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) We detect a source at the optical counterpart location (Li et al., GCN 45021; Izzo et al., GCN 45022; Angulo et al., GCN 45024; Brivio et al., GCN 45025; Jiang et al., GCN 45026; Li et al., GCN 45027; Jelinek et al., GCN 45029; Lee et al., GCN 45030), with magnitude J = 17.9 ± 0.1 mag (AB). 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/45034. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43248] GRB 260617A: Glowbug gamma-ray detection of a short burst
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45033 SUBJECT: GRB 260617A: Glowbug gamma-ray detection of a short burst DATE: 26/06/23 22:12:11 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 260617A, which was also detected by Fermi/GBM (GCN 44969, 44972), Konus-Wind and Mars-Odyssey/HEND (GCN 44982, 44998), and CALET (GCN 44989). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-06-17 21:36:42.640 with a duration of 0.26 s and a total significance of about 27 sigma. The light curve comprises a multi-peaked emission similar to the CALET light curve (GCN 44989). 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/45033. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43247] IceCube-260622A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45032 SUBJECT: IceCube-260622A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/06/23 19:49:02 GMT FROM: Yuhua Yao at IceCube/UW-Madison <yyao255(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-260622A (https:/.gov/circulars/45018) in a time range of 1000 seconds centered on the alert event time (2026-06-22 15:33:34.814 UTC to 2026-06-22 15:50:14.814 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-260622A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.4e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260622A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 3e+02 GeV and 2e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-06-21 15:41:54.814 UTC to 2026-06-23 15:41:54.814 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260622A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/45032. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43246] IPN triangulation of GRB 260605A
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45031 SUBJECT: IPN triangulation of GRB 260605A DATE: 26/06/23 17:47:50 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(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, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP), J. Wei (NAOC), and B. Cordier (CEA) on behalf of the SVOM-GRM team, C. Wang (IHEP), S. Xiong (IHEP), and S. Zhang (IHEP) on behalf of the Insight-HXMT team, E. Burns on behalf of the IPN, 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 260605A (Insight-HXMT/HE detection: Zao et al., GCN 44849) was detected by Insight (HXMT/HE), SVOM (GRM), Konus-Wind, and Mars-Odyssey (HEND) at about 3868 s UT (01:04:28). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: ------------------------------ RA(2000), deg Dec(2000), deg ------------------------------ Corners: 110.4929 +37.9757 110.4379 +38.1277 108.8194 +18.8592 108.8935 +19.0360 ------------------------------ The error box area is 3003 sq. arcmin, and its maximum dimension is 20.3 deg (the minimum one is 2.6 arcmin). The Sun distance was ~27 deg. This localization may be improved. A triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB260605_T03858/IPN The HEALPix triangulation map is the multi-order HEALPix in units of probability density. View this GCN Circular online at https://gcn.nasa.gov/circulars/45031. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43245] EP260623a: Optical follow-up observations with Kinder
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45030 SUBJECT: EP260623a: Optical follow-up observations with Kinder DATE: 26/06/23 16:42:04 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> M.-H. Lee, A. Aryan, T.-W. Chen, W.-J. Hou (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), S. Yang(HNAS), A. Sankar.K, K. N.-T. Ho, A. Dutta, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, C.-S. Lin, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), K. W. Smith, H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260623a (Wang et al., GCN 45020) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in r-band started at 15:26 UTC on the 23rd of June 2026 (MJD 61214.6431), 12.53 hr after the EP-WXT detection. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. Next, we employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. In the difference image, the optical counterpart (Li et al., GCN 45021; Izzo et al., GCN 45022; Angulo et al., GCN 45024; Brivio et al., GCN 45025; Jiang et al., GCN 45026; Li et al., GCN 45027; and Jelinek et al., GCN 45029) was clearly detected. Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and measured photometry (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 61214.6431 | 12.53 | 300 * 6 | 20.74 +/- 0.07 | 1".97 | 1.91 The presented magnitudes are calibrated using the field stars from ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported magnitude is not corrected for an expected galactic extinction of A_r = 0.32 mag, in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/45030. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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