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[vsnet-grb-info 42730] Fermi GRB 260513A: Global MASTER-Net observations report
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44602 SUBJECT: Fermi GRB 260513A: Global MASTER-Net observations report DATE: 26/05/14 00:16:36 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 260513A ( Fermi GBM team, GCN 44599) errorbox 9005 sec after notice time and 9068 sec after trigger time at 2026-05-13 23:55:26 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 56 deg. The sun altitude is -67.4 deg. The galactic latitude b = -46 deg., longitude l = 8 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3312539 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 9098 | 2026-05-13 23:55:26 | MASTER-SAAO | (21h 18m 43.70s , -36d 30m 06.5s) | C | 60 | 18.6 | 9158 | 2026-05-13 23:55:26 | MASTER-SAAO | (21h 18m 43.70s , -36d 30m 06.5s) | C | 180 | 19.3 | 9098 | 2026-05-13 23:55:26 | MASTER-SAAO | (21h 21m 03.32s , -36d 45m 45.9s) | C | 60 | 18.9 | 9158 | 2026-05-13 23:55:26 | MASTER-SAAO | (21h 21m 03.33s , -36d 45m 45.9s) | C | 180 | 19.6 | 9191 | 2026-05-13 23:56:59 | MASTER-SAAO | (21h 18m 50.50s , -36d 31m 06.3s) | C | 60 | 18.6 | 9191 | 2026-05-13 23:56:59 | MASTER-SAAO | (21h 21m 10.07s , -36d 46m 45.8s) | C | 60 | 18.9 | 9285 | 2026-05-13 23:58:34 | MASTER-SAAO | (21h 18m 44.23s , -36d 32m 06.3s) | C | 60 | 18.7 | 9285 | 2026-05-13 23:58:34 | MASTER-SAAO | (21h 21m 03.77s , -36d 47m 45.7s) | C | 60 | 18.9 | 9408 | 2026-05-14 00:00:06 | MASTER-SAAO | (21h 18m 50.60s , -36d 31m 55.6s) | C | 120 | 19.1 | 9558 | 2026-05-14 00:00:06 | MASTER-SAAO | (21h 18m 50.60s , -36d 31m 55.5s) | C | 420 | 19.8 | 9408 | 2026-05-14 00:00:06 | MASTER-SAAO | (21h 21m 10.09s , -36d 47m 34.6s) | C | 120 | 19.4 | 9558 | 2026-05-14 00:00:06 | MASTER-SAAO | (21h 21m 10.09s , -36d 47m 34.6s) | C | 420 | 20.0 | 9562 | 2026-05-14 00:02:40 | MASTER-SAAO | (21h 18m 46.82s , -36d 30m 36.0s) | C | 120 | 19.0 | 9562 | 2026-05-14 00:02:40 | MASTER-SAAO | (21h 21m 06.23s , -36d 46m 14.7s) | C | 120 | 19.2 | 9715 | 2026-05-14 00:05:13 | MASTER-SAAO | (21h 18m 46.52s , -36d 31m 51.3s) | C | 120 | 19.2 | 9715 | 2026-05-14 00:05:13 | MASTER-SAAO | (21h 21m 05.97s , -36d 47m 30.1s) | C | 120 | 19.4 | 9868 | 2026-05-14 00:07:46 | MASTER-SAAO | (21h 18m 49.92s , -36d 30m 29.6s) | C | 120 | 19.3 | 9868 | 2026-05-14 00:07:46 | MASTER-SAAO | (21h 21m 09.35s , -36d 46m 08.2s) | C | 120 | 19.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44602. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42729] Fermi GRB 260512A: Global MASTER-Net observations report
by GCN Circulars 14 May '26

14 May '26

TITLE: GCN CIRCULAR NUMBER: 44601 SUBJECT: Fermi GRB 260512A: Global MASTER-Net observations report DATE: 26/05/14 00:15:51 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260512A ( Fermi GBM team, GCN 44587) errorbox 1 days 24421 sec after notice time and 1 days 24449 sec after trigger time at 2026-05-13 23:44:12 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 51 deg. The sun altitude is -24.8 deg. The galactic latitude b = -22 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=3309891 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 110879 | 2026-05-13 23:44:12 | MASTER-OAFA | (10h 10m 53.82s , -82d 11m 47.5s) | C | 60 | 19.7 | 110939 | 2026-05-13 23:44:12 | MASTER-OAFA | (10h 10m 53.83s , -82d 11m 47.6s) | C | 180 | 19.9 | Coadd 110955 | 2026-05-13 23:45:28 | MASTER-OAFA | (10h 11m 00.56s , -82d 09m 55.3s) | C | 60 | 19.7 | 111036 | 2026-05-13 23:46:49 | MASTER-OAFA | (10h 10m 53.19s , -82d 10m 52.8s) | C | 60 | 19.6 | 111114 | 2026-05-13 23:48:07 | MASTER-OAFA | (10h 10m 56.57s , -82d 09m 54.2s) | C | 60 | 19.6 | 111174 | 2026-05-13 23:48:07 | MASTER-OAFA | (10h 10m 56.60s , -82d 09m 54.2s) | C | 180 | 19.9 | Coadd 111193 | 2026-05-13 23:49:26 | MASTER-OAFA | (10h 11m 01.87s , -82d 10m 51.8s) | C | 60 | 19.5 | 111266 | 2026-05-13 23:50:39 | MASTER-OAFA | (10h 10m 56.31s , -82d 11m 49.2s) | C | 60 | 19.5 | 111342 | 2026-05-13 23:51:55 | MASTER-OAFA | (10h 11m 03.48s , -82d 11m 44.4s) | C | 60 | 19.6 | 111416 | 2026-05-13 23:53:10 | MASTER-OAFA | (10h 11m 03.76s , -82d 09m 59.6s) | C | 60 | 19.6 | 111493 | 2026-05-13 23:54:26 | MASTER-OAFA | (10h 11m 03.44s , -82d 11m 36.7s) | C | 60 | 19.6 | 111569 | 2026-05-13 23:55:42 | MASTER-OAFA | (10h 11m 08.67s , -82d 10m 08.0s) | C | 60 | 19.3 | 111642 | 2026-05-13 23:56:55 | MASTER-OAFA | (10h 11m 04.41s , -82d 10m 48.5s) | C | 60 | 18.6 | 111721 | 2026-05-13 23:58:14 | MASTER-OAFA | (10h 11m 06.38s , -82d 09m 49.6s) | C | 60 | 18.2 | 111805 | 2026-05-13 23:59:38 | MASTER-OAFA | (10h 08m 14.34s , -84d 04m 05.1s) | C | 60 | 17.5 | 111880 | 2026-05-14 00:00:53 | MASTER-OAFA | (10h 08m 08.20s , -84d 05m 00.1s) | C | 60 | 17.9 | 111956 | 2026-05-14 00:02:09 | MASTER-OAFA | (10h 08m 17.81s , -84d 04m 38.0s) | C | 60 | 18.2 | 112035 | 2026-05-14 00:03:28 | MASTER-OAFA | (10h 12m 11.06s , -80d 13m 12.6s) | C | 60 | 18.4 | 112111 | 2026-05-14 00:04:44 | MASTER-OAFA | (10h 12m 11.82s , -80d 14m 41.3s) | C | 60 | 18.3 | 112186 | 2026-05-14 00:05:59 | MASTER-OAFA | (10h 12m 17.07s , -80d 13m 35.4s) | C | 60 | 18.6 | 112262 | 2026-05-14 00:07:15 | MASTER-OAFA | (09h 58m 34.51s , -80d 14m 16.2s) | C | 60 | 19.3 | 112341 | 2026-05-14 00:08:34 | MASTER-OAFA | (09h 58m 35.92s , -80d 13m 16.8s) | C | 60 | 19.3 | 112416 | 2026-05-14 00:09:49 | MASTER-OAFA | (09h 58m 42.73s , -80d 14m 14.8s) | C | 60 | 19.3 | 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/44601. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42728] GRB 260511B: further SAO RAS optical observations
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44600 SUBJECT: GRB 260511B: further SAO RAS optical observations DATE: 26/05/13 22:29:56 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO RAS) and A. Pozanenko (IKI), report on behalf of GRB the follow-up team. We observed the field of the GRB 260511B discovered by Fermi (The Fermi GBM team, GCN 44542; Roberts, GCN 44554), SVOM (Godet et al., GCN 44543), NuSTAR (Waratkar and Grefenstette, GCN 44556), AstroSat CZTI (Arya et al., GCN 44560), EP-FXT (Fu et al., GCN 44578), Konus-Wind (Ridnaia et al. GCN 44597) with the Zeiss-1000, 1m telescope of the SAO RAS equipped with the CCD photometer. The observations were performed in Rc band on May 12 and 13 under moderate weather conditions. The OT (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Vijaykumar et al., GCN 44561; de Ugarte Postigo et al., GCN 44565; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573; Saccardi et al., GCN 44574; Rajabov et al., GCN 44576; Pérez-Fournon et al., GCN 44577; Novotný et al., GCN 44580; Moskvitin and Pozanenko, GCN 44582; Calapai, GCN 44592; also detected in NIR by Li et al., GCN 44557; GCN 44593) is clearly detected in the stacked frames with the following brightness. Date T_start T_end t_mid-T0, exp, filter mag +/- err UL UT UT days s 2026-05-12T18:57:30--20:17:50 1.35912 2760 Rc 20.93 +/- 0.05 23.1 2026-05-13T19:12:53--21:21:03 2.38641 4800 Rc 21.49 +/- 0.07 23.3 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44600. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42727] GRB 260513A: Fermi GBM Final Real-time Localization
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44599 SUBJECT: GRB 260513A: Fermi GBM Final Real-time Localization DATE: 26/05/13 21:34:57 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 21:24:18 UT on 13 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260513A (trigger 800400263.713514 / 260513892). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 320.8, Dec = -36.4 (J2000 degrees, equivalent to J2000 21h 23m, -36d 23'), with a statistical uncertainty of 2.3 degrees. The angle from the Fermi LAT boresight is 65.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260513892/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260513892/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260513892/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44599. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42726] GRB 260509A: SVOM/VT optical observations
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44598 SUBJECT: GRB 260509A: SVOM/VT optical observations DATE: 26/05/13 15:17:36 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. L. Qiu, C. Wu, 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), J. Palmerio, D. Götz and D. Adrien (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations of GRB260509A triggered by SVOM/ECLAIRs (sb26050905, Götz et al., GCN 44504). The observation started at 2026-05-09T22:12:49 UTC, about 21.66 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The afterglow (O’Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Alvarez et al., 44509; Zheng et al., GCN 44510; Lipunov et al., GCN 44512; Belkin et al., GCN 44513; Corcoran et al., GCN 44514; Bochenek et al., GCN 44516; Moskvitin et al., GCN 44563; Mo et al., GCN 44590) was detected clearly in both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 22.08 m VT_B 50 s 20.05 +/- 0.07 mag 22.08 m VT_R 50 s 19.47 +/- 0.06 mag 8.17 h VT_B 16*100 s 21.76 +/- 0.09 mag 8.24 h VT_R 11*100 s 21.48 +/- 0.09 mag The light curves shows fading and brightening at early epochs, followed by a temporal decay with a slope of −1 in the late phase during our observations. 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/44598. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42725] Konus-Wind detection of GRB 260511B
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44597 SUBJECT: Konus-Wind detection of GRB 260511B DATE: 26/05/13 12:12:06 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 260511B (Fermi-GBM detection: Fermi GBM team, GCN 44542; Roberts et al., GCN 44554; SVOM detection: Godet et al., GCN 44543; NuSTAR detection: Waratkar & Grefenstette, GCN 44556; AstroSat-CZTI detection: Arya et al., GCN 44560) triggered Konus-Wind at T0=39635.267 s UT (11:00:35.267). The burst light curve shows two separate multipeaked episodes: the first from ~T0-1.1 s to ~T0+10 s, and the second, which is brighter and spectrally harder, from ~T0+26 s to ~T0+42 s. The total duration of the burst is ~43.4 s. The burst light curve shows two multipeaked episodes started at ~T0-1.1 s with a total duration of ~43.4 s. The emission is seen up to ~6 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260511_T39635/ As observed by Konus-Wind, the burst had a fluence of 2.48(-0.11,+0.12)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+30.512 s, of 6.82(-0.83,+0.84)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+41.216 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.12(-0.09,+0.10) and Ep = 259(-20,+24) keV (chi2 = 92/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.4 (chi2 = 92/98 dof). The spectrum near the maximum count rate (measured from T0+24.832 to T0+33.024 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 = -0.87(-0.23,+0.17), the high energy photon index beta = -2.26(-0.66,+0.13), the peak energy Ep = 273(-40,+102) keV (chi2 = 93/81 dof). Assuming the redshift z=2.006 (de Ugarte Postigo et al., GCN 44565; Wang et al., GCN 44571) and a standard cosmology model with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 2.53(-0.11,+0.12)x10^53 erg, the peak luminosity L_iso is 2.09(-0.25,+0.26)x10^53 erg/s, the rest-frame peak energy of the time-averaged spectrum, Ep,i,z is 778(-60,+72) keV and the spectrum near the maximum count rate Ep,p,z is 821(-120,+307) keV. With the obtained estimates, GRB 260511B is inside 68% prediction bands for both the 'Amati' and the 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB260511_T39635/GRB260511B_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/44597. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42724] The EP-WXT trigger 01709262036 is likely a flaring star
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44596 SUBJECT: The EP-WXT trigger 01709262036 is likely a flaring star DATE: 26/05/13 09:18:58 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, R. D. Liang (NAO, CAS), H. Z. Wu (HUST), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709262036 at the time of 2026-05-13 08:45:48 (UTC), is likely a stellar flare associated with LP 497-99. The estimated flux of the flare is around 1×10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 3.5×10^31 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/44596. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42723] EP260512a: COLIBRÍ optical upper limits
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44595 SUBJECT: EP260512a: COLIBRÍ optical upper limits DATE: 26/05/13 06:18:56 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Camila Angulo (UNAM), Rosa L. Becerra (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (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), 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 the EP260312a (Liang et al., GCN Circ. 44594), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-13 04:09 to 04:25 UTC (from 19.6 to 19.9 hours after the trigger and 6 minutes after the release of the GCN) and obtained 14 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ ASU 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. In the stacked images and after performing image subtraction using templates from the DESI Legacy Survey (Dey et al. 2019), we do not detect any new source within the WXT error region we do not detect any new source at the WXT error position (Liang et al., GCN Circ. 44594) down to the following 5-sigma limits: r > 23.1 z > 21.9 We note the presence of the quasar 2MASS J14554420+282524 within the WXT region and, considering our upper limits and the low SNR reported by the Einstein Probe Team (Liang et al., GCN Circ. 44594), we cannot rule out the possibility that the trigger is related to 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/44595. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42722] EP260512a: Einstein Probe detection of an X-ray transient
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44594 SUBJECT: EP260512a: Einstein Probe detection of an X-ray transient DATE: 26/05/13 04:03:17 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang, M. J. Liu (NAO, CAS), H. Z. Wu (HUST), H. Sun (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 EP260512a. The transient was detected at 2026-05-12 08:31:32 (UTC). The signal-to-noise ratio is below the on-board trigger threshold and hence the transient was discovered by ground-based analysis. The WXT position of the source is R.A. = 223.899 deg, DEC = 28.432 deg (J2000) with an uncertainty of 2.6 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) 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/44594. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42721] GRB 260511B: further J-band observations by the SYSU 80 cm infrared telescope
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44593 SUBJECT: GRB 260511B: further J-band observations by the SYSU 80 cm infrared telescope DATE: 26/05/13 02:15:50 GMT FROM: lijj328(a)mail2.sysu.edu.cn Jin-Ji Li, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Yun Shi, Hao-Nan Yang, Yan Yu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80 cm infrared telescope team: We further observed the field of GRB 260511B detected by SVOM/ECLAIRs (Godet et al., GCN 44543) and Fermi (Fermi GBM team, GCN 44542), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope. The afterglow (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Li et al., GCN 44557; Vijaykumar et al., GCN 44561; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573; Saccardi et al., GCN 44574; Rajabov et al., GCN 44576; Pérez-Fournon et al., GCN 44577; Novotný et al., GCN 44580; Moskvitin, GCN 44582; Calapai, GCN 44592) with the redshift of z=2.006 (Postigo et al., GCN 44565) was clearly detected in our stacked J-band images. The photometric results are summarized in the table below. The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction. Mid time |Band | Exposure | Mag (Vega) ------------|-------|-------------|------------------ 5.362 h | J | 700s | 16.66 +/- 0.14 5.568 h | J | 640s | 16.57 +/- 0.10 5.771 h | J | 640s | 16.85 +/- 0.13 5.985 h | J | 560s | 17.16 +/- 0.18 6.191 h | J | 660s | 17.10 +/- 0.19 7.011 h | J | 960s | 17.11 +/- 0.15 7.367 h | J | 1040s | 17.26 +/- 0.14 7.720 h | J | 1100s | 17.46 +/- 0.18 The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44593. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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