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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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