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[vsnet-grb-info 42890] GRB 260601A: Fermi GBM Observation
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44760 SUBJECT: GRB 260601A: Fermi GBM Observation DATE: 26/06/01 18:13:56 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 11:00:12.44 UT on 01 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260601A (trigger 802004417/260601458). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 15.06, Dec = 44.38 (J2000 degrees, equivalent to J2000 1h 0m, +44d 22'), with a statistical uncertainty of 2.03 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 30 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 0.8 s (50-300 keV). The time-averaged spectrum from T0-0.07 to T0+0.34 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.63 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 960 +/- 30 keV. The event fluence (10-1000 keV) in this time interval is (2.08 +/- 0.06)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.064 s in the 10-1000 keV band is 40 +/- 1 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 750 +/- 20 keV, alpha = -0.57 +/- 0.05 and beta = -2.0 +/- 0.2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44760. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42889] EP260530a/AT 2026nwl: COLIBRÍ optical observations
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44759 SUBJECT: EP260530a/AT 2026nwl: COLIBRÍ optical observations DATE: 26/06/01 17:34:44 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Damien Dornic (CPPM), Alan M. Watson (UNAM), Rosa L. Becerra (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), Nathaniel R. Butler (ASU), , Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (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) and Antonio de Ugarte Postigo (LAM) report: We observed the field of the Einstein Probe X-ray transient EP260530a (Wu et al., ATel #17824) with the DDRAGO two-channel wide-field imager mounted on the COLIBRÍ telescope. The observations targeted the optical counterpart candidate, AT 2026nwl, discovered by GOTO (TNS Astronomical Transient Report No. 306622) and associated with EP260530a. We observed from 2026-06-01 04:59 to 06:02 UTC (from (55.93 to 56.97 hours after the GOTO discovery) and obtained 11, 23, 10, 24, and 20 minutes of exposure in the g, r, i, z, and y filters, respectively. The data were reduced and coadded with the COLIBRÍ ASU 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 detect the optical counterpart previously reported by GOTO (AT 2026nwl). The source is measured at the following preliminary magnitudes: g = 15.22 +/- 0.01, r = 15.33 +/- 0.01, i = 15.41 +/- 0.01, z = 15.52 +/- 0.01, y = 15.58 +/- 0.01. The source is brighter than the magnitude of L = 17.03 at 2026-05-29 21:04 UTC reported by the GOTO team (TNS Astronomical Transient Report 306622), but fainter than the unfiltered magnitude of 14.46 at 2026-05-31 05:24 UTC reported by Sokolovsky et al (TNS Astronomical Transient Report 306654). If the transient has a simple rise and decay, this suggests that it has already reached its maximum. The source shows blue colors, consistent with both a CV and an FBOT. During the 55 minutes of our observations, the source shows a smooth rise from r = 15.35 to r = 15.28 followed by a smooth fall again to r = 15.36. Similar behavior is also seen in the other filters. This variability is reminiscent of that seen in CVs. We encourage spectroscopic observations to determine the redshift of this source and its likely nature. 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/44759. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42888] GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44758 SUBJECT: GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search DATE: 26/06/01 15:40:07 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP), D. Turpin (CEA) report on behalf of the SVOM/ECLAIRs team The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 260530C, starting at 2026-05-30T00:13:15.62 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 6.8 within 8-120 keV over a time window of 20.48 seconds starting at T0-20.48s. The burst that triggered ECLAIRs onground shows a double peak structure. The burst duration is estimated to be around 25s in the 4-120 keV energy band through imaging. The localization of the source is RA, Dec = 196.655, 26.384 degrees: RA (J2000) = 13h 06m 37.2s Dec (J2000) = 26d23m02.4s with a 90% C.L. radius of 12.8 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 T0-20.5 s to T0+4.5 s in the energy range 5-120 keV is best fitted by a powerlaw model with alpha = -1.10 +/- 0.16. With this model, the 4-120 keV fluence is (3.2 +0.3/-1.0) e-7 erg/cm^2 and the 4-120 keV photon flux is 0.26 +0.02/-0.08 ph/cm^2/s. 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 a future Circular. 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/44758. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42887] AT2026nik: EP-FXT X-ray counterpart
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44749 SUBJECT: AT2026nik: EP-FXT X-ray counterpart DATE: 26/05/31 21:01:15 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> J. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), A. A. Chrimes (ESA/ESTEC), A. J. Levan (Radboud & Warwick), A Inkenhaag (Bath), D. Coppejans (Warwick), P. Groot (Radboud/UCT/SAAO): We observed the field of AT2026nik (AstroNotes: 2026-151, 2026-152) with the Follow-up X-ray Telescope (FXT) aboard the Einstein Probe mission. The observation was carried out from 2026 May 29 18:45:25.9 to May 30 00:22:29.8 UT, with a total exposure time of 7.2 ks using Modules A and B. After stacking the data from both modules, we detected an X-ray source with a significance of S/N ≈ 5.5 at the position (with an uncertainty of 10"): RA = 11:22:52.1 Dec = -06:13:21.7 No X-ray source is reported at this position in the ROSAT, eROSITA, Swift-XRT, XMM-Newton, or Chandra catalogs, according to the STONKS Multi-Mission X-ray Catalog (Quintin et al. 2024). The position of the detected X-ray source is consistent with that of AT2026nik, suggesting that it is the X-ray counterpart of the transient. The source has a net count rate of 2.58e-3 counts/s. Assuming a Galactic hydrogen column density of N_H = 4e20 cm-2 and a power-law spectrum with photon index Γ = 1.5, we estimate an absorbed X-ray flux of approximately 5.8e-14 erg/cm2/s. AT2026nik exhibited a blue, nearly featureless optical spectrum (P. Pessi and J. Wise; AstroNotes: 2026-151, 2026-152), with a tentative detection of the interstellar Mg II absorption doublet at z = 0.182. Assuming this redshift, the inferred X-ray luminosity is approximately L_X~5.4e42 erg/s, consistent with that observed in AT2018cow and other LFBOTs at a similar epoch (e.g., Margutti et al. 2019). The blue optical spectrum and the newly detected X-ray counterpart support the classification of AT2026nik as a luminous fast blue optical transient (LFBOT). We thank the Einstein Probe staff for their execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44749. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42886] GRB 260527A/EP260527a: Glowbug gamma-ray detection
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44757 SUBJECT: GRB 260527A/EP260527a: Glowbug gamma-ray detection DATE: 26/06/01 12:58:49 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260527A, which was detected initially by Einstein Probe as EP260527a (GCN 44718). The GRB was also detected by Konus-Wind (GCN 44722), GECAM-B (GCN 44724), CALET (GCN 44726), Insight-HXMT (GCN 44735), and Mars-Odyssey (HEND) with an IPN triangulation (GCN 44744). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-27 06:16:08.912 with a duration of 0.26 s and a total significance of about 40 sigma. The light curve comprises a primary peak at ~T0+0.1s and a fainter peak at ~T0+0.2s. 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/44757. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42885] Fermi GRB 260601A: Global MASTER-Net observations report
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44756 SUBJECT: Fermi GRB 260601A: Global MASTER-Net observations report DATE: 26/06/01 11:45:38 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), M. Segura, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260601A ( Fermi GBM team, GCN 44755) errorbox 301 sec after notice time and 327 sec after trigger time at 2026-06-01 11:05:39 UT, with upper limit up to 19.5 mag. Observations started at twilight. The observations began at zenith distance = 53 deg. The sun altitude is -13.8 deg. The galactic latitude b = -18 deg., longitude l = 125 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3352995 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 357 | 2026-06-01 11:05:39 | MASTER-OAGH | (00h 50m 13.85s , +45d 57m 12.7s) | C | 60 | 19.4 | 430 | 2026-06-01 11:06:52 | MASTER-OAGH | (00h 38m 00.15s , +44d 39m 27.6s) | C | 60 | 19.1 | 430 | 2026-06-01 11:06:52 | MASTER-OAGH | (00h 48m 30.18s , +44d 02m 36.0s) | C | 60 | 19.5 | 576 | 2026-06-01 11:09:18 | MASTER-OAGH | (00h 52m 04.36s , +47d 50m 39.9s) | C | 60 | 19.0 | 678 | 2026-06-01 11:10:30 | MASTER-OAGH | (00h 59m 12.69s , +44d 07m 39.1s) | P- | 120 | 16.9 | 678 | 2026-06-01 11:10:30 | MASTER-OAGH | (01h 01m 18.88s , +43d 31m 06.4s) | P| | 120 | 17.8 | 798 | 2026-06-01 11:10:30 | MASTER-OAGH | (01h 01m 18.88s , +43d 31m 06.6s) | P| | 360 | 18.0 | Coadd 807 | 2026-06-01 11:12:39 | MASTER-OAGH | (00h 59m 19.74s , +44d 08m 01.8s) | P- | 120 | 16.9 | 807 | 2026-06-01 11:12:39 | MASTER-OAGH | (01h 01m 25.92s , +43d 31m 26.7s) | P| | 120 | 17.8 | 936 | 2026-06-01 11:14:48 | MASTER-OAGH | (00h 59m 15.81s , +44d 09m 26.1s) | P- | 120 | 16.9 | 936 | 2026-06-01 11:14:48 | MASTER-OAGH | (01h 01m 22.64s , +43d 32m 53.3s) | P| | 120 | 17.5 | 1065 | 2026-06-01 11:16:57 | MASTER-OAGH | (00h 59m 15.96s , +44d 07m 29.9s) | P- | 120 | 16.6 | 1065 | 2026-06-01 11:16:57 | MASTER-OAGH | (01h 01m 22.92s , +43d 30m 56.4s) | P| | 120 | 17.4 | 1173 | 2026-06-01 11:19:15 | MASTER-OAGH | (00h 59m 32.67s , +44d 39m 48.6s) | C | 60 | 18.5 | 1173 | 2026-06-01 11:19:15 | MASTER-OAGH | (01h 09m 59.11s , +44d 02m 59.4s) | C | 60 | 18.3 | 1246 | 2026-06-01 11:20:28 | MASTER-OAGH | (00h 57m 41.97s , +42d 45m 11.1s) | C | 60 | 18.2 | 1246 | 2026-06-01 11:20:28 | MASTER-OAGH | (01h 07m 49.03s , +42d 08m 22.9s) | C | 60 | 18.1 | 1319 | 2026-06-01 11:21:41 | MASTER-OAGH | (01h 01m 31.23s , +46d 34m 48.3s) | C | 60 | 18.1 | 1319 | 2026-06-01 11:21:41 | MASTER-OAGH | (01h 12m 18.99s , +45d 57m 59.6s) | C | 60 | 18.0 | 1393 | 2026-06-01 11:22:55 | MASTER-OAGH | (00h 55m 58.79s , +40d 51m 00.4s) | C | 60 | 17.8 | 1466 | 2026-06-01 11:24:08 | MASTER-OAGH | (00h 47m 06.39s , +42d 09m 10.0s) | C | 60 | 18.1 | 1541 | 2026-06-01 11:25:23 | MASTER-OAGH | (01h 18m 18.85s , +42d 46m 18.7s) | C | 60 | 17.2 | 1686 | 2026-06-01 11:27:48 | MASTER-OAGH | (01h 20m 55.25s , +44d 40m 22.4s) | C | 60 | 17.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44756. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42884] GRB 260601A: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Jun '26

01 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44755 SUBJECT: GRB 260601A: Fermi GBM Final Real-time Localization DATE: 26/06/01 11:10:43 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely SHORT GRB At 11:00:12 UT on 1 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260601A (trigger 802004417.438878 / 260601458). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 15.1, Dec = 44.4 (J2000 degrees, equivalent to J2000 01h 00m, 44d 23'), with a statistical uncertainty of 2.0 degrees. The angle from the Fermi LAT boresight is 30.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260601458/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260601458/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260601458/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44755. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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