- vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 42494] GRB 260415A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44372 SUBJECT: GRB 260415A: CALET Gamma-Ray Burst Monitor detection DATE: 26/04/21 09:56:37 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> A. Yoshida, T. Sakamoto, 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 260415A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN #44299; Insight-HXMT/HE detection: Ren et al., GCN #44311) at 04:43:58.34 UTC on 15 April 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1460263432/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a double-peaked structure starting at T-1.5 s, peaking at T+30.1 s, and ending at T+41.1 s. The T90 and T50 durations measured with the SGM data are 36.2 +/- 1.5 s and 19.9 +/- 1.9 s (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1460263432/ 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/44372. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42493] GRB 260415B: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44371 SUBJECT: GRB 260415B: CALET Gamma-Ray Burst Monitor detection DATE: 26/04/21 09:51:16 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> P. S. Marrocchesi (U of Siena), A. Yoshida, T. Sakamoto, 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), and the CALET collaboration: The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 260415B (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN #44300; NuSTAR detection: Waratkar et al., GCN #44302; Glowbug gamma-ray detection: Woolf et al., GCN #44313) at 02:28:55.55 UTC on 15 April 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1460255329/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure starting at T-2.9 s, peaking at T+22.1 s, and ending at T+124.5 s. The T90 and T50 durations measured with the SGM data are 111.6 +/- 1.8 s and 50.7 +/- 1.0 s (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1460255329/ 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/44371. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42492] Fermi GRB 260421C: Global MASTER-Net observations report
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44370 SUBJECT: Fermi GRB 260421C: Global MASTER-Net observations report DATE: 26/04/21 09:30:49 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260421C ( Fermi GBM team, GCN 44369) errorbox 165 sec after notice time and 186 sec after trigger time at 2026-04-21 08:28:26 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 51 deg. The sun altitude is -43.9 deg. The galactic latitude b = 19 deg., longitude l = 96 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3263342 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 217 | 2026-04-21 08:28:26 | MASTER-OAGH | (19h 25m 37.26s , +63d 45m 12.4s) | C | 60 | 19.6 | 217 | 2026-04-21 08:28:26 | MASTER-OAGH | (19h 28m 03.53s , +63d 11m 30.5s) | C | 60 | 19.8 | 290 | 2026-04-21 08:29:39 | MASTER-OAGH | (19h 43m 37.39s , +63d 44m 07.3s) | C | 60 | 19.6 | 290 | 2026-04-21 08:29:39 | MASTER-OAGH | (19h 46m 02.78s , +63d 10m 22.7s) | C | 60 | 19.9 | 518 | 2026-04-21 08:33:28 | MASTER-OAGH | (19h 26m 38.22s , +59d 56m 08.4s) | C | 60 | 20.0 | 518 | 2026-04-21 08:33:28 | MASTER-OAGH | (19h 28m 49.30s , +59d 22m 23.7s) | C | 60 | 20.2 | 736 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 39m 52.48s , +63d 57m 57.9s) | C | 120 | 19.9 | 856 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 39m 52.48s , +63d 57m 57.9s) | C | 360 | 20.5 | Coadd 736 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 42m 20.57s , +63d 24m 11.2s) | C | 120 | 20.1 | 856 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 42m 20.57s , +63d 24m 11.2s) | C | 360 | 20.5 | Coadd 936 | 2026-04-21 08:39:55 | MASTER-OAGH | (19h 39m 52.89s , +63d 57m 53.5s) | C | 120 | 19.9 | 936 | 2026-04-21 08:39:55 | MASTER-OAGH | (19h 42m 21.02s , +63d 24m 06.6s) | C | 120 | 20.1 | 1066 | 2026-04-21 08:42:05 | MASTER-OAGH | (19h 39m 58.99s , +63d 56m 50.1s) | C | 120 | 20.0 | 1066 | 2026-04-21 08:42:05 | MASTER-OAGH | (19h 42m 27.17s , +63d 23m 03.5s) | C | 120 | 20.2 | 1197 | 2026-04-21 08:44:16 | MASTER-OAGH | (19h 39m 53.32s , +63d 57m 47.2s) | C | 120 | 20.0 | 1197 | 2026-04-21 08:44:16 | MASTER-OAGH | (19h 42m 21.81s , +63d 24m 00.3s) | C | 120 | 20.2 | 1328 | 2026-04-21 08:46:27 | MASTER-OAGH | (19h 39m 59.23s , +63d 56m 43.3s) | C | 120 | 19.9 | 1328 | 2026-04-21 08:46:27 | MASTER-OAGH | (19h 42m 27.64s , +63d 22m 56.8s) | C | 120 | 20.2 | 2193 | 2026-04-21 09:01:22 | MASTER-OAGH | (19h 26m 48.80s , +59d 56m 20.2s) | C | 60 | 19.9 | 2193 | 2026-04-21 09:01:22 | MASTER-OAGH | (19h 29m 01.44s , +59d 22m 30.8s) | C | 60 | 20.0 | 2326 | 2026-04-21 09:03:35 | MASTER-OAGH | (19h 17m 11.76s , +61d 50m 25.1s) | C | 60 | 19.7 | 2326 | 2026-04-21 09:03:35 | MASTER-OAGH | (19h 19m 32.38s , +61d 16m 36.3s) | C | 60 | 19.9 | 2397 | 2026-04-21 09:04:46 | MASTER-OAGH | (19h 34m 03.19s , +61d 49m 16.1s) | C | 60 | 19.5 | 2397 | 2026-04-21 09:04:46 | MASTER-OAGH | (19h 36m 23.31s , +61d 15m 26.3s) | C | 60 | 19.9 | 2557 | 2026-04-21 09:06:57 | MASTER-OAGH | (19h 51m 54.15s , +63d 51m 04.9s) | C | 120 | 19.9 | 2557 | 2026-04-21 09:06:57 | MASTER-OAGH | (19h 54m 23.17s , +63d 17m 13.8s) | C | 120 | 20.0 | 2688 | 2026-04-21 09:09:07 | MASTER-OAGH | (19h 52m 00.00s , +63d 50m 02.0s) | C | 120 | 19.9 | 2688 | 2026-04-21 09:09:07 | MASTER-OAGH | (19h 54m 29.04s , +63d 16m 12.0s) | C | 120 | 19.9 | 2819 | 2026-04-21 09:11:18 | MASTER-OAGH | (19h 50m 19.75s , +64d 50m 59.2s) | C | 120 | 19.6 | 2819 | 2026-04-21 09:11:18 | MASTER-OAGH | (19h 52m 54.24s , +64d 17m 09.7s) | C | 120 | 19.6 | 2950 | 2026-04-21 09:13:29 | MASTER-OAGH | (19h 50m 26.43s , +64d 49m 56.1s) | C | 120 | 19.8 | 2950 | 2026-04-21 09:13:29 | MASTER-OAGH | (19h 53m 00.91s , +64d 16m 07.5s) | C | 120 | 19.8 | 3125 | 2026-04-21 09:16:54 | MASTER-OAGH | (19h 26m 53.60s , +59d 55m 26.9s) | C | 60 | 19.4 | 3125 | 2026-04-21 09:16:54 | MASTER-OAGH | (19h 29m 07.76s , +59d 21m 41.7s) | C | 60 | 19.4 | 3197 | 2026-04-21 09:18:06 | MASTER-OAGH | (19h 17m 13.13s , +61d 50m 46.4s) | C | 60 | 19.4 | 3197 | 2026-04-21 09:18:06 | MASTER-OAGH | (19h 19m 35.44s , +61d 17m 01.7s) | C | 60 | 19.5 | 3305 | 2026-04-21 09:19:24 | MASTER-OAGH | (19h 36m 06.37s , +65d 49m 10.5s) | C | 120 | 19.7 | 3305 | 2026-04-21 09:19:24 | MASTER-OAGH | (19h 38m 48.49s , +65d 15m 24.8s) | C | 120 | 19.8 | 3436 | 2026-04-21 09:21:35 | MASTER-OAGH | (19h 36m 10.81s , +65d 50m 43.9s) | C | 120 | 19.3 | 3436 | 2026-04-21 09:21:35 | MASTER-OAGH | (19h 38m 53.00s , +65d 16m 58.7s) | C | 120 | 19.5 | 3567 | 2026-04-21 09:23:46 | MASTER-OAGH | (19h 24m 08.88s , +65d 49m 56.4s) | C | 120 | 19.5 | 3567 | 2026-04-21 09:23:46 | MASTER-OAGH | (19h 26m 51.43s , +65d 16m 11.7s) | 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/44370. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42491] GRB 260421C: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44369 SUBJECT: GRB 260421C: Fermi GBM Final Real-time Localization DATE: 26/04/21 08:35:58 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 08:25:19 UT on 21 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260421C (trigger 798452724.59066 / 260421351). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 295.0, Dec = 64.2 (J2000 degrees, equivalent to J2000 19h 40m, 64d 12'), with a statistical uncertainty of 3.1 degrees. The angle from the Fermi LAT boresight is 59.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421351/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421351/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421351/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44369. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42490] GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44368 SUBJECT: GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115 DATE: 26/04/21 06:41:33 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> B. Schneider (LAM), A. Saccardi (CEA/Irfu), N. Habeeb (Leicester), R. Brivio (INAF/OAB), A. L. Thakur (INAF/IAPS), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of the Stargate collaboration: We observed the optical counterpart (He et al., GCN 44363; Sanchez-Alvarez, GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366) of the SVOM and Fermi GRB 260421B (Zhao et al., GCN 44362; Fermi GBM Team, GCN 44360) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-25000 AA, and consist of 4 exposures of 600 s each. The observation mid time was 05:39 UT on 2026 April 21 (1.42 hr after the SVOM/ECLAIRs trigger). In a 5-s acquisition image (taken 61 min after the SVOM/ECLAIRs trigger), the afterglow is detected with a magnitude r = 20.43 +/- 0.05 AB, calibrated against the single Pan-STARRS object lying in our field of view, and not corrected for Galactic extinction. In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. At the blue edge of the spectrum, we identify a broad trough at around 3786 AA, likely due to H I Lyman-alpha. Multiple absorption lines are also detected, which we interpret as due to, among others, S II, Si II, O I, Si II*, C II, C II*, Si IV, C IV, Fe II, Fe II*, Mg II, all at a common redshift z = 2.115. We consider this to be the redshift of GRB 260421B. We acknowledge the excellent expert support from the observing staff in Paranal, in particular Francisco Caceres and Matias Jones. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) We thank the COLIBRÍ (FM-GFT) team for alerting us of the afterglow prior to their GCN release. View this GCN Circular online at https://gcn.nasa.gov/circulars/44368. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42489] Fermi GRB 260421B: Global MASTER-Net observations report
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44367 SUBJECT: Fermi GRB 260421B: Global MASTER-Net observations report DATE: 26/04/21 05:45:38 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260421B ( Fermi GBM team, GCN 44360) errorbox 93 sec after notice time and 126 sec after trigger time at 2026-04-21 04:15:27 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 56 deg. The sun altitude is -28.9 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260421B errorbox 867 sec after notice time and 900 sec after trigger time at 2026-04-21 04:28:21 UT, with upper limit up to 20.2 mag. The observations began at zenith distance = 21 deg. The sun altitude is -70.7 deg. The galactic latitude b = 45 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=3262990 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 142 | 2026-04-21 04:15:27 | MASTER-OAGH | (12h 53m 10.93s , -17d 20m 23.6s) | C | 30 | 18.4 | 177 | 2026-04-21 04:15:27 | MASTER-OAGH | (12h 53m 10.93s , -17d 20m 23.5s) | C | 100 | 19.1 | Coadd 181 | 2026-04-21 04:16:07 | MASTER-OAGH | (12h 53m 17.82s , -17d 20m 17.3s) | C | 30 | 18.5 | 226 | 2026-04-21 04:16:47 | MASTER-OAGH | (12h 53m 13.89s , -17d 18m 44.5s) | C | 40 | 18.4 | 282 | 2026-04-21 04:17:37 | MASTER-OAGH | (12h 53m 13.81s , -17d 20m 10.6s) | C | 50 | 18.7 | 352 | 2026-04-21 04:17:37 | MASTER-OAGH | (12h 53m 13.81s , -17d 20m 10.6s) | C | 190 | 19.7 | Coadd 347 | 2026-04-21 04:18:38 | MASTER-OAGH | (12h 53m 17.74s , -17d 19m 02.7s) | C | 60 | 18.8 | 427 | 2026-04-21 04:19:48 | MASTER-OAGH | (12h 53m 11.54s , -17d 19m 39.5s) | C | 80 | 19.2 | 538 | 2026-04-21 04:21:28 | MASTER-OAGH | (12h 35m 06.04s , -17d 47m 57.6s) | C | 100 | 19.2 | 538 | 2026-04-21 04:21:28 | MASTER-OAGH | (12h 36m 24.29s , -18d 21m 51.5s) | C | 100 | 19.4 | 980 | 2026-04-21 04:28:11 | MASTER-OAGH | (12h 39m 45.91s , -17d 46m 54.8s) | P- | 180 | 17.5 | 980 | 2026-04-21 04:28:11 | MASTER-OAGH | (12h 41m 04.22s , -18d 20m 54.9s) | P| | 180 | 17.7 | 1160 | 2026-04-21 04:28:11 | MASTER-OAGH | (12h 41m 04.22s , -18d 20m 54.8s) | P| | 540 | 18.8 | Coadd 930 | 2026-04-21 04:28:21 | MASTER-OAFA | (12h 40m 14.08s , -17d 24m 25.2s) | C | 60 | 20.0 | 996 | 2026-04-21 04:29:26 | MASTER-OAFA | (12h 40m 14.11s , -17d 24m 23.6s) | C | 60 | 20.1 | 1061 | 2026-04-21 04:30:32 | MASTER-OAFA | (12h 40m 14.15s , -17d 24m 22.0s) | C | 60 | 20.1 | 1170 | 2026-04-21 04:31:21 | MASTER-OAGH | (12h 39m 52.24s , -17d 46m 46.8s) | P- | 180 | 17.7 | 1170 | 2026-04-21 04:31:21 | MASTER-OAGH | (12h 41m 10.67s , -18d 20m 47.4s) | P| | 180 | 18.1 | 1127 | 2026-04-21 04:31:38 | MASTER-OAFA | (12h 40m 14.20s , -17d 24m 20.9s) | C | 60 | 20.2 | 1193 | 2026-04-21 04:32:44 | MASTER-OAFA | (12h 40m 14.23s , -17d 24m 19.6s) | C | 60 | 20.1 | 1259 | 2026-04-21 04:33:49 | MASTER-OAFA | (12h 40m 14.26s , -17d 24m 18.2s) | C | 60 | 20.1 | 1361 | 2026-04-21 04:34:31 | MASTER-OAGH | (12h 39m 49.24s , -17d 45m 09.3s) | P- | 180 | 17.7 | 1361 | 2026-04-21 04:34:31 | MASTER-OAGH | (12h 41m 07.78s , -18d 19m 10.2s) | P| | 180 | 18.3 | 1325 | 2026-04-21 04:34:56 | MASTER-OAFA | (12h 40m 14.30s , -17d 24m 16.6s) | C | 60 | 20.0 | 1391 | 2026-04-21 04:36:01 | MASTER-OAFA | (12h 40m 14.36s , -17d 24m 15.7s) | C | 60 | 20.2 | 1456 | 2026-04-21 04:37:07 | MASTER-OAFA | (12h 40m 14.39s , -17d 24m 14.3s) | C | 60 | 20.1 | 1552 | 2026-04-21 04:37:43 | MASTER-OAGH | (12h 39m 49.10s , -17d 46m 59.8s) | P- | 180 | 17.9 | 1552 | 2026-04-21 04:37:43 | MASTER-OAGH | (12h 41m 07.75s , -18d 21m 00.3s) | P| | 180 | 18.3 | 1522 | 2026-04-21 04:38:13 | MASTER-OAFA | (12h 40m 14.44s , -17d 24m 13.3s) | C | 60 | 20.2 | 1588 | 2026-04-21 04:39:18 | MASTER-OAFA | (12h 40m 14.44s , -17d 24m 12.1s) | C | 60 | 20.1 | 1653 | 2026-04-21 04:40:24 | MASTER-OAFA | (12h 40m 14.48s , -17d 24m 10.8s) | C | 60 | 20.1 | 1742 | 2026-04-21 04:40:53 | MASTER-OAGH | (12h 39m 51.19s , -17d 45m 34.9s) | P- | 180 | 17.7 | 1742 | 2026-04-21 04:40:53 | MASTER-OAGH | (12h 41m 09.87s , -18d 19m 35.1s) | P| | 180 | 18.4 | 1720 | 2026-04-21 04:41:30 | MASTER-OAFA | (12h 40m 14.54s , -17d 24m 09.9s) | C | 60 | 20.1 | 1785 | 2026-04-21 04:42:36 | MASTER-OAFA | (12h 40m 14.54s , -17d 24m 08.9s) | C | 60 | 20.1 | 1850 | 2026-04-21 04:43:41 | MASTER-OAFA | (12h 40m 14.57s , -17d 24m 07.9s) | C | 60 | 20.0 | 1874 | 2026-04-21 04:44:05 | MASTER-OAGH | (12h 34m 22.11s , -17d 48m 09.2s) | C | 60 | 19.5 | 1874 | 2026-04-21 04:44:05 | MASTER-OAGH | (12h 35m 41.12s , -18d 22m 06.8s) | C | 60 | 19.7 | 1917 | 2026-04-21 04:44:48 | MASTER-OAFA | (12h 40m 14.60s , -17d 24m 07.3s) | C | 60 | 20.1 | 1946 | 2026-04-21 04:45:17 | MASTER-OAGH | (12h 25m 58.60s , -17d 47m 08.9s) | C | 60 | 19.3 | 1946 | 2026-04-21 04:45:17 | MASTER-OAGH | (12h 27m 17.78s , -18d 21m 05.4s) | C | 60 | 19.7 | 1982 | 2026-04-21 04:45:53 | MASTER-OAFA | (12h 40m 14.65s , -17d 24m 05.9s) | C | 60 | 20.1 | 2047 | 2026-04-21 04:46:58 | MASTER-OAFA | (12h 40m 14.66s , -17d 24m 04.9s) | C | 60 | 20.1 | 2113 | 2026-04-21 04:48:04 | MASTER-OAFA | (12h 40m 14.68s , -17d 24m 03.9s) | C | 60 | 20.1 | 2179 | 2026-04-21 04:49:09 | MASTER-OAFA | (12h 40m 14.72s , -17d 24m 02.9s) | C | 60 | 20.2 | 2245 | 2026-04-21 04:50:15 | MASTER-OAFA | (12h 40m 14.76s , -17d 24m 02.1s) | C | 60 | 20.2 | 2311 | 2026-04-21 04:51:22 | MASTER-OAFA | (12h 40m 14.77s , -17d 24m 00.8s) | C | 60 | 20.1 | 2376 | 2026-04-21 04:52:27 | MASTER-OAFA | (12h 40m 14.82s , -17d 24m 00.2s) | C | 60 | 20.2 | 2442 | 2026-04-21 04:53:32 | MASTER-OAFA | (12h 40m 14.86s , -17d 23m 59.2s) | C | 60 | 20.2 | 2474 | 2026-04-21 04:54:05 | MASTER-OAGH | (12h 34m 21.59s , -17d 48m 11.5s) | C | 60 | 19.4 | 2474 | 2026-04-21 04:54:05 | MASTER-OAGH | (12h 35m 40.80s , -18d 22m 07.1s) | C | 60 | 19.8 | 2508 | 2026-04-21 04:54:39 | MASTER-OAFA | (12h 40m 14.86s , -17d 23m 58.4s) | C | 60 | 20.1 | 2546 | 2026-04-21 04:55:17 | MASTER-OAGH | (12h 25m 58.36s , -17d 49m 11.4s) | C | 60 | 19.5 | 2546 | 2026-04-21 04:55:17 | MASTER-OAGH | (12h 27m 17.73s , -18d 23m 06.0s) | C | 60 | 19.7 | 2574 | 2026-04-21 04:55:44 | MASTER-OAFA | (12h 40m 14.88s , -17d 23m 57.6s) | C | 60 | 20.0 | 2640 | 2026-04-21 04:56:50 | MASTER-OAFA | (12h 40m 14.94s , -17d 23m 56.9s) | C | 60 | 20.1 | 2706 | 2026-04-21 04:57:57 | MASTER-OAFA | (12h 40m 14.96s , -17d 23m 55.9s) | C | 60 | 20.0 | 2771 | 2026-04-21 04:59:02 | MASTER-OAFA | (12h 40m 15.00s , -17d 23m 54.7s) | C | 60 | 20.0 | 2837 | 2026-04-21 05:00:08 | MASTER-OAFA | (12h 40m 15.01s , -17d 23m 53.9s) | C | 60 | 19.9 | 2903 | 2026-04-21 05:01:14 | MASTER-OAGH | (12h 34m 23.48s , -19d 42m 11.3s) | C | 60 | 18.8 | 2903 | 2026-04-21 05:01:14 | MASTER-OAGH | (12h 35m 43.55s , -20d 16m 06.9s) | C | 60 | 19.0 | 2903 | 2026-04-21 05:01:14 | MASTER-OAFA | (12h 40m 15.04s , -17d 23m 53.2s) | C | 60 | 20.0 | 2968 | 2026-04-21 05:02:19 | MASTER-OAFA | (12h 40m 15.06s , -17d 23m 52.6s) | C | 60 | 20.0 | 2974 | 2026-04-21 05:02:25 | MASTER-OAGH | (12h 42m 52.05s , -19d 41m 12.6s) | C | 60 | 18.6 | 2974 | 2026-04-21 05:02:25 | MASTER-OAGH | (12h 44m 12.00s , -20d 15m 09.4s) | C | 60 | 19.1 | 3034 | 2026-04-21 05:03:25 | MASTER-OAFA | (12h 40m 15.10s , -17d 23m 51.8s) | C | 60 | 20.0 | 3100 | 2026-04-21 05:04:31 | MASTER-OAFA | (12h 40m 15.14s , -17d 23m 51.1s) | C | 60 | 19.9 | 3106 | 2026-04-21 05:04:37 | MASTER-OAGH | (12h 34m 20.33s , -17d 47m 13.7s) | C | 60 | 19.1 | 3106 | 2026-04-21 05:04:37 | MASTER-OAGH | (12h 35m 39.73s , -18d 21m 08.6s) | C | 60 | 19.2 | 3166 | 2026-04-21 05:05:37 | MASTER-OAFA | (12h 40m 15.18s , -17d 23m 50.7s) | C | 60 | 20.0 | 3177 | 2026-04-21 05:05:47 | MASTER-OAGH | (12h 26m 02.37s , -17d 48m 11.9s) | C | 60 | 19.3 | 3177 | 2026-04-21 05:05:47 | MASTER-OAGH | (12h 27m 21.94s , -18d 22m 05.5s) | C | 60 | 19.6 | 3232 | 2026-04-21 05:06:42 | MASTER-OAFA | (12h 40m 15.19s , -17d 23m 50.1s) | C | 60 | 20.0 | 3298 | 2026-04-21 05:07:49 | MASTER-OAFA | (12h 40m 15.22s , -17d 23m 49.4s) | C | 60 | 20.1 | 3307 | 2026-04-21 05:07:58 | MASTER-OAGH | (12h 34m 24.99s , -15d 54m 14.3s) | C | 60 | 19.5 | 3307 | 2026-04-21 05:07:58 | MASTER-OAGH | (12h 35m 43.97s , -16d 28m 07.6s) | C | 60 | 19.6 | 3363 | 2026-04-21 05:08:54 | MASTER-OAFA | (12h 40m 15.24s , -17d 23m 48.3s) | C | 60 | 20.0 | 3378 | 2026-04-21 05:09:08 | MASTER-OAGH | (12h 42m 36.90s , -15d 55m 16.1s) | C | 60 | 19.3 | 3378 | 2026-04-21 05:09:08 | MASTER-OAGH | (12h 43m 55.82s , -16d 29m 09.9s) | C | 60 | 19.6 | 3429 | 2026-04-21 05:09:59 | MASTER-OAFA | (12h 40m 15.26s , -17d 23m 47.3s) | C | 60 | 20.0 | 3495 | 2026-04-21 05:11:05 | MASTER-OAFA | (12h 40m 15.29s , -17d 23m 46.6s) | C | 60 | 20.0 | 3509 | 2026-04-21 05:11:20 | MASTER-OAGH | (12h 34m 22.74s , -19d 41m 12.5s) | C | 60 | 19.6 | 3509 | 2026-04-21 05:11:20 | MASTER-OAGH | (12h 35m 43.08s , -20d 15m 06.9s) | C | 60 | 19.9 | 3560 | 2026-04-21 05:12:11 | MASTER-OAFA | (12h 40m 15.29s , -17d 23m 46.2s) | C | 60 | 20.0 | 3581 | 2026-04-21 05:12:32 | MASTER-OAGH | (12h 42m 57.79s , -19d 42m 14.3s) | C | 60 | 19.6 | 3581 | 2026-04-21 05:12:32 | MASTER-OAGH | (12h 44m 18.06s , -20d 16m 09.5s) | C | 60 | 19.7 | 3626 | 2026-04-21 05:13:17 | MASTER-OAFA | (12h 40m 15.31s , -17d 23m 45.6s) | C | 60 | 20.0 | 3692 | 2026-04-21 05:14:23 | MASTER-OAFA | (12h 40m 15.34s , -17d 23m 45.0s) | C | 60 | 20.0 | 3719 | 2026-04-21 05:14:50 | MASTER-OAGH | (12h 34m 21.06s , -17d 47m 14.4s) | C | 60 | 19.6 | 3719 | 2026-04-21 05:14:50 | MASTER-OAGH | (12h 35m 40.72s , -18d 21m 07.3s) | C | 60 | 19.9 | 3758 | 2026-04-21 05:15:29 | MASTER-OAFA | (12h 40m 15.36s , -17d 23m 44.7s) | C | 60 | 20.1 | 3791 | 2026-04-21 05:16:02 | MASTER-OAGH | (12h 26m 01.87s , -17d 48m 12.2s) | C | 60 | 19.3 | 3791 | 2026-04-21 05:16:02 | MASTER-OAGH | (12h 27m 21.65s , -18d 22m 03.8s) | C | 60 | 19.3 | 3823 | 2026-04-21 05:16:34 | MASTER-OAFA | (12h 40m 15.39s , -17d 23m 44.0s) | C | 60 | 20.1 | 3889 | 2026-04-21 05:17:40 | MASTER-OAFA | (12h 40m 15.43s , -17d 23m 43.4s) | C | 60 | 20.1 | 3930 | 2026-04-21 05:18:21 | MASTER-OAGH | (12h 34m 17.86s , -15d 53m 14.7s) | C | 60 | 19.4 | 3930 | 2026-04-21 05:18:21 | MASTER-OAGH | (12h 35m 37.05s , -16d 27m 06.0s) | C | 60 | 19.5 | 3955 | 2026-04-21 05:18:45 | MASTER-OAFA | (12h 40m 15.45s , -17d 23m 42.8s) | C | 60 | 20.2 | 4002 | 2026-04-21 05:19:32 | MASTER-OAGH | (12h 42m 42.14s , -15d 54m 17.4s) | C | 60 | 18.6 | 4002 | 2026-04-21 05:19:32 | MASTER-OAGH | (12h 44m 01.28s , -16d 28m 08.9s) | C | 60 | 18.9 | 4021 | 2026-04-21 05:19:51 | MASTER-OAFA | (12h 40m 15.46s , -17d 23m 42.1s) | C | 60 | 20.1 | 4087 | 2026-04-21 05:20:58 | MASTER-OAFA | (12h 40m 15.48s , -17d 23m 41.6s) | C | 60 | 20.1 | 4141 | 2026-04-21 05:21:51 | MASTER-OAGH | (12h 34m 22.53s , -19d 41m 12.5s) | C | 60 | 16.1 | 4141 | 2026-04-21 05:21:51 | MASTER-OAGH | (12h 35m 43.04s , -20d 15m 04.4s) | C | 60 | 15.7 | 4153 | 2026-04-21 05:22:04 | MASTER-OAFA | (12h 40m 15.50s , -17d 23m 41.3s) | C | 60 | 20.0 | 4212 | 2026-04-21 05:23:03 | MASTER-OAGH | (12h 42m 58.08s , -19d 42m 15.1s) | C | 60 | 18.5 | 4212 | 2026-04-21 05:23:03 | MASTER-OAGH | (12h 44m 18.55s , -20d 16m 07.7s) | C | 60 | 18.1 | 4219 | 2026-04-21 05:23:09 | MASTER-OAFA | (12h 40m 15.52s , -17d 23m 40.6s) | C | 60 | 20.1 | 4285 | 2026-04-21 05:24:15 | MASTER-OAFA | (12h 40m 15.55s , -17d 23m 40.1s) | C | 60 | 20.0 | 4341 | 2026-04-21 05:25:12 | MASTER-OAGH | (12h 34m 18.76s , -17d 47m 13.7s) | C | 60 | 18.2 | 4341 | 2026-04-21 05:25:12 | MASTER-OAGH | (12h 35m 38.65s , -18d 21m 04.7s) | C | 60 | 17.9 | 4350 | 2026-04-21 05:25:20 | MASTER-OAFA | (12h 40m 15.59s , -17d 23m 39.6s) | C | 60 | 20.0 | 4412 | 2026-04-21 05:26:23 | MASTER-OAGH | (12h 26m 01.58s , -17d 48m 10.3s) | C | 60 | 15.8 | 4412 | 2026-04-21 05:26:23 | MASTER-OAGH | (12h 27m 21.61s , -18d 22m 00.1s) | C | 60 | 16.0 | 4416 | 2026-04-21 05:26:26 | MASTER-OAFA | (12h 40m 15.62s , -17d 23m 39.2s) | C | 60 | 20.1 | 4482 | 2026-04-21 05:27:33 | MASTER-OAFA | (12h 40m 15.64s , -17d 23m 38.8s) | C | 60 | 19.9 | 4542 | 2026-04-21 05:28:33 | MASTER-OAGH | (12h 34m 16.69s , -15d 53m 12.9s) | C | 60 | 14.3 | 4547 | 2026-04-21 05:28:38 | MASTER-OAFA | (12h 40m 15.67s , -17d 23m 38.2s) | C | 60 | 20.0 | 4613 | 2026-04-21 05:29:44 | MASTER-OAGH | (12h 42m 41.80s , -15d 54m 16.3s) | C | 60 | 15.3 | 4613 | 2026-04-21 05:29:44 | MASTER-OAGH | (12h 44m 01.27s , -16d 28m 06.0s) | C | 60 | 14.9 | 4613 | 2026-04-21 05:29:44 | MASTER-OAFA | (12h 40m 15.70s , -17d 23m 37.8s) | C | 60 | 19.9 | 4679 | 2026-04-21 05:30:50 | MASTER-OAFA | (12h 40m 15.74s , -17d 23m 37.2s) | C | 60 | 20.0 | 4743 | 2026-04-21 05:31:54 | MASTER-OAGH | (12h 34m 21.40s , -19d 41m 10.3s) | C | 60 | 14.6 | 4743 | 2026-04-21 05:31:54 | MASTER-OAGH | (12h 35m 42.22s , -20d 15m 00.7s) | C | 60 | 14.5 | 4745 | 2026-04-21 05:31:55 | MASTER-OAFA | (12h 40m 15.77s , -17d 23m 37.0s) | C | 60 | 20.0 | 4810 | 2026-04-21 05:33:01 | MASTER-OAFA | (12h 40m 15.79s , -17d 23m 36.5s) | C | 60 | 20.1 | 4815 | 2026-04-21 05:33:05 | MASTER-OAGH | (12h 42m 56.35s , -19d 42m 13.4s) | C | 60 | 15.5 | 4815 | 2026-04-21 05:33:05 | MASTER-OAGH | (12h 44m 17.15s , -20d 16m 04.5s) | C | 60 | 15.2 | 4876 | 2026-04-21 05:34:07 | MASTER-OAFA | (12h 40m 15.81s , -17d 23m 36.3s) | C | 60 | 20.0 | 4941 | 2026-04-21 05:35:12 | MASTER-OAFA | (12h 40m 15.84s , -17d 23m 36.4s) | C | 60 | 20.0 | 4954 | 2026-04-21 05:35:24 | MASTER-OAGH | (12h 34m 19.16s , -17d 47m 10.7s) | C | 60 | 14.1 | 5007 | 2026-04-21 05:36:17 | MASTER-OAFA | (12h 40m 15.86s , -17d 23m 35.7s) | C | 60 | 20.0 | 5073 | 2026-04-21 05:37:24 | MASTER-OAFA | (12h 40m 15.87s , -17d 23m 35.3s) | C | 60 | 19.9 | 5138 | 2026-04-21 05:38:29 | MASTER-OAFA | (12h 40m 15.91s , -17d 23m 35.2s) | C | 60 | 19.9 | 5184 | 2026-04-21 05:39:15 | MASTER-OAGH | (12h 34m 16.09s , -15d 53m 00.5s) | C | 60 | 17.1 | 5184 | 2026-04-21 05:39:15 | MASTER-OAGH | (12h 35m 37.14s , -16d 26m 52.1s) | C | 60 | 17.1 | 5204 | 2026-04-21 05:39:35 | MASTER-OAFA | (12h 40m 15.93s , -17d 23m 34.8s) | C | 60 | 19.9 | 5256 | 2026-04-21 05:40:27 | MASTER-OAGH | (12h 42m 39.48s , -15d 54m 07.1s) | C | 60 | 17.1 | 5256 | 2026-04-21 05:40:27 | MASTER-OAGH | (12h 44m 00.43s , -16d 27m 59.1s) | C | 60 | 16.8 | 5270 | 2026-04-21 05:40:41 | MASTER-OAFA | (12h 40m 15.94s , -17d 23m 34.3s) | C | 60 | 19.9 | 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/44367. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42488] GRB 260421B: BOOTES-7 early optical afterglow detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44366 SUBJECT: GRB 260421B: BOOTES-7 early optical afterglow detection DATE: 26/04/21 05:37:53 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> S.-Y. Wu, M. Gritsevich, I. Perez-Garcia, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. of Malaga), Y.-D. Hu (GXU, Guanxi), B.-B. Zhang (Nanjing Univ.), and A. Maury (Space Obs., San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of GRB 260421B by Fermi (Fermi Team, GCN 44360, Preis and Greiner, GCN 44361) and SVOM (Zhao et al. GCN 44362), the BOOTES-7 telescope at the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) automatically observed the GRB location starting on Aug. 21, 04:28:36 UT (i.e. 15 min after GRB onset). A series of images in clear filter were gathered and we identify the fading optical afterglow reported by He et al. (GCN 44363) Sánchez-Álvarez et al. (GCN 44364) and Turpin et al. (GCN 44365) at coordinates RA: 12:40:00.50 Dec: -17:44:24.0 (+/- 0.5 “). Preliminary magnitude is 18. Further data analysis is ongoing. We would like to thank the staff at San Pedro de Atacama Space Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44366. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42487] GRB 260421B: LCO optical afterglow confirmation
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44365 SUBJECT: GRB 260421B: LCO optical afterglow confirmation DATE: 26/04/21 05:32:17 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), B. Cordier (CEA/Irfu), W.-L Zhang (PMO), Z.-Y Liu (GZNU), report on behalf of the SVOM mission team: We observed the field of GRB 260421B detected by SVOM (Zhao et al., GCN 44362) and Fermi/GBM (The Fermi GBM team, GCN 44360) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started at 2026-04-21T04:29:54.940 about 16.5 min after the SVOM/ECLAIRs trigger time. We obtained 3x200 s exposures in the SDSS r and PanSTARRS-z filters. An uncatalogued bright optical candidate is well detected in our single images at RA, dec (J2000) = 190.00203, -17.74017 (err = 0.5 arcsec). This position is consistent with the optical counterpart reported by the TRT telescope (He et al, GCN 44363) and the SVOM/COLIBRI FM-GFT (Álvarez et al. GCN 43646). We measure the following magnitude calibrated against the PanSTARRS DR1 catalog, and not corrected for Galactic extinction: r = 18.47 +/- 0.01 (AB) (Tmid - T0 = 18.2 min) z = 18.92 +/- 0.09 (AB) (Tmid - T0 = 30.7 min) This project is funded by the SVOM collaboration. Further observations are scheduled. View this GCN Circular online at https://gcn.nasa.gov/circulars/44365. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42486] GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44364 SUBJECT: GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart DATE: 26/04/21 05:28:06 GMT FROM: freddalvarez(a)astro.unam.mx Fredd Sánchez Álvarez (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), W.L. Zhang (PMO), and Z. Y. Liu (GZNU) report: We imaged the field of the SVOM/ECLAIRs and Fermin/GBM GRB 260421B (Zhao et al., GCN Circ. 44362; Fermi GBM Team, GCN Circ. 44360) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-21 04:15:13 to 04:30:07 (from 1.9 to 16.8 minutes after the trigger) and obtained 430 seconds of simultaneous exposure in the r/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 consistent with the ECLAIRs localization at: RA(J2000) = 12:40:00.48 = 190.00200 degrees Dec(J2000) = -17:44:24.6 = -17.74015 degrees with an uncertainty of 0.5 arcsec. The source was detected in both r and z and was observed to fade from r ≈ 14.5 to r ≈ 18.3 during our observations. The color of the source was r - z ≈ 0.45 +/- 0.02, which is consistent with the expectations for an afterglow. We suggest this is the optical counterpart of the GRB. Subsequent imaging in the g/r/i/z/y filters show detections in all bands, indicating that the redshift is less than 3.5. We encourage spectroscopic observations of the source. Further observations are planned. 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/44364. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42485] GRB 260421B: TRT optical counterpart detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44363 SUBJECT: GRB 260421B: TRT optical counterpart detection DATE: 26/04/21 05:26:32 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), X. Liu, Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC) report: We observed the field of GRB 260421B detected by Fermi (GCN 44360) and SVOM (zhao et al., GCN 44362), 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 r-band. An uncatalogued source is detected within the Fermi error circle at coordinates R.A. (J2000) = 12:40:00.5 Dec. (J2000) = -17:44:24.5 with an uncertainty of ~ 1.0 arcsec. The source had r = 19.14 +/- 0.07 mag, calibrated with Pan-STARRS DR2 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 is the optical counterpart of GRB 260421B. View this GCN Circular online at https://gcn.nasa.gov/circulars/44363. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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