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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 17 Jun '26

17 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 17 Jun '26

17 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 17 Jun '26

17 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 17 Jun '26

17 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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[vsnet-grb-info 43183] Konus-Wind detection of GRB 260616B/EP260616a
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44968 SUBJECT: Konus-Wind detection of GRB 260616B/EP260616a DATE: 26/06/17 15:37:56 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 260616B (BALROG localization: Preis & Greiner, GCN 44951; Fermi-GBM detection: Malacaria et al., GCN 44953; EP-WXT detection: Li et al., GCN 44956; CALET-GBM detection: Asaoka et al., GCN 44966) triggered Konus-Wind at T0=25522.793 s UT (07:05:22.793). The burst light curve shows two multi-peaked emission pulses. The total duration of the burst is ~13 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260616_T25522/ As observed by Konus-Wind, the burst had the total fluence of 2.52(-0.29,+0.30)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+9.760 s, of 8.62(-1.09,+1.12)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+16.832 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.78(-0.18,+0.23), the high energy photon index beta = -2.25(-0.28,+0.16), the peak energy Ep = 279(-49,+62) keV (chi2 = 101/97 dof). The spectrum near the maximum count rate (measured from T0+8.640 to T0+16.832 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 = -1.05(-0.10,+0.11) and Ep = 382(-41,+52) keV (chi2 = 87/85 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.0 (chi2 = 87/84 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/44968. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43182] Konus-Wind detection of GRB 260616A
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44967 SUBJECT: Konus-Wind detection of GRB 260616A DATE: 26/06/17 15:37:03 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 260616A (Fermi-GBM detection: Fermi GBM team, GCN 44948; BALROG localization: Preis & Greiner, GCN 44949; Fermi-LAT detection: Lopez et al., GCN 44960; GECAM-B detection: Guo et al., GCN 44964) triggered Konus-Wind at T0=12085.625 s UT (03:21:25.625). The burst light curve shows a bright, multipeaked pulse, which starts at ~T0-63 s and has a total duration of ~292 s. A weaker possible precursor is clearly visible in the KW waiting mode data around ~T0-422 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/GRB260616_T12085/ As observed by Konus-Wind, the burst had the total fluence of 2.77(-0.09,+0.09)x10^-4 erg/cm2, and the 64-ms peak flux, measured from T0+82.880 s, of 7.35(-1.24,+1.23)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+105.984 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.76(-0.03,+0.04), the high energy photon index beta = -2.28(-0.06,+0.05), the peak energy Ep = 295(-10,+11) keV (chi2 = 118/97 dof). The spectrum near the maximum count rate (measured from T0+81.408 to T0+89.600 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.97(-0.08,+0.09), the high energy photon index beta = -2.23(-0.25,+0.15), the peak energy Ep = 379(-49,+57) keV (chi2 = 87/87 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/44967. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43181] GRB 260616B: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44966 SUBJECT: GRB 260616B: CALET Gamma-Ray Burst Monitor detection DATE: 26/06/17 15:25:21 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> Y. Asaoka (ICRR), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 260616B at 07:05:24.65 UTC on 16 June 2026 (trigger #1465628601; https://cgbm.calet.jp/cgbm_trigger/flight/1465628601/index.html) A CGBM Notice was distributed in near real time. This event was also reported by Fermi GBM (Preis et al., GCN #44951; Malacaria et al., GCN #44953). The burst signal was seen by HXM2 and SGM. The burst light curve shows a double-peaked structure starting at T-7.7 s, peaking at T+2.6 s, and ending at T+4.1 s. The T90 and T50 durations measured with the SGM data are 11.2 +/- 0.3 s and 8.1 +/- 0.2 s in the 40-1000 keV band, respectively. Einstein Probe/WXT detected an X-ray transient, EP 260616a (Li et al., GCN #44956), about 9 s before the CGBM trigger. The position of EP 260616a was marginally above the Earth horizon as seen from CALET/ISS at the trigger time, at an incident angle of 110 degrees. The ground-processed light curve is available at: https://cgbm.calet.jp/cgbm_trigger/ground/1465628601/ The CALET data used in this analysis were provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44966. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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