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

[vsnet-grb-info 42830] GRB 260523A: GECAM-B observation
by GCN Circulars 24 May '26

24 May '26

TITLE: GCN CIRCULAR NUMBER: 44701 SUBJECT: GRB 260523A: GECAM-B observation DATE: 26/05/24 12:00:37 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260523B, at 2026-05-23T19:26:02.800 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44699). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 1.6 +0.4/-0.6 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260523B.png 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/44701. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42829] Fermi GRB 260523A: Global MASTER-Net observations report
by GCN Circulars 23 May '26

23 May '26

TITLE: GCN CIRCULAR NUMBER: 44700 SUBJECT: Fermi GRB 260523A: Global MASTER-Net observations report DATE: 26/05/23 23:46:05 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260523A ( Fermi GBM team, GCN 44698) errorbox 26626 sec after notice time and 26682 sec after trigger time at 2026-05-23 23:30:53 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 61 deg. The sun altitude is -17.4 deg. The galactic latitude b = -33 deg., longitude l = 43 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3334230 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 26713 | 2026-05-23 23:30:53 | MASTER-Kislovodsk | (21h 01m 49.35s , -06d 30m 25.4s) | C | 60 | 18.3 | 26812 | 2026-05-23 23:32:32 | MASTER-Kislovodsk | (20h 55m 10.53s , -08d 23m 36.1s) | C | 60 | 18.4 | 26911 | 2026-05-23 23:34:11 | MASTER-Kislovodsk | (20h 49m 48.74s , -06d 27m 51.5s) | C | 60 | 18.1 | 27006 | 2026-05-23 23:35:46 | MASTER-Kislovodsk | (20h 58m 00.72s , -04d 36m 04.2s) | C | 60 | 18.3 | 27235 | 2026-05-23 23:39:35 | MASTER-Kislovodsk | (21h 07m 20.43s , -08d 24m 37.0s) | C | 60 | 18.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44700. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42828] GRB 260523B: Fermi GBM Final Real-time Localization
by GCN Circulars 23 May '26

23 May '26

TITLE: GCN CIRCULAR NUMBER: 44699 SUBJECT: GRB 260523B: Fermi GBM Final Real-time Localization DATE: 26/05/23 19:36:40 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 19:26:02 UT on 23 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260523B (trigger 801257167.544222 / 260523810). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 34.1, Dec = -63.1 (J2000 degrees, equivalent to J2000 02h 16m, -63d 06'), with a statistical uncertainty of 3.1 degrees. The angle from the Fermi LAT boresight is 121.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260523810/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260523810/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260523810/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44699. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42827] GRB 260523A: Fermi GBM Final Real-time Localization
by GCN Circulars 23 May '26

23 May '26

TITLE: GCN CIRCULAR NUMBER: 44698 SUBJECT: GRB 260523A: Fermi GBM Final Real-time Localization DATE: 26/05/23 16:16:46 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 16:06:10 UT on 23 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260523A (trigger 801245175.681708 / 260523671). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 315.6, Dec = -6.8 (J2000 degrees, equivalent to J2000 21h 02m, -6d 47'), with a statistical uncertainty of 5.5 degrees. The angle from the Fermi LAT boresight is 51.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260523671/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260523671/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260523671/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44698. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42826] GRB 260522A: Fermi GBM Observation
by GCN Circulars 23 May '26

23 May '26

TITLE: GCN CIRCULAR NUMBER: 44697 SUBJECT: GRB 260522A: Fermi GBM Observation DATE: 26/05/23 00:32:40 GMT FROM: Angus Jameson <abj0023(a)uah.edu> A. Jameson (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 02:15:08.78 UT on 22 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260522A (trigger 801108913/260522094), which was also detected by Fermi-LAT ( et al. 2026, GCN 44689). The Fermi GBM on-ground location is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 10 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 1.8 s (50-300 keV). The time-averaged spectrum from T0-0.7 to T0+0.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.48 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 1010 +/- 70 keV. The event fluence (10-1000 keV) in this time interval is (8.1 +/- 0.7)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.51 s in the 10-1000 keV band is 3 +/- 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/44697. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42825] EP260518a (AT2026ndp): LCO observations and Gemini-South Redshift z = 2.28
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44695 SUBJECT: EP260518a (AT2026ndp): LCO observations and Gemini-South Redshift z = 2.28 DATE: 26/05/22 14:46:39 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (Leicester), A. J. Levan (Radboud & Warwick), J. Chacón (PUC), F. E. Bauer (UTA/SSI), P. G. Jonker (Radboud), C. Rodriguez (Gemini), L. Magil (Gemini), report on behalf of a larger collaboration: We observed the optical transient AT2026ndp associated with the Einstein Probe sub-threshold event EP260518a (Liang et al., GCN 44690) using the LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) equipped with SINISTRO instruments. A series of 6x300s exposures were taken in both SDSS-r and SDSS-z bands. In both sequences the optical transient was clearly detected blended with the nearby Legacy Survey object. We carried out image subtraction against Legacy Survey images (DR 10) in both r and z band using PyZOGY (Guevel et al. 2021, Zackay et al. 2016) and obtained the following AB magnitudes, calibrated using nearby stars in the SkyMapper catalog and not corrected for Galactic extinction: r = 20.78 +/- 0.04 (midtime: 2026-05-22 09:54:14 UT, 3.84 days after trigger); z = 20.31 +/- 0.10 (midtime: 2026-05-22 09:15:40 UT, 3.81 days after trigger). We then observed the transient using the GMOS spectrograph equipped on Gemini–South. Our observations consisted of 2 x 600 s spectra taken using a 1" slit and the B480 grating, covering the wavelength range 4470-8500 Å. Observations started at 2026-05-22 09:54:13 UT (3.84 days after trigger). Continuum is detected over the entire wavelength range and a number of absorption features can be seen. We identify lines consistent with Fe II (1608, 2344, 2374, 2383, 2587), Si IV (1394, 1403), Si II 1527, C IV (1548, 1550), Al II (1670), Al III (1855, 1863), Mg I / Zn II 2026 at a redshift of z=2.28. Given the lack of detected fine structure lines or lyman alpha absorption, this redshift is strictly speaking a lower limit however we identify no other higher redshift systems and the lack of a Lyman alpha break in our spectrum sets an upper limit to the redshift of z < 2.75. We therefore conclude that z = 2.28 is likely the redshift for this event. The point-like source in the Legacy Survey noted in Liang et al. (GCN 44690) was also placed on the slit. Its spectrum is consistent with that of a Galactic M-dwarf. View this GCN Circular online at https://gcn.nasa.gov/circulars/44695. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42824] GRB 260522B: NuSTAR detection of prompt emission
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44696 SUBJECT: GRB 260522B: NuSTAR detection of prompt emission DATE: 26/05/22 17:46:34 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260522B in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-05-22T09:35:00.13 UTC, shows a detection of GRB 260522B, also detected by Fermi/GBM (Fermi GBM Team, GCN 44694) and SVOM/GRM (Burst-ID sb26052201). The NuSTAR CsI shield data are recorded at 1 Hz. We detect two peaks lasting for a total of about 100-s, consistent with the GBM lightcurve. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see evidence in the signal above 100 keV in the CZT detectors. The Fermi/GBM localization (GCN 44694) at RA = 278.65, Dec = -33.23 implies an offset from the NuSTAR boresight of 72-deg (i.e. from the side) and an offset from the geocenter of 142-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260522B Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44696. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42823] EP260518a (AT2025ndp): LCO observations and Gemini-South Redshift z = 2.28
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44695 SUBJECT: EP260518a (AT2025ndp): LCO observations and Gemini-South Redshift z = 2.28 DATE: 26/05/22 14:46:39 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (Leicester), A. J. Levan (Radboud & Warwick), J. Chacón (PUC), F. E. Bauer (UTA/SSI), P. G. Jonker (Radboud), C. Rodriguez (Gemini), report on behalf of a larger collaboration: We observed the optical transient AT2026ndp associated with the Einstein Probe sub-threshold event EP260518a (Liang et al., GCN 44690) using the LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) equipped with SINISTRO instruments. A series of 6x300s exposures were taken in both SDSS-r and SDSS-z bands. In both sequences the optical transient was clearly detected blended with the nearby Legacy Survey object. We carried out image subtraction against Legacy Survey images (DR 10) in both r and z band using PyZOGY (Guevel et al. 2021, Zackay et al. 2016) and obtained the following AB magnitudes, calibrated using nearby stars in the SkyMapper catalog and not corrected for Galactic extinction: r = 20.78 +/- 0.04 (midtime: 2026-05-22 09:54:14 UT, 3.84 days after trigger); z = 20.31 +/- 0.10 (midtime: 2026-05-22 09:15:40 UT, 3.81 days after trigger). We then observed the transient using the GMOS spectrograph equipped on Gemini–South. Our observations consisted of 2 x 600 s spectra taken using a 1" slit and the B480 grating, covering the wavelength range 4470-8500 Å. Observations started at 2026-05-22 09:54:13 UT (3.84 days after trigger). Continuum is detected over the entire wavelength range and a number of absorption features can be seen. We identify lines consistent with Fe II (1608, 2344, 2374, 2383, 2587), Si IV (1394, 1403), Si II 1527, C IV (1548, 1550), Al II (1670), Al III (1855, 1863), Mg I / Zn II 2026 at a redshift of z=2.28. Given the lack of detected fine structure lines or lyman alpha absorption, this redshift is strictly speaking a lower limit however we identify no other higher redshift systems and the lack of a Lyman alpha break in our spectrum sets an upper limit to the redshift of z < 2.75. We therefore conclude that z = 2.28 is likely the redshift for this event. The point-like source in the Legacy Survey noted in Liang et al. (GCN 44690) was also placed on the slit. Its spectrum is consistent with that of a Galactic M-dwarf. View this GCN Circular online at https://gcn.nasa.gov/circulars/44695. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42822] GRB 260522B: Fermi GBM Final Real-time Localization
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44694 SUBJECT: GRB 260522B: Fermi GBM Final Real-time Localization DATE: 26/05/22 12:01:10 GMT FROM: Cuán de Barra at UCD <cuan.debarra(a)ucdconnect.ie> The Fermi GBM team reports the detection of a likely LONG GRB "At 09:35:00.13 UT on 22 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260522B (trigger 801135305/260522399). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 278.65, Dec = -33.23 (J2000 degrees, equivalent to J2000 18h 34m, -33d 12'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 76 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260522399/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260522399/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260522399/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44694. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42821] GRB 260522A: GOTO optical upper limit
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44693 SUBJECT: GRB 260522A: GOTO optical upper limit DATE: 26/05/22 11:34:14 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, G. Ramsay, A. Kumar, R. Starling, B. P. Gompertz, S. Belkin, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, M. Pursiainen, on behalf of GOTO collaboration We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the Fermi/GBM and LAT detected GRB 260522A (Fermi GBM team, GCN 44687; Bissaldi, E., GCN 44689). Observations covering the GBM localisation area began at 2026-05-22 03:16:58 UT (+1.03h post trigger) and continued through to 2026-05-22 04:54:51 UT (+2.66h post trigger). Observations covering the LAT position were taken at 2026-05-22 04:14:26 UT (+1.99h post trigger). Images consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks (Lyman et al. 2026). We found no new transients that could be credibly associated with 260522A within the LAT localisation down to a 5-sigma depth of L<19.8 AB mag. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44693. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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