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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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