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

[vsnet-grb-info 42652] EP260509a: Global MASTER-Net observations report
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44525 SUBJECT: EP260509a: Global MASTER-Net observations report DATE: 26/05/10 21:36:20 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) was pointed to the EP260509a ( EP Team et al., GCN 44517) errorbox 24957 sec after notice time and 1 days 27906 sec after trigger time at 2026-05-10 21:29:08 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 61 deg. The sun altitude is -29.1 deg. The galactic latitude b = 25 deg., longitude l = 353 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3305450 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 114336 | 2026-05-10 21:29:08 | MASTER-Kislovodsk | (15h 55m 47.13s , -18d 04m 15.2s) | C | 60 | 12.6 | 114336 | 2026-05-10 21:29:08 | MASTER-Kislovodsk | (15h 55m 58.90s , -18d 27m 08.8s) | C | 60 | 17.8 | 114426 | 2026-05-10 21:30:38 | MASTER-Kislovodsk | (15h 55m 42.18s , -18d 05m 11.2s) | C | 60 | 12.1 | 114426 | 2026-05-10 21:30:38 | MASTER-Kislovodsk | (15h 55m 53.95s , -18d 28m 02.6s) | C | 60 | 17.9 | 114514 | 2026-05-10 21:32:06 | MASTER-Kislovodsk | (15h 55m 55.18s , -18d 27m 07.8s) | C | 60 | 17.9 | 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/44525. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42651] Fermi GBM Sub-Threshold Detection of GRB 260510B
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44524 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 260510B DATE: 26/05/10 21:21:21 GMT FROM: Eva MP at INAOE <eva.palafox(a)gmail.com> E. Palafox (INAOE) reports on behalf of the Fermi-GBM Team: SVOM/ECLAIRs detected GRB 260510B on 2026-05-10 at 12:19:20 UTC (A. Saccardi et al. 2026, [GCN 44515](https://gcn.nasa.gov/circulars/44515)) There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates. The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient approximately 3 s after the ECLAIRs best image SNR time of 2026-05-10T12:19:15. The Targeted Search candidate was found most significantly on the 8 s timescale using the "normal" spectral template (i.e., Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) and has a false alarm rate of 1.1e-04 Hz. The Fermi-MET of the start time of this transient is 800108363.27 s. The Targeted Search localization is found to be spatially consistent with the ECLAIRs one, with a spatial association probability of 98.6%. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/44524. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42650] GRB 260510D: Fermi GBM Final Real-time Localization
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44523 SUBJECT: GRB 260510D: Fermi GBM Final Real-time Localization DATE: 26/05/10 20:48:45 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 20:38:08 UT on 10 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260510D (trigger 800138293.771294 / 260510860). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 3.0, Dec = 37.4 (J2000 degrees, equivalent to J2000 00h 12m, 37d 23'), with a statistical uncertainty of 13.9 degrees. The angle from the Fermi LAT boresight is 61.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510860/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510860/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510860/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44523. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42649] GRB 260510B: GOTO early upper limit
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44522 SUBJECT: GRB 260510B: GOTO early upper limit DATE: 26/05/10 17:44:24 GMT FROM: d.s.oneill(a)bham.ac.uk G. Ramsay, D. O'Neill, S. Belkin, K. Ulaczyk, A. Kumar, K. Ackley, M. Dyer, J. Lyman, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, R. Starling, B. Gompertz, 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 SVOM/ECLAIRS alert GRB 260510B (sb26051001, Saccardi et al. GCN 44515). Observations covering the full extent of the localisation area were started at 2026-05-10 12:23:17 UT, (t0 +4 min) in the L band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations (Lyman et al. 2026). 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. Observations at 2026-05-10 12:23:17 UT (t0 +4 min) and 2026-05-10 13:30:27 UT (t0 +1.19h) did not reveal any new counterpart down to a localised 5-sigma limit of 20.3 and 20.5 AB mag respectively. The GOTO non-detection is consistent with that reported by Saccardi et al (GCN 44518). 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/44522. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42648] GRB 260510C: SVOM detection of a burst
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44521 SUBJECT: GRB 260510C: SVOM detection of a burst DATE: 26/05/10 17:42:51 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Gotz (CEA/Irfu), A. Saccardi (CEA/Irfu), S. Schanne (CEA/Irfu), N. Dagoneau (CEA/Irfu) report on behalf of the SVOM mission team: At 2026-05-10T17:13:44 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260510C (SVOM burst-id sb26051004), also detected by Fermi/GBM (Fermi GRB Team, GCN #44520). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 11 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 12.18 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2026-05-10T17:13:38. The localization of the best alert is R.A., Dec. 157.9595, 2.8711 degrees (J2000) with a 90% confidence level (C.L.) radius of 6.63 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a double peaked structure with a total duration of about 150 s. This burst was also detected by SVOM/GRM with a significance of 7.50. The SVOM/GRM light curve showed two separated peaks with a total duration of about 150 s. SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-05-10T17:16:44 UTC, 179 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 157.941, +2.820 degrees: R.A. (J2000) = 10h31m45.8s Dec. (J2000) = 02d49m12.0s with a 90% C.L. radius of 45 arcseconds. This location is 3.26 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. 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: 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/44521. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42647] GRB 260510C: Fermi GBM Final Real-time Localization
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44520 SUBJECT: GRB 260510C: Fermi GBM Final Real-time Localization DATE: 26/05/10 17:24:27 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 17:13:43 UT on 10 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260510C (trigger 800126028.99095 / 260510718). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 174.6, Dec = 8.6 (J2000 degrees, equivalent to J2000 11h 38m, 8d 35'), with a statistical uncertainty of 10.4 degrees. The angle from the Fermi LAT boresight is 66.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510718/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510718/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510718/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44520. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42646] GRB 260510A: GECAM-B observation
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44519 SUBJECT: GRB 260510A: GECAM-B observation DATE: 26/05/10 16:30:03 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 on-ground by GRB 260510A, at 2026-05-10T02:46:35.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44508). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 38 +6/-5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260510A.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/44519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42645] GRB 260510B: LCO optical upper limits
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44518 SUBJECT: GRB 260510B: LCO optical upper limits DATE: 26/05/10 15:18:38 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), L. Zhang (IHEP), Y. H. Cheng (YNU), report on behalf of the SVOM mission team: We observed the field of GRB 260510B detected by SVOM (Saccardi et al., GCN 44515) with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-10 at 12:33:06 UT (about 14 min after the trigger) and we obtained 2x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. In the stacked images, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limits calibrated against the DESI DR10 catalog, and not corrected for Galactic extinction: r > 20.7 AB (5-sigma, mid-time 1.9 hr after the trigger); z > 20.0 AB (5-sigma, mid-time 19 min after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44518. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42644] EP260509a: Einstein Probe detection of an X-ray transient
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44517 SUBJECT: EP260509a: Einstein Probe detection of an X-ray transient DATE: 26/05/10 14:32:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C.-Y. Wang (THU), S.-Y. Fu (HUST), A. Li (BNU)Y, R. Shi (PMO), Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260509a. The transient was identified during ground-based telemetry analysis. It was started at 2026-05-09T13:44:02 (UTC). The WXT position of the source is R.A. = 239.4813 deg, DEC = -18.4328 deg (J2000) with an uncertainty of 2.78 arcmin in radius (90% C.L. statistical and systematic). The duration of the event is ~ 250 s. The WXT spectrum can be fitted with an absorbed power-law, with the absorption fixed at the Galactic value of 1.05 x 10^21 cm^-2, and a photon index of 2.0 (-0.8, +0.9). The unabsorbed 0.5-4 keV flux is 6.0 (-2.0, +3.1) x 10^-11 erg/s/cm2. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2026-05-10T09:52:54. Further information will be updated when the telemetry data is 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/44517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42643] GRB 260509A: Liverpool Telescope optical observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44516 SUBJECT: GRB 260509A: Liverpool Telescope optical observations DATE: 26/05/10 13:20:53 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 260509A (Götz et al., GCN 44504) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures in SDSS griz filters, starting at 2026-05-09 23:08:01 UT, approximately 1.28 hours after trigger. We detect a source in all filters at the position reported by O'Neill et al. (GCN 44505), observed also by Saccardi et al. (GCN 44506), Wu et al. (GCN 44507), Sánchez Álvarez et al. (GCN 44509), Zheng et al. (GCN 44510), Lipunov et al. (GCN 44512), and Belkin et al. (GCN 44513): MJD (mid) T_mid-T_0 Filter Mag. (AB) 61169.96654 1.34 h g 20.00 ± 0.05 61169.97218 1.48 h r 19.83 ± 0.06 61169.97779 1.61 h i 19.81 ± 0.09 61169.98272 1.73 h z 19.61 ± 0.09 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/44516. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42642] GRB 260510B: SVOM detection of a burst
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44515 SUBJECT: GRB 260510B: SVOM detection of a burst DATE: 26/05/10 12:49:03 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), B. Cordier (CEA/Irfu), N. Dagoneau (CEA/Irfu), Li. Zhang(IHEP), Y. H. Cheng (SWIFAR, YNU), report on behalf of the SVOM mission team: At 2026-05-10T12:19:20 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260510B (SVOM burst-id sb26051001). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 11 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.71 in the [8-50] keV energy band over a time window of 10.20 seconds starting at 2026-05-10T12:19:15. The localization of the best alert is R.A., Dec. 173.2168, -34.5756 degrees: R.A. (J2000) = 11h32m52.04s Dec. (J2000) = -34d34m32.07s with a 90% confidence level (C.L.) radius of 8.18 arcmin (including systematic error of 2 arcmin added in quadrature). This burst was also detected by SVOM/GRM with a significance of 7.40. SVOM slewed to the burst. MXT and VT began observing the field after the slew. The analysis of the data will be published in future circulars. 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 zhangli: zhangli(a)ihep.ac.cn Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44515. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42641] GRB 260509A: NOT spectroscopic redshift upper limit z < 1.95
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44514 SUBJECT: GRB 260509A: NOT spectroscopic redshift upper limit z < 1.95 DATE: 26/05/10 11:07:26 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), A. Saccardi (CEA/Irfu), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), N. R. Tanvir (Univ. Leicester), Kostas Valeckas (NOT and NBI), V. Vuolteenaho (NOT and Oulu Univ.), report on behalf of a larger collaboration: We observed the optical counterpart (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; Lipunov et al. GCN 44512; Belkin GCN 44513) of the SVOM/ECLAIRs GRB 260509A (Götz et al., GCN 44504) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC spectrograph. A spectrum consisting of 4x1200 s exposures was secured starting on 2026 May 10 at 00:22:16 UT (2.52 hr after the SVOM trigger), using grism #4 with the WG345 356_LP order blocker which covers the wavelength range 3400-9600 AA. Based on a preliminary reduction of the spectra using PyLongslit (Valeckas et al. 2025 10.21105/joss.09264), a continuum is detected down to ~3600 AA, setting an upper limit to the redshift z < 1.95 based on the lack of HI absorption. We do not identify clear metal absorption features despite good S/N. Further analysis is ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/44514. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42640] GRB 260509A: LCO optical observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44513 SUBJECT: GRB 260509A: LCO optical observations DATE: 26/05/10 09:43:56 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin (Monash U) reports: We observed the optical counterpart candidate GOTO26emi of GRB 260509A, detected by SVOM/ECLAIRs (Götz et al., GCN 44504), with the Las Cumbres Observatory 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. In the stacked images, we clearly detect the reported optical counterpart candidate GOTO26emi, first identified by GOTO (O'Neill et al., GCN 44505) and subsequently reported by Saccardi et al. (GCN 44506), Wu et al. (GCN 44507), Sánchez Álvarez et al. (GCN 44509), Zheng et al. (GCN 44510), and Lipunov et al. (GCN 44512). The preliminary photometry from the stacked images is: Date (UT) T-T0 (days) Filter Exp. time (s) Magnitude ============================================================================ 2026-05-10 01:53:25 0.16825 r 60 x 5 20.67 +/- 0.13 2026-05-10 02:00:37 0.17324 i 60 x 5 20.51 +/- 0.17 2026-05-10 02:07:48 0.17823 g 60 x 5 20.88 +/- 0.12 The photometry was calibrated against Pan-STARRS field stars. The quoted magnitudes are in the AB system and are not corrected for Galactic extinction. Our r-band measurement is consistent with the fading behaviour reported by Saccardi et al. (GCN 44506) and Sánchez Álvarez et al. (GCN 44509). Further follow-up is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/44513. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42639] SVOM GRB 260509A: MASTER-OAFA optical observation
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44512 SUBJECT: SVOM GRB 260509A: MASTER-OAFA optical observation DATE: 26/05/10 08:23:16 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> Ya.Kechin (Lomonosov MSU), F.Podesta, M.J. Segura, C.Francile, R.Podesta, E. Gonzalez (OAFA, SJNU), A.Kuznetsov, V.Lipunov, I.Panchenko, P.Balanutsa, G.Antipov, N.Tiurina,K.Zhirkov, E.Gorbovskoy, V.Senik, A.Chasovnikov, V.Topolev, D.Vlasenko,A.Sankovich, I.Gorbunov(Lomonosov MSU), N.Budnev, O.Gress (ISU), 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-OAFA robotic telescope of MASTER Global Robotic Net [1-4] was pointed to the SVOM GRB260509A (trigger No 1778363469,11h 47m 32.88s , +00d 12m 34.2s, R=0.0786667 Gotz et al. GCN 44504) errorbox 8054 sec after notice time and 10202 sec after trigger time at 2026-05-10 00:41:11 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 31 deg. The sun altitude is -36.5 deg. MASTER-OAGH robotic telescope located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) was pointed to the SVOM GRB260509.91 errorbox 24424 sec after notice time (26572 sec after trigger time at 2026-05-10 05:14:01 UT), with upper limit up to 19.3 mag. The observations began at zenith distance = 36 deg. The sun altitude is -33.4 deg. The galactic latitude b = 59 deg., longitude l = 272 deg. There is MASTER OT J114735.9135.91+001717.7 optical counterpart at first images with m_OT~20.9 at 2026-05-10 00:41:11UT discovered by GOTO (O'Neill et al. GCN 44505) and observed by LCO (Saccardi et al. GCN 44506), SVOM|VT (Wu et al. GCN 44507), KAIT (Zheng et al. GCN 44510) Real time updated cover map and OT are available here: https://master.sai.msu.ru/site/master2/observ.php?id=3303991 MASTER upper limits: Tmid-T0 | Date Time | Site | Coord J2000) |Filt.| Expt. | Limit| Comment 10233 | 2026-05-10 00:41:11 | MASTER-OAFA | (11h 44m 48.88s , -00d 51m 54.0s) | C | 60 | 20.2 | 10293 | 2026-05-10 00:41:11 | MASTER-OAFA | (11h 44m 48.87s , -00d 51m 54.0s) | C | 180 | 20.5 | Coadd 10311 | 2026-05-10 00:42:29 | MASTER-OAFA | (11h 44m 48.21s , -00d 50m 56.7s) | C | 60 | 20.2 | 10389 | 2026-05-10 00:43:47 | MASTER-OAFA | (11h 44m 52.24s , -00d 51m 59.4s) | C | 60 | 20.2 | 10465 | 2026-05-10 00:45:03 | MASTER-OAFA | (11h 44m 46.21s , -00d 53m 02.8s) | C | 60 | 20.2 | 10525 | 2026-05-10 00:45:03 | MASTER-OAFA | (11h 44m 46.20s , -00d 53m 02.8s) | C | 180 | 20.5 | Coadd 10540 | 2026-05-10 00:46:19 | MASTER-OAFA | (11h 44m 52.06s , -00d 52m 51.7s) | C | 60 | 20.2 | 10618 | 2026-05-10 00:47:36 | MASTER-OAFA | (11h 44m 49.58s , -00d 51m 21.4s) | C | 60 | 20.2 | 10697 | 2026-05-10 00:48:55 | MASTER-OAFA | (11h 44m 49.29s , -00d 53m 05.6s) | C | 60 | 20.2 | 10757 | 2026-05-10 00:48:55 | MASTER-OAFA | (11h 44m 49.28s , -00d 53m 05.6s) | C | 180 | 20.4 | Coadd 10774 | 2026-05-10 00:50:12 | MASTER-OAFA | (11h 44m 52.95s , -00d 51m 27.6s) | C | 60 | 20.2 | 10852 | 2026-05-10 00:51:31 | MASTER-OAFA | (11h 44m 45.40s , -00d 52m 20.8s) | C | 60 | 20.2 | 10930 | 2026-05-10 00:52:48 | MASTER-OAFA | (11h 44m 45.82s , -00d 51m 24.8s) | C | 60 | 20.2 | 10990 | 2026-05-10 00:52:48 | MASTER-OAFA | (11h 44m 45.81s , -00d 51m 24.8s) | C | 180 | 20.4 | Coadd 11007 | 2026-05-10 00:54:06 | MASTER-OAFA | (11h 44m 49.85s , -00d 52m 28.2s) | C | 60 | 20.2 | 11086 | 2026-05-10 00:55:24 | MASTER-OAFA | (11h 44m 45.55s , -00d 53m 32.1s) | C | 60 | 20.2 | 11160 | 2026-05-10 00:56:39 | MASTER-OAFA | (11h 44m 49.59s , -00d 53m 31.6s) | C | 60 | 20.2 | 11220 | 2026-05-10 00:56:39 | MASTER-OAFA | (11h 44m 49.59s , -00d 53m 31.6s) | C | 180 | 20.4 | Coadd [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/44512. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42638] Fermi GRB 260510A: Global MASTER-Net observations report
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44511 SUBJECT: Fermi GRB 260510A: Global MASTER-Net observations report DATE: 26/05/10 06:30:25 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-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260510A ( Fermi GBM team, GCN 44508) errorbox 12795 sec after notice time and 12848 sec after trigger time at 2026-05-10 06:20:28 UT, with upper limit up to 17.6 mag. The observations began at zenith distance = 80 deg. The sun altitude is -61.8 deg. The galactic latitude b = -73 deg., longitude l = 333 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3304437 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 12879 | 2026-05-10 06:20:28 | MASTER-OAFA | (00h 01m 07.12s , -42d 06m 59.6s) | C | 60 | 17.0 | 12956 | 2026-05-10 06:21:45 | MASTER-OAFA | (00h 01m 04.44s , -42d 05m 38.2s) | C | 60 | 16.9 | 13034 | 2026-05-10 06:23:03 | MASTER-OAFA | (00h 01m 02.62s , -44d 07m 12.4s) | C | 60 | 17.4 | 13109 | 2026-05-10 06:24:18 | MASTER-OAFA | (00h 01m 04.74s , -44d 05m 38.9s) | C | 60 | 17.5 | 13186 | 2026-05-10 06:25:35 | MASTER-OAFA | (00h 00m 59.38s , -44d 06m 16.7s) | C | 60 | 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/44511. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42637] GRB 260509A: KAIT optical observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44510 SUBJECT: GRB 260509A: KAIT optical observations DATE: 26/05/10 06:13:38 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of GRB 260509A (Götz et al., GCN 44504 starting at 04:56 UT, 7.08 hours after the burst. A set of clear (roughly R) filter images were obtained. We detected the afterglow (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Álvarez et al., GCN 44509) in our coadd image. We measure its brightness to be 21.1 +/- 0.2 mag (Vega) at mid time of 7.37 hours after the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/44510. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42636] GRB 260509A: SVOM/COLIBRÍ (FM-GFT) observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44509 SUBJECT: GRB 260509A: SVOM/COLIBRÍ (FM-GFT) observations DATE: 26/05/10 04:54:27 GMT FROM: freddalvarez(a)astro.unam.mx Fredd Sánchez Álvarez (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM),Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and D. Adrien (CEA/Irfu) report: We imaged the field of the SVOM/ECLAIRs GRB 260509A (Götz et al. GCN 44504) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-10 03:31 to 03:59 UTC and obtained 8 minutes of exposure in g, r, and i, and simultaneously 24 minutes of exposure in z. The data were reduced, coadded, calibrated, and analyzed 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 optical counterpart reported by O’Neill et al.(GCN 44505), Saccardi et al. (GCN 44506), and Wu et al. (GCN 44507) with preliminary magnitudes of: g = 21.25 +/- 0.05 r = 21.31 +/- 0.08 i = 20.97 +/- 0.08 z = 20.81 +/- 0.09 Our strong detection of the source in g suggests that the redshift is less than 3.0. 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/44509. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42635] GRB 260510A: Fermi GBM Final Real-time Localization
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44508 SUBJECT: GRB 260510A: Fermi GBM Final Real-time Localization DATE: 26/05/10 02:57:06 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 02:46:19 UT on 10 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260510A (trigger 800073984.34868 / 260510115). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 0.5, Dec = -41.9 (J2000 degrees, equivalent to J2000 00h 02m, -41d 53'), with a statistical uncertainty of 6.1 degrees. The angle from the Fermi LAT boresight is 84.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510115/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510115/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510115/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44508. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42634] GRB 260509A: SVOM/VT optical candidate with VHF data
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44507 SUBJECT: GRB 260509A: SVOM/VT optical candidate with VHF data DATE: 26/05/10 01:47:02 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu, H. L. Li, Y. L. Qiu, L. P. Xin (NAOC), J. T. Palmerio (CEA/Irfu), D. Götz (CEA/Irfu), A. Saccardi (CEA/Irfu), L. Zhang (IHEP), Y. H. Cheng (YNU) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs (SVOM burst-id sb26050905) at 2026-05-09T21:51:09 UTC (T0), SVOM/VT began observing the field after the automatic slew on the burst (Götz et al., GCN 44504) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list generated by on-board data processing and downloaded via VHF network, one credible candidate is identified, the details of which are presented below. VT_ID 722: The position of this candidate is R.A., Dec. 176.8997, 0.2882 degrees, corresponding to: R.A. (J2000) = 11:47:35.9 Dec. (J2000) = 00:17:17.6 with an uncertainty of 0.50 arcsec. This candidate was detected in both VT_R and VT_B, and was flagged as an uncatalogued source whose brightness faded during the VT observations. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | | 2026-05-09T23:18:31 | 89.87 min | 6x50 sec | 20.38 ± 0.03 | 19.80 ± 0.04 | | 2026-05-09T23:58:59 | 129.08 min | 3x50 sec | 20.67 ± 0.05 | 20.18 ± 0.06 | Magnitudes were not corrected for Galactic extinction. The mean color of VT_B - VT_R = 0.54 is in line with the expectations of an event at redshift z < 4. The position of this candidate is consisent with the reports (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506) . 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/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/44507. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42633] GRB 260509A: LCO optical counterpart detection
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44506 SUBJECT: GRB 260509A: LCO optical counterpart detection DATE: 26/05/10 01:00:45 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), D. Adrien (CEA/Irfu), L. Zhang (IHEP), Y. H. Cheng (YNU), report on behalf of the SVOM mission team: We observed the field of GRB 260509A detected by SVOM (Götz et al., GCN 44504) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-09 at 23:41:26 UT (about 1.84 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 candidate reported by O'Neill et al. (GCN 44505) is clearly detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r = 19.79 +/- 0.05 AB (mid-time 1.92 hr after the trigger); z = 19.76 +/- 0.15 AB (mid-time 2.65 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44506. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42632] GRB 260509A: GOTO optical counterpart candidate
by GCN Circulars 09 May '26

09 May '26

TITLE: GCN CIRCULAR NUMBER: 44505 SUBJECT: GRB 260509A: GOTO optical counterpart candidate DATE: 26/05/09 23:23:47 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> D. O'Neill, S. Belkin, K. Ulaczyk, A. Kumar, K. Ackley, M. Dyer, J. Lyman, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, R. Starling, B. Gompertz, 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 SVOM/ECLAIRS alert GRB 260509A (sb26050905, Götz et al. GCN 44504). Observations covering the localisation area were taken at 2026-05-09 21:56:19 UT, (t0 +0.09h) with an average 5-sigma depth of 20.8 mag. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations (Lyman et al. 2026). 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. A new optical source GOTO26emi is identified near the edge of the ECLAIRS localisation region, at an angular separation of 4.79 arcmin from the reported GRB position, marginally outside the quoted 4.72 arcmin error radius. The source coordinates: RA,DEC (J2000) = 176.899834, 0.288276, 11:47:35.96, +00:17:17.80 The rapidly rising source was detected with average L = 20.13 ± 0.16 AB mag (+0.09h). We find no evidence of the source prior to the GRB trigger time in previous GOTO observations taken at 2026-05-09 10:38:10 (-11.21h) down to a depth of >20.40 AB mag, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). 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/44505. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42631] GRB 260509A: SVOM detection of a burst
by GCN Circulars 09 May '26

09 May '26

TITLE: GCN CIRCULAR NUMBER: 44504 SUBJECT: GRB 260509A: SVOM detection of a burst DATE: 26/05/09 22:26:24 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> GRB 260509A: SVOM detection of a burst D. Götz (CEA/Irfu), A. Saccardi (CEA/Irfu), H. Goto (RIKEN), F. Lacreu (IAP), D. Adrien (CEA/Irfu), report on behalf of the SVOM mission team: At 2026-05-09T21:51:09 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260509A (SVOM burst-id sb26050905). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 18 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 18.00 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2026-05-09T21:51:03. The localization of the best alert is R.A., Dec. 176.8870, 0.2095 degrees: R.A. (J2000) = 11h47m32.9s Dec. (J2000) = 0d12m34.2s with a 90% confidence level (C.L.) radius of 4.72 arcmin (including systematic error of 2 arcmin added in quadrature). We note the presence of a high proper motion star G 10-49 at a distance of 4.48 arcmin from the ECLAIRs position. The SVOM/ECLAIRs light curve showed a single peak structure with a T90 duration of about 14.7 +/-0.6 s. This burst was also detected by SVOM/GRM with a significance of 6.40. The SVOM/GRM light curve showed a double peak structure with a T90 duration of about 18 (-6/+10) s. SVOM slewed to the burst. MXT and VT began observing the field after the slew. The analysis of the data will be published in future circulars. 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 Dylan Adrien: dylan.adrien(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/44504. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42630] GRB 260506B: AstroSat CZTI detection
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44503 SUBJECT: GRB 260506B: AstroSat CZTI detection DATE: 26/05/08 19:22:25 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), Harsha K. H. (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 CIFT2 framework showed the detection of GRB 260506B which is also detected by the Fermi/GBM (Fermi GBM team, GCN Circ. 44484). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-05-06 13:07:41.9 UTC. The measured peak count rate associated with the burst is 129 (+37, -17) counts/s above the background in the combined data of all four quadrants, with a total of 899 (+239, -328) counts. The local mean background count rate was 289 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 22 (+12, -15) s. We caution that there is a 0.3 s dead time in the CZTI data in the burst, hence the actual T90 may be slightly longer. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-05-06 13:07:42.0 UTC. The measured peak count rate associated with the burst is 440 (+67, -69) counts/s above the background in the combined data of all quadrants, with a total of 3325 (+520, -551) counts. The local mean background count rate was 1313 (+4, -4) counts/s. We measure a T90 of 36 (+3, -7) 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/515768858.51/S515768858.51_det… 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/44503. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42629] IceCube-260504A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44502 SUBJECT: IceCube-260504A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/05/08 18:08:49 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-260504A (https://gcn.nasa.gov/circulars/44464) in a time range of 1000 seconds centered on the alert event time (2026-05-04 21:03:00.958 UTC to 2026-05-04 21:19:40.958 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-260504A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260504A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 5e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-05-03 21:11:20.958 UTC to 2026-05-05 21:11:20.958 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.9e-01 to 2.0e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260504A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/44502. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42628] EP260507a: REM optical/NIR observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44501 SUBJECT: EP260507a: REM optical/NIR observations DATE: 26/05/08 15:30:56 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of EP260507a, detected by EP (Fu et al., GCN 44488) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried out in the g, r, i, z, and H bands, started on 2026-05-07 at 22:56:01 UT (i.e. 9.1 hr after the burst) and lasted for about 1 hour. From preliminary photometry, we do not detect the optical/NIR counterpart (Corcoran et al., GCN Circ. 44489; Sankar et al., GCN Circ. 44490; Jiang et al., GCN Circ. 44491; Kumar et al., GCN Circ. 44492; Eyles-Ferris et al., GCN Circ. 44495; Jiang et al., GCN Circ. 44496; Li et al., GCN 44497; Globus et al., GCN 44498) down to the following 3sigma limits: r > 19.8 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 10.0 hr after the trigger; H > 14.5 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 9.2 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44501. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42627] EP260507a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44500 SUBJECT: EP260507a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/05/08 13:33:09 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.Y.Fu (HUST), Y. L. Wang (NAO, CAS; ICE, CSIC), C.L.Guo (NAO, CAS), X. Tian (GXU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260507a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Fu et al., GCN 44488). The refined analysis of the WXT data shows that the event started at T0=2026-05-07T13:47:44.0 (UTC) and lasted for 15 s before the observation was interrupted by the autonomous follow-up observation (i.e. T90 > 15 s). The average 0.5–4 keV spectrum of WXT can be modeled with an absorbed power law, adopting a fixed Galactic hydrogen column density of 5.55 x 10^20 cm^-2 and an additional column density of 5.77 x 10^21 cm^-2. This additional absorption significantly improves the fit quality, yielding a photon index of 1.47 (+-0.79). The derived average unabsorbed 0.5-4 keV flux is 1.98 (-0.70/+2.20) x 10^(-8) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-05-07T13:51:52 (UTC), about 4 minutes after T0. The exposure time of this observation is 5046 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 206.899, -22.2364 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law adopting a fixed Galactic equivalent hydrogen column density of 5.55 x 10^20 cm^-2 and an additional column density of 8.33 x 10^20 cm^-2，yielding a photon index of 2.10 (+-0.06). The derived average unabsorbed 0.3-10 keV flux is 1.82 (-0.07/+0.08) x 10^(-11) 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/44500. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42626] GRB 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44499 SUBJECT: GRB 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection DATE: 26/05/08 06:22:37 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (ICE-CSIC and Radboud Univ.), P.G. Jonker (Radboud Univ.) and E. Burns (LSU), R. Hamburg (USRA), and P. Veres (UAH) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP260507a detected by EP (Fu et al., GCN 44488). There was no Fermi-GBM onboard trigger around the EP trigger time (T0 = 2026-05-07T13:47:57 UTC). The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+250] s from EP T0, seeking signals between 64 ms and 32.768 s in duration. A weak transient signal was found most significantly at ~T0-4 s on a 16 s timescale, with a false alarm rate of 1.7e-03 Hz. The localisation is consistent with the EP one, with a spatial association probability of 93.5%. Among the three spectral templates tested, the transient was best fit with a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/44499. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42625] EP260507a: COLIBRÍ optical observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44498 SUBJECT: EP260507a: COLIBRÍ optical observations DATE: 26/05/08 06:07:02 GMT FROM: globus(a)astro.unam.mx Noémie Globus (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), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260507a (Fu et al., GCN Circ. 44488) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-08 04:59 to 05:50 UTC (from 15.19 to 16.06 hours after the trigger) and obtained 39 minutes of exposure in the r and z filters, respectively. 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. We detect the optical candidate reported previously (Corcoran et al., GCN Circ. 44489; Sankar et al., GCN Circ. 44490; Jiang et al., GCN Circ. 44491; Kumar et al., GCN Circ. 44492; Bochenek et al., GCN Circ. 44494; Eyles-Ferris et al., GCN Circ. 44495; Jiang et al., GCN Circ. 44496) with preliminary magnitudes of: r = 23.37 +/- 0.14, z = 22.44 +/- 0.21. From a combined power-law fit including our data and previously reported GCN Circular measurements, we derive a temporal decay index of α ≈ 0.6. 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/44498. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42624] EP260507a: SVOM/VT optical observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44497 SUBJECT: EP260507a: SVOM/VT optical observations DATE: 26/05/08 03:08:14 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, 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 (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic follow-up observations to the Xray transient EP260507a triggered by Einstein Probe (Fu et al., GCN 44488). The observation started at 2026-05-07T14:45:27 UTC, i.e. 57.5 minutes post trigger and lasted for 2 orbits (about 1.9 hours) in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Eyles-Ferris et al., GCN 44495; Jiang et al., GCN 44496) was clearly detected in both channels. The measurements in AB magnitude are as follows: Mid time | Band | Exposure Time | Brightness 1.35 h VT_B 56*50 s 21.92 +/- 0.12 mag 1.35 h VT_R 55*50 s 20.91 +/- 0.08 mag 2.96 h VT_B 56*50 s 22.29 +/- 0.14 mag 2.96 h VT_R 55*50 s 21.25 +/- 0.10 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/44497. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42623] EP260507a: NOT optical observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44496 SUBJECT: EP260507a: NOT optical observations DATE: 26/05/08 01:42:18 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang, L.B. He, Z.P. Zhu, J. An, X. Liu, D. Xu (NAOC), S.Y. Fu (HUST), J. P. U. Fynbo (DAWN/NBI), A. L. Bouquin (NOT) report: We observed the field of EP260507a detected by EP (Fu et al., GCN 44488), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 3 x 300 s frames in the Sloan g, r, i-band, respectively. The optical afterglow (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Eyles-Ferris et al., GCN 44495) is detected in our stacked images. Preliminary photometry results are as follows: Tmid-T0(hr) Mag MagErr Filter 9.54 23.04 0.12 r 9.82 23.61 0.17 g 10.10 22.77 0.17 i calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44496. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42622] EP260507a: further Liverpool Telescope observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44495 SUBJECT: EP260507a: further Liverpool Telescope observations DATE: 26/05/08 01:20:37 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 EP260227a (Fu et al., GCN 44488) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x200s exposures in each of the SDSS r’ and z’ filters starting at 2026-05-07 22:51:45 UT, approximately 9.06 hours after the X-ray detection. We detect the optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Bochenek et al., GCN 44494) in both the r’ z’ bands and measure the following magnitudes: r’ = 22.76 +/- 0.21 z’ = 21.98 +/- 0.30 Our photometry is calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44495. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42621] EP260507a: Liverpool Telescope optical upper limits
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44494 SUBJECT: EP260507a: Liverpool Telescope optical upper limits DATE: 26/05/07 23:34:35 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 EP260507a (Fu et al., GCN 44488) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x100s exposures in SDSS g, r, and i filters, starting at 2026-05-07 22:20:09 UT, approximately 8.54 hours after trigger. We do not detect any sources at the position of the optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491, Kumar et al., GCN 44492) down to the 3-sigma limiting magnitude of g > 22.05, r > 21.92 and i > 22.07. Further observations are planned. The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44494. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42620] GRB 260507A: Fermi GBM Final Real-time Localization
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44493 SUBJECT: GRB 260507A: Fermi GBM Final Real-time Localization DATE: 26/05/07 20:38:34 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 20:28:00 UT on 7 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260507A (trigger 799878485.453562 / 260507853). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 287.5, Dec = -21.3 (J2000 degrees, equivalent to J2000 19h 10m, -21d 18'), with a statistical uncertainty of 2.4 degrees. The angle from the Fermi LAT boresight is 79.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260507853/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260507853/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260507853/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44493. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42619] EP260507a: GOTO optical counterpart detection
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44492 SUBJECT: EP260507a: GOTO optical counterpart detection DATE: 26/05/07 19:02:11 GMT FROM: Amit Kumar at The Open University, UK <amitkundu515(a)gmail.com> A. Kumar, S. Belkin, D. O'Neill, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, J. Casares, B. Godson, T. Killestein and M. Pursiainen on behalf of GOTO collaboration We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to EP-WXT triggered EP260507a (Fu et al., GCN 44488). The observations were conducted with GOTO-South at 2026-05-07 13:57:30 UT and 2026-05-07 15:04:48 UT (9.5 and 76.8 mins post-trigger, respectively), consisting of 4x90s exposures in the GOTO L-band (400-700 nm). Difference imaging was performed using deeper template observations of the same pointings. We detect the optical counterpart of EP260507a (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491) in the GOTO L-band at 2026-05-07 13:57:30 UT (9.5 mins post-trigger), with a measured magnitude of 19.56 ± 0.11 AB. The source is no longer detected at the next epoch obtained at 2026-05-07 15:04:48 UT (76.8 mins post-trigger), with a 3-sigma upper limit of 20.4 AB mag. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. 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/44492. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42618] EP260507a: TRT optical counterpart detection
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44491 SUBJECT: EP260507a: TRT optical counterpart detection DATE: 26/05/07 18:11:13 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), X. Liu, Z.P. Zhu, J. An, L.B. He, D. Xu (NAOC) report: We observed the field of EP260507a detected by EP (Fu et. al, GCN 44488), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observation started at 2026-05-07T14:27:55.509 UT, i.e., 39.98 mins post-burst, and a series of R-band frames were obtained. The optical afterglow (Corcoran et. al, GCN 44489; Sankar et. al, GCN 44490) is marginally detected in our stacked images with a brightness of R = 20.8 +/- 0.36 at a median time of 45.88 mins since trigger, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44491. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42617] EP260507a: Kinder optical counterpart candidate
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44490 SUBJECT: EP260507a: Kinder optical counterpart candidate DATE: 26/05/07 15:19:55 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Sankar.K, A. Aryan, Y.-H. Lee, T.-W. Chen, W.-J. Hou (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), S. Yang(HNAS), M.-H. Lee, A. Dutta, K. N.-T. Ho, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, C.-S. Lin, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, K. W. Smith, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260507a (Fu et al., GCN 44488) using the 40cm SLT at the Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86). The first SLT epoch of observations started at 14:06 UTC on 7th May 2026 (MJD 61167.5837), 0.30 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. In the stacked frame as well as in the difference image, we detect an uncatalogued optical counterpart candidate at RA, DEC = 13:47:35.567, -22:14:08.38 with an uncertainty of 1". The optical counterpart candidate is well inside the EP-FXT error circle of 20". The details of the observations and measured PSF magnitude with template subtraction (in the AB system) of the possible counterpart of EP260507a are as follows: -------------------------------------------------------------------------------------------------- Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 61167.5837 | 0.30 | 300 * 6 | 20.64 +/- 0.07 | 2".07 | 1.44 The presented magnitudes are calibrated using the field stars from ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported magnitudes/upper-limits are not corrected for an expected galactic extinction of A_r = 0.16 mag, in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44490. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42616] EP260507a: LCO optical counterpart
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44489 SUBJECT: EP260507a: LCO optical counterpart DATE: 26/05/07 15:16:19 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), J. A. Chácon (PUC), J. N. D. van Dalen (Radboud), F. E. Bauer (SSI and UTA), P. G. Jonker (Radboud), A. J. Levan (Radboud & Warwick) and D. B. Malesani (DAWN/NBI and Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260507a (Fu et al., GCN 44488) using an LCO 1m telescope located at the Siding Spring Observatory (Australia) equipped with the SINISTRO instrument. We obtained 6x300s exposures in the SDSS-r filter starting at 2026-05-07 14:34:48 (~47 minutes after the trigger). Within the EP/FXT error region (Fu et al., GCN 44488), we detect a likely optical counterpart at a position of (J2000): RA 13:47:35.57 (206.89822) Dec -22:14:08.40 (-22.23566) We measure a magnitude of r = 21.21 +/- 0.07 (AB) calibrated to PanSTARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42615] EP260507a: Einstein Probe detection of an X-ray transient
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44488 SUBJECT: EP260507a: Einstein Probe detection of an X-ray transient DATE: 26/05/07 14:40:02 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Y. Fu (HUST), Y. L. Wang (NAO, CAS; ICE, CSIC), C. L. Guo (NAO, CAS), X. Tian (GXU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260507a. The transient triggered EP-WXT (ID: 01709261593) at 2026-05-07T13:47:57 (UTC). The WXT position of the source is R.A. = 206.895 deg, DEC = -22.243 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 206.8963 deg, DEC = -22.2361 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 is 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/44488. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42614] GRB 260504B: AstroSat CZTI detection
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44487 SUBJECT: GRB 260504B: AstroSat CZTI detection DATE: 26/05/07 14:19:14 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (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 GRB 260504B which is also detected by SVOM/GRM (Saccardi et al., GCN Circ. 44454), GECAM-B (Wang et al., GCN Circ. 44473), and Konus-Wind (Frederiks et. al., GCN Circ. 44474). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-04 09:31:16.450 UTC. The measured peak count rate associated with the burst is 1150 (+201, -203) counts/s above the background in the combined data of all four quadrants, with a total of 162 (+33, -36) counts. The local mean background count rate was 319 (+9, -11) counts/s. Using cumulative rates, we measure a T90 of 0.22 (+0.11, -0.07) s. 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/44487. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42613] GRB 260504B: SVOM/ECLAIRs refined analysis
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44486 SUBJECT: GRB 260504B: SVOM/ECLAIRs refined analysis DATE: 26/05/06 16:54:33 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> F. Piron (LUPM), M. Brunet (IRAP), N. Dagoneau (CEA), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), 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 260504B (SVOM burst-id sb26050402 – GCN 44454, trigger time T0 = 2026-05-04T09:31:19 UTC), which was also detected by SVOM/GRM (GCN 44470), GECAM-B (GCN 44473) and Konus-Wind (GCN 44474). The burst that triggered ECLAIRs onboard shows a single peak lightcurve. The burst duration is T90 = 0.46 -0.06/+0.09 s in the 4-120 keV energy band. The time-averaged spectrum from T0+0.40 s to T0+0.86 s in the energy range 5-120 keV is best fitted by a powerlaw model with best-fit parameters: alpha = -0.72 +/-0.06. With this model, the 4-120 keV fluence is (1.87 ± 0.09) e-7 erg/cm^2 and the 4-120 keV photon flux is 6.0 ± 0.3 ph/cm²/s. We note that the photon index is consistent with the one found by SVOM/GRM (GCN 44470). 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: Frédéric Piron (LUPM) (piron at in2p3.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44486. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42612] GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547)
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44485 SUBJECT: GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547) DATE: 26/05/06 14:01:40 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 799765648 at 13:07:23 on 06 May 2026 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 280.7 deg Decl.(2000.0) = -6.1 deg The 1 sigma statistical error radius is 1.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260506547/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260506547/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260506547/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42611] GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547)
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44485 SUBJECT: GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547) DATE: 26/05/06 14:01:40 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 799765648 at 13:07:23 on 06 May 2026 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 280.7 deg Decl.(2000.0) = -6.1 deg The 1 sigma statistical error radius is 1.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260506547/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260506547/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260506547/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42610] GRB 260506B: Fermi GBM Final Real-time Localization
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44484 SUBJECT: GRB 260506B: Fermi GBM Final Real-time Localization DATE: 26/05/06 13:18:06 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 13:07:23 UT on 6 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260506B (trigger 799765648.964258 / 260506547). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 280.5, Dec = -0.5 (J2000 degrees, equivalent to J2000 18h 41m, 0d 30'), with a statistical uncertainty of 1.8 degrees. The angle from the Fermi LAT boresight is 44.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506547/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506547/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506547/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44484. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42609] EP260502a is likely a flaring star
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44483 SUBJECT: EP260502a is likely a flaring star DATE: 26/05/06 10:24:37 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T.Y. Liu (NAO,CAS), Y. Q. Zhao(PRIC,USTC), Y. F. Liang (PMO, CAS), Y. Wang (PMO, CAS; UCB), H. W. Pan (NAO,CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260502a (GCN #44440) at the time of 2026-05-02T06:08:51, is likely a stellar flare associated with SIPS J1809-7613. The estimated flux of the flare is around 1.1×10^(-9) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 9.8×10^(30) erg/s. The telemetry WXT data show that the flare started around 2026-05-02T05:58:08 (UTC) and exhibits no obvious flux variation later in the WXT exposure. The average WXT 0.5-4 keV spectrum of the burst period can be fitted with an absorbed power law with a hydrogen column density of 3.68×10^(-9)（-3.68×10^(-9)/+0.361 ）×10^22 cm^-2 and a photon index of 0.52(-0.52/+1.70). The derived average unabsorbed 0.5-4 keV flux is 9.96 (-3.89/+11.51) ×10^(-11) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source at 2026-05-02T06:19:45 (UTC). The exposure time of this observation is 3.0ks. The flux show a rapid fading of around 5 times in 1ks. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 0.66 (-0.21/+0.25) × 10^22 cm^-2 and a photon index of 5.44 (-1.02/+1.23). The derived average unabsorbed 0.5-10 keV flux is 8.29 (-4.61/+15.56) × 10^(-12) erg/s/cm^2. The optical follow-up observations were performed by Li et al. (GCN 44441), Sharma et al. (GCN 44442, GCN 44444), and catch a fading of 0.7mag of SIPS J1809-7613 in 30min starting from 2026-05-02 06:24:42, consistent with the X-ray fading detected by the FXT autumatic follow-up. A follow-up observation around 3ks with the EP/FXT was carried out starting at 2026-05-02T06:19:45, and no FXT trigger was received during the observation. 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/44483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42608] Fermi GRB 260506A: Global MASTER-Net observations report
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44482 SUBJECT: Fermi GRB 260506A: Global MASTER-Net observations report DATE: 26/05/06 07:00:25 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260506A ( Fermi GBM team, GCN 44481) errorbox 224 sec after notice time and 230 sec after trigger time at 2026-05-06 06:32:38 UT, with upper limit up to 19.3 mag. The observations began at zenith distance = 58 deg. The sun altitude is -41.5 deg. The galactic latitude b = 36 deg., longitude l = 136 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3296217 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 260 | 2026-05-06 06:32:38 | MASTER-OAGH | (08h 44m 39.72s , +75d 23m 45.7s) | C | 60 | 18.5 | 260 | 2026-05-06 06:32:38 | MASTER-OAGH | (08h 37m 44.58s , +75d 59m 45.8s) | C | 60 | 18.7 | 333 | 2026-05-06 06:33:51 | MASTER-OAGH | (09h 16m 22.00s , +75d 24m 42.7s) | C | 60 | 18.8 | 333 | 2026-05-06 06:33:51 | MASTER-OAGH | (09h 09m 15.33s , +76d 01m 00.1s) | C | 60 | 18.9 | 406 | 2026-05-06 06:35:04 | MASTER-OAGH | (08h 52m 23.52s , +77d 19m 08.0s) | C | 60 | 19.1 | 406 | 2026-05-06 06:35:04 | MASTER-OAGH | (08h 44m 14.66s , +77d 55m 18.4s) | C | 60 | 19.3 | 479 | 2026-05-06 06:36:17 | MASTER-OAGH | (09h 28m 38.58s , +77d 18m 24.2s) | C | 60 | 18.3 | 479 | 2026-05-06 06:36:17 | MASTER-OAGH | (09h 20m 26.78s , +77d 54m 22.8s) | C | 60 | 18.6 | 553 | 2026-05-06 06:37:31 | MASTER-OAGH | (09h 32m 43.22s , +73d 30m 24.2s) | C | 60 | 18.8 | 553 | 2026-05-06 06:37:31 | MASTER-OAGH | (09h 26m 27.66s , +74d 06m 31.2s) | C | 60 | 18.9 | 626 | 2026-05-06 06:38:44 | MASTER-OAGH | (10h 00m 45.91s , +73d 28m 55.8s) | C | 60 | 18.7 | 626 | 2026-05-06 06:38:44 | MASTER-OAGH | (09h 54m 25.86s , +74d 05m 06.5s) | C | 60 | 19.0 | 699 | 2026-05-06 06:39:57 | MASTER-OAGH | (09h 44m 54.95s , +75d 25m 08.4s) | C | 60 | 19.0 | 699 | 2026-05-06 06:39:57 | MASTER-OAGH | (09h 37m 45.79s , +76d 01m 15.0s) | C | 60 | 19.2 | 773 | 2026-05-06 06:41:11 | MASTER-OAGH | (10h 16m 39.45s , +75d 23m 04.3s) | C | 60 | 19.0 | 773 | 2026-05-06 06:41:11 | MASTER-OAGH | (10h 09m 25.61s , +75d 59m 15.1s) | C | 60 | 19.2 | 1010 | 2026-05-06 06:45:08 | MASTER-OAGH | (08h 44m 32.03s , +75d 26m 03.2s) | C | 60 | 18.9 | 1010 | 2026-05-06 06:45:08 | MASTER-OAGH | (08h 37m 39.30s , +75d 57m 59.1s) | C | 60 | 18.9 | 1083 | 2026-05-06 06:46:21 | MASTER-OAGH | (09h 16m 23.42s , +75d 24m 39.6s) | C | 60 | 18.8 | 1083 | 2026-05-06 06:46:21 | MASTER-OAGH | (09h 09m 18.88s , +76d 00m 58.5s) | C | 60 | 19.0 | 1156 | 2026-05-06 06:47:34 | MASTER-OAGH | (08h 52m 15.20s , +77d 18m 04.3s) | C | 60 | 19.1 | 1156 | 2026-05-06 06:47:34 | MASTER-OAGH | (08h 44m 14.12s , +77d 54m 09.0s) | C | 60 | 19.1 | 1230 | 2026-05-06 06:48:47 | MASTER-OAGH | (09h 28m 45.20s , +77d 17m 37.2s) | C | 60 | 18.7 | 1230 | 2026-05-06 06:48:47 | MASTER-OAGH | (09h 20m 32.90s , +77d 53m 53.1s) | C | 60 | 19.0 | 1303 | 2026-05-06 06:50:00 | MASTER-OAGH | (09h 32m 40.96s , +73d 31m 11.3s) | C | 60 | 18.9 | 1303 | 2026-05-06 06:50:00 | MASTER-OAGH | (09h 26m 24.09s , +74d 07m 34.1s) | C | 60 | 19.0 | 1376 | 2026-05-06 06:51:14 | MASTER-OAGH | (10h 00m 49.53s , +73d 29m 34.1s) | C | 60 | 18.9 | 1376 | 2026-05-06 06:51:14 | MASTER-OAGH | (09h 54m 31.45s , +74d 05m 45.0s) | C | 60 | 19.2 | 1448 | 2026-05-06 06:52:26 | MASTER-OAGH | (09h 44m 56.50s , +75d 25m 43.2s) | C | 60 | 19.0 | 1448 | 2026-05-06 06:52:26 | MASTER-OAGH | (09h 37m 49.83s , +76d 01m 49.5s) | C | 60 | 19.1 | 1523 | 2026-05-06 06:53:41 | MASTER-OAGH | (10h 16m 36.92s , +75d 24m 10.7s) | C | 60 | 18.9 | 1523 | 2026-05-06 06:53:41 | MASTER-OAGH | (10h 09m 24.89s , +76d 00m 21.4s) | C | 60 | 19.3 | 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/44482. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42607] GRB 260506A: Fermi GBM Final Real-time Localization
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44481 SUBJECT: GRB 260506A: Fermi GBM Final Real-time Localization DATE: 26/05/06 06:39:24 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 06:28:48 UT on 6 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260506A (trigger 799741733.38117 / 260506270). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 145.7, Dec = 76.1 (J2000 degrees, equivalent to J2000 09h 42m, 76d 05'), with a statistical uncertainty of 7.2 degrees. The angle from the Fermi LAT boresight is 18.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506270/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506270/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506270/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42606] GRB 260503A: GECAM-B observation of a burst
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44480 SUBJECT: GRB 260503A: GECAM-B observation of a burst DATE: 26/05/06 05:19:05 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 260503A, at 2026-05-03T20:40:18.050 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44451). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 21 +4/-3 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260503A.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/44480. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42605] IceCube Alert 260505A: Global MASTER-Net observations report
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44479 SUBJECT: IceCube Alert 260505A: Global MASTER-Net observations report DATE: 26/05/05 22:26:33 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) was pointed to the IceCube Alert 260505A (trigger No 58544625,16h 27m 57.60s , +54d 52m 12.0s, R=0.67) errorbox 1 days 3353 sec after notice time and 1 days 3411 sec after trigger time at 2026-05-05 22:08:12 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 13 deg. The sun altitude is -29.0 deg. The galactic latitude b = 42 deg., longitude l = 84 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3293437 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 89842 | 2026-05-05 22:08:12 | MASTER-Kislovodsk | (16h 26m 24.62s , +55d 13m 07.6s) | C | 60 | 13.2 | 89842 | 2026-05-05 22:08:12 | MASTER-Kislovodsk | (16h 26m 52.94s , +54d 49m 59.4s) | C | 60 | 19.1 | 89940 | 2026-05-05 22:09:50 | MASTER-Kislovodsk | (16h 26m 58.23s , +54d 48m 57.5s) | C | 60 | 19.1 | 90036 | 2026-05-05 22:11:26 | MASTER-Kislovodsk | (16h 26m 12.84s , +55d 11m 17.5s) | C | 60 | 13.3 | 90037 | 2026-05-05 22:11:27 | MASTER-Kislovodsk | (16h 26m 52.47s , +54d 47m 56.7s) | C | 60 | 19.1 | 90125 | 2026-05-05 22:12:56 | MASTER-Kislovodsk | (16h 26m 24.80s , +55d 12m 02.6s) | C | 60 | 13.6 | 90125 | 2026-05-05 22:12:56 | MASTER-Kislovodsk | (16h 26m 56.65s , +54d 48m 13.7s) | C | 60 | 19.2 | 90215 | 2026-05-05 22:14:25 | MASTER-Kislovodsk | (16h 26m 17.07s , +55d 12m 10.3s) | C | 60 | 12.9 | 90215 | 2026-05-05 22:14:25 | MASTER-Kislovodsk | (16h 26m 52.12s , +54d 49m 38.8s) | C | 60 | 19.2 | 90303 | 2026-05-05 22:15:54 | MASTER-Kislovodsk | (16h 26m 16.58s , +55d 10m 30.3s) | C | 60 | 13.1 | 90303 | 2026-05-05 22:15:54 | MASTER-Kislovodsk | (16h 26m 51.53s , +54d 48m 00.8s) | C | 60 | 19.1 | 90391 | 2026-05-05 22:17:21 | MASTER-Kislovodsk | (16h 26m 20.13s , +55d 12m 14.8s) | C | 60 | 12.7 | 90391 | 2026-05-05 22:17:21 | MASTER-Kislovodsk | (16h 26m 54.99s , +54d 49m 43.2s) | C | 60 | 19.0 | 90479 | 2026-05-05 22:18:50 | MASTER-Kislovodsk | (16h 26m 12.86s , +55d 11m 27.4s) | C | 60 | 12.7 | 90479 | 2026-05-05 22:18:50 | MASTER-Kislovodsk | (16h 26m 47.70s , +54d 48m 56.2s) | C | 60 | 19.2 | 90568 | 2026-05-05 22:20:18 | MASTER-Kislovodsk | (16h 26m 47.19s , +54d 49m 56.1s) | C | 60 | 19.2 | 90656 | 2026-05-05 22:21:46 | MASTER-Kislovodsk | (16h 26m 19.15s , +55d 11m 26.0s) | C | 60 | 12.7 | 90656 | 2026-05-05 22:21:46 | MASTER-Kislovodsk | (16h 26m 53.95s , +54d 48m 57.0s) | C | 60 | 19.2 | 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/44479. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42604] GRB 260430B: Glowbug gamma-ray detection
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44478 SUBJECT: GRB 260430B: Glowbug gamma-ray detection DATE: 26/05/05 16:06:39 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260430B, which was also detected by AstroSat/CZTI (GCN 44469) and SVOM/GRM (sb26043004). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-04-30 16:04:22.184 with a duration of 49.2 s and a total significance of about 113 sigma. The light curve comprises a complex series of peaks throughout the burst duration. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44478. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42603] GRB 260504B: SVOM/VT optical upper limits
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44477 SUBJECT: GRB 260504B: SVOM/VT optical upper limits DATE: 26/05/05 15:53:02 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, 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 (CEA/Irfu), Y. Wang (PMO,CAS; UCB) report on behalf of the SVOM/VT team. SVOM/VT performed observations with an automatic slew to GRB 260504B detected by SVOM/ECLAIRs (sb26050402, Saccardi et al., GCN 44454), SVOM/GRM (Wang et al., GCN 44470), GECAM-B (Wang et al., GCN 44473) and Konus-Wind (Frederiks et al., GCN 44474). The observation started at 2026-05-04T09:34:59 UTC, 220 seconds post trigger and lasted for 6 orbits (about 8 hours), in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued sources were detected within the error box of SVOM/ECLAIRs (Saccardi et al., GCN 44454) or SVOM/MXT (Maggi et al., GCN 44468), compared to the Legacy Survey. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | 5-sigma upper limit 670 s VT_B 18*50 s > 22.5 mag 670 s VT_R 18*50 s > 22.5 mag 2.59 h VT_B 34*100 s > 23.0 mag 2.59 h VT_R 33*100 s > 23.0 mag Our result is consistent with the results from the rapid decay in SVOM/MXT (Saccardi et al., GCN 44454), upper limit of EP-FXT (Zhou et al., GCN 44467), optical non-detections by MASTER-OAFA(Podesta et al., GCN 44455), LCO (Turpin et al., GCN 44456), AST3-2 (Sun et al., GCN 44457) and REM (Brivio et al., GCN 44460). 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/44477. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42602] GRB 260421B: radio observation with the VLA
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44476 SUBJECT: GRB 260421B: radio observation with the VLA DATE: 26/05/05 15:50:44 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 05:08:16 UT on 2026 April 22 (T_mid = 1.07 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, we do not detect the radio counterpart of GRB 260421B. We derive the following upper limits (UL; 3sigma): ================================================================ T_mid Freq UL r.m.s. Beam PA [days] [GHz] [uJy] [uJy/b] [arcsec^2] [deg] ================================================================ 1.07 6 24 8 0.47x0.28 11 1.07 10 24 8 0.30x0.18 11 1.07 15 27 9 0.20x0.11 -2 ================================================================ 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/44476. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42601] Konus-Wind detection of a burst from SGR 1E1841-045 on 2026 May 2
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44475 SUBJECT: Konus-Wind detection of a burst from SGR 1E1841-045 on 2026 May 2 DATE: 26/05/05 15:28:39 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: A bright burst from SGR 1E1841-045 (IPN triangulation: Ridnaia et al., GCN 44448; SVOM-GRM detection: Zao et al., GCN 44450) triggered Konus-Wind at T0=20396.052 s UT (05:39:56.052) on 2026 May 2. The burst light curve shows a single pulse, which starts at ~T0-50 ms and has a total duration of ~96 ms. The emission is seen up to ~200 keV. The Konus-Wind light curve of this burst is available at http://www.ioffe.ru/LEA/SGRs/260502_T20396/ As observed by Konus-Wind, the burst had a fluence of 8.64(-0.45,+0.46)x10^-7 erg/cm2, and a 16-ms peak flux, measured from T0-0.004 s, of 1.93(-0.16,+0.16)x10^-5 erg/cm2/s (both in the 20 - 500 keV energy range). The spectrum of the burst (measured from T0 to T0+0.064 s) is best fit in the 20 - 500 keV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = 0.16(-0.69,+0.76) and Ep = 48(-4,+3) keV (chi2 = 12/15 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/44475. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42600] Konus-Wind detection of GRB 260504B (short/hard)
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44474 SUBJECT: Konus-Wind detection of GRB 260504B (short/hard) DATE: 26/05/05 14:25:39 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: The short GRB 260504B (SVOM/ECLAIRs detection: Saccardi et al., GCN 44454; SVOM/GRM detection: Wang et al., GCN 44470; GECAM-B detection: Wang et al., GCN 44473) triggered Konus-Wind (KW) at T0=34281.198 s UT (09:31:21.198). The burst light curve shows a single pulse, which starts at ~T0-0.05 s and has a duration of ~0.21 s. The emission is seen up to ~6 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260504_T34281/ As observed by Konus-Wind, the burst had the total fluence of (2.39 ± 0.52)x10^-6 erg/cm^2 and a 16-ms peak energy flux, measured from T0-0.032, of (2.06 ± 0.45)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+0.192 s) is best fitted in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.00 (-0.12, + 0.14) and Ep = 1461(-398,+584) keV, chi^2 = 34/32 dof. Fitting this spectrum by a Band GRB function yields the same values of alpha and Ep, and only an upper limit on the high energy photon index beta of -2.1 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/44474. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42599] GRB 260504B: GECAM-B detection
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44473 SUBJECT: GRB 260504B: GECAM-B detection DATE: 26/05/05 13:41:13 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a hard burst GRB 260504B at 2026-05-04T09:31:19.450 UTC (denoted as T0). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 0.20 +0.02/-0.06 s, which is also detected by SVOM/ECLAIRs and SVOM/GRM (A. Saccardi et al., GCN # 44454). The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260504B.png The time-averaged spectrum from T0-0.07 s to T0+0.1 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +0.29/-0.27 and the cutoff energy, parameterized as Epeak, is 1240 +730/-400 keV. The event fluence (10-1000 keV) in this time interval is (1.06 +0.13/-0.10)E-06 erg/cm^2. Thus GRB 260504B is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/gecambgrb260504B_amati.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/44473. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42598] Fermi-LAT Gamma-ray Observations of IceCube-260504A
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44472 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260504A DATE: 26/05/05 12:53:40 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260504A neutrino event (GCN 44464) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2026-05-04 21:11:20.90 UTC (T0) with J2000 position RA = 246.99 (+0.86, -0.80) deg, Decl. = 54.87 (+0.46, -0.47) deg 90% PSF containment. One cataloged >100 MeV gamma-ray source is located within the 90% IC260504A localization error, at a distance of roughly 0.38 deg (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). This is the object 4FGL J1626.0+5436 associated with 87GB 162528.4+544848. Based on a preliminary analysis of the LAT data over the timescale of 1-day and 1-month prior to T0, this object is not significantly detected at gamma-rays. We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC260504A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260504A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.3e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <4.6e-09 (<4.7e-08) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source the Fermi-LAT contact person is Leonard Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). 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/44472. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42596] GRB 260504C: SVOM/GRM observation of short GRB
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44471 SUBJECT: GRB 260504C: SVOM/GRM observation of short GRB DATE: 26/05/05 12:42:20 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Piron (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a short burst GRB 260504C (SVOM trigger reference: sb26050401) at 2026-05-04T07:10:06.60 UTC (T0). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple spikes with a T90 of 0.26 +0.06/-0.08 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260504C.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: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44471. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42597] GRB 260504B: SVOM/GRM spectral analysis
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44470 SUBJECT: GRB 260504B: SVOM/GRM spectral analysis DATE: 26/05/05 12:31:40 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Stéphane Schanne (CEA) Report on behalf of the SVOM team: With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 260504B. With the localization of ECLAIRs (RA= 351.2451 deg, DEC= -80.3291 deg, GCN#44454), the time-averaged spectrum from T0-0.10 to T0+0.34 s can be fitted by a power law function with an exponential high-energy cutoff adequately. The power law index is -0.72 +0.11/-0.10 and the cutoff energy, parameterized as Epeak, is 1340 +590/-380 keV. The event fluence (10-1000 keV) in this time interval is (1.46 +0.10/-0.09)E-06 erg/cm^2. Thus GRB 260504B is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/svgrb260504B_amati.png The SVOM/GRM light curve was updated using the X-band data： https://www.bursthub.cn//admin/static/svgrb260504B.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/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44470. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42595] GRB 260430B: AstroSat CZTI detection of a long burst
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44469 SUBJECT: GRB 260430B: AstroSat CZTI detection of a long burst DATE: 26/05/05 11:53:54 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 260430B. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-04-30 16:04:26.34 UTC. The measured peak count rate associated with the burst is 100 (+32, -10) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1436 (+290, -227) counts. The local mean background count rate was 219 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 47 (+2, -4) 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 2026-04-30 16:04:22.5 UTC. The measured peak count rate associated with the burst is 417 (+77, -26) counts/s above the background in the combined data of all quadrants, with a total of 6007 (+912, -928) counts. The local mean background count rate was 1271 (+6, -6) counts/s. We measure a T90 of 40 (+11, -6) 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/515261050.0/S515261050.0_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/44469. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42594] GRB 260504B: SVOM/MXT refined analysis and potential detection
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44468 SUBJECT: GRB 260504B: SVOM/MXT refined analysis and potential detection DATE: 26/05/05 09:32:52 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> P. Maggi (ObAS), D. Götz (CEA), H. Goto (RIKEN/CEA), M. Moita (CEA), C. Plasse (UHK), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: GRB 260504B (Saccardi et al. GCN 44454) was observed by SVOM/MXT after an automatic SVOM slew, starting at T_MXT = 2026-05-04T09:33:16, 117 s after trigger time T0. MXT observed for the remainder of the orbit for 730s and the subsequent 5 orbits. Using the full X-band dataset, an uncatalogued X-ray source is only detected significantly at the very start of the MXT observation. Restricting the analysis until T_MXT+60s, the position of the MXT candidate afterglow is refined to: R.A. (J2000) = 23h24m10.8s Dec (J2000) = -80d17m01s with a 90% C.L. radius of 113” (including 25 arcseconds systematic error added in quadrature). This position is compatible with the SVOM/ECLAIRS position, but not with the SVOM/MXT position using the onboard processed data, initially reported. This position supersedes the one published in the GCN 44454. The light curve exhibits a fast decay with temporal index alpha < -6 (with count rate proportional to t^alpha). At t >T_MXT + 60s the source is no longer detected by MXT. The source is below the MXT detection limit in subsequent orbits. We analysed the spectrum extracted from the first 60s of observation, modelled with an absorbed power-law. The absorbing column was fixed to the Galactic NH of 7x1e20 /cm². A photon index Gamma = 1.3 +/- 0.4 is measured. We measure a 0.3-8 keV flux of 2.6 (-1.6/ +2.28) x 1e-10 erg/s/cm² (all uncertainties at 90% C. L.; these preliminary results may be improved) The Space 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. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The Burst Advocate (BA) on shift for this alert is Yun Wang: wangyun(a)pmo.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44468. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42593] GRB 260504B: EP-FXT upper limit
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44467 SUBJECT: GRB 260504B: EP-FXT upper limit DATE: 26/05/05 04:30:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou (PMO, CAS), Y.Q. Zhao (PRIC, USTC), T.Y. Liu, Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: The Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission observed GRB 260504B (Saccardi, GCN 44454) autonomously at 2026-05-04 11:46:16 (UTC, ~ 2.25 hours after the burst). The exposure time of this observation is 1472s. On-ground analysis of the FXT data did not found any significant source within the error circle (90% C.L. radius of 167 arcsec) of GRB 260504B. The 5-sigma upper limit of EP-FXT observation is 4.8 x 10^-13 erg/s/cm^2 in the 0.5-10 keV band. 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/44467. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42592] GRB 260502A: SVOM/GRM observation of a short GRB
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44466 SUBJECT: GRB 260502A: SVOM/GRM observation of a short GRB DATE: 26/05/05 03:09:45 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> SVOM/GRM team: Xing-Hao Luo, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Hui Yang (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 260502A at 2026-05-02T05:01:00.300 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44447). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.61 +0.28/-0.15 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260502A.png In addition, the position of this burst, as determined by Fermi/GBM (RA=283.76 , DEC=57.62, with a statistical uncertainty of 13.77 degrees, Fermi GBM team, GCN #44447), is located at about 82 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-0.04 to T0+0.01 s is best fitted by a power law function. The power law index is -1.12 +/-0.10. The event fluence (10-1000keV) in this time interval is (2.3 +0.37/-0.33)E-07 erg/cm^2. 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: Xing-Hao Luo (luoxh(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44466. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42591] GRB 260503A: SVOM/GRM observation of a GRB
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44465 SUBJECT: GRB 260503A: SVOM/GRM observation of a GRB DATE: 26/05/05 03:08:00 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> SVOM/GRM team: Xing-Hao Luo, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Marius Brunet (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260503A (SVOM trigger reference: sb26050309) at 2026-05-03T20:40:20.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44451). 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 21 +7/-3 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260503A.png In addition, the position of this burst, as determined by Fermi/GBM (RA=287.1 , DEC=-2.0, with a statistical uncertainty of 2.6 degrees, Fermi GBM team, GCN #44451), is located at about 87 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-3 to T0+17 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.12 +0.17/-0.16 and the cutoff energy, parameterized as Epeak, is 128 +21/-15 keV. The event fluence (10-1000keV) in this time interval is (6.65 +0.53/-0.46)E-06 erg/cm^2. The localization of GRB 260503A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260503A_amati.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: Xing-Hao Luo (luoxh(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44465. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42590] IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44464 SUBJECT: IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/05/05 01:46:29 GMT FROM: jliao(a)icecube.wisc.edu The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-05-04 at 21:11:20.90 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of None events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/142545_58544625.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-05-04 Time: 21:11:20.90 UT RA: 246.99 (+0.86/-0.80 deg 90% PSF containment) J2000 Dec: 54.87 (+0.46/-0.47 deg 90% PSF containment) J2000 One gamma-ray source from the Fermi 4FGL-DR4 catalog is located within the 90% uncertainty region of this event: 4FGL J1626.0+5436 , at RA = 246.51° and Dec = 54.61° (J2000), with an angular separation of 0.38° from the best-fit event position. As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/44464. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42589] Konus-Wind detection of GRB 260415C
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44463 SUBJECT: Konus-Wind detection of GRB 260415C DATE: 26/05/04 20:18:18 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260415C triggered Konus-Wind at T0=27659.163 s UT (07:40:59.163). The burst light curve shows a single pulse which starts at ~T0-2.5 s and has a total duration of ~11.3 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/GRB260415_T27659/ As observed by Konus-Wind, the burst had the total fluence of 3.64(-0.42,+0.54)x10^-6 erg/cm2, and the 64-ms peak flux, measured from T0-0.446 s, of 1.56(-0.41,+0.45)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 the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.06(-0.45,+0.60), the high energy photon index beta = -2.91(-0.94,+0.36), the peak energy Ep = 105(-11,+12) keV (chi2 = 92/77 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/44463. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42588] GCN Announcement: New BOOM Notices and Schema v7.0.0
by GCN Announcements 04 May '26

04 May '26

The GCN Team is pleased to announce a new Notice Type and a schema release. BOOM Cross-Correlated Optical Transient Notices The Burst & Outburst Observations Monitor (BOOM)/Babamul Team (https://www.ztf.caltech.edu/ztf-boom-babamul.html) and the GCN Team are pleased to announce the availability of a new notice type via the new GCN in JSON format. BOOM provides real-time brokering, archival context, and coordination tools that enable rapid identification, vetting, and follow-up of astrophysical transients. BOOM is the software stack operating to enable a multi-survey alert broker and data archive (Babamul) that ingests and combines alerts from the Zwicky Transient Facility (ZTF) and the Vera C. Rubin Observatory alert stream. BOOM is contributing a GCN Notices stream, where cross-matches from the BOOM fast transient stream (which analyzes ZTF and LSST alert streams) are checked for (i) gravitational-wave alert candidates consistent with a binary neutron star merger or neutron star-black hole merger and (ii) gamma-ray bursts detected by Fermi, SVOM, and Swift. This enables rapid cross-identification of events across experiments and observatories, enhancing situational awareness and time-critical response for the broader transient astronomy community. Alert includes localization, photometry, cross-matches with other GCN Notices, and classification scores from machine-learning models. BOOM notices are published on the GCN Kafka topic gcn.notices.boom.alert. See the BOOM mission page (https://gcn.nasa.gov/missions/boom) for a more extensive description of the information provided in these new notices. Schema v7.0.0 GCN Schema v7.0.0 is available with recent changes including new Notice types and a modified and generalized Spectral core schema (Release Notes; https://github.com/nasa-gcn/gcn-schema/releases/tag/v7.0.0) For more details on this new feature and an archive of GCN news and announcements, see https://gcn.nasa.gov/news. For questions, issues, or bug reports, please contact us via: - Contact form: https://gcn.nasa.gov/contact - GitHub issue tracker: https://github.com/nasa-gcn/gcn.nasa.gov/issues --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42587] GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44462 SUBJECT: GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN DATE: 26/05/04 19:46:05 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> N. Pankov (IKI), A. Pozanenko (IKI), A. Volnova (IKI), E. Schekotikhin (IKI), E. Klunko (ISTP), M. Eselevich (ISTP), A. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), V. Rumyantsev (CrAO), A. Novichonok (KIAM), A. Kochergin (UAFO IAA), I. Sokolov (INASAN), M. Krugov (FAI), R. Inasaridze (AbAO), A. Tarasenkov (INASAN) report on behalf of IKI GRB-FuN: We observed the optical counterpart AT2026fgk (a.k.a. GOTO26buh, O'Neill et al. 2026, TNS Discovery Report 294132; Hinds et al., AstroNote 2026-65; Konno et al., GCN 43974) associated with GRB 260310A (The Fermi GBM team, GCN 43951; Salunke et la., GCN 43958; Hamburg & Meegan, GCN 43975; Jayaraman et al., GCN 43994). Observations began on March 13, 2026, and continue to this day. Observations were performed with the following telescopes: AZT-33IK (Mondy), Zeiss-1000 (SAO RAS), Zeiss-1000 (Koshka), ZTSh (CrAO), ORI-50 (UAFO), Zeiss-2000 (Terskol), AZT-20 (Assy), AS-32 (AbAO) with BR-filters, and BVRI-filters on a few epochs. We clearly detect the counterpart (Lipunov et al., GCN 43954, 43978; Martin-Carrillo et al., GCN 43979, 44000; Moreno Méndez et al., GCN 43979; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991, 44059; Jin-Ji Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo, GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021, 44067; Pawar et al., GCN 44022; Belkin & Shrestha, GCN 44043; H. L. Li et al., GCN 44044; Gupta et al., GCN 44051; Passaleva et al., GCN 44058, 44104; Volnova et al., GCN 44060; Busmann et al., GCN 44061; Zheng & Filippenko, GCN 44065; Pankov et al., GCN 44073; Serrau et al., GCN 44112; Kang et al., GCN 44119; Effress et al., GCN 44122; Guelfand et al., GCN 44125; O'Connor et al., GCN 44137; Liu et al., GCN 44172; Freeberg et al., GCN 44208). We confirm the break reported by Perly at al. (GCN 44096) on the 8th day after the trigger. After subtracting the image using the template obtained on April, 21 in the R filter with AZT-33IK, we constructed the afterglow + supernova light curve (LC). We note, that the point source is still clearly detected on the image on May, 02. We note that the afterglow power law decay index of -2.1 is steeper than reported by Perly at al. (GCN 44096) and may be affected by the still glowing optical counterpart. Subtracting the power-law afterglow with the power law decay index of -2.1 from the light curve gives us a possible supernova light curve, shown in https://heaiki.ru/lvc/GRB260310A/GRB260310A_subtracred_host_and_PL__aftergl… (for the LC construction we use only observations obtained with AZT-033IK, Mondy.) Thus we can tentatively confirm the maximum of bump which was suggested as possible SN associated with GRB 260310A in R-filter of about 21 days after the GRB trigger reported earlier (Freeberg et al., GCN 44248), however more faint and with apparent magnitude of about R ~ 21.8. Thus absolute magnitude at the redshift of z=0.153 (Hinds et al., GCN 43977; de Ugarte Postigo et al., GCN 43984) would be not fainter than M_R = -17.5. Initially SN rising was suggested by SED evolution (de Ugarte Postigo et al., GCN 44124). We continue to monitor the optical counterpart of the GRB 260310A. View this GCN Circular online at https://gcn.nasa.gov/circulars/44462. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42586] Konus-Wind detection of GRB 260411C
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44461 SUBJECT: Konus-Wind detection of GRB 260411C DATE: 26/05/04 19:38:56 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260411C triggered Konus-Wind at T0=21236.871 s UT (05:53:56.871). The burst light curve shows a single pulse which starts at ~T0-14.9 s and has a total duration of ~24.3 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/GRB260411_T21236/ As observed by Konus-Wind, the burst had the total fluence of 1.31(-0.08,+0.08)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+1.584 s, of 7.72(-0.94,+0.93)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 the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.54(-0.09,+0.08), the high energy photon index beta = -3.23(-6.77,+0.37), the peak energy Ep = 105(-6,+8) keV (chi2 = 85/81 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/44461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42585] GRB 260502A: Fermi GBM Final Localization
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44447 SUBJECT: GRB 260502A: Fermi GBM Final Localization DATE: 26/05/03 05:20:13 GMT FROM: Rushikesh Sonawane at IISER TVM <rushikesh23(a)iisertvm.ac.in> The Fermi GBM team reports the detection of a likely SHORT GRB "At 05:01:00.25 UT on 02 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260502A (trigger 799390865/260502209). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 283.76, Dec = 57.62 (J2000 degrees, equivalent to J2000 18h 55m, +57d 37′), with a statistical uncertainty of 13.77 degrees. The angle from the Fermi LAT boresight is 23 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42584] GRB 260504B: REM optical/NIR observations
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44460 SUBJECT: GRB 260504B: REM optical/NIR observations DATE: 26/05/04 15:24:20 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 260504B detected by SVOM/ECLAIRs (Saccardi et al., GCN 44454) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried out in the g, r, i, z, and H bands, started on 2026 May 04 at 09:41:12 UT (i.e. 9.9 min after the burst), and lasted for about 1.5 hours. From preliminary inspection, we do not detect any counterpart within the SVOM/ECLAIRs and SVOM/MXT error circles down to the following 3sigma limits: r > 19.5 (AB; calibrated against the SkyMapper catalogue), at a mid-time of 33.8 min after the trigger; H > 15.3 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 13.3 min after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44460. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42583] IPN triangulation of GRB 260429A
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44459 SUBJECT: IPN triangulation of GRB 260429A DATE: 26/05/04 15:06:16 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The bright, short-duration GRB 260429A (Ferm-GBM detection: The Fermi GBM team, GCN 44425; Scotton, GCN 44430; SVOM-GRM detection: Yu et al., GCN 44439) was detected by Fermi (GBM trigger 799197847), Konus-Wind, SVOM (GRM), and Mars-Odyssey (HEND) at about 84242 s UT (23:24:02). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 281.153 (18h 44m 37s) +17.279 (+17d 16' 44") Corners: 281.115 (18h 44m 28s) +17.444 (+17d 26' 37") 281.161 (18h 44m 39s) +17.398 (+17d 23' 52") 281.192 (18h 44m 46s) +17.114 (+17d 06' 50") 281.146 (18h 44m 35s) +17.160 (+17d 09' 36") --------------------------------------------- The error box area is 40 sq. arcmin, and its maximum dimension is 20 arcmin (the minimum one is 2.3 arcmin). The Sun distance was 109 deg. This localization may be improved. A triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB260429_T84245/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/44459. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42582] IPN triangulation of GRB 260428A
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44458 SUBJECT: IPN triangulation of GRB 260428A DATE: 26/05/04 15:04:29 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP), J. Wei (NAOC), B. Cordier (CEA) on behalf of the SVOM-GRM team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The short-duration GRB 260428A (Fermi-GBM detection: Fermi GBM team, GCN Circ. 44415; AstroSat-CZTI detection: Goyal et al., GCN Circ. 44421; GECAM-B detection: Wang et al., GCN Circ. 44423; SVOM/GRM observation: Wang et al., GCN Circ. 44424) was detected by Fermi (GBM), Konus-Wind, AstroSat (CZTI), GECAM-B, SVOM (GRM), and Mars-Odyssey (HEND) at about 51636 s UT (14:20:36). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 283.386 (18h 53m 33s) +0.365 ( +0d 21' 53") Corners: 283.274 (18h 53m 06s) +1.978 ( +1d 58' 41") 283.221 (18h 52m 53s) +2.065 ( +2d 03' 56") 283.504 (18h 54m 01s) -1.335 ( -1d 20' 06") 283.558 (18h 54m 14s) -1.435 ( -1d 26' 07") --------------------------------------------- The error box area is 561 sq. arcmin, and its maximum dimension is 3.5 deg (the minimum one is 3 arcmin). The Sun distance was 111 deg. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB260428_T51639/IPN The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/44458. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42581] GRB 260504B: AST3-2 i-band upper limit
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44457 SUBJECT: GRB 260504B: AST3-2 i-band upper limit DATE: 26/05/04 15:02:23 GMT FROM: Tianrui Sun at Purple Mountain Obs,CAS <trsun(a)pmo.ac.cn> Tian-Rui Sun, Yan-Long Hua (Purple Mountain Observatory, CAS), Kun Ma, Jiali Chen, Kai-wen Zheng, Hongjian Guo, Ben Liu, Shuping Wang, Huiping Jin, Jiaheng Liu, Haoyu Yan, Jiajie Yang, Xiao-Yan Li (Nanjing Institute of Astronomical Optics & Technology, CAS), Jin-Jun Geng, Wenlong Zhang, Xue-Feng Wu (Purple Mountain Observatory, CAS), report on behalf of the AST3 Team: Following the detection of GRB 260504B by ECLAIRs aboard SVOM (A. Saccardi et al., GCN 44454), we carried out follow-up observations using the Antarctic Survey Telescope AST3-2 located at Dome A, Antarctica (Lat. −80.4173 deg, Long. 77.0950 deg). Observations began at 2026-05-04 09:48:50 UT. No significant optical counterpart was detected within the ECLAIRs error circle (~4.91 arcmin radius) and the MXT error circle (~167 arcsec), based on comparisons with Gaia DR3 and archival SkyMapper cutout images. The stacked image with a total exposure time of 7170 s in the i-band reached a 5σ limiting magnitude of ~19.7.This result is consistent with the non-detections reported by MASTA-OAFA (F. Podesta et al., GCN 44455) and by LCO (D. Turpin et al., GCN 44456). Photometric calibration was performed using the ATLAS Reference Catalog (Tonry et al. 2018). We thank Prof. Michael Ashley (UNSW) for his continuous support in the operation of AST3-2. View this GCN Circular online at https://gcn.nasa.gov/circulars/44457. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42580] GRB 260504B: LCO z-band upper limit
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44456 SUBJECT: GRB 260504B: LCO z-band upper limit DATE: 26/05/04 10:38:06 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), L. P. Xin (NAOC), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), report on behalf of the SVOM mission team: We observed the field of the short GRB 260504B detected by SVOM (Saccardi et al., GCN 44454) with the LCO 1m telescope at Cerro Tololo equipped with the Sinistro instrument. Our observation started on 2026-05-04 at 09:40:18 UT (about 9 min after the trigger) and we obtained 3x200 s exposures in the Pan-STARRS z filter. No new source is detected within the ECLAIRs and MXT error circles, down to a limiting magnitude: z > 19.66 (AB, 5-sigma, mid-time 14.4 min after the SVOM trigger). This value was calibrated against the SkyMapper survey DR4 and is not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44456. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42579] SVOM GRB 260504B: MASTER-OAFA optical observations
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44455 SUBJECT: SVOM GRB 260504B: MASTER-OAFA optical observations DATE: 26/05/04 10:30:53 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> F.Podesta, M.J. Segura, C.Francile, R.Podesta, E. Gonzalez (OAFA, SJNU), A.Kuznetsov, V.Lipunov, I.Panchenko, P.Balanutsa, G.Antipov, N.Tiurina, K.Zhirkov, E.Gorbovskoy, V.Senik, A.Chasovnikov, Ya.Kechin, V.Topolev, D.Vlasenko,A.Sankovich, I.Gorbunov (Lomonosov MSU), N.Budnev, O.Gress (ISU), 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-OAFA robotic telescope of MASTER Global Robotic Net [1-4] was pointed to the SVOM GRB260504.40 (trigger No 1777887197,23h 24m 54.98s, -80d 21m 09.7s, R=0.0491, Saccardi et al. GCN 44454 ) errorbox 434 sec after trigger time at 2026-05-04 09:40:30 UT, with upper limit up to 19.7 mag. The observations began at zenith distance = 54 deg. The sun altitude was -18.8 deg. The galactic latitude b = -36 deg., longitude l = 307 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3291780 MASTER upper limits: Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment 489 | 2026-05-04 09:40:30 | MASTER-OAFA | (23h 23m 41.35s , -81d 33m 14.0s) | C | 110 | 18.9 | 634 | 2026-05-04 09:40:30 | MASTER-OAFA | (23h 23m 41.33s , -81d 33m 14.1s) | C | 400 | 19.7 | Coadd 615 | 2026-05-04 09:42:26 | MASTER-OAFA | (23h 23m 41.51s , -81d 33m 07.2s) | C | 130 | 19.1 | 767 | 2026-05-04 09:44:43 | MASTER-OAFA | (23h 23m 41.18s , -81d 33m 00.8s) | C | 160 | 19.2 | 883 | 2026-05-04 09:47:29 | MASTER-OAFA | (23h 23m 40.81s , -81d 32m 56.0s) | C | 60 | 18.8 | 943 | 2026-05-04 09:47:29 | MASTER-OAFA | (23h 23m 40.80s , -81d 32m 56.1s) | C | 180 | 19.5 | Coadd 948 | 2026-05-04 09:48:35 | MASTER-OAFA | (23h 23m 40.67s , -81d 32m 53.0s) | C | 60 | 18.8 | 1014 | 2026-05-04 09:49:40 | MASTER-OAFA | (23h 23m 40.42s , -81d 32m 50.2s) | C | 60 | 18.8 | 1080 | 2026-05-04 09:50:46 | MASTER-OAFA | (23h 23m 40.47s , -81d 32m 47.6s) | C | 60 | 18.9 | 1140 | 2026-05-04 09:50:46 | MASTER-OAFA | (23h 23m 40.46s , -81d 32m 47.6s) | C | 180 | 19.6 | Coadd 1145 | 2026-05-04 09:51:51 | MASTER-OAFA | (23h 23m 40.03s , -81d 32m 44.5s) | C | 60 | 18.7 | 1211 | 2026-05-04 09:52:57 | MASTER-OAFA | (23h 23m 39.95s , -81d 32m 41.8s) | C | 60 | 18.8 | 1277 | 2026-05-04 09:54:03 | MASTER-OAFA | (23h 23m 39.77s , -81d 32m 39.0s) | C | 60 | 18.8 | 1342 | 2026-05-04 09:55:09 | MASTER-OAFA | (23h 23m 39.54s , -81d 32m 36.0s) | C | 60 | 18.7 | 1408 | 2026-05-04 09:56:14 | MASTER-OAFA | (23h 23m 39.36s , -81d 32m 33.3s) | C | 60 | 18.7 | 1474 | 2026-05-04 09:57:21 | MASTER-OAFA | (23h 23m 39.24s , -81d 32m 30.3s) | C | 60 | 18.8 | 1540 | 2026-05-04 09:58:26 | MASTER-OAFA | (23h 23m 39.00s , -81d 32m 27.3s) | C | 60 | 18.9 | Filter C is a clear (unfiltred) band. Observation and reduction will continue. [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/44455. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42578] GRB 260504B: SVOM detection of a short burst
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44454 SUBJECT: GRB 260504B: SVOM detection of a short burst DATE: 26/05/04 10:00:59 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), D. Adrien (CEA/Irfu), F. Piron (LUPM), D. Gotz (CEA/Irfu), P. Maggi (ObAS), C. W. Wang (IHEP), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), report on behalf of the SVOM mission team: At 2026-05-04T09:31:19 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260504B (SVOM burst-id sb26050402). 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 Count-Rate Trigger (CRT), which produced a sequence of 6 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 17.15 in the [8-120] keV energy band over a time window of 0.30 seconds starting at 2026-05-04T09:31:19. The localization of the best alert is R.A., Dec. 351.2451, -80.3291 degrees (J2000) with a 90% confidence level (C.L.) radius of 4.91 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve shows a single narrow peak structure with a T90 duration of 0.5 +/- 0.1 s (5-120 keV). This burst also triggered SVOM/GRM at 2026-05-04T09:31:19 on a timescale of 0.10 seconds with an SNR of 31.30. The SVOM/GRM light curve shows a single narrow peak structure with a T90 duration of 0.22 +/- 0.02 s (8-1100 keV). The SVOM/GRM light curve can be found here： https://www.bursthub.cn//admin/static/svgrb260504B.png SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-05-04T09:33:16 UTC, 117 seconds after T0. Using onboard processed data we found a possible uncatalogued X-ray source located at R.A., Dec. 351.285, -80.383 degrees: R.A. (J2000) = 23h25m08s Dec. (J2000) = -80d22m69s with a 90% C.L. radius of 167 arcseconds. This location is 3.2 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. 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 Yun Wang: wangyun(a)pmo.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44454. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42577] Fermi GRB 260504A: Global MASTER-Net observations report
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44453 SUBJECT: Fermi GRB 260504A: Global MASTER-Net observations report DATE: 26/05/04 09:46:26 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 260504A ( Fermi GBM team, GCN 44452) errorbox 578 sec after notice time and 612 sec after trigger time at 2026-05-04 09:23:10 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 79 deg. The sun altitude is -22.5 deg. The galactic latitude b = 5 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=3291732 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 672 | 2026-05-04 09:23:10 | MASTER-OAFA | (20h 30m 50.42s , +46d 55m 36.5s) | C | 120 | 16.4 | 813 | 2026-05-04 09:25:16 | MASTER-OAFA | (20h 30m 48.57s , +46d 55m 44.3s) | C | 150 | 16.1 | 924 | 2026-05-04 09:27:52 | MASTER-OAFA | (20h 30m 47.07s , +46d 55m 48.4s) | C | 60 | 16.4 | 990 | 2026-05-04 09:28:58 | MASTER-OAFA | (20h 30m 46.11s , +46d 55m 50.2s) | C | 60 | 16.5 | 1056 | 2026-05-04 09:30:03 | MASTER-OAFA | (20h 30m 45.24s , +46d 55m 54.1s) | C | 60 | 16.4 | 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/44453. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42576] GRB 260504A: Fermi GBM Final Real-time Localization
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44452 SUBJECT: GRB 260504A: Fermi GBM Final Real-time Localization DATE: 26/05/04 09:21:13 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 09:12:58 UT on 4 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260504A (trigger 799578783.057988 / 260504384). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 308.8, Dec = 48.4 (J2000 degrees, equivalent to J2000 20h 35m, 48d 23'), with a statistical uncertainty of 5.0 degrees. The angle from the Fermi LAT boresight is 44.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260504384/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260504384/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260504384/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44452. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42575] GRB 260503A: Fermi GBM Final Real-time Localization
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44451 SUBJECT: GRB 260503A: Fermi GBM Final Real-time Localization DATE: 26/05/03 20:50:53 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 20:40:17 UT on 3 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260503A (trigger 799533622.581348 / 260503861). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 287.1, Dec = -2.0 (J2000 degrees, equivalent to J2000 19h 08m, -2d 00'), with a statistical uncertainty of 2.6 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/bn260503861/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260503861/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260503861/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44451. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42574] SVOM/GRM observation of a bright burst from SGR 1E1841-045
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44450 SUBJECT: SVOM/GRM observation of a bright burst from SGR 1E1841-045 DATE: 26/05/03 16:26:46 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> SVOM/GRM team: Xue-Yuan Zao, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Hui Yang, Sebastien Guillot (IRAP) Report on behalf of the SVOM team: SVOM/GRM detected a bright burst from SGR 1E1841-045 at 2026-05-02T05:39:51.950 UTC (T0), which is also detected by Konus-Wind (A. Ridnaia el at., GCN#44448). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.08 +0.08/-0.02 s in the 15-5000 keV band. All the signal is detected below 100 keV. The SVOM/GRM light curve can be found here： https://www.bursthub.cn//admin/static/svsgr_260502_053951.png In addition, the localization of SGR 1E1841-045 is located at about 94 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. The time-averaged spectrum from T0-0.04 to T0+0.07 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.49 +0.28/-0.27 and the cutoff energy, parameterized as Epeak, is 37.08 +1.88/-2.12 keV. The event fluence (10-1000 keV) in this time interval is (7.29 +0.32/-0.31) E-07 erg/cm^2. 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/GRM point of contact for this burst is: Xue-Yuan Zao (IHEP) (zaoxy(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44450. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42573] GRB 260502A: GECAM-B observation of a short burst
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44449 SUBJECT: GRB 260502A: GECAM-B observation of a short burst DATE: 26/05/03 15:58:17 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 260502A, at 2026-05-02T05:01:00.300 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44447). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse pulses with a duration (T90) of 0.40 +0.14/-0.08 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260502A.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/44449. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42572] IPN triangulation of a bright burst from SGR 1E1841-045
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44448 SUBJECT: IPN triangulation of a bright burst from SGR 1E1841-045 DATE: 26/05/03 15:05:53 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP), J. Wei (NAOC), B. Cordier (CEA) on behalf of the SVOM-GRM team, and E. Burns on behalf of the IPN, report: A bright, short-duration, soft burst was detected by Konus-Wind and SVOM (GRM) at about 20396 s UT (05:39:56) on May 2. We have triangulated it to a Konus-GRM annulus centered at RA(2000)=243.691 deg (16h 14m 46s) Dec(2000)=-21.870 deg (-21d 52' 12"), whose radius is 39.329 +/- 0.068 deg (3 sigma). Among known SGRs, only the position of SGR 1E1841-045 is inside the annulus. Given the positional coincidence of this burst with SGR 1E1841-045, its time history, and softness of its spectrum (as observed by Konus-Wind), we conclude this burst likely originated from SGR 1E1841-045. A triangulation map is posted at http://www.ioffe.ru/LEA/SGRs/260502_T20396/IPN/ The time history and spectrum will be given in forthcoming GCN circulars. View this GCN Circular online at https://gcn.nasa.gov/circulars/44448. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42571] GRB 260502A: Fermi GBM Final Localization
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44447 SUBJECT: GRB 260502A: Fermi GBM Final Localization DATE: 26/05/03 05:20:13 GMT FROM: Rushikesh Sonawane at IISER TVM <rushikesh23(a)iisertvm.ac.in> The Fermi GBM team reports the detection of a likely SHORT GRB "At 05:01:00.25 UT on 05 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260502A (trigger 799390865/260502209). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 283.76, Dec = 57.62 (J2000 degrees, equivalent to J2000 18h 55m, +57d 37′), with a statistical uncertainty of 13.77 degrees. The angle from the Fermi LAT boresight is 23 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42570] The EP-WXT trigger 01709261576 is likely a flaring star
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44446 SUBJECT: The EP-WXT trigger 01709261576 is likely a flaring star DATE: 26/05/02 19:25:21 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. Mao (NAO, CAS; OAPa, INAF), H. Zhou (PMO), Z. C. Zou (NJU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709261576 at the time of 2026-05-02T18:35:45, is likely a stellar flare associated with Sz 30. The estimated flux of the flare is around 1.8e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 7.3e32 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/44446. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42569] GRB 260429B / EP260429a: EP-FXT follow-up observation
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44445 SUBJECT: GRB 260429B / EP260429a: EP-FXT follow-up observation DATE: 26/05/02 16:46:33 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS; UCB), Y. L. Wang (NAO, CAS; ICE, CSIC), G. J. Yang, C.C Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed two follow-up observations of the EP-WXT detected transient GRB 260429B / EP260429a (Wang et al., GCN), also triggered by AstroSat CZTI (Arya et al., GCN 44443). The observations started at 2026-04-30T07:26:44 UTC and 2026-05-01T21:53:58 UTC, corresponding to approximately 16.8 and 55.2 hours after the EP-WXT trigger, with total exposure times of 9064 s and 5262 s, respectively. Two X-ray sources were detected by FXT within the WXT error region: EPF_J160221.2-093607 RA (J2000): 240.5884 deg Dec (J2000): -9.6018 deg with an uncertainty of 10 arcsec (radius, 90% C.L., statistical and systematic). EPF_J160226.1-093337 RA (J2000): 240.6088 deg Dec (J2000): -9.5602 deg with an uncertainty of 10 arcsec (radius, 90% C.L., statistical and systematic). The 0.5-10 keV flux of EPF_J160221.2-093607 decreased from 2.1e-12 to 5.8e-13 erg cm^-2 s^-1 between the two observations. In contrast, the flux of EPF_J160226.1-093337 remained nearly constant at about 6.6e-13 erg cm^-2 s^-1 in the same energy band. In addition, the position of EPF_J160226.1-093337 is 1.264 arcsec from Gaia DR3 4346772233753744896, suggesting that this Gaia source may be its counterpart. Therefore, EPF_J160221.2-093607 is the more likely X-ray afterglow of GRB 260429B / EP260429a. We note that follow-up observations were carried out by Eyles-Ferris et al. (GCN 44433), Fortin et al. (GCN 44434) and Lipunov et al. (GCN 44437), but no optical counterpart was detected in these observations. Further follow-up observations are encouraged. 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/44445. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42568] EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44444 SUBJECT: EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position DATE: 26/05/02 15:48:54 GMT FROM: I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg(a)iaa.es> S.-Y. Wu, I. Perez-Garcia, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, M. Gritsevich and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar, A. Castellon, A. Reina (Univ. de Malaga),Y.-D. Hu (GXU), L. Hernandez-Garcia (Univ. de Valparaiso), D. R. Xiong (Yunnan Observatories of CAS), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Further to our previous report on EP260502a (Perez-Garcia et al., GCN 44442), and following a comment by D. B. Malesani, we have inspected the BOOTES-7 images at the position of a bright catalogued source close to the EP/FXT position, located at RA(J2000) = 18:09:07.01 Dec(J2000) = -76:13:26.79. This source is reported as an eROSITA source and lies close to the boundary of the EP/WXT error region. Relative photometry of this source in the BOOTES-7 r'-band images shows a fading trend during the first observing sequence. In the 9 s r'-band exposures, the source faded from r' = 13.8 +/- 0.06 at 2026-05-02 06:24:42 UT to r' = 14.5 +/- 0.08 at 2026-05-02 06:57:36 UT, corresponding to a decline of 0.7 mag over ~30 min. No significant fading trend is observed in the BOOTES-7 i' and Z band images over the same time interval. The final measured value is consistent with the archival SkyMapper magnitude of the source, r = 14.5. We thank D. B. Malesani for pointing out this source. View this GCN Circular online at https://gcn.nasa.gov/circulars/44444. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42567] GRB 260429B / EP260429a: AstroSat CZTI detection
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44443 SUBJECT: GRB 260429B / EP260429a: AstroSat CZTI detection DATE: 26/05/02 12:54:35 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (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 long GRB 260429B which is also detected by Konus-Wind (priv. comm), and is associated with EP260429a (Wang et al., GCN Circ. 44426). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-29 14:42:59.27 UTC. The measured peak count rate associated with the burst is 147 (+31, -33) counts/s above the background in the combined data of all quadrants, with a total of 1802 (+485, -554) counts. The local mean background count rate was 1313 (+3, -3) counts/s. We measure a T90 of 34 (+6, -9) s from the cumulative Veto light curve. The source was also faintly detected in the CZT detectors in the 20-200 keV energy range. 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/515169782.27/S515169782.27_det… 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/44443. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42566] GRB EP260502a: BOOTES-7: early optical upper limit
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44442 SUBJECT: GRB EP260502a: BOOTES-7: early optical upper limit DATE: 26/05/02 09:00:37 GMT FROM: I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, M. Gritsevich and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar, A. Castellon, A. Reina (Univ. de Malaga),Y.-D. Hu (GXU), L. Hernandez-Garcia (Univ. de Valparaiso), D. R. Xiong (Yunnan Observatories of CAS), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP260502a by the Einstein Probe (Liu et al., GCN 44440), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) observed the fast X-ray transient location starting on May 2, 06:23:31 UT (~14.7 min after trigger) in different optical bands. No new optical source is detected within the EP/WXT 3 arcmin error circle on the initial 10s image or on the first co-added clear-filter images (mid exposure time 2026-05-02 07:34 UT) down to 15.3 mag or 18.3 mag respectively, in agreement with the LCO upper limit (Li et al. GCN 44441). We thank the staff at San Pedro de Atacama Celestial Explorations observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42565] EP260502a: Las Cumbres upper limit
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44441 SUBJECT: EP260502a: Las Cumbres upper limit DATE: 26/05/02 07:43:21 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li (NAOC), Iair Arcavi (TAU), Runduo Liang (NAOC), Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of EP260502a (Liu et al., GCN 44440) with a Las Cumbres 1m telescope at Cerro Tololo Interamerican Observatory, Chile, 19 mins after the Einstein Probe WXT trigger. We took 2x300s exposures in each visit in the broad optical w band. We didn’t detect any uncataloged source within the EP-FXT error circle down to a 3-sigma limiting r-band mag of 20.0 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/44441. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42564] EP260502a: Einstein Probe detection of an X-ray transient
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44440 SUBJECT: EP260502a: Einstein Probe detection of an X-ray transient DATE: 26/05/02 07:20:32 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T.Y. Liu (NAO,CAS), Y. Q. Zhao(PRIC,USTC), Y. F. Liang (PMO, CAS), Y. Wang (PMO, CAS; UCB), H. W. Pan (NAO,CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260502a. The transient triggered EP-WXT (ID: 01709261349) at 2026-05-02T06:08:51 (UTC). The WXT position of the source is R.A. = 272.190 deg, DEC = -76.244 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 272.2762 deg, DEC =-76.2297 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 is 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/44440. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42563] GRB 251013C: ABObservatory optical observations
by GCN Circulars 01 May '26

01 May '26

TITLE: GCN CIRCULAR NUMBER: 42251 SUBJECT: GRB 251013C: ABObservatory optical observations DATE: 25/10/14 10:53:56 GMT FROM: A. Brosio at ABObservatory Rosarno <antonino.brosio(a)gmail.com> A. Brosio (ABObservatory Rosarno), M. A. Tripodi (ABObservatory Rosarno), S. Savaglio (University of Calabria), G. Bracco, P. Cianfarra, L. Sangaletti, S. Tosi & S. Zappatore (University of Genoa), S. Benatti & M. G. Guarcello (INAF Palermo), L.Cabona, M. Rainer, F. M. Zerbi, M. Basilicata (INAF Brera), D. Ricci (INAF Padova), A. Di Dato (INAF Capodimonte), S. Masiero & A. Nastasi (GAL Hassin), D. Liguori (Osservatorio "G. Galilei" Cariati), L. Betti (Osservatorio Polifunzionale del Chianti), R. Nesci (Associazione Astronomica Antares APS di Foligno), for the NOCTIS team report We observed the field of GRB 251013C, which was detected by Fermi GBM team (GCN 42221) with the 30-cm automated telescope at ABObservatory (Rosarno, Italy) in V filter. The observations began on 2025 october 13 at 20:56:53 UT, approximately 2.38 hours after the trigger. The observation consisted of 50 exposures of 120 seconds each,with good sky conditions. The mid-exposure time was 22:12:46 UT, and the final exposure ended at 23:32:52 UT. From photometry, we detect the optical counterpart in our images at the following coordinates: R.A (J2000.0) = 23 03 19.712 Dec. (J2000.0) = -00 12 53.17 From the full photometric sequence, we obtained a mean magnitude of V = 17.244 +/- 0.213 at mean JD 2460962.42529 with SNR 14.98 (AB, calibrated with the GAIA DR3 on SIMBAD). We also performed time-series photometry and obtained a light curve of the optical counterpart during our observing run and the source shows a fading trend, reaching V = 17.848 ± 0.509 at JD 2460962.47774. View this GCN Circular online at https://gcn.nasa.gov/circulars/42251. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42562] GRB 260429A: SVOM/GRM observation of a short burst
by GCN Circulars 01 May '26

01 May '26

TITLE: GCN CIRCULAR NUMBER: 44439 SUBJECT: GRB 260429A: SVOM/GRM observation of a short burst DATE: 26/05/01 13:44:00 GMT FROM: yzh807926(a)163.com SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Chao Zheng, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Sebastien Guillot, Olivier GODET (IRAP), Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 260429A (SVOM trigger reference: sb26042902) at 2026-04-29T23:24:02.100 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44425). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single peak a T90 of 0.12 +0.12/-0.03 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260429A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 283.9 deg, DEC= 18.1 deg, ERR=2.6 deg, GCN#44425), is located at about 99 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. Nevertheless, ECLAIRs detected the GRB through the shield above 50 keV. With this localization, the time-averaged spectrum from T0-0.2 to T0+0.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.19 +0.12/-0.14 and the cutoff energy, parameterized as Epeak, is 961 +672/-308 keV. The event fluence (10-1000 keV) in this time interval is (2.57 +/-0.16)E-06 erg/cm^2. The localization of GRB 260429A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260429A_amati.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: Zheng-Hang Yu(IHEP)(zhyu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44439. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42561] SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
by GCN Circulars 01 May '26

01 May '26

TITLE: GCN CIRCULAR NUMBER: 44438 SUBJECT: SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China DATE: 26/05/01 13:00:52 GMT FROM: Chenxi Bao at Peking University <2300011608(a)stu.pku.edu.cn> Chenxi Bao (PKU), Zhuokai Liu (PKU), Yacheng Kang (PKU) report on behalf of the Interestar Collaboration and the PKU HiTF (High-energy Transients Follow-up) group: We observed the field of SN 2026kid (ZTF26aatswhm), discovered and first reported by Yasuo Sano (TNS Discovery Report 300955; T0 = 2026-04-22T14:23:47.00). Observations began on 2026 Apr 24, approximately 2.2 days after the first detection of the SN, using a 13cm optical telescope located in Yanchi, China. We subsequently employed a 28cm optical telescope located in Castillejar, Spain, to continue monitoring SN 2026kid. In total, our observations spanned 3 nights in the Luminance filter and 2 nights in the Red filter. In the Luminance- and Red-band exposures, we clearly detect the Type II SN 2026kid in the nearby edge-on spiral galaxy NGC 5907, located at a distance of 16.5 Mpc (Rehemtulla et al.,TNS AstroNote 2026-114). Our observations show that SN 2026kid has brightened since discovery, reaching approximately 16.1 mag in the Luminance band and 15.5 mag in the Red band, indicating continued early-time photometric evolution. Preliminary photometry was derived from image subtraction using pre-explosion reference images, calibrated against nearby field stars, and is reported as approximate AB-equivalent magnitudes, without correction for Galactic extinction. The observation log is summarized below: | Date | Start_UT | T_mid - T0 (days) | Filter | Exposure (s) | Magnitude (AB) | | :--------: | :------: | :---------------: | :-------: | :----------: | :------------: | | 2026-04-24 | 18:04:42 | 2.15 | Luminance | 200 | 16.22 +/- 0.02 | | 2026-04-26 | 23:00:24 | 4.40 | Luminance | 6600 | 16.11 +/- 0.04 | | 2026-04-27 | 20:11:25 | 5.25 | Luminance | 1200 | 16.16 +/- 0.26 | | 2026-04-27 | 20:46:12 | 5.29 | Red | 3600 | 15.60 +/- 0.16 | | 2026-04-29 | 20:18:58 | 7.30 | Red | 8400 | 15.42 +/- 0.22 | Further analysis and follow-up observations are ongoing. The two small-aperture telescopes are operated by the Interestar Collaboration. The PKU HiTF group is dedicated to rapid follow-up observations of high-energy transients. View this GCN Circular online at https://gcn.nasa.gov/circulars/44438. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42560] EP260429a: Global MASTER-Net observations report
by GCN Circulars 01 May '26

01 May '26

TITLE: GCN CIRCULAR NUMBER: 44437 SUBJECT: EP260429a: Global MASTER-Net observations report DATE: 26/05/01 10:09:31 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) was pointed to the EP260429a ( EP Team et al., GCN 44426) errorbox 1 days 24768 sec after notice time and 1 days 69627 sec after trigger time at 2026-05-01 10:01:38 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 44 deg. The sun altitude is -29.1 deg. The galactic latitude b = 30 deg., longitude l = 2 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3281864 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 156117 | 2026-05-01 10:01:38 | MASTER-OAGH | (16h 00m 56.52s , -09d 05m 48.0s) | C | 180 | 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/44437. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42559] EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
by GCN Circulars 01 May '26

01 May '26

TITLE: GCN CIRCULAR NUMBER: 44436 SUBJECT: EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations DATE: 26/05/01 07:13:34 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS; UCB), Y. L. Wang (NAO, CAS; ICE, CSIC), G. J. Yang, C.C Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260430a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 44427) at 2026-04-30T02:32:47 (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 0.3× 10^21 cm^-2, and a photon index of 0.84 (+0.19/-0.18). The derived average unabsorbed 0.5-4 keV flux is 4.63 (+2.54/-1.56) × 10^(-10) erg/s/cm^2. Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-04-30T02:34:41 (UTC). The exposure time of the observation is around 3 ks. The on-ground analysis of the FXT data found an uncatalogued source at R.A. = 178.3355, DEC = -10.2146 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT light curve shows a raipd decay. The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a fixed Galactic hydrogen column density of 0.3× 10^21 cm^-2, and a photon index of 4.61 (+/-0.20). The derived average unabsorbed 0.5-10 keV flux is 1.27 (-0.16/+0.17) × 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. We note that follow-up observations were carried out by Lipunov et al. (GCN 44428), Fortin et al. (GCN 44431) and Chácon et al. (GCN 44432), but no optical counterpart was detected in these observation. 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/44436. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42558] GRB 260424B: AstroSat CZTI detection
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44435 SUBJECT: GRB 260424B: AstroSat CZTI detection DATE: 26/04/30 14:43:24 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Goyal (IITB), A. Arya (IITB), U. Pathak (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 short GRB 260424B which was also detected by SVOM/GRM (Wang et al., GCN Circ. 44410), IPN triangulation (Kozyrev et al., GCN Circ. 44411), Konus-Wind (Ridnaia et al., 44416), and Glowbug (Cheung et al., 44418). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-24 23:37:24.97 UTC. The measured peak count rate associated with the burst is 646 (+75, -82) counts/s above the background in the combined data of all quadrants, with a total of 685 (+158, -170) counts. The local mean background count rate was 1368 (+14, -15) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 for our detection. The source was also faintly detected in the CZT detectors in the 20-200 keV energy range. 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/514769843.98/S514769843.98_det… 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/44435. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42557] GRB 260429B / EP260429a: COLIBRÍ optical upper limit
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44434 SUBJECT: GRB 260429B / EP260429a: COLIBRÍ optical upper limit DATE: 26/04/30 13:54:36 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Enrique Moreno Méndez (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), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP GRB 260429A (Wang et al., GCN Circ. 44426) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-30 07:47:50 to 11:42:06 UTC (from 17.1 to 21.0 hours after the trigger) and obtained 139 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the ASU COLIBRÍ 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 image, we do not detect any new source at the WXT source position (Wang et al., GCN Circ. 44426) down to the following 5-sigma limit: r > 23.56 z > 22.84 These upper limits are consistent with the ones reported by Eyles-Ferris et al. GCN Circ. 44433. 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/44434. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42556] EP260429a: LCO optical upper limits
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44433 SUBJECT: EP260429a: LCO optical upper limits DATE: 26/04/30 11:20:40 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), J. A. Chácon (PUC), F. E. Bauer (SSI and UTA), J. Quirola-Vasquez (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. J. Levan (Radboud & Warwick), P. G. Jonker (Radboud), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP26029a (Wang et al., GCN 44426) using LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) equipped with the SINISTRO instrument. A series of 6x300 s exposures were taken in each of the SDSS-r and SDSS-z filters, starting at 2026-04-30 08:23:54 UT (~18.0 hr after the trigger). No new source is detected within or at the border of the EP/WXT uncertainty region (Wang et al., GCN 44426) nor do we identify any significant residuals in subtractions using PanSTARRS DR1 templates. From the stacked images, we obtain the following 3-sigma upper limits:  r > 22.5 z > 20.9 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/44433. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42555] EP260430a: LCO optical upper limits
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44432 SUBJECT: EP260430a: LCO optical upper limits DATE: 26/04/30 10:50:21 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> J. A. Chácon (PUC), F. E. Bauer (SSI and UTA), D. B. Malesani (DAWN/NBI and Radboud), J. Quirola-Vasquez (Radboud), A. J. Levan (Radboud & Warwick), P. G. Jonker (Radboud), R. A. J. Eyles-Ferris (Leicester), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260430a (Wang et al., GCN 44427) using LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) equipped with the SINISTRO instrument. A series of 6x300 s exposures was taken using the SDSS-r filter, starting at 2026-04-30 03:32:35 UT (~1 hr after the trigger). No new source is detected within or at the border of the EP/FXT uncertainty region (Wang et al., GCN 44427). From the stacked images, we obtain the following 3-sigma upper limit:  r > 22.1 This upper limit is in AB magnitudes, calibrated using nearby stars from the Pan-STARRS catalog, and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44432. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42554] GRB 260430A / EP260430a: COLIBRÍ optical upper limit
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44431 SUBJECT: GRB 260430A / EP260430a: COLIBRÍ optical upper limit DATE: 26/04/30 10:30:34 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Enrique Moreno Méndez (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), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of theEP GRB 260430A (Wang et al., GCN Circ. 44427) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-30 05:06:00 to 08:49:04 UTC (from 2.55 to 6.29 hours after the trigger) and obtained 43 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 image, we do not detect any new source at the WXT source position (Wang et al., GCN Circ. 44427) down to the following 3-sigma limit: r > 22.38 z > 21.78 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/44431. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42553] GRB 260429A: Fermi GBM Detection
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44430 SUBJECT: GRB 260429A: Fermi GBM Detection DATE: 26/04/30 07:10:23 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> L. Scotton (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:24:02.02 UT on 29 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260429A (trigger 799197847/260429975). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 283.92, Dec = 18.10 (J2000 degrees, equivalent to J2000 18h 55m, +18d 6'), with a statistical uncertainty of 2.61 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 76 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 0.16 s (50-300 keV). The time-averaged spectrum from T0-0.1 to T0+0.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 900 +/- 20 keV. The event fluence (10-1000 keV) in this time interval is (2.41 +/- 0.07)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 69 +/- 2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 600 +/- 20 keV, alpha = -0.92 +/- 0.03 and beta = -2 +/- 0.09. 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/44430. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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