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

[vsnet-grb-info 43681] Fermi GBM trigger 809666623/260829141 is not a GRB
by GCN Circulars 29 Aug '26

29 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45460 SUBJECT: Fermi GBM trigger 809666623/260829141 is not a GRB DATE: 26/08/29 04:11:56 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA) reports report on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 809666623/260829141 at 03:23:38.10 UT on 29 August 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/45460. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43680] GRB 260818B: Further EP-FXT observation
by GCN Circulars 28 Aug '26

28 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45459 SUBJECT: GRB 260818B: Further EP-FXT observation DATE: 26/08/28 17:30:16 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang, Eleonora Troja (U Rome), Jun Yang (ZZU), Qinyu Wu (NAO, CAS) report: We re-observed the field of the short GRB 260818B (SVOM/ECLAIRs; Cordier et al., GCN 45398) with EP-FXT through a ToO request. The observation started on 2026-08-27 at 16:48:47 UT (9.5 d post-trigger), with a total exposure of ~6 ks. Compared with the previous EP-FXT observation (Wu et al., GCN 45407), the X-ray source EPF_J025955.0+072535, located close to the radio source S10 (Schroeder et al., GCN 45418; Ricci et al. GCN 45452) and the candidate optical counterpart (Ducoin et al., GCN 45450; Yadav et al., GCN 45458), shows no significant variability. No fading X-ray source is found within the 90% confidence region of the ECLAIRs localization (Cordier et al., GCN 45398). Expanding the search region to 5-sigma level, we identify a fading X-ray source EPF_J025906.7+072552 at R.A. = 44.7791 deg, Dec. = 7.4315 deg (J2000), with a localization uncertainty of 10 arcsec (radius, 90% C.L., statistical and systematic). The source lies 9.7 arcmin away from the center of the ECLAIRs localization. We thank the EP team for scheduling and executing the ToO observation. View this GCN Circular online at https://gcn.nasa.gov/circulars/45459. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43679] GRB 260818B: VLT optical and nIR observations
by GCN Circulars 28 Aug '26

28 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45458 SUBJECT: GRB 260818B: VLT optical and nIR observations DATE: 26/08/28 14:56:05 GMT FROM: muskan.yadav(a)students.uniroma2.eu Muskan Yadav, Massine El Kabir, Nicolás Monsalves, Hira Waseem, Yu-Han Yang and Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of short duration GRB 260818B detected by SVOM/ECLAIRs (Cordier et al., GCN 45398) with the FORS2 imager on the ESO VLT UT1 (Antu) and the HAWKI imager on the ESO VLT UT4 (Yepun). Both observations began 9.5 days after the trigger and were carried out at an average airmass ~1.2 and with an average seeing ~0.8 arcsec. At the position of the candidate optical counterpart reported by COLIBRÍ (Ducoin et al., GCN 45450) we detect a faint (~24.7 AB) source in the z-band, but not in the J-band down to a 3-sigma limit >24.2 AB mag. Magnitudes are calibrated using nearby stars in the Pan-STARRS1 DR1 catalog (Chambers et al. 2016) and the 2MASS catalog (Skrutskie et al. 2006). Reported magnitudes are not corrected for Galactic extinction. Our observations show that the optical source faded significantly between the two epochs, by at least ~2 mag between 6.5 d and 9.5 d after the burst. This would correspond to a power-law decay slope of ~-4.6, steeper than expected for standard GRB afterglows. The lack of a nIR detection suggests that its red color (r-z~1.8; Ducoin et al., GCN 45450) could be due to dust along the line of sight or, alternatively, that the late observations are dominated by the host galaxy light. Further observations are planned. We thank the staff at the VLT for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/45458. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43678] GRB 260818B: TNG NIR observations
by GCN Circulars 28 Aug '26

28 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45457 SUBJECT: GRB 260818B: TNG NIR observations DATE: 26/08/28 10:09:39 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio (INAF-OAB), D. B. Malesani (DAWN/NBI and Radboud), M. Ferro (INAF-OAB), A. Rossi (INAF-OAS), A. Melandri (INAF-OAR), M. De Pasquale (U. of Messina), V. Lorenzi (INAF-TNG) report on behalf of the CIBO collaboration: We observed the field of GRB 260818B detected by SVOM/ECLAIRs (Cordier et al., GCN 45398) with the Italian 3.6m TNG telescope equipped with the near-infrared camera NICS. A series of images were obtained with the J filter starting on 2026-08-28 at 02:19:43 UT (i.e. 9.26 days after the trigger). The transient candidate identified by the COLIBRI telescope (Ducoin et al., GCN 45450) is not detected in the co-added image. We measure a 3-sigma limiting magnitude of: J > 21.9 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 9.28 days after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/45457. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43677] MAXI GRB260827.40: Global MASTER-Net observations report
by GCN Circulars 28 Aug '26

28 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45456 SUBJECT: MAXI GRB260827.40: Global MASTER-Net observations report DATE: 26/08/28 03:34:33 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> M. Segura, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA) 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 (Lomonosov MSU) D.Buckley (SAAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) A.Sosnovskij (CrAO RAS) A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory) L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) R.Rebolo (The Instituto de Astrofisica de Canarias) O.Gress, N.Budnev(ISU) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the MAXI GRB260827.40 (trigger No 279310912,17h 04m 14.40s , +24d 00m 32.4s, R=1) errorbox 219 sec after notice time and 63740 sec after trigger time at 2026-08-28 03:21:39 UT, with upper limit up to 16.9 mag. The observations began at zenith distance = 81 deg. The sun altitude is -61.9 deg. The galactic latitude b = 33 deg., longitude l = 45 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3494572 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 63770 | 2026-08-28 03:21:39 | MASTER-OAFA | (17h 03m 43.44s , +24d 07m 33.8s) | C | 60 | 16.9 | 63836 | 2026-08-28 03:22:44 | MASTER-OAFA | (17h 03m 43.27s , +24d 07m 33.3s) | C | 60 | 16.7 | 63901 | 2026-08-28 03:23:50 | MASTER-OAFA | (17h 03m 43.11s , +24d 07m 32.4s) | C | 60 | 16.5 | 63967 | 2026-08-28 03:24:56 | MASTER-OAFA | (17h 03m 43.00s , +24d 07m 31.2s) | C | 60 | 16.4 | 64032 | 2026-08-28 03:26:01 | MASTER-OAFA | (17h 03m 42.85s , +24d 07m 29.7s) | C | 60 | 16.3 | 64097 | 2026-08-28 03:27:06 | MASTER-OAFA | (17h 03m 42.76s , +24d 07m 27.7s) | C | 60 | 16.2 | 64163 | 2026-08-28 03:28:11 | MASTER-OAFA | (17h 03m 42.47s , +24d 07m 27.5s) | C | 60 | 15.8 | 64228 | 2026-08-28 03:29:17 | MASTER-OAFA | (17h 03m 42.34s , +24d 07m 26.3s) | C | 60 | 15.4 | 64294 | 2026-08-28 03:30:22 | MASTER-OAFA | (17h 03m 42.31s , +24d 07m 23.8s) | C | 60 | 15.1 | 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/45456. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43676] IceCube-260827A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 27 Aug '26

27 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45455 SUBJECT: IceCube-260827A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/08/27 17:55:09 GMT FROM: Mayra Velazquez at Georgia Institute of Technology <mvelazquez(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-08-27 at 15:35:36.97 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD alert stream. Documentation regarding the alert streams and their astrophysical purity can be found here: https://gcn.nasa.gov/missions/icecube. This alert has an estimated false alarm rate of 1.134 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/143048_12474624.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-08-27 Time: 15:35:36.97 UT RA: 86.31 (+0.65/-0.47 deg 90% PSF containment) J2000 Dec: 8.12 (+0.42/-0.41 deg 90% PSF containment) J2000 As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. No known gamma-ray sources listed in the Fermi LAT 16-year Source List (FL16Y) are located within the 90% uncertainty region of this event. We report here sources within the 90% confidence contour available in the multi-order probability map, rather than those selected using the simplified rectangular error-box reported in this Circular. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/45455. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43675] The EP-WXT trigger 01709291839 is likely the known LMXB 4U 1745-203
by GCN Circulars 27 Aug '26

27 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45454 SUBJECT: The EP-WXT trigger 01709291839 is likely the known LMXB 4U 1745-203 DATE: 26/08/27 14:03:57 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z. X. Li (IHEP), R. Shi, Y. L. Hua (PMO，CAS) and Z. X. Ling (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709291839 occurred at 2026-08-27 08:32:56. The follow-up FXT observations yield a triggered position at R.A. = 267.2150 deg, Dec = -20.3583 deg (J2000) with a 20 arcsec radius uncertainty. This event is likely a detection of 4U 1745-203 (identical to SAX J1748.9-2021; ATel #18011). The estimated flux from the observation is approximately 1.585e-10 erg/s/cm^2 in 0.5-10.0 keV. 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/45454. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43674] GRB 260827A: Fermi GBM Final Real-time Localization
by GCN Circulars 27 Aug '26

27 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45453 SUBJECT: GRB 260827A: Fermi GBM Final Real-time Localization DATE: 26/08/27 10:54:27 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 LONG GRB At 10:42:59 UT on 27 Aug 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260827A (trigger 809520184.770226 / 260827447). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 247.9, Dec = -53.5 (J2000 degrees, equivalent to J2000 16h 31m, -53d 30'), with a statistical uncertainty of 2.4 degrees. The angle from the Fermi LAT boresight is 41.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260827447/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260827447/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260827447/… View this GCN Circular online at https://gcn.nasa.gov/circulars/45453. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43673] GRB 260818B: 6 GHz VLA observations
by GCN Circulars 27 Aug '26

27 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45452 SUBJECT: GRB 260818B: 6 GHz VLA observations DATE: 26/08/27 08:00:19 GMT FROM: Roberto Ricci at INAF-IRA <ricci(a)ira.inaf.it> R. Ricci, M. Yadav, E. Troja (U Rome) report: We observed the field of short duration GRB 260818B, detected by SVOM (Cordier et al., GCN 45398) with the Karl G. Jansky Very Large Array in C-band at the centre frequency of 6 GHz with a bandwidth of 4 GHz on August 25th 2026 at mid-time 13:37 UT(6.7 days after the trigger). Data were calibrated and imaged using standard procedures in CASA (v6.6.1). 3C48 was used for flux density and bandpass calibration and J0321+1221 was used for complex gain calibration. The full C-band field-of-view centred at the SVOM/ECLAIRs position (Cordier et al., GCN 45398) was imaged in CASA using the task tclean. We detect all the radio sources previously reported by Schroeder et al. (GCN 45418). S3 is detected at a flux of ~75 uJy and we cannot confirm it as a possible radio counterpart. Among the remaining sources, S5, S9 and S10 show a consistent fading trend across all epochs. S5 and S10 are coincident with catalogued sources and, given the relatively large beam size (11x9 arcsec), we cannot distinguish whether their variability is intrinsic or caused by the GRB afterglow. However, we note that S10 lies close to the candidate optical afterglow (Ducoin et al., GCN 45450). Further observations are planned. We thank the VLA staff for executing the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/45452. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43672] GRB 2600818B: SVOM/VT optical upper limit and continuous observations
by GCN Circulars 27 Aug '26

27 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45451 SUBJECT: GRB 2600818B: SVOM/VT optical upper limit and continuous observations DATE: 26/08/27 06:21:49 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu, J. Wang, X. H. Han, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio, Bertrand Cordier (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed several ToO observations for GRB 260818B, which was triggered by SVOM/ECLAIRs (sb26081807, Cordier et al., GCN 45398; Yang et al., GCN 45405). This burst was also detected by SVOM/GRM (Ren et al., GCN 45411), HXMT (Wang et al., GCN 45408). The earliest observation started at 2026-08-18T23:33:18 UTC, about 3.4 hr post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. Additional ToO observations were performed at 1.02 d and 7.5 d post trigger. No credible candidate was found in the stacked images for each epoch, within the SVOM/ECLAIRs error box (Cordier et al., GCN 45398), the VLA radio sources (Schroeder et al., GCN 45418) and the Einstein Probe X-ray sources (Wu et al., GCN 45407). The typical 5-sigma upper limits are 23.0 mag in both channels. Our measurements are in AB magnitudes and are not corrected for Galactic extinction. This non-detection is consitent with the report from LCO (Shi et al., GCN 45399), SVOM/COLIBRÍ (Guelfand et al., GCN 45401), NOT (O'Neill et al., GCN 45403) and SVOM-CGFT (Guan et al., GCN 45417). We noticed that there seemed to be an optical brightening trend for the VLA radio source S10 (Schroeder et al., GCN 45418). Its brightness in VT_R was 22.2+/-0.3 mag at 5.1 hr to 21.7+/-0.2 mag at day 7. The position of S10 is spatially coincident with EPF_J025955.0+072535 reported by EP-FXT (Wu et al., GCN 45407). In the vicinity of S10, an optical candidate was proposed by SVOM/COLIBRÍ (FM-GFT) (Ducoin et al., GCN 45450). Some contributions from the COLIBRÍ candidate may be blended into our photometry, since the angular separation between the two sources is only 1.7 arcsec. Given the limited spatial resolution of VT and the faintness of the candidate (Ducoin et al., GCN 45450), we cannot confirm its detection. But the light curve of S10 shows some positive trend which needs to be further confirmed. 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. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/45451. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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