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

[vsnet-grb-info 42883] GRB 260531B: GECAM-B observation
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44754 SUBJECT: GRB 260531B: GECAM-B observation DATE: 26/06/01 10:08:05 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260531B, at 2026-05-31T13:58:00.050 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44747). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 12 +5/-3 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260531B.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44754. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42882] GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44753 SUBJECT: GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp DATE: 26/06/01 09:04:52 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 an X-ray source starting at 2026-05-18T07:53:22 UTC (trigger time T0), labelled GRB 260518B, through an offline targeted search with the event-by-event data downloaded through the X-band ground station. The source localization is RA, Dec = 299.003 , -48.620 degrees: RA (J2000) =19h56m00.7s Dec (J2000) = -48d37m12.0s with a 90% C.L. radius of 11.1 arcmin (including a systematic error of 6 arcmin added in quadrature). This position is consistent with those of EP 260518a (Liang et al., GCN 44690) and of the optical transient AT 2026ndp with an angular separation of 1.1 and 1.0 arcmin, respectively. This event was detected within several energy ranges and timescales. The best detection is obtained by the on-ground Image Trigger with a signal-to-noise ratio of 8.2 within 4-20 keV over a time window of 40.96 seconds starting at T0-7.68 s. The burst that triggered ECLAIRs on-ground shows a multiple peak lightcurve. The burst duration is estimated to be around 52 s in the 4-20 keV energy band through imaging. The source being detected when the source was emerging from behind the Earth, ECLAIRs may have missed part of the event emission. The ECLAIRs light curve can be found here: https://docs.google.com/document/d/1DvqHDMZI5uQY-K7kINk7iSFot71MQIoEbDZZ7Yv… The time-averaged spectrum from T0-11 s to T0+41 s in the 5-120 keV energy range is best fitted by a broken powerlaw model with alpha = -1.14 +0.28/-0.26, beta = -2.98 +0.72/-1.12 and a break energy of 21.0 +3.5/-6.7 keV. With this model, the 4-120 keV fluence is (7.8 +1.6/-2.1)e-7 erg/cm^2 and the 4-120 keV photon flux is 0.63 +0.05/-0.17 ph/cm^2/s. This event is very soft and if it is a GRB, then it should be probably classified as an X-Ray Flash. Assuming a redshift of z=2.28 (Corcoran et al., GCN 44695) and a standard cosmology with H_0 = 67.3 km/s/Mpc and Omega_M = 0.315 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is (1.25 +0.27/-0.34)e+52 erg, and the rest-frame peak energy of the time-averaged spectrum Ep,z is 68.9 +11.5/-22.0 keV. With these estimates, GRB 260518B is consistent with the distribution of Type II (collapsar-like) GRBs on the Amati relation reported by Willingale et al. 2017 (figure available with the light curve). This further strengthens the nature of the event to be a Gamma-ray burst. If GRB 260518B is related to EP 260518a and the optical transient AT 2026ndp, ECLAIRs may have detected the prompt phase 5.8 h prior to the EP detection while EP and ATLAS may have observed the afterglow phase. 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/44753. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42881] The EP-WXT trigger 01709266272 is likely a flaring star
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44752 SUBJECT: The EP-WXT trigger 01709266272 is likely a flaring star DATE: 26/06/01 02:03:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), Q.-C. Liu (THU), G.-J. Yang and H.-W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709266272 at the time of 2026-05-31T17:22:11, is likely a stellar flare associated with StKM 1-1106 (Eclipsing Binary Candidate). The estimated flux of the flare is around 1 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.4 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/44752. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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