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[vsnet-grb-info 42752] GRB 260515A: SVOM/VT optical candidate from VHF data
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44624 SUBJECT: GRB 260515A: SVOM/VT optical candidate from VHF data DATE: 26/05/15 20:26:50 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi, J. T. Palmerio (CEA/Irfu), Y. L. Qiu, C. Wu, L. P. Xin (NAOC) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2026-05-15T19:08:19 UTC (T0), SVOM performed an automatic slew on the burst location (Brunet et al., GCN 44622). SVOM/VT began observing the field at 2026-05-15T19:12:34, 254.71 seconds after T0, 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 downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below. VT_ID 32: The position of this candidate is R.A., Dec. 227.6852, 24.5562 degrees, corresponding to: R.A. (J2000) = 15h10m44.4s Dec. (J2000) = 24d33m22.4s with an uncertainty of 0.50 arcsec. This location is consistent with the optical afterglow reported by He et al. (GCN 44623). This candidate was detected in both VT_R and VT_Band was flagged as an uncatalogued source. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | | 2026-05-15T19:12:34 | 5.08 min | 2*50 sec | 16.16 ± 0.01 | 15.78 ± 0.01 | Magnitudes were not corrected for Galactic reddening. The mean color of VT_B - VT_R = 0.38 is in line with the expectations of an event at redshift z < 4. 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. 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/44624. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42751] GRB 260515A: JinShan optical counterpart candidate
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44623 SUBJECT: GRB 260515A: JinShan optical counterpart candidate DATE: 26/05/15 19:51:51 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, Z.P. Zhu, X. Liu, D. Xu, J. An,S.Q. Jiang (NAOC), S.Y. Fu, A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report: We observed the field of GRB 260515A (sb26051504; Brunet et al., GCN 44622) using the JinShan 100B telescope located at Altay, Xinjiang, China. We obtained a series of frames in the Sloan i-band. An uncatalogued and varing source is detected within the EP/WXT/FXT error circle at coordinates R.A. (J2000) = 227.6852 deg Dec. (J2000) = 24.5562 deg with an uncertainty of ~ 1.0 arcsec. The source had i ~ 16.5 mag (optional: at a median time of ~ 11 min post-trigger, calibrated with Pan-STARRS DR2 and not corrected for Galactic extinction. We acknowledge the excellent support from T.Q. Chen, and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44623. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42750] GRB 260515A: SVOM detection of a burst
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44622 SUBJECT: GRB 260515A: SVOM detection of a burst DATE: 26/05/15 19:36:12 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, L. Bouchet (IRAP), A. Saccardi (CEA/Irfu), D. Gotz (CEA/Irfu) report on behalf of the SVOM mission team: At 2026-05-15T19:08:19 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260515A (SVOM burst-id sb26051504). 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 17 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 24.06 in the [5-20] keV energy band over a time window of 10.20 seconds starting at 2026-05-15T19:08:19. The localization of the best alert is R.A., Dec. 227.6800, 24.5706 degrees: R.A. (J2000) = 15h10m43.20s Dec. (J2000) = 24d34m14.13s with a 90% confidence level (C.L.) radius of 3.77 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a single peak structure with a T90 duration of 16.6 +/-1.5 s in the 5-120 keV. This burst was also detected by SVOM/GRM with a significance of 10.2 . SVOM slewed to the burst. MXT and 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 (CEA): andrea.saccardi(a)cea.fr Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44622. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42749] GRB 260510C: Glowbug gamma-ray detection
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44621 SUBJECT: GRB 260510C: Glowbug gamma-ray detection DATE: 26/05/15 18:39:46 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 260510C, which was detected by Fermi/GBM (GCN 44520, 44564), SVOM (GCN 44521), MAXI/GSC (GCN 44526), AstroSat/CZTI (GCN 44544), and CALET (GCN 44616). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-10 17:15:37.096 with a duration of 4.1 s and a total significance of about 5.2 sigma. The lightcurve comprises a single peak corresponding to the portion of the burst observed by CALET/CGBM (GCN 44616). 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/44621. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42748] IceCube-260504A: No Candidate Transients from the Zwicky Transient Facility
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44620 SUBJECT: IceCube-260504A: No Candidate Transients from the Zwicky Transient Facility DATE: 26/05/15 18:10:11 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Robert Stein (JSI), Jannis Necker (Leiden University), Akshay Eranhalodi (DESY), and Anna Franckowiak (Ruhr University Bochum) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-260504A (IceCube Collaboration, GCN 44464) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2026-05-07 04:25 UTC, approximately 55.2 hours after event time due to bad weather. We covered 68.2% (0.6 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 30s with a typical depth of 20.5 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019) . No candidate counterparts were detected. ZTF and GROWTH are worldwide collaborations comprising Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; OKC, Sweden; DZA, Germany. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). Alert filtering is performed with the nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ). View this GCN Circular online at https://gcn.nasa.gov/circulars/44620. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42747] EP260514a: GROWTH-India Telescope optical upper limit
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44619 SUBJECT: EP260514a: GROWTH-India Telescope optical upper limit DATE: 26/05/15 17:20:18 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan (IITB), V. Vijaykumar (IITB), V. Swain (IITB), D. Eappachen (IIA), A.P. Saikia (IITB), S. Patil (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of EP260514a (Cheng et al., GCN 44613), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-05-15 16:27:06 (UTC), i.e., 0.98 days after the trigger, and obtained single exposure in the r' filter. We did not detect any transient in our image within the WXT localization region. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hour) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | -------------- | ------------------- | ---------------- | | 61175.68756 | r' | 23.57 | 360 | 20.5 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our results are consistent with other optical observation (Lipunov et al., GCN 44614). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/44619. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42746] GRB 260511B: NOT optical observations
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44618 SUBJECT: GRB 260511B: NOT optical observations DATE: 26/05/15 16:42:48 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S. Q. Jiang, D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), J. P. U. Fynbo (DAWN/NBI), A. M. Kadela (NOT & NBI) report on behalf of a large collaboration: We observed the optical counterpart (Wu et al., GCNs 44547, 44552; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Li et al., GCNs 44557, 44593; Vijaykumar et al., GCN 44561; de Ugarte Postigo et al., GCN 44565; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573; Saccardi et al., GCN 44574; Rajabov et al., GCN 44576; Pérez-Fournon et al., GCN 44577; Novotný et al., GCN 44580; Moskvitin et al., GCNs 44582, 44600; Calapai et al., GCN 44592; Liu et al., GCN 44610; Li et al., GCN 44615) of GRB 260511B, detected by Fermi/GBM (Fermi GBM Team, GCN 44542), SVOM (Godet et al., GCN 44543), NuSTAR (Waratkar & Grefenstette, GCN 44556), AstroSat CZTI (Arya et al., GCN 44560), and Konus-Wind (Ridnaia et al., GCN 44597) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera, and obtained 3 x 90 s frames in each of the Sloan g, r, and i bands, and 3x200 s frames in the Sloan z band, starting at 21:12:00.450 UT on 2026-05-12, i.e., 34.192 hr after the Fermi/GBM trigger. The afterglow is clearly detected in our stacked images, with a magnitude r = 21.33 +/- 0.06 (AB) at a median time of 34.337 hr after the trigger, calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44618. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42745] Konus-Wind detection of GRB 260512A
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44617 SUBJECT: Konus-Wind detection of GRB 260512A DATE: 26/05/15 10:45:03 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260512A (Fermi-GBM detection: The Fermi GBM team, GCN 44587; NuSTAR-ACS detection: Waratkar et al., GCN 44591; AstroSat-CZTI detection: Tembhurnikar et al., GCN 44608; IPN triangulation: Kozyrev et al., GCN 44611) triggered Konus-Wind at T0=61005.883 s UT (16:56:45.883). The burst light curve shows a multipeaked structure which starts at ~T0-0.7 s and has a total duration of ~23 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/GRB260512_T61005/ As observed by Konus-Wind, the burst had the total fluence of 2.45(-0.24,+0.20)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+4.464 s, of 6.32(-0.82,+0.83)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+24.832 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.99(-0.09,+0.09), the high energy photon index beta = -2.60(-0.46,+0.17), the peak energy Ep = 202(-16,+22) keV (chi2 = 117/98 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.82(-0.08,+0.08), the high energy photon index beta = -2.53(-0.13,+0.10), the peak energy Ep = 193(-11,+13) keV (chi2 = 93/79 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/44617. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42744] GRB 260510C: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44616 SUBJECT: GRB 260510C: CALET Gamma-Ray Burst Monitor detection DATE: 26/05/15 07:23:20 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> T. Sakamoto, A. Yoshida, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 260510C (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN #44520; SVOM detection of a burst: Gotz et al., GCN #44521; MAXI/GSC detection: Iwakiri et al., GCN #44526; AstroSat CZTI detection: Arya et al., GCN #44544; Fermi GBM Observation: Palafox et al., GCN #44564) at 17:15:37.60 UTC on 10 May 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1462468483/index.html) The burst signal was seen by all CGBM detectors. The onboard CGBM trigger corresponds to the second peak of the double-peaked structure reported by Fermi/GBM and SVOM/ECLAIRs. In the CGBM ground analysis, the first peak was also marginally visible in the SGM data. The second peak started at T+0.3 s, peaked at T+2.9 s, and ended at T+8.9 s. The T90 and T50 durations of the second peak, measured with the SGM data, are 7.4 +/- 0.8 s and 3.2 +/- 0.8 s in the 40-1000 keV band, respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1462468483/ The CALET data used in this analysis were provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44616. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42743] GRB 260511B: GMG Optical Upper Limit
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44615 SUBJECT: GRB 260511B: GMG Optical Upper Limit DATE: 26/05/15 04:58:07 GMT FROM: Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi(a)ynao.ac.cn> R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, J.-G. Wang and B. Wang (YNAO, CAS) report: We observed the field of GRB 260511B (Godet et al., GCN 44543, T0 at 2026-05-11T11:00:32) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2026-05-14 12:45:02, about 73.74 hours after the trigger. The optical counterpart (Wu et al. GCN 44547, Sasada et al. GCN 44549, Jiang et al. GCN 44551, Wu et al. GCN 44552, Vijaykumar et al. GCN 44561, de Ugarte Postigo et al. GCN 44565, Lee et al. GCN 44567, Li et al. GCN 44568, Wang et al. GCN 44571, Belkin et al. GCN 44572, Adami et al. GCN 44573, Saccardi et al. GCN 44574, Rajabov et al. GCN 44576, Perez-Fournon et al. GCN 44577, Novotny et al. GCN 44580, Moskvitin et al. GCN 44582, Calapai et al. GCN 44592, Moskvitin et al. GCN 44600 and Liu et al. GCN 44610) of GRB 260511B was not detected in our r-band image. The preliminary analysis results are shown as follows: +-------------------------+----------------+---------------+----------+----------------+ | Start time [UTC] | Exposure [s] | Tmid-T0 [h] | Filter | 5-sigma U.L. | +=========================+================+===============+==========+================+ | 2026-05-14 12:45:02.730 | 900 | 73.867 | r | 21.6 | +-------------------------+----------------+---------------+----------+----------------+ The given magnitudes are derived based on calibrating against Pan-STARRS1 field stars. View this GCN Circular online at https://gcn.nasa.gov/circulars/44615. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42742] EP260514a: Global MASTER-Net observations report
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44614 SUBJECT: EP260514a: Global MASTER-Net observations report DATE: 26/05/15 03:27:20 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-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260514a ( EP Team et al., GCN 44613) errorbox 35348 sec after trigger time at 2026-05-15 02:45:14 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 81 deg. The sun altitude is -63.2 deg. The galactic latitude b = 62 deg., longitude l = 91 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3315353 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 35378 | 2026-05-15 02:45:14 | MASTER-OAFA | (14h 15m 58.14s , +49d 22m 48.5s) | C | 60 | 18.0 | 35443 | 2026-05-15 02:46:19 | MASTER-OAFA | (14h 15m 57.12s , +49d 22m 52.2s) | C | 60 | 18.0 | 35509 | 2026-05-15 02:47:24 | MASTER-OAFA | (14h 15m 56.10s , +49d 22m 55.1s) | C | 60 | 18.3 | 35575 | 2026-05-15 02:48:31 | MASTER-OAFA | (14h 15m 54.95s , +49d 22m 57.3s) | C | 60 | 18.2 | 35641 | 2026-05-15 02:49:37 | MASTER-OAFA | (14h 15m 54.43s , +49d 23m 01.2s) | C | 60 | 18.3 | 35701 | 2026-05-15 02:49:37 | MASTER-OAFA | (14h 15m 54.41s , +49d 23m 01.1s) | C | 180 | 18.6 | Coadd 35707 | 2026-05-15 02:50:42 | MASTER-OAFA | (14h 15m 54.22s , +49d 23m 03.8s) | C | 60 | 18.2 | 35773 | 2026-05-15 02:51:49 | MASTER-OAFA | (14h 15m 54.02s , +49d 23m 06.1s) | C | 60 | 17.9 | 35838 | 2026-05-15 02:52:54 | MASTER-OAFA | (14h 15m 53.77s , +49d 23m 08.7s) | C | 60 | 18.0 | 35904 | 2026-05-15 02:53:59 | MASTER-OAFA | (14h 15m 53.54s , +49d 23m 11.4s) | C | 60 | 18.1 | 35970 | 2026-05-15 02:55:05 | MASTER-OAFA | (14h 15m 53.30s , +49d 23m 11.7s) | C | 60 | 18.2 | 36035 | 2026-05-15 02:56:11 | MASTER-OAFA | (14h 15m 53.06s , +49d 23m 14.8s) | C | 60 | 18.4 | 36101 | 2026-05-15 02:57:16 | MASTER-OAFA | (14h 15m 52.80s , +49d 23m 16.2s) | C | 60 | 18.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44614. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42741] EP260514a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 15 May '26

15 May '26

TITLE: GCN CIRCULAR NUMBER: 44613 SUBJECT: EP260514a: Einstein Probe detection of a fast X-ray transient DATE: 26/05/15 03:20:32 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. Cheng (SWIFAR, YNU), K.R. Ni (CCNU), R.-Z. Li (YNAO, CAS) and W.-D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260514a. The ground analysis of the WXT data shows that the event started at T0 = 2026-05-14T16:56:06 (UTC) and lasted for around 500 s. The WXT position of the source is R.A. = 214.297 deg, DEC = 49.365 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) on board EP has been scheduled. 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/44613. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42740] EP260512a: LCO optical upper limits
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44612 SUBJECT: EP260512a: LCO optical upper limits DATE: 26/05/14 18:45:03 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> J. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), G. Corcoran (UCD), P. G. Jonker (Radboud), M. Fraser (UCD), A. J. Levan (Radboud & Warwick) and D. B. Malesani (DAWN/NBI and Radboud), J. A. Chacón (PUC), F. E. Bauer (SSI and UTA), report on behalf of a larger collaboration: We observed the field of the X-ray transient EP260512a (Liang et al., GCN 44594) using LCO 1m telescopes located at the McDonald Observatory (USA) equipped with SINISTRO instruments. A series of 6x300 s exposures was taken using the SDSS-r filter, starting at 2026-05-13 06:54:11 UT (i.e., ~0.93 days after the first X-ray detection). No new source is detected within or at the border of the EP/WXT (Liang et al., GCN 44594) uncertainty region compared with the Legacy Survey. From the stacked images, we obtain the following 3-sigma upper limits:  r > 22.2 These upper limits are in AB magnitudes, calibrated using nearby stars from the PanSTARRS catalogue, and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44612. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42739] IPN triangulation of GRB 260512A
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44611 SUBJECT: IPN triangulation of GRB 260512A DATE: 26/05/14 15:55:38 GMT FROM: Dmitry Svinkin at Ioffe Institute <dmitrysvinkin(a)gmail.com> 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 long-duration GRB 260512A (Ferm-GBM detection: The Fermi GBM team, GCN 44587; NuSTAR-ACS detection: Waratkar et al., GCN 44591; AstroSat-CZTI detection: Tembhurnikar et al., GCN 44608) was detected by Fermi (GBM trigger 800297808), Konus-Wind, NuSTAR (ACS), AstroSat (CZTI), and Mars-Odyssey (HEND) at about 61003 s UT (16:56:43). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 131.305 (08h 45m 13s) -83.033 (-83d 02' 00") Corners: 128.432 (08h 33m 44s) -81.525 (-81d 31' 31") 128.203 (08h 32m 49s) -81.573 (-81d 34' 22") 135.825 (09h 03m 18s) -84.513 (-84d 30' 48") 136.100 (09h 04m 24s) -84.461 (-84d 27' 41") --------------------------------------------- The error box area is 485 sq. arcmin, and its maximum dimension is 3.1 deg (the minimum one is 2.6 arcmin). The Sun distance was 106 deg. This localization may be improved. A triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB260512_T61005/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/44611. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42738] GRB 260511B: Mephisto multi-band optical followup
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44610 SUBJECT: GRB 260511B: Mephisto multi-band optical followup DATE: 26/05/14 15:51:44 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Chenxu Liu, Chenxi Shang, Guowang Du, Brajesh Kumar, Xian Liu, Haipeng Lei, Weikang Lin, Yu Pan, Xingzhu Zou, Xinlei Chen, Yuan Fang, Jinghua Zhang, Xufeng Zhu, Tao Wang, Xinzhong Er, Yuanpei Yang (SWIFAR, YNU), Chao Wu (NAOC), Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: We performed simultaneous multi-band (uvgriz) photometric observations of GRB 260511B (Godet et al., GCN 44543) at 2026-05-12T16:17:44 (~1.2d after the the SVOM/ECLAIRs trigger) using the 1.6-m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory. The optical counterpart was clearly detected in our stacked images and preliminary photometry is listed below (without Galactic extinction correction): ------------------------------------------------------- Start Time (UT) | Band | Exp(s) | Mag (AB) ------------------------------------------------------- 2026-05-12T16:17:44 | u | 300*2 | 22.45 (+/-0.20) 2026-05-12T16:29:15 | v | 300*2 | 21.77 (+/-0.19) 2026-05-12T16:17:47 | g | 300*2 | 21.19 (+/-0.08) 2026-05-12T16:29:17 | r | 300*2 | 21.03 (+/-0.07) 2026-05-12T16:17:46 | i | 300*2 | 20.70 (+/-0.11) 2026-05-12T16:29:17 | z | 300*2 | 20.40 (+/-0.16) These results are consistent with previous optical observations reported by Wu et al. (GCN 44547), Sasada et al. (GCN 44549), Jiang et al. (GCN 44551), Wu et al. (GCN 44552), Vijaykumar et al. (GCN 44561), de Ugarte Postigo et al. (GCN 44565), Lee et al. (GCN 44567), Li et al. (GCN 44568), Wang et al. (GCN 44571), Belkin et al. (GCN 44572), Adami et al. (GCN 44573), Saccardi et al. (GCN 44574), Rajabov et al. (GCN 44576), Perez-Fournon et al. (GCN 44577), Novotny et al. (GCN 44580), Moskvitin et al. (GCN 44582), Calapai et al. (GCN 44592), and Moskvitin et al. (GCN 44600). ---------------------------------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025 and presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. We note that the current data-processing pipeline is still at a preliminary stage, with flux calibration precision of about 2% in the u and v bands, about 1% in the g and r bands, and better than 1% in the i and z bands. View this GCN Circular online at https://gcn.nasa.gov/circulars/44610. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42737] Fermi GRB 260514A: Global MASTER-Net observations report
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44609 SUBJECT: Fermi GRB 260514A: Global MASTER-Net observations report DATE: 26/05/14 11:15:36 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 260514A ( Fermi GBM team, GCN 44604) errorbox 19843 sec after notice time and 19904 sec after trigger time at 2026-05-14 10:28:25 UT, with upper limit up to 17.1 mag. Observations started at twilight. The observations began at zenith distance = 71 deg. The sun altitude is -10.0 deg. The galactic latitude b = 15 deg., longitude l = 334 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3313250 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 19935 | 2026-05-14 10:28:25 | MASTER-OAFA | (15h 23m 20.52s , -37d 30m 31.8s) | C | 60 | 16.6 | 20013 | 2026-05-14 10:29:43 | MASTER-OAFA | (15h 23m 26.39s , -37d 31m 33.2s) | C | 60 | 17.1 | 20088 | 2026-05-14 10:30:58 | MASTER-OAFA | (15h 23m 19.45s , -39d 52m 36.3s) | C | 60 | 17.1 | 20165 | 2026-05-14 10:32:15 | MASTER-OAFA | (15h 23m 25.28s , -39d 52m 31.6s) | C | 60 | 17.1 | 20244 | 2026-05-14 10:33:34 | MASTER-OAFA | (15h 23m 24.08s , -34d 50m 45.0s) | C | 60 | 16.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44609. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42736] GRB 260512A: AstroSat CZTI detection
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44608 SUBJECT: GRB 260512A: AstroSat CZTI detection DATE: 26/05/14 10:11:36 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (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 260512A which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44587), and NuSTAR (Waratkar et. al. , GCN Circ. 44591). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-12 16:56:47.5 UTC. The measured peak count rate associated with the burst is 302 (+33, -31) counts/s above the background in the combined data of two quadrants (out of four), with a total of 1755 (+142, -215) counts. The local mean background count rate was 159 (+2, -5) counts/s. We measure a T90 of 13 (+1, -1) s from the cumulative CZT light curve. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-05-12 16:56:46.4 UTC. The measured peak count rate associated with the burst is 655 (+88, -70) counts/s above the background in the combined data of all quadrants, with a total of 3682 (+588, -378) counts.The local mean background count rate was 1822 (+7, -14) counts/s. We measure a T90 of 10 (+2, -2) 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 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/44608. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42735] The EP-WXT trigger 01709262077 is likely a flaring star
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44607 SUBJECT: The EP-WXT trigger 01709262077 is likely a flaring star DATE: 26/05/14 09:39:59 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang (NAO, CAS), C. Y. Dai (NJU), H. Y. Ren, H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709262077 at the time of 2026-05-14T08:58:30, is likely a stellar flare associated with the high proper motion star Gaia DR3 5390947154990629248. The estimated flux of the flare is around 8.6 × 10^(-11) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.0 × 10^(31) erg/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44607. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42734] EP260512a: EP-FXT follow-up observation
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44606 SUBJECT: EP260512a: EP-FXT follow-up observation DATE: 26/05/14 07:08:03 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang, M. J. Liu (NAO, CAS), H. Z. Wu (HUST), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT observed the field of EP260512a (detected by EP-WXT, Liang et al., GCN 44594; and followed by COLIBRÍ, Diego et al. GCN 44595, and MASTER-Net observations, Lipunov et al., GCN 44603) for 2.6 ks starting at 2026-05-13 10:06:08, around 25.6 hours after the detection by EP-WXT. No significant X-ray source is detected within the 2.6 arcmin radius of the EP-WXT position (Liang et al., GCN 44594) to a preliminary 0.5-10 keV upper limit of 7e-14 erg/cm^2/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/44606. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42733] EP260507a: Xinglong Schmidt optical counterpart detection
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44605 SUBJECT: EP260507a: Xinglong Schmidt optical counterpart detection DATE: 26/05/14 05:07:46 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Zhen Wang (SDU), Wenxiong Li, Niu Li, Hu Zou, and Yunao Xiao (NAOC) report: We observed the field of the fast X-ray transient EP260507a (Fu et al., GCN 44488) with the Schmidt telescope at Xinglong Observatory, China. Observations started at May 7 14:09:41 UTC, 0.36 hr after the EP trigger. We obtained a series of 120 s clear-band exposures. The images were processed and stacked with the ASTERIS framework (Guo et al. 2026). PSF photometry was performed using AutoPhOT (Brennan & Fraser 2022). The photometry was calibrated against stars from the DESI Legacy Imaging Surveys catalog in the r band. We detected the optical counterpart reported by Corcoran et al. (GCN 44489), Sankar et al. (GCN 44490), Kumar et al. (GCN 44492), Bochenek et al. (GCN 44494), Eyles-Ferris et al. (GCN 44495), Jiang et al. (GCN 44496), Li et al. (GCN 44497), and Globus et al. (GCN 44498). The measured magnitudes are: T_median (MJD) T-T0 (hr) Exposure (s) Mag (r) 61167.596 0.50 8 x 120 20.37 +/- 0.06 61167.608 0.81 8 x 120 20.55 +/- 0.06 61167.621 1.11 8 x 120 20.94 +/- 0.08 61167.634 1.42 8 x 120 21.08 +/- 0.09 61167.652 1.85 8 x 120 >22.3 (3σ) 61167.685 2.64 12 x 120 21.75 +/- 0.10 The 60/90-cm Schmidt telescope situated at the Xinglong station is supported by the CAS Special Funds for Observatory and Facility Development, alongside a generous contribution from the Zhengjia Enterprise Group. View this GCN Circular online at https://gcn.nasa.gov/circulars/44605. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42732] GRB 260514A: Fermi GBM Final Real-time Localization
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44604 SUBJECT: GRB 260514A: Fermi GBM Final Real-time Localization DATE: 26/05/14 05:05:36 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 04:56:40 UT on 14 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260514A (trigger 800427405.55421 / 260514206). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 231.1, Dec = -37.7 (J2000 degrees, equivalent to J2000 15h 24m, -37d 42'), with a statistical uncertainty of 10.9 degrees. The angle from the Fermi LAT boresight is 97.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260514206/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260514206/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260514206/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44604. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42731] EP260512a: Global MASTER-Net observations report
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44603 SUBJECT: EP260512a: Global MASTER-Net observations report DATE: 26/05/14 00:45:25 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-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP260512a ( EP Team et al., GCN 44594) errorbox 73819 sec after notice time and 1 days 57787 sec after trigger time at 2026-05-14 00:34:39 UT, with upper limit up to 18.1 mag. Observations started at twilight. The observations began at zenith distance = 49 deg. The sun altitude is -12.2 deg. The galactic latitude b = 62 deg., longitude l = 43 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3310827 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 144248 | 2026-05-14 00:34:39 | MASTER-Kislovodsk | (14h 54m 15.49s , +28d 52m 29.4s) | C | 120 | 18.1 | 144397 | 2026-05-14 00:37:08 | MASTER-Kislovodsk | (14h 54m 18.37s , +28d 54m 03.0s) | C | 120 | 18.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44603. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42730] Fermi GRB 260513A: Global MASTER-Net observations report
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44602 SUBJECT: Fermi GRB 260513A: Global MASTER-Net observations report DATE: 26/05/14 00:16:36 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 260513A ( Fermi GBM team, GCN 44599) errorbox 9005 sec after notice time and 9068 sec after trigger time at 2026-05-13 23:55:26 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 56 deg. The sun altitude is -67.4 deg. The galactic latitude b = -46 deg., longitude l = 8 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3312539 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 9098 | 2026-05-13 23:55:26 | MASTER-SAAO | (21h 18m 43.70s , -36d 30m 06.5s) | C | 60 | 18.6 | 9158 | 2026-05-13 23:55:26 | MASTER-SAAO | (21h 18m 43.70s , -36d 30m 06.5s) | C | 180 | 19.3 | 9098 | 2026-05-13 23:55:26 | MASTER-SAAO | (21h 21m 03.32s , -36d 45m 45.9s) | C | 60 | 18.9 | 9158 | 2026-05-13 23:55:26 | MASTER-SAAO | (21h 21m 03.33s , -36d 45m 45.9s) | C | 180 | 19.6 | 9191 | 2026-05-13 23:56:59 | MASTER-SAAO | (21h 18m 50.50s , -36d 31m 06.3s) | C | 60 | 18.6 | 9191 | 2026-05-13 23:56:59 | MASTER-SAAO | (21h 21m 10.07s , -36d 46m 45.8s) | C | 60 | 18.9 | 9285 | 2026-05-13 23:58:34 | MASTER-SAAO | (21h 18m 44.23s , -36d 32m 06.3s) | C | 60 | 18.7 | 9285 | 2026-05-13 23:58:34 | MASTER-SAAO | (21h 21m 03.77s , -36d 47m 45.7s) | C | 60 | 18.9 | 9408 | 2026-05-14 00:00:06 | MASTER-SAAO | (21h 18m 50.60s , -36d 31m 55.6s) | C | 120 | 19.1 | 9558 | 2026-05-14 00:00:06 | MASTER-SAAO | (21h 18m 50.60s , -36d 31m 55.5s) | C | 420 | 19.8 | 9408 | 2026-05-14 00:00:06 | MASTER-SAAO | (21h 21m 10.09s , -36d 47m 34.6s) | C | 120 | 19.4 | 9558 | 2026-05-14 00:00:06 | MASTER-SAAO | (21h 21m 10.09s , -36d 47m 34.6s) | C | 420 | 20.0 | 9562 | 2026-05-14 00:02:40 | MASTER-SAAO | (21h 18m 46.82s , -36d 30m 36.0s) | C | 120 | 19.0 | 9562 | 2026-05-14 00:02:40 | MASTER-SAAO | (21h 21m 06.23s , -36d 46m 14.7s) | C | 120 | 19.2 | 9715 | 2026-05-14 00:05:13 | MASTER-SAAO | (21h 18m 46.52s , -36d 31m 51.3s) | C | 120 | 19.2 | 9715 | 2026-05-14 00:05:13 | MASTER-SAAO | (21h 21m 05.97s , -36d 47m 30.1s) | C | 120 | 19.4 | 9868 | 2026-05-14 00:07:46 | MASTER-SAAO | (21h 18m 49.92s , -36d 30m 29.6s) | C | 120 | 19.3 | 9868 | 2026-05-14 00:07:46 | MASTER-SAAO | (21h 21m 09.35s , -36d 46m 08.2s) | C | 120 | 19.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44602. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42729] Fermi GRB 260512A: Global MASTER-Net observations report
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44601 SUBJECT: Fermi GRB 260512A: Global MASTER-Net observations report DATE: 26/05/14 00:15:51 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260512A ( Fermi GBM team, GCN 44587) errorbox 1 days 24421 sec after notice time and 1 days 24449 sec after trigger time at 2026-05-13 23:44:12 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 51 deg. The sun altitude is -24.8 deg. The galactic latitude b = -22 deg., longitude l = 298 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3309891 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 110879 | 2026-05-13 23:44:12 | MASTER-OAFA | (10h 10m 53.82s , -82d 11m 47.5s) | C | 60 | 19.7 | 110939 | 2026-05-13 23:44:12 | MASTER-OAFA | (10h 10m 53.83s , -82d 11m 47.6s) | C | 180 | 19.9 | Coadd 110955 | 2026-05-13 23:45:28 | MASTER-OAFA | (10h 11m 00.56s , -82d 09m 55.3s) | C | 60 | 19.7 | 111036 | 2026-05-13 23:46:49 | MASTER-OAFA | (10h 10m 53.19s , -82d 10m 52.8s) | C | 60 | 19.6 | 111114 | 2026-05-13 23:48:07 | MASTER-OAFA | (10h 10m 56.57s , -82d 09m 54.2s) | C | 60 | 19.6 | 111174 | 2026-05-13 23:48:07 | MASTER-OAFA | (10h 10m 56.60s , -82d 09m 54.2s) | C | 180 | 19.9 | Coadd 111193 | 2026-05-13 23:49:26 | MASTER-OAFA | (10h 11m 01.87s , -82d 10m 51.8s) | C | 60 | 19.5 | 111266 | 2026-05-13 23:50:39 | MASTER-OAFA | (10h 10m 56.31s , -82d 11m 49.2s) | C | 60 | 19.5 | 111342 | 2026-05-13 23:51:55 | MASTER-OAFA | (10h 11m 03.48s , -82d 11m 44.4s) | C | 60 | 19.6 | 111416 | 2026-05-13 23:53:10 | MASTER-OAFA | (10h 11m 03.76s , -82d 09m 59.6s) | C | 60 | 19.6 | 111493 | 2026-05-13 23:54:26 | MASTER-OAFA | (10h 11m 03.44s , -82d 11m 36.7s) | C | 60 | 19.6 | 111569 | 2026-05-13 23:55:42 | MASTER-OAFA | (10h 11m 08.67s , -82d 10m 08.0s) | C | 60 | 19.3 | 111642 | 2026-05-13 23:56:55 | MASTER-OAFA | (10h 11m 04.41s , -82d 10m 48.5s) | C | 60 | 18.6 | 111721 | 2026-05-13 23:58:14 | MASTER-OAFA | (10h 11m 06.38s , -82d 09m 49.6s) | C | 60 | 18.2 | 111805 | 2026-05-13 23:59:38 | MASTER-OAFA | (10h 08m 14.34s , -84d 04m 05.1s) | C | 60 | 17.5 | 111880 | 2026-05-14 00:00:53 | MASTER-OAFA | (10h 08m 08.20s , -84d 05m 00.1s) | C | 60 | 17.9 | 111956 | 2026-05-14 00:02:09 | MASTER-OAFA | (10h 08m 17.81s , -84d 04m 38.0s) | C | 60 | 18.2 | 112035 | 2026-05-14 00:03:28 | MASTER-OAFA | (10h 12m 11.06s , -80d 13m 12.6s) | C | 60 | 18.4 | 112111 | 2026-05-14 00:04:44 | MASTER-OAFA | (10h 12m 11.82s , -80d 14m 41.3s) | C | 60 | 18.3 | 112186 | 2026-05-14 00:05:59 | MASTER-OAFA | (10h 12m 17.07s , -80d 13m 35.4s) | C | 60 | 18.6 | 112262 | 2026-05-14 00:07:15 | MASTER-OAFA | (09h 58m 34.51s , -80d 14m 16.2s) | C | 60 | 19.3 | 112341 | 2026-05-14 00:08:34 | MASTER-OAFA | (09h 58m 35.92s , -80d 13m 16.8s) | C | 60 | 19.3 | 112416 | 2026-05-14 00:09:49 | MASTER-OAFA | (09h 58m 42.73s , -80d 14m 14.8s) | 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/44601. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42728] GRB 260511B: further SAO RAS optical observations
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44600 SUBJECT: GRB 260511B: further SAO RAS optical observations DATE: 26/05/13 22:29:56 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO RAS) and A. Pozanenko (IKI), report on behalf of GRB the follow-up team. We observed the field of the GRB 260511B discovered by Fermi (The Fermi GBM team, GCN 44542; Roberts, GCN 44554), SVOM (Godet et al., GCN 44543), NuSTAR (Waratkar and Grefenstette, GCN 44556), AstroSat CZTI (Arya et al., GCN 44560), EP-FXT (Fu et al., GCN 44578), Konus-Wind (Ridnaia et al. GCN 44597) with the Zeiss-1000, 1m telescope of the SAO RAS equipped with the CCD photometer. The observations were performed in Rc band on May 12 and 13 under moderate weather conditions. The OT (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Vijaykumar et al., GCN 44561; de Ugarte Postigo et al., GCN 44565; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573; Saccardi et al., GCN 44574; Rajabov et al., GCN 44576; Pérez-Fournon et al., GCN 44577; Novotný et al., GCN 44580; Moskvitin and Pozanenko, GCN 44582; Calapai, GCN 44592; also detected in NIR by Li et al., GCN 44557; GCN 44593) is clearly detected in the stacked frames with the following brightness. Date T_start T_end t_mid-T0, exp, filter mag +/- err UL UT UT days s 2026-05-12T18:57:30--20:17:50 1.35912 2760 Rc 20.93 +/- 0.05 23.1 2026-05-13T19:12:53--21:21:03 2.38641 4800 Rc 21.49 +/- 0.07 23.3 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44600. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42727] GRB 260513A: Fermi GBM Final Real-time Localization
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44599 SUBJECT: GRB 260513A: Fermi GBM Final Real-time Localization DATE: 26/05/13 21:34:57 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 21:24:18 UT on 13 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260513A (trigger 800400263.713514 / 260513892). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 320.8, Dec = -36.4 (J2000 degrees, equivalent to J2000 21h 23m, -36d 23'), with a statistical uncertainty of 2.3 degrees. The angle from the Fermi LAT boresight is 65.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260513892/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260513892/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260513892/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44599. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42726] GRB 260509A: SVOM/VT optical observations
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44598 SUBJECT: GRB 260509A: SVOM/VT optical observations DATE: 26/05/13 15:17:36 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. L. Qiu, C. Wu, L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio, D. Götz and D. Adrien (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations of GRB260509A triggered by SVOM/ECLAIRs (sb26050905, Götz et al., GCN 44504). The observation started at 2026-05-09T22:12:49 UTC, about 21.66 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The afterglow (O’Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Alvarez et al., 44509; Zheng et al., GCN 44510; Lipunov et al., GCN 44512; Belkin et al., GCN 44513; Corcoran et al., GCN 44514; Bochenek et al., GCN 44516; Moskvitin et al., GCN 44563; Mo et al., GCN 44590) was detected clearly in both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 22.08 m VT_B 50 s 20.05 +/- 0.07 mag 22.08 m VT_R 50 s 19.47 +/- 0.06 mag 8.17 h VT_B 16*100 s 21.76 +/- 0.09 mag 8.24 h VT_R 11*100 s 21.48 +/- 0.09 mag The light curves shows fading and brightening at early epochs, followed by a temporal decay with a slope of −1 in the late phase during our observations. 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/44598. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42725] Konus-Wind detection of GRB 260511B
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44597 SUBJECT: Konus-Wind detection of GRB 260511B DATE: 26/05/13 12:12:06 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260511B (Fermi-GBM detection: Fermi GBM team, GCN 44542; Roberts et al., GCN 44554; SVOM detection: Godet et al., GCN 44543; NuSTAR detection: Waratkar & Grefenstette, GCN 44556; AstroSat-CZTI detection: Arya et al., GCN 44560) triggered Konus-Wind at T0=39635.267 s UT (11:00:35.267). The burst light curve shows two separate multipeaked episodes: the first from ~T0-1.1 s to ~T0+10 s, and the second, which is brighter and spectrally harder, from ~T0+26 s to ~T0+42 s. The total duration of the burst is ~43.4 s. The burst light curve shows two multipeaked episodes started at ~T0-1.1 s with a total duration of ~43.4 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/GRB260511_T39635/ As observed by Konus-Wind, the burst had a fluence of 2.48(-0.11,+0.12)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+30.512 s, of 6.82(-0.83,+0.84)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+41.216 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.12(-0.09,+0.10) and Ep = 259(-20,+24) keV (chi2 = 92/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.4 (chi2 = 92/98 dof). The spectrum near the maximum count rate (measured from T0+24.832 to T0+33.024 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 = -0.87(-0.23,+0.17), the high energy photon index beta = -2.26(-0.66,+0.13), the peak energy Ep = 273(-40,+102) keV (chi2 = 93/81 dof). Assuming the redshift z=2.006 (de Ugarte Postigo et al., GCN 44565; Wang et al., GCN 44571) and a standard cosmology model with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 2.53(-0.11,+0.12)x10^53 erg, the peak luminosity L_iso is 2.09(-0.25,+0.26)x10^53 erg/s, the rest-frame peak energy of the time-averaged spectrum, Ep,i,z is 778(-60,+72) keV and the spectrum near the maximum count rate Ep,p,z is 821(-120,+307) keV. With the obtained estimates, GRB 260511B is inside 68% prediction bands for both the 'Amati' and the 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB260511_T39635/GRB260511B_rest_frame.pdf 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/44597. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42724] The EP-WXT trigger 01709262036 is likely a flaring star
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44596 SUBJECT: The EP-WXT trigger 01709262036 is likely a flaring star DATE: 26/05/13 09:18:58 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, R. D. Liang (NAO, CAS), H. Z. Wu (HUST), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709262036 at the time of 2026-05-13 08:45:48 (UTC), is likely a stellar flare associated with LP 497-99. The estimated flux of the flare is around 1×10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 3.5×10^31 erg/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44596. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42723] EP260512a: COLIBRÍ optical upper limits
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44595 SUBJECT: EP260512a: COLIBRÍ optical upper limits DATE: 26/05/13 06:18:56 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Camila Angulo (UNAM), Rosa L. Becerra (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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), Nikos Mandarakas (LAM), 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 EP260312a (Liang et al., GCN Circ. 44594), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-13 04:09 to 04:25 UTC (from 19.6 to 19.9 hours after the trigger and 6 minutes after the release of the GCN) and obtained 14 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ ASU pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images and after performing image subtraction using templates from the DESI Legacy Survey (Dey et al. 2019), we do not detect any new source within the WXT error region we do not detect any new source at the WXT error position (Liang et al., GCN Circ. 44594) down to the following 5-sigma limits: r > 23.1 z > 21.9 We note the presence of the quasar 2MASS J14554420+282524 within the WXT region and, considering our upper limits and the low SNR reported by the Einstein Probe Team (Liang et al., GCN Circ. 44594), we cannot rule out the possibility that the trigger is related to this source. 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/44595. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42722] EP260512a: Einstein Probe detection of an X-ray transient
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44594 SUBJECT: EP260512a: Einstein Probe detection of an X-ray transient DATE: 26/05/13 04:03:17 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang, M. J. Liu (NAO, CAS), H. Z. Wu (HUST), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260512a. The transient was detected at 2026-05-12 08:31:32 (UTC). The signal-to-noise ratio is below the on-board trigger threshold and hence the transient was discovered by ground-based analysis. The WXT position of the source is R.A. = 223.899 deg, DEC = 28.432 deg (J2000) with an uncertainty of 2.6 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) is scheduled. 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/44594. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42721] GRB 260511B: further J-band observations by the SYSU 80 cm infrared telescope
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44593 SUBJECT: GRB 260511B: further J-band observations by the SYSU 80 cm infrared telescope DATE: 26/05/13 02:15:50 GMT FROM: lijj328(a)mail2.sysu.edu.cn Jin-Ji Li, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Yun Shi, Hao-Nan Yang, Yan Yu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80 cm infrared telescope team: We further observed the field of GRB 260511B detected by SVOM/ECLAIRs (Godet et al., GCN 44543) and Fermi (Fermi GBM team, GCN 44542), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope. The afterglow (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Li et al., GCN 44557; Vijaykumar et al., GCN 44561; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573; Saccardi et al., GCN 44574; Rajabov et al., GCN 44576; Pérez-Fournon et al., GCN 44577; Novotný et al., GCN 44580; Moskvitin, GCN 44582; Calapai, GCN 44592) with the redshift of z=2.006 (Postigo et al., GCN 44565) was clearly detected in our stacked J-band images. The photometric results are summarized in the table below. The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction. Mid time |Band | Exposure | Mag (Vega) ------------|-------|-------------|------------------ 5.362 h | J | 700s | 16.66 +/- 0.14 5.568 h | J | 640s | 16.57 +/- 0.10 5.771 h | J | 640s | 16.85 +/- 0.13 5.985 h | J | 560s | 17.16 +/- 0.18 6.191 h | J | 660s | 17.10 +/- 0.19 7.011 h | J | 960s | 17.11 +/- 0.15 7.367 h | J | 1040s | 17.26 +/- 0.14 7.720 h | J | 1100s | 17.46 +/- 0.18 The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44593. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42720] GRB 260511B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44592 SUBJECT: GRB 260511B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation. DATE: 26/05/13 00:24:14 GMT FROM: Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai(a)tiscali.it> Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. Report: We observed the field of GRB 260511B detected by Fermi/GBM (Fermi GBM Team, GCN 44542) and SVOM/ECLAIRs (Godet et al., GCN 44543) with the 14 inches Schmidt-Cassegrain (Celestron 14) telescope F/D=7. The observations were started at 2026-05-11 21:24:23 UT (approximately 10.40 hours after burst) stacking two sets of unfiltered CCD image. The observations were carried out with clear skies and good visibility conditions. The OT was detected at the following position: RA (J2000.0) 12h 50m 17.18s Decl. (J2000.0) +04° 03' 10.2" Photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Mag. err. 2026-05-11 21:54:50 UT 10.91 60x60s CR 18.85 +/-0.04 2026-05-11 23:01:52 UT 12.02 72x60s CR 18.95 +/-0.04 Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied. Our observations are consistent with other already reported Wu et al. (GCN 44547); Sasada et al. (GCN 44549); Jiang et al. (GCN 44551); Wu et al. (GCN 44552); Li et al. (GCN 44557); Vijaykumar et al. (GCN 44561); De Ugarte Postigo et al. (GCN 44565); Lee et al. (GCN 44567); Li et al. (44568); Belkin et al. (GCN 44572); Saccardi et al. (GCN 44574); Rajabov et al. (GCN 44576); Pérez-Fournon et al. (GCN 44577); Novotný et al. (GCN 44580); Moskvitin (GCN 44582). The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44592. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42719] GRB 260512A: NuSTAR detection of prompt emission
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44591 SUBJECT: GRB 260512A: NuSTAR detection of prompt emission DATE: 26/05/12 23:53:06 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260512A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-05-12T16:56:43.530 UTC, shows a detection of GRB 260512A, also detected by Fermi/GBM (Fermi GBM Team, GCN 44542). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a 10-s long burst consistent with the Fermi/GBM lightcurve. The peak count rate is ~2500-cps with a baseline rate of ~1000-cps during this time period. We do not see evidence in the signal above 100 keV in the CZT detectors. The Fermi/GBM localization (GCN 44542) at RA = 153.56, Dec = -82.64 implies an offset from the NuSTAR boresight of 15-deg (i.e. near the boresight) and an offset from the geocenter of 96-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260512A Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44591. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42718] GRB 260509A: Infrared J and Hs observations with MDM/MIRAGE
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44590 SUBJECT: GRB 260509A: Infrared J and Hs observations with MDM/MIRAGE DATE: 26/05/12 20:45:37 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Carnegie/Caltech), K. De, V. Karambelkar, S. Ibrahim, D. Schiminovich (Columbia University) report: We observed the field of GRB 260509A (Gotz et al., GCN 44504) in the near-infrared J and Hs bands with the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3 m telescope. Observations began at 2026-05-10T04:00:51 (+6.2 hours after the GRB trigger) in the J band and 2026-05-10T03:27:31 (+5.6 hours) in the Hs band, lasting 1560 s in J and 1260 s in Hs. The optical counterpart (O’Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Alvarez et al., 44509; Zheng et al., GCN 44510; Lipunov et al., GCN 44512; Belkin et al., GCN 44513; Corcoran et al., GCN 44514; Bochenek et al., GCN 44516; Moskvitin et al., GCN 44563) is detected in the J filter at low significance and undetected in H band, with the following AB magnitudes: J = 20.91 ± 0.40, Hs > 19.6. MIRAGE is a new YJHs-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44590. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42717] GRB 260510C: Infrared J and Hs detections with MDM/MIRAGE
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44589 SUBJECT: GRB 260510C: Infrared J and Hs detections with MDM/MIRAGE DATE: 26/05/12 20:44:36 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Carnegie/Caltech), K. De, V. Karambelkar, S. Ibrahim, D. Schiminovich (Columbia University) report: We observed the field of GRB 260510C (Fermi GBM Team, GCN 44520; Gotz et al., GCN 44521; Iwakiri et al., GCN 44526; Fu et al., GCN 44541; Arya et al., GCN 44544; Palafox et al., GCN 44564) in the near-infrared J and Hs bands with the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3 m telescope. Observations began at 2026-05-11T03:31:14 (+10.3 hours after the GRB trigger) in the J band and 2026-05-11T04:04:31 (+10.8 hours) in the Hs band, lasting 1620 s in each filter. The optical counterpart (Li et al, GCN 44527; Angulo et al., GCN 44530; Li et al., GCN 44540; Lee et al., GCN 44570) is detected in both filters, with the following AB magnitudes: J = 19.64 ± 0.16, Hs = 19.42 ± 0.24. MIRAGE is a new YJHs-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44589. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42716] EP260507a: Infrared J and Hs upper limits with MDM/MIRAGE
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44588 SUBJECT: EP260507a: Infrared J and Hs upper limits with MDM/MIRAGE DATE: 26/05/12 20:43:26 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Carnegie/Caltech), K. De, V. Karambelkar, S. Ibrahim, D. Schiminovich (Columbia University) report: We observed the field of EP260507a (Fu et al., GCN 44488, GCN 44500) in the near-infrared J and Hs bands with the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3 m telescope. Observations began at 2026-05-08T05:49:04 (+16.0 hours after the GRB trigger) in the J band and 2026-05-08T06:22:36 (+16.6 hours) in the Hs band, lasting 1620 s in each filter. 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; Eyles-Ferris et al., GCN 44495; Jiang et al., GCN 44496; Li et al., GCN 44497; Globus et al., GCN 44498; Brivio et al., GCN 44501) is not detected in either band, with the following 5-sigma upper limits in AB magnitudes: J > 19.84, Hs > 19.2. MIRAGE is a new YJHs-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44588. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42715] GRB 260512A: Fermi GBM Final Real-time Localization
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44587 SUBJECT: GRB 260512A: Fermi GBM Final Real-time Localization DATE: 26/05/12 17:07:17 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 16:56:43 UT on 12 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260512A (trigger 800297808.529848 / 260512706). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 153.6, Dec = -82.6 (J2000 degrees, equivalent to J2000 10h 14m, -82d 35'), with a statistical uncertainty of 2.0 degrees. The angle from the Fermi LAT boresight is 136.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260512706/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260512706/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260512706/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44587. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42714] GRB 260511A: Glowbug gamma-ray detection
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44586 SUBJECT: GRB 260511A: Glowbug gamma-ray detection DATE: 26/05/12 17:03:10 GMT FROM: Richard S. Woolf at US Naval Research Laboratory <richard.s.woolf.civ(a)us.navy.mil> R. Woolf, C.C. Cheung, 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 260511A, which was also detected by Fermi GBM (GCN 44529), SVOM (GCN 44532), NuSTAR (GCN 44555), and Konus–Wind (GCN 44585). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-11 06:13:28.904 with a duration of 11.3 s and a total significance of about 41.6 sigma. The light curve comprises three primary peaks from T0 to ~T0+11s. 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/44586. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42713] Konus-Wind detection of GRB 260511A
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44585 SUBJECT: Konus-Wind detection of GRB 260511A DATE: 26/05/12 16:55:02 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260511A (Fermi-GBM detection: Fermi GBM team, GCN 44529; Roberts et al., GCN 44548; BALROG localization: Preis & Greiner, GCN 44531; SVOM detection: Godet et al., GCN 44532; NuSTAR detection: Waratkar et al., GCN 44555) triggered Konus-Wind at T0=22416.401 s UT (06:13:36.401). The burst light curve shows a multipeaked structure which starts at ~T0-4.6 s and has a total duration of ~20.5 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/GRB260511_T22416/ As observed by Konus-Wind, the burst had a fluence of 1.72(-0.05,+0.05)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.482 s, of 6.96(-0.71,+0.71)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+16.640 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.79(-0.08,+0.09) and Ep = 187(-8,+8) keV (chi2 = 107/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.1 (chi2 = 107/98 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.66(-0.08,+0.08) and Ep = 187(-6,+7) keV (chi2 = 88/86 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.9 (chi2 = 87/85 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/44585. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42712] MASS-Cube (GRID 2.0) detection of GRB 260511A
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44584 SUBJECT: MASS-Cube (GRID 2.0) detection of GRB 260511A DATE: 26/05/12 16:35:13 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Jiahuan Zhu, Chenyu Wang, Xutao Zheng, Hao Chang, Zirui Yang report on behalf of the MASS-Cube Collaboration: MASS-Cube reports the detection of the long-duration GRB 260511A, which was also observed by Fermi/GBM (GCN #44548, #44548), SVOM (GCN #44532) and GRID. The optical counterpart was detected by TRT (GCN #44533). The event was triggered by MASS-Cube on 2026-05-11 at 06:13:29.2 UTC. The measured burst duration (T90) in the 50-10000 keV range is approximately 9.7 +/- 2.3 seconds. The second peak is not clearly detected by MASS-Cube due to its limited sensitivity. The MASS-Cube light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260511A/MASS_Cub…. MASS-Cube is a pathfinder for a 3D position-sensitive Compton telescope in space, currently considered the next generation of the GRID constellation in the era of multi-messenger astronomy. For more information about MASS-Cube, please refer to the following reference: https://doi.org/10.1007/s10686-024-09920-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/44584. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42711] MASS-Cube (GRID 2.0) detection of GRB 260507A
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44583 SUBJECT: MASS-Cube (GRID 2.0) detection of GRB 260507A DATE: 26/05/12 16:33:06 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Jiahuan Zhu, Chenyu Wang, Xutao Zheng, Hao Chang, Zirui Yang report on behalf of the MASS-Cube Collaboration: MASS-Cube reports the detection of the long-duration GRB 260507A, which was also detected by Fermi/GBM (GCN Circular 44493) and GRID-09. The event was triggered by MASS-Cube on 2026-05-07 at 20:27:59.7 UTC. The measured burst duration (T90) in the 50-10000 keV range is approximately 19.3 +/- 3.2 seconds. The MASS-Cube light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260507A/MASS_Cub…. MASS-Cube is a pathfinder for a 3D position-sensitive Compton telescope in space, currently considered the next generation of the GRID constellation in the era of multi-messenger astronomy. For more information about MASS-Cube, please refer to the following reference: https://doi.org/10.1007/s10686-024-09920-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/44583. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42710] GRB 260511B: SAO RAS optical observations
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44582 SUBJECT: GRB 260511B: SAO RAS optical observations DATE: 26/05/12 15:32:19 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS) and A. Pozanenko (IKI), report on behalf of GRB the follow-up team. We observed the field of the GRB 260511B discovered by Fermi (The Fermi GBM team, GCN 44542; Roberts, GCN 44554), SVOM (Godet et al., GCN 44543), NuSTAR (Waratkar and Grefenstette, GCN 44556), AstroSat CZTI (Arya et al., GCN 44560); EP-FXT (Fu et al., GCN 44578) with the Zeiss-1000, 1m telescope of the SAO RAS equipped with the CCD photometer. Observations were performed in B, V, Rc, Ic filters and started on May 11, 19:08:40 UT (8.14 hours after the trigger). The OT (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Vijaykumar et al., GCN 44561; de Ugarte Postigo et al., GCN 44565; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573; Saccardi et al., GCN 44574; Rajabov et al., GCN 44576; Pérez-Fournon et al., GCN 44577; Novotný et al., GCN 44580; also detected in NIR by Li et al., GCN 44557) is clearly detected in all frames with the following brightness. Date T_start T_end t_mid-T0, exp, s filter mag +/- err UT hours 2026-05-11T19:14:19--19:54:19 8.56306 3*300 B 19.56 +/- 0.03 2026-05-11T19:20:15--19:40:09 8.49444 2*120 V 19.09 +/- 0.04 2026-05-11T19:08:40--19:43:12 8.42333 3*120 Rc 18.75 +/- 0.02 2026-05-11T19:11:24--19:51:31 8.51542 5*120 Ic 18.50 +/- 0.05 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44582. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42709] GRB 260510D: Glowbug gamma-ray detection of a likely short burst
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44581 SUBJECT: GRB 260510D: Glowbug gamma-ray detection of a likely short burst DATE: 26/05/12 14:39:43 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 the likely short burst GRB 260510D, which was detected by Fermi/GBM (GCN 44523). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-10 20:38:07.656 with a duration of 0.13 s and a total significance of about 9.7 sigma. The lightcurve comprises a single peak. 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/44581. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42708] GRB 260511B: FRAM-ORM optical detection
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44580 SUBJECT: GRB 260511B: FRAM-ORM optical detection DATE: 26/05/12 13:59:31 GMT FROM: Filip Novotný at Masaryk University <filip.novotny(a)talentovani.cz> Filip Novotný, Martin Jelínek, Jan Štrobl (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Mašek, Petr Janeček, Jakub Juryšek, Jan Ebr, Ronan Cunniffe, Petr Travníček and Michael Prouza (Institute of Physics, Prague, CZ) report: We observed the field of GRB 260511B detected by Fermi/GBM (Fermi GBM Team, GCN 44542) and SVOM/ECLAIRs (Godet et al., GCN 44543) with the FRAM robotic telescope at the Observatorio del Roque de los Muchachos (ORM), La Palma, Spain. Observations were carried out in the clear filter from T+9.6 hr to T+17.4 hr with 60-second exposures stacked per epoch. The optical afterglow(Wu et al., GCN 44547 ; Sasada et al., GCN 44549 ; Jiang et al., GCN 44551 ; Wu et al., GCN 44552 ; Li et al., GCN 44557 ; Vijaykumar et al., GCN 44561 ; de Ugarte Postigo et al., GCN 44565 ; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572) of GRB 260511B (FERMI team, GCN 44542 ; Godet et al., GCN 44543; Roberts et al., GCN 44554; Waratkar et al., GCN 44556; Arya et al., GCN 44560) is clearly detected throughout the night, fading from CR = 18.89 +/- 0.10 at T+9.8 hr till about T+16 hr, when the target terminated due to dawn. Magnitudes were reduced using the PyRT pipeline and calibrated to r-band AB magnitudes against the ATLAS catalog. No correction for Galactic extinction has been applied. Fitting a power law F(t) ~ t^(-alpha) to our data yields alpha = 1.39 +/- 0.29, consistent with the power-law decay reported by earlier observers (GCN 44547, 44549, 44551, 44561). View this GCN Circular online at https://gcn.nasa.gov/circulars/44580. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42707] GRB 260511A: EP-FXT follow-up observation
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44579 SUBJECT: GRB 260511A: EP-FXT follow-up observation DATE: 26/05/12 13:12:09 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.-Y. Fu (HUST), X. Tian (GXU), H.-N. Yang, Z.-X. Ling (NAOC, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260511A (SVOM/sb26051101, Godet et al., GCN 44532), which also triggered Fermi-GBM (Fermi GBM team, GCN 44529). The follow-up obervation started at 2026-05-11T07:00:13 UTC, approximately 46.7 minutes after the SVOM trigger, with a total exposure time of 2.2ks. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 197.8992, -33.8042 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic) near the ECLAIRs error circle. This position is consistent with the optical counterpart reported by TRT (Jiang et al., GCN 44533) and FM-GFT (Akl et al. GCN 44534). The average FXT 0.3-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value, adittional hydrogen column density of 5.9 (+-1.3) ×10^20 cm^-2, and a photon index of 1.93 +- 0.05. The derived average unabsorbed flux in the 0.3-10 keV band is 6.33 (+-0.18)×10^-11 erg s^-1 cm^-2. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44579. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42706] GRB 260511B: EP-FXT follow-up observation
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44578 SUBJECT: GRB 260511B: EP-FXT follow-up observation DATE: 26/05/12 12:55:37 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.-Y. Fu (HUST), X. Tian (GXU), H.-N. Yang, Z.-X. Ling (NAOC, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of GRB 260511B detected by Fermi/GBM (the Fermi GBM team, GCN 44542) and SVOM/ECLAIRs (SVOM/sb26051102, Godet et al., GCN 44543). The follow-up obervation started at 2026-05-11T11:41:41 UTC, approximately 40.7 minutes after the SVOM trigger, with a total exposure time of 5.9 ks. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 192.574, 4.0549 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic) near the ECLAIRs error circle. This position is consistent with the optical counterpart reported by SVOM/C-GFT (Wu et al., GCN 44547) and MITSuME (Sasada et al. GCN 44549). The average FXT 0.3-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value, intrinsic hydrogen column density of 3.8 (+-0.10) ×10^21 cm^-2, and a photon index of 2.10 +- 0.04. The derived average unabsorbed flux in the 0.3-10 keV band is 2.07 (+-0.05)×10^-11 erg s^-1 cm^-2. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44578. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42705] GRB 260511B: LCO optical counterpart detection
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44577 SUBJECT: GRB 260511B: LCO optical counterpart detection DATE: 26/05/12 12:22:26 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), A. López-Oramas (IAC and ULL), and D. Aguado (IAC and ULL) We report on Las Cumbres Observatory (LCO) observations of the long GRB 260511B, detected by Fermi GBM (Fermi GBM team, GCN circ. 44542; Roberts et al., GCN circ. 44554), SVOM ECLAIRs and MXT (Godet et al., GCN circ. 44543), NuSTAR (Waratkar and Grefenstette, GCN circ. 44556), and AstroSat (Arya et al., GCN circ. 44560). We observed the field of GRB 260511B with one of the two LCO 1-m telescopes equipped with Sinistro cameras located at the LCO node at McDonald Observatory, Texas, in the SDSS r´ (300 sec), g' (200 sec), and i' (200 sec) filters. The first observation, in the SDSS r' filter, started on 2026-05-12 at 03:00:47 UT, 16.00 hours after the Fermi and SVOM trigger. The optical conterpart, first reported by Wu et al. (GCN circ. 44547), at a redshift of z = 2.006 (de Ugarte Postigo et al., GCN circ. 44565; Wang et al., GCN circ. 44571; and Adami et al., GCN circ. 44573), is clearly detected in our LCO images. The AB magnitudes, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction are: r' = 19.81 +/- 0.06 (mid-time 16.05 hours after the trigger) g' = 20.21 +/- 0.06 (mid-time 16.67 hours after the trigger) i' = 19.71 +/- 0.07 (mid-time 16.73 hours after the trigger) These results are consistent with other optical and near-IR detections of the afterglow (Wu et al., GCN circ. 44547; Sasada et al., GCN circ. 44549; Jiang et al., GCN circ. 44551; Wu et al., GCN circ. 44552; Li et al., GCN circ. 44557; Vijaykumar et al., GCN circ. 44561; de Ugarte Postigo et al., GCN circ. 44565; Lee et al., GCN circ. 44567; Li et al., GCN circ. 44568; Wang et al., GCN circ. 44571; Belkin et al., GCN circ. 44572; Adami et al., GCN circ. 44573; Saccardi et al., GCN circ. 44574); and Rajabov et al., GCN circ. 44576). This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026A-011, SGLF and Superluminous Supernovae surveys). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/44577. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42704] GRB260511B: MAO/AZT-22 optical observations
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44576 SUBJECT: GRB260511B: MAO/AZT-22 optical observations DATE: 26/05/12 11:51:54 GMT FROM: Yodgor Rajabov at UBAI <rajabov(a)astrin.uz> Y. Rajabov, B.Abidkhanov, O. Burkhonov, S. Ehgamberdiev, Y. Tillayev (UBAI), T. Boyqobilov, A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team. We observed the field of GRB 260511B detected by SVOM (Godet et al., GCN 44543) and Fermi (Fermi GBM team, GCN 44542) with the AZT-22 1.5m telescope of the Maidanak Observatory (MAO) starting on 2026-05-11 at 16:49:08 UT, i.e, ~6.81 hours after the FERMI GBM trigger. In total we obtained 6x300 s exposures in the R-band using 4kx4k CCD SNUCAM camera (Im et al., 2010). We detect the optical counterpart reported by many teams (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Vijaykumar et al., GCN 44561; de Ugarte Postigo et al., GCN 44565; Lee et al., GCN 44567; Li et al., GCN 44568; Belkin et al., GCN 44572; Saccardi et al., GCN 44574). Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL SNR Site/Telescope (nxs) (hours) 2026-05-11 16:49:08 6x300 6.81 R 18.32 0.01 23.0 142 MAO/AZT-22 The red shift (z = 2.006) measured by de Ugarte Postigo et al., GCN 44565. Then confirmed by Wang et al., GCN 44571 and Adami et al., GCN 44573. All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog. We used PanSTARRS DR2 catalog for template subtraction. The data has not corrected for the Galactic extinction. Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/) View this GCN Circular online at https://gcn.nasa.gov/circulars/44576. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42703] GRB 260511A: SVOM/VT optical observations
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44575 SUBJECT: GRB 260511A: SVOM/VT optical observations DATE: 26/05/12 09:53:21 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, Y. L. Qiu, L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations of GRB260511A triggered by SVOM/ECLAIRs (sb26051101, Godet et al., GCN 44532). The burst was also detected by Fermi/GBM (Fermi GBM team, GCN 44529; Preis et al., GCN 44531; Preis et al., GCN 44531; Roberts et al., GCN 44548) and NuSTAR (Waratkar et al. GCN 44555). The observation started at 2026-05-11T22:13:58 UTC, about 16.0 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The afterglow (Jiang et al., GCN 44533; Akl et al. GCN 44534; Saccardi et al. GCN 44535; Zheng et al. GCN 44536; Wu et al., GCN 44538, Harper et al., GCN 44545; Brivio et al., GCN 44562) was detected in stack images of both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 18.00 h VT_B 35*70 s 23.43 +/- 0.27 mag 18.00 h VT_R 39*70 s 21.82 +/- 0.13 mag The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44575. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42702] GRB 260511B: LCO optical observations
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44574 SUBJECT: GRB 260511B: LCO optical observations DATE: 26/05/12 09:48:43 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. X. Cao (GXU), L. Zhang (IHEP), D. Kong (GXU), report on behalf of the SVOM mission team: We observed the field of the SVOM/ECLAIRs GRB 260511B (Godet et al., GCN 44543), also detected by Fermi/GBM (Fermi GBM team, GCN 44542; Roberts et al., GCN 44554), NuSTAR (Waratkar et al., GCN 44556), and AstroSat (Arya et al., GCN 44560), with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-12 at 00:14:08 UT (about 13.23 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical counterpart (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Li et al., GCN 44557; Vijaykumar et al., GCN 44561; de Ugarte Postigo et al., GCN 44565; Lee et al. GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573) 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 = 19.68 +/- 0.02 AB (mid-time 13.29 hr after the trigger); z = 19.71 +/- 0.09 AB (mid-time 18.14 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44574. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42701] GRB 260511B: OHP/T193 spectroscopic observations
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44573 SUBJECT: GRB 260511B: OHP/T193 spectroscopic observations DATE: 26/05/12 09:05:55 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), D. Russeil (LAM/Pytheas/AMU), E. Le Floc'h (CEA-Saclay) report on behalf of a larger collaboration and on behalf of the transient team of the OHP 2026 special call: We observed the optical counterpart (Wu et al., GCN 44547 ; Sasada et al., GCN 44549 ; Jiang et al., GCN 44551 ; Wu et al., GCN 44552 ; Li et al., GCN 44557 ; Vijaykumar et al., GCN 44561 ; de Ugarte Postigo et al., GCN 44565 ; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572) of GRB 260511B (FERMI team, GCN 44542 ; Godet et al., GCN 44543; Roberts et al., GCN 44554; Waratkar et al., GCN 44556; Arya et al., GCN 44560) in spectroscopic mode using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained a total of 145 min of exposures (10min + 15min + 4 x 30min) with the MISTRAL spectroscopic blue setting from 4200 to 8000 AA, starting at 2026-05-11 22:04:34 UT under modest weather conditions. The host environment at z=2.006 detected by the GTC and reported by de Ugarte Postigo et al. (GCN 44565) and Wang et al. (GCN 44571) is visible in our data, in particular with the 2344 AA and 2600 AA (rest-frame) FeII lines observed at a consistent redshift of z=2.007 +/- 0.001. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen. View this GCN Circular online at https://gcn.nasa.gov/circulars/44573. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42700] GRB 260511B: GOTO optical counterpart detection
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44572 SUBJECT: GRB 260511B: GOTO optical counterpart detection DATE: 26/05/12 08:15:30 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin, G. Ramsay, D. O'Neill, B. P. Gompertz, M. Wortley, R. Starling, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar, M. Pursiainen, on behalf of GOTO collaboration We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the Fermi/GBM (Fermi GBM team, GCN 44542) and SVOM/ECLAIRs (Godet et al. GCN 44543) triggers for GRB 260511B. Observations started at 2026-05-11 21:09:05 UT, (+10.13h post trigger) in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations (Lyman et al. 2026). We detect the previously reported optical counterpart of GRB 260511B at a position consistent with the source reported by Wu et al. (GCN 44547), Sasada et al. (GCN 44549), Jiang et al. (GCN 44551), Wu et al. (GCN 44552), Vijaykumar et al. (GCN 44561), de Ugarte Postigo et al. (GCN 44565), Lee et al. (GCN 44567), and Li et al. (GCN 44568). The source is detected in the GOTO L-band (400-700 nm) with L=19.45 ± 0.09 AB mag at a mid-time of 2026-05-11 21:44:06 UT (+10.73 h). 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/44572. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42699] GRB 260511B: Xinglong 2.16m/BEFOSC redshift confirmation
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44571 SUBJECT: GRB 260511B: Xinglong 2.16m/BEFOSC redshift confirmation DATE: 26/05/12 07:55:07 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> J. Wang, L. P. Xin, J. Zheng, H. L. Li, C. Wu, Y. L. Qiu, X. H. Han, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, J. Y. Wei (NAOC) reports on behalf of SVOM follow-up team The follow-up for the optical counterpart (Wu et al. GCN 44547; Sasada et al. GCN 44549; Jiang et al. GCN 44551; Wu et al. GCN 44552; Waratkar et al. GCN 44556; Li et al. GCN 44557; Vijaykumar et al. GCN 44561) of GRB 260511B (Fermi GBM team GCN 44542; Godet et al. GCN 44543; Roberts et al. GCN 44544; Arya et al. GCN 44560; de Ugarte Postigo et al., GCN 44565; Lee et al, GCN 44567; Li et al., GCN 44568) within the errorbox of X-ray counterpart (Godet et al. GCN 44543; Li et al., GCN 44566;) was performed at 2026-05-11T12:46:21 UTC, about 1.76 hours after the trigger, using the NAOC 2.16m telescope at Xinglong observatory, China. A total of 2*1800s exposure was performed by BEFOSC spectrograph in our spectroscopic observation. The wavelength ranges from 4000-8800A in the obsever frame. After combining the two frames, absorption features of multiple ions: CIV, FeII and MgII can be identified at a common redshift of ~2.006. In addition, there is a feature possibly due to MgII double let resulted from an intervening system at redshift of 1.435. Our results are consistent with the report of redshift (de Ugarte Postigo et al., GCN 44565). The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/44571. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42698] GRB 260510C: SVOM/COLIBRÍ (FM-GFT) further optical observations
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44570 SUBJECT: GRB 260510C: SVOM/COLIBRÍ (FM-GFT) further optical observations DATE: 26/05/12 05:34:29 GMT FROM: William H. Lee at UNAM <wlee(a)astro.unam.mx> William H. Lee (UNAM), Dalya Akl (NYUAD), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM), and Andrea Saccardi (CEA/Irfu) report: We reimaged the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260510C (Fermi GBM Team, GCN Circ. 44520; Gotz et al., GCN Circ. 44521) and also detected by AstroSat (Angulo et al. GCN Circ. 44544) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-12 03:45 to 04:44 UTC (from 34.52 to 35.53 hours after the trigger) and obtained 47 minutes of simultaneous exposure in r and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect the source reported by Angulo et al. (GCN Circ. 44530) with preliminary unsubtracted magnitudes of: r = 22.36 + /- 0.07, z = 21.33 + /- 0.08. Compared with our first epoch (Angulo et al. GCN Circ. 44530), we estimate an optical decay temporal index of alpha ≈ -0.9 for the source. 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/44570. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42697] GRB 260510A: AstroSat CZTI detection
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44569 SUBJECT: GRB 260510A: AstroSat CZTI detection DATE: 26/05/12 05:10:46 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (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 260510A which is also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44508), and GECAM-B (Luo et al., GCN Circ. 44519). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-10 02:51:20.28 UTC. The measured peak count rate associated with the burst is 98 (+27, -16) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1136 (+230, -210) counts. The local mean background count rate was 180 (+2, -2) counts/s. We measure a T90 of 30 (+5, -8) s from the cumulative CZT light curve. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 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/516077480.79/S516077480.79_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/44569. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42696] GRB 260511B: SVOM/VT optical observations
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44568 SUBJECT: GRB 260511B: SVOM/VT optical observations DATE: 26/05/12 04:28:34 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, Y. L. Qiu, L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), L. Zhang (IHEP) and D. Kong (GXU) report on behalf of the SVOM/VT team. SVOM/VT performed observations of GRB260511B triggered by SVOM/ECLAIRs (sb26051102, Godet et al., GCN 44543). The burst was also detected by Fermi-GBM (Fermi GBM team, GCN 44542; Roberts et al., GCN 44554)，AstroSat (Arya et al., GCN 44560) and NuSTAR (Waratkar et al. GCN 44556). Our available data via automatic slew started at 2026-05-11T14:26:43 UTC, approximately 3.45 hours post trigger, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The ToO observations started at 2026-05-11T20:37:09 UTC, about 9.62 hours post trigger. The afterglow (Wu et al. GCN 44547; Sasada et al. GCN 44549; Jiang et al. GCN 44551; Wu et al. GCN 44552; Li et al. GCN 44557; Vijaykumar et al. GCN 44561) with the redshift of z=2.006 (Postigo et al., GCN 44565) was clearly detected in both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 3.450 h VT_B 100 s 18.00 +/- 0.03 mag 3.450 h VT_R 100 s 17.61 +/- 0.03 mag 10.159 h VT_B 100 s 19.52 +/- 0.05 mag 10.159 h VT_R 100 s 19.05 +/- 0.05 mag The source showed a fading slope of about -1.3 during the observations above. 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/44568. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42695] GRB 260511B: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44567 SUBJECT: GRB 260511B: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 26/05/12 04:22:36 GMT FROM: William H. Lee at UNAM <wlee(a)astro.unam.mx> William H. Lee (UNAM), Dalya Akl (NYUAD), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM), L. Zhang (IHEP), and D. Kong (GXU) report: We imaged the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511B (Fermi GBM Team, GCN Circ. 44529; Godet et al., GCN Circ. 44532) and also detected by AstroSat (Arya et al. GCN Circ. 44560) and NuSTAR (Waratkar et al. GCN Circ. 44556) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-12 03:24 to 03:43 UTC (from 16.35 to 16.67 hours after the trigger) and obtained 16 minutes of simultaneous exposure in r and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. At the position of the optical counterpart reported by SVOM/C-GFT (Wu et al. GCN Circ. 44547), MITSuME (Sasada et al. GCN Circ. 44549), TRT (Jiang et al. GCN Circ. 44551), SVOM/VT (Wu et al. GCN Circ. 44552), we detect a source with preliminary magnitudes of: r = 19.99 +/- 0.01, z = 19.67 +/- 0.02. Compared with the optical observations reported by de Ugarte Postigo (GCN Circ. 44565), we estimate an optical decay temporal index of alpha ≈ -1.3 for the source. 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/44567. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42694] GRB 260510B: EP-FXT follow-up observation
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44566 SUBJECT: GRB 260510B: EP-FXT follow-up observation DATE: 26/05/12 02:31:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li (BNU), S.-Y. Fu (HUST), C.-Y. Wang (THU), R. Shi (PMO), Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260510B (SVOM/sb26051001, Saccardi et al., GCN 44515). The follow-up obervation started at 2026-05-10T13:15:11 UTC, approximately 55 minutes after the SVOM trigger, with a total exposure time of 6.1 ks. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 173.2323, -34.5399 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic) within the ECLAIRs error circle. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value and a photon index of 2.24 (-0.56/+0.60). The derived average unabsorbed flux in the 0.5-10 keV band is 1.17 (-0.3/+1.7)×10^-12 erg s^-1 cm^-2. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44566. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42693] GRB 260511B: OSIRIS+/GTC redshift z=2.006
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44565 SUBJECT: GRB 260511B: OSIRIS+/GTC redshift z=2.006 DATE: 26/05/11 23:06:28 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> A. de Ugarte Postigo (LAM), C. C. Thoene (AbAO), A. Martin-Carrillo (UCD), S. Geier (GTC), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), L. Izzo (INAF/OACN and DARK/NBI), G. Lombardi (GTC), D. B. Malesani (DAWN/NBI and Radboud), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), A. M. García Rodríguez (GTC) and D. González González (GTC) report: We observed the optical counterpart (Wu et al. GCN 44547; Sasada et al. GCN 44549; Jiang et al. GCN 4455; Wu et al. GCN 44552; Waratkar et al. GCN 44556; Li et al. GCN 44557; Vijaykumar et al. GCN 44561) of GRB 260511B (Fermi GBM team GCN 44542; Godet et al. GCN 44543; Roberts et al. GCN 44554; Arya et al. GCN 44560) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. In the 30-s acquisition image (beginning on 2026-05-11 at 21:05:13.010 UT, that is 10.08 hr after trigger), the optical afterglow is well detected with a preliminary magnitude of r = 19.30 ± 0.05 (AB), calibrated against nearby SDSS objects, and not corrected for Galactic extinction. A total of 3 spectra of 900 s were secured, starting on 2026-05-11 at 21:11:43.011 UT (10.19 hr after trigger), using grism R1000B. Continuum is visible over the complete wavelength range 3620-7800 AA. A trough is detected at the blue edge of the spectrum at ~3650 AA, which we identify as a DLA. A number of strong metal absorption features are detected, which we interpret as due to SII, SiII, SiII*, OI, CII, SiIV, CIV, FeII, FeII* AlII, NiII, NiII*, AlIII, CrII, ZnII, and MnII all at a common redshift of 2.006 +/- 0.001, which we suggest to be the redshift of GRB 260511B. Multiple intervening systems are also detected in the spectrum, including a strong system at z = 1.437 with lines due to SiII, CIV, FeII, AlII, AlIII, MgII. This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). View this GCN Circular online at https://gcn.nasa.gov/circulars/44565. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42692] GRB 260510C: Fermi GBM Observation
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44564 SUBJECT: GRB 260510C: Fermi GBM Observation DATE: 26/05/11 20:51:58 GMT FROM: Eva MP at INAOE <eva.palafox(a)gmail.com> E. Palafox (INAOE, Mexico) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 17:13:43.99 UT on 10 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260510C (trigger 800126028/260510718), which was also detected by SVOM/ECLAIRs (Gotz et al. 2026, GCN 44521), MAXI (Iwakiri et al. 2026, GCN 44526), COLIBRI (Angulo et al. 2026, GCN 44530), SVOM/VT (Li et al. 2026, GCN 44527 and GCN 44540), EP-FXT (Fu et al. 2026, GCN 44541) and AstroSat CZTI (Arya et al. 2026,GCN 44544). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. The angle from the Fermi LAT boresight is 68 degrees. The GBM light curve consists of two bright emission episodes with a duration (T90) of about 162 s (50-300 keV). The time-averaged spectrum from T0-8.2 to T0+143.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.3 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 176 +/- 55 keV. The event fluence (10-1000 keV) in this time interval is (4.9 +/- 0.7)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+120 s in the 10-1000 keV band is 2.6 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44564. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42691] GRB 260509A: SAO RAS optical observations
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44563 SUBJECT: GRB 260509A: SAO RAS optical observations DATE: 26/05/11 18:46:55 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin and O. Spiridonova (SAO RAS), report on behalf of the GRB follow-up team. We observed the field of the GRB 260509A (Götz et al., GCN 44504) with the Zeiss-1000, 1m telescope of the SAO RAS equipped with the CCD photometer. We obtained 12 * 300 sec. images in Rc band on May 10, 18:18:31--19:49:52 UT (21.22 hr after the trigger). The OT (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Sánchez Álvarez et al., GCN 44509; Zheng et al., GCN 44510; Kechin et al., GCN 44512; Belkin, GCN 44513; Corcoran et al., GCN 44514; Bochenek and Perley, GCN 44516) is marginally detected with the brightness of R = 24.0 +/- 0.3. This preliminary photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44563. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42690] GRB 260511A: REM near-infrared detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44562 SUBJECT: GRB 260511A: REM near-infrared detection DATE: 26/05/11 18:00:39 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), A. Melandri (INAF-OAR) report on behalf of the REM team: We observed the field of GRB 260511A, detected by SVOM/ECLAIRs (Godet et al., GCN 44532) and Fermi/GBM (Fermi GBM Team, GCN 44529) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried out in the H band, started on 2026-05-11 at 06:15:22 UT (i.e. 110 s after the burst) and lasted for about 10 minutes. From preliminary photometry, we detect the optical/NIR counterpart (Jiang et al., GCN 44533; Akl et al. GCN 44534; Saccardi et al. GCN 44535; Zheng et al. GCN 44536; Wu et al., GCN 44538, Harper et al., GCN 44545) with the following magnitude: H = 12.9 +/- 0.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 115 s after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44562. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42689] GRB 260511B: GROWTH-India Telescope optical observations
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44561 SUBJECT: GRB 260511B: GROWTH-India Telescope optical observations DATE: 26/05/11 17:39:26 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Vijaykumar (IITB), A.P. Saikia (IITB), V. Swain (IITB), T. Mohan (IITB), S. Patil (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team: We observed the field of GRB 260511B detected by Fermi (Fermi GBM Team, GCN 44542), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-05-11 16:19:32 (UTC), i.e., 5.32 hours after the trigger, and obtained multiple exposures in the SDSS r', g', and i' filters. We detect the optical counterpart in our images at the position reported by Wu et al., GCN 44547. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Magnitude (AB) | | -------------- | ------ | --------------- | ------------------- | ---------------- | | 61171.68255 | r' | 5.37 | 1x400 | 18.27 +/- 0.05 | | 61171.68758 | g' | 5.49 | 1x400 | 18.54 +/- 0.06 | | 61171.69242 | i' | 5.61 | 1x360 | 18.10 +/- 0.10 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our results are consistent with other optical observations (Wu et al., GCN 44547 and GCN 44552; Sasada et al. GCN 44549; Jiang et al., GCN 44551.) The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/44561. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42688] GRB 260511B: AstroSat CZTI detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44560 SUBJECT: GRB 260511B: AstroSat CZTI detection DATE: 26/05/11 17:32:28 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 260511B which is also detected by Fermi/GBM (Fermi GBM Team, GCN 44542), SVOM/ECLAIRs (Godet et al., GCN 44543), and NuSTAR (Waratkar et. al. , GCN Circ. 44556). 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 2026-05-11 11:01:02.99 UTC. The measured peak count rate associated with the burst is 398 (+41, -36) counts/s above the background in the combined data of all quadrants, with a total of 3131 (+342, -481) counts.The local mean background count rate was 282 (+2, -4) counts/s. We measure a T90 of 39 (+3, -2) s from the cumulative CZT light curve. The source was 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 2026-05-11 11:01:02.74. The measured peak count rate associated with the burst is 1362 (+85, -90) counts/s above the background in the combined data of all quadrants, with a total of 7777 (+766, -805) counts.The local mean background count rate was 1287 (+4, -5) counts/s. We measure a T90 of 37 (+16, -3) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/516193231.75/S516193231.75_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/44560. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42687] GRB 260506B: Glowbug gamma-ray detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44559 SUBJECT: GRB 260506B: Glowbug gamma-ray detection DATE: 26/05/11 17:12:04 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 260506B, which was also detected by Fermi/GBM (GCN 44484, 44485) and AstroSat/CZTI (GCN 44503). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-06 13:07:30.824 with a duration of 20.5 s and a total significance of about 34 sigma. The lightcurve comprises a faint initial peak at ~T0+1s, a complex structure from ~T0+7s to +15s, and a peak at ~T0+21s — the peaks correspond to the brightest features seen in the GBM lightcurve. Note that data from ~T0-1s to +1s suffered from deadtime in various detectors. 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/44559. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42686] GRB 260506A: Glowbug gamma-ray detection of a short burst
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44558 SUBJECT: GRB 260506A: Glowbug gamma-ray detection of a short burst DATE: 26/05/11 16:37:58 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 the short burst GRB 260506A, which was detected by Fermi/GBM (GCN 44481). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-06 06:28:47.264 with a duration of 0.32 s and a total significance of about 19.0 sigma. The lightcurve comprises a single peak. 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/44558. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42685] GRB 260511B: J-band observations by the SYSU 80 cm infrared telescope
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44557 SUBJECT: GRB 260511B: J-band observations by the SYSU 80 cm infrared telescope DATE: 26/05/11 16:10:48 GMT FROM: lijj328(a)mail2.sysu.edu.cn Jin-Ji Li, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Yun Shi, Hao-Nan Yang, Yan Yu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team: We observed the field of GRB 260511B (SVOM burst-id sb26051102) detected by SVOM/ECLAIRs (Godet et al., GCN 44543) and Fermi (Fermi GBM team, GCN 44542), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope. Our observations started on 2026 May 11 at 13:51 UT, 2.9 hours after the GRB trigger, with a total exposure time of 1800 s in the J-band images. We clearly detect the source at the position of the optical counterpart (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552), and we measure J = 16.02 +/- 0.07 Vega mag. The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction. Further observations are planned. The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44557. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42684] GRB 260511B: NuSTAR detection of prompt emission
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44556 SUBJECT: GRB 260511B: NuSTAR detection of prompt emission DATE: 26/05/11 16:08:21 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260511B in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-05-11T11:00:31.7 UTC, shows a detection of GRB 260511B, also detected by Fermi/GBM (Fermi GBM Team, GCN 44542) and SVOM (Godet et al., GCN 44532). The NuSTAR CsI shield data are recorded at 1 Hz. We detect an initial faint burst followed by a 20-s long brighter burst consistent with the Fermi/GBM lightcurve. The peak count rate is ~2500-cps with a baseline rate of ~1000-cps during this time period. We also see marginal evidence in the signal above 100 keV in the CZT detectors. The optical counterpart candidate (Wu et al., GCN 44547) at RA = 192.57345, Dec = 4.05512 implies an offset from the NuSTAR boresight of 93-deg (i.e. from the side of the instrument) and an offset from the geocenter of 164-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260511B Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44556. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42683] GRB 260511A: NuSTAR detection of prompt emission
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44555 SUBJECT: GRB 260511A: NuSTAR detection of prompt emission DATE: 26/05/11 16:06:48 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260511A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-05-11T06:13:30.0 UTC, shows a detection of GRB 260511A, also detected by Fermi/GBM (Fermi GBM Team, GCN 44529) and SVOM (Godet et al., GCN 44532). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a ~10-s burst consistent with Fermi/GBM. The peak count rate is ~3500-cps with a baseline rate of ~1000-cps during this time period. We do not see evidence in the signal above 100 keV in the CZT detectors. The optical counterpart candidate (Akl et al., GCN 44534) at RA = 197.8996, Dec = -33.80446 implies an offset from the NuSTAR boresight of 57-deg and an offset from the geocenter of 144-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260511A Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44555. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42682] GRB 260511B: Fermi GBM Detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44554 SUBJECT: GRB 260511B: Fermi GBM Detection DATE: 26/05/11 15:37:39 GMT FROM: oliver.roberts(a)universityofgalway.ie O.J. Roberts (Uni. Of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 11:00:31.70 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511B (trigger 800190036 / 260511459), which was also detected by SVOM /ECLAIRs and MXT (Godet et al. 2026, GCN 44543), with an optical counterpart initially detected by C-GFT (Wu et al. 2026, GCN 44547). The GBM localization is consistent with the SVOM position. The angle from the Fermi LAT boresight is 100 degrees. The GBM light curve consists of a two bright emission episodes with a duration (T90) of about 41 s (50-300 keV). The time-averaged spectrum from T0-0.5 to T0+47.6 s is best fit by a Band function, with Epeak = 209 +/- 16 keV, alpha = -1.01 +/- 0.04, and beta = -2.14 +/- 0.08. The event fluence (10-1000 keV) in this time interval is (2.62 +/- 0.04) E-05 erg/cm^2. The 1-s peak photon flux measured starting from T0+33.5 s in the 10-1000 keV band is 18.3 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44554. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42681] GRB 260511C: Fermi GBM Final Real-time Localization
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44553 SUBJECT: GRB 260511C: Fermi GBM Final Real-time Localization DATE: 26/05/11 15:26:25 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 15:15:49 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511C (trigger 800205354.688558 / 260511636). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 219.4, Dec = 39.3 (J2000 degrees, equivalent to J2000 14h 37m, 39d 17'), with a statistical uncertainty of 14.9 degrees. The angle from the Fermi LAT boresight is 50.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511636/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511636/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511636/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44553. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42680] GRB 260511B: SVOM/VT optical observation with VHF data
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44552 SUBJECT: GRB 260511B: SVOM/VT optical observation with VHF data DATE: 26/05/11 15:08:48 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu, L. P. Xin, Y. L. Qiu, H. L. Li (NAOC), J. T. Palmerio (CEA/Irfu), L. Zhang (IHEP), D. Kong (GXU) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2026-05-11T11:00:32 UTC (T0), SVOM performed an automatic slew on the burst of GRB 260511B location (Godet et al.,GCN 44543; The Fermi GBM team, GCN 44542;). SVOM/VT took images of the field 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 downloaded via VHF network, the candidate (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551) was clearly detected in VT-VHF data. The candidate's magnitude is : | date-obs (UTC) | mid-time (T-T0) | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | |2026-05-11T13:14:19 | 2.23 hr | 5*50 sec | 17.83 +/- 0.01 | -- | Magnitude was not corrected for Galactic reddening. (Note:The missing magnitude is likely caused by either onboard processing interference or saturation of the bright source at early epoch.） 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/44552. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42679] GRB 260511B: TRT optical observation
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44551 SUBJECT: GRB 260511B: TRT optical observation DATE: 26/05/11 14:21:35 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), L.B. He, X. Liu, Z.P. Zhu, J. An, D. Xu (NAOC), S.Y. Fu (HUST) report: We observed the field of GRB 260511B detected by SVOM (Godet et al., GCN 44543) and Fermi (Fermi GBM team, GCN 44542), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observation started at 2026-05-11T12:52:30.855 UT, i.e., 1.867 hrs post-burst, and a series of R-band frames were obtained. The optical counterpart (Wu et al., GCN 44547; Sasada et al., GCN 44549) is clearly detected in our images with a brightness of R = 16.82 +/- 0.01 at a median time of 1.875 hrs 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/44551. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42678] GRB 260510B: SVOM/ECLAIRs refined analysis
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44550 SUBJECT: GRB 260510B: SVOM/ECLAIRs refined analysis DATE: 26/05/11 14:12:00 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> N. Dagoneau (CEA), A. Saccardi (CEA), B. Cordier (CEA), report on behalf of the SVOM/ECLAIRs team: Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 260510B (SVOM burst-id sb26051001). The burst that triggered ECLAIRs onboard (GCN 44515) consists of a multiple peaks lightcurve with a duration of T90 = 12.05 -3.49 / +2.22 s in the 4-120 keV energy band. The time-averaged spectrum (from T0-0.13s to T0+12.16s) in the energy range 5-120 keV is best fitted by a simple power-law model with a photon index -1.43 +/- 0.12. With this model,the 4-120 keV fluence is (4.604 ± 0.481)E-7 erg/cm² and the 4-120 keV photon flux is 0.93 ± 0.09 ph/cm²/s. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The SVOM/ECLAIRs point of contact for this burst is: Nicolas Dagoneau (CEA) (nicolas.dagoneau at cea.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44550. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42677] GRB 260511B : MITSuME Akeno optical afterglow candidate detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44549 SUBJECT: GRB 260511B : MITSuME Akeno optical afterglow candidate detection DATE: 26/05/11 13:40:52 GMT FROM: Mahito Sasada at Institute of Science Tokyo <sasada(a)hp.phys.titech.ac.jp> M. Sasada, I. Takahashi, H. Hagio, Y. Kubo, A. Ochi, R. Kato, N. Hosoya, J. Yonamine, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 260511B detected by SVOM (Godet et al., GCN 44543) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2026-05-11 11:11:58 UT (11.4 min after the trigger). We stacked the images taken under good conditions. We detected a candidate of the optical afterglow in all-band images at R.A. = 192.5739 deg and Dec. = 4.0554 deg, which is near the candidate position of SVOM/ECLAIRs reported by Wu et al., GCN 44547. Here we report the preliminary magnitudes of the source as follows. T0+[sec] | MID-UT | T-EXP[sec] | magnitudes --------------------------------------------------------------------------------------------------------------- 716 | 2026-05-11 11:12:28 | 60 | Rc=13.1+/-0.1, Ic=13.1+/-0.1 1337 | 2026-05-11 11:22:49 | 240 | g'=14.9+/-0.1, Rc=14.9+/-0.1, Ic=14.5+/-0.1 --------------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the trigger T-EXP: Total exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire) View this GCN Circular online at https://gcn.nasa.gov/circulars/44549. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42676] GRB 260511A: Fermi GBM Detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44548 SUBJECT: GRB 260511A: Fermi GBM Detection DATE: 26/05/11 13:25:00 GMT FROM: oliver.roberts(a)universityofgalway.ie O.J. Roberts (Uni. Of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 06:13:30.286 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511A (trigger 800172815/260511259), which was also detected by SVOM /ECLAIRs and MXT (Godet et al. 2026, GCN 44532), with an optical counterpart was initially detected by Colibri (Akl et al. 2026, GCN 44534). The angle from the Fermi LAT boresight is 118 degrees. The GBM light curve consists of a two bright emission episodes with a duration (T90) of about 14 s (50-300 keV). The time-averaged spectrum from T0-0.26 to T0+18.43 s is best fit by a Band function, with Epeak = 166 +/- 9 keV, alpha = -0.66 +/- 0.05, and beta = -2.31 +/- 0.07. The event fluence (10-1000 keV) in this time interval is (1.973 +/- 0.032) E-05 erg/cm^2. The 1-s peak photon flux measured starting from T0+2.6 s in the 10-1000 keV band is 27.3 +/- 0.5 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44548. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42675] GRB 260511B SVOM/C-GFT optical counterpart detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44547 SUBJECT: GRB 260511B SVOM/C-GFT optical counterpart detection DATE: 26/05/11 13:03:12 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), Z. Kang (CHO), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC) ，O. Go-det, M. Brunet (IRAP), L. Zhang (IHEP), D. Kong (GXU) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 260511B (SVOM burst-id sb26051102) detected by SVOM/ECLAIRs (Godet et al., GCN 44543) with LATIOS on SVOM/C-GFT. Observations start-ed at 2026-05-11T11:29:37 UTC, ~0.48 hr after the trigger. An uncatalogued optical source compared to Pan-STARRS1 is detected in our images within the ECLAIRs localization error circle. Its position is R.A., Dec. 192.57345, 4.05512 degrees: R.A. (J2000) = 12h50m17.63s Dec. (J2000) = +04d03m18.4s with an uncertainty of ~0.5 arcsec. The magnitudes is mag_r = 15.56 +/- 0.04 at 45.32 min post-trigger. The photometry was calibrated against nearby Pan-STARRS1 stars and no correction for Galactic dust extinction was applied. We propose that this source is the optical counterpart of GRB 260511B. Further analyses are ongoing. We thank the observation assistants Bo-Wen Li and Hong-Xv Xue at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/44547. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42674] EP260509a: LCO optical upper limits
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44546 SUBJECT: EP260509a: LCO optical upper limits DATE: 26/05/11 12:37:13 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), G. Corcoran (UCD), P. G. Jonker (Radboud), J. A. Chácon (PUC), F. E. Bauer (SSI and UTA), report on behalf of a larger collaboration: We observed the field of the X-ray transient EP260509a (Wang et al., GCN 44517; Fu et al., GCN 44539) using LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) and McDonald Observatory (USA) equipped with SINISTRO instruments. A series of 6x300 s exposures were taken in each of the SDSS-r and SDSS-z filters, starting at 2026-05-10 08:04:39 UT and 2026-05-10 06:53:47 UT respectively (~17.2 and 18.3 hr after the first X-ray detection). No new source is detected within or at the border of the EP/WXT uncertainty region (Wang et al., GCN 44517) 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 > 22.8 z > 21.4 These upper limits are in AB magnitudes, calibrated using nearby stars from the PanSTARRS catalogue, and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44546. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42673] GRB 260511A: UTGO H50 optical afterglow observation
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44545 SUBJECT: GRB 260511A: UTGO H50 optical afterglow observation DATE: 26/05/11 12:13:03 GMT FROM: Harrison at University of Tasmania <hgharper9962(a)gmail.com> H. Harper (UTAS), K. Siellez (UTAS), B. Emptage (UTAS), K. Hill (UTAS), T. Plunkett (UTAS), A. Cole (UTAS), J.-P. Beaulieu (IAP/UTAS) report: We observed the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Godet et al., GCN [44532](gcn.nasa.gov/circulars/44532); Fermi GBM Team, GCN [44529](gcn.nasa.gov/circulars/44529)) with the Harlingten 50cm (H50) at Greenhill Observatory, University of Tasmania (UTGO). Our observation started on 2026-05-11 at 08:58:59UT, ~165 minutes after Fermi trigger Observations. We obtained 11 x 120s exposure in the SDSS r’ filter. The optical counterpart (Jiang et al., GCN [44533](gcn.nasa.gov/circulars/44533); Akl et al. GCN [44534](gcn.nasa.gov/circulars/44534); Saccardi et al. GCN [44535](gcn.nasa.gov/circulars/44535); Zheng et al. GCN [44536](gcn.nasa.gov/circulars/44536); Wu et al., GCN [44538](gcn.nasa.gov/circulars/44538)) is clearly detected in our images at RA = 13:11:35.9244 (J2000) (197.8996850 deg) and Dec = -33:48:15.887 (J2000) (-33.8044130 deg) with an uncertainty of ~0.4 arcsec. Image subtraction was performed using STDpipe. We measured the following magnitude not corrected for Galactic extinction: r = 20.68 +/- 0.12 AB (mid time ~176minutes after trigger) Refined processing and more observations are still ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/44545. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42672] GRB 260510C: AstroSat CZTI detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44544 SUBJECT: GRB 260510C: AstroSat CZTI detection DATE: 26/05/11 11:30:38 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 260510C which is also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44520), SVOM/GRM (Gotz et al., GCN Circ. 44521), and MAXI/GSC (Iwari et al., GCN Circ. 44526). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-05-10 17:15:41.94 UTC. The measured peak count rate associated with the burst is 168 (+65, -24) counts/s above the background in the combined data of all quadrants, with a total of 1298 (+346, -375) counts. The local mean background count rate was 1125 (5, -6) counts/s. We measure a T90 of 14 (+3, -3) 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 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/44544. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42671] GRB 260511B: SVOM detection of a burst
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44543 SUBJECT: GRB 260511B: SVOM detection of a burst DATE: 26/05/11 11:25:44 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> O. Godet, M. Brunet (IRAP), L. Zhang (IHEP), D. Kong (GXU) report on behalf of the SVOM mission team: At 2026-05-11T11:00:32 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260511B (SVOM burst-id sb26051102). This transient was also detected by Fermi/GM (GCN Circular 44542). 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 15 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 45.21 in the [8-120] keV energy band over a time window of 5.10 seconds starting at 2026-05-11T11:01:00. The localization of the best alert is R.A., Dec. 192.606, 4.094 degrees: R.A. (J2000) = 12h50m25.47s Dec. (J2000) = 4d05m40.00s with a 90% confidence level (C.L.) radius of 2.63 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a multiple peak structure with a T90 duration of about 41.2 -0.6/+1.0 (5-120 keV). This burst also triggered SVOM/GRM at 2026-05-11T11:00:31 on a timescale of 0.10 seconds with an SNR of 7. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 54.2 -5.2/+5.1 s (8-1100 keV). SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-05-11T11:03:32 UTC, 180 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 192.5735, 4.0405 degrees: R.A. (J2000) = 12h50m17.65s Dec. (J2000) = 4d02m25.68s with a 90% C.L. radius of 32.02 arcseconds. This location is 3.78 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 zhangli: zhangli at 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/44543. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42670] GRB 260511B: Fermi GBM Final Real-time Localization
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44542 SUBJECT: GRB 260511B: Fermi GBM Final Real-time Localization DATE: 26/05/11 11:10:56 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 11:00:31 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511B (trigger 800190036.70394 / 260511459). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 192.2, Dec = 5.0 (J2000 degrees, equivalent to J2000 12h 48m, 5d 00'), with a statistical uncertainty of 1.4 degrees. The angle from the Fermi LAT boresight is 101.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511459/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511459/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511459/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44542. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42669] GRB 260510C: EP-FXT follow-up observation
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44541 SUBJECT: GRB 260510C: EP-FXT follow-up observation DATE: 26/05/11 10:10:16 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.-Y. Fu (HUST), A. Li (BNU), C.-Y. Wang (THU), R. Shi (PMO), Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260510C (SVOM/sb26051004, Gotz et al., GCN 44521), which also triggered Fermi-GBM (Fermi GBM team, GCN 44520) and MAXI/GSC (Iwakiri et al., GCN 44526). The follow-up obervation started at 2026-05-10T18:03:40 UTC, approximately 50 minutes after the SVOM trigger, with a total exposure time of 5370 s. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 157.9391, 2.837 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic) within the ECLAIRs error circle, which is spatially consistent with the optical counterpart (Angulo et al., GCN 44530; Li et al., GCN 44540). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value and a photon index of 2.15 (-0.07/+0.07). The derived average unabsorbed flux in the 0.5-10 keV band is 4.1 (-0.1/+0.1)×10^-11 erg s^-1 cm^-2. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44541. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42668] GRB 260510C: SVOM/VT optical counterpart confirmation
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44540 SUBJECT: GRB 260510C: SVOM/VT optical counterpart confirmation DATE: 26/05/11 09:42:07 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. We refined the analysis of SVOM/VT images (Li et al., GCN 44527) on GRB 260510C (Gotz et al., GCN 44521; Fermi GBM team, GCN 44520; Iwakiri et al., GCN 44526) with more data available. The optical counterpart found by SVOM/COLIBRÍ (Angulo et al., GCN 44530) was clearly detected in both channels of SVOM/VT. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 1.79 h VT_B 40*50 sec 21.13 +/- 0.09 mag 1.18 h VT_R 41*50 sec 19.94 +/- 0.06 mag 8.06 h VT_B 9*100 sec 22.13 +/- 0.14 mag 8.14 h VT_R 3*100 sec 20.61 +/- 0.08 mag The source showed a fading slope of -0.45 during the observations above. 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/44540. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42667] EP260509a: EP-FXT non-detection and upper limit
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44539 SUBJECT: EP260509a: EP-FXT non-detection and upper limit DATE: 26/05/11 09:39:15 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.-Y. Fu (HUST), A. Li (BNU), C.-Y. Wang (THU), R. Shi (PMO), Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT observed the field of EP260509a (detected by EP-WXT, Wang et al., GCN 44517; and followed by MASTER-Net observations, Lipunov et al., GCN 44525) for 5475 seconds starting at 2026-05-10T10:15:44, around 20.5 hours after the detection by EP-WXT. No significant X-ray source is detected within the 2.78 arcmin radius of the EP-WXT position (Wang et al., GCN 44517) to a preliminary 0.5-10 keV upper limit of 3e-14 erg/cm2/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/44539. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42666] GRB 260511A: SVOM/VT optical observation with VHF data
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44538 SUBJECT: GRB 260511A: SVOM/VT optical observation with VHF data DATE: 26/05/11 09:18:19 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), Y.N. Ma, L. P. Xin, Y. L. Qiu, H. L. Li (NAOC), L. Zhang (IHEP), D. F. Kong (GXU) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2026-05-11T06:13:32 UTC (T0), SVOM performed an automatic slew on the burst location ( Godet et al., GCN 44532; Fermi GBM team, GCN 44529;Preis et al., GCN44531). SVOM/VT took images of the field 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 downloaded via VHF network, the candidate (Jiang et al., GCN 44533; Akl et al., GCN 44534; Saccardi et al., GCN 44535; Zheng et al., GCN 44536) was clearly detected in VT-VHF data. This candidate was detected in both VT_R and VT_B, and was flagged as an uncatalogued source whose brightness faded over the course of the VT observations. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | |2026-05-11T06:26:52.000 | 13.32 min | 6*50 sec | -- | 18.61 ± 0.02 | |2026-05-11T07:42:49.000 | 89.27 min | 6*50 sec | 21.15 ± 0.08 | 19.65 ± 0.07 | Magnitudes were not corrected for Galactic reddening. ( Note: The missing VT_B magnitude is likely caused by onboard processing interference. ) The color of VT_B - VT_R = 1.5 is in line with the expectations of an event at redshift z < 4. Further follow-up is encouraged. 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/44538. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42665] Fermi GRB 260511A: Global MASTER-Net observations report
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44537 SUBJECT: Fermi GRB 260511A: Global MASTER-Net observations report DATE: 26/05/11 08:30:44 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260511A ( Fermi GBM team, GCN 44529) errorbox 5184 sec after notice time and 5215 sec after trigger time at 2026-05-11 07:40:25 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 64 deg. The sun altitude is -45.2 deg. MASTER-OAGH robotic telescope located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260511A errorbox 6822 sec after notice time and 6853 sec after trigger time at 2026-05-11 08:07:44 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 77 deg. The sun altitude is -39.6 deg. The galactic latitude b = 29 deg., longitude l = 310 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3306895 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 5246 | 2026-05-11 07:40:25 | MASTER-OAFA | (13h 10m 55.69s , -33d 35m 27.4s) | C | 60 | 19.5 | 5306 | 2026-05-11 07:40:25 | MASTER-OAFA | (13h 10m 55.69s , -33d 35m 27.5s) | C | 180 | 20.0 | Coadd 5366 | 2026-05-11 07:40:25 | MASTER-OAFA | (13h 10m 55.68s , -33d 35m 27.5s) | C | 300 | 20.0 | Coadd 5636 | 2026-05-11 07:40:25 | MASTER-OAFA | (13h 10m 55.69s , -33d 35m 27.5s) | C | 840 | 20.5 | Coadd 5322 | 2026-05-11 07:41:42 | MASTER-OAFA | (13h 10m 55.74s , -33d 37m 08.5s) | C | 60 | 19.4 | 5400 | 2026-05-11 07:43:00 | MASTER-OAFA | (13h 10m 59.00s , -33d 35m 34.7s) | C | 60 | 19.2 | 5475 | 2026-05-11 07:44:14 | MASTER-OAFA | (13h 10m 53.33s , -33d 36m 24.9s) | C | 60 | 19.5 | 5535 | 2026-05-11 07:44:14 | MASTER-OAFA | (13h 10m 53.33s , -33d 36m 24.9s) | C | 180 | 20.0 | Coadd 5554 | 2026-05-11 07:45:34 | MASTER-OAFA | (13h 10m 53.06s , -33d 35m 26.1s) | C | 60 | 19.3 | 5631 | 2026-05-11 07:46:51 | MASTER-OAFA | (13h 10m 59.98s , -33d 36m 26.7s) | C | 60 | 19.4 | 5708 | 2026-05-11 07:48:07 | MASTER-OAFA | (13h 10m 53.23s , -33d 37m 28.2s) | C | 60 | 19.3 | 5768 | 2026-05-11 07:48:07 | MASTER-OAFA | (13h 10m 53.23s , -33d 37m 28.1s) | C | 180 | 19.9 | Coadd 5781 | 2026-05-11 07:49:21 | MASTER-OAFA | (13h 11m 00.12s , -33d 37m 27.8s) | C | 60 | 19.3 | 5858 | 2026-05-11 07:50:37 | MASTER-OAFA | (13h 10m 56.28s , -33d 35m 51.6s) | C | 60 | 19.4 | 5935 | 2026-05-11 07:51:54 | MASTER-OAFA | (13h 10m 56.39s , -33d 37m 16.0s) | C | 60 | 19.3 | 5995 | 2026-05-11 07:51:54 | MASTER-OAFA | (13h 10m 56.39s , -33d 37m 16.0s) | C | 180 | 19.9 | Coadd 6012 | 2026-05-11 07:53:11 | MASTER-OAFA | (13h 10m 58.63s , -33d 35m 39.5s) | C | 60 | 19.3 | 6087 | 2026-05-11 07:54:27 | MASTER-OAFA | (13h 10m 52.96s , -33d 36m 32.8s) | C | 60 | 19.2 | 6163 | 2026-05-11 07:55:43 | MASTER-OAFA | (13h 10m 53.42s , -33d 35m 33.6s) | C | 60 | 19.2 | 6223 | 2026-05-11 07:55:43 | MASTER-OAFA | (13h 10m 53.41s , -33d 35m 33.6s) | C | 180 | 19.9 | Coadd 6239 | 2026-05-11 07:56:59 | MASTER-OAFA | (13h 10m 59.31s , -33d 36m 35.2s) | C | 60 | 19.2 | 6313 | 2026-05-11 07:58:13 | MASTER-OAFA | (13h 10m 52.93s , -33d 37m 36.1s) | C | 60 | 19.2 | 6391 | 2026-05-11 07:59:31 | MASTER-OAFA | (13h 11m 00.57s , -33d 37m 29.1s) | C | 60 | 19.2 | 6451 | 2026-05-11 07:59:31 | MASTER-OAFA | (13h 11m 00.57s , -33d 37m 29.2s) | C | 180 | 19.8 | Coadd 6464 | 2026-05-11 08:00:44 | MASTER-OAFA | (13h 10m 57.03s , -33d 35m 54.4s) | C | 60 | 19.1 | 6541 | 2026-05-11 08:02:01 | MASTER-OAFA | (13h 10m 57.13s , -33d 37m 22.1s) | C | 60 | 19.1 | 6617 | 2026-05-11 08:03:16 | MASTER-OAFA | (13h 10m 59.39s , -33d 35m 57.2s) | C | 60 | 19.2 | 6677 | 2026-05-11 08:03:16 | MASTER-OAFA | (13h 10m 59.40s , -33d 35m 57.2s) | C | 180 | 19.8 | Coadd 6692 | 2026-05-11 08:04:32 | MASTER-OAFA | (13h 10m 53.41s , -33d 36m 41.7s) | C | 60 | 19.2 | 6766 | 2026-05-11 08:05:46 | MASTER-OAFA | (13h 10m 54.96s , -33d 35m 42.7s) | C | 60 | 19.0 | 6840 | 2026-05-11 08:07:00 | MASTER-OAFA | (13h 10m 59.75s , -33d 36m 43.9s) | C | 60 | 19.1 | 6900 | 2026-05-11 08:07:00 | MASTER-OAFA | (13h 10m 59.75s , -33d 36m 43.9s) | C | 180 | 19.7 | Coadd 6884 | 2026-05-11 08:07:44 | MASTER-OAGH | (13h 11m 20.18s , -33d 45m 22.0s) | C | 60 | 18.2 | 6944 | 2026-05-11 08:07:44 | MASTER-OAGH | (13h 11m 20.19s , -33d 45m 21.9s) | C | 180 | 19.0 | Coadd 6884 | 2026-05-11 08:07:44 | MASTER-OAGH | (13h 09m 49.25s , -33d 12m 34.9s) | C | 60 | 18.8 | 6944 | 2026-05-11 08:07:44 | MASTER-OAGH | (13h 09m 49.25s , -33d 12m 34.9s) | C | 180 | 19.5 | Coadd 6917 | 2026-05-11 08:08:17 | MASTER-OAFA | (13h 10m 54.11s , -33d 37m 45.2s) | C | 60 | 19.0 | 6953 | 2026-05-11 08:08:52 | MASTER-OAGH | (13h 11m 26.44s , -33d 45m 03.2s) | C | 60 | 18.4 | 6953 | 2026-05-11 08:08:52 | MASTER-OAGH | (13h 09m 55.72s , -33d 12m 16.6s) | C | 60 | 18.8 | 6990 | 2026-05-11 08:09:30 | MASTER-OAFA | (13h 11m 01.38s , -33d 37m 35.3s) | C | 60 | 19.0 | 7021 | 2026-05-11 08:10:01 | MASTER-OAGH | (13h 11m 22.36s , -33d 43m 39.0s) | C | 60 | 18.3 | 7021 | 2026-05-11 08:10:01 | MASTER-OAGH | (13h 09m 51.74s , -33d 10m 53.0s) | C | 60 | 18.7 | 7066 | 2026-05-11 08:10:46 | MASTER-OAFA | (13h 10m 57.89s , -33d 36m 10.1s) | C | 60 | 19.1 | 7126 | 2026-05-11 08:10:46 | MASTER-OAFA | (13h 10m 57.89s , -33d 36m 10.1s) | C | 180 | 19.6 | Coadd 7091 | 2026-05-11 08:11:11 | MASTER-OAGH | (13h 11m 22.26s , -33d 45m 14.7s) | C | 60 | 18.2 | 7151 | 2026-05-11 08:11:11 | MASTER-OAGH | (13h 11m 22.26s , -33d 45m 14.7s) | C | 180 | 18.9 | Coadd 7091 | 2026-05-11 08:11:11 | MASTER-OAGH | (13h 09m 51.67s , -33d 12m 28.6s) | C | 60 | 18.5 | 7151 | 2026-05-11 08:11:11 | MASTER-OAGH | (13h 09m 51.67s , -33d 12m 28.5s) | C | 180 | 19.4 | Coadd 7143 | 2026-05-11 08:12:03 | MASTER-OAFA | (13h 10m 58.00s , -33d 37m 28.1s) | C | 60 | 19.1 | 7161 | 2026-05-11 08:12:21 | MASTER-OAGH | (13h 11m 25.40s , -33d 43m 36.4s) | C | 60 | 18.2 | 7161 | 2026-05-11 08:12:21 | MASTER-OAGH | (13h 09m 54.89s , -33d 10m 50.9s) | C | 60 | 18.6 | 7217 | 2026-05-11 08:13:17 | MASTER-OAFA | (13h 11m 02.04s , -33d 35m 52.5s) | C | 60 | 18.9 | 7231 | 2026-05-11 08:13:31 | MASTER-OAGH | (13h 11m 18.85s , -33d 44m 19.2s) | C | 60 | 18.2 | 7231 | 2026-05-11 08:13:31 | MASTER-OAGH | (13h 09m 48.37s , -33d 11m 33.8s) | C | 60 | 18.6 | 7294 | 2026-05-11 08:14:34 | MASTER-OAFA | (13h 10m 54.24s , -33d 36m 51.2s) | C | 60 | 18.9 | 7354 | 2026-05-11 08:14:34 | MASTER-OAFA | (13h 10m 54.24s , -33d 36m 51.1s) | C | 180 | 19.6 | Coadd 7300 | 2026-05-11 08:14:40 | MASTER-OAGH | (13h 11m 19.17s , -33d 43m 17.9s) | C | 60 | 18.3 | 7360 | 2026-05-11 08:14:40 | MASTER-OAGH | (13h 11m 19.17s , -33d 43m 17.9s) | C | 180 | 18.8 | Coadd 7300 | 2026-05-11 08:14:40 | MASTER-OAGH | (13h 09m 48.71s , -33d 10m 32.7s) | C | 60 | 18.6 | 7360 | 2026-05-11 08:14:40 | MASTER-OAGH | (13h 09m 48.71s , -33d 10m 32.5s) | C | 180 | 19.2 | Coadd 7370 | 2026-05-11 08:15:49 | MASTER-OAGH | (13h 11m 25.51s , -33d 44m 17.0s) | C | 60 | 18.2 | 7370 | 2026-05-11 08:15:49 | MASTER-OAGH | (13h 09m 55.12s , -33d 11m 31.7s) | C | 60 | 18.6 | 7371 | 2026-05-11 08:15:51 | MASTER-OAFA | (13h 10m 55.41s , -33d 35m 51.5s) | C | 60 | 18.9 | 7438 | 2026-05-11 08:16:58 | MASTER-OAGH | (13h 11m 19.31s , -33d 45m 15.5s) | C | 60 | 18.1 | 7438 | 2026-05-11 08:16:58 | MASTER-OAGH | (13h 09m 48.97s , -33d 12m 30.0s) | C | 60 | 18.5 | 7449 | 2026-05-11 08:17:09 | MASTER-OAFA | (13h 11m 00.93s , -33d 36m 53.0s) | C | 60 | 18.9 | 7507 | 2026-05-11 08:18:07 | MASTER-OAGH | (13h 11m 24.61s , -33d 45m 00.1s) | C | 60 | 18.2 | 7567 | 2026-05-11 08:18:07 | MASTER-OAGH | (13h 11m 24.62s , -33d 44m 60.0s) | C | 180 | 18.8 | Coadd 7507 | 2026-05-11 08:18:07 | MASTER-OAGH | (13h 09m 54.39s , -33d 12m 14.6s) | C | 60 | 18.6 | 7567 | 2026-05-11 08:18:07 | MASTER-OAGH | (13h 09m 54.39s , -33d 12m 14.6s) | C | 180 | 19.4 | Coadd 7523 | 2026-05-11 08:18:23 | MASTER-OAFA | (13h 10m 55.99s , -33d 37m 53.5s) | C | 60 | 18.9 | 7583 | 2026-05-11 08:18:23 | MASTER-OAFA | (13h 10m 55.99s , -33d 37m 53.5s) | C | 180 | 19.6 | Coadd 7577 | 2026-05-11 08:19:17 | MASTER-OAGH | (13h 11m 21.64s , -33d 43m 38.5s) | C | 60 | 18.0 | 7577 | 2026-05-11 08:19:17 | MASTER-OAGH | (13h 09m 51.53s , -33d 10m 53.2s) | C | 60 | 18.5 | 7598 | 2026-05-11 08:19:38 | MASTER-OAFA | (13h 11m 00.75s , -33d 37m 31.6s) | C | 60 | 18.8 | 7647 | 2026-05-11 08:20:26 | MASTER-OAGH | (13h 11m 21.58s , -33d 44m 48.6s) | C | 60 | 18.1 | 7647 | 2026-05-11 08:20:26 | MASTER-OAGH | (13h 09m 51.49s , -33d 12m 02.7s) | C | 60 | 18.6 | 7676 | 2026-05-11 08:20:55 | MASTER-OAFA | (13h 10m 58.71s , -33d 36m 14.3s) | C | 60 | 18.9 | 7722 | 2026-05-11 08:21:42 | MASTER-OAGH | (13h 11m 24.04s , -33d 43m 24.1s) | C | 60 | 18.1 | 7782 | 2026-05-11 08:21:42 | MASTER-OAGH | (13h 11m 24.03s , -33d 43m 24.0s) | C | 180 | 18.6 | Coadd 7722 | 2026-05-11 08:21:42 | MASTER-OAGH | (13h 09m 54.00s , -33d 10m 38.6s) | C | 60 | 18.5 | 7782 | 2026-05-11 08:21:42 | MASTER-OAGH | (13h 09m 54.00s , -33d 10m 38.5s) | C | 180 | 19.1 | Coadd 7752 | 2026-05-11 08:22:12 | MASTER-OAFA | (13h 10m 58.85s , -33d 37m 45.7s) | C | 60 | 18.9 | 7792 | 2026-05-11 08:22:51 | MASTER-OAGH | (13h 11m 17.55s , -33d 44m 06.7s) | C | 60 | 18.0 | 7792 | 2026-05-11 08:22:52 | MASTER-OAGH | (13h 09m 47.49s , -33d 11m 21.0s) | C | 60 | 18.3 | 7826 | 2026-05-11 08:23:26 | MASTER-OAFA | (13h 11m 02.50s , -33d 36m 10.9s) | C | 60 | 18.9 | 7861 | 2026-05-11 08:24:01 | MASTER-OAGH | (13h 11m 18.56s , -33d 43m 05.0s) | C | 60 | 18.0 | 7861 | 2026-05-11 08:24:01 | MASTER-OAGH | (13h 09m 48.54s , -33d 10m 19.5s) | C | 60 | 18.4 | 7903 | 2026-05-11 08:24:43 | MASTER-OAFA | (13h 10m 56.54s , -33d 36m 58.6s) | C | 60 | 18.9 | 7931 | 2026-05-11 08:25:11 | MASTER-OAGH | (13h 11m 24.27s , -33d 44m 03.0s) | C | 60 | 18.1 | 7931 | 2026-05-11 08:25:11 | MASTER-OAGH | (13h 09m 54.32s , -33d 11m 17.1s) | C | 60 | 18.5 | 8000 | 2026-05-11 08:26:20 | MASTER-OAGH | (13h 11m 17.71s , -33d 45m 00.9s) | C | 60 | 18.1 | 8000 | 2026-05-11 08:26:20 | MASTER-OAGH | (13h 09m 47.79s , -33d 12m 14.9s) | C | 60 | 18.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44537. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42664] GRB 260511A: KAIT optical afterglow observations
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44536 SUBJECT: GRB 260511A: KAIT optical afterglow observations DATE: 26/05/11 07:56:17 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 260511A (Fermi GBM Team, GCN Circ. 44529; Godet et al., GCN Circ. 44532) starting at 06:15:44, 132 seconds after SVOM trigger. Observations were performed in 3 x 3 tiling mode, and a set of clear (roughly R) filter images were obtained. The first image covered the optical afterglow (Jiang et al., GCN 44533; Akl et al. GCN 44534 Saccardi et al., GCN 44535) was at 06:16:57, 205 seconds after the burst, in which we measure the afterglow brightness to be 16.7 +/- 0.1 mag (Vega) calibrated to APASS catalog. Observations are on going. View this GCN Circular online at https://gcn.nasa.gov/circulars/44536. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42663] GRB 260511A: LCO optical afterglow detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44535 SUBJECT: GRB 260511A: LCO optical afterglow detection DATE: 26/05/11 07:20:44 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), L. Zhang (IHEP), D. Kong (GXU), report on behalf of the SVOM mission team: We observed the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Godet et al., GCN 44532; Fermi GBM Team, GCN 44529) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-11 at 06:24:46 UT (about 11 min after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical counterpart (Jiang et al., GCN 44533; Akl et al. GCN 44534) 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 = 18.88 +/- 0.02 AB (mid-time 21 min after the trigger); z = 18.05 +/- 0.04 AB (mid-time 15 min after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44535. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42662] GRB 260511A: SVOM/COLIBRÍ (FM-GFT) optical counterpart
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44534 SUBJECT: GRB 260511A: SVOM/COLIBRÍ (FM-GFT) optical counterpart DATE: 26/05/11 07:11:33 GMT FROM: Dalya Akl at New York University Abu Dhabi <dka2010(a)nyu.edu> Dalya Akl (NYUAD), Camila Angulo (UNAM), Alan M. Watson, Rosa L. Becerra (UNAM), (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM), L. Zhang (IHEP), and D. Kong (GXU) report: We imaged the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Fermi GBM Team, GCN Circ. 44529; Godet et al., GCN Circ. 44532) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-11 06:14:45 to 06:27:52 UTC (from 72 seconds to 14 minutes after the trigger) and obtained 520 seconds of simultaneous exposure in r and z filters. 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 a bright, fading source at: RA(J2000) = 13:11:35.90 = 197.89960 degrees Dec(J2000) = -33:48:16.1 = -33.80446 degrees with an uncertainty of 0.5 arcsec. The preliminary, unsubtracted magnitudes derived for that source are: r = 16.86 +/- 0.01, z = 16.43 +/- 0.01. This position is 3.25 arcmin and 0.87 arcmin away from the ECLAIRs and MXT positions, respectively, released via notices. 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/44534. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42661] GRB 260511A: TRT optical counterpart detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44533 SUBJECT: GRB 260511A: TRT optical counterpart detection DATE: 26/05/11 06:45:10 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), J. An, L.B. He, X. Liu, Z.P. Zhu, D. Xu (NAOC) report: We observed the field of GRB 260511A detected by Fermi GBM (GCN 44529) and SVOM (GCN 44532) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT) located at Cerro Tololo Inter-American Observatory, Chile (CTO). We obtained a series of frames in the Sloan r-band. An uncatalogued and varing source is detected near the SVOM MXT error circle at coordinates R.A. (J2000) = 13:11:35.94 (197.8997 deg) Dec. (J2000) = -33:48:16.3 (-33.8045 deg) with an uncertainty of ~ 1.0 arcsec. The source had r ~ 17.9 mag at a median time of 2026-05-11T06:19:37.771, calibrated with Legacy DR10 and not corrected for Galactic extinction. No NEO would be at the above position at the observational time by checking MPC. We thus think the source could be the optical counterpart of GRB 260511A. View this GCN Circular online at https://gcn.nasa.gov/circulars/44533. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42660] GRB 260511A: SVOM detection of a bright burst
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44532 SUBJECT: GRB 260511A: SVOM detection of a bright burst DATE: 26/05/11 06:37:49 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> O. Godet, M. Brunet (IRAP), L. Zhang (IHEP), D. Kong (GXU) report on behalf of the SVOM mission team: At 2026-05-11T06:13:32 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260511A (SVOM burst-id sb26051101). This transient was also detected by Fermi/GM (GCN Circular 44529). 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 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 55.22 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2026-05-11T06:13:32. The localization of the best alert is R.A., Dec. 197.929, -33.853 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.44 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a single/multiple broad/narrow peak structure with a T90 duration of about 13.5 (-0.4/ +0.6) s in the 5-120 keV. This burst also triggered SVOM/GRM at 2026-05-11T06:13:30 on a timescale of 1 seconds with an SNR of 12.10. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 14.3 (-0.4 / +0.8) s in the 8-1100 keV. SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-05-11T06:16:38 UTC, 186 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 197.9145, -33.8120 degrees: R.A. (J2000) = 13h11m39.48s Dec. (J2000) = -33d48m43.09s with a 90% C.L. radius of 39.05 arcseconds. This location is 2.54 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 zhangli: zhangli at 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/44532. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42659] GRB 260511A: BALROG localization (Fermi Trigger 800172815 / GRB 260511259)
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44531 SUBJECT: GRB 260511A: BALROG localization (Fermi Trigger 800172815 / GRB 260511259) DATE: 26/05/11 06:37:48 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 800172815 at 06:13:30 on 11 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) = 197.3 deg Decl.(2000.0) = -33.7 deg The 1 sigma statistical error radius is 1.3 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260511259/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260511259/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260511259/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44531. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42658] GRB 260510C: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44530 SUBJECT: GRB 260510C: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate DATE: 26/05/11 06:35:13 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Camila Angulo (UNAM), Dalya Akl (NYUAD), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) and Andrea Saccardi (CEA/Irfu ) report: We imaged the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260510C (Fermi GBM Team, GCN Circ. 44520; Gotz et al., GCN Circ. 44521) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-11 04:46 to 05:39 UTC (from 11.54 to 12.44 hours after the trigger) and obtained 24 minutes of simultaneous exposure in r and z filters. 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 an uncatalogued source 1.06 arcmin away from the MXT position and slightly outside the 90% uncertainty region reported by SVOM, but still inside the ECLAIRs region (Gotz et al., GCN Circ. 44521), at: RA(J2000) = 10:31:45:49 = 157.9394 degrees Dec(J2000) = +02:50:15.5 = 2.83763 degrees with an uncertainty of 0.5 arcsec. The preliminary unsubtracted magnitudes derived for that source are: r = 21.32 + /- 0.03, z = 20.23 + /- 0.03. We suggest this is the optical counterpart of the GRB. The position of the candidate is consistent with a faint galaxy with reported magnitudes of g = 23.61 +/- 0.10, r = 23.49 +/- 0.14, i = 23.02 +/- 0.12 and z = 23.03 +/- 0.21 and a photo-z of =0.89 +/- 0.63 in the DESI Legacy Survey catalog (Dey et al. 2019), so our candidate is two magnitudes brighter than the galaxy. We suggest this galaxy may be the host. 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/44530. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42657] GRB 260511A: Fermi GBM Final Real-time Localization
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44529 SUBJECT: GRB 260511A: Fermi GBM Final Real-time Localization DATE: 26/05/11 06:22:11 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 06:13:30 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511A (trigger 800172815.286154 / 260511259). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 199.1, Dec = -33.0 (J2000 degrees, equivalent to J2000 13h 16m, -33d 00'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 117.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511259/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511259/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511259/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44529. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42656] GRB 260510B: SVOM/VT optical upper limits
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44528 SUBJECT: GRB 260510B: SVOM/VT optical upper limits DATE: 26/05/11 03:48:57 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 automatic observations of GRB260510B triggered by SVOM/ECLAIRs (sb26051001, Saccardi et al., GCN 44515). The burst was also detected at sub-threshold level by Fermi-GBM (Palafox et al., GCN 44524). VT observations started at 2026-05-10T12:23:54 UTC, 274 seconds post trigger, 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 44515), 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 | 3-sigma upper limit 23.3 min VT_B 45*50 sec > 23.0 mag 23.3 min VT_R 45*50 sec > 23.0 mag Our non-detection is consistent with the non-detections reported by LCO (Saccardi et al., GCN 44518) and GOTO (Ramsay et al., GCN 44522). 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/44528. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42655] GRB 260510C: SVOM/VT optical upper limits
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44527 SUBJECT: GRB 260510C: SVOM/VT optical upper limits DATE: 26/05/11 01:03:32 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 automatic observations of GRB260510C triggered by SVOM/ECLAIRs (sb26051004, Gotz et al., GCN 44521). The burst was also detected by Fermi GBM (Fermi GBM team, GCN 44520) and MAXI/GSC (Iwakiri et al., GCN 44526). The VT observations started at 2026-05-10T17:18:48 UTC, i.e., 304 seconds post trigger, 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/MXT (Gotz et al., GCN 44521) and SVOM/ECLAIRs (Gotz et al., GCN 44521), 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 | 3 sigma upper limit 1.10 h VT_B 47*50 sec > 23.2 mag 1.18 h VT_R 41*50 sec > 23.1 mag Further analyses are ongoing. 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/44527. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42654] EP260507a: further Liverpool Telescope observations
by GCN Circulars 11 May '26

11 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 EP260507a (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 42653] GRB 260510C: MAXI/GSC detection
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44526 SUBJECT: GRB 260510C: MAXI/GSC detection DATE: 26/05/10 21:42:33 GMT FROM: Wataru Iwakiri at Chiba University <iwakiri.wataru.buz(a)gmail.com> W. Iwakiri (Chiba U.),　M. Serino(AGU), H. Negoro, M. Nakajima, K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), S. Ogawa (TUS) report on behalf of the MAXI team: At 17:13:42 UT on 2026 May 10, the MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source. The trigger time and position are consistent with GRB 260510C reported by the Fermi team (GCN #44520) and the SVOM team (GCN #44521). The X-ray flux averaged over the scan was 338 +/- 36 mCrab (4.0-10.0 keV, 1-sigma error). Assuming that the source flux was constant over the transit, we obtain the source position at: (R.A., Dec) = (157.881 deg, 2.824 deg) = (10 31 31, +02 49 26) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.17 deg and 0.14 deg, respectively. The roll angle of the long axis is 73.0 deg counterclockwise from the north. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (157.267, 2.290) deg = (10 29 04, +02 17 24) (J2000) (157.477, 2.117) deg = (10 29 54, +02 07 01) (J2000) (158.505, 3.360) deg = (10 34 01, +03 21 35) (J2000) (158.295, 3.533) deg = (10 33 10, +03 31 58) (J2000) There was no significant excess flux in the previous transit at 15:40 UT with an upper limit of 20 mCrab. View this GCN Circular online at https://gcn.nasa.gov/circulars/44526. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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