August 2026 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 43629] GRB 260818B: Insight-HXMT detection
by GCN Circulars 20 Aug '26

20 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45408 SUBJECT: GRB 260818B: Insight-HXMT detection DATE: 26/08/20 05:32:14 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Yang-Zhao Ren, Shao-Lin Xiong, Cheng-Kui Li, and Chao Zheng report on behalf of the Insight-HXMT team: At 2026-08-18T20:11:12.600 (T0), Insight-HXMT/HE detected the short burst GRB 260818B, which is also detected by SVOM/ECLAIRs (Bertrand Cordier et al., GCN#45398) and SVOM/GRM. The Insight-HXMT/HE light curve mainly consists of a narrow pulse with a T90 of 0.15 +0.15/-0.10 s. The HXMT/HE light curve can be found here: https://www.bursthub.cn/gcn/2026/hxmtgrb260818B.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 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://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/45408. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43628] GRB 260818B: EP-FXT follow-up observation
by GCN Circulars 20 Aug '26

20 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45407 SUBJECT: GRB 260818B: EP-FXT follow-up observation DATE: 26/08/20 05:17:32 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. Y. Wu (NAO, CAS), H. Zhou, Y. L. Hua (PMO, CAS), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of GRB 260818B detected by SVOM/ECLAIRs (Cordier et al., GCN 45398). The observation started at 2026-08-18 22:01:25(UTC), about 1.84 hr after the SVOM trigger, with a total exposure time of around 6.0 ks. On-ground analysis of the FXT data found several uncataloged sources inside the ECLAIRs error region Name | RA | DEC | Sep_obj (arcmin) | Flux (erg/cm^2/s) EPF_J025951.6+072917 | 44.9651 | 7.4881 | 2.47 | 4.4e-14 EPF_J025955.0+072535 | 44.9791 | 7.4263 | 2.85 | 4.5e-14 EPF_J025936.6+072418 | 44.9024 | 7.4049 | 3.76 | 1.5e-12 EPF_J025950.9+073127 | 44.9619 | 7.5242 | 4.36 | 9.8e-14 with uncertainties of 10 arcsec (radius, 90% C.L. statistical and systematic). None of these sources showed significant variability during this observation. 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/45407. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43627] GRB 260818A: J-band observations with WINTER
by GCN Circulars 20 Aug '26

20 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45406 SUBJECT: GRB 260818A: J-band observations with WINTER DATE: 26/08/20 03:58:10 GMT FROM: tanishk.mohan(a)iitb.ac.in Tanishk Mohan (IITB), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 260818A (Yin et al., GCN 45391) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-08-18T07:40:58.776 UTC in the J band (6.61 hr after the SVOM/ECLAIRs trigger), consisting of 15*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) Of the five unique uncatalogued X-ray sources (EPF_J231953.3-320838 is repeated in the FXT circular) reported by FXT (Wang et al., GCN 45400), four lie within our WINTER image, with EPF_J231912.9-320034 falling outside the field of view. Of these four sources, two are coincident with catalogued sources: EPF_J231936.3-320537 is classified as a star, while EPF_J231953.3-320838 is classified as a quasar in the Gaia catalog. We also note that EPF_J231953.3-320838 has a measured redshift of z=0.1898 in the GAMA survey (Yao et al. 2020; https://ui.adsabs.harvard.edu/abs/2020ApJ...903...91Y/abstract) We do not detect counterparts at the positions of the remaining two FXT sources (Ducoin et al., GCN 45393; Shi et al., GCN 45395). We obtain a 5-sigma upper limit of J=19.14 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/45406. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43626] GRB 260818B: SVOM/ECLAIRs refined analysis
by GCN Circulars 19 Aug '26

19 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45405 SUBJECT: GRB 260818B: SVOM/ECLAIRs refined analysis DATE: 26/08/19 20:28:53 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. Yang, O. Godet, S. Guillot (IRAP), Bertrand Cordier, S. Schanne (CEA), Hatsune Goto (RIKEN, CEA) 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 the short burst GRB 260818B (SVOM burst-id sb26081807, GCN 45398, trigger time T0 = 2026-08-18T20:11:12.618 UTC). The burst that triggered ECLAIRs shows a typical fast-rise, exponential-decay (FRED) light curve in the 4-120 keV band, with T90(4-120 keV) = (0.22 +0.07/-0.02) s. The light curve in the 4-20 keV band shows possible extended emission following the main pulse, with a corresponding T90(4-20 keV) = (0.71 +0.40/-0.39) s. The time-averaged spectrum of the main pulse, extracted from T0 to T0 + 0.22 s in the 5-120 keV range, is well fitted by a cutoff power-law model with a photon index of -0.61 +/-0.14, a cutoff energy of (40 +11/-7) keV, a 4-120 keV photon flux of (32.3 +0.1/-4.8) photons/cm^2/s, and a corresponding 4-120 keV fluence of (2.9 +/-0.2)e-7 erg/cm^2. The time-averaged spectrum of the possible extended emission, extracted from T0 + 0.22 s to T0 + 0.71 s in the 5-20 keV, can be well fitted by a blackbody model with a temperature of (1.6 +0.4/-0.3) keV, a 4-120 keV photon flux of (2.1 +0.3/-0.7) photons/cm^2/s, and a corresponding 4-120 keV fluence of (1.1+/-0.3) e-8 erg/cm^2. 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: Hui Yang (IRAP) (hui.yang(a)cnrs.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/45405. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43625] GRB 260818A: SVOM/ECLAIRs refined analysis
by GCN Circulars 19 Aug '26

19 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45404 SUBJECT: GRB 260818A: SVOM/ECLAIRs refined analysis DATE: 26/08/19 20:26:12 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. Yang, O. Godet (IRAP), W.-J. Xie (NAOC), Clara Plasse (HKU) 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 the possible faint burst GRB 260818A (SVOM burst-id sb26081801, GCN 45391, trigger time T0 = 2026-08-18T01:04:36 UTC). The burst that triggered ECLAIRs shows a featureless light curve, and is detected from T0-82 s to T0 in the 8-120 keV energy band. The time-averaged spectrum from T0-82 s to T0 in the 5-120 keV is well fitted by a blackbody model with a temperature of (7 +2/-1) keV, a 4-120 keV photon flux of (0.26 +0.06/-0.05) photons/cm^2/s, and a corresponding 4-120 keV fluence of (7 +/-2)e-7 erg/cm^2. 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: Hui Yang (IRAP) (hui.yang(a)cnrs.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/45404. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43624] GRB 260818B: NOT optical upper limits
by GCN Circulars 19 Aug '26

19 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45403 SUBJECT: GRB 260818B: NOT optical upper limits DATE: 26/08/19 16:13:31 GMT FROM: d.s.oneill(a)bham.ac.uk We observed the field of GRB 260818B detected by SVOM/ECLAIRs (Cordier et al., GCN 45398), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 4x200 s exposures in the SDSS r-band starting on 2026-08-19 at 03:43:55 UT (7.55 hr post trigger) and 5x200 s in the SDSS z-band starting on 2026-08-19 at 03:59:24 UT (7.80 hr post trigger). Because of the size of the ALFOSC field of view, only 58% of the ECLAIRs error circle could is covered in our stacked images. In the stacked images we identify no new source and obtain the following upper limits: r > 23.7 AB mag z > 22.6 AB mag Magnitudes are calibrated against nearby stars from the Pan-STARRS catalog, and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/45403. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43623] GRB 260810A: SVOM/GRM observation
by GCN Circulars 19 Aug '26

19 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45402 SUBJECT: GRB 260810A: SVOM/GRM observation DATE: 26/08/19 15:26:19 GMT FROM: guohx(a)ihep.ac.cn SVOM/GRM team: Hao-Xuan Guo, Yue Wang, Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Oliver Godet (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 260810A at 2026-08-10T19:09:43.050 UTC (T0), which is also detected by AstroSat CZTI (Arya et al., GCN #45363), Glowbug (Cheung et al., GCN #45365) and Insight-HXMT/HE (Yu et al. GCN #45392). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a pulse with a T90 of 18.0 +5.5/-2.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn/gcn/2026/svgrb260810A.png In addition, the position of this burst, as determined by SVOM/GRM (RA = 234.55 deg, Dec = 2.02 deg, Err = 1.64 deg, 90% C. L., statistical only), is located at about 105 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. But the burst emission has been detected by ECLAIRs through reflection onto the Earth atmosphere, and GRM may also detected through atmosphere reflection. With this localization, the time-averaged spectrum from T0-0.55 to T0+20.95 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.60 +/-0.03 and the cutoff energy, parameterized as Epeak, is 974 +281/-193 keV. The event fluence (10-1000 keV) in this time interval is (4.84 +0.07/-0.06)E-05 erg/cm^2. The 1s peak spectrum, measured from T0+0.45 to T0+1.45 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.04 +0.08/-0.07 and the cutoff energy, parameterized as Epeak, is 835 +152/-115 keV. The flux (10-1000 keV) in this time interval is (9.99 +0.21/-0.22)E-06 erg/cm^2/s. The localization of GRB 260810A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn/gcn/2026/svgrb260810A_amati.png The localization of GRB 260810A in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn/gcn/2026/svgrb260810A_yonetoku.png 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Hao-Xuan Guo (IHEP)(guohx(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/45402. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43622] GRB 260818B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 19 Aug '26

19 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45401 SUBJECT: GRB 260818B: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 26/08/19 11:53:08 GMT FROM: Marion G <marion.guelfand(a)gmail.com> Marion Guelfand (CPPM), Diego López-Cámara (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (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), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM) and Clare Plasse (HKU) report: We imaged the field of the SVOM GRB 260818B (Cordier et al., GCN Circ. 45398) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-08-19 08:03:24 to 10:40:40 UTC (from 11.87 to 14.51 hours after the trigger) and obtained 118 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded and analysed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR2 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 ECLAIRs source position (Cordier et al., GCN Circ. 45398) down to the following 10-sigma limit: r > 23.8 z > 22.4 This is consistent with the non-detection reported by the LCO 1m telescope (Shi et al., GCN 45399). Further observations 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/45401. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43621] GRB260818A: EP-FXT follow-up observation
by GCN Circulars 19 Aug '26

19 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45400 SUBJECT: GRB260818A: EP-FXT follow-up observation DATE: 26/08/19 03:49:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z.M. Wang(BNU), C.Y. Dai(NJU), D. F. Hu(PMO,CAS) and H.W. Pan(NAOC) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of GRB 260818A detected by SVOM/ECLAIRs (Yin et al., GCN 45391). The observation started at 2026-08-18 02:43:32(UTC), about 1.67 hr after the SVOM trigger, with a total exposure time of around 4.6 ks. On-ground analysis of the FXT data found several uncataloged sources inside the ECLAIRs error region. Name | RA | DEC | Sep_obj (arcmin) | Flux (erg/cm^2/s) EPF_J232025.8-320549 | 350.1077 | -32.0971 | 6.101382 | 1.3205e-13 EPF_J231936.3-320537 | 349.9012 | -32.0935 | 6.582593 | 5.9746e-14 EPF_J231953.3-320838 | 349.9729 | -32.1449 | 6.812141 | 2.0801e-13 EPF_J231912.9-320034 | 349.8036 | -32.0095 | 10.701601 | 1.0260e-12 EPF_J231953.3-320838 | 349.9722 | -32.1440 | 6.770902 | 2.0112e-13 EPF_J232037.7-320633 | 350.1572 | -32.1093 | 8.604395 | 4.5878e-14 with uncertainties of 10 arcsec (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/45400. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43620] GRB 260818B: LCO optical upper limits
by GCN Circulars 19 Aug '26

19 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45399 SUBJECT: GRB 260818B: LCO optical upper limits DATE: 26/08/19 03:42:13 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y.Y. Shi (GXU), C. Wu, L.P. Xin (NAOC), A. Saccardi, D. Turpin (CEA/Irfu), Bertrand Cordier (CEA), Hatsune Goto (RIKEN, CEA), report on behalf of the SVOM mission team: We observed the field of GRB 260818B (SVOM burst-id sb26081807) detected by SVOM (Cordier et al., GCN 45398) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2026-08-18 at 23:44:55 UT (about 3.56 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and PS1 zs filter. In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limits calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r > 21.9 AB (5-sigma, mid-time 3.65 hr after the trigger), z > 19.7 AB (5-sigma, mid-time 3.65 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/45399. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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