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

[vsnet-grb-info 42852] GRB 260526A: GECAM-B observation
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44723 SUBJECT: GRB 260526A: GECAM-B observation DATE: 26/05/28 13:17:55 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 260526A, at 2026-05-26T23:04:00.200 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44707). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 42 +/-6 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260526A.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/44723. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42851] Konus-Wind detection of GRB 260527A (short/hard) ~4 min before EP260527a
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44722 SUBJECT: Konus-Wind detection of GRB 260527A (short/hard) ~4 min before EP260527a DATE: 26/05/28 12:11:41 GMT FROM: Dmitry Svinkin at Ioffe Institute <dmitrysvinkin(a)gmail.com> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The short-duration GRB 260527A triggered Konus-Wind at T0=22572.142 s UT (06:16:12.142). The burst light curve shows a multi-peaked structure which starts at ~T0-0.1 s and has a total duration of ~0.2 s. The emission is seen up to ~10 MeV. The burst occurred ~4 min before the Einstein Probe detection of EP260527a (Yang et al., GCN 44718), and also the KW ecliptic latitude response is consistent with the EP260527a position. This suggests a common origin of two events, which will be further investigated. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260527_T22572/ As observed by Konus-Wind, the burst had the total fluence of 1.99(-0.46,+0.57)x10^-6 erg/cm2, and the 16-ms peak flux, measured from T0-0.008 s, of 3.09(-1.06,+1.28)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+0.064 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 = -0.67(-0.36,+0.46), the high energy photon index beta = -2.13(-0.85,+0.36), the peak energy Ep = 541(-204,+367) keV (pgstat = 33/45 dof). A power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.79(-0.42,+0.49) and Ep = 670(-240,+1097) keV fits this spectrum equally well (pgstat = 35/46 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/44722. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42850] EP260526a: EP-FXT follow-up observation
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44721 SUBJECT: EP260526a: EP-FXT follow-up observation DATE: 26/05/28 08:53:38 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), B. T. Wang (YNAO, CAS), D. F. Hu (PMO, CAS), J. P. Feng, B. Zhang (USTC), D. Zhu, K. J. Zhang (YNU) and W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of EP260526a (detected by EP-WXT, GCN 44712; and followed by LCO, GCN 44713) about 27 hours after the WXT detection, with an exposure time of 6 ks. The FXT telemetry data show that an uncatalogued source was detected within the WXT error circle at R.A. = 236.0897, DEC = -23.7507 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 2.13 x 10^21 cm^-2 and a photon index of 1.8 (+1.5/-1.0). The derived unabsorbed 0.5-10 keV flux is approximately 5.2 (+5.2/-2.7) x 10^-14 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/44721. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42849] EP260527a: SVOM/VT optical observation
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44720 SUBJECT: EP260527a: SVOM/VT optical observation DATE: 26/05/28 07:13:15 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, Y. L. Qiu, L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) and J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations to the field of EP260527a triggered by Einstein Probe (Yang et al., GCN 44718). The observation started at 2026-05-28T02:57:38 UTC, 20.63 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Aguilar-Ruiz et al., GCN 44719) was detected by VT in both channels. The following measurements are in the AB magnitude without correction for Galactic extinction: Mid time | Band | Exposure Time | Brightness 21.76 h VT_B 29*50 s 22.32 +/- 0.22 mag 21.81 h VT_R 23*50 s 21.77 +/- 0.19 mag The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44720. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42848] EP260527a: COLIBRÍ optical detection
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44719 SUBJECT: EP260527a: COLIBRÍ optical detection DATE: 26/05/28 06:36:51 GMT FROM: Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Edilberto Aguilar-Ruiz (UNAM), Francesco Magnani (CPPM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (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), Fredd Sánchez Álvarez (UNAM), and Benjamin Schneider (LAM) and report: We imaged the field of the EP260527a (J. Yang et al, GCN Circ. 44718) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-28 04:13 to 06:05 UTC (from 21.90 to 23.76 hours after the trigger) and obtained 18, 62, and 82 minutes of exposure in the g, r, and z filters. The data were reduced and coadded with the COLIBRÍ ASU 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 this case with a relatively high value of A_v = 1.1 mag, according to Schlafly et al. 2011). In the stacked images, we detect an uncatalogued source within the FXT uncertainty region at: RA (J2000) = 12:52:13.13 = 193.05473 degrees Dec (J2000) = +01:28:56.8 = 1.48244 degrees The preliminary magnitudes derived for that source is: g = 22.25 +/- 0.32, r = 22.19 +/- 0.17, z = 21.52 +/- 0.15. The detection in g suggests that it is not a high-redshift event. Further observations are ongoing. 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/44719. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42847] EP260527a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44718 SUBJECT: EP260527a: Einstein Probe detection of a fast X-ray transient DATE: 26/05/28 03:21:10 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), B. T. Wang (YNAO, CAS), D. F. Hu (PMO, CAS), J. P. Feng, B. Zhang (USTC), D. Zhu, K. J. Zhang (YNU) and W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260527a. The transient triggered EP-WXT (ID: 01709266119) at 2026-05-27T06:19:54 (UTC). The WXT position of the source is R.A. = 193.057 deg, DEC = 1.473 deg (J2000) with an uncertainty of 2.3 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the event started at 2026-05-27T06:16:18 (UTC) and lasted for about 200 seconds. The average WXT 0.5-4.0 keV spectrum can be fitted with an absorbed powerlaw model, with a fixed Galactic hydrogen column density of 1.57 x 10^20 cm^-2 and a photon index of 0.73(+0.44/-0.42). The unabsorbed 0.5-4.0 keV flux is 1.12(+0.33/-0.28) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. This event did not trigger the Follow-up X-ray Telescope (FXT) autonomous follow-up. A follow-up observation with the FXT was performed about 20.5 hours after the WXT detection. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 193.0519 deg, DEC = 1.4832 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data are received. 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/44718. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42846] The EP-WXT trigger 01709266172 is likely a flaring star
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44717 SUBJECT: The EP-WXT trigger 01709266172 is likely a flaring star DATE: 26/05/28 01:48:41 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), D. Zhu, K.-J. Zhang (YNU), D.-F. Hu (PMO, CAS), M.-H. Zhang and Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709266172 at the time of 2026-05-28T01:30:15, is likely a stellar flare associated with CD-33 8642 (High Proper Motion Star). The estimated flux of the flare is around 6 x 10^(-11) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 6.5 x 10^(31) 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/44717. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42845] The EP-WXT trigger 01709266147 is likely a flaring star
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44716 SUBJECT: The EP-WXT trigger 01709266147 is likely a flaring star DATE: 26/05/28 01:10:19 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), D. Zhu, K.-J. Zhang (YNU), D.-F. Hu (PMO, CAS), M.-H. Zhang and Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709266147 at the time of 2026-05-27T19:27:35, is likely a stellar flare associated with UCAC4 262-085424 (Young Stellar Object Candidate). 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 3.9 x 10^(32) 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/44716. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42844] Fermi trigger No 801580882: Global MASTER-Net observations report
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44715 SUBJECT: Fermi trigger No 801580882: Global MASTER-Net observations report DATE: 26/05/27 23:32:27 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), M. Segura, 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 GRB260527.56 (trigger No 801580882,04h 33m 31.92s , +25d 09m 00.0s, R=34.02) errorbox 32285 sec after notice time and 32319 sec after trigger time at 2026-05-27 22:19:57 UT, with upper limit up to 16.2 mag. The observations began at zenith distance = 79 deg. The sun altitude is -22.7 deg. MASTER-Tavrida robotic telescope located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB260527.56 errorbox 35876 sec after notice time and 35911 sec after trigger time at 2026-05-27 23:19:48 UT, with upper limit up to 14.4 mag. The observations began at zenith distance = 79 deg. The sun altitude is -20.1 deg. The galactic latitude b = -15 deg., longitude l = 174 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3342387 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 32350 | 2026-05-27 22:19:57 | MASTER-Kislovodsk | (02h 18m 21.64s , +48d 14m 30.3s) | C | 60 | 15.8 | 32548 | 2026-05-27 22:23:15 | MASTER-Kislovodsk | (02h 42m 51.73s , +50d 08m 35.3s) | C | 60 | 15.6 | 32648 | 2026-05-27 22:24:55 | MASTER-Kislovodsk | (02h 13m 21.39s , +46d 22m 36.9s) | C | 60 | 14.4 | 32856 | 2026-05-27 22:28:22 | MASTER-Kislovodsk | (02h 36m 35.69s , +48d 14m 11.1s) | C | 60 | 15.2 | 33178 | 2026-05-27 22:33:44 | MASTER-Kislovodsk | (02h 08m 47.36s , +44d 29m 27.5s) | C | 60 | 14.9 | 33494 | 2026-05-27 22:39:01 | MASTER-Kislovodsk | (02h 30m 48.83s , +46d 22m 41.4s) | C | 60 | 15.0 | 33817 | 2026-05-27 22:44:24 | MASTER-Kislovodsk | (02h 04m 47.76s , +42d 34m 55.9s) | C | 60 | 14.8 | 34202 | 2026-05-27 22:50:49 | MASTER-Kislovodsk | (02h 25m 46.25s , +44d 28m 34.2s) | C | 60 | 13.9 | 34313 | 2026-05-27 22:52:40 | MASTER-Kislovodsk | (02h 54m 41.12s , +48d 16m 38.9s) | C | 60 | 14.7 | 34422 | 2026-05-27 22:54:29 | MASTER-Kislovodsk | (02h 00m 58.83s , +40d 43m 24.4s) | C | 60 | 14.8 | 34722 | 2026-05-27 22:59:28 | MASTER-Kislovodsk | (02h 48m 29.20s , +46d 22m 19.9s) | C | 60 | 14.9 | 34843 | 2026-05-27 23:01:30 | MASTER-Kislovodsk | (02h 21m 06.32s , +42d 36m 37.1s) | C | 60 | 15.3 | 34940 | 2026-05-27 23:03:07 | MASTER-Kislovodsk | (01h 57m 39.49s , +38d 48m 17.6s) | C | 60 | 15.3 | 35715 | 2026-05-27 23:16:02 | MASTER-Kislovodsk | (02h 16m 57.39s , +40d 42m 08.4s) | C | 60 | 16.2 | 35941 | 2026-05-27 23:19:48 | MASTER-Tavrida | (03h 04m 17.85s , +49d 18m 29.0s) | C | 60 | 14.4 | 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/44715. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42843] GRB 260524A: SVOM/ECLAIRs detection of a burst through on-ground search
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44714 SUBJECT: GRB 260524A: SVOM/ECLAIRs detection of a burst through on-ground search DATE: 26/05/27 17:11:22 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP), S. Schanne, N. Dagoneau (CEA), report on behalf of the SVOM/ECLAIRs team The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 260524A, starting at 2026-05-24T12:01:52 UTC (trigger time T0) through an on-ground search with the event-by-event data downloaded through the X-band ground station. The burst was detected within several energy ranges and timescales. The best detection is obtained by the Image Trigger with a signal-to-noise ratio of 9.5 within 4-20 keV over a time window of 20.48 seconds starting at T0-20.48s. The burst shows a single peak lightcurve in the event-by-event data. The burst duration is estimated to be about 36 s in the 4-20 keV energy band through imaging. We note that just before the trigger, the source was masked by the Earth, so that part of the GRB emission may not have been observed by ECLAIRs. The localization of the source is RA, Dec = 115.192, -55.287 degrees: RA (J2000) = 07h 40m 46.1s Dec (J2000) = −55d17m13.2s with a 90% C.L. radius of 10.1 arcmin (including systematic error of 6 arcmin added in quadrature). We note that no bright catalogued X-ray sources are found in the error box. The time-averaged spectrum from T0-32 s to T0+4 s in the energy range 5-50 keV is best fitted by a blackbody model with kT = 2.63 +/-0.27. With this model, the 4-120 keV fluence is (3.3 +0.2/-0.7) e-7 erg/cm² and the 4-120 keV photon flux is 0.63 +0.04/-0.13 ph/cm²/s. We note that a powerlaw model does not give a good fit. Other models such as broken power-law and power-law with an exponential cutoff do not yield constrained parameters. The spectral parameters indicate that this GRB is very soft and should probably be classified as an X-Ray Flash. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44714. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42842] EP260526a: LCO optical upper limits
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44713 SUBJECT: EP260526a: LCO optical upper limits DATE: 26/05/27 12:19:35 GMT FROM: Agnes van Hoof at Radboud University <agnes.vanhoof(a)ru.nl> A. P. C. van Hoof (Radboud), R. A. J. Eyles-Ferris (Leicester), J. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), J. A. Chacón (PUC), F. E. Bauer (SSI and UTA), report on behalf of a larger collaboration: We observed the field of the X-ray transient EP260526a (Yang et al, GCN 44712) using LCO 1m telescopes located at the Cerro Tololo observatory equipped with SINISTRO instruments. A series of 5x300 s exposures were taken using the SDSS-r filter and 3x300 s using the SDSS-z filter, starting on 2026-05-27 at 08:07:52 UT (i.e., ~1.4 days after the first X-ray detection). No new source is detected within the EP/WXT uncertainty region compared with the Legacy and Pan-STARRS surveys. From the stacked images, we obtain the following 3-sigma upper limits, consistent with those reported by Becerra et al. (GCN 44710):  r > 22.5 z > 20.6 These upper limits are in AB magnitudes, calibrated using nearby stars from the Pan-STARRS catalogue, and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44713. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42841] EP260526a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44712 SUBJECT: EP260526a: Einstein Probe detection of a fast X-ray transient DATE: 26/05/27 07:03:44 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), B. T. Wang (YNAO, CAS), D. F. Hu (PMO, CAS), J. P. Feng, B. Zhang (USTC), D. Zhu, K. J. Zhang (YNU) and W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260526a. The transient did not trigger the onboard unit, a GCN notice (ID: 06800001478) was sent manually. The WXT position of the source is R.A. = 236.063 deg, DEC = -23.771 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the event started at 2026-05-26T09:43:34 (UTC) and lasted for about 140 seconds. The average WXT 0.5-4.0 keV spectrum can be fitted with an absorbed powerlaw model, with a fixed Galactic hydrogen column density of 2.13 x 10^21 cm^-2 and a photon index of 1.98 (+0.78/-0.70). The unabsorbed 0.5-4.0 keV flux is 8.2 (+2.8/-2.2) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT observations are scheduled. Additional information will be updated when the telemetry data are received. 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/44712. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42840] GRB 260525A: AstroSat CZTI detection
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44711 SUBJECT: GRB 260525A: AstroSat CZTI detection DATE: 26/05/27 06:38:46 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), A. Goyal (IITB), A. Arya (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260525A which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44703). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-25 23:33:44.45 UTC. The measured peak count rate associated with the burst is 209 (+36, -36) counts/s above the background in the combined data of four quadrants, with a total of 259 (+56, -54) counts. The local mean background count rate was 728 (+177, -140) counts/s. Using cumulative rates, we measure a T90 of 8 (+2, -2) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/517448022.55/S517448022.55_det… CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/44711. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42839] EP260526.405: COLIBRÍ optical upper limits
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44710 SUBJECT: EP260526.405: COLIBRÍ optical upper limits DATE: 26/05/27 06:34:35 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (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), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Benjamin Schneider (LAM) and report: We imaged the field of the EP260526.405 (ID=06800001478) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-27 05:30 to 06:06 UTC (from 19.79 to 20.39 hours after the trigger, beginning 32 seconds after the notice was received) and obtained 29 minutes of simultaneous exposure in the r/z filters. The data were reduced and coadded with the ASU 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 this case with a relatively high value of A_v = 1.1 mag, according to Schlafly et al. 2011). In the stacked image, we do not detect any new source at the WXT source position down to the following 5-sigma limit: r > 22.5 z > 21.6 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/44710. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42838] The EP-WXT trigger 01709266106 is not a real source
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44709 SUBJECT: The EP-WXT trigger 01709266106 is not a real source DATE: 26/05/27 03:40:10 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. P. Feng, B. Zhang (USTC), J. Yang (ZZU), B.T. Wang (YNAO, CAS), D. Zhu, K. J. Zhang (YNU), D. F. Hu (PMO, CAS), W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: The Einstein Probe Wide-field X-ray Telescope (EP-WXT) trigger 01709266106, detected at 2026-05-26T17:37:56 and followed by GCN 44705 and GCN 44706, was not a real astrophysical source. View this GCN Circular online at https://gcn.nasa.gov/circulars/44709. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42837] Fermi GRB 260526A: Global MASTER-Net observations report
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44708 SUBJECT: Fermi GRB 260526A: Global MASTER-Net observations report DATE: 26/05/27 00:32:25 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-Tavrida robotic telescope [1] located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 260526A ( Fermi GBM team, GCN 44707) errorbox 872 sec after notice time and 1002 sec after trigger time at 2026-05-26 23:20:42 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 79 deg. The sun altitude is -20.1 deg. The galactic latitude b = -14 deg., longitude l = 143 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3341266 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 1032 | 2026-05-26 23:20:42 | MASTER-Tavrida | (02h 40m 21.49s , +46d 38m 05.4s) | C | 60 | 14.9 | 1113 | 2026-05-26 23:22:03 | MASTER-Tavrida | (02h 25m 12.72s , +46d 35m 35.0s) | C | 60 | 12.0 | 3275 | 2026-05-26 23:58:05 | MASTER-Tavrida | (02h 32m 55.74s , +43d 58m 52.2s) | C | 60 | 16.5 | 4690 | 2026-05-27 00:21:40 | MASTER-Tavrida | (02h 36m 20.55s , +45d 17m 15.2s) | C | 60 | 16.8 | 4769 | 2026-05-27 00:22:59 | MASTER-Tavrida | (02h 15m 28.16s , +42d 39m 11.4s) | C | 60 | 17.1 | 4848 | 2026-05-27 00:24:17 | MASTER-Tavrida | (02h 12m 43.82s , +41d 19m 58.6s) | C | 60 | 16.9 | 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/44708. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42836] GRB 260526A: Fermi GBM Final Real-time Localization
by GCN Circulars 26 May '26

26 May '26

TITLE: GCN CIRCULAR NUMBER: 44707 SUBJECT: GRB 260526A: Fermi GBM Final Real-time Localization DATE: 26/05/26 23:14:33 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 23:04:00 UT on 26 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260526A (trigger 801529445.20122 / 260526961). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 40.1, Dec = 43.9 (J2000 degrees, equivalent to J2000 02h 40m, 43d 53'), with a statistical uncertainty of 3.8 degrees. The angle from the Fermi LAT boresight is 30.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260526961/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260526961/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260526961/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44707. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42835] EP01709266106 (EP260526a?): Liverpool Telescope upper limits
by GCN Circulars 26 May '26

26 May '26

TITLE: GCN CIRCULAR NUMBER: 44706 SUBJECT: EP01709266106 (EP260526a?): Liverpool Telescope upper limits DATE: 26/05/26 22:48:18 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester) reports on behalf of a larger collaboration: We observed the field of the Einstein Probe WXT trigger EP01709266106 (EP260526a?) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS g’r’i’z’ filters starting at 2026-05-26 21:25:48 UT, approximately 3.80 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 | | ------------- | ------ | ------------ | | 3.94 | r’ | >21.52 | | 4.24 | g’ | >21.47 | | 4.53 | i’ | >21.69 | | 4.82 | z’ | >21.25 | View this GCN Circular online at https://gcn.nasa.gov/circulars/44706. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42834] EP-WXT 01709266106: NOT optical upper limits
by GCN Circulars 26 May '26

26 May '26

TITLE: GCN CIRCULAR NUMBER: 44705 SUBJECT: EP-WXT 01709266106: NOT optical upper limits DATE: 26/05/26 22:44:16 GMT FROM: Agnes van Hoof at Radboud University <agnes.vanhoof(a)ru.nl> A. P. C. van Hoof (Radboud), G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), J. Chacón (PUC), J. N. D. van Dalen (Radboud), P. G. Jonker (Radboud), report on behalf of a larger collaboration: We observed the field of the Einstein Probe trigger WXT 01709266106, using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the SDSS r (3x300 s) and z (5x200 s) bands, starting on 2026-05-26 at 21:01:29 UT (~3.4 hours after the WXT trigger). We do not find any new, uncatalogued sources within the EP-WXT uncertainty region compared to Hyper Suprime-Cam and Legacy Survey images (DR10). From the stacked images we obtain the following 3-sigma upper limits: r > 20.17 z > 19.40 These limits are in the AB system, were calibrated using nearby stars from the Pan-STARRS catalog and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44705. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42833] Fermi GRB 260525A: Global MASTER-Net observations report
by GCN Circulars 26 May '26

26 May '26

TITLE: GCN CIRCULAR NUMBER: 44704 SUBJECT: Fermi GRB 260525A: Global MASTER-Net observations report DATE: 26/05/26 00:30:29 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-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260525A ( Fermi GBM team, GCN 44703) errorbox 28 sec after notice time and 62 sec after trigger time at 2026-05-25 23:34:44 UT, with upper limit up to 18.1 mag. The observations began at zenith distance = 38 deg. The sun altitude is -23.6 deg. The galactic latitude b = -4 deg., longitude l = 262 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3339200 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 67 | 2026-05-25 23:34:44 | MASTER-OAFA | (08h 07m 12.80s , -39d 50m 18.8s) | C | 10 | 18.1 | 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/44704. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42832] GRB 260525A: Fermi GBM Final Real-time Localization
by GCN Circulars 25 May '26

25 May '26

TITLE: GCN CIRCULAR NUMBER: 44703 SUBJECT: GRB 260525A: Fermi GBM Final Real-time Localization DATE: 26/05/25 23:44:11 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 23:33:42 UT on 25 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260525A (trigger 801444827.592448 / 260525982). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 125.2, Dec = -44.5 (J2000 degrees, equivalent to J2000 08h 20m, -44d 30'), with a statistical uncertainty of 6.3 degrees. The angle from the Fermi LAT boresight is 35.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260525982/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260525982/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260525982/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44703. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42831] GRB 260523B: AstroSat CZTI detection
by GCN Circulars 25 May '26

25 May '26

TITLE: GCN CIRCULAR NUMBER: 44702 SUBJECT: GRB 260523B: AstroSat CZTI detection DATE: 26/05/25 11:38:44 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a short GRB 260523B which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44699). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-23 19:26:02.85 UTC. The measured peak count rate associated with the burst is 259 (+123, -28) counts/s above the background in the combined data of three quadrants (out of four), with a total of 259 (+56, -54) counts. The local mean background count rate was 184 (+4, -7) counts/s. Using cumulative rates, we measure a T90 of 1.74 (+0.57, -0.46) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-05-23 19:26:02.79 UTC. The measured peak count rate associated with the burst is 318 (+68, -53) counts/s above the background in the combined data of all quadrants, with a total of 408 (+166, -174) counts. The local mean background count rate was 1282 (+11, -12) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 for our detection. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/517260365.54/ET20260523T192602… CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/44702. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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[vsnet-grb-info 42820] Fermi trigger No 801135305: Global MASTER-Net observations report
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44692 SUBJECT: Fermi trigger No 801135305: Global MASTER-Net observations report DATE: 26/05/22 09:45:51 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB260522.40 (trigger No 801135305,18h 40m 52.08s , -25d 33m 00.0s, R=7.7) errorbox 88 sec after notice time and 124 sec after trigger time at 2026-05-22 09:37:04 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 57 deg. The sun altitude is -28.5 deg. The galactic latitude b = -10 deg., longitude l = 9 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3331401 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 134 | 2026-05-22 09:37:04 | MASTER-OAGH | (18h 37m 12.05s , -25d 49m 53.1s) | C | 20 | 17.7 | 169 | 2026-05-22 09:37:04 | MASTER-OAGH | (18h 37m 12.06s , -25d 49m 53.1s) | C | 90 | 18.0 | Coadd 170 | 2026-05-22 09:37:34 | MASTER-OAGH | (18h 37m 06.41s , -25d 50m 55.7s) | C | 30 | 17.9 | 215 | 2026-05-22 09:38:15 | MASTER-OAGH | (18h 37m 10.52s , -25d 50m 55.1s) | C | 40 | 17.6 | 270 | 2026-05-22 09:39:05 | MASTER-OAGH | (18h 37m 08.18s , -25d 49m 24.5s) | C | 50 | 18.0 | 270 | 2026-05-22 09:39:05 | MASTER-OAGH | (18h 45m 29.90s , -26d 25m 48.5s) | C | 50 | 18.4 | 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/44692. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42819] Fermi GRB 260522A: Global MASTER-Net observations report
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44691 SUBJECT: Fermi GRB 260522A: Global MASTER-Net observations report DATE: 26/05/22 09:15:54 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260522A ( Fermi GBM team, GCN 44687) errorbox 20242 sec after notice time and 20291 sec after trigger time at 2026-05-22 07:53:20 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 81 deg. The sun altitude is -37.9 deg. The galactic latitude b = -40 deg., longitude l = 86 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3330735 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 20321 | 2026-05-22 07:53:20 | MASTER-OAGH | (22h 29m 21.04s , +17d 30m 10.0s) | C | 60 | 17.6 | 20736 | 2026-05-22 08:00:14 | MASTER-OAGH | (22h 31m 10.56s , +15d 35m 11.4s) | C | 60 | 17.8 | 20961 | 2026-05-22 08:04:00 | MASTER-OAGH | (22h 44m 59.44s , +19d 24m 13.9s) | C | 60 | 17.6 | 21293 | 2026-05-22 08:09:31 | MASTER-OAGH | (22h 37m 34.70s , +18d 07m 52.6s) | C | 60 | 18.5 | 21293 | 2026-05-22 08:09:31 | MASTER-OAGH | (22h 45m 20.15s , +17d 30m 06.7s) | C | 60 | 17.7 | 21552 | 2026-05-22 08:13:50 | MASTER-OAGH | (22h 47m 01.86s , +15d 35m 01.0s) | C | 60 | 17.6 | 21552 | 2026-05-22 08:13:50 | MASTER-OAGH | (22h 39m 21.07s , +16d 12m 47.8s) | C | 60 | 18.5 | 21807 | 2026-05-22 08:18:05 | MASTER-OAGH | (22h 31m 54.37s , +12d 23m 27.9s) | C | 60 | 18.2 | 21807 | 2026-05-22 08:18:05 | MASTER-OAGH | (22h 39m 27.63s , +11d 45m 47.0s) | C | 60 | 17.9 | 21879 | 2026-05-22 08:19:17 | MASTER-OAGH | (22h 27m 00.97s , +14d 18m 45.6s) | C | 60 | 18.8 | 21879 | 2026-05-22 08:19:17 | MASTER-OAGH | (22h 34m 37.36s , +13d 41m 11.6s) | C | 60 | 18.3 | 21965 | 2026-05-22 08:20:43 | MASTER-OAGH | (22h 42m 42.24s , +14d 19m 33.9s) | C | 60 | 18.5 | 21965 | 2026-05-22 08:20:43 | MASTER-OAGH | (22h 50m 18.96s , +13d 41m 45.4s) | C | 60 | 17.5 | 22042 | 2026-05-22 08:22:00 | MASTER-OAGH | (22h 53m 22.36s , +20d 01m 39.3s) | C | 60 | 18.4 | 22042 | 2026-05-22 08:22:00 | MASTER-OAGH | (23h 01m 12.71s , +19d 23m 51.7s) | C | 60 | 17.6 | 22189 | 2026-05-22 08:24:27 | MASTER-OAGH | (22h 53m 34.68s , +18d 06m 41.9s) | C | 60 | 18.5 | 22189 | 2026-05-22 08:24:27 | MASTER-OAGH | (23h 01m 19.97s , +17d 28m 52.6s) | C | 60 | 17.6 | 22410 | 2026-05-22 08:28:08 | MASTER-OAGH | (22h 38m 08.15s , +10d 29m 27.1s) | C | 60 | 18.7 | 22410 | 2026-05-22 08:28:08 | MASTER-OAGH | (22h 45m 38.44s , +09d 51m 42.6s) | C | 60 | 18.1 | 22633 | 2026-05-22 08:31:52 | MASTER-OAGH | (22h 47m 29.08s , +12d 24m 15.1s) | C | 60 | 18.6 | 22634 | 2026-05-22 08:31:52 | MASTER-OAGH | (22h 55m 02.26s , +11d 46m 29.2s) | C | 60 | 17.6 | 22713 | 2026-05-22 08:33:12 | MASTER-OAGH | (22h 55m 14.36s , +16d 11m 27.2s) | C | 60 | 18.3 | 22713 | 2026-05-22 08:33:12 | MASTER-OAGH | (23h 02m 54.91s , +15d 33m 41.2s) | C | 60 | 17.8 | 22938 | 2026-05-22 08:36:56 | MASTER-OAGH | (23h 09m 34.33s , +20d 00m 02.3s) | C | 60 | 18.6 | 23357 | 2026-05-22 08:43:56 | MASTER-OAGH | (22h 58m 25.81s , +14d 18m 37.0s) | C | 60 | 18.5 | 23357 | 2026-05-22 08:43:56 | MASTER-OAGH | (23h 06m 02.72s , +13d 40m 58.6s) | C | 60 | 17.9 | 23430 | 2026-05-22 08:45:08 | MASTER-OAGH | (23h 01m 03.75s , +09d 52m 16.5s) | C | 60 | 17.9 | 23430 | 2026-05-22 08:45:08 | MASTER-OAGH | (22h 53m 33.23s , +10d 29m 56.5s) | C | 60 | 18.4 | 23607 | 2026-05-22 08:48:05 | MASTER-OAGH | (23h 03m 00.46s , +12d 23m 19.5s) | C | 60 | 18.2 | 23607 | 2026-05-22 08:48:05 | MASTER-OAGH | (23h 10m 33.91s , +11d 45m 40.8s) | C | 60 | 17.8 | 23679 | 2026-05-22 08:49:17 | MASTER-OAGH | (23h 11m 07.56s , +16d 12m 42.7s) | C | 60 | 18.2 | 23679 | 2026-05-22 08:49:17 | MASTER-OAGH | (23h 18m 48.36s , +15d 35m 03.0s) | C | 60 | 17.5 | 23760 | 2026-05-22 08:50:39 | MASTER-OAGH | (22h 45m 45.40s , +08d 34m 28.4s) | C | 60 | 18.5 | 23760 | 2026-05-22 08:50:39 | MASTER-OAGH | (22h 53m 13.26s , +07d 57m 00.4s) | C | 60 | 18.5 | 24000 | 2026-05-22 08:54:38 | MASTER-OAGH | (23h 14m 05.04s , +14d 17m 27.5s) | C | 60 | 18.1 | 24073 | 2026-05-22 08:55:51 | MASTER-OAGH | (23h 09m 34.28s , +18d 06m 37.0s) | C | 60 | 18.6 | 24073 | 2026-05-22 08:55:51 | MASTER-OAGH | (23h 17m 19.72s , +17d 29m 07.5s) | C | 60 | 18.1 | 24253 | 2026-05-22 08:58:51 | MASTER-OAGH | (23h 09m 06.45s , +10d 28m 56.4s) | C | 60 | 18.7 | 24253 | 2026-05-22 08:58:51 | MASTER-OAGH | (23h 16m 37.32s , +09d 51m 15.3s) | C | 60 | 18.4 | 24325 | 2026-05-22 09:00:04 | MASTER-OAGH | (23h 01m 10.70s , +08d 36m 20.3s) | C | 60 | 18.6 | 24325 | 2026-05-22 09:00:04 | MASTER-OAGH | (23h 08m 39.11s , +07d 58m 43.5s) | C | 60 | 18.2 | 24618 | 2026-05-22 09:04:56 | MASTER-OAGH | (23h 18m 37.97s , +12d 23m 55.7s) | 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/44691. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42818] EP260518a: Einstein Probe detection of an sub-threshold X-ray transient with counterpart AT 2026ndp
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44690 SUBJECT: EP260518a: Einstein Probe detection of an sub-threshold X-ray transient with counterpart AT 2026ndp DATE: 26/05/22 08:38:05 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang, W. X. Li, D. Y. Li, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report the detection of a sub-threshold X-ray transient, EP260518a, associated with the optical transient AT 2026ndp. EP260518a was detected by the Wide-field X-ray Telescope (WXT) aboard the Einstein Probe (EP) mission at R.A. = 299.034 deg, Dec. = -48.618 deg (J2000), with an uncertainty radius of 3 arcmin, at 2026-05-18 13:44:21 UTC. The measured 0.5–4 keV flux was approximately 2.5 x 10^-11 erg cm^-2 s^-1. Due to the low signal-to-noise ratio, no significant flare-like feature is apparent in the X-ray light curve. A candidate optical counterpart, AT 2026ndp, was identified through real-time cross-matching. The transient was discovered by ATLAS at 2026-05-19 07:44:02.400 UTC, approximately 17 hours after the WXT detection, with a c-band magnitude of 18.73 +/- 0.10. There is a faint point-like source in Legacy Survey dr10, which is 1.8 arcsec away. Follow-up observations were performed with the Follow-up X-ray Telescope (FXT) aboard EP, starting at 2026-05-21 08:23:08 UTC (~66 hr after the WXT detection). An uncatalogued X-ray source was detected within the WXT error region at R.A. = 299.0407 deg, Dec. = -48.6362 deg (J2000), with an uncertainty of 10 arcsec. The FXT position is offset by 4.7 arcsec from the optical counterpart. The FXT spectrum can be fitted with an absorbed power-law model with a photon index of 2.5 (+0.8/-0.7) and hydrogen column density of 2.3 (+2.0/-1.7) x 10^21 cm^-2. The estimated average 0.3–10 keV flux is around 4.6 (+1.9/-1.2) x 10^-13 erg cm^-2 s^-1. 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/44690. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42817] GRB 260522A: Fermi-LAT detection
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44689 SUBJECT: GRB 260522A: Fermi-LAT detection DATE: 26/05/22 08:24:21 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi(a)ba.infn.it> At 02:15:08 UT on May 22nd, 2026, Fermi-LAT detected high-energy emission from GRB 260522A, which was also detected by Fermi-GBM (trigger 801108913 / 260522094, GCN #44687). The best LAT on-ground location is found to be RA, Dec = 346.67, 9.66 (J2000) with an error radius of 0.55 deg (90 % containment, statistical error only). This was 15 deg from the LAT boresight at the time of the trigger. The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 0 - 50 s after the GBM trigger is (2.89 ± 0.97)E-5 ph/cm2/s. The estimated photon index above 100 MeV is -2.14 ± 0.38. The highest-energy photon is a 820 MeV event, which is observed 1.3 seconds after the GBM trigger. The Fermi-LAT point of contact for this burst is Elisabetta Bissaldi (elisabetta.bissaldi(a)ba.infn.it ). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/44689. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42816] GRB 260519C: SVOM/GRM observation
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44688 SUBJECT: GRB 260519C: SVOM/GRM observation DATE: 26/05/22 06:32:44 GMT FROM: renyz16607(a)163.com SVOM/GRM team: Yang-Zhao Ren, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Feliu Lacreu (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260519C (SVOM trigger reference: sb26051904) at 2026-05-19T13:45:38.000 UTC (T0), which is also detected by Konus-Wind (Svinkin, GCN #44677), and NuSTAR (Waratkar et al., GCN #44672). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 26.5 +1.0/-1.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260519C.png With this localization, the time-averaged spectrum from T0-5 to T0+30 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.78 +0.08/-0.09 and the cutoff energy, parameterized as Epeak, is 135 +7/-6 keV. The event fluence (10-1000 keV) in this time interval is (2.07 +0.07/-0.06)E-05 erg/cm^2. The 1s peak spectrum, measured from T0+12.5 to T0+13.5 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -0.60 +0.19/-0.20 and the cutoff energy, parameterized as Epeak, is 93.47 +6.95/-5.93 keV. The flux (10-1000 keV) in this time interval is (1.10 +0.21/-0.06)E-06 erg/cm^2/s. The localization of GRB 260519C in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260519C_amati.png The localization of GRB 260519C in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260519C_yonetoku.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Yang-Zhao Ren (IHEP)(renyz(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44688. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42815] GRB 260522A: Fermi GBM Final Real-time Localization
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44687 SUBJECT: GRB 260522A: Fermi GBM Final Real-time Localization DATE: 26/05/22 02:25:32 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 02:15:08 UT on 22 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260522A (trigger 801108913.782424 / 260522094). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 343.6, Dec = 14.1 (J2000 degrees, equivalent to J2000 22h 54m, 14d 05'), with a statistical uncertainty of 5.1 degrees. The angle from the Fermi LAT boresight is 10.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260522094/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260522094/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260522094/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44687. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42814] GRB 260511A: iTelescope T-75 optical detection
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44686 SUBJECT: GRB 260511A: iTelescope T-75 optical detection DATE: 26/05/21 22:55:39 GMT FROM: Takanori Sakamoto at AGU <tsakamoto(a)phys.aoyama.ac.jp> H. Ban, T. Kato, K. Hotta, Y. Kawakubo, M. Serino, T. Sakamoto (AGU) We observed the field of GRB 260511A detected by the Fermi/GBM (Fermi GBM Team, GCN Circ. 44529), the SVOM/ECLAIRs (Godet et al., GCN Circ. 44532), the NuSTAR CsI anti-coincidence shields (Waratkar et al., GCN Circ. 44555), the Konus-Wind (Ridnaia et al., GCN Circ. 44585), the Glowbug (Woolf et al., GCN Circ. 44586), and the GRID (Li et al., GCN Circ. 44664) with the iTelescope.Net (http://www.itelescope.net) T75 (ASAN250) telescope located at Rio Hurtado Valley, Chile. We took 20 images of 60 sec exposures in the Red filter starting from May 11 at 06:37:27 (UT), about 24 minutes after the Fermi/GBM trigger and stopped at 07:07:42. The afterglow (Jiang et al., GCN Circ. 44533; Akl et al., GCN Circ. 44534; Saccardi et al., GCN Circ. 44535; Zheng et al., GCN Circ. 44536; Wu et al., GCN Circ. 44538; Harper et al., GCN Circ. 44545; Brivio et al., GCN Circ. 44562; Li et al., GCN Circ. 44575; Fu et al., GCN Circ. 44579; Zhu et al., GCN Circ. 44584) is detected in the stacked image of the first eight images (total exposure of 480 s) collected between 06:37:27 and 06:49:12. The afterglow magnitude is 19.3 +- 0.6 using the USNO-B1 catalog. No afterglow was detected in the following twelve images collected between 06:49:44 and 07:07:42. The 5-sigma upper limit of the stacked image of the last twelve images (total exposure of 720 s) is 18.3 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/44686. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42813] GRB 260520B: SVOM/GRM observation
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44685 SUBJECT: GRB 260520B: SVOM/GRM observation DATE: 26/05/21 15:23:56 GMT FROM: yzh807926(a)163.com SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier Godet (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 260520B at 2026-05-20T09:35:53.000 (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44676). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a main episode with a single peak a T90 of 6.0 +7.0/-5.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260520B.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 346.68 deg, DEC= 39.68 deg, ERR=14.4 deg, GCN#44425), is located at about 94 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Zheng-Hang Yu (IHEP)(zhyu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44685. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42812] GRB 260411B: TERI Gamma-ray detection
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44684 SUBJECT: GRB 260411B: TERI Gamma-ray detection DATE: 26/05/21 14:08:14 GMT FROM: nicholasjkirschner(a)gmail.com Nicholas Kirschner (a), Daniel Shy (b), C.C. Cheung (b), Bernard Phlips (b), Michael Streicher (c), James Mason (c), Douglas M. Groves (c), Feng Zhang (c), and Willy Kaye (c) (a) National Research Council Research Associate resident at the U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (c) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 260411B, which was also detected by Fermi GBM (GCN 44262, 44266), SVOM/GRM (GCN 44268), Fermi LAT (GCN 44277), GECAM (GCN 44285), Glowbug (GCN 44312), and Konus-Wind (GCN 44332). Using 1 Hz binning, and adopting T0 = 2026-04-11T08:04:43.568 Z, we observe one peak at T0+1.5s, with peak excess count rate of 69 above the 192 cps baseline rate observed in nearby off-source intervals. The analysis results presented here are preliminary and currently lack a detailed response function. TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy range of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. Analysis of TERI data at NRL is supported by the Office of Naval Research 6.1. [1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559). Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44684. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42811] GRB 260407A: TERI Gamma-ray detection
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44683 SUBJECT: GRB 260407A: TERI Gamma-ray detection DATE: 26/05/21 14:07:39 GMT FROM: nicholasjkirschner(a)gmail.com Nicholas Kirschner (a), Daniel Shy (b), C.C. Cheung (b), Bernard Phlips (b), Michael Streicher (c), James Mason (c), Douglas M. Groves (c), Feng Zhang (c), and Willy Kaye (c) (a) National Research Council Research Associate resident at the U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (c) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 260407A, which was also detected by Fermi/GBM (GCN 44226), Glowbug (GCN 44237), CALET (GCN 44242), InsightHXMT/HE (GCN 44245), and GECAM-A (GCN 44246). Using 1 Hz binning, and adopting T0 = 2026-04-07T09:11:06.112Z, we observe one peak at T0+1.5s, with peak excess count rate of 45 above the 133 cps baseline rate observed in nearby off-source intervals. The analysis results presented here are preliminary and currently lack a detailed response function. TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy range of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. Analysis of TERI data at NRL is supported by the Office of Naval Research 6.1. [1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559). Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44683. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42810] GRB 260307A: TERI Gamma-ray detection
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44682 SUBJECT: GRB 260307A: TERI Gamma-ray detection DATE: 26/05/21 14:06:50 GMT FROM: nicholasjkirschner(a)gmail.com Nicholas Kirschner (a), Daniel Shy (b), C.C. Cheung (b), Bernard Phlips (b), Michael Streicher (c), James Mason (c), Douglas M. Groves (c), Feng Zhang (c), and Willy Kaye (c) (a) National Research Council Research Associate resident at the U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (c) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 260307A, which was also detected by Fermi/GBM (GCN 43939), Glowbug (GCN 43950), GECAM-B (GCN 43961), and CALET (GCN 43982). Using 1 Hz binning and adopting T0 = 2026-03-07T11:27:59.32Z, we observe three peaks at T0+1.375s, T0+3.125s, and T0+5.125s with peak excess count rate of 144, 116, 96 above the 100 cps baseline rate observed in nearby off-source intervals. The analysis results presented here are preliminary and currently lack a detailed response function. TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy range of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. Analysis of TERI data at NRL is supported by the Office of Naval Research 6.1. [1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559). Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44682. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42809] GRB 260225D: TERI Gamma-ray detection
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44681 SUBJECT: GRB 260225D: TERI Gamma-ray detection DATE: 26/05/21 14:06:05 GMT FROM: nicholasjkirschner(a)gmail.com Nicholas Kirschner (a), Daniel Shy (b), C.C. Cheung (b), Bernard Phlips (b), Michael Streicher (c), James Mason (c), Douglas M. Groves (c), Feng Zhang (c), and Willy Kaye (c) (a) National Research Council Research Associate resident at the U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (c) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 260225D, which was also detected by Glowbug (GCN 43856), Konus-Wind (Trig_Time 19:51:32.84), SVOM/GRM (GCN 43885), and GRID (GCN 43890). Using 1 Hz binning and adopting T0 = 2026-02-25T19:51:28.768Z, we observe two peaks at T0+1.375s and 2.625s and peak excess count rate of 108 and 149 counts per second (cps) above the 128 cps baseline rate observed in nearby off-source intervals. The analysis results presented here are preliminary and currently lack a detailed response function. TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy range of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. Analysis of TERI data at NRL is supported by the Office of Naval Research 6.1. [1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559). Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44681. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42808] GRB 251118A: TERI Gamma-ray detection
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44680 SUBJECT: GRB 251118A: TERI Gamma-ray detection DATE: 26/05/21 14:05:27 GMT FROM: nicholasjkirschner(a)gmail.com Nicholas Kirschner (a), Daniel Shy (b), C.C. Cheung (b), Bernard Phlips (b), Michael Streicher (c), James Mason (c), Douglas M. Groves (c), Feng Zhang (c), and Willy Kaye (c) (a) National Research Council Research Associate resident at the U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (c) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 251118A, which was also detected by Glowbug (GCN 42784), Fermi GBM (GCN 42743, 42745, 42783), Fermi LAT (GCN 42752), NuSTAR (GCN 42774), and GECAM-B (GCN 42779). Using 1 Hz binning, and adopting T0 = 2025-11-18T20:31:43.57Z, we observe two peaks at T0+4.5s and 40.5s. The analysis results presented here are preliminary and currently lack a detailed response function. TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy range of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. Analysis of TERI data at NRL is supported by the Office of Naval Research 6.1. [1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559). Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44680. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42807] GRB 251113A: TERI Gamma-ray detection
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44679 SUBJECT: GRB 251113A: TERI Gamma-ray detection DATE: 26/05/21 14:04:30 GMT FROM: nicholasjkirschner(a)gmail.com Nicholas Kirschner (a), Daniel Shy (b), C.C. Cheung (b), Bernard Phlips (b), Michael Streicher (c), James Mason (c), Douglas M. Groves (c), Feng Zhang (c), and Willy Kaye (c) (a) National Research Council Research Associate resident at the U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (c) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 251113A, which was also detected by Glowbug (GCN 42689), Fermi GBM (GCN 42671, 42672), and AstroSat/CZTI (GCN 42688). Using 1 Hz binning, and adopting T0 = 2025-11-13T17:37:28.512ZZ we observe one peak at T0+14.5, with peak excess count rate of 64 cps above the 83 cps baseline rate observed in nearby off-source intervals. The analysis results presented here are preliminary and currently lack a detailed response function. TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy range of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. Analysis of TERI data at NRL is supported by the Office of Naval Research 6.1. [1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559). Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44679. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42806] GRB 260428A: TERI Gamma-ray detection
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44678 SUBJECT: GRB 260428A: TERI Gamma-ray detection DATE: 26/05/21 14:02:09 GMT FROM: nicholasjkirschner(a)gmail.com Nicholas Kirschner (a), Daniel Shy (b), C.C. Cheung (b), Bernard Phlips (b), Michael Streicher (c), James Mason (c), Douglas M. Groves (c), Feng Zhang (c), and Willy Kaye (c) (a) National Research Council Research Associate resident at the U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (c) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 260411B, which was also detected by Fermi GBM (GCN 44415), AstroSat (GCN 44421), GECAM-B (GCN 44423), and SVOM/GRM (GCN 44424). Using 1 Hz binning, and adopting T0 = 2026-04-28T14:20:34.992Z, we observe one peak at T0+1.5s, with peak excess count rate of 49 above the 97 cps baseline rate observed in nearby offsource intervals. The analysis results presented here are preliminary and currently lack a detailed response function. TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy range of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. Analysis of TERI data at NRL is supported by the Office of Naval Research 6.1. [1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559). Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44678. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42805] Konus-Wind detection of GRB 260519C
by GCN Circulars 21 May '26

21 May '26

TITLE: GCN CIRCULAR NUMBER: 44677 SUBJECT: Konus-Wind detection of GRB 260519C DATE: 26/05/21 13:10:04 GMT FROM: Dmitry Svinkin at Ioffe Institute <dmitrysvinkin(a)gmail.com> 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 260519C (NuSTAR-ACS detection: Waratkar et al., GCN 44672) triggered Konus-Wind at T0=49536.443 s UT (13:45:36.443). The burst light curve shows a multipeaked structure which starts at ~T0-3.5 s and has a total duration of ~27 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/GRB260519_T49536/ As observed by Konus-Wind, the burst had the total fluence of 2.47(-0.15,+0.13)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+2.192 s, of 2.45(-0.46,+0.46)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+24.832 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(-0.16,+0.18), the high energy photon index beta = -3.17(-0.94,+0.28), the peak energy Ep = 119(-7,+8) keV (chi2 = 96/96 dof). The spectrum near the maximum count rate (measured from T0+0.256 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 = -0.70(-0.11,+0.11) and Ep = 209(-10,+11) keV (chi2 = 91/78 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.6 (chi2 = 91/77 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/44677. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42804] GRB 260520B: Fermi GBM Final Localization
by GCN Circulars 20 May '26

20 May '26

TITLE: GCN CIRCULAR NUMBER: 44676 SUBJECT: GRB 260520B: Fermi GBM Final Localization DATE: 26/05/20 18:00:48 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 09:35:52.73 UT on 20 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB260520B (trigger 800962557/260520400). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 346.68, Dec = 39.68 (J2000 degrees, equivalent to J2000 23h 6m, -39d 40'), with a statistical uncertainty of 14 degrees. The angle from the Fermi LAT boresight is 21 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260520400/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260520400/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260520400/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44676. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42803] GRB 260509A: SVOM/ECLAIRs refined analysis
by GCN Circulars 20 May '26

20 May '26

TITLE: GCN CIRCULAR NUMBER: 44675 SUBJECT: GRB 260509A: SVOM/ECLAIRs refined analysis DATE: 26/05/20 07:09:29 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> F. Daigne (IAP), F. Lacreu (IAP), U. Jacob (LUPM), M. Brunet (IRAP), D. Götz (CEA/Irfu), A. Saccardi (CEA/Irfu), H. Goto (RIKEN), D. Adrien (CEA) report on behalf of the SVOM/ECLAIRs team: Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260509A (SVOM burst-id sb26050905). The burst that triggered ECLAIRs onboard at T0 = 2026-05-09T21:51:09 UTC (GCN 44504) shows a multiple peaks lightcurve with a precursor starting at about T0-22 s for about 8 s. The burst duration is T90 = 14.3 +0.9/-1.3 s in the 4-120 keV energy band. The time-averaged spectrum from T0-1.4 s to T0+12.9 s in the energy range 5-120 keV is best fitted by a power-law model with a photon index -2.20 +/- 0.09. With this model, the 4-120 keV fluence is (4.1 +/- 0.3)E-7 erg/cm^2 and the 4-120 keV photon flux is 1.49 +/- 0.07 ph/cm^2/s. The value of the photon index indicates that this GRB is very soft and should probably be classified as an X-Ray Flash. The time-averaged spectrum of the precursor, from T0-22 s to T0-14.5 s in the energy range 5-20 keV is best fitted by a power-law model with a photon-index -3.0 +0.5/-0.6. It can also be fitted with a blackbody with temperature kT = 1.5 +0.4/-0.3 keV. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: F. Daigne (IAP) (daigne at iap.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44675. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42802] GRB 260520A: Fermi GBM Final Localization
by GCN Circulars 20 May '26

20 May '26

TITLE: GCN CIRCULAR NUMBER: 44674 SUBJECT: GRB 260520A: Fermi GBM Final Localization DATE: 26/05/20 06:47:26 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 01:24:47.42 UT on 20 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260520A (trigger 800933092/260520059). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 191.01, Dec = -34.56 (J2000 degrees, equivalent to J2000 12h 44m, -34d 33’), with a statistical uncertainty of 14 degrees. The angle from the Fermi LAT boresight is 114 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260520059/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260520059/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260520059/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44674. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42801] GRB 260519D: Fermi GBM Final Localization Correction
by GCN Circulars 20 May '26

20 May '26

TITLE: GCN CIRCULAR NUMBER: 44673 SUBJECT: GRB 260519D: Fermi GBM Final Localization Correction DATE: 26/05/20 03:51:26 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 19:37:23.371 UT on 19 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260519D (trigger 800912248/260519818). This trigger was initially not classified as a GRB by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 87.37, Dec = -6.37 (J2000 degrees, equivalent to J2000 5h 49m, -6d 22’), with a statistical uncertainty of 14 degrees. The angle from the Fermi LAT boresight is 26 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260519818/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260519818/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260519818/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44673. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42800] GRB 260519C: NuSTAR detection of prompt emission
by GCN Circulars 19 May '26

19 May '26

TITLE: GCN CIRCULAR NUMBER: 44672 SUBJECT: GRB 260519C: NuSTAR detection of prompt emission DATE: 26/05/19 23:06:15 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 260519C 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 2026-05-19T13:45:37.0 UTC, shows a detection of GRB 260519C, also detected by Konus-Wind (GCN Notices) & SVOM/GRM (GCN Notices). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a 25-s long burst consistent with the Konus-Wind lightcurve. The peak count rate is ~2000-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. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260519C 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/44672. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42799] Konus-Wind detection of GRB 260518A
by GCN Circulars 19 May '26

19 May '26

TITLE: GCN CIRCULAR NUMBER: 44671 SUBJECT: Konus-Wind detection of GRB 260518A DATE: 26/05/19 22:18:00 GMT FROM: Dmitry Svinkin at Ioffe Institute <dmitrysvinkin(a)gmail.com> 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 260518A (AstroSat-CZTI detection: Harsha et al., GCN 44668) triggered Konus-Wind at T0=27873.529 s UT (07:44:33.529). The burst light curve shows a multipeaked structure which starts at ~T0-9 s and has a total duration of ~18 s. The emission is seen up to ~1 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260518_T27873/ As observed by Konus-Wind, the burst had the total fluence of 4.59(-0.38,+0.42)x10^-6 erg/cm2, and the 64-ms peak flux, measured from T0-0.016 s, of 2.35(-0.47,+0.48)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+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 = -0.11(-0.36,+0.42) and Ep = 213(-24,+31) keV (chi2 = 66/85 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.9 (chi2 = 66/84 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/44671. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42798] GRB 260519B: Fermi GBM Final Localization
by GCN Circulars 19 May '26

19 May '26

TITLE: GCN CIRCULAR NUMBER: 44670 SUBJECT: GRB 260519B: Fermi GBM Final Localization DATE: 26/05/19 18:43:23 GMT FROM: oindabimukherjee(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 03:37:41.37 UT on 19 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260519B (trigger 800854666/260519151). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 85.76, Dec = -73.67 (J2000 degrees, equivalent to J2000 -4h 54m, +17d 0'), with a statistical uncertainty of 17.01 degrees. The angle from the Fermi LAT boresight is 25 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260519151/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260519151/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260519151/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44670. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42797] GRB 260519A: Fermi GBM Final Localization
by GCN Circulars 19 May '26

19 May '26

TITLE: GCN CIRCULAR NUMBER: 44669 SUBJECT: GRB 260519A: Fermi GBM Final Localization DATE: 26/05/19 18:03:52 GMT FROM: rhamburg(a)usra.edu The Fermi GBM team reports the detection of a likely LONG GRB "At 10:56:45.51 UT on 19 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260519A (trigger 800881010/260519456). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 273.75, Dec = 14.25 (J2000 degrees, equivalent to J2000 18h 15m, +14d 15'), with a statistical uncertainty of 17 degrees. The angle from the Fermi LAT boresight is 83 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260519456/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260519456/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260519456/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44669. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42796] GRB 260518A: AstroSat CZTI detection of a long burst
by GCN Circulars 19 May '26

19 May '26

TITLE: GCN CIRCULAR NUMBER: 44668 SUBJECT: GRB 260518A: AstroSat CZTI detection of a long burst DATE: 26/05/19 16:41:44 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260518A. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-18 07:44:29.50 UTC. The measured peak count rate associated with the burst is 380 (+84, -78) counts/s above the background in the combined data of all quadrants, with a total of 654 (+182, -192) counts. The local mean background count rate was 295 (+5, -6) counts/s. Using cumulative rates, we measure a T90 of 9 (+2, -2) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-05-18 07:44:29.10 UTC. The measured peak count rate associated with the burst is 417 (+67, -72) counts/s above the background in the combined data of all quadrants, with a total of 1270 (+298, -329) counts. The local mean background count rate was 1301 (+5, -5) counts/s. We measure a T90 of 10 (+2, -3) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/516786266.6/S516786266.6_detai… CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/44668. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42795] GRB 260516D: SVOM/ECLAIRs refined analysis
by GCN Circulars 19 May '26

19 May '26

TITLE: GCN CIRCULAR NUMBER: 44667 SUBJECT: GRB 260516D: SVOM/ECLAIRs refined analysis DATE: 26/05/19 15:29:15 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet, J.-L. Atteia (IRAP), A. Saccardi (CEA/ Irfu), report on behalf of the SVOM/ECLAIRs team Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260516D (SVOM burst-id sb260511616 – GCN 44649, trigger time T0 = 2026-05-16T20:39:50 UTC). The burst that triggered ECLAIRs shows a multiple peak light curve with most emission detected below 50 keV. The burst duration is estimated to be 152 s in the 4-20 keV energy band. The time-averaged spectrum from T0-78 s to T0+74 s in the energy range 5-50 keV is best fitted by a powerlaw model with alpha = -2.46 +0.32/-0.38. With this model, the 4-120 keV fluence is (5.3 +0.5/-2.4)e-7 erg/cm² and the 4-120 keV photon flux is 0.22 +0.1/-1.1 ph/cm²/s. We note that given the value of the photon index, the peak energy is likely to be below 5 keV, which classifies this GRB as an X-Ray Flash. By considering a Band model with alpha = -1, beta = -2.46 and a peak energy of 4 keV, a redshift of z=1.801 (GCN 44656) and a standard cosmology with H_0 = 67.3 km/s/Mpc and Omega_M = 0.315 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy E_iso is 8.9e51 erg, and the rest-frame peak energy of the time-averaged spectrum Ep,z is 11.2 keV. With these estimates, GRB 260516D lies below the track of Type-II GRBs on the Amati relation reported by Willingale et al. 2017. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44667. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42794] GRB 260515A: SVOM/ECLAIRs refined analysis
by GCN Circulars 19 May '26

19 May '26

TITLE: GCN CIRCULAR NUMBER: 44666 SUBJECT: GRB 260515A: SVOM/ECLAIRs refined analysis DATE: 26/05/19 14:14:04 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, L. Bouchet (IRAP), A. Saccardi (CEA/ Irfu), report on behalf of the SVOM/ECLAIRs team Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260515A (SVOM burst-id sb26051504 – GCN 44622, trigger time T0 = 2026-05-15T19:08:19 UTC), which was also detected by Konus-Wind (GCN 44647). The burst that triggered ECLAIRs shows a FRED like shape light curve preceded by a faint hard precursor at T0-4.2s. The burst duration is T90 = 16.33 +0.54/-0.35 s in the 4-120 keV energy band. The time-averaged spectrum from T0-0.31 s to T0+16.0 s in the energy range 5-120 keV is best fitted by a powerlaw model with alpha = -1.69 +/-0.04. With this model, the 4-120 keV fluence is (1.09 -0.07/+0.04)e-6 erg/cm² and the 4-120 keV photon flux is 2.26 -0.06/+0.04 ph/cm²/s. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44666. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42793] GRB 260421B: radio detection with the VLA
by GCN Circulars 19 May '26

19 May '26

TITLE: GCN CIRCULAR NUMBER: 44665 SUBJECT: GRB 260421B: radio detection with the VLA DATE: 26/05/19 13:17:22 GMT FROM: Stefano Giarratana at INAF-OAB <s.giarratana(a)ira.inaf.it> S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA), G. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.), N. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB), L. Nava (INAF-OAB) At 01:30:46 UT on 2026 April 24 (T_mid = 2.92 days post-burst) and at 01:38:23 UT on 2026 April 30 (T_mid = 8.92 days post-burst) the Karl G. Jansky VLA observed the field of GRB 260421B (Fermi GBM team, GCN 44360, 44382; SVOM mission team, GCN 44362, GCN 44389, 44397; Insight-HXMT team, GCN 44401) at central frequencies of 6, 10 and 15 GHz. The standard 3C286 was used as bandpass and flux density calibrator, while J1239-1023 was used as phase calibrator. From a preliminary analysis, an unresolved radio source is detected at 8.92 days post-burst at a position (J2000): RA: 12:40:00.478 +- 0.002 Dec: -17:44:24.70 +- 0.03 consistent with the X-ray (SVOM mission team, GCN 44362; Einstein Probe team, GCN 44387) and optical (He et al., GCN 44363; Sánchez Álvarez et al., GCN 44364; SVOM mission team, GCN 44365, 44377; Wu et al., GCN 44366; Pérez-Fournon et al., GCN 44383; GRANDMA/Kilonova-Catcher collaboration, GCN 44402) position of the transient. The preliminary analysis yields the following results: ================================================================ T_mid Freq Peak r.m.s. Beam PA [days] [GHz] [uJy/b] [uJy/b] [arcsec^2] [deg] ================================================================ 2.92 6 - 8 0.72x0.28 -38 2.92 10 - 9 0.50x0.19 -43 2.92 15 - 12 0.41x0.11 -43 8.92 6 52 8 0.58x0.27 -33 8.92 10 81 9 0.40x0.21 -38 8.92 15 137 9 0.32x0.12 -38 ================================================================ We would like to thank the staff of the VLA for approving, executing, and processing the observations. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. These observations were carried out as part of project SF181027, approved in the framework of the Fermi - NRAO joint program agreement. View this GCN Circular online at https://gcn.nasa.gov/circulars/44665. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42792] GRID detection of GRB 260511A
by GCN Circulars 19 May '26

19 May '26

TITLE: GCN CIRCULAR NUMBER: 44664 SUBJECT: GRID detection of GRB 260511A DATE: 26/05/19 08:18:09 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Longhao Li, Siqi Wu, Chenyu Wang, report on behalf of the GRID Collaboration: GRID-10B and GRID-11B reports the detection of the long-duration GRB 260511A, which was also detected by Fermi GBM (GCN Circular 44529), SVOM (GCN Circular 44532), NuSTAR(GCN Circular 44555), MASS-Cube(GCN Circular 44584), Konus-Wind (GCN Circular 44585), Glowbug(GCN Circular 44586). The event was triggered with GRID on 2026-05-11 at 06:13:30 UTC. The measured burst duration (T90) in the 30-2000 keV range is approximately T90 = 26.0 +/- 1.3 seconds. The GRID light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260511A/GRID_260…. GRID is a student-led project to monitor the transient gamma-ray sky with multiple detectors onboard different nanosatellites in the era of multi-messenger astronomy. For more information about GRID, please refer to the following references: https://doi.org/10.1007/s10686-019-09636-w and https://doi.org/10.1007/s10686-021-09819-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/44664. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42791] GRB 260509A: CrAO ZTSh optical upper limit
by GCN Circulars 18 May '26

18 May '26

TITLE: GCN CIRCULAR NUMBER: 44663 SUBJECT: GRB 260509A: CrAO ZTSh optical upper limit DATE: 26/05/18 13:50:25 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), A. Pozanenko (IKI), V. Rumyantsev (CrAO), N. Pankov (IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN. We observed the field of the GRB 260509A (Götz et al., GCN 44504) with the Shajn 2.6-meter telescope (ZTSh) of the Crimean Astrophysical Observatory (CrAO). We obtained 40*120 s exposures R filter on 2026-05-15 19:45:59--21:09:48 UT (5.94218 days after trigger). We did not detect the OT (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Sánchez Álvarez et al., GCN 44509; Zheng et al., GCN 44510; Kechin et al., GCN 44512; Belkin, GCN 44513; Corcoran et al., GCN 44514; Bochenek and Perley, GCN 44516; Moskvitin and Spiridonova, GCN 44563; Mo et al., GCN 44590; Li et al., GCN 44598) down to the 3-sigma limiting magnitude of R_lim = 24.2. This preliminary photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44663. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42790] GRB 260509A: CrAO ZTSh optical upper limit
by GCN Circulars 18 May '26

18 May '26

TITLE: GCN CIRCULAR NUMBER: 44662 SUBJECT: GRB 260509A: CrAO ZTSh optical upper limit DATE: 26/05/18 13:49:55 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), A. Pozanenko (IKI), V. Rumyantsev (CrAO), N. Pankov (IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN. We observed the field of the GRB 260509A (Götz et al., GCN 44504) with the Shajn 2.6-meter telescope (ZTSh) of the Crimean Astrophysical Observatory (CrAO). We obtained 40*120 s exposures R filter on 2026-05-15 19:45:59--21:09:48 UT (5.94218 days after trigger). We did not detect the OT (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Sánchez Álvarez et al., GCN 44509; Zheng et al., GCN 44510; Kechin et al., GCN 44512; Belkin, GCN 44513; Corcoran et al., GCN 44514; Bochenek and Perley, GCN 44516; Moskvitin and Spiridonova, GCN 44563; Mo et al., GCN 44590; Li et al., GCN 44598) down to the 3-sigma limiting magnitude of R_lim = 24.2. This preliminary photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44662. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42789] GRB 260516D: EP-FXT follow-up observation
by GCN Circulars 17 May '26

17 May '26

TITLE: GCN CIRCULAR NUMBER: 44661 SUBJECT: GRB 260516D: EP-FXT follow-up observation DATE: 26/05/17 10:45:05 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (HKU), Z.M. Wang (BNU), W.F. Wen (SZTU), Z.-X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed an automatic follow-up observation of GRB 260516D detected by SVOM/ECLAIRs (SVOM/sb26051616, Brunet et al., GCN 44649). The follow-up obervation started at 2026-05-16 22:46:58 UTC, approximately 2.1 hours after the SVOM trigger, with a total exposure time of 6080 s. On-ground analysis of the FXT data found an uncatalogued fading source within the ECLAIRs error circle at R.A., Dec. = 233.8275, 6.5288 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). This position is consistent with the optical counterpart (Li et al., GCN 44654, Mohan et al., GCN 44655, Izzo et al., GCN 44656, García et al., GCN 44657, Wu et al., GCN 44659, Belkin et al., GCN 44660). The average FXT 0.3-10 keV spectrum can be fitted with an absorbed power-law model, with the Galactic hydrogen column density fixed at 4.71 x 10^20 cm^-2, an intrinsic hydrogen column density of 6.29 (-1.71/+1.71) x 10^21 cm^-2, and a photon index of 2.43 (-0.08/+0.08). The derived unabsorbed average flux in the 0.3-10 keV band is 3.99 (-0.14/+0.15) x 10^(-12) erg/s/cm^2. 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/44661. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42788] GRB 260516D: GOTO optical counterpart detection
by GCN Circulars 17 May '26

17 May '26

TITLE: GCN CIRCULAR NUMBER: 44660 SUBJECT: GRB 260516D: GOTO optical counterpart detection DATE: 26/05/17 08:55:51 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin, B. P. Gompertz, M. Wortley, G. Ramsay, D. O'Neill, R. Starling, 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, A. Kumar, 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 SVOM/ECLAIRs detection of the possible short faint burst GRB 260516D (Brunet et al., GCN 44649). Observations of the field were obtained with GOTO-N on 2026-05-16 and 2026-05-17 UT in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline (Lyman et al. 2026). Difference imaging was performed using deeper template observations of the same pointings. We detect the optical afterglow candidate reported by SVOM/VT (Li et al., GCN 44654), the GROWTH-India Telescope (Mohan et al., GCN 44655), GTC/OSIRIS+ (Izzo et al., GCN 44656), SVOM/COLIBRÍ (García García et al., GCN 44657), and LCO (Wu et al., GCN 44659). The source was initially detected with L = 19.29 +/- 0.05 AB mag at 2026-05-16 22:03:56 UT (T0 +1.40 hr), before fading to L = 21.01 +/- 0.34 AB mag at 2026-05-17 01:26:52 UT (T0 +4.78 hr). These two detections imply a preliminary temporal decay index of alpha_L = 1.30 +/- 0.26, consistent with the optical decay reported by García García et al. (GCN 44657). 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/44660. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42787] GRB 260516D: LCO optical observations
by GCN Circulars 17 May '26

17 May '26

TITLE: GCN CIRCULAR NUMBER: 44659 SUBJECT: GRB 260516D: LCO optical observations DATE: 26/05/17 08:22:30 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), A. Saccardi (CEA/Irfu), L.P. Xin (NAOC) report on behalf of the SVOM mission team: We observed the field of the SVOM/ECLAIRs GRB 260516D (Brunet et al., GCN 44649) with the LCO 1m telescope at McDonald Observatory and Cerro Tololo equipped with the Sinistro instrument. Our observation started on 2026-05-17 at 06:26:56 UT (about 9.79 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical counterpart (Li et al., GCN 44654; Mohan et al., GCN 44655; García et al., GCN 44657) with redshift of 1.801 (Izzo et al., GCN 44656) is faintly detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r = 21.75 +/- 0.10 AB (mid-time 9.88 hr after the trigger); z > 21.2 AB (3-sigma, mid-time 10.00 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44659. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42786] GRB 260515A: further Liverpool Telescope observations
by GCN Circulars 17 May '26

17 May '26

TITLE: GCN CIRCULAR NUMBER: 44658 SUBJECT: GRB 260515A: further Liverpool Telescope observations DATE: 26/05/17 08:10:40 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 GRB 260515A (Brunetet al., GCN 44622) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x110s exposures in SDSS r and i filters, starting at 2026-05-12 00:42:25 UT, approximately 5.55 hours after trigger. We detect a source in the stacked images in both filters at the position reported by He et al. (GCN 44623), and observed also by Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628, Dennefeld et al., GCN 44633; Li et al., GCN 44634, Antier et al., GCN 44643; Dimple et al. GCN 44646; and Moskvitin et al., GCN 44652: MJD (mid) T_mid-T_0 Filter Mag. (AB) 61176.03308 5.64 h r 21.32 ± 0.06 61176.04059 5.82 h i 21.26 ± 0.07 The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44658. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42785] GRB 260516D: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 17 May '26

17 May '26

TITLE: GCN CIRCULAR NUMBER: 44657 SUBJECT: GRB 260516D: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 26/05/17 06:24:29 GMT FROM: Leonardo Enrique García García <lgarcia(a)astro.unam.mx> Leonardo García García (UNAM), Francis Fortin (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (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), Jean-Grégoire Ducoin (CPPM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM) and Andrea Saccardi (CEA) report: We imaged the field of the SVOM/ECLAIRs GRB 260516D (M. Brunet et al., GCN Circ. 44649) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-17 04:04 to 05:51 UTC (from to 7.48 to 9.25 hours after the trigger) and obtained 15 minutes of exposure in the r filter and 44 minutes of exposure in the z filter. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU 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. We detect the source reported by Li et al. (GCN Circ. 44654) and de Ugarte Postigo et al. (GCN Circ. 44656) with preliminary unsubtracted magnitudes of: r = 21.65 +/- 0.07, z = 21.66 +/- 0.16. Using the combined r’ and r- band photometry from GCNs 44655 and 44656 together with our COLIBRI observations, we estimate the optical afterglow temporal decay index to be approximately alpha ≈ 1.4. 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/44657. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42784] GRB 260516D: GTC/OSIRIS+ spectroscopic redshift z = 1.801
by GCN Circulars 17 May '26

17 May '26

TITLE: GCN CIRCULAR NUMBER: 44656 SUBJECT: GRB 260516D: GTC/OSIRIS+ spectroscopic redshift z = 1.801 DATE: 26/05/17 04:17:13 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> L. Izzo (INAF/OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), A. de Ugarte Postigo (LAM), S. Geier (GTC), A. Martin-Carrillo (UCD), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), F. Perez Toledo (GTC) report: We observed the optical counterpart (Li et al., GCN 44654; Mohan et al., GCN 44655) of GRB 260516D (Brunet et al., GCN 44649) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. In the 30-s acquisition image (beginning on 2026-05-17 at 02:54:51, that is 6.25 hr after trigger), the optical afterglow is well detected with a magnitude 21.0 ± 0.1 (AB), calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction. A total of 3 spectra of 900 s were secured, starting at 03:06:24.010 UT (6.44 hr after trigger), using grism R1000B. Continuum is visible over the range 3650-7800 AA. A number of metal absorption features are detected, which we interpret as due to, among others, C II, C IV, Si II, Fe II, Al II, and Al III, all at a common redshift z = 1.801, which we suggest to be the redshift of GRB 260516D. This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). View this GCN Circular online at https://gcn.nasa.gov/circulars/44656. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42783] GRB 260516D: GROWTH-India Telescope optical counterpart discovery
by GCN Circulars 17 May '26

17 May '26

TITLE: GCN CIRCULAR NUMBER: 44655 SUBJECT: GRB 260516D: GROWTH-India Telescope optical counterpart discovery DATE: 26/05/17 01:33:09 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan (IITB), V. Swain (IITB), A.P. Saikia (IITB), S. Patil (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team: We observed the field of GRB 260515D (Brunet et al., GCN 44649), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-05-16 22:19:57 (UTC), i.e., 1.67 hours after the trigger, and obtained multiple exposures in the r' filter. The observations were carried out at relatively high airmass (~2). We report the discovery of the possible counterpart whose coordinates are RA, Dec = 233.827989 (deg), 6.529308 (deg). No known minor planet was found at the source position during the time of observation. The photometric results are as follows: | MJD (mid) | Filter | tmid-t0 (minutes) | Exposure Time (sec) | Magnitude (AB) | | ------------ | ------ | ----------------- | ------------------- | -------------- | | 61176.93225 | r' | 102.62 | 1x300 | 19.17 +- 0.10 | | 61176.94497 | r' | 120.93 | 1x420 | 19.45 +- 0.09 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our results are consistent with other optical observations (Jelinek et al., GCN 44653) The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/44655. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42782] GRB 260516D: SVOM/VT optical bright candidate
by GCN Circulars 17 May '26

17 May '26

TITLE: GCN CIRCULAR NUMBER: 44654 SUBJECT: GRB 260516D: SVOM/VT optical bright candidate DATE: 26/05/17 01:27:37 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio and A. Saccardi (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observation to the field of possible short burst GRB 260516D detected by SVOM/ECLAIRs (Brunet et al., GCN 44619). The observation started at 2026-05-16T22:20:51 UTC, 1.69 hour post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued optical source was clearly detected in single frames of both channels within the errobox of SVOM/ECLAIRs, compared to the Legacy Survey. The position is at R.A., Dec. = 233.827956, 6.529103 degrees, equivalent to: R.A. (J2000) = 15:35:18.71 Dec. (J2000) = +6:31:44.77 with an uncertainty of 0.5 arcsec. The measurements in AB magnitudes are given below: Mid_time Band Exposure Time Magnitude (AB) 1.71 hour VT_B 70 sec 19.62 +/- 0.05 mag 1.69 hour VT_R 70 sec 19.00 +/- 0.05 mag Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44654. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42781] GRB 260516D: FRAM-ORM optical limit
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44653 SUBJECT: GRB 260516D: FRAM-ORM optical limit DATE: 26/05/16 23:59:09 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> Martin Jelinek, Filip Novotny and Jan Strobl (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Masek, Petr Janecek, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ) report: The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted robotically to the SVOM/ECLAIRs alert of GRB 260516D (Brunet et al., GCNC 44649), obtaining a series of unfiltered 60s images starting at 20:54:16 UT, i.e. ~948s post trigger. We do not detect any new or strongly variable source in comparison to the ATLAS REFCAT2 catalog. In single images the detection limit gradually improved from R_C > 17.1 in the first frame (midtime ~978s post trigger), stabilizing at R_C > ~18.3–18.4 around ~2000s post trigger and remaining there for the rest of the ~one hour sequence. Combining images in groups of 10 (10x60s), we reach limits of R_C > ~20 (R_C > ~19.3 for the first combined frame). View this GCN Circular online at https://gcn.nasa.gov/circulars/44653. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42780] GRB 260515A: CrAO ZTSh BVRI optical observations
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44652 SUBJECT: GRB 260515A: CrAO ZTSh BVRI optical observations DATE: 26/05/16 23:52:00 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), A. Pozanenko (IKI), V. Rumyantsev (CrAO), N. Pankov (IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN. We observed the field of the GRB 260515A (Brunet et al., GCN 44622; Wang et al., GCN 44642; Frederiks et al., GCN 44647) with the Shajn 2.6-meter telescope (ZTSh) of the Crimean Astrophysical Observatory (CrAO). We obtained series of 120 s exposures in BVRI filters starting on 2026-05-15 22:10:11 UT (about 3 hours after trigger). The OT (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Malesani et al., GCN 44629; Dennefeld et al., GCN 44633; Li et al., GCN 44634; Antier et al., GCN 44643; Pérez-Fournon et al., GCN 44645; Dimple et al., GCN 44646) is clearly detected in the stacked frames. Details of the photometry is the following. Start_UT, t_mid-T0, exp, filter, mag, err, UL(3 sigma) 2026-05-15T22:54:33 4.79 15*120 B 21.53 0.04 23.9 2026-05-15T22:56:41 4.75 13*120 V 21.30 0.05 23.7 2026-05-15T22:10:11 3.12 5*120 R 20.56 0.04 23.4 2026-05-15T22:20:40 3.29 5*120 R 20.57 0.04 23.4 2026-05-15T22:31:09 3.46 5*120 R 20.65 0.04 23.5 2026-05-15T22:41:44 3.66 6*120 R 20.64 0.03 23.6 2026-05-15T22:56:41 4.26 7*120 R 20.87 0.03 23.7 2026-05-15T23:58:56 5.35 8*120 R 21.03 0.04 23.4 2026-05-15T23:00:57 4.89 15*120 I 20.75 0.05 22.8 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44652. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42779] Fermi GRB 260516C: Global MASTER-Net observations report
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44651 SUBJECT: Fermi GRB 260516C: Global MASTER-Net observations report DATE: 26/05/16 22:15:42 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-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 260516C ( Fermi GBM team, GCN 44648) errorbox 31 sec after notice time and 63 sec after trigger time at 2026-05-16 19:35:42 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 27 deg. The sun altitude is -48.6 deg. The galactic latitude b = 1 deg., longitude l = 293 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3319181 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 68 | 2026-05-16 19:35:42 | MASTER-SAAO | (11h 28m 29.01s , -56d 15m 46.9s) | C | 10 | 17.3 | 68 | 2026-05-16 19:35:42 | MASTER-SAAO | (11h 31m 55.60s , -56d 31m 08.1s) | C | 10 | 17.5 | 102 | 2026-05-16 19:36:11 | MASTER-SAAO | (11h 28m 28.89s , -56d 15m 46.7s) | C | 20 | 17.7 | 102 | 2026-05-16 19:36:11 | MASTER-SAAO | (11h 31m 55.42s , -56d 31m 08.1s) | C | 20 | 18.0 | 155 | 2026-05-16 19:36:58 | MASTER-SAAO | (11h 22m 44.28s , -59d 38m 52.0s) | C | 30 | 17.1 | 200 | 2026-05-16 19:36:58 | MASTER-SAAO | (11h 22m 44.28s , -59d 38m 52.0s) | C | 120 | 17.4 | 155 | 2026-05-16 19:36:58 | MASTER-SAAO | (11h 26m 31.14s , -59d 54m 11.9s) | C | 30 | 17.4 | 200 | 2026-05-16 19:36:58 | MASTER-SAAO | (11h 26m 31.15s , -59d 54m 11.8s) | C | 120 | 17.8 | 209 | 2026-05-16 19:37:47 | MASTER-SAAO | (11h 22m 44.18s , -59d 38m 51.3s) | C | 40 | 17.1 | 209 | 2026-05-16 19:37:47 | MASTER-SAAO | (11h 26m 31.02s , -59d 54m 11.2s) | C | 40 | 17.5 | 273 | 2026-05-16 19:38:46 | MASTER-SAAO | (11h 22m 44.06s , -59d 38m 50.3s) | C | 50 | 17.1 | 273 | 2026-05-16 19:38:46 | MASTER-SAAO | (11h 26m 30.89s , -59d 54m 10.4s) | C | 50 | 17.5 | 347 | 2026-05-16 19:39:55 | MASTER-SAAO | (11h 22m 43.88s , -59d 38m 48.6s) | C | 60 | 17.3 | 347 | 2026-05-16 19:39:55 | MASTER-SAAO | (11h 26m 30.80s , -59d 54m 08.8s) | C | 60 | 17.6 | 626 | 2026-05-16 19:44:34 | MASTER-SAAO | (11h 24m 24.54s , -59d 37m 32.6s) | C | 60 | 17.4 | 686 | 2026-05-16 19:44:34 | MASTER-SAAO | (11h 24m 24.54s , -59d 37m 32.6s) | C | 180 | 17.5 | 626 | 2026-05-16 19:44:34 | MASTER-SAAO | (11h 28m 06.66s , -59d 53m 08.5s) | C | 60 | 17.7 | 686 | 2026-05-16 19:44:34 | MASTER-SAAO | (11h 28m 06.70s , -59d 53m 08.6s) | C | 180 | 17.9 | 705 | 2026-05-16 19:45:53 | MASTER-SAAO | (11h 24m 24.42s , -59d 37m 32.0s) | C | 60 | 17.4 | 705 | 2026-05-16 19:45:53 | MASTER-SAAO | (11h 28m 06.55s , -59d 53m 07.8s) | C | 60 | 17.6 | 784 | 2026-05-16 19:47:13 | MASTER-SAAO | (11h 24m 24.31s , -59d 37m 30.4s) | C | 60 | 17.4 | 784 | 2026-05-16 19:47:13 | MASTER-SAAO | (11h 28m 06.41s , -59d 53m 06.3s) | C | 60 | 17.6 | 863 | 2026-05-16 19:48:31 | MASTER-SAAO | (11h 24m 24.22s , -59d 37m 28.7s) | C | 60 | 17.3 | 863 | 2026-05-16 19:48:31 | MASTER-SAAO | (11h 28m 06.25s , -59d 53m 04.6s) | C | 60 | 17.6 | 1850 | 2026-05-16 20:04:28 | MASTER-SAAO | (11h 24m 04.79s , -59d 36m 36.8s) | C | 120 | 17.5 | 1850 | 2026-05-16 20:04:28 | MASTER-SAAO | (11h 27m 46.76s , -59d 52m 15.2s) | C | 120 | 17.8 | 2004 | 2026-05-16 20:07:02 | MASTER-SAAO | (11h 37m 54.80s , -59d 44m 27.2s) | C | 120 | 17.6 | 2004 | 2026-05-16 20:07:02 | MASTER-SAAO | (11h 41m 37.73s , -60d 00m 05.4s) | C | 120 | 17.8 | 2157 | 2026-05-16 20:09:35 | MASTER-SAAO | (11h 37m 55.16s , -59d 43m 25.3s) | C | 120 | 17.6 | 2157 | 2026-05-16 20:09:35 | MASTER-SAAO | (11h 41m 37.91s , -59d 59m 03.3s) | C | 120 | 17.9 | 2310 | 2026-05-16 20:12:09 | MASTER-SAAO | (11h 37m 59.95s , -59d 44m 22.1s) | C | 120 | 17.6 | 2310 | 2026-05-16 20:12:09 | MASTER-SAAO | (11h 41m 42.75s , -60d 00m 00.1s) | C | 120 | 17.8 | 2463 | 2026-05-16 20:14:41 | MASTER-SAAO | (11h 38m 07.66s , -57d 45m 21.9s) | C | 120 | 18.2 | 2463 | 2026-05-16 20:14:41 | MASTER-SAAO | (11h 41m 38.03s , -58d 01m 00.6s) | C | 120 | 18.5 | 2616 | 2026-05-16 20:17:15 | MASTER-SAAO | (11h 38m 13.31s , -57d 45m 08.0s) | C | 120 | 18.2 | 2616 | 2026-05-16 20:17:15 | MASTER-SAAO | (11h 41m 43.61s , -58d 00m 46.9s) | C | 120 | 18.5 | 2769 | 2026-05-16 20:19:47 | MASTER-SAAO | (11h 38m 10.50s , -57d 43m 18.7s) | C | 120 | 18.2 | 2769 | 2026-05-16 20:19:47 | MASTER-SAAO | (11h 41m 40.63s , -57d 58m 57.8s) | C | 120 | 18.5 | 2922 | 2026-05-16 20:22:21 | MASTER-SAAO | (11h 22m 13.66s , -57d 44m 42.9s) | C | 120 | 17.7 | 2922 | 2026-05-16 20:22:21 | MASTER-SAAO | (11h 25m 44.03s , -58d 00m 21.7s) | C | 120 | 17.9 | 3076 | 2026-05-16 20:24:54 | MASTER-SAAO | (11h 22m 15.81s , -57d 42m 54.4s) | C | 120 | 17.8 | 3076 | 2026-05-16 20:24:54 | MASTER-SAAO | (11h 25m 46.05s , -57d 58m 33.5s) | C | 120 | 18.0 | 3229 | 2026-05-16 20:27:28 | MASTER-SAAO | (11h 22m 10.17s , -57d 43m 35.0s) | C | 120 | 17.8 | 3229 | 2026-05-16 20:27:28 | MASTER-SAAO | (11h 25m 40.54s , -57d 59m 14.2s) | C | 120 | 18.0 | 3383 | 2026-05-16 20:30:01 | MASTER-SAAO | (11h 13m 44.65s , -61d 42m 13.8s) | C | 120 | 18.2 | 3383 | 2026-05-16 20:30:01 | MASTER-SAAO | (11h 17m 41.85s , -61d 57m 51.5s) | C | 120 | 18.6 | 3536 | 2026-05-16 20:32:34 | MASTER-SAAO | (11h 13m 50.07s , -61d 43m 09.6s) | C | 120 | 18.2 | 3536 | 2026-05-16 20:32:34 | MASTER-SAAO | (11h 17m 47.42s , -61d 58m 47.3s) | C | 120 | 18.7 | 3689 | 2026-05-16 20:35:07 | MASTER-SAAO | (11h 13m 44.81s , -61d 44m 05.2s) | C | 120 | 18.2 | 3689 | 2026-05-16 20:35:07 | MASTER-SAAO | (11h 17m 42.30s , -61d 59m 42.9s) | C | 120 | 18.7 | 3842 | 2026-05-16 20:37:41 | MASTER-SAAO | (11h 24m 03.00s , -59d 37m 40.6s) | C | 120 | 17.5 | 3842 | 2026-05-16 20:37:41 | MASTER-SAAO | (11h 27m 45.41s , -59d 53m 19.5s) | C | 120 | 17.6 | 3995 | 2026-05-16 20:40:14 | MASTER-SAAO | (11h 23m 59.91s , -59d 35m 52.6s) | C | 120 | 17.5 | 3995 | 2026-05-16 20:40:14 | MASTER-SAAO | (11h 27m 42.09s , -59d 51m 31.5s) | C | 120 | 17.6 | 4149 | 2026-05-16 20:42:48 | MASTER-SAAO | (11h 23m 59.68s , -59d 37m 31.9s) | C | 120 | 17.5 | 4149 | 2026-05-16 20:42:48 | MASTER-SAAO | (11h 27m 42.06s , -59d 53m 11.0s) | C | 120 | 17.6 | 4303 | 2026-05-16 20:45:21 | MASTER-SAAO | (11h 24m 02.31s , -59d 35m 54.7s) | C | 120 | 17.5 | 4303 | 2026-05-16 20:45:21 | MASTER-SAAO | (11h 27m 44.51s , -59d 51m 33.8s) | C | 120 | 17.6 | 4456 | 2026-05-16 20:47:54 | MASTER-SAAO | (11h 27m 39.44s , -59d 52m 02.8s) | C | 120 | 17.6 | 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/44651. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42778] SVOM GRB260516.86: Global MASTER-Net observations report
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44650 SUBJECT: SVOM GRB260516.86: Global MASTER-Net observations report DATE: 26/05/16 21:14:44 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-Tavrida robotic telescope [1] located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the SVOM GRB260516.86 (trigger No 1778963908,15h 35m 23.71s , +06d 22m 21.4s, R=0.1937) errorbox 767 sec after notice time and 1684 sec after trigger time at 2026-05-16 21:06:32 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 39 deg. The sun altitude is -25.7 deg. The galactic latitude b = 45 deg., longitude l = 13 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3319281 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 1714 | 2026-05-16 21:06:32 | MASTER-Tavrida | (15h 35m 16.63s , +06d 23m 55.5s) | C | 60 | 18.6 | 1783 | 2026-05-16 21:07:41 | MASTER-Tavrida | (15h 35m 20.66s , +06d 25m 06.4s) | C | 60 | 18.6 | 1852 | 2026-05-16 21:08:50 | MASTER-Tavrida | (15h 35m 12.84s , +06d 24m 31.1s) | C | 60 | 18.6 | 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/44650. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42777] GRB 260516D: SVOM possible detection of a short faint burst
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44649 SUBJECT: GRB 260516D: SVOM possible detection of a short faint burst DATE: 26/05/16 21:08:26 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP), H. Goto (RIKEN/CEA), A. Saccardi (CEA/Irfu) report on behalf of the SVOM mission team: At 2026-05-16T20:39:50 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260516D (SVOM burst-id sb26051616). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 6.73 in the [5-20] keV energy band over a time window of 81.92 seconds starting at 2026-05-16T20:38:28. The localization of the best alert is R.A., Dec. 233.849, 6.373 degrees: R.A. (J2000) = 15h35m23.71s Dec. (J2000) = 6d22m21.34s with a 90% confidence level (C.L.) radius of 11.62 arcmin (including systematic error of 2 arcmin added in quadrature). Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst. A Svom ToO has been scheduled. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Andrea Saccardi (CEA): andrea.saccardi(a)cea.fr Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44649. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42776] GRB 260516C: Fermi GBM Final Real-time Localization
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44648 SUBJECT: GRB 260516C: Fermi GBM Final Real-time Localization DATE: 26/05/16 19:45:10 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 LONG GRB At 19:34:38 UT on 16 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260516C (trigger 800652883.931176 / 260516816). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 172.6, Dec = -59.9 (J2000 degrees, equivalent to J2000 11h 30m, -59d 53'), with a statistical uncertainty of 3.2 degrees. The angle from the Fermi LAT boresight is 36.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516816/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516816/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516816/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44648. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42775] Konus-Wind detection of GRB 260515A
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44647 SUBJECT: Konus-Wind detection of GRB 260515A DATE: 26/05/16 19:07:11 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: A long-duration GRB 260515A (SVOM detection: Brunet et al., GCN 44622) was detected by Konus-Wind (KW)in the waiting mode at T0=T0(KW)~19:08:19UT. A Bayesian block analysis of the KW data in the 20-1500 keV band reveals a ~8 sigma count rate increase in the interval from ~T0+0.4 s to ~T0+9.3 s from the SVOM detection time. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260515A/ Modeling the time-integrated spectrum of the burst by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.37 (-0.17, + 0.17) and Ep = 95(-9,+10) keV. In the 10 keV -10 MeV band, standard for the KW analysis, the burst fluence is (7.70 ± 0.81)x10^-6 erg/cm^2 and the 2.944 s peak energy flux is (1.47 ± 0.22)x10^-7 erg/cm^2/s. Assuming the redshift z=0.764 (Malesani et al., GCN 44629) 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 burst isotropic energy release E_iso to (1.25 ± 0.15)x10^52 erg, the isotropic peak luminosity L_iso to (5.70 ± 0.85)x10^50 erg/s, and the rest-frame peak spectral energy Ep,z to (168 ± 18) keV. With the obtained estimates, GRB 260515A is consistent with 68% prediction bands of both 'Amati' relation and 90% prediction bands of 'Yonetoku' relation 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/GRB260515A/GRB260515A_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/44647. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42774] GRB 260515A: Liverpool Telescope optical detection
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44646 SUBJECT: GRB 260515A: Liverpool Telescope optical detection DATE: 26/05/16 14:32:40 GMT FROM: Dimple at University of Birmingham <dimplepanchal96(a)gmail.com> Dimple (U. Birmingham), B. P. Gompertz (U. Birmingham), P. O'Brien (U. Leicester), D. O'Neill (U. Birmingham) and D. B. Malesani (DAWN/NBI and Radboud) report on behalf of a larger collaboration: We conducted follow-up observations of GRB 260515A (Brunet et al., GCN 44622) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 22:42:40 UT on 2026-05-15, ~3.57 hr after the burst, and consisted of 5 x 200 s exposures in each of the SDSS g and i filters. We detect the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628, Dennefeld et al., GCN 44633; Li et al., GCN 44634, Antier et al., GCN 44643) in both filters, and measure an AB magnitude of g = 21.06 ± 0.04. Magnitudes are calibrated against nearby Pan-STARRS stars and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44646. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42773] GRB 260515A: LCO optical counterpart detection
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44645 SUBJECT: GRB 260515A: LCO optical counterpart detection DATE: 26/05/16 14:16:15 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), A. López-Oramas (IAC and ULL), and D. Aguado (IAC and ULL) Following the detection of the SVOM/ECLAIRs GRB 260515A (Brunet et al., GCN 44622), detected also in Einstein Probe FXT follow-up observations (Wang et al., GCN 44642), we observed the field with one of the three Las Cumbres Observatory (LCO) 1-m telescopes, equipped with Sinistro cameras, located at the LCO node at Sutherland Observatory, South Africa. The observation, a single exposure of 180 sec in the SDSS r' filter, started on 2026-05-15 at 21:17:54 UT, 2.16 hours after the SVOM trigger. The optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Malesani et al., GCN 44629; Dennefeld et al., GCN 44633; Li et al., GCN 44634; and Antier et al., GCN 44643) with redshift of z = 0.764 (Malesani et al., GCN 44629) is clearly detected in our image with an AB magnitude of r' = 20.32 +/- 0.10, calibrated against the PanSTARRS-1 DR2 catalog and not corrected for Galactic extinction. This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026A-011, SGLF and Superluminous Supernovae surveys). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/44645. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42772] Fermi Gamma-ray Burst Monitor trigger 800627191/260516518 is not a GRB
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44644 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 800627191/260516518 is not a GRB DATE: 26/05/16 14:08:33 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> U. Pathak (IITB) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 800627191/260516518 at 12:26:26.60 UT on 16 May 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/44644. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42771] GRB 260515A: SVOM/COLIBRÍ (FM-GFT) further optical observations
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44643 SUBJECT: GRB 260515A: SVOM/COLIBRÍ (FM-GFT) further optical observations DATE: 26/05/16 11:06:13 GMT FROM: antier(a)ijclab.in2p3.fr Sarah Antier (IJCLAB), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Dalya Akl (NYUAD), William H. Lee (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (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), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM), and Andrea Saccardi (CEA/Irfu) report: We imaged the field of the SVOM/ECLAIRs GRB 260515A (M. Brunet et al., GCN Circ. 44622) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-16 08:25 to 09:49 UTC (from to 13.3 hours after the trigger) and obtained 128 minutes of simultaneous exposure in r and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU 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. We detect the source reported by Saccardi et al. (GCN Circ. 44624) with preliminary unsubtracted magnitudes of: r = 21.78 +/- 0.02 z = 21.50 +/- 0.05 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/44643. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42770] GRB 260515A: EP-FXT follow-up observation
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44642 SUBJECT: GRB 260515A: EP-FXT follow-up observation DATE: 26/05/16 09:39:53 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z.M. Wang (BNU), X.X. Sun(NAO, CAS), Y.H.Cheng (SWIFAR, YNU), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed an automatic follow-up observation of GRB 260515A detected by SVOM/ECLAIRs (SVOM/sb26051504, Brunet et al., GCN 44622). The follow-up obervation started at 2026-05-15T20:51:27 UTC, approximately 1.7 hours after the SVOM trigger, with a total exposure time of 5.9 ks. On-ground analysis of the FXT data found an uncatalogued fading source within the ECLAIRs error circle at R.A., Dec. = 227.6846, 24.5566 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). This position is consistent with the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Dennefeld et al., GCN 44633; Li et al., GCN 44634). The average FXT 0.3-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value of 3.47×10^20 cm^-2 and a photon index of 1.71(-0.09/+0.09). The derived average unabsorbed flux in the 0.3-10 keV band is 7.13(-0.19/+0.21) x 10^(-12) erg/s/cm^2. 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/44642. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42769] EP260514a: refined analysis of the EP-WXT and follow-up EP-FXT observations
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44641 SUBJECT: EP260514a: refined analysis of the EP-WXT and follow-up EP-FXT observations DATE: 26/05/16 08:08:24 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. Cheng (SWIFAR, YNU), K.R. Ni (CCNU), R.-Z. Li (YNAO, CAS) and W.-D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260514a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Cheng et al., GCN 44613) at 2026-05-14T16:56:06 (UTC). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.49 × 10^20 cm^-2, and a photon index of 1.32 (+/-0.22). The derived average unabsorbed 0.5-4 keV flux is 4.24 (+0.70/-0.60) × 10^(-10) erg/s/cm^2. Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-05-15 08:20:00(UTC), ~15.5 hours after the WXT detection. The exposure time of the observation is around 5 ks. The on-ground analysis of the FXT data found an uncatalogued source at R.A. = 214.2955 deg, DEC = 49.3733 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a fixed hydrogen column density of 1.49 × 10^20 cm^-2 and a photon index of 1.28 (+0.76/-0.67). The derived average unabsorbed 0.5-10 keV flux is 2.28 (-0.55/+1.17) × 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The optical observations of EP260514a were reported by Lipunov et al. (GCN 44614), Mohan et al. (GCN 44619), Sánchez et al. (GCN 44632) and Li et al. (GCN 44638), Liu et al.,(GCN 44639) and Liu et al.,(GCN 44640). 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/44641. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42768] EP260514a: NOT optical counterpart confirmation
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44640 SUBJECT: EP260514a: NOT optical counterpart confirmation DATE: 26/05/16 07:51:09 GMT FROM: liuxing(a)nao.cas.cn X. Liu, Z.P. Zhu, J. An, S.Q. Jiang, L.B. He, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), L. Fuglsang, A. S. Martensson（NOT）report: We observed the field of EP260514a detected by EP/WXT (Cheng et al., GCN 44613; Lipunov et al., GCN 44614; Mohan et al., GCN 44619; Sánchez et al., GCN 44632; Li et al., GCN 44638; Liu et al., GCN 44639) using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observation started at 2026-05-15 23:05:35 UT, i.e., about 1.26 days post-burst, and 4x300s r-band frames were obtained. The optical counterpart candidate (Liu et al., GCN 44639) has decayed to r = 23.1 +/- 0.1 in our stacked image at a median time of 1.26 days post-trigger, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. Its coordinares are improved as R.A.(J2000)= 14:17:10.49 Dec.(J2000)= +49:22:31.4 with an uncertainty of ~0.5 arcsec. No optical source could be detected in the Legacy DR10 image at the corresponding coordinates, down to a limiting magnitude of r ~ 24.3. We thus think the source is likely the optical counterpart of EP260514a. View this GCN Circular online at https://gcn.nasa.gov/circulars/44640. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42767] EP260514a: TRT optical counterpart candidate
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44639 SUBJECT: EP260514a: TRT optical counterpart candidate DATE: 26/05/16 07:39:15 GMT FROM: liuxing(a)nao.cas.cn X. Liu, (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan, K. Noysena, K. Chanchaiworawit (NARIT), S.Q. Jiang, J. An, Z.P. Zhu, L.B. He, D. Xu, Z. Fan, W.X. Li, N.C. Sun (NAOC), S.Y. Fu (HUST) report: We observed the field of EP260514a dtected by EP/WXT (Cheng et al., GCN 44613), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO). Observation started at 2026-05-15 04:25:07 UT, i.e., 0.48 day post-burst, and 6x300 s R-band frames were obtained. Image subtraction using Legacy-DR10 reveals an uncatalogued optical source within the EP/WXT (Cheng et al., GCN 44613) error circle at coordinates R.A. (J2000) = 14:17:10.41 Dec. (J2000) = +49:22:30.9 with an uncertainty of ~ 1.5 arcsec. The source had R ~ 21.8 mag with SNR of ~3 at a median time of 11.74 hrs post-trigger, calibrated with Pan-STARRS DR2 converted using Lupton (2005) equations and not corrected for Galactic extinction. No NEO would be at the above position at the observational time by checking MPC. We think the source could be the optical cointerpart of EP260514a. View this GCN Circular online at https://gcn.nasa.gov/circulars/44639. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42766] EP260514a: SVOM/VT optical candidate
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44638 SUBJECT: EP260514a: SVOM/VT optical candidate DATE: 26/05/16 06:59:29 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. L. Qiu, C. Wu, L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) and J. Palmerio report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations to the field of EP260514a (Lipunov et al., GCN 44614; Mohan et al., GCN 44619; Sánchez et al., GCN 44632), which was triggered by Einstein Probe (EP260514a, Cheng et al., GCN 44613). The observation started at 2026-05-15T03:03:58 UTC, 10.13 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. An uncatalogued optical source was detected within WXT's error box (Cheng et al., GCN 44613) in both channels, compared to the Legacy Survey. The following measurements are in the AB magnitude without correction for Galactic extinction: Mid time | Band | Exposure Time | Brightness 11.96 h VT_B 44*50 s 23.15 +/- 0.22 mag 11.97 h VT_R 39*50 s 22.03 +/- 0.14 mag The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44638. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42765] Fermi GRB 260516B: Global MASTER-Net observations report
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44637 SUBJECT: Fermi GRB 260516B: Global MASTER-Net observations report DATE: 26/05/16 05:31:19 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260516B ( Fermi GBM team, GCN 44636) errorbox 25 sec after notice time and 66 sec after trigger time at 2026-05-16 05:13:43 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 33 deg. The sun altitude is -31.9 deg. The galactic latitude b = 62 deg., longitude l = 185 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3317801 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 71 | 2026-05-16 05:13:43 | MASTER-OAGH | (10h 51m 27.92s , +35d 52m 25.3s) | C | 10 | 17.7 | 71 | 2026-05-16 05:13:43 | MASTER-OAGH | (10h 42m 00.53s , +36d 28m 21.0s) | C | 10 | 18.1 | 96 | 2026-05-16 05:14:03 | MASTER-OAGH | (10h 51m 34.28s , +35d 52m 45.8s) | C | 20 | 18.5 | 96 | 2026-05-16 05:14:03 | MASTER-OAGH | (10h 42m 07.12s , +36d 28m 41.3s) | C | 20 | 18.7 | 127 | 2026-05-16 05:14:33 | MASTER-OAGH | (10h 47m 53.89s , +37d 48m 21.6s) | C | 20 | 18.5 | 127 | 2026-05-16 05:14:33 | MASTER-OAGH | (10h 38m 11.43s , +38d 24m 12.2s) | C | 20 | 18.9 | 164 | 2026-05-16 05:15:05 | MASTER-OAGH | (10h 50m 08.55s , +31d 29m 37.4s) | C | 30 | 18.4 | 209 | 2026-05-16 05:15:05 | MASTER-OAGH | (10h 50m 08.53s , +31d 29m 37.5s) | C | 120 | 19.5 | Coadd 164 | 2026-05-16 05:15:05 | MASTER-OAGH | (10h 41m 11.47s , +32d 05m 27.5s) | C | 30 | 19.0 | 209 | 2026-05-16 05:15:05 | MASTER-OAGH | (10h 41m 11.47s , +32d 05m 27.7s) | C | 120 | 19.9 | Coadd 209 | 2026-05-16 05:15:45 | MASTER-OAGH | (10h 50m 12.93s , +31d 31m 17.3s) | C | 40 | 18.6 | 209 | 2026-05-16 05:15:45 | MASTER-OAGH | (10h 41m 15.84s , +32d 07m 06.8s) | C | 40 | 19.2 | 264 | 2026-05-16 05:16:36 | MASTER-OAGH | (10h 50m 05.67s , +31d 30m 35.8s) | C | 50 | 19.0 | 264 | 2026-05-16 05:16:36 | MASTER-OAGH | (10h 41m 08.74s , +32d 06m 25.1s) | C | 50 | 19.4 | 329 | 2026-05-16 05:17:36 | MASTER-OAGH | (10h 50m 05.11s , +31d 31m 37.8s) | C | 60 | 19.0 | 329 | 2026-05-16 05:17:36 | MASTER-OAGH | (10h 41m 08.14s , +32d 07m 26.7s) | C | 60 | 19.5 | 637 | 2026-05-16 05:22:14 | MASTER-OAGH | (10h 49m 47.37s , +36d 49m 59.5s) | C | 120 | 19.7 | 637 | 2026-05-16 05:22:14 | MASTER-OAGH | (10h 40m 14.19s , +37d 25m 42.5s) | C | 120 | 20.0 | 768 | 2026-05-16 05:24:24 | MASTER-OAGH | (10h 49m 47.37s , +36d 48m 29.8s) | C | 120 | 19.7 | 768 | 2026-05-16 05:24:24 | MASTER-OAGH | (10h 40m 14.62s , +37d 24m 14.1s) | C | 120 | 19.8 | 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/44637. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42764] GRB 260516B: Fermi GBM Final Real-time Localization
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44636 SUBJECT: GRB 260516B: Fermi GBM Final Real-time Localization DATE: 26/05/16 05:23:15 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 05:12:36 UT on 16 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260516B (trigger 800601161.994496 / 260516217). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 161.5, Dec = 36.8 (J2000 degrees, equivalent to J2000 10h 46m, 36d 47'), with a statistical uncertainty of 4.8 degrees. The angle from the Fermi LAT boresight is 58.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516217/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516217/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516217/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44636. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42763] Fermi Gamma-ray Burst Monitor trigger 800592653/260516119 is not a GRB
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44635 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 800592653/260516119 is not a GRB DATE: 26/05/16 05:07:27 GMT FROM: atrigg2(a)lsu.edu A. C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 800592653/260516119 at 02:50:48.94 UT on 16 May 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to an accidental trigger." View this GCN Circular online at https://gcn.nasa.gov/circulars/44635. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42762] GRB 260515A: SVOM/VT optical observations
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44634 SUBJECT: GRB 260515A: SVOM/VT optical observations DATE: 26/05/16 03:45:58 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. L. Qiu, C. Wu, L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio, A. Saccardi (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic slew of GRB260515A triggered by SVOM/ECLAIRs (sb26051504, Brunet et al., GCN 44622). The observation started at 2026-05-15T19:10:54 UTC, i.e., 155 seconds post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. An additional ToO observation was performed started at 2026-05-15T20:59:23 UTC, 1.85 hours post trigger. The optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Dennefeld et al., GCN 44633) with redshift z=0.764 (Malesani et al., GCN 44629) was detected clearly in both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 3.00 m VT_B 50 s 16.06 +/- 0.05 mag 3.00 m VT_R 50 s 15.49 +/- 0.04 mag 3.91 m VT_B 26*70 s 21.27 +/- 0.08 mag 3.92 h VT_R 19*70 s 20.93 +/- 0.07 mag During our observations the decay slope changed from 1.3 to 0.8. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44634. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42761] GRB 260515A: OHP/T193 optical observations
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44633 SUBJECT: GRB 260515A: OHP/T193 optical observations DATE: 26/05/16 03:39:29 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> M. Dennefeld (IAP), B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Saccardi (CEA/Irfu) report on behalf of a larger collaboration: We observed the field of the SVOM/ECLAIRs GRB 260515A (Brunet et al., GCN 44622; He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Lipunov et al., GCN 44627; Wu et al., GCN 44628; Malesani et al., GCN 44629) using the T193cm telescope at Observatoire de Haute-Provence (France) with the MISTRAL spectro-imager. We obtained two epochs: 2x5 minutes of exposure in the r-band starting at 2026-05-15T21:29:45 UT (2.36 hr after the trigger), and 3x10 minutes of exposure in the r-band starting at 2026-05-16T001045UT (5.04 hr after the trigger). In the stacked images, the optical counterpart is visible with preliminary magnitudes of: r = 20.42 +/- 0.13 mag (1st visit) r = 21.34 +/- 0.12 mag (2nd visit) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction. We acknowledge the excellent support from Observatoire de Haute-Provence and in particular Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/44633. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42760] EP260514a: COLIBRÍ optical upper limits
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44632 SUBJECT: EP260514a: COLIBRÍ optical upper limits DATE: 26/05/16 03:23:14 GMT FROM: freddalvarez(a)astro.unam.mx Fredd Sánchez Álvarez (UNAM), Noémie Globus (UNAM), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260514a detected by Einstein Probe/WXT (Cheng et al., GCN Circ. 44613 ) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-15 03:27 to 03:44 UTC, corresponding to 10.52 to 10.80 hours after the trigger, and obtained 14 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ ASU pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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 images and after performing image subtraction using templates from the DESI Legacy Survey (Dey et al. 2019), we do not detect any new sources within the WXT error region (Cheng et al., GCN Circ. 44613) down to the following 5-sigma limits: r > 22.1. z > 20.9. Our upper limits are consistent with the previously reported by MASTER (Lipunov et al., GCN Circ. 44614) and GROWTH-India Telescope (Mohan et al., GCN Circ. 44619). We note the presence of four quasars: SDSS J141722.46+492142.1 SDSS J141658.83+492220.9 SDSS J141720.92+492351.5 SDSS J141653.45+492109.8 within the WXT region and, considering our upper limits, we cannot rule out the possibility that the trigger is related to one of these sources. 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/44632. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42759] GRB 260516A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44631 SUBJECT: GRB 260516A: Fermi GBM Final Real-time Localization DATE: 26/05/16 03:01:20 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 02:50:48 UT on 16 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260516A (trigger 800592653.936132 / 260516119). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 111.5, Dec = -37.6 (J2000 degrees, equivalent to J2000 07h 26m, -37d 36'), with a statistical uncertainty of 7.7 degrees. The angle from the Fermi LAT boresight is 163.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516119/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516119/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516119/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44631. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42758] GRID detection of GRB 260507A
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44630 SUBJECT: GRID detection of GRB 260507A DATE: 26/05/16 01:47:43 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Longhao Li, Tingkai Sun, Chenyv Wang report on behalf of the GRID Collaboration: GRID-09 reports the detection of the long-duration GRB 260507A, which was also detected by Fermi GBM (GCN Circular 44493). The event was triggered with GRID on 2026-05-07 at 20:28:00 UTC. The measured burst duration (T90) in the 30-2000 keV range is approximately 12.102083333333333 +/- 2.8242414050797913 seconds. The GRID light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260507A/GRID_260…. GRID is a student-led project to monitor the transient gamma-ray sky with multiple detectors onboard different nanosatellites in the era of multi-messenger astronomy. For more information about GRID, please refer to the following references: https://doi.org/10.1007/s10686-019-09636-w and https://doi.org/10.1007/s10686-021-09819-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/44630. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42757] GRB 260515A: GTC/OSIRIS+ spectroscopic redshift z = 0.764
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44629 SUBJECT: GRB 260515A: GTC/OSIRIS+ spectroscopic redshift z = 0.764 DATE: 26/05/16 01:11:21 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), S. Geier (GTC), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), L. Izzo (INAF/OACN and DARK/NBI), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), F. Perez Toledo (GTC) report: We observed the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628) of GRB 260515A (Brunet et al., GCN 44622) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. In the 20-s acquisition image (beginning on 2026-05-15 at 23:48:49.010 UT, that is 4.67 hr after trigger), the optical afterglow is well detected with a magnitude r = 21.15 ± 0.10 (AB), calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction. A total of 3 spectra of 1200 s were secured, starting on 2026-05-15 at 23:52:26.010 UT (4.73 hr after trigger), using grism R1000B. Continuum is visible over the range 3650-7800 AA. A number of metal absorption features are detected, which we interpret as due to Fe II, Mg II, and Mg I, all at a common redshift z = 0.764, which we suggest to be the redshift of GRB 260515A. We also detect emission due to the [O II] doublet at the same redshift. This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). View this GCN Circular online at https://gcn.nasa.gov/circulars/44629. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42756] GRB 260515A: LCO optical observations
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44628 SUBJECT: GRB 260515A: LCO optical observations DATE: 26/05/16 00:11:51 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of the SVOM mission team: We observed the field of the SVOM/ECLAIRs GRB 260515A (Brunet et al., GCN 44622) with the LCO 1m telescope at Teide Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-15 at 22:42:33 UT (about 3.57 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626) is faintly detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction: r = 21.22 +/- 0.09 AB (mid-time 4.44 hr after the trigger); z > 20.5 AB (3-sigma, mid-time 3.63 hr after the trigger). A marginal detection is recovered through forced photometry in the z band as well, to the level of z = 20.6 +/- 0.4 AB. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44628. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42755] SVOM GRB 260515A: Global MASTER-Net observations report
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44627 SUBJECT: SVOM GRB 260515A: Global MASTER-Net observations report DATE: 26/05/15 21:53:05 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-Tavrida robotic telescope [1] located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the SVOM GRB 260515A ( SVOM/ECLAIRs Commissioning Team et al., GCN 44622) errorbox 30 sec after notice time and 659 sec after trigger time at 2026-05-15 19:19:18 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 32 deg. The sun altitude is -18.8 deg. The galactic latitude b = 58 deg., longitude l = 36 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3316887 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 719 | 2026-05-15 19:19:18 | MASTER-Tavrida | (15h 10m 30.15s , +24d 42m 28.1s) | C | 120 | 18.8 | 842 | 2026-05-15 19:21:20 | MASTER-Tavrida | (15h 10m 30.34s , +24d 42m 18.6s) | C | 120 | 19.1 | 965 | 2026-05-15 19:23:23 | MASTER-Tavrida | (15h 10m 30.45s , +24d 42m 11.4s) | C | 120 | 19.1 | 1087 | 2026-05-15 19:25:26 | MASTER-Tavrida | (15h 10m 30.55s , +24d 42m 04.2s) | C | 120 | 18.9 | 1210 | 2026-05-15 19:27:28 | MASTER-Tavrida | (15h 10m 30.61s , +24d 41m 58.5s) | C | 120 | 19.4 | 1332 | 2026-05-15 19:29:31 | MASTER-Tavrida | (15h 10m 30.65s , +24d 41m 52.9s) | C | 120 | 19.4 | 1455 | 2026-05-15 19:31:33 | MASTER-Tavrida | (15h 10m 30.66s , +24d 41m 47.7s) | C | 120 | 19.5 | 1577 | 2026-05-15 19:33:36 | MASTER-Tavrida | (15h 10m 30.65s , +24d 41m 42.7s) | C | 120 | 19.5 | 1700 | 2026-05-15 19:35:38 | MASTER-Tavrida | (15h 10m 30.62s , +24d 41m 38.1s) | C | 120 | 19.6 | 1822 | 2026-05-15 19:37:41 | MASTER-Tavrida | (15h 10m 30.62s , +24d 41m 33.2s) | C | 120 | 19.6 | 1945 | 2026-05-15 19:39:44 | MASTER-Tavrida | (15h 10m 30.62s , +24d 41m 28.5s) | C | 120 | 19.6 | 2068 | 2026-05-15 19:41:46 | MASTER-Tavrida | (15h 10m 30.61s , +24d 41m 24.0s) | C | 120 | 19.6 | 2190 | 2026-05-15 19:43:49 | MASTER-Tavrida | (15h 10m 30.62s , +24d 41m 19.0s) | C | 120 | 19.6 | 2313 | 2026-05-15 19:45:52 | MASTER-Tavrida | (15h 10m 30.63s , +24d 41m 14.6s) | C | 120 | 19.5 | 2436 | 2026-05-15 19:47:54 | MASTER-Tavrida | (15h 10m 30.61s , +24d 41m 09.9s) | C | 120 | 19.6 | 2558 | 2026-05-15 19:49:57 | MASTER-Tavrida | (15h 10m 30.58s , +24d 41m 05.5s) | C | 120 | 19.6 | 2681 | 2026-05-15 19:51:59 | MASTER-Tavrida | (15h 10m 30.55s , +24d 41m 00.9s) | C | 120 | 19.6 | 2804 | 2026-05-15 19:54:02 | MASTER-Tavrida | (15h 10m 30.53s , +24d 40m 56.5s) | C | 120 | 19.7 | 2926 | 2026-05-15 19:56:05 | MASTER-Tavrida | (15h 10m 30.51s , +24d 40m 52.0s) | C | 120 | 19.6 | 3049 | 2026-05-15 19:58:07 | MASTER-Tavrida | (15h 10m 30.50s , +24d 40m 47.5s) | C | 120 | 19.7 | 3179 | 2026-05-15 20:00:18 | MASTER-Tavrida | (15h 10m 34.07s , +24d 41m 17.5s) | C | 120 | 19.7 | 3302 | 2026-05-15 20:02:20 | MASTER-Tavrida | (15h 10m 34.06s , +24d 41m 13.1s) | C | 120 | 19.7 | 3424 | 2026-05-15 20:04:23 | MASTER-Tavrida | (15h 10m 34.06s , +24d 41m 08.9s) | C | 120 | 19.7 | 3547 | 2026-05-15 20:06:26 | MASTER-Tavrida | (15h 10m 34.02s , +24d 41m 04.4s) | C | 120 | 19.7 | 3670 | 2026-05-15 20:08:28 | MASTER-Tavrida | (15h 10m 34.02s , +24d 41m 00.1s) | C | 120 | 19.7 | 3793 | 2026-05-15 20:10:31 | MASTER-Tavrida | (15h 10m 34.02s , +24d 40m 55.8s) | C | 120 | 19.7 | 3915 | 2026-05-15 20:12:34 | MASTER-Tavrida | (15h 10m 34.02s , +24d 40m 51.4s) | C | 120 | 19.7 | 4038 | 2026-05-15 20:14:36 | MASTER-Tavrida | (15h 10m 34.01s , +24d 40m 47.0s) | C | 120 | 19.7 | 4161 | 2026-05-15 20:16:39 | MASTER-Tavrida | (15h 10m 34.00s , +24d 40m 42.8s) | C | 120 | 19.6 | 4283 | 2026-05-15 20:18:42 | MASTER-Tavrida | (15h 10m 34.02s , +24d 40m 38.5s) | C | 120 | 19.8 | 4406 | 2026-05-15 20:20:44 | MASTER-Tavrida | (15h 10m 34.01s , +24d 40m 34.2s) | C | 120 | 19.9 | 4529 | 2026-05-15 20:22:47 | MASTER-Tavrida | (15h 10m 34.01s , +24d 40m 30.0s) | C | 120 | 19.9 | 4651 | 2026-05-15 20:24:50 | MASTER-Tavrida | (15h 10m 33.97s , +24d 40m 26.2s) | C | 120 | 19.8 | 4774 | 2026-05-15 20:26:53 | MASTER-Tavrida | (15h 10m 33.93s , +24d 40m 22.2s) | C | 120 | 19.8 | 4897 | 2026-05-15 20:28:55 | MASTER-Tavrida | (15h 10m 33.91s , +24d 40m 17.9s) | C | 120 | 19.9 | 5020 | 2026-05-15 20:30:58 | MASTER-Tavrida | (15h 10m 33.93s , +24d 40m 13.4s) | C | 120 | 19.9 | 5143 | 2026-05-15 20:33:01 | MASTER-Tavrida | (15h 10m 33.94s , +24d 40m 09.2s) | C | 120 | 19.9 | 5265 | 2026-05-15 20:35:04 | MASTER-Tavrida | (15h 10m 33.96s , +24d 40m 04.8s) | C | 120 | 19.9 | 5388 | 2026-05-15 20:37:06 | MASTER-Tavrida | (15h 10m 33.97s , +24d 40m 00.6s) | C | 120 | 19.9 | 5510 | 2026-05-15 20:39:09 | MASTER-Tavrida | (15h 10m 33.95s , +24d 39m 56.5s) | C | 120 | 19.9 | 5633 | 2026-05-15 20:41:12 | MASTER-Tavrida | (15h 10m 33.91s , +24d 39m 52.7s) | C | 120 | 19.8 | 5756 | 2026-05-15 20:43:14 | MASTER-Tavrida | (15h 10m 33.93s , +24d 39m 48.3s) | C | 120 | 19.9 | 5878 | 2026-05-15 20:45:17 | MASTER-Tavrida | (15h 10m 33.94s , +24d 39m 43.8s) | C | 120 | 19.9 | 6001 | 2026-05-15 20:47:20 | MASTER-Tavrida | (15h 10m 33.96s , +24d 39m 39.5s) | C | 120 | 19.9 | 6124 | 2026-05-15 20:49:23 | MASTER-Tavrida | (15h 10m 33.99s , +24d 39m 35.1s) | C | 120 | 19.9 | 6246 | 2026-05-15 20:51:25 | MASTER-Tavrida | (15h 10m 33.93s , +24d 39m 31.4s) | C | 120 | 19.7 | 6369 | 2026-05-15 20:53:28 | MASTER-Tavrida | (15h 10m 33.93s , +24d 39m 27.2s) | C | 120 | 19.9 | 6492 | 2026-05-15 20:55:31 | MASTER-Tavrida | (15h 10m 33.95s , +24d 39m 22.9s) | C | 120 | 19.8 | 6615 | 2026-05-15 20:57:33 | MASTER-Tavrida | (15h 10m 34.00s , +24d 39m 18.6s) | C | 120 | 19.9 | 6737 | 2026-05-15 20:59:36 | MASTER-Tavrida | (15h 10m 34.00s , +24d 39m 14.5s) | C | 120 | 19.9 | 6860 | 2026-05-15 21:01:38 | MASTER-Tavrida | (15h 10m 34.02s , +24d 39m 10.3s) | C | 120 | 19.9 | 6983 | 2026-05-15 21:03:41 | MASTER-Tavrida | (15h 10m 34.07s , +24d 39m 06.1s) | C | 120 | 19.8 | 7105 | 2026-05-15 21:05:44 | MASTER-Tavrida | (15h 10m 34.10s , +24d 39m 01.9s) | C | 120 | 19.9 | 7228 | 2026-05-15 21:07:46 | MASTER-Tavrida | (15h 10m 34.10s , +24d 38m 57.7s) | C | 120 | 19.9 | 7350 | 2026-05-15 21:09:49 | MASTER-Tavrida | (15h 10m 34.11s , +24d 38m 53.5s) | C | 120 | 19.7 | 7472 | 2026-05-15 21:11:51 | MASTER-Tavrida | (15h 10m 34.14s , +24d 38m 49.3s) | C | 120 | 19.8 | 7595 | 2026-05-15 21:13:54 | MASTER-Tavrida | (15h 10m 34.17s , +24d 38m 45.0s) | C | 120 | 19.8 | 7718 | 2026-05-15 21:15:56 | MASTER-Tavrida | (15h 10m 34.22s , +24d 38m 40.5s) | C | 120 | 19.8 | 7840 | 2026-05-15 21:17:58 | MASTER-Tavrida | (15h 10m 34.23s , +24d 38m 36.3s) | C | 120 | 19.9 | 7962 | 2026-05-15 21:20:01 | MASTER-Tavrida | (15h 10m 34.25s , +24d 38m 31.9s) | C | 120 | 19.9 | 8085 | 2026-05-15 21:22:03 | MASTER-Tavrida | (15h 10m 34.28s , +24d 38m 27.7s) | C | 120 | 19.8 | 8207 | 2026-05-15 21:24:06 | MASTER-Tavrida | (15h 10m 34.33s , +24d 38m 23.2s) | C | 120 | 19.9 | 8330 | 2026-05-15 21:26:08 | MASTER-Tavrida | (15h 10m 34.34s , +24d 38m 19.1s) | C | 120 | 19.9 | 8452 | 2026-05-15 21:28:11 | MASTER-Tavrida | (15h 10m 34.36s , +24d 38m 14.5s) | C | 120 | 19.9 | 8575 | 2026-05-15 21:30:14 | MASTER-Tavrida | (15h 10m 34.36s , +24d 38m 09.9s) | C | 120 | 19.8 | 8698 | 2026-05-15 21:32:16 | MASTER-Tavrida | (15h 10m 34.41s , +24d 38m 05.3s) | C | 120 | 19.9 | 8820 | 2026-05-15 21:34:19 | MASTER-Tavrida | (15h 10m 34.43s , +24d 38m 00.8s) | C | 120 | 19.9 | 8943 | 2026-05-15 21:36:21 | MASTER-Tavrida | (15h 10m 34.46s , +24d 37m 56.3s) | C | 120 | 19.9 | 9065 | 2026-05-15 21:38:24 | MASTER-Tavrida | (15h 10m 34.51s , +24d 37m 51.7s) | C | 120 | 19.9 | 9188 | 2026-05-15 21:40:27 | MASTER-Tavrida | (15h 10m 34.53s , +24d 37m 47.2s) | C | 120 | 19.8 | 9311 | 2026-05-15 21:42:29 | MASTER-Tavrida | (15h 10m 34.57s , +24d 37m 42.6s) | C | 120 | 19.8 | 9433 | 2026-05-15 21:44:32 | MASTER-Tavrida | (15h 10m 34.59s , +24d 37m 38.0s) | C | 120 | 19.8 | 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/44627. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42754] GRB 260515A: NOT optical observations.
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44626 SUBJECT: GRB 260515A: NOT optical observations. DATE: 26/05/15 21:31:23 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> L. B. He (NAOC), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), B. Schneider (LAM), L. Fuglsang (NOT), A. A. Djupvik (NOT), report on behalf of a larger collaboration: We observed the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625) of the SVOM/ECLAIRs GRB 260515A (Brunet et al., GCN 44622) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. In a single 300-s exposure commencing on May 15.8696 UT (1.73 hr after trigger), the optical afterglow is well detected in our images, with an AB magnitude of r = 20.22 +- 0.04 (calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction). View this GCN Circular online at https://gcn.nasa.gov/circulars/44626. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42753] SVOM GRB 260515A: MASTER OT J151044.43+243321.7 optical counterpart detection
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44625 SUBJECT: SVOM GRB 260515A: MASTER OT J151044.43+243321.7 optical counterpart detection DATE: 26/05/15 20:41:12 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> A.Sosnovskij, A.Kuznetsov, V.Lipunov, I.Panchenko, P.Balanutsa, K.Zhirkov, E.Gorbovskoy, G.Antipov, N.Tiurina, Ya.Kechin, V.Senik, A.Chasovnikov, V.Topolev,D.Vlasenko, A.Sankovich, I.Gorbunov, V.Fedorova, A.Telnova (Lomonosov MSU), N.Budnev, O.Gress (ISU), F.Podesta, M.J. Segura, C.Francile, R.Podesta, E. Gonzalez (OAFA, SJNU), D.Buckley (SAAO), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich (Blagoveschensk Educational StateUniversity) R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tavrida robotic telescope of MASTER Global Robotic Net [1-4] was pointed to the SVOM GRB260516A (Brunet et al. GCN 44622) error-box at 2026-05-15 19:19:18UT (notice time=2026-05-15 19:18:47) with upper limit up to 19.6m at single images. MASTER OT J151044.43+243321.7 / AT2026msu detection by Lomonosov MSU: MASTER-Tavrida auto-detection system discovered OT source at (RA, Dec) = 15h 10m 44.43s +24d 33m 21.7s on 2026-05-15.80648 UT. The OT magnitude (unfiltered) is 17.4m (mlim=19.1). The OT is seen in all images. There is no minor planet at this place. We have reference image on 2024-03-17.95291 UT with unfiltered mlim=19.5m. Spectral observations are required. Optical counterpart first was publishied by JinShan 100B Telescope (He et al. GCN 44623) and observed by Svom/VT (GCN 44624) Real time updated cover map and OT are available here: https://master.sai.msu.ru/site/master2/observ.php?id=3316865 [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/44625. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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