June 2026 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 43193] EP260618a: EP-WXT detection of an X-ray transient
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44978 SUBJECT: EP260618a: EP-WXT detection of an X-ray transient DATE: 26/06/18 15:21:15 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), S. Q. Jiang (NAO, CAS), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient, designated EP260618a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission through the ground data analysis. The transient was detected in one WXT observation starting at 2026-06-18T08:34:46 (UTC). No significant variability was detected during the 2.7 ks exposure. The position of the transient is R.A. = 276.676 deg, Dec. = 23.849 deg (J2000), with an uncertainty radius of 2.5 arcmin (90% confidence level, including both statistical and systematic uncertainties). There is no historical X-ray source in the WXT error circle. The average 0.5-4 keV spectrum can be fitted by an absorbed power law with a fixed Galactic hydrogen column density of 1.32^21 cm^-2 and a photon index of 1.4 (-0.4/+0.5). The derived average unabsorbed 0.5-4 keV flux is 6.9 (-1.7/+2.1) x 10^(-11) erg cm^-2 s^-1. The position of EP260618a falls within the error circle of GRB 260618A reported by Fermi/GBM (GCN 44973), suggesting that EP260618a may be the X-ray afterglow of GRB 260618A. Follow-up observation with the Follow-up X-ray Telescope (FXT) onboard EP has been scheduled. 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/44978. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43192] GRB 260610B: AbAO optical observations
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44977 SUBJECT: GRB 260610B: AbAO optical observations DATE: 26/06/18 10:47:10 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> N. Pankov (IKI), R. Ya. Inasaridze (AbAO), A. Moskvitin (SAO RAS), V. Aivazyan (AbAO), A. Pozanenko (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 260610B (The Fermi GBM team, GCN 44891; GCN 44901) with the AS-32 70-cm telescope of the Abastumani Astrophysical Observatory (AbAO). We acquired a series of 98x60 sec images in the R-band using a CCD-photometer, starting on 2026-06-12 20:18 UT (i.e. 1.856 days since trigger). The OT (O'Neill et al., GCN 44903; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCN 44910; Akl et al., GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918; Jackson-Horne et al., GCN 44919; Izzo, GCN 44920; Li et al., GCN 44921; Bochenek and Perley, GCN 44927; Moskvitin et al., GCN 44929; Akl et al., GCN 44930; Bochenek & Perley, GCN 44932; Pankov et al., GCN 44946; Gillanders et al., GCN 44955; Angulo et al., GCN 44958; Dimple et al., GCN 44959; Moskvitin et al., GCN 44963) is detected in the co-add image of 96x60 sec. The observational properties and preliminary photometry are provided further: Date UTstart t-T0 Exp. Filter Mag Err UL (mid,d) (n*s) (3-sigma) 2026-06-12 20:18:50 1.88931 96x60 R 20.59 0.10 22.0 The photometry is based on nearby SDSS stars (R-magnitudes obtained via Lupton 2005 transformation equations; Moskvitin et al., GCN 44918) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44977. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43191] EP260616a/GRB 260616B: EP-FXT follow-up observation
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44976 SUBJECT: EP260616a/GRB 260616B: EP-FXT follow-up observation DATE: 26/06/18 10:37:23 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. Y. Li, T. Y. Liu (NAO, CAS), J. H. WU(GZHU), Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe team EP-FXT performed a follow-up observation of EP260616a/GRB 260616B (Li et al., GCN 44956; Preis & Greiner, GCN 44951; Malacaria et al., GCN 44953; Asaoka et al., GCN 44966) about 25.5 hours after the WXT detection, with an exposure time of 6.2 ks. An uncatalogued source was detected within the WXT error circle at R.A. = 256.0839, DEC = -32.3007 (J2000) with an uncertainty of 10 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 3.4 x 10^21 cm^-2 and a photon index of 1.62 (+0.27, -0.26). The derived unabsorbed 0.5-10 keV flux is approximately 8.7 (+2.2, -1.7) x 10^-13 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. No optical counterpart have been detected (Mandarakas et al., GCN 44965). Further EP-FXT follow-up observations will be arranged. 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/44976. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43190] GRB 260506B: cubesat Avion detection
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44975 SUBJECT: GRB 260506B: cubesat Avion detection DATE: 26/06/18 09:57:49 GMT FROM: Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> From Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report: At 2026-05-06 ~13:07:28 UT the long-duration GRB 260506B (Fermi GBM detection: GCN #44484, AstroSat CZTI detection: GCN #44503, Glowbug detection: GCN #44559) was detected by the DeCoR-3 instrument on the cubesat Avion of the Moscow University project “Sozvezdie-270” [1]. Total amount of photons detected by Avion is 428 (energy band >30 keV), it corresponds to a fluence of ~3.8*10^(-6) erg/cm^2 in the range 30-500 keV. LC in the energy range of 30-500 keV has a multiple peak structure including a faint peak of ~1 s duration at ~13:07:29 with a maximum flux of ~60 phot/(cm^2*s) and a main peak of ~5 s duration at ~13:07:40 with a maximum flux of ~80 phot/(cm^2*s) at ~13:07:42 UT. А total duration (T90) of the burst is ~15 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260506B_LC_Avion.png Parameters of GRB 260506B as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion is one of 5 cubesats of the Moscow University project “Sozvezdie-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s. [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282 View this GCN Circular online at https://gcn.nasa.gov/circulars/44975. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43189] GRB 260616C: GECAM-B observation of a burst
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44974 SUBJECT: GRB 260616C: GECAM-B observation of a burst DATE: 26/06/18 07:27:43 GMT FROM: renyz16607(a)163.com Yang-Zhao Ren, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 260616C, at 2026-06-16T14:47:01.950 UTC (denoted as T0), which is also detected by MAXI/GSC (Iwakiri et al., GCN #44961). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a pulse with a duration (T90) of 29.5 +3.5/-4.5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260616C.png The time-averaged spectrum from T0-4 s to T0+8 s is best fitted by a power law function. The power law index is -2.32 +0.16/-0.13. The event fluence (10-1000 keV) in this time interval is (1.99 +0.30/-0.26)E-04 erg/cm^2. 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/44974. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43188] GRB 260618A: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44973 SUBJECT: GRB 260618A: Fermi GBM Final Real-time Localization DATE: 26/06/18 06:56:28 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 06:45:34 UT on 18 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260618A (trigger 803457939.281242 / 260618282). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 281.5, Dec = 21.1 (J2000 degrees, equivalent to J2000 18h 45m, 21d 06'), with a statistical uncertainty of 6.3 degrees. The angle from the Fermi LAT boresight is 72.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260618282/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260618282/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260618282/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44973. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43187] GRB 260617A: Fermi GBM Detection
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44972 SUBJECT: GRB 260617A: Fermi GBM Detection DATE: 26/06/18 05:18:48 GMT FROM: Matt Godwin <msg0028(a)uah.edu> Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 21:36:43.68 UT on 17 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260617A (trigger 803425008/260617900). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 224.34, Dec = -12.61 (J2000 degrees, equivalent to J2000 15h 47m, -16d 43'), with a statistical uncertainty of 7.08 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 99 degrees. The GBM light curve consists of a short, bright burst with a duration (T90) of about 0.14 s (50-300 keV). The time-averaged spectrum from T0-0.08 to T0+0.259 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.56 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 700 +/- 40 keV. The event fluence (10-1000 keV) in this time interval is (7.4 +/- 0.5)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 21 +/- 1 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/44972. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43186] GRB 260616A: Fermi GBM Observation
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44971 SUBJECT: GRB 260616A: Fermi GBM Observation DATE: 26/06/18 02:49:59 GMT FROM: Matt Godwin <msg0028(a)uah.edu> Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 03:21:54.33 UT on 16 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260616A (trigger 803272919/260616140), which was also detected by Fermi-LAT ( et al. 2026, GCN 44960). The Fermi GBM on-ground location is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 111 degrees. The GBM light curve consists of one long burst with a duration (T90) of about 69 s (50-300 keV). The time-averaged spectrum from T0+0.3 to T0+74.1 s is best fit by a Band function with Epeak = 246 +/- 1 keV, alpha = -0.63 +/- 0.01, and beta = -2.00 +/- 0.01. The event fluence (10-1000 keV) in this time interval is (1.22 +/- 0.02)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+50 s in the 10-1000 keV band is 16.9 +/- 0.4 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/44971. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43185] GRB 260617A: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44970 SUBJECT: GRB 260617A: Fermi GBM Final Real-time Localization DATE: 26/06/17 21:51:34 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 21:36:43 UT on 17 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260617A (trigger 803425008.678884 / 260617900). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 236.9, Dec = -16.7 (J2000 degrees, equivalent to J2000 15h 47m, -16d 41'), with a statistical uncertainty of 12.7 degrees. The angle from the Fermi LAT boresight is 100.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260617900/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260617900/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260617900/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44970. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43184] GRB 260617A: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Jun '26

18 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44969 SUBJECT: GRB 260617A: Fermi GBM Final Real-time Localization DATE: 26/06/17 21:49:10 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 21:36:43 UT on 17 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260617A (trigger 803425008.678884 / 260617900). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 236.9, Dec = -16.7 (J2000 degrees, equivalent to J2000 15h 47m, -16d 41'), with a statistical uncertainty of 12.7 degrees. The angle from the Fermi LAT boresight is 100.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260617900/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260617900/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260617900/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44969. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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