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[vsnet-grb-info 43030] EP260610b: Gemini North optical counterpart candidate
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44897 SUBJECT: EP260610b: Gemini North optical counterpart candidate DATE: 26/06/10 16:54:45 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> A. J. Levan (Radboud & Warwick), J. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), G. Corcoran (UCD), A. P. C. van Hoof (Radboud), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), J. Chacón (PUC), H. Sun (NAO, CAS), F. E. Bauer (SSI and UTA) report on behalf of a larger collaboration: We observed the localisation region of EP260610b (Wu et al. 2026, GCN 44895) with the Gemini North Telescope and the GMOS-N instrument on Mauna Kea, Hawaii, USA. Observations began at 13:36:51 UT on 10 June 2026 and consisted of 7 × 100 s exposures in the SDSS r band (~0.81 hr after T0) and 3 × 100 s exposures in the SDSS z band (~1.08 hr after T0). By comparison with the Legacy Survey images, we identify a candidate optical counterpart at the following coordinates (J2000): RA = 17:50:29.72 Dec = +46:32:10.6 Photometry performed on the stacked images yields r = 22.23 ± 0.03 and z = 22.19 ± 0.05 AB mag, calibrated against nearby stars from the Pan-STARRS catalog and not corrected for Galactic extinction. We acknowledge the excellent support from the Gemini North staff in the execution of these challenging observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44897. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43029] EP260610a: SVOM/VT optical upper limits
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44896 SUBJECT: EP260610a: SVOM/VT optical upper limits DATE: 26/06/10 14:40:01 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, 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, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed a ToO observation of the field of EP260610a triggered by Einstein Probe (Wu et al., GCN 44889). The observation started at 2026-06-10T05:47:51 UTC, i.e., about 1.18 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued optical source was detected at the FXT source position (Wu et al., GCN 44889) in our stacked images, compared to the Legacy Survey. The 3-sigma upper limits are: Mid_time Band Exposure Time Magnitude (AB) 2.27 h VT_B 83*50 s > 23.8 mag 2.27 h VT_R 84*50 s > 23.4 mag The magnitudes are in the AB system and are not corrected for Galactic extinction. Our non-detection is consistent with the observation from COLIBRÍ (Postigo et al., GCN 44890). 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/44896. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43028] EP260610b: Einstein Probe detection of an X-ray transient
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44895 SUBJECT: EP260610b: Einstein Probe detection of an X-ray transient DATE: 26/06/10 13:28:05 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Z. Wu, (HUST, CAS),C. L. Guo, H. Y. Ren, Z. X. Ling (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 EP260610b. The transient triggered EP-WXT (ID: 01709268876) at 2026-06-10T12:48:17 (UTC). The WXT position of the source is R.A. = 267.601 deg, DEC = 46.534 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 267.6268 deg, DEC = 46.5388 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). 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/44895. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43027] Konus-Wind detection of GRB 260601A
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44894 SUBJECT: Konus-Wind detection of GRB 260601A DATE: 26/06/10 13:16:20 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 short-duration GRB 260601A (Fermi-GBM detection: Fermi GBM team, GCN 44755, Holzmann Airasca et al., GCN 44760; Glowbug detection: Cheung et al., GCN 44763; GECAM-B detection: Wang et al., GCN 44778; SVOM-GRM detection: Wang et al., GCN 44793; CALET-GBM detection: Yamaoka et al., GCN 44817; IPN triangulation: Svinkin et al., GCN 44893) triggered Konus-Wind at T0=39609.166 s UT (11:00:09.166). The burst light curve shows a multipeaked structure which starts at ~T0 and has a total duration of ~0.2 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260601_T39609/ As observed by Konus-Wind, the burst had the total fluence of 3.05(-0.27,+0.29)x10^-6 erg/cm2, and the 16-ms peak flux, measured from T0+0.078 s, of 4.04(-0.53,+0.55)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+0.192 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 = -0.44(-0.13,+0.14) and Ep = 780(-91,+107) keV (chi2 = 36/39 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.6 (chi2 = 36/38 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44894. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43026] IPN triangulation of GRB 260601A (short/hard)
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44893 SUBJECT: IPN triangulation of GRB 260601A (short/hard) DATE: 26/06/10 13:06:10 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng, Cheng-Kui Li (IHEP) on behalf of GECAM team, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP), J. Wei (NAOC), B. Cordier (CEA) on behalf of the SVOM-GRM team, 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), on behalf of the CALET collaboration, report: The short-duration GRB 260601A (Fermi-GBM detection: The Fermi GBM team, GCN 44755; Holzmann Airasca, GCN 44760; Glowbug detection: Cheung et al., GCN 44763; GECAM-B detection: Y. Wang et al., GCN 44778; SVOM-GRM detection: Y. Wang et al., GCN 44793; CALET-GBM detection: Yamaoka et al., GCN 44817) was detected by Fermi (GBM trigger 802004417), CALET (GBM trigger 1464346716), Konus-Wind, Glowbug, SVOM (GRM), and GECAM-B at about 39612 s UT (11:00:12). We have triangulated it to the 3 sigma localization region whose area is 2.8 sq. deg, and its maximum dimension is 73 deg (the minimum one is 2.7 arcmin). A triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB260601_T39609/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/44893. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43025] GRB 260610b: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44892 SUBJECT: GRB 260610b: Fermi GBM Final Real-time Localization DATE: 26/06/10 10:19:57 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 10:07:46 UT on 10 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260610b (trigger 802778871.805202 / 260610422). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 354.7, Dec = 8.4 (J2000 degrees, equivalent to J2000 23h 38m, 8d 24'), with a statistical uncertainty of 10.5 degrees. The angle from the Fermi LAT boresight is 102.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44892. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43024] GRB 260610b: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44891 SUBJECT: GRB 260610b: Fermi GBM Final Real-time Localization DATE: 26/06/10 10:18:35 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 10:07:46 UT on 10 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260610b (trigger 802778871.805202 / 260610422). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 354.7, Dec = 8.4 (J2000 degrees, equivalent to J2000 23h 38m, 8d 24'), with a statistical uncertainty of 10.5 degrees. The angle from the Fermi LAT boresight is 102.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44891. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43023] GRB 260610a: COLIBRÍ optical upper limits
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44890 SUBJECT: GRB 260610a: COLIBRÍ optical upper limits DATE: 26/06/10 10:12:50 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Diego López-Cámara (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), 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), 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) report: We imaged the field of EP260610a (Wu et al., GCN Circ. 44889) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-10 08:23:40 to 09:56:22 UTC (from 3.78 to 5.32 hours after the trigger) and obtained 69 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded and analysed 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 the stacked image, we do not detect any new source at the FXT source position (Wu et al., GCN Circ. 44889) down to the following 5-sigma limits: r > 24.0 mag z > 22.6 mag 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/44890. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43022] EP260610a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44889 SUBJECT: EP260610a: Einstein Probe detection of a fast X-ray transient DATE: 26/06/10 06:22:59 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Z. Wu, (HUST, CAS),C. L. Guo, H. Y. Ren, Z. X. Ling (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 EP260610a. The transient triggered EP-WXT (ID: 01709268833) at 2026-06-10 04:37:09(UTC). The WXT position of the source is R.A. = 306.104 deg, DEC = -25.926 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2026-06-10T04:49:21(UTC). Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 306.1055 deg, DEC = -25.9057 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). 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/44889. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43021] GRB 260609A: Fermi GBM Final Localization
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44888 SUBJECT: GRB 260609A: Fermi GBM Final Localization DATE: 26/06/09 21:40:53 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 20:05:42.61 UT on 09 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260609A (trigger 802728347/260609837). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 42.43, Dec = -7.99 (J2000 degrees, equivalent to J2000 2h 49m, -7d 59'), with a statistical uncertainty of 8.05 degrees. The angle from the Fermi LAT boresight is 86 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260609837/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260609837/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260609837/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44888. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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