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

[vsnet-grb-info 42841] EP260526a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44712 SUBJECT: EP260526a: Einstein Probe detection of a fast X-ray transient DATE: 26/05/27 07:03:44 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: 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 EP260526a. The transient did not trigger the onboard unit, a GCN notice (ID: 06800001478) was sent manually. The WXT position of the source is R.A. = 236.063 deg, DEC = -23.771 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the event started at 2026-05-26T09:43:34 (UTC) and lasted for about 140 seconds. The average WXT 0.5-4.0 keV spectrum can be fitted with an absorbed powerlaw model, with a fixed Galactic hydrogen column density of 2.13 x 10^21 cm^-2 and a photon index of 1.98 (+0.78/-0.70). The unabsorbed 0.5-4.0 keV flux is 8.2 (+2.8/-2.2) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT observations are scheduled. Additional information will be updated when the telemetry data are 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/44712. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42840] GRB 260525A: AstroSat CZTI detection
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44711 SUBJECT: GRB 260525A: AstroSat CZTI detection DATE: 26/05/27 06:38:46 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), A. Goyal (IITB), A. Arya (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260525A which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44703). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-25 23:33:44.45 UTC. The measured peak count rate associated with the burst is 209 (+36, -36) counts/s above the background in the combined data of four quadrants, with a total of 259 (+56, -54) counts. The local mean background count rate was 728 (+177, -140) counts/s. Using cumulative rates, we measure a T90 of 8 (+2, -2) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/517448022.55/S517448022.55_det… CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/44711. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42839] EP260526.405: COLIBRÍ optical upper limits
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44710 SUBJECT: EP260526.405: COLIBRÍ optical upper limits DATE: 26/05/27 06:34:35 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Antonio de Ugarte Postigo (LAM), 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), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Benjamin Schneider (LAM) and report: We imaged the field of the EP260526.405 (ID=06800001478) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-27 05:30 to 06:06 UTC (from 19.79 to 20.39 hours after the trigger, beginning 32 seconds after the notice was received) and obtained 29 minutes of simultaneous exposure in the r/z filters. The data were reduced and coadded with the ASU COLIBRÍ 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 (in this case with a relatively high value of A_v = 1.1 mag, according to Schlafly et al. 2011). In the stacked image, we do not detect any new source at the WXT source position down to the following 5-sigma limit: r > 22.5 z > 21.6 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/44710. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42838] The EP-WXT trigger 01709266106 is not a real source
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44709 SUBJECT: The EP-WXT trigger 01709266106 is not a real source DATE: 26/05/27 03:40:10 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. P. Feng, B. Zhang (USTC), J. Yang (ZZU), B.T. Wang (YNAO, CAS), D. Zhu, K. J. Zhang (YNU), D. F. Hu (PMO, CAS), W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: The Einstein Probe Wide-field X-ray Telescope (EP-WXT) trigger 01709266106, detected at 2026-05-26T17:37:56 and followed by GCN 44705 and GCN 44706, was not a real astrophysical source. View this GCN Circular online at https://gcn.nasa.gov/circulars/44709. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42837] Fermi GRB 260526A: Global MASTER-Net observations report
by GCN Circulars 27 May '26

27 May '26

TITLE: GCN CIRCULAR NUMBER: 44708 SUBJECT: Fermi GRB 260526A: Global MASTER-Net observations report DATE: 26/05/27 00:32:25 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tavrida robotic telescope [1] located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 260526A ( Fermi GBM team, GCN 44707) errorbox 872 sec after notice time and 1002 sec after trigger time at 2026-05-26 23:20:42 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 79 deg. The sun altitude is -20.1 deg. The galactic latitude b = -14 deg., longitude l = 143 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3341266 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 1032 | 2026-05-26 23:20:42 | MASTER-Tavrida | (02h 40m 21.49s , +46d 38m 05.4s) | C | 60 | 14.9 | 1113 | 2026-05-26 23:22:03 | MASTER-Tavrida | (02h 25m 12.72s , +46d 35m 35.0s) | C | 60 | 12.0 | 3275 | 2026-05-26 23:58:05 | MASTER-Tavrida | (02h 32m 55.74s , +43d 58m 52.2s) | C | 60 | 16.5 | 4690 | 2026-05-27 00:21:40 | MASTER-Tavrida | (02h 36m 20.55s , +45d 17m 15.2s) | C | 60 | 16.8 | 4769 | 2026-05-27 00:22:59 | MASTER-Tavrida | (02h 15m 28.16s , +42d 39m 11.4s) | C | 60 | 17.1 | 4848 | 2026-05-27 00:24:17 | MASTER-Tavrida | (02h 12m 43.82s , +41d 19m 58.6s) | C | 60 | 16.9 | 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/44708. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42836] GRB 260526A: Fermi GBM Final Real-time Localization
by GCN Circulars 26 May '26

26 May '26

TITLE: GCN CIRCULAR NUMBER: 44707 SUBJECT: GRB 260526A: Fermi GBM Final Real-time Localization DATE: 26/05/26 23:14:33 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 23:04:00 UT on 26 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260526A (trigger 801529445.20122 / 260526961). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 40.1, Dec = 43.9 (J2000 degrees, equivalent to J2000 02h 40m, 43d 53'), with a statistical uncertainty of 3.8 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/bn260526961/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260526961/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260526961/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44707. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42835] EP01709266106 (EP260526a?): Liverpool Telescope upper limits
by GCN Circulars 26 May '26

26 May '26

TITLE: GCN CIRCULAR NUMBER: 44706 SUBJECT: EP01709266106 (EP260526a?): Liverpool Telescope upper limits DATE: 26/05/26 22:48:18 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester) reports on behalf of a larger collaboration: We observed the field of the Einstein Probe WXT trigger EP01709266106 (EP260526a?) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS g’r’i’z’ filters starting at 2026-05-26 21:25:48 UT, approximately 3.80 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Within the EP/WXT localisation, we detect no new sources in any of the bands. We derive the following 3-sigma upper limits for our stacked images. Our photometry is calibrated to PanSTARRS and not corrected for Galactic extinction. | t_mid (hours) | Filter | AB magnitude | | ------------- | ------ | ------------ | | 3.94 | r’ | >21.52 | | 4.24 | g’ | >21.47 | | 4.53 | i’ | >21.69 | | 4.82 | z’ | >21.25 | View this GCN Circular online at https://gcn.nasa.gov/circulars/44706. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42834] EP-WXT 01709266106: NOT optical upper limits
by GCN Circulars 26 May '26

26 May '26

TITLE: GCN CIRCULAR NUMBER: 44705 SUBJECT: EP-WXT 01709266106: NOT optical upper limits DATE: 26/05/26 22:44:16 GMT FROM: Agnes van Hoof at Radboud University <agnes.vanhoof(a)ru.nl> A. P. C. van Hoof (Radboud), G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), J. Chacón (PUC), J. N. D. van Dalen (Radboud), P. G. Jonker (Radboud), report on behalf of a larger collaboration: We observed the field of the Einstein Probe trigger WXT 01709266106, using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the SDSS r (3x300 s) and z (5x200 s) bands, starting on 2026-05-26 at 21:01:29 UT (~3.4 hours after the WXT trigger). We do not find any new, uncatalogued sources within the EP-WXT uncertainty region compared to Hyper Suprime-Cam and Legacy Survey images (DR10). From the stacked images we obtain the following 3-sigma upper limits: r > 20.17 z > 19.40 These limits are in the AB system, were calibrated using nearby stars from the Pan-STARRS catalog and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44705. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42833] Fermi GRB 260525A: Global MASTER-Net observations report
by GCN Circulars 26 May '26

26 May '26

TITLE: GCN CIRCULAR NUMBER: 44704 SUBJECT: Fermi GRB 260525A: Global MASTER-Net observations report DATE: 26/05/26 00:30:29 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 260525A ( Fermi GBM team, GCN 44703) errorbox 28 sec after notice time and 62 sec after trigger time at 2026-05-25 23:34:44 UT, with upper limit up to 18.1 mag. The observations began at zenith distance = 38 deg. The sun altitude is -23.6 deg. The galactic latitude b = -4 deg., longitude l = 262 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3339200 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 67 | 2026-05-25 23:34:44 | MASTER-OAFA | (08h 07m 12.80s , -39d 50m 18.8s) | C | 10 | 18.1 | 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/44704. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42832] GRB 260525A: Fermi GBM Final Real-time Localization
by GCN Circulars 25 May '26

25 May '26

TITLE: GCN CIRCULAR NUMBER: 44703 SUBJECT: GRB 260525A: Fermi GBM Final Real-time Localization DATE: 26/05/25 23:44:11 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 23:33:42 UT on 25 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260525A (trigger 801444827.592448 / 260525982). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 125.2, Dec = -44.5 (J2000 degrees, equivalent to J2000 08h 20m, -44d 30'), with a statistical uncertainty of 6.3 degrees. The angle from the Fermi LAT boresight is 35.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260525982/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260525982/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260525982/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44703. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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