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

[vsnet-grb-info 42952] GRB 260515A: SVOM/VT optical detection at about 18 days post trigger
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44821 SUBJECT: GRB 260515A: SVOM/VT optical detection at about 18 days post trigger DATE: 26/06/04 15:44:09 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, J. R. Xu, Y. N. Ma, Z. H. Yao, 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, A. Saccardi and D. Gotz (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed further ToO observations of GRB260515A triggered by SVOM/ECLAIRs (sb26051504, Brunet et al., GCN 44622, GCN 44666). The burst was also detected by Konus-Wind (Frederiks et al., GCN 44647). The observation started at 2026-06-03T02:02:18 UTC, i.e., 18.28 days post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Lipunov et al., GCN 44627; Wu et al., GCN 44628; Dennefeld et al., GCN 44633; Li et al., GCN 44634; Wang et al., GCN 44642; Antier et al., GCN 44643; Pérez-Fournon et al., GCN 44645; Dimple et al. GCN 44646; Moskvitin et al., GCN 44652; Bochenek et al., GCN 44658) with redshift z=0.764 (Malesani et al., GCN 44629) was faintly detected VT_R. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 18.38 d VT_R 108*70 s 23.5 +/- 0.3 mag 18.38 d VT_B 110*70 s >24.0 mag (3 sigma upper limit) 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/44821. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42951] GRB 260603A: NOT optical observations
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44820 SUBJECT: GRB 260603A: NOT optical observations DATE: 26/06/04 12:05:46 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), L. Izzo (INAF/OACN and DARK/NBI), G. Corcoran (UCD), A. Martin-Carrillo (UCD), N. Pyykkinen (NOT), A. S. Mårtensson (NOT) report on behalf of a larger collaboration: We observed the optical afterglow (Guelfand et al., GCNs 44791, 44797; Li et al., GCN 44799) of the SVOM GRB 260603A (Zhao et al., GCN 44787) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out in the SDSS r band. The optical afterglow is detected with an AB magnitude r = 23.27 +- 0.21, at a mean epoch of Jun 4.02 UT (0.786 days after trigger). This magnitude is calibrated against nearby stars from the Pan-STARRS catalog, and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44820. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42950] GRB 260603A: Simeiz Zeiss-1000 optical upper limit
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44819 SUBJECT: GRB 260603A: Simeiz Zeiss-1000 optical upper limit DATE: 26/06/04 09:46:23 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> N. Pankov (IKI), A. Pozanenko (IKI), A. Novichonok (KIAM), A. Volnova (IKI) report on behalf of IKI-GRB-FuN We observed the field of GRB 260603A (Zhao et al., GCN 44787; Li et al., GCN 44805) with the Zeiss-1000 1-meter telescope of Simeiz Observatory starting on 2026-06-03 UT 19:38:36 (~0.6 days since trigger). A series of 20x180 sec exposures was acquired in the R-filter using a CCD-photometer. We do not detect the optical afterglow (Guelfand et al., GCN 44791, 44797; Li et al., GCN 44799; Freeberg et al., GCN 44800). The preliminary upper limit and the observation details are summarized below: Date UTstart t-T0 Exp. Filter Mag Err. UL (mid,days) (n*s) (3-sigma) 2026-06-03 19:38:36 0.60443 20*180 R n/d n/d 22.3 The photometry is based on nearby USNO-B1.0 stars and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44819. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42949] GRB 260604B: Fermi GBM Final Real-time Localization
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44818 SUBJECT: GRB 260604B: Fermi GBM Final Real-time Localization DATE: 26/06/04 08:58:18 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 SHORT GRB At 08:45:55 UT on 4 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260604B (trigger 802255560.356374 / 260604365). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 173.4, Dec = -19.9 (J2000 degrees, equivalent to J2000 11h 33m, -19d 53'), with a statistical uncertainty of 10.8 degrees. The angle from the Fermi LAT boresight is 60.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604365/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604365/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604365/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44818. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42948] GRB 260601A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44817 SUBJECT: GRB 260601A: CALET Gamma-Ray Burst Monitor detection DATE: 26/06/04 08:23:39 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> K. Yamaoka (Nagoya U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), 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 the short GRB 260601A at 11:00:12.042 UTC on 1 June 2026 (trigger #1464346716; https://cgbm.calet.jp/cgbm_trigger/flight/1464346716/index.html) A CGBM Notice was distributed in near real time. This event was also reported by Fermi GBM (The Fermi GBM team, GCN #44755; Holzmann Airasca et al., GCN #44760), Glowbug (Cheung et al., GCN #44763), GECAM-B (Wang et al., GCN #44778), SVOM/GRM (Wang et al., GCN #44793), and KONUS-Wind (IPN_RAW Notice at 2026-06-01 11:00:09.16 UTC). The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure, starting at T+0.40 s, peaking at T+0.50 s, and ending at T+0.59 s. The T90 and T50 durations measured with the SGM data are 0.18 +/- 0.01 s and 0.05 +/- 0.03 s in the 40-1000 keV band, respectively. The ground-processed light curve is available at: https://cgbm.calet.jp/cgbm_trigger/ground/1464346716/ 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/44817. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42947] EP260602a: EP-FXT follow-up observation
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44816 SUBJECT: EP260602a: EP-FXT follow-up observation DATE: 26/06/04 07:09:04 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), Y. Wang (PMO, CAS; UCB), G. J. Yang, W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260602a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Li et al., GCN 44770) at 2026-06-02T08:11:20 (UTC). Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-06-03T14:02:47(UTC), ~30 hours after the WXT detection. The exposure time of the observation is around 6 ks. The on-ground analysis of the FXT B data found an uncatalogued source at R.A. = 240.8343 deg, DEC = 50.4636 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is approximately consistent with the position of the optical counterpart (Xu et al., GCN 44781; Watson et al., GCN 44790; Malesani et al., GCN 44807). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.03×10^20 cm^-2, and a photon index of 1.6 (-0.9, +1.2). The derived average unabsorbed 0.5-10 keV flux is 7.1 (-4.3, +13.0) ×10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/44816. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42946] EP260603a: Global MASTER-Net observations report
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44815 SUBJECT: EP260603a: Global MASTER-Net observations report DATE: 26/06/04 06:18:16 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), M. Segura, 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) was pointed to the EP260603a ( EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> et al., GCN 44814) errorbox 436 sec after notice time and 43770 sec after trigger time at 2026-06-04 06:00:42 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 58 deg. The sun altitude is -33.4 deg. The galactic latitude b = 25 deg., longitude l = 340 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3359661 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 43860 | 2026-06-04 06:00:42 | MASTER-OAGH | (15h 18m 40.19s , -26d 59m 12.9s) | C | 180 | 17.9 | 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/44815. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42945] EP260603a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44814 SUBJECT: EP260603a: Einstein Probe detection of a fast X-ray transient DATE: 26/06/04 05:48:48 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. F. Liang (PMO), J. W. Hu, Y. L. Wang, Z. X. Ling(NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260603a. The ground analysis of the WXT data shows that the event started at 2026-06-03T17:51:12 (UTC) and lasted for about 350 s. The WXT position of the source is R.A. = 229.721 deg, DEC = -26.940 deg (J2000) with an uncertainty of 2.8 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.56 × 10^21 cm^-2, and a photon index of 1.11 (-0.77, +0.80). The derived average unabsorbed 0.5-4 keV flux is 1.2 (-0.4, +0.6)×10^(-10) erg/s/cm^2. The peak flux is about 9.5×10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. A Target-of-Opportunity observation with the Follow-up X-ray Telescope (FXT) has been scheduled. Further information will be updated when the telemetry data is received. Further multi-wavelength observations are encouraged to determine the nature of this source. 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/44814. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42944] EP260602d: Optical Upper limits with kinder observations
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44813 SUBJECT: EP260602d: Optical Upper limits with kinder observations DATE: 26/06/04 02:54:17 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, T.-W. Chen, W.-J. Hou, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), S. Yang (HNAS), Y.-H. Lee, A. Sankar.K, M.-H. Lee, A. Dutta, Y.-C. Pan, C.-C. Ngeow, K. N.-T. Ho, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, K. W. Smith, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the FXT EP260602d (Cao et al., GCN 44796) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in r-band started at 14:34 UTC on the 3rd of June 2026 (MJD 61194.6066), 17.33 hours after the EP-WXT detection. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We next used the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Neither in the stacked nor in the difference image did we detect any signature of any new or uncataloged source within the WXT region of uncertainty. Moreover, we further employed AutoPhOT to perform PSF photometry. The details of the observations and the 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude| avg. Seeing | Med. Airmass LOT | r | 61194.6066 | 17.33 | 300 * 6 | >22.8 | 1".28 | 1.18 The presented upper limit is calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105) and is not corrected for an expected galactic extinction of A_r = 0.19 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44813. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42943] GRB 260604A: Fermi GBM Final Real-time Localization
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44812 SUBJECT: GRB 260604A: Fermi GBM Final Real-time Localization DATE: 26/06/04 02:36:52 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 02:24:27 UT on 4 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260604A (trigger 802232672.54125 / 260604100). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 60.4, Dec = -12.8 (J2000 degrees, equivalent to J2000 04h 01m, -12d 48'), with a statistical uncertainty of 9.3 degrees. The angle from the Fermi LAT boresight is 94.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604100/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604100/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604100/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44812. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42942] EP260602b: Liverpool Telescope observations
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44811 SUBJECT: EP260602b: Liverpool Telescope observations DATE: 26/06/03 20:01:36 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU) report: We observed the field of EP260602b (Hu et al., GCN 44786) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x150s exposures in SDSS i and z filters, starting at 2026-06-02 02:53:23 UT, approximately 8.99h hours after trigger. We report an i-band detection at the position of the counterpart (He et al., GCN 44780; Hu et al., GCN 44802; Eyles-Ferris et al., GCN 44809), with i = 20.7 ± 0.25, and a tentative z-band detection of z = 20.8 ± 0.4 (or a 3 sigma upper limit of z > 20.4 mag). The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44811. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42941] EP260602a: Liverpool Telescope optical upper limits
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44810 SUBJECT: EP260602a: Liverpool Telescope optical upper limits DATE: 26/06/03 19:58:47 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley, J. L. Wise (LJMU), report: We observed the field of EP260602a (Li et al., GCN 44770) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained multiple 150s exposures in SDSS gri filters, starting at 2026-06-02 21:15:26 UT, approximately 13.07 hours after trigger. The observations were interrupted and consequently resumed due to weather conditions and telescope tracking issues; some exposures needed to be discarded. We do not detect any sources at the position of the counterpart (Xu et al., GCN 44781, Li et al., GCN 44794; also Watson et al., GCN 44790; He et al., GCN 44798, Malesani et al., GCN 44807) down to the 3 sigma limiting magnitudes of: | MJD (mid) | T_mid-T_0 | Exp. Time | Filter | Mag limit. (AB) | | ------------ | ------------ | ------------ | ------------ | --------------- | | 61193.93925 | 14.34 h | 600 s | g | > 21.8 | | 61193.91413 | 13.75 h | 960 s | r | > 22.1 | | 61194.11373 | 18.54 h | 720 s | i | > 21.9 | The stacked exposures were subtracted from PanSTARRS reference imaging using custom PSF-matching image subtraction code utilising Swarp, SourceExtractor, and PSFex. The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44810. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42940] EP260602b: Liverpool Telescope and LCO observations
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44809 SUBJECT: EP260602b: Liverpool Telescope and LCO observations DATE: 26/06/03 18:45:03 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), J. N. D. van Dalen (Radboud), J. Chacón (PUC), F. E. Bauer (SSI and UTA), R. L. C. Starling (Leicester), P. G. Jonker (Radboud), A. J. Levan (Radboud & Warwick), report on behalf of a larger collaboration: We observed the field of EP260602b (Hu et al., GCNs 44786, 44802) with the 2m Liverpool Telescope (LT) on La Palma using the IO:O instrument and an LCO 1m telescope located at Cerro Tololo Interamerican Observatory (Chile) and equipped with the SINISTRO instrument. We obtained exposures in the Sloan r and g filters. We detect the optical counterpart (He et al., GCN 44780) in our LT and LCO r band stacked images. We obtain the following photometry for the counterpart calibrated to Pan-STARRS and not corrected for Galactic extinction: | t_mid - t_0 (hours) | Telescope/Instrument | Filter | Exposure (s) | AB magnitude | | --- | --- | --- | --- | --- | | 8.2 | LT/IO:O | r | 6x150 | 21.61 +/- 0.28 | | 8.5 | LT/IO:O | g | 6x150 | >21.80 | | 8.8 | LCO/SINISTRO | r | 5x300 | 21.68 +/- 0.23 | View this GCN Circular online at https://gcn.nasa.gov/circulars/44809. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42939] GRB 260603B: Fermi GBM Final Localization
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44808 SUBJECT: GRB 260603B: Fermi GBM Final Localization DATE: 26/06/03 18:16:31 GMT FROM: Eva M. Palafox at INAOE <eva.palafox(a)gmail.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 16:44:46.61 UT on 03 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260603B (trigger 802197891/260603698). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 350.27, Dec = 39.20 (J2000 degrees, equivalent to J2000 +23h 21m, +39d 12'), with a statistical uncertainty of 3.16 degrees. The angle from the Fermi LAT boresight is 63 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260603698/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260603698/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260603698/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44808. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42938] EP260602a: GTC and Liverpool Telescope optical observations
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44807 SUBJECT: EP260602a: GTC and Liverpool Telescope optical observations DATE: 26/06/03 16:41:18 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (Leicester), J. N. D. van Dalen (Radboud), P. G. Jonker (Radboud), R. L. C. Starling (Leicester), A. J. Levan (Radboud & Warwick), J. Chacón (PUC), I. Yanes (GTC), A. Tejero (GTC), S. Geier (GTC) report on behalf of a larger collaboration: We observed the field of EP260602a (Li et al., GCN 44770) with the Gran Telescopio Canarias (GTC) and the Liverpool Telescope (LT), both on the island of La Palma, equipped with the OSIRIS+ and IO:O instruments, respectively. Observations were performed in the Sloan r and z filters. We detect the optical/NIR counterpart (Xu et al., GCN 44781; Watson et al., GCN 44790; Li, GCN 44794; He et al. GCN 44798) in the GTC r and z stacked images, and marginally in the LT r image. We obtain the following photometry for the counterpart, calibrated to Pan-STARRS and not corrected for Galactic extinction: | t_mid - t_0 (hours) | Telescope/instrument | Filter | Exposure (s) | AB magnitude | | --- | --- | --- | --- | --- | | 16.7 | LT/IO:O | r | 7x150 | 22.62 +/- 0.29 | | 17.0 | GTC/OSIRIS+ | r | 10x60 | 23.20 +/- 0.10 | | 17.1 | GTC/OSIRIS+ | z | 10x45 | 22.70 +/- 0.10 | | 17.4 | LT/IO:O | z | 4x150 | >22.15 | View this GCN Circular online at https://gcn.nasa.gov/circulars/44807. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42937] Konus-Wind detection of GRB 260601B/EP260601a
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44806 SUBJECT: Konus-Wind detection of GRB 260601B/EP260601a DATE: 26/06/03 16:14:45 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260601B (GECAM-B detection: Yu et al., GCN 44767; Wang et al., GCN 44768; NuSTAR detection: Waratkar et al., GCN 44771; CALET-GBM detection: Sugita et al., GCN 44773; Insight-HXMT detection: Wang et al., GCN 44785; Glowbug detection: Cheung et al., GCN 44801) triggered Konus-Wind at T0=69173.304 s UT (19:12:53.304). The burst light curve shows a multipeaked structure which starts at ~T0-3.2 s and has a total duration of ~230 s. The emission is seen up to ~8 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260601_T69173/ As observed by Konus-Wind, the burst had the total fluence of 3.34(-0.17,+0.17)x10^-4 erg/cm2, and the 64-ms peak flux, measured from T0+27.552 s, of 1.66(-0.19,+0.19)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+210.688 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 = -0.79(-0.10,+0.12), the high energy photon index beta = -1.74(-0.05,+0.04), the peak energy Ep = 441(-68,+82) keV (chi2 = 125/97 dof). The 'peak-flux' spectrum (measured from T0+24.832 to T0+31.232 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 = -0.89(-0.07,+0.07), the high energy photon index beta = -1.82(-0.06,+0.05), the peak energy Ep = 671(-98,+117) keV (chi2 = 108/82 dof). Assuming a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimated the burst isotropic energy release E_iso, the isotropic peak luminosity L_iso, and the rest-frame peak spectral energy Ep,z of the burst at different redshifts. With the obtained estimates GRB 260601B is consistent with the 68% prediction band of the 'Amati' relation for z >~0.2 and with the 68% prediction band of the 'Yonetoku' relation for z>~1.0 (see http://www.ioffe.ru/LEA/GRBs/GRB260601_T69173/GRB260601B_rest_frame.pdf) 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/44806. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42936] GRB 260603A: EP-FXT follow-up observation
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44805 SUBJECT: GRB 260603A: EP-FXT follow-up observation DATE: 26/06/03 14:21:26 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed an automatic follow-up observation of GRB 260603A detected by SVOM/ECLAIRs (SVOM/sb26051504, ZHAO et al., GCN 44787). The follow-up observation started at 2026-06-03T07:38:06 UTC, approximately 2 hours after the SVOM trigger, with a total exposure time of 2.4 ks. On-ground analysis of the FXT data found an uncatalogued source within the ECLAIRs error circle at R.A., Dec. = 233.1435, 40.0258 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). This position is consistent with the optical counterpart (Guelfand et al., GCN 44791). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density of 1.7 (-0.8/+0.8) × 10^21 cm^-2 and a photon index of 2.4 (-0.3/+0.3). The derived average unabsorbed flux in the 0.5-10 keV band is 4.0 (-0.4, +0.5) x 10^(-12) erg/s/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/44805. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42935] EP260601a/GRB 260601B: EP-FXT follow-up observation
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44804 SUBJECT: EP260601a/GRB 260601B: EP-FXT follow-up observation DATE: 26/06/03 14:11:07 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G. J. Yang (NAO, CAS), Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), Y. Wang (PMO, CAS; UCB), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the fast X-ray transient EP260601a (detected by EP-WXT, GCN 44766; followed by Liu et al., GCN 44764, Guelfand et al., GCN 44765, Li et al., GCN 44769, Mo et al., GCN 44777 and Liu et al., GCN 44789). This event is also temporally consistent with GRB 260601B reported by GECAM-B (Yu et al., GCN 44767, Wang et al., GCN 44768), NuSTAR (Waratkar et al., GCN 44771), CALET (Sugita et al., GCN 44773) and Insight-HXMT (Wang et al., GCN 44785). The observation started at 2026-06-03 01:13:47 UTC, about 30 hours after the WXT trigger, with an exposure time of 3.5 ks. The FXT telemetry data show that an uncatalogued source was detected within the WXT error circle at R.A. = 257.6584, DEC = -1.6447 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 9 x 10^20 cm^-2. The best-fit photon index is 1.31 (-0.28/+0.29). The unabsorbed 0.5-10 keV flux is 9.2 (-2.2/+3.2) x 10^-13 erg cm^-2 s^-1. 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/44804. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42934] GRB 260601B / EP260601a: Mondy optical upper limit
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44803 SUBJECT: GRB 260601B / EP260601a: Mondy optical upper limit DATE: 26/06/03 13:30:59 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), E. Klunko (ISTP), A. Pozanenko (IKI), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient GRB 260601B / EP260601a (Yang et al., GCN 44766; Yu et al., GCN 44767; Wang et al., GCN 44768, 44785; Waratkar et al., GCN 44771; Sugita et al., GCN 44773; Cheung GCN 44801) with the AZT-33IK telescope of the Mondy observatory starting on 2026-06-02 UT 15:45:12 and taking several 120-second exposures in the R-band. In the sdtacked frame we do not detect the optical counterpart reported previously (Liu et al., GCN 44764; Guelfand et al., GCN 44765; Mo et al., GCN 44777; Liu et al., GCN 44789 ). Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-06-02 15:45:12 0.87559 20*120 R n/d n/d 21.1 Mondy/AZT-33IK The photometry is based on nearby USNO-B1.0 stars (R2-magnitudes) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44803. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42933] EP260602b: EP-FXT follow-up observation
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44802 SUBJECT: EP260602b: EP-FXT follow-up observation DATE: 26/06/03 13:21:53 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. W. Hu (NAO, CAS), Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260602b was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 44786) at 2026-06-02T17:53:12 (UTC). Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-06-03T04:30:31(UTC), ~10.5 hours after the WXT detection. The exposure time of the observation is around 4 ks. The on-ground analysis of the FXT data found an uncatalogued source at R.A. = 273.4737 deg, DEC = 7.5702 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the position of the optical counterpart (He et al., GCN 44780). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.9×10^21 cm^-2, and a photon index of 2.0 (-0.7, +0.8). The derived average unabsorbed 0.5-10 keV flux is 1.4 (-0.6, +1.1)×10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/44802. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42932] GRB 260601B/EP260601a: Glowbug gamma-ray detection
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44801 SUBJECT: GRB 260601B/EP260601a: Glowbug gamma-ray detection DATE: 26/06/03 12:57:03 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260601B, which was detected initially by Einstein Probe as EP260601a (GCN 44766). The GRB was also detected by GECAM-B (GCN 44767, 44768), NuSTAR (GCN 44771), CALET (GCN 44773), and Insight-HXMT (GCN 44785). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-06-01 19:12:50.296 with a duration of 39.7 s and a total significance of about 17.3 sigma. The light curve comprises an initial 2.05-s duration burst followed by a long-duration episode from ~T0+16.4s to +39.7s. Note that data from ~T0-2s to +1s, ~T0+5s to +10s, and ~T0+37s to +40s suffered from deadtime in various detectors. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44801. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42931] GRB 260603A: Kilonova-Catcher optical upper limit
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44800 SUBJECT: GRB 260603A: Kilonova-Catcher optical upper limit DATE: 26/06/03 12:36:36 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 260603A detected by SVOM/ECLAIRs (Zhao et al., GCN 44787) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the T11 itelescope located at the Utah Desert Remote Observatory (USA) and operated by M. Freeberg. Our observations started at TGRB+1.78 hours and were taken with the sdssr filter. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we do not detect the optical counterpart reported by SVOM/COLIBRÍ (FM-GFT) (Guelfand et al., GCN 44791; GCN 44797) and SVOM/VT (Li et al., GCN 44799). We report our follow-up results in the table below: | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | | ------------ | ------------ |------------ |--------------- |------------ | | 2.25 | 11 x 300s | r (AB) | 20.1 (3 sigma) | iT11 | All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Sloan filters were calibrated using the PanSTARRS DR1 catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/44800. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42930] GRB 260603A: SVOM/VT optical observations
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44799 SUBJECT: GRB 260603A: SVOM/VT optical observations DATE: 26/06/03 12:00:59 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, Y. L. Qiu, J. R. Xu, L. P. Xin, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), R. Z. Li (YNAO) and Z. M. Wang (BNU) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations to the field of GRB 260603A triggered by SVOM/ECLAIRs (sb26060303, Zhao et al., GCN 44787). The observation started at 2026-06-03T07:04:07 UTC, 1.44 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Guelfand et al., GCN 44791; GCN 44797) was detected by VT in both channels. The following measurements are in the AB magnitude without correction for Galactic extinction: Mid time | Band | Exposure Time | Brightness 1.78 h VT_B 36*70 s 22.08 +/- 0.12 mag 1.78 h VT_R 30*70 s 21.37 +/- 0.10 mag 3.41 h VT_B 36*70 s 22.40 +/- 0.14 mag 3.40 h VT_R 31*70 s 21.74 +/- 0.11 mag The source showed a fading slope of about -0.53 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/44799. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42929] EP260602a: NOT NIR J-band observations
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44798 SUBJECT: EP260602a: NOT NIR J-band observations DATE: 26/06/03 11:14:23 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, X. Liu, Z.P. Zhu, J. An, S.Q. Jiang, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), A.M. Kadela (NOT) report: We observed the field of EP260602a detected by EP (Li et al., GCN 44770), using the 2.56m Nordic Optical Telescope (NOT) equipped with the NOTCam camera. A series of J-band frames were obtained. The previously reported optical counterpart candidate (Xu et al., GCN 44781; Watson et al., GCN 44790) was detected in our stacked image with J = 21.47 +/- 0.18 (Vega), at a median time of ~ 16.44 hrs post-burst, calibrated with nearby 2MASS catalog and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44798. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42928] GRB 260603A: SVOM/COLIBRÍ (FM-GFT) photometric redshift z = 3.57
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44797 SUBJECT: GRB 260603A: SVOM/COLIBRÍ (FM-GFT) photometric redshift z = 3.57 DATE: 26/06/03 10:00:53 GMT FROM: Marion G <marion.guelfand(a)gmail.com> Marion Guelfand (CPPM), Alan M. Watson (UNAM), Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), 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), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), 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), Antonio de Ugarte Postigo (LAM), Ruizhi Li (YNAO), and Ziming Wang (BNU) report: We continued to image the field of the SVOM/ECLAIRs GRB 260603A (Zhao et al., GCN Circ. 44787) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-03 06:27 to 07:24 UTC (from 0.83 to 1.79 hours after the trigger) and obtained 16, 16, 16, 16, and 32 minutes of exposure in the g, r, i, z, and y filters, respectively. The data were reduced and coadded 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. The candidate counterpart reported by Guelfand et al. (GCN Circ. 44791) is detected with preliminary magnitudes of: g = 21.97 +/- 0.10 r = 21.23 +/- 0.05 i = 20.96 +/- 0.05 z = 20.87 +/- 0.09 y = 20.91 +/- 0.18 The counterpart has continued to fade. After correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.019 mag (Schlafly & Finkbeiner 2011) and fitting a power-law model to the grizy-bands using no dust, SMC, LMC and MW extinction curves, we derive a photometric redshift of z = 3.57 +- 0.42 (1-sigma c.l.). We note the presence of a galaxy about 3.5 arcsec to the north of the counterpart. This galaxy is seen in both Pan-STARRS DR2 and LS DR10 images and has g ≈ 22.11 +/- 0.04, r ≈ 21.33 +/- 0.03, and z ≈ 20.93 +/- 0.04 in the LS DR10. However, the photometric redshift in the LS DR9 is 0.343 +/- 0.088, which is not compatible with the derived photometric redshift of the counterpart, and so this galaxy is unlikely to be the host. On the other hand, a deep g-band image from the Hyper Suprime-Cam Legacy Archive (HSCLA, Tanaka et al. 2021) reveals an underlying object at a position consistent with the optical counterpart, suggesting a possible host galaxy. We encourage spectroscopic observations of the counterpart. 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/44797. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42927] EP260602d: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44796 SUBJECT: EP260602d: Einstein Probe detection of a fast X-ray transient DATE: 26/06/03 09:46:29 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J.Y. Cao, Z. X. Li, G. L. Huang, (IHEP, CAS), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260602d. The source did not trigger the WXT on-board trigger unit. A GCN Notice was sent manually (trigger ID: 13616654987). The ground analysis of the WXT data shows that the event started at T0=2026-06-02T21:13:25 (UTC) and lasted for about 200 s. The WXT position of the source is R.A. = 267.958 deg, DEC = 18.173 deg (J2000) with an uncertainty of 2.3 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 6.7 × 10^20 cm^-2, and a photon index of 0.8 (-0.5, +0.6). The derived average unabsorbed 0.5-4 keV flux is 1.4 (-0.9, +0.7)×10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. A Target-of-Opportunity observation with the Follow-up X-ray Telescope (FXT) has been scheduled. Further information will be updated when the telemetry data is received. 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/44796. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42926] Fermi trigger No 802141998: Global MASTER-Net observations report
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44795 SUBJECT: Fermi trigger No 802141998: Global MASTER-Net observations report DATE: 26/06/03 09:19:22 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), M. Segura, 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 GRB260603.05 (trigger No 802141998,01h 39m 40.08s , +12d 19m 58.8s, R=36.47) errorbox 25938 sec after notice time and 26215 sec after trigger time at 2026-06-03 08:30:09 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 79 deg. The sun altitude is -33.9 deg. The galactic latitude b = -48 deg., longitude l = 142 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3356750 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 26305 | 2026-06-03 08:30:09 | MASTER-OAGH | (00h 59m 23.30s , +44d 15m 28.5s) | C | 180 | 18.0 | 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/44795. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42925] EP260602a: SVOM/VT optical magnitudes correction
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44794 SUBJECT: EP260602a: SVOM/VT optical magnitudes correction DATE: 26/06/03 08:16:36 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> The prior reporting of the magnitudes of EP260602a (Xu et al., GCN 44781) was affected by light blooming near the target. The corrected measurements are as below: Mid time | Band | Exposure Time | Brightness 9.49 h VT_B 93*50 s 22.7 +/- 0.2 mag 9.51 h VT_R 84*50 s 21.5 +/- 0.1 mag The measurements are in the AB magnitude without correction for Galactic extinction: We apologize for the errors, and gratefully acknowledge the critical support from the COLIBRÍ team in identifying this discrepancy (Watson et al., GCN 44790). View this GCN Circular online at https://gcn.nasa.gov/circulars/44794. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42924] GRB 260601A: SVOM/GRM observation of a short burst
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44793 SUBJECT: GRB 260601A: SVOM/GRM observation of a short burst DATE: 26/06/03 07:52:54 GMT FROM: Yue Wang <m18509381757(a)163.com> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 260601A at 2026-06-01T11:00:12.500 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44755) and GECAM-B (Yue Wang et. al., GCN #44778). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of muplti-pulses with a T90 of 0.20 +0.47/-0.09 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260601A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 15.1, Dec = 44.4, Error = 2.0, GCN #44755), is located at about 116 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-0.06 to T0+0.16 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.04 +0.15/-0.17 and the cutoff energy, parameterized as Epeak, is 899 +210/-150 keV. The event fluence (10-1000 keV) in this time interval is (3.28 +0.138/−0.13)E-06 erg/cm^2. The localization of GRB 260601A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260601A_amati.png 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44793. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42923] EP260602c: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44792 SUBJECT: EP260602c: Einstein Probe detection of a fast X-ray transient DATE: 26/06/03 07:24:41 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J.Y. Cao, Z. X. Li, G. L. Huang, (IHEP, CAS), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260602c. The source did not trigger the WXT on-board trigger unit. A GCN Notice was sent manually (trigger ID: 13616654964). The ground analysis of the WXT data shows that the event started at T0=2026-06-02T09:06:44 (UTC) and lasted for about 200 s. The WXT position of the source is R.A. = 134.673 deg, DEC = -75.673 deg (J2000) with an uncertainty of 2.3 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 8 × 10^20 cm^-2, and a photon index of 2.14 (-0.41, +0.46). The derived average unabsorbed 0.5-4 keV flux is 1.9 (-0.5, +0.6)×10^(-10) erg/s/cm^2. A Target-of-Opportunity observation with the Follow-up X-ray Telescope (FXT) has been scheduled. Further information will be updated when the telemetry data is received. 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/44792. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42922] EP260602c: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44792 SUBJECT: EP260602c: Einstein Probe detection of a fast X-ray transient DATE: 26/06/03 07:24:41 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J.Y. Cao, Z. X. Li, G. L. Huang, (IHEP, CAS), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260602c. The source did not trigger the WXT on-board trigger unit. A GCN Notice was sent manually (trigger ID: 13616654964). The ground analysis of the WXT data shows that the event started at T0=2026-06-02T09:06:44 (UTC) and lasted for about 200 s. The WXT position of the source is R.A. = 134.673 deg, DEC = -75.673 deg (J2000) with an uncertainty of 2.3 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 8 × 10^20 cm^-2, and a photon index of 2.14 (-0.41, +0.46). The derived average unabsorbed 0.5-4 keV flux is 1.9 (-0.5, +0.6)×10^(-10) erg/s/cm^2. A Target-of-Opportunity observation with the Follow-up X-ray Telescope (FXT) has been scheduled. Further information will be updated when the telemetry data is received. 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/44792. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42921] GRB 260603A : SVOM/COLIBRÍ optical counterpart candidate
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44791 SUBJECT: GRB 260603A : SVOM/COLIBRÍ optical counterpart candidate DATE: 26/06/03 06:54:17 GMT FROM: Marion G <marion.guelfand(a)gmail.com> Marion Guelfand (CPPM), 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), 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), Antonio de Ugarte Postigo (LAM), Ruizhi Li (YNAO), and Ziming Wang (BNU) report: We imaged the field of the SVOM GRB 260603A (Zhao et al., GCN Circ. 44787) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-06-03 05:39:27 to 06:02:56 UTC (from 133 seconds to 27 minutes after the trigger) and obtained 1000 seconds of simultaneous exposure in the r/z filters. The data were reduced, coadded, and analyzed with the COLIBRI ASU pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect an uncatalogued source consistent with the ECLAIRs 5.42 arcmin error circle (Zhao et al., GCN Circ. 44787) at: RA (J2000) = 15:32:34.55 = 233.14397 degrees Dec (J2000) = +40:01:33.3 = 40.02591 degrees The preliminary magnitudes derived for this source are: r = 19.78 +/- 0.01 z = 19.27 +/- 0.01 The source is observed to brighten and then fade. We suggest this is the counterpart of the GRB. Further observations are ongoing. 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 Observa View this GCN Circular online at https://gcn.nasa.gov/circulars/44791. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42920] EP260602a: COLIBRÍ optical observations
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44790 SUBJECT: EP260602a: COLIBRÍ optical observations DATE: 26/06/03 06:45:07 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Marion Guelfand (CPPM), Rosa L. Becerra (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), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), 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) report: We imaged the field of EP260602a (Li et al., GCN Circ. 44770) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-03 03:38 to 05:17 UTC (from 19.45 to 21.10 hours after the trigger) and obtained 15, 30, 29, and 74 minutes of exposure in the g, r, i, and z filters, respectively. The data were reduced and coadded 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 faint source at a position consistent with that of the counterpart reported by Xu et al. (GCN Circ. 44781). This source is not seen in Pan-STARRS DR2 or Legacy Survey DR10 (Dey et al. 2019) images. The preliminary magnitudes of the source are, after subtracting the PS images to remove the 20-mag source 3.5 arcsec to the south, are: g = 23.27 +/- 0.40 r = 23.26 +/- 0.21 i = 23.28 +/- 0.24 z = 22.98 +/- 0.39 The colors in our photometry are moderately red and do not suggest a high-redshift counterpart. Xu et al. report a very red color of VT_B - VT_R ≈ 2.0 +/- 0.3. Comparing griz photometry to VT photometry is not straightforward, but approximating VT_B ≈ g + r and VT_R ≈ i + z, we estimate much less extreme colors of VT_B - VT_R ≈ 0.13 +/- 0.32. One possible explanation for this difference is that Xu et al. observed a high-redshift or highly-reddened afterglow which has now faded, and we are observing the host or an intervening galaxy. However, the lack of detection of a corresponding source in both Pan-STARRS and Legacy Survey images argues against this. We currently do not have an explanation for this difference. 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/44790. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42919] GRB260601B/EP260601a: NOT near-infrared observations
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44789 SUBJECT: GRB260601B/EP260601a: NOT near-infrared observations DATE: 26/06/03 06:41:27 GMT FROM: liuxing(a)nao.cas.cn X. Liu, J. An, L.B. He, S.Q. Jiang, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), A. M. Kadela report (NOT): We observed the field of GRB260601B/EP260601a (Yang et al., GCN 44766; Yu et al., GCN 44767; Waratkar et al., GCN 44771; Sugita et al., 44773), using the 2.56m Nordic Optical Telescope (NOT) equipped with the NOTCam near-infrared camera. Observation started at 2026-06-03 00:53:22 UT, i.e., 29.67 hr post-burst, and 25x60s J-band frames were obtained. The previously reported optical counterpart (Liu et al., GCN 44764; Guelfand et al., GCN 44765; Li et al., GCN 44769) was detected in our stacked image with a brightness of J = 20.7 +/- 0.1 (Vega) at a median time of 29.94 hr post-trigger, calibrated with the 2MASS catalog and not corrected for Galactic extinction. We acknowledge the excellent support from the NOT staff, in particular A. M. Kadela. View this GCN Circular online at https://gcn.nasa.gov/circulars/44789. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42918] SVOM GRB260603.23: Global MASTER-Net observations report
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44788 SUBJECT: SVOM GRB260603.23: Global MASTER-Net observations report DATE: 26/06/03 06:30:40 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), M. Segura, 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) was pointed to the SVOM GRB260603.23 (trigger No 1780465035,15h 32m 48.05s , +40d 06m 06.5s, R=0.1222) errorbox 6 sec after notice time and 1357 sec after trigger time at 2026-06-03 05:59:52 UT, with upper limit up to 17.4 mag. The observations began at zenith distance = 9 deg. The sun altitude is -33.5 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) was pointed to the SVOM GRB260603.23 errorbox 241 sec after notice time and 1593 sec after trigger time at 2026-06-03 06:03:48 UT, with upper limit up to 16.4 mag. The observations began at zenith distance = 81 deg. The sun altitude is -67.9 deg. The galactic latitude b = 54 deg., longitude l = 64 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3357257 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 1418 | 2026-06-03 05:59:52 | MASTER-OAGH | (15h 33m 43.57s , +40d 02m 45.7s) | P- | 120 | 16.8 | 1546 | 2026-06-03 06:02:01 | MASTER-OAGH | (15h 33m 43.89s , +40d 01m 28.2s) | P- | 120 | 17.1 | 1624 | 2026-06-03 06:03:48 | MASTER-OAFA | (15h 32m 34.31s , +40d 16m 14.5s) | C | 60 | 15.8 | 1684 | 2026-06-03 06:03:48 | MASTER-OAFA | (15h 32m 34.31s , +40d 16m 14.2s) | C | 180 | 15.9 | Coadd 1676 | 2026-06-03 06:04:10 | MASTER-OAGH | (15h 33m 46.25s , +40d 02m 43.1s) | P- | 120 | 17.4 | 1689 | 2026-06-03 06:04:54 | MASTER-OAFA | (15h 32m 34.09s , +40d 16m 14.9s) | C | 60 | 15.8 | 1755 | 2026-06-03 06:05:59 | MASTER-OAFA | (15h 32m 33.86s , +40d 16m 15.8s) | C | 60 | 15.5 | 1804 | 2026-06-03 06:06:18 | MASTER-OAGH | (15h 33m 41.29s , +40d 02m 06.6s) | P- | 120 | 17.4 | 1824 | 2026-06-03 06:07:08 | MASTER-OAFA | (15h 32m 33.78s , +40d 16m 13.7s) | C | 60 | 15.6 | 1884 | 2026-06-03 06:07:08 | MASTER-OAFA | (15h 32m 33.73s , +40d 16m 14.9s) | C | 180 | 15.9 | Coadd 1890 | 2026-06-03 06:08:14 | MASTER-OAFA | (15h 32m 33.62s , +40d 16m 13.5s) | C | 60 | 15.5 | 1955 | 2026-06-03 06:09:20 | MASTER-OAFA | (15h 32m 33.33s , +40d 16m 14.8s) | C | 60 | 15.1 | 2087 | 2026-06-03 06:11:32 | MASTER-OAFA | (15h 32m 32.85s , +40d 16m 17.2s) | C | 60 | 14.9 | 2285 | 2026-06-03 06:14:49 | MASTER-OAFA | (15h 32m 32.35s , +40d 16m 15.8s) | C | 60 | 12.8 | 2416 | 2026-06-03 06:17:01 | MASTER-OAFA | (15h 32m 31.97s , +40d 16m 14.5s) | C | 60 | 12.7 | 2482 | 2026-06-03 06:18:07 | MASTER-OAFA | (15h 32m 31.82s , +40d 16m 13.7s) | C | 60 | 12.8 | 2542 | 2026-06-03 06:18:07 | MASTER-OAFA | (15h 32m 31.54s , +40d 16m 17.3s) | C | 180 | 15.8 | Coadd 2548 | 2026-06-03 06:19:12 | MASTER-OAFA | (15h 32m 31.62s , +40d 16m 12.7s) | C | 60 | 15.1 | 2614 | 2026-06-03 06:20:18 | MASTER-OAFA | (15h 32m 31.86s , +40d 16m 06.4s) | C | 60 | 16.0 | 2679 | 2026-06-03 06:21:23 | MASTER-OAFA | (15h 32m 31.35s , +40d 16m 10.4s) | C | 60 | 15.9 | 2744 | 2026-06-03 06:22:29 | MASTER-OAFA | (15h 32m 30.72s , +40d 16m 16.0s) | C | 60 | 16.4 | 2810 | 2026-06-03 06:23:35 | MASTER-OAFA | (15h 32m 30.85s , +40d 16m 11.4s) | C | 60 | 16.3 | 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/44788. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42917] GRB 260603A: SVOM detection of a burst
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44787 SUBJECT: GRB 260603A: SVOM detection of a burst DATE: 26/06/03 06:28:01 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Donghua ZHAO, Wenjin Xie (NAOC), Ruizhi Li (YNAO), Ziming Wang (BNU) report on behalf of the SVOM mission team: At 2026-06-03T05:38:16 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260603A (SVOM burst-id sb26060303). 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 13 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 15.29 in the [5-20] keV energy band over a time window of 81.92 seconds starting at 2026-06-03T05:37:55. The localization of the best alert is R.A., Dec. 233.1366,40.0801 degrees: R.A. (J2000) = 15h32m32.79s Dec. (J2000) = 40d04m48.22s with a 90% confidence level (C.L.) radius of 5.42 arcmin (including systematic error of 2 arcmin added in quadrature). One high proper motion star named TYC 3055-1389-1 is at 194.45 arcsec away. Due to a ToO-EX in performance, no immediate slew was performed on this burst. 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 Ruizhi Li: liruizhi(a)ynao.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44787. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42916] EP260602b: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44786 SUBJECT: EP260602b: Einstein Probe detection of a fast X-ray transient DATE: 26/06/03 06:14:44 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. W. Hu (NAO, CAS), Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260602b. The transient triggered EP-WXT (ID: 01709266414) at 2026-06-02T17:54:02 (UTC). The WXT position of the source is R.A. = 273.487 deg, DEC = 7.595 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The refined analysis of the WXT data shows that the event was detected at R.A. = 273.483 deg, DEC = 7.579 deg (J2000) with an uncertainty of 2.6 arcmin in radius. The event started at T0=2026-06-02T17:53:12 (UTC), and lasted for about 60 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.9 × 10^21 cm^-2, and a photon index of 1.36 (-0.80, +0.87). The derived average unabsorbed 0.5-4 keV flux is 1.8 (-0.6, +0.7)×10^(-9) erg/s/cm^2. The optical counterpart of EP260602b was reported by He et al. (GCN 44780). No autonomous follow-up observation with Follow-up X-ray Telescope (FXT) was performed. A Target-of-Opportunity observation with the FXT has been scheduled. Further information will be updated when the telemetry data is received. 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/44786. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42915] GRB 260601B/EP260601a: Insight-HXMT detection
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44785 SUBJECT: GRB 260601B/EP260601a: Insight-HXMT detection DATE: 26/06/03 06:12:43 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Zheng-Hang Yu, Shao-Lin Xiong, Cheng-Kui Li, and Chao Zheng report on behalf of the Insight-HXMT team: At 2026-06-01T19:12:49.900 (T0), Insight-HXMT/HE detected the possible long duration Type I burst GRB 260601B/EP260601a, which is also detected by GECAM-B (Yu et al., GCN #44767; Wang et al., GCN #44768), NuSTAR (Waratkar et al., GCN #44771), CGBM (S. Sugita et al., GCN #44773) and EP (Yang et al., GCN #44766). The Insight-HXMT/HE light curve mainly consists of a possible precursor and then a short pulse followed by a long emission with a T90 of 76.0 +4.5/-4.0 s. The total counts from this burst is 175433 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260601B.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/44785. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42914] Fermi GRB 260602B: Global MASTER-Net observations report
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44784 SUBJECT: Fermi GRB 260602B: Global MASTER-Net observations report DATE: 26/06/03 03:35:27 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), M. Segura, 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 260602B ( Fermi GBM team, GCN 44779) errorbox 9521 sec after notice time and 9563 sec after trigger time at 2026-06-03 01:20:54 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 23 deg. The sun altitude is -46.3 deg. MASTER-OAGH robotic telescope located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260602B errorbox 16498 sec after notice time and 16540 sec after trigger time at 2026-06-03 03:17:11 UT, with upper limit up to 17.3 mag. Observations started at twilight. The observations began at zenith distance = 45 deg. The sun altitude is -11.4 deg. The galactic latitude b = 46 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=3356506 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 9594 | 2026-06-03 01:20:54 | MASTER-OAFA | (12h 27m 05.82s , -13d 47m 16.2s) | C | 60 | 19.1 | 9654 | 2026-06-03 01:20:54 | MASTER-OAFA | (12h 27m 05.83s , -13d 47m 16.2s) | C | 180 | 19.4 | Coadd 9670 | 2026-06-03 01:22:10 | MASTER-OAFA | (12h 35m 13.14s , -13d 48m 26.4s) | C | 60 | 18.9 | 9730 | 2026-06-03 01:22:10 | MASTER-OAFA | (12h 35m 13.13s , -13d 48m 26.4s) | C | 180 | 19.2 | Coadd 9750 | 2026-06-03 01:23:31 | MASTER-OAFA | (12h 27m 05.16s , -13d 47m 57.0s) | C | 60 | 19.0 | 9828 | 2026-06-03 01:24:48 | MASTER-OAFA | (12h 35m 17.15s , -13d 46m 53.5s) | C | 60 | 18.8 | 9903 | 2026-06-03 01:26:04 | MASTER-OAFA | (12h 27m 02.72s , -13d 48m 07.0s) | C | 60 | 18.7 | 9985 | 2026-06-03 01:27:26 | MASTER-OAFA | (12h 26m 59.87s , -13d 47m 08.8s) | C | 60 | 18.5 | 10045 | 2026-06-03 01:27:26 | MASTER-OAFA | (12h 26m 59.86s , -13d 47m 08.8s) | C | 180 | 19.1 | Coadd 10078 | 2026-06-03 01:28:59 | MASTER-OAFA | (12h 35m 14.02s , -13d 46m 18.6s) | C | 60 | 18.5 | 10154 | 2026-06-03 01:30:15 | MASTER-OAFA | (12h 27m 05.70s , -13d 47m 05.8s) | C | 60 | 18.5 | 10235 | 2026-06-03 01:31:36 | MASTER-OAFA | (12h 35m 14.80s , -13d 48m 15.9s) | C | 60 | 18.6 | 10295 | 2026-06-03 01:31:36 | MASTER-OAFA | (12h 35m 14.79s , -13d 48m 15.9s) | C | 180 | 19.6 | Coadd 10312 | 2026-06-03 01:32:53 | MASTER-OAFA | (12h 27m 05.42s , -13d 48m 01.8s) | C | 60 | 18.8 | 10390 | 2026-06-03 01:34:10 | MASTER-OAFA | (12h 25m 20.90s , -17d 35m 31.1s) | C | 60 | 18.9 | 10450 | 2026-06-03 01:34:10 | MASTER-OAFA | (12h 25m 20.90s , -17d 35m 31.1s) | C | 180 | 19.6 | Coadd 10467 | 2026-06-03 01:35:27 | MASTER-OAFA | (12h 33m 47.10s , -17d 34m 19.6s) | C | 60 | 18.7 | 10527 | 2026-06-03 01:35:27 | MASTER-OAFA | (12h 33m 47.11s , -17d 34m 19.6s) | C | 180 | 19.2 | Coadd 10547 | 2026-06-03 01:36:48 | MASTER-OAFA | (12h 33m 40.74s , -17d 34m 01.3s) | C | 60 | 18.1 | 10613 | 2026-06-03 01:37:54 | MASTER-OAFA | (12h 33m 40.67s , -17d 34m 00.6s) | C | 60 | 18.8 | 10684 | 2026-06-03 01:39:05 | MASTER-OAFA | (12h 25m 23.88s , -17d 34m 49.3s) | C | 60 | 19.0 | 10772 | 2026-06-03 01:40:33 | MASTER-OAFA | (12h 25m 23.93s , -17d 35m 34.0s) | C | 60 | 19.0 | 10848 | 2026-06-03 01:41:49 | MASTER-OAFA | (12h 33m 44.40s , -17d 34m 11.7s) | C | 60 | 18.7 | 10908 | 2026-06-03 01:41:49 | MASTER-OAFA | (12h 33m 44.40s , -17d 34m 11.7s) | C | 180 | 19.5 | Coadd 10925 | 2026-06-03 01:43:05 | MASTER-OAFA | (12h 25m 21.11s , -17d 35m 36.9s) | C | 60 | 18.5 | 11002 | 2026-06-03 01:44:23 | MASTER-OAFA | (12h 33m 48.05s , -17d 34m 23.8s) | C | 60 | 18.8 | 11098 | 2026-06-03 01:45:59 | MASTER-OAFA | (12h 25m 17.61s , -17d 34m 43.3s) | C | 60 | 18.8 | 11175 | 2026-06-03 01:47:16 | MASTER-OAFA | (12h 33m 50.32s , -19d 28m 49.0s) | C | 60 | 18.6 | 11235 | 2026-06-03 01:47:16 | MASTER-OAFA | (12h 33m 50.32s , -19d 28m 49.0s) | C | 180 | 19.1 | Coadd 11279 | 2026-06-03 01:49:00 | MASTER-OAFA | (12h 33m 50.36s , -19d 29m 26.5s) | C | 60 | 18.6 | 11356 | 2026-06-03 01:50:17 | MASTER-OAFA | (12h 42m 16.13s , -19d 28m 13.0s) | C | 60 | 19.0 | 11416 | 2026-06-03 01:50:17 | MASTER-OAFA | (12h 42m 16.13s , -19d 28m 13.0s) | C | 180 | 19.8 | Coadd 11432 | 2026-06-03 01:51:33 | MASTER-OAFA | (12h 33m 47.20s , -19d 29m 21.2s) | C | 60 | 18.2 | 11498 | 2026-06-03 01:52:39 | MASTER-OAFA | (12h 57m 10.66s , -17d 35m 20.6s) | C | 60 | 18.8 | 11558 | 2026-06-03 01:52:39 | MASTER-OAFA | (12h 57m 10.66s , -17d 35m 20.6s) | C | 180 | 19.7 | Coadd 12298 | 2026-06-03 02:05:59 | MASTER-OAFA | (13h 05m 37.50s , -17d 36m 14.8s) | C | 60 | 19.4 | 12358 | 2026-06-03 02:05:59 | MASTER-OAFA | (13h 05m 37.50s , -17d 36m 14.8s) | C | 180 | 19.8 | Coadd 12375 | 2026-06-03 02:07:16 | MASTER-OAFA | (12h 57m 18.25s , -17d 34m 48.1s) | C | 60 | 19.1 | 12453 | 2026-06-03 02:08:34 | MASTER-OAFA | (13h 05m 34.06s , -17d 35m 30.3s) | C | 60 | 19.1 | 12529 | 2026-06-03 02:09:50 | MASTER-OAFA | (12h 57m 11.85s , -17d 34m 15.1s) | C | 60 | 19.5 | 12607 | 2026-06-03 02:11:08 | MASTER-OAFA | (12h 35m 21.57s , -13d 46m 50.3s) | C | 60 | 19.5 | 12691 | 2026-06-03 02:12:32 | MASTER-OAFA | (12h 35m 17.62s , -13d 47m 19.1s) | C | 60 | 19.5 | 12783 | 2026-06-03 02:14:03 | MASTER-OAFA | (12h 33m 41.62s , -17d 35m 40.6s) | C | 60 | 19.5 | 12860 | 2026-06-03 02:15:20 | MASTER-OAFA | (12h 33m 48.15s , -17d 35m 16.2s) | C | 60 | 19.6 | 12920 | 2026-06-03 02:15:20 | MASTER-OAFA | (12h 33m 48.15s , -17d 35m 16.2s) | C | 180 | 20.0 | Coadd 12943 | 2026-06-03 02:16:44 | MASTER-OAFA | (12h 33m 44.94s , -17d 33m 47.4s) | C | 60 | 19.6 | 13038 | 2026-06-03 02:18:18 | MASTER-OAFA | (12h 33m 48.58s , -17d 33m 59.3s) | C | 60 | 19.3 | 13114 | 2026-06-03 02:19:34 | MASTER-OAFA | (12h 33m 41.07s , -17d 34m 36.6s) | C | 60 | 19.3 | 13193 | 2026-06-03 02:20:54 | MASTER-OAFA | (12h 33m 41.82s , -17d 33m 35.9s) | C | 60 | 19.4 | 13272 | 2026-06-03 02:22:13 | MASTER-OAFA | (12h 42m 13.61s , -19d 29m 40.3s) | C | 60 | 19.1 | 13351 | 2026-06-03 02:23:32 | MASTER-OAFA | (12h 42m 20.13s , -19d 29m 30.9s) | C | 60 | 19.2 | 13427 | 2026-06-03 02:24:48 | MASTER-OAFA | (12h 42m 16.91s , -19d 28m 04.8s) | C | 60 | 19.2 | 13503 | 2026-06-03 02:26:04 | MASTER-OAFA | (12h 33m 47.96s , -19d 29m 08.3s) | C | 60 | 19.5 | 13580 | 2026-06-03 02:27:20 | MASTER-OAFA | (12h 33m 50.86s , -19d 27m 42.5s) | C | 60 | 19.4 | 13680 | 2026-06-03 02:29:00 | MASTER-OAFA | (12h 35m 28.54s , -21d 21m 26.8s) | C | 60 | 19.6 | 13755 | 2026-06-03 02:30:16 | MASTER-OAFA | (12h 35m 36.14s , -21d 22m 26.3s) | C | 60 | 19.4 | 13839 | 2026-06-03 02:31:40 | MASTER-OAFA | (12h 49m 32.63s , -15d 39m 55.0s) | C | 60 | 19.4 | 13930 | 2026-06-03 02:33:11 | MASTER-OAFA | (12h 57m 44.22s , -15d 40m 57.7s) | C | 60 | 19.4 | 13990 | 2026-06-03 02:33:11 | MASTER-OAFA | (12h 57m 44.22s , -15d 40m 57.8s) | C | 180 | 19.8 | Coadd 14009 | 2026-06-03 02:34:30 | MASTER-OAFA | (12h 57m 51.10s , -15d 40m 56.7s) | C | 60 | 19.3 | 14092 | 2026-06-03 02:35:53 | MASTER-OAFA | (12h 57m 48.25s , -15d 40m 23.1s) | C | 60 | 19.5 | 14179 | 2026-06-03 02:37:19 | MASTER-OAFA | (12h 57m 48.26s , -15d 41m 48.9s) | C | 60 | 19.3 | 14261 | 2026-06-03 02:38:42 | MASTER-OAFA | (13h 05m 40.78s , -17d 34m 19.7s) | C | 60 | 19.5 | 14333 | 2026-06-03 02:39:54 | MASTER-OAFA | (13h 05m 35.77s , -17d 35m 00.3s) | C | 60 | 19.4 | 14415 | 2026-06-03 02:41:16 | MASTER-OAFA | (13h 05m 42.30s , -17d 34m 59.5s) | C | 60 | 18.8 | 14494 | 2026-06-03 02:42:35 | MASTER-OAFA | (12h 57m 12.14s , -17d 35m 48.3s) | C | 60 | 19.4 | 14554 | 2026-06-03 02:42:35 | MASTER-OAFA | (12h 57m 12.14s , -17d 35m 48.3s) | C | 180 | 19.9 | Coadd 14573 | 2026-06-03 02:43:54 | MASTER-OAFA | (12h 57m 18.62s , -17d 35m 22.0s) | C | 60 | 19.4 | 14648 | 2026-06-03 02:45:08 | MASTER-OAFA | (12h 57m 15.39s , -17d 34m 02.6s) | C | 60 | 19.3 | 14726 | 2026-06-03 02:46:27 | MASTER-OAFA | (12h 57m 15.42s , -17d 35m 38.7s) | C | 60 | 19.3 | 14819 | 2026-06-03 02:48:00 | MASTER-OAFA | (13h 05m 20.11s , -15d 40m 05.6s) | C | 60 | 19.3 | 16571 | 2026-06-03 03:17:11 | MASTER-OAGH | (12h 28m 33.45s , -14d 00m 32.3s) | C | 60 | 17.3 | 16671 | 2026-06-03 03:18:52 | MASTER-OAGH | (12h 33m 22.10s , -17d 46m 24.2s) | C | 60 | 17.3 | 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/44784. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42913] Fermi GRB 260602B: Global MASTER-Net observations report
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44783 SUBJECT: Fermi GRB 260602B: Global MASTER-Net observations report DATE: 26/06/03 03:32:58 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), M. Segura, 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 260602B ( Fermi GBM team, GCN 44779) errorbox 9521 sec after notice time and 9563 sec after trigger time at 2026-06-03 01:20:54 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 23 deg. The sun altitude is -46.3 deg. MASTER-OAGH robotic telescope located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260602B errorbox 16498 sec after notice time and 16540 sec after trigger time at 2026-06-03 03:17:11 UT, with upper limit up to 17.3 mag. Observations started at twilight. The observations began at zenith distance = 45 deg. The sun altitude is -11.4 deg. The galactic latitude b = 46 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=3356506 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 9594 | 2026-06-03 01:20:54 | MASTER-OAFA | (12h 27m 05.82s , -13d 47m 16.2s) | C | 60 | 19.1 | 9654 | 2026-06-03 01:20:54 | MASTER-OAFA | (12h 27m 05.83s , -13d 47m 16.2s) | C | 180 | 19.4 | Coadd 9670 | 2026-06-03 01:22:10 | MASTER-OAFA | (12h 35m 13.14s , -13d 48m 26.4s) | C | 60 | 18.9 | 9730 | 2026-06-03 01:22:10 | MASTER-OAFA | (12h 35m 13.13s , -13d 48m 26.4s) | C | 180 | 19.2 | Coadd 9750 | 2026-06-03 01:23:31 | MASTER-OAFA | (12h 27m 05.16s , -13d 47m 57.0s) | C | 60 | 19.0 | 9828 | 2026-06-03 01:24:48 | MASTER-OAFA | (12h 35m 17.15s , -13d 46m 53.5s) | C | 60 | 18.8 | 9903 | 2026-06-03 01:26:04 | MASTER-OAFA | (12h 27m 02.72s , -13d 48m 07.0s) | C | 60 | 18.7 | 9985 | 2026-06-03 01:27:26 | MASTER-OAFA | (12h 26m 59.87s , -13d 47m 08.8s) | C | 60 | 18.5 | 10045 | 2026-06-03 01:27:26 | MASTER-OAFA | (12h 26m 59.86s , -13d 47m 08.8s) | C | 180 | 19.1 | Coadd 10078 | 2026-06-03 01:28:59 | MASTER-OAFA | (12h 35m 14.02s , -13d 46m 18.6s) | C | 60 | 18.5 | 10154 | 2026-06-03 01:30:15 | MASTER-OAFA | (12h 27m 05.70s , -13d 47m 05.8s) | C | 60 | 18.5 | 10235 | 2026-06-03 01:31:36 | MASTER-OAFA | (12h 35m 14.80s , -13d 48m 15.9s) | C | 60 | 18.6 | 10295 | 2026-06-03 01:31:36 | MASTER-OAFA | (12h 35m 14.79s , -13d 48m 15.9s) | C | 180 | 19.6 | Coadd 10312 | 2026-06-03 01:32:53 | MASTER-OAFA | (12h 27m 05.42s , -13d 48m 01.8s) | C | 60 | 18.8 | 10390 | 2026-06-03 01:34:10 | MASTER-OAFA | (12h 25m 20.90s , -17d 35m 31.1s) | C | 60 | 18.9 | 10450 | 2026-06-03 01:34:10 | MASTER-OAFA | (12h 25m 20.90s , -17d 35m 31.1s) | C | 180 | 19.6 | Coadd 10467 | 2026-06-03 01:35:27 | MASTER-OAFA | (12h 33m 47.10s , -17d 34m 19.6s) | C | 60 | 18.7 | 10527 | 2026-06-03 01:35:27 | MASTER-OAFA | (12h 33m 47.11s , -17d 34m 19.6s) | C | 180 | 19.2 | Coadd 10547 | 2026-06-03 01:36:48 | MASTER-OAFA | (12h 33m 40.74s , -17d 34m 01.3s) | C | 60 | 18.1 | 10613 | 2026-06-03 01:37:54 | MASTER-OAFA | (12h 33m 40.67s , -17d 34m 00.6s) | C | 60 | 18.8 | 10684 | 2026-06-03 01:39:05 | MASTER-OAFA | (12h 25m 23.88s , -17d 34m 49.3s) | C | 60 | 19.0 | 10772 | 2026-06-03 01:40:33 | MASTER-OAFA | (12h 25m 23.93s , -17d 35m 34.0s) | C | 60 | 19.0 | 10848 | 2026-06-03 01:41:49 | MASTER-OAFA | (12h 33m 44.40s , -17d 34m 11.7s) | C | 60 | 18.7 | 10908 | 2026-06-03 01:41:49 | MASTER-OAFA | (12h 33m 44.40s , -17d 34m 11.7s) | C | 180 | 19.5 | Coadd 10925 | 2026-06-03 01:43:05 | MASTER-OAFA | (12h 25m 21.11s , -17d 35m 36.9s) | C | 60 | 18.5 | 11002 | 2026-06-03 01:44:23 | MASTER-OAFA | (12h 33m 48.05s , -17d 34m 23.8s) | C | 60 | 18.8 | 11098 | 2026-06-03 01:45:59 | MASTER-OAFA | (12h 25m 17.61s , -17d 34m 43.3s) | C | 60 | 18.8 | 11175 | 2026-06-03 01:47:16 | MASTER-OAFA | (12h 33m 50.32s , -19d 28m 49.0s) | C | 60 | 18.6 | 11235 | 2026-06-03 01:47:16 | MASTER-OAFA | (12h 33m 50.32s , -19d 28m 49.0s) | C | 180 | 19.1 | Coadd 11279 | 2026-06-03 01:49:00 | MASTER-OAFA | (12h 33m 50.36s , -19d 29m 26.5s) | C | 60 | 18.6 | 11356 | 2026-06-03 01:50:17 | MASTER-OAFA | (12h 42m 16.13s , -19d 28m 13.0s) | C | 60 | 19.0 | 11416 | 2026-06-03 01:50:17 | MASTER-OAFA | (12h 42m 16.13s , -19d 28m 13.0s) | C | 180 | 19.8 | Coadd 11432 | 2026-06-03 01:51:33 | MASTER-OAFA | (12h 33m 47.20s , -19d 29m 21.2s) | C | 60 | 18.2 | 11498 | 2026-06-03 01:52:39 | MASTER-OAFA | (12h 57m 10.66s , -17d 35m 20.6s) | C | 60 | 18.8 | 11558 | 2026-06-03 01:52:39 | MASTER-OAFA | (12h 57m 10.66s , -17d 35m 20.6s) | C | 180 | 19.7 | Coadd 12298 | 2026-06-03 02:05:59 | MASTER-OAFA | (13h 05m 37.50s , -17d 36m 14.8s) | C | 60 | 19.4 | 12358 | 2026-06-03 02:05:59 | MASTER-OAFA | (13h 05m 37.50s , -17d 36m 14.8s) | C | 180 | 19.8 | Coadd 12375 | 2026-06-03 02:07:16 | MASTER-OAFA | (12h 57m 18.25s , -17d 34m 48.1s) | C | 60 | 19.1 | 12453 | 2026-06-03 02:08:34 | MASTER-OAFA | (13h 05m 34.06s , -17d 35m 30.3s) | C | 60 | 19.1 | 12529 | 2026-06-03 02:09:50 | MASTER-OAFA | (12h 57m 11.85s , -17d 34m 15.1s) | C | 60 | 19.5 | 12607 | 2026-06-03 02:11:08 | MASTER-OAFA | (12h 35m 21.57s , -13d 46m 50.3s) | C | 60 | 19.5 | 12691 | 2026-06-03 02:12:32 | MASTER-OAFA | (12h 35m 17.62s , -13d 47m 19.1s) | C | 60 | 19.5 | 12783 | 2026-06-03 02:14:03 | MASTER-OAFA | (12h 33m 41.62s , -17d 35m 40.6s) | C | 60 | 19.5 | 12860 | 2026-06-03 02:15:20 | MASTER-OAFA | (12h 33m 48.15s , -17d 35m 16.2s) | C | 60 | 19.6 | 12920 | 2026-06-03 02:15:20 | MASTER-OAFA | (12h 33m 48.15s , -17d 35m 16.2s) | C | 180 | 20.0 | Coadd 12943 | 2026-06-03 02:16:44 | MASTER-OAFA | (12h 33m 44.94s , -17d 33m 47.4s) | C | 60 | 19.6 | 13038 | 2026-06-03 02:18:18 | MASTER-OAFA | (12h 33m 48.58s , -17d 33m 59.3s) | C | 60 | 19.3 | 13114 | 2026-06-03 02:19:34 | MASTER-OAFA | (12h 33m 41.07s , -17d 34m 36.6s) | C | 60 | 19.3 | 13193 | 2026-06-03 02:20:54 | MASTER-OAFA | (12h 33m 41.82s , -17d 33m 35.9s) | C | 60 | 19.4 | 13272 | 2026-06-03 02:22:13 | MASTER-OAFA | (12h 42m 13.61s , -19d 29m 40.3s) | C | 60 | 19.1 | 13351 | 2026-06-03 02:23:32 | MASTER-OAFA | (12h 42m 20.13s , -19d 29m 30.9s) | C | 60 | 19.2 | 13427 | 2026-06-03 02:24:48 | MASTER-OAFA | (12h 42m 16.91s , -19d 28m 04.8s) | C | 60 | 19.2 | 13503 | 2026-06-03 02:26:04 | MASTER-OAFA | (12h 33m 47.96s , -19d 29m 08.3s) | C | 60 | 19.5 | 13580 | 2026-06-03 02:27:20 | MASTER-OAFA | (12h 33m 50.86s , -19d 27m 42.5s) | C | 60 | 19.4 | 13680 | 2026-06-03 02:29:00 | MASTER-OAFA | (12h 35m 28.54s , -21d 21m 26.8s) | C | 60 | 19.6 | 13755 | 2026-06-03 02:30:16 | MASTER-OAFA | (12h 35m 36.14s , -21d 22m 26.3s) | C | 60 | 19.4 | 13839 | 2026-06-03 02:31:40 | MASTER-OAFA | (12h 49m 32.63s , -15d 39m 55.0s) | C | 60 | 19.4 | 13930 | 2026-06-03 02:33:11 | MASTER-OAFA | (12h 57m 44.22s , -15d 40m 57.7s) | C | 60 | 19.4 | 13990 | 2026-06-03 02:33:11 | MASTER-OAFA | (12h 57m 44.22s , -15d 40m 57.8s) | C | 180 | 19.8 | Coadd 14009 | 2026-06-03 02:34:30 | MASTER-OAFA | (12h 57m 51.10s , -15d 40m 56.7s) | C | 60 | 19.3 | 14092 | 2026-06-03 02:35:53 | MASTER-OAFA | (12h 57m 48.25s , -15d 40m 23.1s) | C | 60 | 19.5 | 14179 | 2026-06-03 02:37:19 | MASTER-OAFA | (12h 57m 48.26s , -15d 41m 48.9s) | C | 60 | 19.3 | 14261 | 2026-06-03 02:38:42 | MASTER-OAFA | (13h 05m 40.78s , -17d 34m 19.7s) | C | 60 | 19.5 | 14333 | 2026-06-03 02:39:54 | MASTER-OAFA | (13h 05m 35.77s , -17d 35m 00.3s) | C | 60 | 19.4 | 14415 | 2026-06-03 02:41:16 | MASTER-OAFA | (13h 05m 42.30s , -17d 34m 59.5s) | C | 60 | 18.8 | 14494 | 2026-06-03 02:42:35 | MASTER-OAFA | (12h 57m 12.14s , -17d 35m 48.3s) | C | 60 | 19.4 | 14554 | 2026-06-03 02:42:35 | MASTER-OAFA | (12h 57m 12.14s , -17d 35m 48.3s) | C | 180 | 19.9 | Coadd 14573 | 2026-06-03 02:43:54 | MASTER-OAFA | (12h 57m 18.62s , -17d 35m 22.0s) | C | 60 | 19.4 | 14648 | 2026-06-03 02:45:08 | MASTER-OAFA | (12h 57m 15.39s , -17d 34m 02.6s) | C | 60 | 19.3 | 14726 | 2026-06-03 02:46:27 | MASTER-OAFA | (12h 57m 15.42s , -17d 35m 38.7s) | C | 60 | 19.3 | 14819 | 2026-06-03 02:48:00 | MASTER-OAFA | (13h 05m 20.11s , -15d 40m 05.6s) | C | 60 | 19.3 | 16571 | 2026-06-03 03:17:11 | MASTER-OAGH | (12h 28m 33.45s , -14d 00m 32.3s) | C | 60 | 17.3 | 16671 | 2026-06-03 03:18:52 | MASTER-OAGH | (12h 33m 22.10s , -17d 46m 24.2s) | C | 60 | 17.3 | 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/44783. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42912] EP260530a: Xinglong optical spectroscopy of EP260530a / AT 2026nwl
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44782 SUBJECT: EP260530a: Xinglong optical spectroscopy of EP260530a / AT 2026nwl DATE: 26/06/03 03:03:14 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Xinglong optical observations Junjie-Jin (NAOC), Yiming-Mao (NAOC), Junjun-Jia (NAOC), Pengliang-Du (NAOC), Yu-Zhang (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report: We obtained an optical spectrum of the Einstein Probe transient EP260530a (Wu et al., ATel #17824) using the Xinglong 2.16-m telescope. The observations targeted the optical counterpart candidate, AT 2026nwl, discovered by GOTO (TNS Astronomical Transient Report No. 306622). The observation was carried out on 2026 June 1 at 12:53:59 UT with BFOSC using the G4 grism and a 2.3-arcsec slit. The exposure time was 1800 s. The spectrum shows clear narrow emission lines from hydrogen and helium. View this GCN Circular online at https://gcn.nasa.gov/circulars/44782. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42911] EP260602a: SVOM/VT optical candidate
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44781 SUBJECT: EP260602a: SVOM/VT optical candidate DATE: 26/06/03 02:55:12 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> J. R. Xu, H. L. Li, C. Wu, Y. L. Qiu, L. P. Xin, Y. N. Ma, Z. H. Yao, 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) and J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations to the field of EP260602a triggered by Einstein Probe (Li et al., GCN 44770). The observation started at 2026-06-02T15:37:33 UTC, 7.44 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. An uncatalogued optical source was detected within WXT's error box (Li et al., GCN 44770) in both VT channels, compared to the Legacy Survey. The position is at R.A., Dec. = 240.862173, 50.563348 degrees, equivalent to: R.A. (J2000) = +16:03:26.92 Dec. (J2000) = +50:33:48.05 with an uncertainty of 0.5 arcsec. The following measurements are in the AB magnitude without correction for Galactic extinction: Mid time | Band | Exposure Time | Brightness 9.49 h VT_B 93*50 s 23.2 +/- 0.3 mag 9.51 h VT_R 84*50 s 21.17 +/- 0.15 mag 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/44781. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42910] EP-WXT trigger 01709266414 (EP260602b): JinShan optical counterpart detection
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44780 SUBJECT: EP-WXT trigger 01709266414 (EP260602b): JinShan optical counterpart detection DATE: 26/06/03 02:11:44 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, X. Liu, Z.P. Zhu, D. Xu, J. An, S.Q. Jiang (NAOC), S.Y. Fu, A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report: We observed the field of EP-WXT Trigger 01709266414 (presumably EP260602b) detected by Einstein Probe (EP), using the JinShan 100B and 100C telescopes located at Altay, Xinjiang, China. A series of r-band frames were obtained. An uncatalogued and decaying source is detected within the EP/WXT error circle at coordinates R.A. (J2000) = 18:13:53.7 (273.4738 deg) Dec. (J2000) = +07:34:16.4 (7.5712 deg) with an uncertainty of ~ 1.0 arcsec. The source had r ~ 19.0 mag at a median time of ~ 1.0 hr post-trigger, calibrated with Pan-STARRS DR2 and not corrected for Galactic extinction of A_V ~ 0.94 mag. We thus think the source is the optical counterpart. We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44780. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42909] GRB 260602B: Fermi GBM Final Localization
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44779 SUBJECT: GRB 260602B: Fermi GBM Final Localization DATE: 26/06/03 01:14:31 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> The Fermi GBM team reports the detection of a likely SHORT GRB "At 22:41:31.26 UT on 02 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260602B (trigger 802132896/260602945). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 187.55, Dec = -16.61 (J2000 degrees, equivalent to J2000 12h 30m, -16d 36'), with a statistical uncertainty of 4.88 degrees. The angle from the Fermi LAT boresight is 71 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260602945/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260602945/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260602945/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44779. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42908] GRB 260601A: GECAM-B observation of a short burst
by GCN Circulars 03 Jun '26

03 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44778 SUBJECT: GRB 260601A: GECAM-B observation of a short burst DATE: 26/06/03 00:54:14 GMT FROM: Yue Wang <m18509381757(a)163.com> Yue Wang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260601A at 2026-06-01T11:00:12.500 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44755). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of muplti-pulses with a duration (T90) of 0.78 +0.21/-0.57 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260601A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44778. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42907] GRB 260601B/EP260601a: J-band upper limit with WINTER
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44777 SUBJECT: GRB 260601B/EP260601a: J-band upper limit with WINTER DATE: 26/06/02 23:04:15 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (NOIRLab), Benjamin Schneider (LAM), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 260601B/EP260601a (Yang et al., GCN 44766; Yu et al., GCN 44767; Wang et al., GCN 44768; Waratkar et al., GCN 44771; Sugita et al., GCN 44773) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-06-02T11:12:20 UTC in the J band (~16 hr after the GRB trigger), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We do not detect a source at the optical counterpart location (Liu et al., GCN 44764; Guelfand et al., GCN 44765; Li et al., GCN 44769). We obtain the following 5-sigma upper limit: J = 18.8 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/44777. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42906] EP260530a/AT 2026nwl: COLIBRÍ optical follow up
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44776 SUBJECT: EP260530a/AT 2026nwl: COLIBRÍ optical follow up DATE: 26/06/02 20:15:16 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Marion Guelfand (CPPM), Camila Angulo (UNAM), Noémie Globus (UNAM), Alan M. Watson (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), 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) report: We observed the field of the optical source AT 2026nwl, discovered by GOTO (Godson et al., TNS Astronomical Transient Report No. 306622), associated with EP260530a (Wu et al., ATel #17824), further observed by COLIBRÍ (Globus et al., GCN Circ. 44759) and KAIT (Zheng et al., GCN Circ. 44775), and classified as a CV (Pursiainen et al., TNS Classification Report No. 23885), with the DDRAGO two-channel wide-field imager mounted on the COLIBRÍ telescope. We observed from 2026-06-02 04:19 to 07:11 UTC (from 79.21 to 82.15 hours after the GOTO discovery) and obtained 24 minutes of exposure in each of the g, r, and i filters, and 72 minutes of exposure in the z filter. The data were reduced and coadded 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 continue to detect the source at the following preliminary magnitudes: g = 15.77 +/- 0.01, r = 15.87 +/- 0.01, i = 15.98 +/- 0.01, z = 16.07 +/- 0.01. We observe a quasi-periodic modulation of the light curve in the different photometric bands with a characteristic timescale of approximately 1 hour, typical of certain classes of accreting binary stars, and a peak-to-valley amplitude of about 0.1 mag Further observations and analysis are ongoing. 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/44776. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42905] EP260530a/AT 2026nwl: KAIT optical observations
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44775 SUBJECT: EP260530a/AT 2026nwl: KAIT optical observations DATE: 26/06/02 18:47:59 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 EP260530a (Wu et al., ATel #17824) on May 31 and again on Jun 02 UT. A set of clear (roughly R) filter images were obtained. We clearly detected the bright CV outburst associated with AT 2026nwl (TNS Astronomical Transient Report 306622, 306654; TNS Classification Reports 23885; Globus et al., GCN 44759). We measure its brightness decayed from 14.4 +/- 0.1 mag (Vega) at 0.98d after the burst, to 15.6 +/- 0.1 mag at 2.95d after the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/44775. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42904] GRB 260602A: Fermi GBM Final Real-time Localization
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44774 SUBJECT: GRB 260602A: Fermi GBM Final Real-time Localization DATE: 26/06/02 18:40:24 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 18:29:53 UT on 2 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260602A (trigger 802117798.896848 / 260602771). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 26.3, Dec = 48.7 (J2000 degrees, equivalent to J2000 01h 45m, 48d 42'), with a statistical uncertainty of 2.0 degrees. The angle from the Fermi LAT boresight is 28.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260602771/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260602771/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260602771/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44774. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42903] GRB 260601B: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44773 SUBJECT: GRB 260601B: CALET Gamma-Ray Burst Monitor detection DATE: 26/06/02 18:35:44 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> S. Sugita, A. Yoshida, T. Sakamoto, 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 260601B at 19:12:46.66 UTC on 1 June 2026 (trigger #1464376270; https://cgbm.calet.jp/cgbm_trigger/flight/1464376270/index.html) A CGBM Notice was distributed in near real time. This event was also reported by GECAM-B (Yu et al., GCN #44767; Wang et al., GCN #44768) and NuSTAR (Waratkar et al., GCN #44771). The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure starting at T+0.1 s, peaking at T+4.9 s, and ending at T+101.4 s. The T90 and T50 durations measured with the SGM data are 70.0 +/- 4.7 s and 21.9 +/- 1.0 s in the 40-1000 keV band, respectively. Einstein Probe/WXT detected an X-ray transient, EP 260601a (Yang et al., GCN #44766), about 35 s after the CGBM trigger. The position of EP 260601a was above the Earth horizon as seen from CALET, and was observable by CGBM at the trigger time, with an incident angle of 83 degrees. The ground-processed light curve is available at: https://cgbm.calet.jp/cgbm_trigger/ground/1464376270/ 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/44773. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42902] EP260602a: Optical upper limits with Kinder observations
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44772 SUBJECT: EP260602a: Optical upper limits with Kinder observations DATE: 26/06/02 17:23:06 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Aryan, T.-W. Chen, W.-J. Hou, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), S. Yang (HNAS), Y.-H. Lee, A. Sankar.K, M.-H. Lee, A. Dutta, Y.-C. Pan, C.-C. Ngeow, K. N.-T. Ho, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, K. W. Smith, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the FXT EP260602a (Li et al., GCN 44770) using the 40cm Seisi Lulin Telescope (SLT) at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations in r-band started at 15:31 UTC on the 2nd of June 2026 (MJD 61140.5068), 7.34 hours after the EP-WXT detection. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Neither in the stacked nor in the difference image did we detect any signature of any new or uncatalogued source. Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude| avg. Seeing | Med. Airmass SLT | r | 61140.5068 | 7.34 | 300 * 6 | >20.0 | 1".77 | 1.13 The presented upper limit is calibrated using the field stars from the PanSTARRS catalog and is not corrected for an expected galactic extinction of A_r = 0.06 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44772. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42901] GRB 260601B / EP260601a: NuSTAR detection of prompt emission
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44771 SUBJECT: GRB 260601B / EP260601a: NuSTAR detection of prompt emission DATE: 26/06/02 16:42:17 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260601B, associated with EP260601a, in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-06-01T19:12:46.65 UTC, shows a detection of GRB 260601B, also detected by CALET-GBM (Trigger 1464376270), GECAM-B (Yu et al., GCN 44767), and is associated with EP260601a detected by EP-WXT (Yang et al., GCN 44766). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a short peak followed by a long burst lasting for a total of about 75-s, consistent with the CALET-GBM & GECAM-B lightcurve. The peak count rate is ~2500-cps with a baseline rate of ~1000-cps during this time period. We also see marginal evidence in the signal above 100 keV in the CZT detectors. The EP/WXT localization (GCN 44766) at RA = 257.649, Dec = -1.647 implies an offset from the NuSTAR boresight of 98-deg (i.e. from the side) and an offset from the geocenter of 120-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260601B Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44771. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42900] EP260602a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44770 SUBJECT: EP260602a: Einstein Probe detection of a fast X-ray transient DATE: 26/06/02 16:35:29 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), Y. Wang (PMO, CAS; UCB), G. J. Yang, W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260602a. The transient triggered EP-WXT (ID: 01709266359) at 2026-06-02T08:11:20 (UTC). The WXT position of the source is R.A. = 240.886 deg, DEC = 50.563 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The WXT spectrum can be fitted with an absorbed power-law, with the absorption fixed at the Galactic value of 2.03 x 10^20 cm^-2, and a photon index of 1.7 (-0.5, +0.5). The unabsorbed 0.5-4 keV flux is 9.0 (-2.4, +3.2) x 10^-11 erg/s/cm2. A follow-up observation with the Follow-up X-ray Telescope (FXT) onboard EP is scheduled. 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/44770. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42899] GRB 260601B/EP260601a: SVOM/VT optical observations
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44769 SUBJECT: GRB 260601B/EP260601a: SVOM/VT optical observations DATE: 26/06/02 15:23:39 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, Y. L. Qiu, L. P. Xin, 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) and J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations to the field of GRB 260601B/EP260601a triggered by Einstein Probe (Yang et al., GCN 44766), which was also detected by GECAM-B (Yu et al., GCN 44767; Wang et al., GCN 44768). The VT observation started at 2026-06-02T08:56:14 UTC, 13.72 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Liu et al., GCN 44764; Guelfand et al., GCN 44765) was detected by VT in both channels. The following measurements are in the AB magnitude without correction for Galactic extinction: Mid time | Band | Exposure Time | Brightness 14.65 h VT_B 76*50 s 23.4 +/- 0.3 mag 14.63 h VT_R 62*50 s 21.43 +/- 0.15 mag The VT red color suggests a moderate redshift ~ 4 (Wang et al.,2020). 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/44769. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42898] GRB 260601B/EP260601a: GECAM-B analysis suggests a possible long duration Type I burst
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44768 SUBJECT: GRB 260601B/EP260601a: GECAM-B analysis suggests a possible long duration Type I burst DATE: 26/06/02 15:04:42 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Zheng-Hang Yu, Shao-Lin Xiong, Chao Zheng, Cheng-Kui Li (IHEP) report on behalf of GECAM team: With the event-by-event data downloaded through the ground station, we conducted the standard analysis of GRB 260601B/EP260601a. The GECAM-B light curve shows that this burst exhibits a temporal profile similar to that of GRB 060614, together with an exceptionally hard spectrum. The initial pulse is clearly detected above 500 keV, while the subsequent “extended” emission, which is temporally consistent with the EP/WXT trigger, is even harder than the initial pulse and is clearly detected above 1 MeV. Using the localization reported by EP/WXT (R.A. = 257.649 deg, Dec = -1.647 deg, GCN#44766) , the time-averaged spectrum from T0-8 s to T0+90 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.36 +0.05/-0.05 and the cutoff energy, parameterized as Epeak, is 3600 +830/-770 keV. The event fluence (10-1000 keV) in this time interval is (1.03 +/-0.02)E-04 erg/cm^2. GRB 260601B is therefore consistent with Type I GRBs in the Amati-relation diagram, as shown at: https://www.bursthub.cn//admin/static/gecambgrb260601B_amati.png Moreover, the main pulse, corresponding to T0+1 s to T0+5 s, can also be fitted by a power law function with an exponential high-energy cutoff, with power law index of -1.10 +0.14/-0.15, and Epeak of 715 +249/-162 keV. Considering its GRB 060614-like light-curve pattern, exceptionally hard spectrum, and location in the Amati-relation diagram, GRB 260601B/EP260601a could be a possible long-duration Type I GRB. Follow-up observations are strongly encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/44768. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42897] GRB 260601B: GECAM-B detection of a burst probably associated with EP260601a
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44767 SUBJECT: GRB 260601B: GECAM-B detection of a burst probably associated with EP260601a DATE: 26/06/02 13:22:14 GMT FROM: yzh807926(a)163.com Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a burst GRB 260601B at 2026-06-01T19:12:48.050 UTC (denoted as T0). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a possible precursor and then a short pulse followed by a long emission with a duration (T90) of 66.5 +2.5/-3.5 s. The on-ground localization of GECAM-B is: Ra: 271.2 deg Dec: -5.48 deg Err: 2.66 deg (1-sigma, statistical only) Considering systematic uncertainties, this localization is consistent with the EP/WXT localization of EP260601a (Yang et al., GCN#44766). The time coincidence and localization coincidence between GRB 260601B and EP260601a strongly support the association of these two events. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260601B.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44767. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42896] EP260601a: Einstein Probe detection of an X-ray transient
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44766 SUBJECT: EP260601a: Einstein Probe detection of an X-ray transient DATE: 26/06/02 11:52:06 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G. J. Yang (NAO, CAS), Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), Y. Wang (PMO, CAS; UCB), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260601a. The transient triggered EP-WXT (ID: 01709266307) at 2026-06-01T19:13:22 UTC. The WXT position of the source is R.A. = 257.649 deg, Dec = -1.647 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the burst started at T_0 = 2026-06-01T19:12:41 UTC. The light curve shows an initial flare lasting approximately 100 s, followed by tail emission. During the flare, the unabsorbed 0.5-4 keV flux was 5.2 (-1.7/+3.6) x 10^-08 erg cm^-2 s^-1. The time-averaged WXT 0.5-4 keV spectrum over the entire detected emission can be described by an absorbed power law, with the hydrogen column density left as a free parameter. The best-fit hydrogen column density is 6.7 (-1.5/+1.6) x 10^21 cm^-2. The best-fit photon index is 1.2 (-0.3/+0.3). The unabsorbed 0.5-4 keV flux is 2.4 (-0.2/+0.3) x 10^-10 erg cm^-2 s^-1. A follow-up observation with the Follow-up X-ray Telescope (FXT) onboard EP is scheduled. Further information will be updated when the telemetry data is received. 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/44766. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42895] EP-WXT trigger 01709266307 (EP260601a): COLIBRÍ optical observations
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44765 SUBJECT: EP-WXT trigger 01709266307 (EP260601a): COLIBRÍ optical observations DATE: 26/06/02 11:05:28 GMT FROM: Marion G <marion.guelfand(a)gmail.com> Marion Guelfand (CPPM), Camila Angulo (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), 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) report: We observed the field of the EP-WXT Trigger 01709266307 (EP260601a) with the DDRAGO two-channel wide-field imager mounted on the COLIBRÍ telescope. We observed from 2026-06-02 08:36 UTC to 09:00 UTC (from 13.38 to 13.39 hours after the trigger) and obtained 20 minutes of simultaneous exposure in the r and z filters, respectively. The data were reduced and coadded with the COLIBRI pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the Pan-STARRS-DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart reported by Liu et al., GCN Circ. 44764. The preliminary magnitude derived for that source is: r = 21.93 +/- 0.15 z = 21.07 +/- 0.12 The source is fading between the two observations. Further observations are ongoing. 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/44765. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42894] EP-WXT trigger 01709266307 (EP260601a): JinShan optical counterpart detection
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44764 SUBJECT: EP-WXT trigger 01709266307 (EP260601a): JinShan optical counterpart detection DATE: 26/06/02 10:23:04 GMT FROM: liuxing(a)nao.cas.cn X. Liu, Z.P. Zhu, D. Xu, J. An, S.Q. Jiang, L.B. He (NAOC), S.Y. Fu, A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report: We observed the field of EP-WXT Trigger 01709266307 (EP260601a) detected by Einstein Probe (EP), using the JinShan 100B telescope located at Altay, Xinjiang, China. A series of r-band frames were obtained. An uncatalogued and decaying source is detected within the EP/WXT error circle at coordinates R.A. (J2000) = 17:10:38.24 Dec. (J2000) = -01:38:42.4 with an uncertainty of ~ 1.0 arcsec. The source had r ~ 18.4 mag at a median time of ~ 0.73 hr post-trigger, calibrated with Pan-STARRS DR2 and not corrected for Galactic extinction of A_V ~ 1.15 mag. We thus think the source is the optical counterpart of EP260601a. We also note the presence of a faint source with g ~ 25.2 mag in the Legacy Survey DR10 image at the above position, which could be the host of EP260601a. We acknowledge the excellent support from T.Q. Chen, and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44764. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42893] GRB 260601A: Glowbug gamma-ray detection of a short burst
by GCN Circulars 02 Jun '26

02 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44763 SUBJECT: GRB 260601A: Glowbug gamma-ray detection of a short burst DATE: 26/06/02 01:04:27 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260601A, which was also detected by Fermi/GBM (GCN 44755, 44760) and CALET (Trigger ID Num 1464346716). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-06-01 11:00:11.408 with a duration of 0.26 s and a total significance of about 77 sigma. The light curve comprises a triple-peaked structure. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44763. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42892] GRB 260531B: Glowbug gamma-ray detection
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44762 SUBJECT: GRB 260531B: Glowbug gamma-ray detection DATE: 26/06/01 22:31:42 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260531B, which was also detected by Fermi/GBM (GCN 44747) and GECAM-B (GCN 44754). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-31 13:57:58.840 with a duration of 8.2 s and a total significance of about 31.6 sigma. The light curve comprises a complex multi-peaked structure. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44762. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42891] GRB 260516D: VLA radio detection
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44761 SUBJECT: GRB 260516D: VLA radio detection DATE: 26/06/01 21:56:18 GMT FROM: Daniel Perley at Liverpool JMU <d.a.perley(a)ljmu.ac.uk> Daniel A. Perley (LJMU), Genevieve Schroeder (Cornell), and Anna Y. Q. Ho (Cornell) report: We observed the location of the X-ray flash GRB 260516D (Brunet et al., GCN 44649; Brunet et al., 44667) using the Karl G. Jansky Very Large Array on 2026-05-22 between 10:46-11:33 UT (approximately 5.6 days after the GRB trigger) using the X-band receivers (mean frequency 10 GHz). A source is detected at the location of the optical transient (Li et al., GCN 44654) with a flux density of 34.9 +/- 8.8 uJy. The inferred luminosity of 2.9 x 10^30 erg/s/Hz is characteristic of GRB afterglows at the equivalent rest-frame post-GRB time, but at the low end of the distribution. We thank the NRAO staff for scheduling and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44761. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42890] GRB 260601A: Fermi GBM Observation
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44760 SUBJECT: GRB 260601A: Fermi GBM Observation DATE: 26/06/01 18:13:56 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 11:00:12.44 UT on 01 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260601A (trigger 802004417/260601458). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 15.06, Dec = 44.38 (J2000 degrees, equivalent to J2000 1h 0m, +44d 22'), with a statistical uncertainty of 2.03 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 30 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 0.8 s (50-300 keV). The time-averaged spectrum from T0-0.07 to T0+0.34 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.63 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 960 +/- 30 keV. The event fluence (10-1000 keV) in this time interval is (2.08 +/- 0.06)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.064 s in the 10-1000 keV band is 40 +/- 1 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 750 +/- 20 keV, alpha = -0.57 +/- 0.05 and beta = -2.0 +/- 0.2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44760. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42889] EP260530a/AT 2026nwl: COLIBRÍ optical observations
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44759 SUBJECT: EP260530a/AT 2026nwl: COLIBRÍ optical observations DATE: 26/06/01 17:34:44 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Damien Dornic (CPPM), Alan M. Watson (UNAM), Rosa L. Becerra (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), Nathaniel R. Butler (ASU), , Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (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) report: We observed the field of the Einstein Probe X-ray transient EP260530a (Wu et al., ATel #17824) with the DDRAGO two-channel wide-field imager mounted on the COLIBRÍ telescope. The observations targeted the optical counterpart candidate, AT 2026nwl, discovered by GOTO (TNS Astronomical Transient Report No. 306622) and associated with EP260530a. We observed from 2026-06-01 04:59 to 06:02 UTC (from (55.93 to 56.97 hours after the GOTO discovery) and obtained 11, 23, 10, 24, and 20 minutes of exposure in the g, r, i, z, and y filters, respectively. The data were reduced and coadded 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 optical counterpart previously reported by GOTO (AT 2026nwl). The source is measured at the following preliminary magnitudes: g = 15.22 +/- 0.01, r = 15.33 +/- 0.01, i = 15.41 +/- 0.01, z = 15.52 +/- 0.01, y = 15.58 +/- 0.01. The source is brighter than the magnitude of L = 17.03 at 2026-05-29 21:04 UTC reported by the GOTO team (TNS Astronomical Transient Report 306622), but fainter than the unfiltered magnitude of 14.46 at 2026-05-31 05:24 UTC reported by Sokolovsky et al (TNS Astronomical Transient Report 306654). If the transient has a simple rise and decay, this suggests that it has already reached its maximum. The source shows blue colors, consistent with both a CV and an FBOT. During the 55 minutes of our observations, the source shows a smooth rise from r = 15.35 to r = 15.28 followed by a smooth fall again to r = 15.36. Similar behavior is also seen in the other filters. This variability is reminiscent of that seen in CVs. We encourage spectroscopic observations to determine the redshift of this source and its likely nature. 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/44759. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42888] GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44758 SUBJECT: GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search DATE: 26/06/01 15:40:07 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP), D. Turpin (CEA) report on behalf of the SVOM/ECLAIRs team The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 260530C, starting at 2026-05-30T00:13:15.62 UTC (trigger time T0), through an on-ground search with the event-by-event data downloaded through the X-band ground station. The burst was detected within several energy ranges and timescales. The best detection is obtained by the Image Trigger with a signal-to-noise ratio of 6.8 within 8-120 keV over a time window of 20.48 seconds starting at T0-20.48s. The burst that triggered ECLAIRs onground shows a double peak structure. The burst duration is estimated to be around 25s in the 4-120 keV energy band through imaging. The localization of the source is RA, Dec = 196.655, 26.384 degrees: RA (J2000) = 13h 06m 37.2s Dec (J2000) = 26d23m02.4s with a 90% C.L. radius of 12.8 arcmin (including systematic error of 6 arcmin added in quadrature). We note that no bright catalogued X-ray sources are found in the error box. The time-averaged spectrum from T0-20.5 s to T0+4.5 s in the energy range 5-120 keV is best fitted by a powerlaw model with alpha = -1.10 +/- 0.16. With this model, the 4-120 keV fluence is (3.2 +0.3/-1.0) e-7 erg/cm^2 and the 4-120 keV photon flux is 0.26 +0.02/-0.08 ph/cm^2/s. All the quoted errors are at the 68% confidence level. A SVOM ToO observation has been requested to follow-up this trigger with both MXT and VT instruments. The results of these observations will be reported later 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44758. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42887] AT2026nik: EP-FXT X-ray counterpart
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44749 SUBJECT: AT2026nik: EP-FXT X-ray counterpart DATE: 26/05/31 21:01:15 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> J. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), A. A. Chrimes (ESA/ESTEC), A. J. Levan (Radboud & Warwick), A Inkenhaag (Bath), D. Coppejans (Warwick), P. Groot (Radboud/UCT/SAAO): We observed the field of AT2026nik (AstroNotes: 2026-151, 2026-152) with the Follow-up X-ray Telescope (FXT) aboard the Einstein Probe mission. The observation was carried out from 2026 May 29 18:45:25.9 to May 30 00:22:29.8 UT, with a total exposure time of 7.2 ks using Modules A and B. After stacking the data from both modules, we detected an X-ray source with a significance of S/N ≈ 5.5 at the position (with an uncertainty of 10"): RA = 11:22:52.1 Dec = -06:13:21.7 No X-ray source is reported at this position in the ROSAT, eROSITA, Swift-XRT, XMM-Newton, or Chandra catalogs, according to the STONKS Multi-Mission X-ray Catalog (Quintin et al. 2024). The position of the detected X-ray source is consistent with that of AT2026nik, suggesting that it is the X-ray counterpart of the transient. The source has a net count rate of 2.58e-3 counts/s. Assuming a Galactic hydrogen column density of N_H = 4e20 cm-2 and a power-law spectrum with photon index Γ = 1.5, we estimate an absorbed X-ray flux of approximately 5.8e-14 erg/cm2/s. AT2026nik exhibited a blue, nearly featureless optical spectrum (P. Pessi and J. Wise; AstroNotes: 2026-151, 2026-152), with a tentative detection of the interstellar Mg II absorption doublet at z = 0.182. Assuming this redshift, the inferred X-ray luminosity is approximately L_X~5.4e42 erg/s, consistent with that observed in AT2018cow and other LFBOTs at a similar epoch (e.g., Margutti et al. 2019). The blue optical spectrum and the newly detected X-ray counterpart support the classification of AT2026nik as a luminous fast blue optical transient (LFBOT). We thank the Einstein Probe staff for their execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44749. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42886] GRB 260527A/EP260527a: Glowbug gamma-ray detection
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44757 SUBJECT: GRB 260527A/EP260527a: Glowbug gamma-ray detection DATE: 26/06/01 12:58:49 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260527A, which was detected initially by Einstein Probe as EP260527a (GCN 44718). The GRB was also detected by Konus-Wind (GCN 44722), GECAM-B (GCN 44724), CALET (GCN 44726), Insight-HXMT (GCN 44735), and Mars-Odyssey (HEND) with an IPN triangulation (GCN 44744). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-27 06:16:08.912 with a duration of 0.26 s and a total significance of about 40 sigma. The light curve comprises a primary peak at ~T0+0.1s and a fainter peak at ~T0+0.2s. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44757. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42885] Fermi GRB 260601A: Global MASTER-Net observations report
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44756 SUBJECT: Fermi GRB 260601A: Global MASTER-Net observations report DATE: 26/06/01 11:45:38 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), M. Segura, 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 260601A ( Fermi GBM team, GCN 44755) errorbox 301 sec after notice time and 327 sec after trigger time at 2026-06-01 11:05:39 UT, with upper limit up to 19.5 mag. Observations started at twilight. The observations began at zenith distance = 53 deg. The sun altitude is -13.8 deg. The galactic latitude b = -18 deg., longitude l = 125 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3352995 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 357 | 2026-06-01 11:05:39 | MASTER-OAGH | (00h 50m 13.85s , +45d 57m 12.7s) | C | 60 | 19.4 | 430 | 2026-06-01 11:06:52 | MASTER-OAGH | (00h 38m 00.15s , +44d 39m 27.6s) | C | 60 | 19.1 | 430 | 2026-06-01 11:06:52 | MASTER-OAGH | (00h 48m 30.18s , +44d 02m 36.0s) | C | 60 | 19.5 | 576 | 2026-06-01 11:09:18 | MASTER-OAGH | (00h 52m 04.36s , +47d 50m 39.9s) | C | 60 | 19.0 | 678 | 2026-06-01 11:10:30 | MASTER-OAGH | (00h 59m 12.69s , +44d 07m 39.1s) | P- | 120 | 16.9 | 678 | 2026-06-01 11:10:30 | MASTER-OAGH | (01h 01m 18.88s , +43d 31m 06.4s) | P| | 120 | 17.8 | 798 | 2026-06-01 11:10:30 | MASTER-OAGH | (01h 01m 18.88s , +43d 31m 06.6s) | P| | 360 | 18.0 | Coadd 807 | 2026-06-01 11:12:39 | MASTER-OAGH | (00h 59m 19.74s , +44d 08m 01.8s) | P- | 120 | 16.9 | 807 | 2026-06-01 11:12:39 | MASTER-OAGH | (01h 01m 25.92s , +43d 31m 26.7s) | P| | 120 | 17.8 | 936 | 2026-06-01 11:14:48 | MASTER-OAGH | (00h 59m 15.81s , +44d 09m 26.1s) | P- | 120 | 16.9 | 936 | 2026-06-01 11:14:48 | MASTER-OAGH | (01h 01m 22.64s , +43d 32m 53.3s) | P| | 120 | 17.5 | 1065 | 2026-06-01 11:16:57 | MASTER-OAGH | (00h 59m 15.96s , +44d 07m 29.9s) | P- | 120 | 16.6 | 1065 | 2026-06-01 11:16:57 | MASTER-OAGH | (01h 01m 22.92s , +43d 30m 56.4s) | P| | 120 | 17.4 | 1173 | 2026-06-01 11:19:15 | MASTER-OAGH | (00h 59m 32.67s , +44d 39m 48.6s) | C | 60 | 18.5 | 1173 | 2026-06-01 11:19:15 | MASTER-OAGH | (01h 09m 59.11s , +44d 02m 59.4s) | C | 60 | 18.3 | 1246 | 2026-06-01 11:20:28 | MASTER-OAGH | (00h 57m 41.97s , +42d 45m 11.1s) | C | 60 | 18.2 | 1246 | 2026-06-01 11:20:28 | MASTER-OAGH | (01h 07m 49.03s , +42d 08m 22.9s) | C | 60 | 18.1 | 1319 | 2026-06-01 11:21:41 | MASTER-OAGH | (01h 01m 31.23s , +46d 34m 48.3s) | C | 60 | 18.1 | 1319 | 2026-06-01 11:21:41 | MASTER-OAGH | (01h 12m 18.99s , +45d 57m 59.6s) | C | 60 | 18.0 | 1393 | 2026-06-01 11:22:55 | MASTER-OAGH | (00h 55m 58.79s , +40d 51m 00.4s) | C | 60 | 17.8 | 1466 | 2026-06-01 11:24:08 | MASTER-OAGH | (00h 47m 06.39s , +42d 09m 10.0s) | C | 60 | 18.1 | 1541 | 2026-06-01 11:25:23 | MASTER-OAGH | (01h 18m 18.85s , +42d 46m 18.7s) | C | 60 | 17.2 | 1686 | 2026-06-01 11:27:48 | MASTER-OAGH | (01h 20m 55.25s , +44d 40m 22.4s) | C | 60 | 17.2 | 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/44756. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42884] GRB 260601A: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44755 SUBJECT: GRB 260601A: Fermi GBM Final Real-time Localization DATE: 26/06/01 11:10:43 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 SHORT GRB At 11:00:12 UT on 1 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260601A (trigger 802004417.438878 / 260601458). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 15.1, Dec = 44.4 (J2000 degrees, equivalent to J2000 01h 00m, 44d 23'), with a statistical uncertainty of 2.0 degrees. The angle from the Fermi LAT boresight is 30.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260601458/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260601458/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260601458/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44755. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42883] GRB 260531B: GECAM-B observation
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44754 SUBJECT: GRB 260531B: GECAM-B observation DATE: 26/06/01 10:08:05 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260531B, at 2026-05-31T13:58:00.050 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44747). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 12 +5/-3 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260531B.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44754. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42882] GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44753 SUBJECT: GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp DATE: 26/06/01 09:04:52 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP) report on behalf of the SVOM/ECLAIRs team The SVOM/ECLAIRs telescope detected an X-ray source starting at 2026-05-18T07:53:22 UTC (trigger time T0), labelled GRB 260518B, through an offline targeted search with the event-by-event data downloaded through the X-band ground station. The source localization is RA, Dec = 299.003 , -48.620 degrees: RA (J2000) =19h56m00.7s Dec (J2000) = -48d37m12.0s with a 90% C.L. radius of 11.1 arcmin (including a systematic error of 6 arcmin added in quadrature). This position is consistent with those of EP 260518a (Liang et al., GCN 44690) and of the optical transient AT 2026ndp with an angular separation of 1.1 and 1.0 arcmin, respectively. This event was detected within several energy ranges and timescales. The best detection is obtained by the on-ground Image Trigger with a signal-to-noise ratio of 8.2 within 4-20 keV over a time window of 40.96 seconds starting at T0-7.68 s. The burst that triggered ECLAIRs on-ground shows a multiple peak lightcurve. The burst duration is estimated to be around 52 s in the 4-20 keV energy band through imaging. The source being detected when the source was emerging from behind the Earth, ECLAIRs may have missed part of the event emission. The ECLAIRs light curve can be found here: https://docs.google.com/document/d/1DvqHDMZI5uQY-K7kINk7iSFot71MQIoEbDZZ7Yv… The time-averaged spectrum from T0-11 s to T0+41 s in the 5-120 keV energy range is best fitted by a broken powerlaw model with alpha = -1.14 +0.28/-0.26, beta = -2.98 +0.72/-1.12 and a break energy of 21.0 +3.5/-6.7 keV. With this model, the 4-120 keV fluence is (7.8 +1.6/-2.1)e-7 erg/cm^2 and the 4-120 keV photon flux is 0.63 +0.05/-0.17 ph/cm^2/s. This event is very soft and if it is a GRB, then it should be probably classified as an X-Ray Flash. Assuming a redshift of z=2.28 (Corcoran et al., GCN 44695) and a standard cosmology with H_0 = 67.3 km/s/Mpc and Omega_M = 0.315 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is (1.25 +0.27/-0.34)e+52 erg, and the rest-frame peak energy of the time-averaged spectrum Ep,z is 68.9 +11.5/-22.0 keV. With these estimates, GRB 260518B is consistent with the distribution of Type II (collapsar-like) GRBs on the Amati relation reported by Willingale et al. 2017 (figure available with the light curve). This further strengthens the nature of the event to be a Gamma-ray burst. If GRB 260518B is related to EP 260518a and the optical transient AT 2026ndp, ECLAIRs may have detected the prompt phase 5.8 h prior to the EP detection while EP and ATLAS may have observed the afterglow phase. All the quoted errors are at the 68% confidence level. 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44753. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42881] The EP-WXT trigger 01709266272 is likely a flaring star
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44752 SUBJECT: The EP-WXT trigger 01709266272 is likely a flaring star DATE: 26/06/01 02:03:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), Q.-C. Liu (THU), G.-J. Yang and H.-W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709266272 at the time of 2026-05-31T17:22:11, is likely a stellar flare associated with StKM 1-1106 (Eclipsing Binary Candidate). The estimated flux of the flare is around 1 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.4 x 10^(31) erg/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/44752. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42880] GRB 260531C: Fermi GBM Final Localization Correction
by GCN Circulars 31 May '26

31 May '26

TITLE: GCN CIRCULAR NUMBER: 44751 SUBJECT: GRB 260531C: Fermi GBM Final Localization Correction DATE: 26/05/31 23:57:21 GMT FROM: rhamburg(a)usra.edu The Fermi GBM team reports the detection of a likely SHORT GRB. "At 21:14:58.91 UT on 31 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260531C (trigger 801954903/260531885). This trigger was initially classified as Below Horizon by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 40.6, Dec = 36.2 (J2000 degrees, equivalent to J2000 2h 42m, +36d 12'), with a statistical uncertainty of 11.6 degrees. The angle from the Fermi LAT boresight is 82 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260531885/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260531885/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260531885/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44751. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42879] Fermi Gamma-ray Burst Monitor trigger 801900520/260531256 is not a GRB
by GCN Circulars 31 May '26

31 May '26

TITLE: GCN CIRCULAR NUMBER: 44750 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 801900520/260531256 is not a GRB DATE: 26/05/31 21:26:24 GMT FROM: Eva M. Palafox at INAOE <eva.palafox(a)gmail.com> B. Mailyan (Florida Tech), E. Palafox (INAOE, Mexico) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 801900520/260531256 at 06:08:35.57 UT on 31 May 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to particle activity." View this GCN Circular online at https://gcn.nasa.gov/circulars/44750. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42878] AT2026nik: EP-FXT X-ray counterpart
by GCN Circulars 31 May '26

31 May '26

TITLE: GCN CIRCULAR NUMBER: 44749 SUBJECT: AT2026nik: EP-FXT X-ray counterpart DATE: 26/05/31 21:01:15 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> J. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), A. A. Chrimes (ESA/ESTEC), A. J. Levan (Radboud & Warwick), A Inkenhaag (Bath), D. Coppejans (Warwick), P. Groot (Radboud/UCT/SAAO): We observed the field of AT2026nik (AstroNotes: 2026-151, 2026-152) with the Follow-up X-ray Telescope (FXT) aboard the Einstein Probe mission. The observation was carried out from 2026 May 29 18:45:25.9 UT to 19:34:24.9 UT, with a total exposure time of 2.9 ks using Modules A and B. After stacking the data from both modules, we detected an X-ray source with a significance of S/N ≈ 3.4 at the position (with an uncertainty of 20"): RA = 11:22:52.6 Dec = -06:13:22.2 No X-ray source is reported at this position in the ROSAT, eROSITA, Swift-XRT, XMM-Newton, or Chandra catalogs, according to the STONKS Multi-Mission X-ray Catalog (Quintin et al. 2024). The position of the detected X-ray source is consistent with that of AT2026nik, suggesting that it is the X-ray counterpart of the transient. The source has a net count rate of 2.57e-3 counts/s. Assuming a Galactic hydrogen column density of N_H = 4e20 cm-2 and a power-law spectrum with photon index Γ = 1.5, we estimate an absorbed X-ray flux of approximately 6.1e-14 erg/cm2/s. AT2026nik exhibited a blue, nearly featureless optical spectrum (P. Pessi and J. Wise; AstroNotes: 2026-151, 2026-152), with a tentative detection of the interstellar Mg II absorption doublet at z = 0.182. Assuming this redshift, the inferred X-ray luminosity is approximately L_X~5.3e42 erg/s, consistent with that observed in AT2018cow and other LFBOTs at a similar epoch (e.g., Margutti et al. 2019). The blue optical spectrum and the newly detected X-ray counterpart support the classification of AT2026nik as a luminous fast blue optical transient (LFBOT). We thank the Einstein Probe staff for their execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44749. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42877] Fermi trigger No 801900520: Global MASTER-Net observations report
by GCN Circulars 31 May '26

31 May '26

TITLE: GCN CIRCULAR NUMBER: 44748 SUBJECT: Fermi trigger No 801900520: Global MASTER-Net observations report DATE: 26/05/31 18:30:43 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), M. Segura, 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 GRB260531.26 (trigger No 801900520,19h 13m 33.60s , -54d 13m 12.0s, R=3.3) errorbox 2033 sec after notice time and 2082 sec after trigger time at 2026-05-31 06:43:18 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 21 deg. The sun altitude is -59.5 deg. MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB260531.26 errorbox 42758 sec after notice time and 42807 sec after trigger time at 2026-05-31 18:02:03 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 76 deg. The sun altitude is -29.8 deg. The galactic latitude b = -25 deg., longitude l = 343 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3350277 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 2113 | 2026-05-31 06:43:18 | MASTER-OAFA | (19h 11m 50.85s , -51d 54m 44.5s) | C | 60 | 18.3 | 2173 | 2026-05-31 06:43:18 | MASTER-OAFA | (19h 11m 50.85s , -51d 54m 44.5s) | C | 180 | 18.7 | Coadd 2191 | 2026-05-31 06:44:36 | MASTER-OAFA | (19h 24m 42.46s , -51d 56m 13.7s) | C | 60 | 18.1 | 2251 | 2026-05-31 06:44:36 | MASTER-OAFA | (19h 24m 42.47s , -51d 56m 13.7s) | C | 180 | 18.6 | Coadd 2272 | 2026-05-31 06:45:57 | MASTER-OAFA | (19h 24m 42.83s , -51d 55m 12.0s) | C | 60 | 18.0 | 2351 | 2026-05-31 06:47:16 | MASTER-OAFA | (19h 11m 51.26s , -51d 55m 16.0s) | C | 60 | 17.9 | 2427 | 2026-05-31 06:48:32 | MASTER-OAFA | (19h 24m 43.21s , -51d 57m 07.7s) | C | 60 | 18.0 | 2503 | 2026-05-31 06:49:48 | MASTER-OAFA | (19h 24m 50.56s , -51d 56m 49.6s) | C | 60 | 18.1 | 2563 | 2026-05-31 06:49:48 | MASTER-OAFA | (19h 24m 50.56s , -51d 56m 49.6s) | C | 180 | 18.9 | Coadd 2571 | 2026-05-31 06:50:56 | MASTER-OAFA | (19h 11m 49.05s , -51d 54m 34.6s) | C | 60 | 18.1 | 2650 | 2026-05-31 06:52:15 | MASTER-OAFA | (18h 46m 18.02s , -53d 46m 35.9s) | C | 60 | 18.1 | 2710 | 2026-05-31 06:52:15 | MASTER-OAFA | (18h 46m 18.03s , -53d 46m 35.9s) | C | 180 | 18.8 | Coadd 2724 | 2026-05-31 06:53:29 | MASTER-OAFA | (18h 46m 11.08s , -53d 47m 17.1s) | C | 60 | 18.2 | 2802 | 2026-05-31 06:54:48 | MASTER-OAFA | (18h 59m 43.87s , -53d 47m 10.3s) | C | 60 | 18.2 | 2862 | 2026-05-31 06:54:48 | MASTER-OAFA | (18h 59m 43.87s , -53d 47m 10.3s) | C | 180 | 18.8 | Coadd 2882 | 2026-05-31 06:56:07 | MASTER-OAFA | (18h 59m 50.56s , -53d 48m 08.5s) | C | 60 | 18.1 | 2965 | 2026-05-31 06:57:30 | MASTER-OAFA | (18h 46m 13.09s , -53d 48m 10.7s) | C | 60 | 18.1 | 3042 | 2026-05-31 06:58:47 | MASTER-OAFA | (18h 59m 51.14s , -53d 48m 44.6s) | C | 60 | 18.2 | 3120 | 2026-05-31 07:00:05 | MASTER-OAFA | (18h 46m 15.86s , -53d 46m 11.8s) | C | 60 | 18.0 | 3180 | 2026-05-31 07:00:05 | MASTER-OAFA | (18h 46m 15.86s , -53d 46m 11.8s) | C | 180 | 18.6 | Coadd 3199 | 2026-05-31 07:01:24 | MASTER-OAFA | (18h 46m 17.98s , -53d 46m 06.1s) | C | 60 | 18.0 | 3290 | 2026-05-31 07:02:55 | MASTER-OAFA | (18h 46m 13.31s , -53d 47m 01.3s) | C | 60 | 18.0 | 3370 | 2026-05-31 07:04:15 | MASTER-OAFA | (18h 59m 44.89s , -53d 46m 54.0s) | C | 60 | 17.8 | 3430 | 2026-05-31 07:04:15 | MASTER-OAFA | (18h 59m 44.88s , -53d 46m 54.0s) | C | 180 | 18.3 | Coadd 3450 | 2026-05-31 07:05:35 | MASTER-OAFA | (18h 59m 52.98s , -53d 47m 52.6s) | C | 60 | 17.6 | 3530 | 2026-05-31 07:06:55 | MASTER-OAFA | (18h 46m 14.94s , -53d 47m 55.3s) | C | 60 | 17.6 | 3590 | 2026-05-31 07:06:55 | MASTER-OAFA | (18h 46m 14.94s , -53d 47m 55.3s) | C | 180 | 18.0 | Coadd 3607 | 2026-05-31 07:08:12 | MASTER-OAFA | (18h 59m 52.02s , -53d 48m 41.0s) | C | 60 | 17.8 | 3684 | 2026-05-31 07:09:29 | MASTER-OAFA | (18h 46m 18.07s , -53d 46m 20.6s) | C | 60 | 17.8 | 3761 | 2026-05-31 07:10:46 | MASTER-OAFA | (18h 47m 18.97s , -51d 52m 21.5s) | C | 60 | 17.7 | 3821 | 2026-05-31 07:10:46 | MASTER-OAFA | (18h 47m 18.98s , -51d 52m 21.6s) | C | 180 | 18.4 | Coadd 3833 | 2026-05-31 07:11:58 | MASTER-OAFA | (19h 00m 10.19s , -51d 53m 44.8s) | C | 60 | 17.7 | 3893 | 2026-05-31 07:11:58 | MASTER-OAFA | (19h 00m 10.19s , -51d 53m 44.8s) | C | 180 | 18.4 | Coadd 3919 | 2026-05-31 07:13:24 | MASTER-OAFA | (19h 00m 10.57s , -51d 52m 42.2s) | C | 60 | 17.7 | 3985 | 2026-05-31 07:14:30 | MASTER-OAFA | (19h 00m 16.18s , -51d 53m 40.5s) | C | 60 | 17.9 | 4064 | 2026-05-31 07:15:49 | MASTER-OAFA | (18h 47m 13.98s , -51d 53m 47.1s) | C | 60 | 17.8 | 4141 | 2026-05-31 07:17:06 | MASTER-OAFA | (19h 00m 18.54s , -51d 54m 13.1s) | C | 60 | 18.0 | 4201 | 2026-05-31 07:17:06 | MASTER-OAFA | (19h 00m 18.54s , -51d 54m 13.1s) | C | 180 | 18.5 | Coadd 4218 | 2026-05-31 07:18:23 | MASTER-OAFA | (18h 47m 17.91s , -51d 52m 10.0s) | C | 60 | 18.1 | 4299 | 2026-05-31 07:19:44 | MASTER-OAFA | (19h 16m 32.50s , -57d 35m 27.0s) | C | 60 | 18.5 | 4359 | 2026-05-31 07:19:44 | MASTER-OAFA | (19h 16m 32.50s , -57d 35m 27.0s) | C | 180 | 19.1 | Coadd 4377 | 2026-05-31 07:21:02 | MASTER-OAFA | (19h 31m 23.40s , -57d 37m 24.8s) | C | 60 | 18.6 | 4437 | 2026-05-31 07:21:02 | MASTER-OAFA | (19h 31m 23.39s , -57d 37m 24.9s) | C | 180 | 19.2 | Coadd 4468 | 2026-05-31 07:22:33 | MASTER-OAFA | (19h 31m 23.11s , -57d 36m 22.0s) | C | 60 | 18.6 | 4547 | 2026-05-31 07:23:52 | MASTER-OAFA | (19h 16m 34.90s , -57d 36m 18.8s) | C | 60 | 18.6 | 4636 | 2026-05-31 07:25:21 | MASTER-OAFA | (19h 16m 29.15s , -57d 37m 16.0s) | C | 60 | 18.6 | 4733 | 2026-05-31 07:26:58 | MASTER-OAFA | (19h 31m 31.66s , -57d 37m 51.1s) | C | 60 | 18.7 | 4809 | 2026-05-31 07:28:14 | MASTER-OAFA | (19h 16m 32.52s , -57d 35m 30.3s) | C | 60 | 18.6 | 4869 | 2026-05-31 07:28:14 | MASTER-OAFA | (19h 16m 32.52s , -57d 35m 30.3s) | C | 180 | 19.0 | Coadd 4896 | 2026-05-31 07:29:41 | MASTER-OAFA | (19h 24m 54.82s , -51d 55m 38.1s) | C | 60 | 18.5 | 4974 | 2026-05-31 07:30:59 | MASTER-OAFA | (19h 24m 58.03s , -51d 53m 53.1s) | C | 60 | 18.4 | 5049 | 2026-05-31 07:32:14 | MASTER-OAFA | (19h 24m 52.09s , -51d 54m 46.8s) | C | 60 | 18.4 | 5109 | 2026-05-31 07:32:14 | MASTER-OAFA | (19h 24m 52.09s , -51d 54m 46.8s) | C | 180 | 19.0 | Coadd 5126 | 2026-05-31 07:33:31 | MASTER-OAFA | (19h 24m 53.16s , -51d 53m 44.0s) | C | 60 | 18.4 | 5206 | 2026-05-31 07:34:51 | MASTER-OAFA | (19h 12m 01.79s , -51d 53m 51.5s) | C | 60 | 18.3 | 5266 | 2026-05-31 07:34:51 | MASTER-OAFA | (19h 12m 01.80s , -51d 53m 51.5s) | C | 180 | 18.6 | Coadd 5288 | 2026-05-31 07:36:13 | MASTER-OAFA | (19h 12m 00.74s , -51d 54m 20.9s) | C | 60 | 17.3 | 5354 | 2026-05-31 07:37:19 | MASTER-OAFA | (19h 12m 00.96s , -51d 54m 19.5s) | C | 60 | 18.4 | 5432 | 2026-05-31 07:38:37 | MASTER-OAFA | (19h 11m 59.11s , -51d 53m 02.6s) | C | 60 | 17.8 | 5492 | 2026-05-31 07:38:37 | MASTER-OAFA | (19h 11m 59.11s , -51d 53m 02.5s) | C | 180 | 18.5 | Coadd 5499 | 2026-05-31 07:39:44 | MASTER-OAFA | (18h 59m 57.09s , -53d 47m 47.5s) | C | 60 | 18.3 | 5559 | 2026-05-31 07:39:44 | MASTER-OAFA | (18h 59m 57.09s , -53d 47m 47.5s) | C | 180 | 18.8 | Coadd 5583 | 2026-05-31 07:41:08 | MASTER-OAFA | (19h 00m 00.32s , -53d 46m 09.8s) | C | 60 | 18.1 | 5649 | 2026-05-31 07:42:14 | MASTER-OAFA | (18h 59m 54.17s , -53d 46m 49.6s) | C | 60 | 18.3 | 5728 | 2026-05-31 07:43:33 | MASTER-OAFA | (18h 59m 54.45s , -53d 45m 47.8s) | C | 60 | 17.8 | 5788 | 2026-05-31 07:43:33 | MASTER-OAFA | (18h 59m 54.45s , -53d 45m 47.7s) | C | 180 | 18.7 | Coadd 5795 | 2026-05-31 07:44:40 | MASTER-OAFA | (18h 46m 29.24s , -53d 45m 55.6s) | C | 60 | 17.8 | 5860 | 2026-05-31 07:45:46 | MASTER-OAFA | (18h 46m 23.45s , -53d 46m 53.3s) | C | 60 | 18.2 | 5920 | 2026-05-31 07:45:46 | MASTER-OAFA | (18h 46m 23.45s , -53d 46m 53.3s) | C | 180 | 18.9 | Coadd 5937 | 2026-05-31 07:47:02 | MASTER-OAFA | (18h 46m 29.93s , -53d 46m 45.6s) | C | 60 | 18.3 | 6015 | 2026-05-31 07:48:20 | MASTER-OAFA | (18h 46m 27.83s , -53d 45m 04.0s) | C | 60 | 18.2 | 6092 | 2026-05-31 07:49:38 | MASTER-OAFA | (18h 59m 59.51s , -53d 47m 11.8s) | C | 60 | 18.1 | 6159 | 2026-05-31 07:50:44 | MASTER-OAFA | (19h 00m 02.74s , -53d 45m 42.7s) | C | 60 | 18.3 | 6239 | 2026-05-31 07:52:04 | MASTER-OAFA | (18h 59m 58.05s , -53d 46m 35.6s) | C | 60 | 18.0 | 6299 | 2026-05-31 07:52:04 | MASTER-OAFA | (18h 59m 58.04s , -53d 46m 35.7s) | C | 180 | 18.6 | Coadd 6306 | 2026-05-31 07:53:11 | MASTER-OAFA | (18h 59m 57.98s , -53d 45m 33.8s) | C | 60 | 18.3 | 6395 | 2026-05-31 07:54:40 | MASTER-OAFA | (18h 46m 32.33s , -53d 45m 41.7s) | C | 60 | 18.2 | 6455 | 2026-05-31 07:54:40 | MASTER-OAFA | (18h 46m 32.33s , -53d 45m 41.7s) | C | 180 | 18.8 | Coadd 6487 | 2026-05-31 07:56:12 | MASTER-OAFA | (18h 46m 26.96s , -53d 46m 39.8s) | C | 60 | 18.2 | 6565 | 2026-05-31 07:57:30 | MASTER-OAFA | (18h 46m 33.86s , -53d 46m 12.0s) | C | 60 | 18.2 | 6642 | 2026-05-31 07:58:47 | MASTER-OAFA | (18h 46m 30.67s , -53d 44m 47.0s) | C | 60 | 18.0 | 6702 | 2026-05-31 07:58:47 | MASTER-OAFA | (18h 46m 30.67s , -53d 44m 47.0s) | C | 180 | 17.8 | Coadd 6720 | 2026-05-31 08:00:05 | MASTER-OAFA | (19h 00m 24.77s , -51d 53m 14.9s) | C | 60 | 18.1 | 6800 | 2026-05-31 08:01:25 | MASTER-OAFA | (19h 00m 27.28s , -51d 51m 36.1s) | C | 60 | 18.1 | 6876 | 2026-05-31 08:02:41 | MASTER-OAFA | (19h 00m 21.83s , -51d 52m 26.9s) | C | 60 | 18.1 | 6936 | 2026-05-31 08:02:41 | MASTER-OAFA | (19h 00m 21.84s , -51d 52m 27.0s) | C | 180 | 18.0 | Coadd 6952 | 2026-05-31 08:03:57 | MASTER-OAFA | (19h 00m 22.92s , -51d 51m 25.9s) | C | 60 | 18.0 | 7030 | 2026-05-31 08:05:15 | MASTER-OAFA | (18h 47m 31.26s , -51d 51m 37.6s) | C | 60 | 18.0 | 7090 | 2026-05-31 08:05:15 | MASTER-OAFA | (18h 47m 31.26s , -51d 51m 37.5s) | C | 180 | 18.6 | Coadd 7109 | 2026-05-31 08:06:34 | MASTER-OAFA | (18h 47m 26.86s , -51d 52m 35.5s) | C | 60 | 18.0 | 7185 | 2026-05-31 08:07:50 | MASTER-OAFA | (18h 47m 33.69s , -51d 52m 33.5s) | C | 60 | 17.9 | 7262 | 2026-05-31 08:09:07 | MASTER-OAFA | (18h 47m 30.42s , -51d 50m 54.8s) | C | 60 | 18.0 | 7341 | 2026-05-31 08:10:26 | MASTER-OAFA | (19h 31m 38.78s , -57d 36m 37.1s) | C | 60 | 18.4 | 7401 | 2026-05-31 08:10:26 | MASTER-OAFA | (19h 31m 38.78s , -57d 36m 37.2s) | C | 180 | 19.2 | Coadd 7423 | 2026-05-31 08:11:48 | MASTER-OAFA | (19h 31m 41.47s , -57d 35m 19.3s) | C | 60 | 18.5 | 7499 | 2026-05-31 08:13:04 | MASTER-OAFA | (19h 31m 37.44s , -57d 35m 53.0s) | C | 60 | 18.5 | 7576 | 2026-05-31 08:14:22 | MASTER-OAFA | (19h 31m 37.85s , -57d 34m 50.7s) | C | 60 | 18.5 | 7636 | 2026-05-31 08:14:22 | MASTER-OAFA | (19h 31m 37.78s , -57d 34m 50.9s) | C | 180 | 18.6 | Coadd 7654 | 2026-05-31 08:15:39 | MASTER-OAFA | (19h 16m 47.51s , -57d 34m 53.5s) | C | 60 | 18.4 | 7746 | 2026-05-31 08:17:11 | MASTER-OAFA | (19h 16m 43.21s , -57d 35m 51.2s) | C | 60 | 18.4 | 7834 | 2026-05-31 08:18:39 | MASTER-OAFA | (19h 16m 49.04s , -57d 35m 26.2s) | C | 60 | 18.3 | 7914 | 2026-05-31 08:19:59 | MASTER-OAFA | (19h 16m 46.29s , -57d 34m 03.8s) | C | 60 | 18.2 | 8005 | 2026-05-31 08:21:30 | MASTER-OAFA | (19h 25m 06.71s , -51d 54m 22.7s) | C | 60 | 18.3 | 8095 | 2026-05-31 08:23:00 | MASTER-OAFA | (19h 25m 09.34s , -51d 52m 44.0s) | C | 60 | 18.2 | 8155 | 2026-05-31 08:23:00 | MASTER-OAFA | (19h 25m 09.34s , -51d 52m 44.0s) | C | 180 | 18.8 | Coadd 8183 | 2026-05-31 08:24:28 | MASTER-OAFA | (19h 25m 03.90s , -51d 53m 26.1s) | C | 60 | 18.2 | 8265 | 2026-05-31 08:25:50 | MASTER-OAFA | (19h 25m 04.32s , -51d 52m 24.1s) | C | 60 | 18.1 | 8331 | 2026-05-31 08:26:57 | MASTER-OAFA | (19h 12m 14.55s , -51d 52m 37.2s) | C | 60 | 18.0 | 8408 | 2026-05-31 08:28:13 | MASTER-OAFA | (19h 12m 09.06s , -51d 53m 35.4s) | C | 60 | 18.0 | 8493 | 2026-05-31 08:29:38 | MASTER-OAFA | (19h 12m 13.79s , -51d 53m 04.8s) | C | 60 | 18.0 | 8572 | 2026-05-31 08:30:57 | MASTER-OAFA | (19h 12m 12.05s , -51d 51m 59.9s) | C | 60 | 18.0 | 8654 | 2026-05-31 08:32:19 | MASTER-OAFA | (19h 00m 11.05s , -53d 46m 14.3s) | C | 60 | 18.0 | 8746 | 2026-05-31 08:33:51 | MASTER-OAFA | (19h 00m 13.99s , -53d 45m 00.1s) | C | 60 | 17.9 | 8806 | 2026-05-31 08:33:51 | MASTER-OAFA | (19h 00m 13.99s , -53d 45m 00.1s) | C | 180 | 18.5 | Coadd 8836 | 2026-05-31 08:35:21 | MASTER-OAFA | (19h 00m 09.05s , -53d 45m 39.9s) | C | 60 | 17.9 | 8911 | 2026-05-31 08:36:36 | MASTER-OAFA | (19h 00m 08.70s , -53d 44m 38.2s) | C | 60 | 17.9 | 9004 | 2026-05-31 08:38:09 | MASTER-OAFA | (18h 46m 44.75s , -53d 44m 51.5s) | C | 60 | 17.7 | 9114 | 2026-05-31 08:39:59 | MASTER-OAFA | (18h 46m 30.23s , -53d 52m 59.6s) | C | 60 | 17.8 | 9180 | 2026-05-31 08:41:05 | MASTER-OAFA | (18h 46m 36.47s , -53d 52m 41.7s) | C | 60 | 17.9 | 9261 | 2026-05-31 08:42:26 | MASTER-OAFA | (18h 46m 34.22s , -53d 51m 00.2s) | C | 60 | 17.9 | 9350 | 2026-05-31 08:43:55 | MASTER-OAFA | (19h 00m 07.00s , -53d 53m 37.7s) | C | 60 | 16.4 | 9410 | 2026-05-31 08:43:55 | MASTER-OAFA | (19h 00m 07.00s , -53d 53m 37.7s) | C | 180 | 17.9 | Coadd 9497 | 2026-05-31 08:46:23 | MASTER-OAFA | (19h 00m 04.66s , -53d 52m 39.3s) | C | 60 | 17.5 | 9578 | 2026-05-31 08:47:43 | MASTER-OAFA | (19h 00m 04.92s , -53d 51m 38.1s) | C | 60 | 17.9 | 9662 | 2026-05-31 08:49:07 | MASTER-OAFA | (19h 00m 33.52s , -51d 59m 01.0s) | C | 60 | 17.9 | 9740 | 2026-05-31 08:50:25 | MASTER-OAFA | (19h 00m 30.52s , -51d 57m 57.7s) | C | 60 | 18.0 | 9800 | 2026-05-31 08:50:25 | MASTER-OAFA | (19h 00m 30.51s , -51d 57m 57.7s) | C | 180 | 18.6 | Coadd 9824 | 2026-05-31 08:51:49 | MASTER-OAFA | (19h 00m 30.70s , -51d 59m 13.4s) | C | 60 | 18.0 | 9902 | 2026-05-31 08:53:07 | MASTER-OAFA | (19h 00m 33.85s , -51d 57m 39.7s) | C | 60 | 18.1 | 9989 | 2026-05-31 08:54:34 | MASTER-OAFA | (19h 31m 49.04s , -57d 42m 31.4s) | C | 60 | 18.5 | 10064 | 2026-05-31 08:55:50 | MASTER-OAFA | (19h 31m 42.78s , -57d 43m 30.9s) | C | 60 | 18.4 | 10144 | 2026-05-31 08:57:09 | MASTER-OAFA | (19h 31m 49.15s , -57d 43m 13.2s) | C | 60 | 17.6 | 10217 | 2026-05-31 08:58:22 | MASTER-OAFA | (19h 31m 47.05s , -57d 41m 44.9s) | C | 60 | 18.3 | 10309 | 2026-05-31 08:59:55 | MASTER-OAFA | (19h 25m 08.75s , -51d 59m 40.0s) | C | 60 | 18.2 | 10369 | 2026-05-31 08:59:55 | MASTER-OAFA | (19h 25m 08.75s , -51d 59m 40.0s) | C | 180 | 18.7 | Coadd 10392 | 2026-05-31 09:01:17 | MASTER-OAFA | (19h 25m 08.62s , -51d 58m 38.4s) | C | 60 | 18.1 | 10477 | 2026-05-31 09:02:42 | MASTER-OAFA | (19h 25m 14.18s , -51d 59m 37.6s) | C | 60 | 17.8 | 10546 | 2026-05-31 09:03:51 | MASTER-OAFA | (19h 25m 08.91s , -52d 00m 36.7s) | C | 60 | 17.7 | 10667 | 2026-05-31 09:05:53 | MASTER-OAFA | (19h 02m 08.96s , -50d 04m 19.5s) | C | 60 | 18.0 | 10746 | 2026-05-31 09:07:11 | MASTER-OAFA | (19h 02m 02.62s , -50d 05m 18.5s) | C | 60 | 17.9 | 10843 | 2026-05-31 09:08:48 | MASTER-OAFA | (19h 36m 55.75s , -51d 59m 09.3s) | C | 60 | 18.3 | 10903 | 2026-05-31 09:08:48 | MASTER-OAFA | (19h 36m 55.75s , -51d 59m 09.3s) | C | 180 | 18.9 | Coadd 10919 | 2026-05-31 09:10:04 | MASTER-OAFA | (19h 36m 49.81s , -52d 00m 06.7s) | C | 60 | 18.2 | 11010 | 2026-05-31 09:11:35 | MASTER-OAFA | (19h 36m 49.96s , -52d 00m 05.7s) | C | 60 | 18.4 | 11102 | 2026-05-31 09:13:07 | MASTER-OAFA | (19h 36m 50.16s , -52d 00m 04.8s) | C | 60 | 18.5 | 11162 | 2026-05-31 09:13:07 | MASTER-OAFA | (19h 36m 50.16s , -52d 00m 04.8s) | C | 180 | 19.2 | Coadd 11270 | 2026-05-31 09:15:55 | MASTER-OAFA | (19h 36m 56.81s , -52d 00m 59.2s) | C | 60 | 18.4 | 11348 | 2026-05-31 09:17:13 | MASTER-OAFA | (19h 36m 54.49s , -52d 00m 45.3s) | C | 60 | 18.4 | 11599 | 2026-05-31 09:21:24 | MASTER-OAFA | (19h 36m 53.46s , -51d 58m 57.5s) | C | 60 | 18.3 | 11659 | 2026-05-31 09:21:24 | MASTER-OAFA | (19h 36m 53.46s , -51d 58m 57.5s) | C | 180 | 19.0 | Coadd 11677 | 2026-05-31 09:22:43 | MASTER-OAFA | (19h 36m 57.97s , -51d 59m 57.0s) | C | 60 | 18.2 | 11824 | 2026-05-31 09:25:09 | MASTER-OAFA | (19h 36m 58.67s , -52d 00m 50.4s) | C | 60 | 18.2 | 42838 | 2026-05-31 18:02:03 | MASTER-SAAO | (19h 12m 51.00s , -50d 21m 54.7s) | C | 60 | 16.2 | 42838 | 2026-05-31 18:02:03 | MASTER-SAAO | (19h 10m 01.45s , -50d 06m 26.3s) | C | 60 | 16.5 | 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/44748. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42876] GRB 260531B: Fermi GBM Final Real-time Localization
by GCN Circulars 31 May '26

31 May '26

TITLE: GCN CIRCULAR NUMBER: 44747 SUBJECT: GRB 260531B: Fermi GBM Final Real-time Localization DATE: 26/05/31 14:08:37 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 13:57:59 UT on 31 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260531B (trigger 801928684.989378 / 260531582). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 282.6, Dec = 6.4 (J2000 degrees, equivalent to J2000 18h 50m, 6d 24'), with a statistical uncertainty of 2.2 degrees. The angle from the Fermi LAT boresight is 48.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260531582/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260531582/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260531582/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44747. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42875] GRB 260531A: MAXI/GSC detection
by GCN Circulars 31 May '26

31 May '26

TITLE: GCN CIRCULAR NUMBER: 44746 SUBJECT: GRB 260531A: MAXI/GSC detection DATE: 26/05/31 09:28:53 GMT FROM: Motoko Serino at Aoyama Gakuin U. <serino(a)phys.aoyama.ac.jp> H. Aoe (Ehime U.), H. Negoro (Nihon U.), M. Serino, S. Sugita (AGU), M. Nakajima, K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), S. Ogawa (TUS) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 05:30:18 UT on 2026 May 31. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (69.904 deg, -10.627 deg) = (04 39 36, -10 37 37) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.23 deg and 0.17 deg, respectively. The roll angle of long axis from the north direction is 64.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 230 +- 36 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (R.A., Dec) = (69.234, -11.160) deg = (04 36 56, -11 09 36) (J2000) (R.A., Dec) = (69.533, -11.386) deg = (04 38 07, -11 23 09) (J2000) (R.A., Dec) = (70.598, -10.018) deg = (04 42 23, -10 01 04) (J2000) (R.A., Dec) = (70.300, -9.794) deg = (04 41 11, -09 47 38) (J2000) There was no significant excess flux in the previous transit at 03:57 UT and in the next transit at 07:03 UT with an upper limit of 20 mCrab for each. Note that this position is consistent with the position of Seyfert Galaxy MCG-02-12-050, but it is not clear if this transient is related to MCG-02-12-050 at this time. View this GCN Circular online at https://gcn.nasa.gov/circulars/44746. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42874] AT 2026nuz: COLIBRÍ optical observations
by GCN Circulars 30 May '26

30 May '26

TITLE: GCN CIRCULAR NUMBER: 44745 SUBJECT: AT 2026nuz: COLIBRÍ optical observations DATE: 26/05/30 16:56:24 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Alan M. Watson (UNAM), Rosa L. Becerra (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), 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), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the AT 2026nuz (Habeeb et al., GCN Circ. 44737) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-30 08:34 to 11:17 UTC (from 30.4 to 32.4 hours after the trigger for GRB 260529A; Fermi GBM team, GCN 44733) and obtained 30, 30, 62, and 122 minutes of exposure in the g, r, i, and z filters. The data were reduced and coadded 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 detected the optical transient AT 2026nuz reported by Habeeb et al. (GCN Circ. 44737) at preliminary magnitudes of: g = 18.29 +/- 0.01 r = 18.32 +/- 0.01 i = 18.46 +/- 0.01 z = 18.51 +/- 0.01 The blue colors suggest that this is not the afterglow of GRB 260529A but could be CV, as suggested by Habeeb et al., or possibly an FBOT. That said, in addition to the reasons given by Habeeb et al., the lack of an obvious host in Legacy Survey imaging (Dey et al. 2019) argues against this being an FBOT. Nevertheless, we encourage spectroscopic observation to determine the nature of this source. 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/44745. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42873] IPN triangulation of GRB 260527A / EP260527a
by GCN Circulars 30 May '26

30 May '26

TITLE: GCN CIRCULAR NUMBER: 44744 SUBJECT: IPN triangulation of GRB 260527A / EP260527a DATE: 26/05/30 14:35:28 GMT FROM: Dmitry Svinkin at Ioffe Institute <dmitrysvinkin(a)gmail.com> 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, E. Burns on behalf of the IPN, Y. Kawakubo, A. Yoshida, T. Sakamoto, S. Sugita (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), on behalf of the CALET collaboration, Chen-Wei Wang (IHEP), Shao-Lin Xiong (IHEP), Shuang-Nan Zhang (IHEP) on behalf of the Insight-HXMT team, Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng, Cheng-Kui Li (IHEP) on behalf of GECAM 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 260527A (Konus-Wind detection: Svinkin et al., GCN 44722; GECAM-B detection: Yu et al., GCN 44724; CALET-GBM detection: Kawakubo et al., GCN 44726; Insight-HXMT detection: Wang et al., GCN 44735) was detected by Konus-Wind, CALET (GBM trigger 1463897683), GECAM-B, Insight-HXMT(HE), and Mars-Odyssey (HEND) at about 22570 s UT (06:16:10). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 192.924 (12h 51m 42s) +1.318 ( +1d 19' 03") Corners: 192.308 (12h 49m 14s) +0.301 ( +0d 18' 02") 192.793 (12h 51m 10s) +1.224 ( +1d 13' 25") 193.417 (12h 53m 40s) +2.085 ( +2d 05' 08") 193.052 (12h 52m 13s) +1.406 ( +1d 24' 23") --------------------------------------------- The error box area is 457 sq. arcmin, and its maximum dimension is 2.1 deg (the minimum one is 6.4 arcmin). The Sun distance was 125 deg. This localization may be improved. The fast X-ray transient EP260527a (Yang et al., GCN 44718) is inside the box strengthen the association of the transient and GRB 260527A. A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB260527_T22572/IPN/ View this GCN Circular online at https://gcn.nasa.gov/circulars/44744. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42872] EP260527a/GRB 260527A: further FTW optical and NIR observations
by GCN Circulars 30 May '26

30 May '26

TITLE: GCN CIRCULAR NUMBER: 44743 SUBJECT: EP260527a/GRB 260527A: further FTW optical and NIR observations DATE: 26/05/30 13:40:09 GMT FROM: Ziyuan.Zhu(a)campus.lmu.de Ziyuan Zhu (LMU), Malte Busmann (LMU), Brendan O'Connor (CMU), Julius Gassert (LMU/CMU), Daniel Gruen (LMU), Xander Hall (CMU), and Antonella Palmese (CMU) report: We observed the counterpart of EP260527a/GRB 260527A (Yang et al., GCN 44718; Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Svinkin et al., GCN 44722; Yu et al., GCN 44724; Yang et al., GCN 44725; Kawakubo et al., GCN 44726; Mo et al., GCN 44727; Busman et al., GCN 44728) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands for 48x 180s starting at starting at 2026-05-29 20:47 UT (2.6 days after the trigger). In the r band, we do not detect the counterpart down to a limiting magnitude of r > 24.0 AB mag. The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Christoph Ries from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44743. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42871] GRB 260530B: SVOM/GRM detection of a possible bright short GRB
by GCN Circulars 30 May '26

30 May '26

TITLE: GCN CIRCULAR NUMBER: 44742 SUBJECT: GRB 260530B: SVOM/GRM detection of a possible bright short GRB DATE: 26/05/30 13:26:56 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Marius Brunet (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a bright short burst GRB 260530B (SVOM trigger reference: sb26053001) at 2026-05-30T06:00:05.600 UTC (T0). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single symmetrical smooth pulse with a T90 of 1.55 +0.20/-0.15 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260530B.png ECLAIRs was not collecting data at the time of this burst. We note that this signal was detected near the NWC transmitter and may be associated with the artificial electron belt, so it is not yet clear whether it is a genuine astrophysical burst. 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44742. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42870] GRB 260530A: Fermi GBM Final Real-time Localization
by GCN Circulars 30 May '26

30 May '26

TITLE: GCN CIRCULAR NUMBER: 44741 SUBJECT: GRB 260530A: Fermi GBM Final Real-time Localization DATE: 26/05/30 06:21:32 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 06:10:52 UT on 30 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260530A (trigger 801814257.752724 / 260530258). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 93.0, Dec = 12.7 (J2000 degrees, equivalent to J2000 06h 12m, 12d 41'), with a statistical uncertainty of 6.4 degrees. The angle from the Fermi LAT boresight is 87.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260530258/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260530258/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260530258/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44741. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42869] GRB 260527A / EP260527a: VLA radio detection
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44740 SUBJECT: GRB 260527A / EP260527a: VLA radio detection DATE: 26/05/29 16:53:30 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), J. Rastinejad (UMD), W. Fong (Northwestern) report: We observed the location of the short-duration GRB 260527A / EP260527a (Yang et al. GCN 44718, Svinkin et al. GCN 44722, Yu et al. GCN 44724) with the Karl G. Jansky Very Large Array (VLA) in A configuration under program 26A-062 (PI Schroeder) at a mid time of 2026 May 29 at 04:47 UT (1.9 days post-burst) for 0.75 hours at a mean frequency of 6 GHz. In preliminary analysis, we detect a 3-sigma radio source with a flux density of ~50 microJy at the position: RA(J2000) = 12:52:13.141 Dec(J2000) = +01:28:56.47 with an uncertainty of ~0.1" in each coordinate. This position is offset by ~0.4" from the optical counterpart (Aguilar-Ruiz et al. GCN 44719). At the proposed event redshift of z=0.8 (Yang et al. GCN 44736), this corresponds to a rest-frame luminosity of ~ 9e29erg/s/Hz, on the bright end of typical short-duration Gamma-ray burst radio afterglow luminosities at a similar rest-frame time (e.g., Laskar et al. 2022, Anderson et al. 2025, Belkin et al. 2026). Further observations are planned to assess the variability of the radio source and its connection to GRB 260527A and EP260527a. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44740. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42868] EP260527a/GRB 260527A: optical upper limit with Kinder observations
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44739 SUBJECT: EP260527a/GRB 260527A: optical upper limit with Kinder observations DATE: 26/05/29 15:40:44 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> K. N.-T. Ho, A. Aryan, T.-W. Chen, W.-J. Hou, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), S. Yang(HNAS), Y.-H. Lee, A. Sankar.K, M.-H. Lee, A. Dutta, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, C.-S. Lin, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, K. W. Smith, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260527a (Yang et al., GCN 44718, GCN 44725; Svinkin, GCN 44722; Yu et al., GCN 44724; Kawakubo et al., GCN 44726; Wang et al., GCN 44735) using the 1m LOT at the Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86). The first SLT epoch of observations started at 16:02 UTC on 28th May 2026 (MJD 61188.6683), 33.71 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. Neither in the individual frames nor in the stacked frame did we detect the reported optical/NIR counterpart candidate (Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Mo et al., GCN 44727; Busmann et al., GCN 44728; Corcoran et al., GCN 44729; Kabir et al., GCN 44730; O'Connor et al., GCN 44731; Yang et al., GCN 44736). The details of the observations and measured PSF magnitude with template subtraction (in the AB system) of the possible counterpart of EP260507a are as follows: -------------------------------------------------------------------------------------------------- Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 61188.6683 | 33.71 | 120 * 15 | >21.1 | 1".24 | 2.02 The presented magnitudes are calibrated using the field stars from the Pan-STARRS catalogue. The reported upper limit is not corrected for an expected galactic extinction of A_r = 0.04 mag, in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44739. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42867] GRB 260429B / EP260429a: COLIBRÍ optical counterpart candidate
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44738 SUBJECT: GRB 260429B / EP260429a: COLIBRÍ optical counterpart candidate DATE: 26/05/29 15:17:32 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Enrique Moreno Méndez (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We reimaged the field of GRB 260429B / EP260429a (Wang et al., GCN Circ. 44426, Arya et al., GCN Circ. 44443) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-27 06:34 to 08:42 UTC (from 27.7 to 27.8 days after the trigger) and obtained 1.57 hours of exposure in the r and z filters. The data were reduced and coadded with the ASU COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. By comparing these observations with our first epoch reported by Fortin et al. (GCN Circ. 44434), we found that an uncatalogued optical source located at: RA (J2000) = 240.58812 (16:02:21.15) Dec (J2000) = -9.60116 (-09:36:04.2) and with an uncertainty of 0.5”, is no longer detected in this second epoch down to the following (3-sigma) limits: r > 23.90 z > 23.07 In our first epoch, for this source, we measured: r = 21.95 +/- 0.05 z = 21.08 +/- 0.04 Given the fading nature of the source, the spatial coincidence with the source EPF J160221.2-093607 reported in by the EP team (Wang et al., GCN Circ. 44445), and the absence of any known minor planet at this position, we suggest this is the optical counterpart of GRB 260429B / EP260429a. 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/44738. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42866] GRB 260529A: GOTO tentative optical afterglow candidate
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44737 SUBJECT: GRB 260529A: GOTO tentative optical afterglow candidate DATE: 26/05/29 12:21:36 GMT FROM: Nusrin Habeeb at University of Leicester <nh312(a)leicester.ac.uk> N. Habeeb, A. Kumar, D. O’Neill, R. Starling, B. Gompertz, G. Ramsay, S. Belkin, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, M. Pursiainen, on behalf of the GOTO collaboration We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the Fermi/GBM detected GRB 260529A (fermi_801715802, Fermi GBM team, GCN 44733). Observations covering the GBM localization began at 2026-05-29 03:00:27 UT (+0.18h post trigger) and continued through to 2026-05-29 04:55:50 UT(+2.10 h post trigger). Images consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline (Lyman et al. 2026) and difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. A new optical transient, GOTO26fez (AT 2026nuz), is identified within the 90% localization region of the Fermi/GBM trigger. The source was detected in the GOTO L-band with magnitudes of 17.85 ± 0.06 and 17.90 ± 0.04 AB mag at +0.23 h and +1.3 h post-trigger, respectively. We would like to caution that, given the source location close to the Galactic plane, we cannot exclude the possibility that the transient is of Galactic origin, such as a stellar flare or a CV. We find no evidence of this source prior to the GRB trigger time in previous GOTO observations, in the archival ATLAS forced photometry server (Shingles et al. 2021) to a magnitude limit of m_o > 18.06 AB mag ~26.3h prior to the trigger, nor in archival ZTF observations provided by the Lasair broker (Smith et al. 2019). We note, however, that the most recent pre-trigger observations from GOTO were obtained approximately one month prior to the burst, and therefore do not provide constraints on shorter-timescale pre-burst variability. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44737. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42865] GRB 260527A/EP260527a: VLT/X-shooter tentative redshift
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44736 SUBJECT: GRB 260527A/EP260527a: VLT/X-shooter tentative redshift DATE: 26/05/29 10:15:04 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Y.-H. Yang, E. Troja, M. El Kabir (U Rome) report on behalf of the ERC BHianca team: We observed the field of EP260527a (Yang et al., GCN 44718), likely associated with the short GRB 260527A (Svinkin et al., GCN 44722, Yu et al., GCN 44724; Kawakubo et al., GCN 44726, Wang et al., GCN 44735) with the X-shooter spectrograph on the ESO Very Large Telescope (VLT). Observations were performed beginning at 41 hours after the GRB trigger, at an average airmass of 1.3 and in excellent conditions. Our spectra cover the wavelength range 3000-25000 AA, and consist of 4x600 s exposures. Using a nearby bright star for blind offsets, we placed the 1 arcsec slit at the position of the optical counterpart (Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Busmann et al.44728; Corcoran et al. GCN 44729, El Kabir et al. GCN 44730, O’Connor et al. GCN 44731). Based on a preliminary analysis, we report the identification of weak emission features consistent with the [OII] 3727 doublet at z ~ 0.80, which we propose as the tentative redshift of the EP transient and its underlying host galaxy. Further observations to confirm this value are planned. We thank the staff at the VLT for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44736. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42864] GRB 260527A/EP260527a: Insight-HXMT detection
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44735 SUBJECT: GRB 260527A/EP260527a: Insight-HXMT detection DATE: 26/05/29 03:21:07 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Zheng-Hang Yu, Shao-Lin Xiong, Cheng-Kui Li, and Chao Zheng report on behalf of the Insight-HXMT team: At 2026-05-27T06:16:10.000 (T0), Insight-HXMT/HE detected the short burst GRB 260527A/EP260527a, which is also detected by Konus-Wind (D. Svinkin et al., GCN#44722), GECAM-B (Yu et al., GCN #44724), and EP (Yang et al., GCN # 44718). The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 0.50 +0.30/-0.11 s. The total counts from this burst is 721 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260527A.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/44735. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42863] Fermi GRB 260529A: Global MASTER-Net observations report
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44734 SUBJECT: Fermi GRB 260529A: Global MASTER-Net observations report DATE: 26/05/29 03:17:39 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), M. Segura, 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 260529A ( Fermi GBM team, GCN 44733) errorbox 564 sec after notice time and 606 sec after trigger time at 2026-05-29 03:00:04 UT, with upper limit up to 17.5 mag. The observations began at zenith distance = 74 deg. The sun altitude is -66.9 deg. The galactic latitude b = -25 deg., longitude l = 28 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3345808 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 666 | 2026-05-29 03:00:04 | MASTER-OAFA | (20h 10m 08.98s , -15d 23m 33.3s) | C | 120 | 17.3 | 807 | 2026-05-29 03:02:10 | MASTER-OAFA | (20h 10m 09.05s , -15d 23m 24.1s) | C | 150 | 17.5 | 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/44734. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42862] GRB 260529A: Fermi GBM Final Real-time Localization
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44733 SUBJECT: GRB 260529A: Fermi GBM Final Real-time Localization DATE: 26/05/29 03:00:37 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 02:49:57 UT on 29 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260529A (trigger 801715802.916756 / 260529118). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 302.8, Dec = -15.3 (J2000 degrees, equivalent to J2000 20h 11m, -15d 18'), with a statistical uncertainty of 4.2 degrees. The angle from the Fermi LAT boresight is 90.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260529118/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260529118/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260529118/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44733. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42861] EP250526a: SVOM/VT optical upper limits
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44732 SUBJECT: EP250526a: SVOM/VT optical upper limits DATE: 26/05/29 02:52:08 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> J. R. Xu, H. L. Li, C. Wu, Y. L. Qiu, L. P. Xin, Y. N. Ma, Z. H. Yao, 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) and J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations to the field of EP260526a triggered by Einstein Probe (Yang et al., GCN 44712). The observation started at 2026-05-27T05:44:54 UTC, 20.022 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued sources were detected in stacked images within the error box of EP-FXT (Yang et al, GCN 44721) and EP-WXT (Yang et al, GCN 44712), compared to the Legacy Survey. The 3 sigma limit magnitudes are derived as follows: Mid time | Band | Exposure Time | 3 sigma upper limit 21.53 h VT_B 57*50 s > 23.5 mag 21.53 h VT_R 57*50 s > 23.3 mag Our non-detection is consistent with the observations from COLIBRÍ (Becerra et al., GCN 44710) and LCO (van Hoof et al., GCN 44713). 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/44732. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42860] GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44731 SUBJECT: GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations DATE: 26/05/29 02:17:48 GMT FROM: Brendan O'Connor at Carnegie Mellon University <boconno2(a)andrew.cmu.edu> Brendan O'Connor (CMU), Malte Busmann (LMU), Julius Gassert (LMU/CMU), Daniel Gruen (LMU), Xander Hall (CMU), and Antonella Palmese (CMU) report: We observed the counterpart of GRB 260527A/EP260527a (Yang et al., GCN 44718; Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Svinkin et al., GCN 44722; Yu et al., GCN 44724; Yang et al., GCN 44725; Kawakubo et al., GCN 44726; Mo et al., GCN 44727) using the GMOS-S instrument mounted on the Gemini-South telescope. Our observations were carried out in the r and i filters for 10x90 s exposure in each band. At the location of the optical counterpart (Aguilar-Ruiz et al., GCN 44719), we detect a source with magnitude i = 23.2 +/- 0.1 AB mag, consistent with recent reports (Busmann et al., GCN 44728; Corcoran et al., GCN 44729; El Kabir et al., GCN 44730). The photometry is calibrated against the PS1 catalog and is not corrected for the minimal Galactic extinction along the line of sight. We thank the Gemini staff, in particular Aleksandar Cikota, for the rapid scheduling and execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44731. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42859] EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44730 SUBJECT: EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart DATE: 26/05/29 02:09:56 GMT FROM: Massine El Kabir <m.elkabir(a)campus.unimib.it> M. El Kabir, Y. Yang and E. Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of EP260527a (Yang et al., GCN 44718), likely associated with the short GRB 260527A (Svinkin et al., GCN 44722, Yu et al., GCN 44724; Kawakubo et al., GCN 44726), with the FORS2 and HAWK-I on the ESO Very Large Telescope (VLT). Observations started about 41.4 hrs after the GRB trigger and were performed at an airmass of ~1.2 in excellent conditions. The field was imaged using the r, z, J and K filters. Photometric calibration was performed using nearby stars from the Pan-STARRS and 2MASS catalogues. Magnitudes are reported in the AB system and are not corrected for Galactic extinction. At the position of the optical counterpart (Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Busmann et al.44728; Corcoran et al. GCN 44729 ), we detect a source with the following preliminary magnitude: z = 23.1 +/- 0.1 J = 23.0 +/- 0.1 Compared to earlier observations (Aguilar-Ruiz et al., GCN 44719), our measurements suggest a rapid fading of the afterglow, consistent with the observed X-ray behavior (Yang et al. GCN, 44725). We thank the staff at the VLT for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44730. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42858] EP260527a / GRB 260527A: NOT optical observations
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44729 SUBJECT: EP260527a / GRB 260527A: NOT optical observations DATE: 26/05/28 23:47:22 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> G. Corcoran (UCD), J. An (NAOC), A. van Hoof (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), Dimple (Birmingham), R. A. J. Eyles-Ferris (Leicester), B. P. Gompertz (Birmingham), P. G. Jonker (Radboud), A. J. Levan (Radboud and Warwick), J. A. Quirola-Vasquez (Radboud), A. M. Kadela (NOT and NBI), report on behalf of a larger collaboration: We observed the optical afterglow (Aguilar-Ruiz et al., GCN 44719; Li et al. GCN 44720; Busman et al., GCN 44728) of EP260527a (Yang et al., GCN 44718), likely associated with GRB 260527A (Svinkin et al., GCN 44722; Yu et al., GCN 44724; Kawakubo et al., GCN 44726), using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Observations were secured in both the i (25x120 s) and z (16x120 s) bands. At mean epochs of 2026 May 28.911 and 28.946 UT (39.59 and 40.44 hr after the Konus/Wind trigger time, respectively), we measure for the counterpart the following magnitudes: i = 23.17 +- 0.15 z = 23.25 +- 0.31 These magnitudes are calibrated against the Pan-STARRS catalog and are not corrected for Galactic extinction. We note the presence of a faint, underlying object cataloged in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey (Aihara et al., doi:10.1093/pasj/psab122) at r = 25.72 +/- 0.17, i = 25.44 +/- 0.18 and z = 25.32 +/- 0.29 (all AB). Due to the lack of sufficient high S/N multiband detections, there is no reliable reported photometric redshift for this object. View this GCN Circular online at https://gcn.nasa.gov/circulars/44729. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42857] GRB 260527A/EP260527a: FTW optical and NIR observations
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44728 SUBJECT: GRB 260527A/EP260527a: FTW optical and NIR observations DATE: 26/05/28 23:03:55 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O'Connor (CMU), Julius Gassert (LMU/CMU), Daniel Gruen (LMU), Xander Hall (CMU), and Antonella Palmese (CMU) report: We observed the counterpart of GRB 260527A/EP260527a (Yang et al., GCN 44718; Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Svinkin et al., GCN 44722; Yu et al., GCN 44724; Yang et al., GCN 44725; Kawakubo et al., GCN 44726; Mo et al., GCN 44727) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J-band simultaneously for 45 x 180 s starting at 2026-05-28T19:58:32 UT (1.57 days after the trigger). We detect the counterpart at r = (23.1 +/- 0.2) AB mag, calibrated against the PS1 catalog and not corrected for the Galactic extinction of A_V = 0.050 mag (Schlafly & Finkbeiner 2011). We note that there is a potential host galaxy with a DESI DR1 (DESI Collaboration et al., 2026, AJ, 171, 285) redshift of z = 0.3656 located ~13" North-East from the afterglow position. At this redshift, the projected physical offset is ~66 kpc, which is at the high end of the distribution of short GRB offsets but not unprecedented (O'Connor 2022, MNRAS, 515, 4890). We derive a probability of chance coincidence of Pcc~0.09, suggesting a possible association. However, as this is a very large offset, deep imaging may reveal additional candidate host galaxies. We do note that based on the available DESI DR1 spectra, there appears to be an overdensity of z~0.36 galaxies along this line-of-sight, suggesting a possible origin within or intersection with a low redshift galaxy cluster (Dichiara et al., 2026, ApJL, 999, L42). The spectrum can be viewed at: https://www.legacysurvey.org/viewer/desi-spectrum/dr1/targetid3962782420566…. We thank Christoph Ries for obtaining the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44728. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42856] EP260527a/GRB 260527A: Infrared J upper limit with MDM/MIRAGE
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44727 SUBJECT: EP260527a/GRB 260527A: Infrared J upper limit with MDM/MIRAGE DATE: 26/05/28 22:59:26 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Carnegie/Caltech), K. De, V. Karambelkar, S. Ibrahim, D. Schiminovich (Columbia University) report: We observed the field of EP260527a/GRB 260527A (Yang et al., GCN 44718; Svinkin et al., GCN 44722; Yu et al., GCN 44724; Yang et al., GCN 44725; Kawakubo et al., GCN 44726) in the near-infrared J band with the MDM InfraRed Astronomy inGaas Experiment (MIRAGE) camera on the MDM 1.3 m telescope. Observations began at 2026-05-28T05:00:58 (+23 hours after the EP trigger) in the J band, lasting 600 s under cloudy conditions. We do not detect the optical counterpart (Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720), with the following 5-sigma upper limit: J > 18.4 mag AB. MIRAGE is a new YJHs-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44727. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42855] GRB 260527A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44726 SUBJECT: GRB 260527A: CALET Gamma-Ray Burst Monitor detection DATE: 26/05/28 17:22:16 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> Y. Kawakubo, A. Yoshida, T. Sakamoto, S. Sugita (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 the short GRB 260527A (Konus-Wind detection: Svinkin et al., GCN #44722; GECAM-B detection: Yu et al., GCN #44724) at 06:16:09.76 UTC on 27 May 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1463897683/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure starting at T+0.16 s, peaking at T+0.28 s, and ending at T+0.38 s. The T90 and T50 durations measured with the SGM data are 0.19 +/- 0.04 s and 0.06 +/- 0.02 s (40-1000 keV), respectively. Einstein Probe/WXT detected a fast X-ray transient, EP 260527a (Yang et al., GCN #44718), about 4 minutes before the CGBM trigger, and Einstein Probe/FXT follow-up observations were also reported by Yang et al. (GCN Circ. 44725). The position of EP 260527a was observable by CGBM at the CGBM trigger time, with an incident angle of approximately 40 degrees. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1463897683/ 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/44726. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42854] EP260527a/GRB 260527A: EP-FXT follow-up observation
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44725 SUBJECT: EP260527a/GRB 260527A: EP-FXT follow-up observation DATE: 26/05/28 15:02:24 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), B. T. Wang (YNAO, CAS), D. F. Hu (PMO, CAS), J. P. Feng, B. Zhang (USTC), D. Zhu, K. J. Zhang (YNU) and W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260527a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Yang et al., GCN 44718), was also detected by Konus-Wind and GECAM-B as GRB 260527A (Svinkin et al., GCN 44722, Yu et al., GCN 44724), and was followed by several optical telescopes (Aguilar-Ruiz et al., GCN 44719, Li et al., GCN 44720). EP-FXT performed a follow-up observation of EP260527a about 21 hours after the WXT detection, with an exposure time of 3.4 ks. The FXT telemetry data show that an uncatalogued source was detected within the WXT error circle at R.A. = 193.0548, DEC = 1.4806 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 1.57 x 10^20 cm^-2 and a photon index of 2.6 (+1.2/-0.7). The derived unabsorbed 0.5-10 keV flux is approximately 7.7 (+3.7/-3.9) x 10^-14 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/44725. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42853] GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44724 SUBJECT: GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a DATE: 26/05/28 14:41:34 GMT FROM: yzh807926(a)163.com Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng, Cheng-Kui Li (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a short burst GRB 260527A at 2026-05-27T06:16:10.050 UTC (denoted as T0), which is also detected by Konus-Wind (D. Svinkin et al., GCN#44722). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multi-pulses with a duration (T90) of 0.40 +0.02/-0.04 s. The on-ground localization of GECAM-B is: Ra: 206.1 deg Dec: 6.7 deg Err: 4.9 deg (1-sigma, statistical only) Considering possible systematic uncertainties, this localization is consistent with the EP/WXT localization of EP260257a (Yang et al., GCN#44718). The time coincidence and localization coincidence between GRB 260527A and EP260527a strongly support the association of these two events. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260527A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44724. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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