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[vsnet-grb-info 42980] GRB260603A: SVOM/ECLAIRs refined analysis
by GCN Circulars 06 Jun '26

06 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44848 SUBJECT: GRB260603A: SVOM/ECLAIRs refined analysis DATE: 26/06/06 09:24:50 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP),N. Dagoneau (CEA), Donghua ZHAO, Wenjin Xie (NAOC), Ruizhi Li (YNAO), Ziming Wang (BNU) report on behalf of the SVOM/ECLAIRs team: Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260603A (SVOM burst-id sb26060303 – GCN 44787, trigger time T0 = 2026-06-03T05:38:16 UTC). The burst that triggered ECLAIRs onboard shows a single peak lightcurve. The burst duration is T90 = 101 +4/-7 s in the 4-120 keV energy band. The time-averaged spectrum from T0-51.0 s to T0+50.7 s in the 5-120 keV energy range is best fitted by a powerlaw model with alpha = -1.75 +0.08/-0.09. With this model, the 4-120 keV fluence is (1.33 +0.11/-0.12)e-6 erg/cm^2 and the 4-120 keV photon flux is 0.47 +0.02/-0.03 ph/cm^2/s. All the quoted errors are at the 68% confidence level. 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/44848. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42979] EP260605a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 06 Jun '26

06 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44847 SUBJECT: EP260605a: Einstein Probe detection of a fast X-ray transient DATE: 26/06/06 06:30:27 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A.Li (BNU), C. Y. Wang (THU), Z.-C. Zou (NJU), X. H. Tang (THU), 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 EP260605a. The transient was identified during ground-based telemetry analysis. The WXT light curve started at 2026-06-05T09:31:00 (UTC). The WXT position of the source is R.A. = 273.360 deg, DEC = -40.392 deg (J2000) with an uncertainty of 3.2 arcmin in radius (90% C.L. statistical and systematic). The duration of the event is around 500 s. The WXT spectrum can be fitted with an absorbed power-law, with the absorption fixed at the Galactic value of 1.03 x 10^21 cm^-2, and a photon index of 1.76 (-0.58, +0.61). The unabsorbed 0.5-4 keV flux is 4.3 (-1.3, +1.6) x 10^-11 erg/s/cm2. All uncertainties are reported in 90% C.L. We have arranged follow-up observation with the Follow-up X-ray Telescope onboard EP and will update the information upon receiving the data. 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/44847. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42978] EP260603a: COLIBRÍ optical upper limit
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44846 SUBJECT: EP260603a: COLIBRÍ optical upper limit DATE: 26/06/05 22:08:07 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Enrique Moreno Méndez (UNAM), Dalya Akl (NYUAD), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), 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), 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 EP260603a (Liang et al., GCN Circ. 44814) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-04 06:09 to 06:25 UTC (from 12.30 to 12.58 hours after the trigger) and obtained 14 minutes of simultaneous exposure in the r/z filters. The data were reduced, 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 within the WXT source region (Liang et al., GCN Circ. 44814) down to the following 5-sigma limit: r > 22.5 z > 21.3 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/44846. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42977] GRB 260604A: Glowbug gamma-ray detection
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44845 SUBJECT: GRB 260604A: Glowbug gamma-ray detection DATE: 26/06/05 22:03:48 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260604A, which was also detected by Fermi/GBM (GCN 44812). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-06-04 02:24:24.648 with a duration of 4.1 s and a total significance of about 9.8 sigma. The light curve comprises a single peak. Note that data from ~T0-5s to +1s suffered from deadtime in various detectors. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44845. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42976] GRB 260604C: LCO optical upper limit
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44844 SUBJECT: GRB 260604C: LCO optical upper limit DATE: 26/06/05 21:22:48 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), S. Bisero (CEA/Irfu) report on behalf of the SVOM mission team: We observed the field of GRB 260604C (Fermi GBM Team, GCN 44822; Gotz et al., GCN 44823) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2026-06-05 at 20:08:32 UT (about 1 day after the trigger) and we obtained 3x200 s exposures in the SDSS r filter. In the stacked image we do not detect the optical counterpart (Lipunov et al., GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832, Becerra et al., GCN 44834; Hellot et al., GCN 44835; Gompertz et al., GCN 44837; Gompertz et al., GCN 44843). We measure the following upper limit calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction: r > 21.8 AB (3-sigma, mid-time 0.997 days after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44844. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42975] GRB 260604C: Liverpool Telescope optical detection
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44843 SUBJECT: GRB 260604C: Liverpool Telescope optical detection DATE: 26/06/05 14:01:06 GMT FROM: Dimple at University of Birmingham <dimplepanchal96(a)gmail.com> B. P. Gompertz (U. Birmingham), D. B. Malesani (DAWN/NBI and Radboud) and Dimple (U. Birmingham) report on behalf of a larger collaboration: We conducted follow-up observations of GRB 260604C (Fermi Team, GCN Circ. 44822, Gotz et al., GCN Circ. 44823) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 00:14:01 UT on 2026-06-05, ~3.92 hr after the burst, and consisted of 5 x 120 s exposures in each of the SDSS r, g, i and z filters. We detect the optical counterpart (Lipunov et al., GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832, Becerra et al., GCN 44834; Hellot et al., GCN 44835; Gompertz et al. 44837) in all the filters, and measure an AB magnitude of r = 18.60 ± 0.05. Magnitudes are calibrated against nearby Pan-STARRS stars and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44843. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42974] The EP-WXT trigger 01709267001 is likely a flaring star
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44842 SUBJECT: The EP-WXT trigger 01709267001 is likely a flaring star DATE: 26/06/05 12:57:39 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO), X. Tian (GXU), C.-L. Guo and C.-C. Jin (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709267001 at the time of 2026-06-05T12:42:11, is likely a stellar flare associated with RX J1431.6+0047 (High Proper Motion Star). The estimated flux of the flare is around 1.8 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4.8 x 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/44842. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42973] EP260602d: EP-FXT follow-up observation
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44841 SUBJECT: EP260602d: EP-FXT follow-up observation DATE: 26/06/05 12:47:27 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J.Y. Cao, Z. X. Li, G. L. Huang, (IHEP, CAS), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260602d was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Cao et al., GCN 44796) at 2026-06-02T21:13:25 (UTC). Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-06-04T04:27:19(UTC), ~31 hours after the WXT detection. The exposure time of the observation is around 4 ks. The on-ground analysis of the FXT data found a source within the error circle of WXT at R.A. = 267.9681 deg, DEC = 18.1658 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic) which have no historical X-ray source within 10 arcsec. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 6.7×10^20 cm^-2, and a photon index of 0.8 (-0.3, +0.4). The derived average unabsorbed 0.5-10 keV flux is 3.2 (-1.2, +1.8) ×10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Since this source is below the RASS upper limit and shows no significant fading, we cannot identify it as the counterpart of EP260602d at present. The optical and infrared follow-up observations were performed by A. Aryan et al. (GCN 44813) and Tanishk Mohan et al. (GCN 44830) without detection. 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/44841. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42972] EP260602c: EP-FXT follow-up observation
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44840 SUBJECT: EP260602c: EP-FXT follow-up observation DATE: 26/06/05 11:56:50 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> EP260602c: EP-FXT follow-up observation J.Y. Cao, Z. X. Li, G. L. Huang, (IHEP, CAS), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260602c was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Cao et al., GCN 44792) at 2026-06-02T09:06:44 (UTC). Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-06-03T18:37:43(UTC), ~33 hours after the WXT detection. The exposure time of the observation is around 4 ks. The on-ground analysis of the FX-A data found three sources within the error circle of WXT. Source 1 is at R.A. = 134.8551 deg, DEC = -75.673 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). This position is 12 arcsec from a known X-ray source 1eRASS J085924.9-754010 with the historical flux of 1.8 ×10^(-14) erg/s/cm^2 in 0.3-2.3 keV band. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 8×10^20 cm^-2, and a photon index of 1.9 (-1.2, +1.2). The observed 0.5-10.0 keV flux is 9.1 (+/-2.9) ×10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Source 2 is at R.A. = 134.5839 deg, DEC = -75.7147 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). This position is 5 arcsec from a known X-ray source 1eRASS J085820.6-754257 with the historical flux of 2.0 ×10^(-14) erg/s/cm^2 in 0.3-2.3 keV band. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 8×10^20 cm^-2, and a photon index of 0.13 (-0.68, +0.61). The observed 0.5-10.0 keV flux is 5.1 (+/-2.0) ×10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Source 3 is at R.A. = 134.5079 deg, DEC = -75.6493 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic) which have no historical X-ray source within 10 arcsec. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 8×10^20 cm^-2, and a photon index of 3.1 (-1.3, +1.7). The observed 0.5-10.0 keV flux is 3.51 (+/-1.6) ×10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Since none of them is significantly above the eRASS1 upper limit or shows fading trends, we cannot identify the counterpart of EP260602c at present. 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/44840. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42971] GRB 260601B / EP260601a: AstroSat CZTI detection
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44839 SUBJECT: GRB 260601B / EP260601a: AstroSat CZTI detection DATE: 26/06/05 11:44:11 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), 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 260601B, associated with EP260601a, which was also detected by Einstein Probe / WXT (Yang et. al., GCN Circ. 44766), GECAM-C (Yu et al., GCN Circ. 44767), NuSTAR (Waratkar et. al. , GCN Circ. 44771), CALET (Sugita et. al., GCN Circ. 44773), and Insight HXMT (Wang et. al., GCN Circ. 44785). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-06-01 19:12:50.54 UTC. AstroSat was departing the South Atlantic Anomaly (SAA) region and hence the background rates were higher. The measured peak count rate associated with the burst is 498 (+39, -46) counts/s above the background in the combined data of three quadrants (out of four), with a total of 12100 (+491, -799) counts. The local mean background count rate was 278 (+4, -4) counts/s. Using cumulative rates, we measure a T90 of 54 (+2, -2) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-06-01 19:12:50.66 UTC. The measured peak count rate associated with the burst is 1468 (+92, -129) counts/s above the background in the combined data of four quadrants, with a total of 29202 (+2008, -3307) counts. The local mean background count rate was 1805 (+20, -8) counts/s. We measure a T90 of 51 (+1, -2) s from the cumulative Veto light curve. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/ET20260601T191246/ET20260601T1… 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/44839. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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