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

[vsnet-grb-info 42586] Konus-Wind detection of GRB 260411C
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44461 SUBJECT: Konus-Wind detection of GRB 260411C DATE: 26/05/04 19:38:56 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260411C triggered Konus-Wind at T0=21236.871 s UT (05:53:56.871). The burst light curve shows a single pulse which starts at ~T0-14.9 s and has a total duration of ~24.3 s. The emission is seen up to ~1 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260411_T21236/ As observed by Konus-Wind, the burst had the total fluence of 1.31(-0.08,+0.08)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+1.584 s, of 7.72(-0.94,+0.93)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.54(-0.09,+0.08), the high energy photon index beta = -3.23(-6.77,+0.37), the peak energy Ep = 105(-6,+8) keV (chi2 = 85/81 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42585] GRB 260502A: Fermi GBM Final Localization
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44447 SUBJECT: GRB 260502A: Fermi GBM Final Localization DATE: 26/05/03 05:20:13 GMT FROM: Rushikesh Sonawane at IISER TVM <rushikesh23(a)iisertvm.ac.in> The Fermi GBM team reports the detection of a likely SHORT GRB "At 05:01:00.25 UT on 02 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260502A (trigger 799390865/260502209). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 283.76, Dec = 57.62 (J2000 degrees, equivalent to J2000 18h 55m, +57d 37′), with a statistical uncertainty of 13.77 degrees. The angle from the Fermi LAT boresight is 23 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42584] GRB 260504B: REM optical/NIR observations
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44460 SUBJECT: GRB 260504B: REM optical/NIR observations DATE: 26/05/04 15:24:20 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 260504B detected by SVOM/ECLAIRs (Saccardi et al., GCN 44454) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried out in the g, r, i, z, and H bands, started on 2026 May 04 at 09:41:12 UT (i.e. 9.9 min after the burst), and lasted for about 1.5 hours. From preliminary inspection, we do not detect any counterpart within the SVOM/ECLAIRs and SVOM/MXT error circles down to the following 3sigma limits: r > 19.5 (AB; calibrated against the SkyMapper catalogue), at a mid-time of 33.8 min after the trigger; H > 15.3 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 13.3 min after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44460. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42583] IPN triangulation of GRB 260429A
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44459 SUBJECT: IPN triangulation of GRB 260429A DATE: 26/05/04 15:06:16 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The bright, short-duration GRB 260429A (Ferm-GBM detection: The Fermi GBM team, GCN 44425; Scotton, GCN 44430; SVOM-GRM detection: Yu et al., GCN 44439) was detected by Fermi (GBM trigger 799197847), Konus-Wind, SVOM (GRM), and Mars-Odyssey (HEND) at about 84242 s UT (23:24:02). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 281.153 (18h 44m 37s) +17.279 (+17d 16' 44") Corners: 281.115 (18h 44m 28s) +17.444 (+17d 26' 37") 281.161 (18h 44m 39s) +17.398 (+17d 23' 52") 281.192 (18h 44m 46s) +17.114 (+17d 06' 50") 281.146 (18h 44m 35s) +17.160 (+17d 09' 36") --------------------------------------------- The error box area is 40 sq. arcmin, and its maximum dimension is 20 arcmin (the minimum one is 2.3 arcmin). The Sun distance was 109 deg. This localization may be improved. A triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB260429_T84245/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/44459. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42582] IPN triangulation of GRB 260428A
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44458 SUBJECT: IPN triangulation of GRB 260428A DATE: 26/05/04 15:04:29 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP), J. Wei (NAOC), B. Cordier (CEA) on behalf of the SVOM-GRM team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The short-duration GRB 260428A (Fermi-GBM detection: Fermi GBM team, GCN Circ. 44415; AstroSat-CZTI detection: Goyal et al., GCN Circ. 44421; GECAM-B detection: Wang et al., GCN Circ. 44423; SVOM/GRM observation: Wang et al., GCN Circ. 44424) was detected by Fermi (GBM), Konus-Wind, AstroSat (CZTI), GECAM-B, SVOM (GRM), and Mars-Odyssey (HEND) at about 51636 s UT (14:20:36). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 283.386 (18h 53m 33s) +0.365 ( +0d 21' 53") Corners: 283.274 (18h 53m 06s) +1.978 ( +1d 58' 41") 283.221 (18h 52m 53s) +2.065 ( +2d 03' 56") 283.504 (18h 54m 01s) -1.335 ( -1d 20' 06") 283.558 (18h 54m 14s) -1.435 ( -1d 26' 07") --------------------------------------------- The error box area is 561 sq. arcmin, and its maximum dimension is 3.5 deg (the minimum one is 3 arcmin). The Sun distance was 111 deg. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB260428_T51639/IPN The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/44458. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42581] GRB 260504B: AST3-2 i-band upper limit
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44457 SUBJECT: GRB 260504B: AST3-2 i-band upper limit DATE: 26/05/04 15:02:23 GMT FROM: Tianrui Sun at Purple Mountain Obs,CAS <trsun(a)pmo.ac.cn> Tian-Rui Sun, Yan-Long Hua (Purple Mountain Observatory, CAS), Kun Ma, Jiali Chen, Kai-wen Zheng, Hongjian Guo, Ben Liu, Shuping Wang, Huiping Jin, Jiaheng Liu, Haoyu Yan, Jiajie Yang, Xiao-Yan Li (Nanjing Institute of Astronomical Optics & Technology, CAS), Jin-Jun Geng, Wenlong Zhang, Xue-Feng Wu (Purple Mountain Observatory, CAS), report on behalf of the AST3 Team: Following the detection of GRB 260504B by ECLAIRs aboard SVOM (A. Saccardi et al., GCN 44454), we carried out follow-up observations using the Antarctic Survey Telescope AST3-2 located at Dome A, Antarctica (Lat. −80.4173 deg, Long. 77.0950 deg). Observations began at 2026-05-04 09:48:50 UT. No significant optical counterpart was detected within the ECLAIRs error circle (~4.91 arcmin radius) and the MXT error circle (~167 arcsec), based on comparisons with Gaia DR3 and archival SkyMapper cutout images. The stacked image with a total exposure time of 7170 s in the i-band reached a 5σ limiting magnitude of ~19.7.This result is consistent with the non-detections reported by MASTA-OAFA (F. Podesta et al., GCN 44455) and by LCO (D. Turpin et al., GCN 44456). Photometric calibration was performed using the ATLAS Reference Catalog (Tonry et al. 2018). We thank Prof. Michael Ashley (UNSW) for his continuous support in the operation of AST3-2. View this GCN Circular online at https://gcn.nasa.gov/circulars/44457. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42580] GRB 260504B: LCO z-band upper limit
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44456 SUBJECT: GRB 260504B: LCO z-band upper limit DATE: 26/05/04 10:38:06 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), L. P. Xin (NAOC), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), report on behalf of the SVOM mission team: We observed the field of the short GRB 260504B detected by SVOM (Saccardi et al., GCN 44454) with the LCO 1m telescope at Cerro Tololo equipped with the Sinistro instrument. Our observation started on 2026-05-04 at 09:40:18 UT (about 9 min after the trigger) and we obtained 3x200 s exposures in the Pan-STARRS z filter. No new source is detected within the ECLAIRs and MXT error circles, down to a limiting magnitude: z > 19.66 (AB, 5-sigma, mid-time 14.4 min after the SVOM trigger). This value was calibrated against the SkyMapper survey DR4 and is not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44456. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42579] SVOM GRB 260504B: MASTER-OAFA optical observations
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44455 SUBJECT: SVOM GRB 260504B: MASTER-OAFA optical observations DATE: 26/05/04 10:30:53 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> F.Podesta, M.J. Segura, C.Francile, R.Podesta, E. Gonzalez (OAFA, SJNU), A.Kuznetsov, V.Lipunov, I.Panchenko, P.Balanutsa, G.Antipov, N.Tiurina, K.Zhirkov, E.Gorbovskoy, V.Senik, A.Chasovnikov, Ya.Kechin, V.Topolev, D.Vlasenko,A.Sankovich, I.Gorbunov (Lomonosov MSU), N.Budnev, O.Gress (ISU), D.Buckley (SAAO), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich (Blagoveschensk Educational StateUniversity) R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope of MASTER Global Robotic Net [1-4] was pointed to the SVOM GRB260504.40 (trigger No 1777887197,23h 24m 54.98s, -80d 21m 09.7s, R=0.0491, Saccardi et al. GCN 44454 ) errorbox 434 sec after trigger time at 2026-05-04 09:40:30 UT, with upper limit up to 19.7 mag. The observations began at zenith distance = 54 deg. The sun altitude was -18.8 deg. The galactic latitude b = -36 deg., longitude l = 307 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3291780 MASTER upper limits: Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment 489 | 2026-05-04 09:40:30 | MASTER-OAFA | (23h 23m 41.35s , -81d 33m 14.0s) | C | 110 | 18.9 | 634 | 2026-05-04 09:40:30 | MASTER-OAFA | (23h 23m 41.33s , -81d 33m 14.1s) | C | 400 | 19.7 | Coadd 615 | 2026-05-04 09:42:26 | MASTER-OAFA | (23h 23m 41.51s , -81d 33m 07.2s) | C | 130 | 19.1 | 767 | 2026-05-04 09:44:43 | MASTER-OAFA | (23h 23m 41.18s , -81d 33m 00.8s) | C | 160 | 19.2 | 883 | 2026-05-04 09:47:29 | MASTER-OAFA | (23h 23m 40.81s , -81d 32m 56.0s) | C | 60 | 18.8 | 943 | 2026-05-04 09:47:29 | MASTER-OAFA | (23h 23m 40.80s , -81d 32m 56.1s) | C | 180 | 19.5 | Coadd 948 | 2026-05-04 09:48:35 | MASTER-OAFA | (23h 23m 40.67s , -81d 32m 53.0s) | C | 60 | 18.8 | 1014 | 2026-05-04 09:49:40 | MASTER-OAFA | (23h 23m 40.42s , -81d 32m 50.2s) | C | 60 | 18.8 | 1080 | 2026-05-04 09:50:46 | MASTER-OAFA | (23h 23m 40.47s , -81d 32m 47.6s) | C | 60 | 18.9 | 1140 | 2026-05-04 09:50:46 | MASTER-OAFA | (23h 23m 40.46s , -81d 32m 47.6s) | C | 180 | 19.6 | Coadd 1145 | 2026-05-04 09:51:51 | MASTER-OAFA | (23h 23m 40.03s , -81d 32m 44.5s) | C | 60 | 18.7 | 1211 | 2026-05-04 09:52:57 | MASTER-OAFA | (23h 23m 39.95s , -81d 32m 41.8s) | C | 60 | 18.8 | 1277 | 2026-05-04 09:54:03 | MASTER-OAFA | (23h 23m 39.77s , -81d 32m 39.0s) | C | 60 | 18.8 | 1342 | 2026-05-04 09:55:09 | MASTER-OAFA | (23h 23m 39.54s , -81d 32m 36.0s) | C | 60 | 18.7 | 1408 | 2026-05-04 09:56:14 | MASTER-OAFA | (23h 23m 39.36s , -81d 32m 33.3s) | C | 60 | 18.7 | 1474 | 2026-05-04 09:57:21 | MASTER-OAFA | (23h 23m 39.24s , -81d 32m 30.3s) | C | 60 | 18.8 | 1540 | 2026-05-04 09:58:26 | MASTER-OAFA | (23h 23m 39.00s , -81d 32m 27.3s) | C | 60 | 18.9 | Filter C is a clear (unfiltred) band. Observation and reduction will continue. [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/44455. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42578] GRB 260504B: SVOM detection of a short burst
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44454 SUBJECT: GRB 260504B: SVOM detection of a short burst DATE: 26/05/04 10:00:59 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), D. Adrien (CEA/Irfu), F. Piron (LUPM), D. Gotz (CEA/Irfu), P. Maggi (ObAS), C. W. Wang (IHEP), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), report on behalf of the SVOM mission team: At 2026-05-04T09:31:19 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260504B (SVOM burst-id sb26050402). 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 Count-Rate Trigger (CRT), which produced a sequence of 6 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 17.15 in the [8-120] keV energy band over a time window of 0.30 seconds starting at 2026-05-04T09:31:19. The localization of the best alert is R.A., Dec. 351.2451, -80.3291 degrees (J2000) with a 90% confidence level (C.L.) radius of 4.91 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve shows a single narrow peak structure with a T90 duration of 0.5 +/- 0.1 s (5-120 keV). This burst also triggered SVOM/GRM at 2026-05-04T09:31:19 on a timescale of 0.10 seconds with an SNR of 31.30. The SVOM/GRM light curve shows a single narrow peak structure with a T90 duration of 0.22 +/- 0.02 s (8-1100 keV). The SVOM/GRM light curve can be found here： https://www.bursthub.cn//admin/static/svgrb260504B.png SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-05-04T09:33:16 UTC, 117 seconds after T0. Using onboard processed data we found a possible uncatalogued X-ray source located at R.A., Dec. 351.285, -80.383 degrees: R.A. (J2000) = 23h25m08s Dec. (J2000) = -80d22m69s with a 90% C.L. radius of 167 arcseconds. This location is 3.2 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 Yun Wang: wangyun(a)pmo.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44454. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42577] Fermi GRB 260504A: Global MASTER-Net observations report
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44453 SUBJECT: Fermi GRB 260504A: Global MASTER-Net observations report DATE: 26/05/04 09:46:26 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 260504A ( Fermi GBM team, GCN 44452) errorbox 578 sec after notice time and 612 sec after trigger time at 2026-05-04 09:23:10 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 79 deg. The sun altitude is -22.5 deg. The galactic latitude b = 5 deg., longitude l = 86 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3291732 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 672 | 2026-05-04 09:23:10 | MASTER-OAFA | (20h 30m 50.42s , +46d 55m 36.5s) | C | 120 | 16.4 | 813 | 2026-05-04 09:25:16 | MASTER-OAFA | (20h 30m 48.57s , +46d 55m 44.3s) | C | 150 | 16.1 | 924 | 2026-05-04 09:27:52 | MASTER-OAFA | (20h 30m 47.07s , +46d 55m 48.4s) | C | 60 | 16.4 | 990 | 2026-05-04 09:28:58 | MASTER-OAFA | (20h 30m 46.11s , +46d 55m 50.2s) | C | 60 | 16.5 | 1056 | 2026-05-04 09:30:03 | MASTER-OAFA | (20h 30m 45.24s , +46d 55m 54.1s) | C | 60 | 16.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44453. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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