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[vsnet-grb-info 43632] GRB 260818B: SVOM/GRM observation
by GCN Circulars 20 Aug '26

20 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45411 SUBJECT: GRB 260818B: SVOM/GRM observation DATE: 26/08/20 09:16:25 GMT FROM: renyz16607(a)163.com SVOM/GRM team: Yang-Zhao Ren, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Sebastien Guillot (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260818B at 2026-08-18T20:11:12.700 UTC (T0), which is also detected by SVOM/ECLAIRs (Cordier et. al., GCN #45398) and HXMT (Wang et. al., GCN #45408). 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 0.16 +0.12/-0.04 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn/gcn/2026/svgrb260818B.png In addition, the position of this burst, as determined by SVOM/ECLAIRs (RA= 44.9407, Dec=7.4547, ERR= 4.60 arcmin, GCN #45398), is located at about 29 degrees from the SVOM optical axis. With this localization, the time-averaged spectrum from T0-0.08 to T0+0.12 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.00 +0.22/-0.23 and the cutoff energy, parameterized as Epeak, is 70 +7/-6 keV. The event fluence (10-1000 keV) in this time interval is (2.67 +0.18/-0.16)E-07 erg/cm^2. The localization of GRB 260818B in the 'Amati' relation diagram is shown at: https://www.bursthub.cn/gcn/2026/svgrb260818B_amati.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: Yang-Zhao Ren (IHEP)(renyz(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/45411. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43631] EP detected a brightening of LMXB 1ES 1735-26.9
by GCN Circulars 20 Aug '26

20 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45410 SUBJECT: EP detected a brightening of LMXB 1ES 1735-26.9 DATE: 26/08/20 08:16:57 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Tian-Yu Liu (NAO, CAS), Xin-Xiang Sun (NAO, CAS), Y.J. Yi (BNU) , Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of X-ray brightening of Low Mass X-ray Binary (LMXB) 1ES 1735-26.9 by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The burst triggered EP-WXT (ID: 01709285030) at the time of 2026-08-20 07:27:33 UTC. The WXT position of the source is R.A. = 264.58 deg, DEC = -26.997 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The estimated flux in the 0.5-4 keV band is around 8.80 x 10^-10 erg/cm^2/s, which is an order of magnitude higher than the previous detection. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. An X-ray source was detected at R.A. = 264.5673 deg, DEC = 26.9930 (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic), which is consistent with the position of known LMXB 1ES 1735-26.9. The estimated flux in the 0.5-10 keV band is around 1.95 x 10^-9 erg/cm^2/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/45410. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43630] GRB260820A: Fermi GBM Final Real-Time Localization
by GCN Circulars 20 Aug '26

20 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45409 SUBJECT: GRB260820A: Fermi GBM Final Real-Time Localization DATE: 26/08/20 07:41:32 GMT FROM: Cuán de Barra at UCD <cuan.debarra(a)ucdconnect.ie> The Fermi GBM team reports the detection of a likely SHORT GRB. "At 04:24:39.99 UT on 20 August 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260820A (trigger 808892684/260820184). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 118.3, Dec = -6.1 (J2000 degrees, equivalent to J2000 7h 53m, -6d 5'), with a statistical uncertainty of 11.5 degrees. The angle from the Fermi LAT boresight is 56 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260820184/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260820184/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260820184/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/45409. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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