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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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[vsnet-grb-info 43234] GRB 260614B: EP-FXT follow-up observation
by GCN Circulars 22 Jun '26

22 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45019 SUBJECT: GRB 260614B: EP-FXT follow-up observation DATE: 26/06/22 22:10:22 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Pillas (IAP), A. Saccardi (CEA/Irfu), Ziming Wang (PKU), report on behalf of the SVOM and EP collaborations: EP-FXT performed a follow-up observation of GRB 260614B detected by SVOM/ECLAIRs (Godet et al., GCN 44938). The follow-up observation started on 2026-06-15 at 15:05:04 (UTC), about 25.3 hr after the SVOM trigger, with a total exposure time of 4 ks. On-ground analysis of the FXT data found an uncatalogued source within the ECLAIRs and MXT error circles at R.A., Dec. = 353.9080, -54.1164 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). This position is consistent with the optical counterpart (Palmerio et al., GCN 44939; Li et al., GCN 44943). The derived average unabsorbed flux is (1.64 +/- 0.25) x 10^(-13) erg/s/cm^2 (0.5-10 keV; 1-sigma uncertainty). 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/45019. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43233] IceCube-260622A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 22 Jun '26

22 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45018 SUBJECT: IceCube-260622A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/06/22 19:24:32 GMT FROM: janeth.phd(a)gmail.com The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-06-22 at 15:41:54.81 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 2.8158 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/142752_1835003.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-06-22 Time: 15:41:54.81 UT RA: 173.36 (+0.5/-0.52 deg 90% PSF containment) J2000 Dec: 1.34 (+0.58/-0.58 deg 90% PSF containment) J2000 As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of this event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/45018. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43232] GRB 260618C: SVOM/ECLAIRs detection of a possible burst through on-ground search
by GCN Circulars 22 Jun '26

22 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45017 SUBJECT: GRB 260618C: SVOM/ECLAIRs detection of a possible burst through on-ground search DATE: 26/06/22 14:33:28 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 a transient source, labelled GRB 260618C, starting at 2026-06-18T04:02:26.6 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 8.6 within 4-20 keV over a time window of 7 seconds starting at T0-7s. The burst that triggered ECLAIRs onground shows a single peak structure. The burst duration is T90 = 6 +/-1 s in the 4-20 keV energy band. The localization of the source is RA, Dec = 294.933, -65.710 degrees: RA (J2000) = 19h39m43.9s Dec (J2000) = -65d42m36.0s with a 90% C.L. radius of 10.7 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 T0-7 s to T0 in the 5-50 keV energy range is best fitted by a blackbody model with kT = 3.65 +0.47/-0.42 keV.. With this model, the 4-120 keV fluence is (8.3 +0.7/-2.4) e-8 erg/cm^2 and the 4-120 keV photon flux is 0.65 +0.04 /-0.15 ph/cm^2/s. Both broken power-law and power-law with an exponential cutoff models can equally fit the spectrum, however, their parameters can not be constrained due to the faintness of this burst. This event is very soft and if it is a GRB, then it should be probably classified as an X-Ray Flash. 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 future circulars. 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/45017. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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