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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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