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[vsnet-grb-info 43244] EP260623a: FRAM-ORM detection of the optical afterglow rise, peak and decay
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45029 SUBJECT: EP260623a: FRAM-ORM detection of the optical afterglow rise, peak and decay DATE: 26/06/23 14:29:58 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> Martin Jelinek, Jan Strobl and Filip Novotny (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Masek, Petr Janecek, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ) report: The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted robotically to the alert of EP260623a (Wang et al. GCN 45020), obtaining a series of unfiltered images starting at 02:59:17 UT, i.e. ~5 min post trigger. The observation consists of a set of 20 x 20 s exposures followed by a longer set of 120 x 60 s exposures. We clearly detect the optical counterpart reported by other telescopes (Li et al. GCN 45021; Izzo et al. GCN 45022; Angulo et al. GCN 45024; Brivio et al. GCN 45025; Jiang et al. GCN 45026). The FRAM observations cover the rise of the transient, its peak and the subsequent decay. The source peaked at ~T0+24 min at a brightness of r ~ 15.4, after which it decays with a power-law index alpha ~ 1.7, with a few rebrightenings. The photometry is calibrated against the Atlas-REFCAT2 catalogue (Tonry et al. 2018, ApJ, 867, 105) and is not corrected for Galactic extinction. Extrapolating the observed decay to T0+24h yields a predicted brightness of r ~ 22.0. View this GCN Circular online at https://gcn.nasa.gov/circulars/45029. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43243] GRB 260623A: Fermi GBM Final Real-time Localization
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45028 SUBJECT: GRB 260623A: Fermi GBM Final Real-time Localization DATE: 26/06/23 13:09:24 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 12:56:49 UT on 23 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260623A (trigger 803912214.021094 / 260623539). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 39.3, Dec = -10.4 (J2000 degrees, equivalent to J2000 02h 37m, -10d 24'), with a statistical uncertainty of 11.8 degrees. The angle from the Fermi LAT boresight is 88.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260623539/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260623539/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260623539/… View this GCN Circular online at https://gcn.nasa.gov/circulars/45028. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43242] EP260623a: SVOM/VT optical observations
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45027 SUBJECT: EP260623a: SVOM/VT optical observations DATE: 26/06/23 12:19:38 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 ToO observations to the field of EP260623a triggered by Einstein Probe (Wang et al., GCN 45020). The observation started at 2026-06-10T04:10:37 UTC, about 1.28 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Li et al., GCN 45021; Angulo et al., GCN 45024; Brivio et al., GCN 45025; Jiang et al., GCN 45026) with the redshift of z=0.703 (Izzo et al., GCN 45022) was clearly 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 1.283 h VT_B 50 s 17.00 +/- 0.04 mag 1.283 h VT_R 50 s 16.34 +/- 0.04 mag 3.191 h VT_B 50 s 18.59 +/- 0.07 mag 3.191 h VT_R 50 s 17.85 +/- 0.05 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/45027. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43241] EP260623a: TRT optical observations
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45026 SUBJECT: EP260623a: TRT optical observations DATE: 26/06/23 10:40:56 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang, X. Liu (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan, K. Noysena (NARIT), L.B. He, Z.P. Zhu, J. An, Z. Fan, W.X. Li, N.C. Sun, D. Xu (NAOC), S.Y. Fu (HUST) report: We observed the field of EP260623a detected by EP (Wang et al., GCN 45020) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 04:32:21.6 UTC on 2026-06-23, i.e., 1.638 hrs after the EP trigger, and a series of frames were obtained in Sloan r-band. The optical counterpart (Li et al., GCN 45021; Izzo et al., GCN 45022; Angulo et al., GCN 45024; Brivio et al., GCN 45025) is clearly detected in our r-band images, with r = 17.13 +/- 0.02 at 1.767 hrs post-burst, calibrated with Panstarrs DR2 stars in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/45026. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43240] EP260623a: REM optical/NIR afterglow detection
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45025 SUBJECT: EP260623a: REM optical/NIR afterglow detection DATE: 26/06/23 10:05:07 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB), L. Izzo (INAF-OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), A. Melandri (INAF-OAR) report on behalf of the REM team: We observed the field of EP260623a, detected by EP/WXT (Wang et al., GCN 45020) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried out in the g, r, i, z, K bands, started on 2026-06-23 at 03:57:45 UT (i.e. 1.1 hr after the burst) and lasted for about 1 hr. From preliminary photometry, we detect the optical/NIR counterpart (Li et al., GCN 45021; Izzo et al., GCN 45022; Angulo et al., GCN 45024) with the following magnitudes: r = 16.35 +/- 0.04 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 1.1 hr after the trigger; K = 13.51 +/- 0.17 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 1.1 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/45025. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43239] EP 260323a: COLIBRÍ optical observations
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45024 SUBJECT: EP 260323a: COLIBRÍ optical observations DATE: 26/06/23 07:02:10 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Camila Angulo (UNAM), Francis Fortin (IRAP), 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), 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), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Alan M. Watson (UNAM) report: We imaged the field of the EP 260623a (Wang et al., GCN Circ. 45020) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-23T06:23:26 to 06:37:31 UTC (from 3.49 to 3.69 hours after the trigger) and obtained 4 minutes of exposure in the g, r, i, z, filters and 8 minutes in the y filter. 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. We detected the optical counterpart reported by Las Cumbres (Li et al., GCN Circ. 45021), at preliminary magnitudes of: g = 18.73 +/- 0.04 r = 18.30 +/- 0.01 i = 18.00 +/- 0.01 z = 17.78 +/- 0.03 y = 17.55 +/- 0.03 Our detection in all bands suggests that this is a low-redshift event. Spectroscopic observations are encouraged. We also note that the source is located near the southern edge of the Sh 2-113 (the Flying Dragon Nebula), which may contribute to the moderate extinction observed at its position. 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/45024. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43238] GRB 260616B/EP260616a: Insight-HXMT/HE detection
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45023 SUBJECT: GRB 260616B/EP260616a: Insight-HXMT/HE detection DATE: 26/06/23 06:06:51 GMT FROM: yzh807926(a)163.com GRB 260616B/EP260616a: Insight-HXMT/HE detection Zheng-Hang Yu, Chen-Wei Wang, Chao Zheng, and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team: At 2026-06-16T07:05:26.950 (T0), Insight-HXMT/HE detected GRB 260616B/EP260616a, which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44953), AstroSat CZTI (A. Arya et al., GCN #44997) and SVOM/GRM (Yu et al., GCN #45011). The Insight-HXMT/HE light curve mainly consists of two pulses with a T90 of 11.6 +1.4/-0.3 s. The 1 s peak rate, measured from T0-0.25 s, is 2154 cnts/sec. Insight-HXMT/HE detected a total of 8808 counts from this burst. The Insight-HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260616B.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the normal gain mode with the energy range of about 6-900 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://hxmten.ihep.ac.cn View this GCN Circular online at https://gcn.nasa.gov/circulars/45023. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43237] EP260623a: OSIRIS+/GTC redshift z = 0.703
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45022 SUBJECT: EP260623a: OSIRIS+/GTC redshift z = 0.703 DATE: 26/06/23 05:47:48 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> L. Izzo (INAF/OACN and DARK/NBI), A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud), S. Geier (GTC), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), G. Lombardi (GTC), A. Martin-Carrillo (UCD), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), F. Pérez Toledo (GTC) and A. Pérez (GTC) report: We observed the optical counterpart (Li et al. GCN 45021) of EP260623a (Wang et al, GCN 45020) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. In the 10-s acquisition image (beginning on 2026-06-23 at 04:44:12 UT, that is 1.83 hr after trigger), the optical afterglow is well detected with a magnitude 17.01 ± 0.05 (AB), calibrated against nearby LS objects, and not corrected for Galactic extinction. A total of 2 spectra of 600 s were secured, starting on 2026-06-23 at 04:49:58 UT (1.93 hr after EP trigger), using grism R1000B. Continuum is visible over the wavelength range 3615-7800 AA. A number of metal absorption features are detected, which we interpret as due to FeII, MnII, MgII, MgI, as well as multiple FeII fine structure transitions all at a common redshift z = 0.703, which we suggest to be the redshift of EP 260623a. This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). View this GCN Circular online at https://gcn.nasa.gov/circulars/45022. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43236] EP260623a: Las Cumbres discovery of the optical counterpart
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45021 SUBJECT: EP260623a: Las Cumbres discovery of the optical counterpart DATE: 26/06/23 04:16:44 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li, Runduo Liang (NAOC), Iair Arcav, Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of EP260623a with a Las Cumbres 1m telescope at Teide Observatory, Tenerife, 8 mins after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical w-band. We find an uncataloged source at RA=328.2698, Dec=12.7939 within the EP-FXT error circle and measure the following preliminary photometry calibrated to the r band: MJD 61214.12687 Mag 16.54 +- 0.01 MJD 61214.13064 Mag 15.62 +- 0.01 This target brightened by ~0.9 mag within 6 minutes. The presented magnitudes are calibrated with Pan-STARRS sources in the field and not corrected for Galactic extinction. Additional follow-up is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/45021. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43235] EP260623a: Einstein Probe detection of an X-ray transient
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45020 SUBJECT: EP260623a: Einstein Probe detection of an X-ray transient DATE: 26/06/23 03:52:21 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B. T. Wang (YNAO, CAS), Y. L. Hua (PMO, CAS) and C. C. Jin (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 EP260623a. The transient triggered EP-WXT (ID: 01709272000) at 2026-06-23T02:54:05 (UTC). The WXT position of the source is R.A. = 328.262 deg, DEC = 12.813 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. = 328.2725 deg, DEC = 12.7946 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/45020. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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