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[vsnet-grb-info 43268] GRB 260628A: Fermi GBM Final Real-time Localization
by GCN Circulars 28 Jun '26

28 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45053 SUBJECT: GRB 260628A: Fermi GBM Final Real-time Localization DATE: 26/06/28 22:03:44 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 SHORT GRB At 21:51:24 UT on 28 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260628A (trigger 804376289.020238 / 260628911). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 308.2, Dec = -6.9 (J2000 degrees, equivalent to J2000 20h 32m, -6d 54'), with a statistical uncertainty of 14.3 degrees. The angle from the Fermi LAT boresight is 63.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260628911/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260628911/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260628911/… View this GCN Circular online at https://gcn.nasa.gov/circulars/45053. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43267] The EP-WXT trigger 01709272671 is likely a flaring star
by GCN Circulars 28 Jun '26

28 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45052 SUBJECT: The EP-WXT trigger 01709272671 is likely a flaring star DATE: 26/06/28 02:08:13 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. P. Chen (SYSU), K. J. Zhang, D. Zhu (YNU), Y. J. Yi (BNU), Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709272671 at the time of 2026-06-27T17:53:04 (UTC), is likely a stellar flare associated with RX J1942.2-2045. The estimated flux of the flare is around 1.6 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4.8 x 10^(30) erg/s. 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/45052. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43266] EP260626a: further Liverpool Telescope optical upper limits
by GCN Circulars 27 Jun '26

27 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45051 SUBJECT: EP260626a: further Liverpool Telescope optical upper limits DATE: 26/06/27 17:25:38 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of EP260626a (Chen et al., GCN 45047; Chen et al., GCN 45050) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x150s exposures in SDSS r and z filters, starting at 2026-06-27 01:59:23 UT, approximately 20.57 hours after EP trigger. The stacked exposures were subtracted from PanSTARRS reference imaging using custom PSF-matching image subtraction code utilising Swarp, SourceExtractor, and PSFex. We do not detect any new sources in the error EP/WXT region (Chen et al., GCN 45047), including at the position of the uncatalogued X-ray source reported by Chen et al. (GCN 45047), down to 3 sigma upper limits of r> 23.44 and z> 22.94. This is consistent with upper limits from Eyles-Ferris et al. (GCN 45048) and Magnani et al. (GCN 45049). The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/45051. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43265] EP260626a: EP-FXT follow-up observation
by GCN Circulars 27 Jun '26

27 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45050 SUBJECT: EP260626a: EP-FXT follow-up observation DATE: 26/06/27 15:28:42 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. P. Chen (SYSU), K. J. Zhang, D. Zhu (YNU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of EP260626a (J. P. Chen et al., GCN 45047) approximately 10.8 hours after the WXT detection, with an exposure time of 6.1 ks. An uncatalogued X-ray source was detected within the WXT error circle at R.A. = 277.4479, Dec. = 21.2498 (J2000), with a positional uncertainty of 10.0 arcsec (radius, 90% C.L. statistical and systematic). The FXT spectrum can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 2.04 x 10^21 cm^-2 and a photon index of 2.13 (+0.6, -0.6). The derived unabsorbed 0.5-10 keV flux is approximately 9.3 (+4.5, -2.1) x 10^-14 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. No optical counterpart has been detected (R. A. J. Eyles-Ferris et al., GCN 45048; Francesco Magnani et al., GCN 45049). 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/45050. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43264] EP260526a: COLIBRÍ optical upper limit
by GCN Circulars 27 Jun '26

27 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45049 SUBJECT: EP260526a: COLIBRÍ optical upper limit DATE: 26/06/27 10:31:22 GMT FROM: F. Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Fredd Sánchez Álvarez (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Alan M. Watson (UNAM) report: We imaged the field of the EP 260526a (J.P. Chen et al., GCN Circ. 45047) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-27T07:56:30 to 09:19:26 UTC (from 26.5 to 27.9 hours after the trigger) and obtained 64 minutes of simultaneous exposure in the r, z filters. The data were reduced, coadded, and analysed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the WXT source position (J.P. Chen et al., GCN Circ. 45047) down to the following 3-sigma limit: r > 23.87 z > 23.15 This upper limit is consistent with the one reported by R. A. J. Eyles-Ferris et al., GCN Circ. 45048. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/45049. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43263] EP260626a: Liverpool Telescope upper limits
by GCN Circulars 27 Jun '26

27 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45048 SUBJECT: EP260626a: Liverpool Telescope upper limits DATE: 26/06/27 08:25:50 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), J. Sanchez-Sierras (Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), report on behalf of a larger collaboration: We observed the field of the Einstein Probe fast X-ray transient EP260626a (Chen et al., GCN 45047) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x150 s exposures in each of the SDSS r’ and z’ filters starting at 2026-06-27 02:24:23 UT, approximately 21 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Within the EP/WXT localisation, we detect no new sources in any of the bands. We derive the following 3-sigma upper limits for our stacked images. Our photometry is calibrated to PanSTARRS and not corrected for Galactic extinction. | t_mid (hours) | Filter | AB magnitude | | ------------- | ------ | ------------ | | 21.13 | r’ | >22.89 | | 21.44 | z’ | >22.37 | View this GCN Circular online at https://gcn.nasa.gov/circulars/45048. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43262] EP260626a: EP-WXT detection of a fast X-ray transient
by GCN Circulars 26 Jun '26

26 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45047 SUBJECT: EP260626a: EP-WXT detection of a fast X-ray transient DATE: 26/06/26 15:13:06 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J.P. Chen (SYSU), K. J. Zhang, D. Zhu (YNU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient, designated EP260626a, 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 was detected in the WXT observation starting at 2026-06-26T05:25:04 (UTC). A significant flare was detected in the source light curve, which started before the beginning of the observation and ended approximately 100 seconds after the start of the observation. The position of the transient is R.A. = 277.4417 deg, Dec. = 21.2403 deg (J2000), with an uncertainty radius of 2.7 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 2.04×10^21 cm^-2 and a photon index of 1.93 (-0.4/+0.42). The derived average unabsorbed 0.5-4 keV flux is 8.02 (-1.7/+2.1) 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/45047. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43261] Konus-Wind detection of GRB 260623B / EP260623a
by GCN Circulars 26 Jun '26

26 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45046 SUBJECT: Konus-Wind detection of GRB 260623B / EP260623a DATE: 26/06/26 15:11:51 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A.Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260623B was detected by Konus-Wind (KW) in the waiting mode at about T0 = T0(EP) = 10445 s UT (02:54:05). A Bayesian block analysis of the KW waiting mode data in the 20-300 keV band reveals a ~10 sigma count-rate increase in the interval from T0-259 s to T0+327 s. The burst overlaps in time with EP260623a (EP-WXT detection: Wang et al., GCN 45020; Wang et al., GCN 45035) and the KW ecliptic latitude response is consistent with the EP260623a localization. The positional and temporal coincidence of GRB 260623B with the EP260623a supports the conclusion that both events have a common origin. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB260623B The total burst fluence is 8.2(-1.2,+1.2)x10^-6 erg/cm^2, and the 2.944 s peak energy flux, measured from T0+3.366 s, is 0.7(-0.3,+0.4)x10^-7 erg/cm^2/s. (both in the 20 keV - 1500 keV energy range). The time-integrated spectrum of the burst, measured from T0-258.650 s to T0+327.206 s, can be described by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha > -1.16 and Ep = 76(-8,+28) keV. The spectrum near the maximum count rate (measured from T0-2.522 to T0+38.694 s) can be described with the CPL model with alpha > -1.42 and Ep = 87(-15,+83) keV. Assuming the redshift z=0.703 (Izzo et al., GCN 45022) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 1.13(-0.16,+0.24)x10^52 erg, the peak luminosity L_iso is 1.71(-0.72,+0.97)x10^50 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 130(-14,+47) keV and the spectrum near the maximum count rate Ep,p,z is 148(-26,+143) keV. With the obtained estimates, GRB 260623B is inside the 68% prediction band for the 'Amati' and inside the 90% prediction band for the 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB260623B/GRB260623B_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/45046. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43260] EP260623a: TNG NIR afterglow detection
by GCN Circulars 25 Jun '26

25 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45045 SUBJECT: EP260623a: TNG NIR afterglow detection DATE: 26/06/25 15:50:24 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio (INAF-OAB), M. Ferro (INAF-OAB), L. Izzo (INAF-OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), A. Melandri (INAF-OAR), V. Lorenzi (INAF-TNG), A. G. de Gurtubai Escudero (INAF-TNG) report on behalf of the CIBO collaboration: We observed the field of EP260623a detected by EP/WXT (Wang et al., GCN 45020) with the Italian 3.6m TNG telescope equipped with the near-infrared camera NICS to follow up its afterglow. A series of images were obtained with the K filter starting on 2026-06-25 at 01:29:13 UT (i.e. 1.94 days after the trigger). The afterglow (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; Saikia et al., GCN 45034; Bochenek & Perley, GCN 45040; Busmann et al., GCN 45042) is detected in the co-added image with a preliminary magnitude of K = 19.9 +/- 0.2 mag (Vega; calibrated against the 2MASS catalogue), at a mid-time of 1.96 days after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/45045. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43259] GRB 260618A: Fermi GBM Observation
by GCN Circulars 25 Jun '26

25 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45044 SUBJECT: GRB 260618A: Fermi GBM Observation DATE: 26/06/25 13:02:58 GMT FROM: Christian Malacaria at INAF-OAR <cmalacaria.astro(a)gmail.com> C. Malacaria (INAF-OAR) and R. Sonawane (IISER, TVM) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 06:45:34.28 UT on 18 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260618A (trigger 803457939/260618282). Final Real-time localization was reported in GCN 44973. A possible afterglow is detected by EP (Yang et al., GCN 44978, Jiang et al., GCN 44991). The GBM light curve consists of a variable emission episode with a duration (T90) of about 140 s (50-300 keV). The time-averaged spectrum from T0-17 to T0+150 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.4 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 43 +/- 2 keV. The event fluence (10-1000 keV) in this time interval is (5.9 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+25 s in the 10-1000 keV band is 2.7 +/- 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/45044. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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