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[vsnet-grb-info 42780] GRB 260515A: CrAO ZTSh BVRI optical observations
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44652 SUBJECT: GRB 260515A: CrAO ZTSh BVRI optical observations DATE: 26/05/16 23:52:00 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), A. Pozanenko (IKI), V. Rumyantsev (CrAO), N. Pankov (IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN. We observed the field of the GRB 260515A (Brunet et al., GCN 44622; Wang et al., GCN 44642; Frederiks et al., GCN 44647) with the Shajn 2.6-meter telescope (ZTSh) of the Crimean Astrophysical Observatory (CrAO). We obtained series of 120 s exposures in BVRI filters starting on 2026-05-15 22:10:11 UT (about 3 hours after trigger). The OT (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Malesani et al., GCN 44629; Dennefeld et al., GCN 44633; Li et al., GCN 44634; Antier et al., GCN 44643; Pérez-Fournon et al., GCN 44645; Dimple et al., GCN 44646) is clearly detected in the stacked frames. Details of the photometry is the following. Start_UT, t_mid-T0, exp, filter, mag, err, UL(3 sigma) 2026-05-15T22:54:33 4.79 15*120 B 21.53 0.04 23.9 2026-05-15T22:56:41 4.75 13*120 V 21.30 0.05 23.7 2026-05-15T22:10:11 3.12 5*120 R 20.56 0.04 23.4 2026-05-15T22:20:40 3.29 5*120 R 20.57 0.04 23.4 2026-05-15T22:31:09 3.46 5*120 R 20.65 0.04 23.5 2026-05-15T22:41:44 3.66 6*120 R 20.64 0.03 23.6 2026-05-15T22:56:41 4.26 7*120 R 20.87 0.03 23.7 2026-05-15T23:58:56 5.35 8*120 R 21.03 0.04 23.4 2026-05-15T23:00:57 4.89 15*120 I 20.75 0.05 22.8 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44652. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42779] Fermi GRB 260516C: Global MASTER-Net observations report
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44651 SUBJECT: Fermi GRB 260516C: Global MASTER-Net observations report DATE: 26/05/16 22:15:42 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 260516C ( Fermi GBM team, GCN 44648) errorbox 31 sec after notice time and 63 sec after trigger time at 2026-05-16 19:35:42 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 27 deg. The sun altitude is -48.6 deg. The galactic latitude b = 1 deg., longitude l = 293 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3319181 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 68 | 2026-05-16 19:35:42 | MASTER-SAAO | (11h 28m 29.01s , -56d 15m 46.9s) | C | 10 | 17.3 | 68 | 2026-05-16 19:35:42 | MASTER-SAAO | (11h 31m 55.60s , -56d 31m 08.1s) | C | 10 | 17.5 | 102 | 2026-05-16 19:36:11 | MASTER-SAAO | (11h 28m 28.89s , -56d 15m 46.7s) | C | 20 | 17.7 | 102 | 2026-05-16 19:36:11 | MASTER-SAAO | (11h 31m 55.42s , -56d 31m 08.1s) | C | 20 | 18.0 | 155 | 2026-05-16 19:36:58 | MASTER-SAAO | (11h 22m 44.28s , -59d 38m 52.0s) | C | 30 | 17.1 | 200 | 2026-05-16 19:36:58 | MASTER-SAAO | (11h 22m 44.28s , -59d 38m 52.0s) | C | 120 | 17.4 | 155 | 2026-05-16 19:36:58 | MASTER-SAAO | (11h 26m 31.14s , -59d 54m 11.9s) | C | 30 | 17.4 | 200 | 2026-05-16 19:36:58 | MASTER-SAAO | (11h 26m 31.15s , -59d 54m 11.8s) | C | 120 | 17.8 | 209 | 2026-05-16 19:37:47 | MASTER-SAAO | (11h 22m 44.18s , -59d 38m 51.3s) | C | 40 | 17.1 | 209 | 2026-05-16 19:37:47 | MASTER-SAAO | (11h 26m 31.02s , -59d 54m 11.2s) | C | 40 | 17.5 | 273 | 2026-05-16 19:38:46 | MASTER-SAAO | (11h 22m 44.06s , -59d 38m 50.3s) | C | 50 | 17.1 | 273 | 2026-05-16 19:38:46 | MASTER-SAAO | (11h 26m 30.89s , -59d 54m 10.4s) | C | 50 | 17.5 | 347 | 2026-05-16 19:39:55 | MASTER-SAAO | (11h 22m 43.88s , -59d 38m 48.6s) | C | 60 | 17.3 | 347 | 2026-05-16 19:39:55 | MASTER-SAAO | (11h 26m 30.80s , -59d 54m 08.8s) | C | 60 | 17.6 | 626 | 2026-05-16 19:44:34 | MASTER-SAAO | (11h 24m 24.54s , -59d 37m 32.6s) | C | 60 | 17.4 | 686 | 2026-05-16 19:44:34 | MASTER-SAAO | (11h 24m 24.54s , -59d 37m 32.6s) | C | 180 | 17.5 | 626 | 2026-05-16 19:44:34 | MASTER-SAAO | (11h 28m 06.66s , -59d 53m 08.5s) | C | 60 | 17.7 | 686 | 2026-05-16 19:44:34 | MASTER-SAAO | (11h 28m 06.70s , -59d 53m 08.6s) | C | 180 | 17.9 | 705 | 2026-05-16 19:45:53 | MASTER-SAAO | (11h 24m 24.42s , -59d 37m 32.0s) | C | 60 | 17.4 | 705 | 2026-05-16 19:45:53 | MASTER-SAAO | (11h 28m 06.55s , -59d 53m 07.8s) | C | 60 | 17.6 | 784 | 2026-05-16 19:47:13 | MASTER-SAAO | (11h 24m 24.31s , -59d 37m 30.4s) | C | 60 | 17.4 | 784 | 2026-05-16 19:47:13 | MASTER-SAAO | (11h 28m 06.41s , -59d 53m 06.3s) | C | 60 | 17.6 | 863 | 2026-05-16 19:48:31 | MASTER-SAAO | (11h 24m 24.22s , -59d 37m 28.7s) | C | 60 | 17.3 | 863 | 2026-05-16 19:48:31 | MASTER-SAAO | (11h 28m 06.25s , -59d 53m 04.6s) | C | 60 | 17.6 | 1850 | 2026-05-16 20:04:28 | MASTER-SAAO | (11h 24m 04.79s , -59d 36m 36.8s) | C | 120 | 17.5 | 1850 | 2026-05-16 20:04:28 | MASTER-SAAO | (11h 27m 46.76s , -59d 52m 15.2s) | C | 120 | 17.8 | 2004 | 2026-05-16 20:07:02 | MASTER-SAAO | (11h 37m 54.80s , -59d 44m 27.2s) | C | 120 | 17.6 | 2004 | 2026-05-16 20:07:02 | MASTER-SAAO | (11h 41m 37.73s , -60d 00m 05.4s) | C | 120 | 17.8 | 2157 | 2026-05-16 20:09:35 | MASTER-SAAO | (11h 37m 55.16s , -59d 43m 25.3s) | C | 120 | 17.6 | 2157 | 2026-05-16 20:09:35 | MASTER-SAAO | (11h 41m 37.91s , -59d 59m 03.3s) | C | 120 | 17.9 | 2310 | 2026-05-16 20:12:09 | MASTER-SAAO | (11h 37m 59.95s , -59d 44m 22.1s) | C | 120 | 17.6 | 2310 | 2026-05-16 20:12:09 | MASTER-SAAO | (11h 41m 42.75s , -60d 00m 00.1s) | C | 120 | 17.8 | 2463 | 2026-05-16 20:14:41 | MASTER-SAAO | (11h 38m 07.66s , -57d 45m 21.9s) | C | 120 | 18.2 | 2463 | 2026-05-16 20:14:41 | MASTER-SAAO | (11h 41m 38.03s , -58d 01m 00.6s) | C | 120 | 18.5 | 2616 | 2026-05-16 20:17:15 | MASTER-SAAO | (11h 38m 13.31s , -57d 45m 08.0s) | C | 120 | 18.2 | 2616 | 2026-05-16 20:17:15 | MASTER-SAAO | (11h 41m 43.61s , -58d 00m 46.9s) | C | 120 | 18.5 | 2769 | 2026-05-16 20:19:47 | MASTER-SAAO | (11h 38m 10.50s , -57d 43m 18.7s) | C | 120 | 18.2 | 2769 | 2026-05-16 20:19:47 | MASTER-SAAO | (11h 41m 40.63s , -57d 58m 57.8s) | C | 120 | 18.5 | 2922 | 2026-05-16 20:22:21 | MASTER-SAAO | (11h 22m 13.66s , -57d 44m 42.9s) | C | 120 | 17.7 | 2922 | 2026-05-16 20:22:21 | MASTER-SAAO | (11h 25m 44.03s , -58d 00m 21.7s) | C | 120 | 17.9 | 3076 | 2026-05-16 20:24:54 | MASTER-SAAO | (11h 22m 15.81s , -57d 42m 54.4s) | C | 120 | 17.8 | 3076 | 2026-05-16 20:24:54 | MASTER-SAAO | (11h 25m 46.05s , -57d 58m 33.5s) | C | 120 | 18.0 | 3229 | 2026-05-16 20:27:28 | MASTER-SAAO | (11h 22m 10.17s , -57d 43m 35.0s) | C | 120 | 17.8 | 3229 | 2026-05-16 20:27:28 | MASTER-SAAO | (11h 25m 40.54s , -57d 59m 14.2s) | C | 120 | 18.0 | 3383 | 2026-05-16 20:30:01 | MASTER-SAAO | (11h 13m 44.65s , -61d 42m 13.8s) | C | 120 | 18.2 | 3383 | 2026-05-16 20:30:01 | MASTER-SAAO | (11h 17m 41.85s , -61d 57m 51.5s) | C | 120 | 18.6 | 3536 | 2026-05-16 20:32:34 | MASTER-SAAO | (11h 13m 50.07s , -61d 43m 09.6s) | C | 120 | 18.2 | 3536 | 2026-05-16 20:32:34 | MASTER-SAAO | (11h 17m 47.42s , -61d 58m 47.3s) | C | 120 | 18.7 | 3689 | 2026-05-16 20:35:07 | MASTER-SAAO | (11h 13m 44.81s , -61d 44m 05.2s) | C | 120 | 18.2 | 3689 | 2026-05-16 20:35:07 | MASTER-SAAO | (11h 17m 42.30s , -61d 59m 42.9s) | C | 120 | 18.7 | 3842 | 2026-05-16 20:37:41 | MASTER-SAAO | (11h 24m 03.00s , -59d 37m 40.6s) | C | 120 | 17.5 | 3842 | 2026-05-16 20:37:41 | MASTER-SAAO | (11h 27m 45.41s , -59d 53m 19.5s) | C | 120 | 17.6 | 3995 | 2026-05-16 20:40:14 | MASTER-SAAO | (11h 23m 59.91s , -59d 35m 52.6s) | C | 120 | 17.5 | 3995 | 2026-05-16 20:40:14 | MASTER-SAAO | (11h 27m 42.09s , -59d 51m 31.5s) | C | 120 | 17.6 | 4149 | 2026-05-16 20:42:48 | MASTER-SAAO | (11h 23m 59.68s , -59d 37m 31.9s) | C | 120 | 17.5 | 4149 | 2026-05-16 20:42:48 | MASTER-SAAO | (11h 27m 42.06s , -59d 53m 11.0s) | C | 120 | 17.6 | 4303 | 2026-05-16 20:45:21 | MASTER-SAAO | (11h 24m 02.31s , -59d 35m 54.7s) | C | 120 | 17.5 | 4303 | 2026-05-16 20:45:21 | MASTER-SAAO | (11h 27m 44.51s , -59d 51m 33.8s) | C | 120 | 17.6 | 4456 | 2026-05-16 20:47:54 | MASTER-SAAO | (11h 27m 39.44s , -59d 52m 02.8s) | C | 120 | 17.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44651. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42778] SVOM GRB260516.86: Global MASTER-Net observations report
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44650 SUBJECT: SVOM GRB260516.86: Global MASTER-Net observations report DATE: 26/05/16 21:14:44 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-Tavrida robotic telescope [1] located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the SVOM GRB260516.86 (trigger No 1778963908,15h 35m 23.71s , +06d 22m 21.4s, R=0.1937) errorbox 767 sec after notice time and 1684 sec after trigger time at 2026-05-16 21:06:32 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 39 deg. The sun altitude is -25.7 deg. The galactic latitude b = 45 deg., longitude l = 13 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3319281 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 1714 | 2026-05-16 21:06:32 | MASTER-Tavrida | (15h 35m 16.63s , +06d 23m 55.5s) | C | 60 | 18.6 | 1783 | 2026-05-16 21:07:41 | MASTER-Tavrida | (15h 35m 20.66s , +06d 25m 06.4s) | C | 60 | 18.6 | 1852 | 2026-05-16 21:08:50 | MASTER-Tavrida | (15h 35m 12.84s , +06d 24m 31.1s) | C | 60 | 18.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44650. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42777] GRB 260516D: SVOM possible detection of a short faint burst
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44649 SUBJECT: GRB 260516D: SVOM possible detection of a short faint burst DATE: 26/05/16 21:08:26 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP), H. Goto (RIKEN/CEA), A. Saccardi (CEA/Irfu) report on behalf of the SVOM mission team: At 2026-05-16T20:39:50 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260516D (SVOM burst-id sb26051616). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 6.73 in the [5-20] keV energy band over a time window of 81.92 seconds starting at 2026-05-16T20:38:28. The localization of the best alert is R.A., Dec. 233.849, 6.373 degrees: R.A. (J2000) = 15h35m23.71s Dec. (J2000) = 6d22m21.34s with a 90% confidence level (C.L.) radius of 11.62 arcmin (including systematic error of 2 arcmin added in quadrature). Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst. A Svom ToO has been scheduled. 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/44649. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42776] GRB 260516C: Fermi GBM Final Real-time Localization
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44648 SUBJECT: GRB 260516C: Fermi GBM Final Real-time Localization DATE: 26/05/16 19:45:10 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 19:34:38 UT on 16 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260516C (trigger 800652883.931176 / 260516816). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 172.6, Dec = -59.9 (J2000 degrees, equivalent to J2000 11h 30m, -59d 53'), with a statistical uncertainty of 3.2 degrees. The angle from the Fermi LAT boresight is 36.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516816/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516816/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260516816/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44648. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42775] Konus-Wind detection of GRB 260515A
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44647 SUBJECT: Konus-Wind detection of GRB 260515A DATE: 26/05/16 19:07:11 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: A long-duration GRB 260515A (SVOM detection: Brunet et al., GCN 44622) was detected by Konus-Wind (KW)in the waiting mode at T0=T0(KW)~19:08:19UT. A Bayesian block analysis of the KW data in the 20-1500 keV band reveals a ~8 sigma count rate increase in the interval from ~T0+0.4 s to ~T0+9.3 s from the SVOM detection time. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260515A/ Modeling the time-integrated spectrum of the burst by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.37 (-0.17, + 0.17) and Ep = 95(-9,+10) keV. In the 10 keV -10 MeV band, standard for the KW analysis, the burst fluence is (7.70 ± 0.81)x10^-6 erg/cm^2 and the 2.944 s peak energy flux is (1.47 ± 0.22)x10^-7 erg/cm^2/s. Assuming the redshift z=0.764 (Malesani et al., GCN 44629) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (1.25 ± 0.15)x10^52 erg, the isotropic peak luminosity L_iso to (5.70 ± 0.85)x10^50 erg/s, and the rest-frame peak spectral energy Ep,z to (168 ± 18) keV. With the obtained estimates, GRB 260515A is consistent with 68% prediction bands of both 'Amati' relation and 90% prediction bands of 'Yonetoku' relation 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/GRB260515A/GRB260515A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44647. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42774] GRB 260515A: Liverpool Telescope optical detection
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44646 SUBJECT: GRB 260515A: Liverpool Telescope optical detection DATE: 26/05/16 14:32:40 GMT FROM: Dimple at University of Birmingham <dimplepanchal96(a)gmail.com> Dimple (U. Birmingham), B. P. Gompertz (U. Birmingham), P. O'Brien (U. Leicester), D. O'Neill (U. Birmingham) and D. B. Malesani (DAWN/NBI and Radboud) report on behalf of a larger collaboration: We conducted follow-up observations of GRB 260515A (Brunet et al., GCN 44622) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 22:42:40 UT on 2026-05-15, ~3.57 hr after the burst, and consisted of 5 x 200 s exposures in each of the SDSS g and i filters. We detect the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628, Dennefeld et al., GCN 44633; Li et al., GCN 44634, Antier et al., GCN 44643) in both filters, and measure an AB magnitude of g = 21.06 ± 0.04. Magnitudes are calibrated against nearby Pan-STARRS stars and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44646. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42773] GRB 260515A: LCO optical counterpart detection
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44645 SUBJECT: GRB 260515A: LCO optical counterpart detection DATE: 26/05/16 14:16:15 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) Following the detection of the SVOM/ECLAIRs GRB 260515A (Brunet et al., GCN 44622), detected also in Einstein Probe FXT follow-up observations (Wang et al., GCN 44642), we observed the field with one of the three Las Cumbres Observatory (LCO) 1-m telescopes, equipped with Sinistro cameras, located at the LCO node at Sutherland Observatory, South Africa. The observation, a single exposure of 180 sec in the SDSS r' filter, started on 2026-05-15 at 21:17:54 UT, 2.16 hours after the SVOM trigger. The optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Malesani et al., GCN 44629; Dennefeld et al., GCN 44633; Li et al., GCN 44634; and Antier et al., GCN 44643) with redshift of z = 0.764 (Malesani et al., GCN 44629) is clearly detected in our image with an AB magnitude of r' = 20.32 +/- 0.10, calibrated against the PanSTARRS-1 DR2 catalog and not corrected for Galactic extinction. 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/44645. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42772] Fermi Gamma-ray Burst Monitor trigger 800627191/260516518 is not a GRB
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44644 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 800627191/260516518 is not a GRB DATE: 26/05/16 14:08:33 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> U. Pathak (IITB) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 800627191/260516518 at 12:26:26.60 UT on 16 May 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/44644. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42771] GRB 260515A: SVOM/COLIBRÍ (FM-GFT) further optical observations
by GCN Circulars 16 May '26

16 May '26

TITLE: GCN CIRCULAR NUMBER: 44643 SUBJECT: GRB 260515A: SVOM/COLIBRÍ (FM-GFT) further optical observations DATE: 26/05/16 11:06:13 GMT FROM: antier(a)ijclab.in2p3.fr Sarah Antier (IJCLAB), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Dalya Akl (NYUAD), William H. Lee (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), 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) and Antonio de Ugarte Postigo (LAM), and Andrea Saccardi (CEA/Irfu) report: We imaged the field of the SVOM/ECLAIRs GRB 260515A (M. Brunet et al., GCN Circ. 44622) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-16 08:25 to 09:49 UTC (from to 13.3 hours after the trigger) and obtained 128 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 Saccardi et al. (GCN Circ. 44624) with preliminary unsubtracted magnitudes of: r = 21.78 +/- 0.02 z = 21.50 +/- 0.05 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/44643. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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