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[vsnet-grb-info 43552] GRB 260808B: SVOM/ECLAIRs refined analysis
by GCN Circulars 09 Aug '26

09 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45333 SUBJECT: GRB 260808B: SVOM/ECLAIRs refined analysis DATE: 26/08/09 19:10:45 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Authors: M. Brunet, L. Bouchet, S. Guillot (IRAP), Michela Dinatolo (U. Milano) 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 GRB 260808B (SVOM burst-id sb26080812 – GCN 45316, trigger time T0 = 2026-08-08T14:20:58 UTC). The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve with a possible precursor at T0-84.5 s lasting around 2 s. The burst duration is T90 = 178 +12/-8 s in the 4-120 keV energy band. The time-averaged spectrum before the slew, from T0-45s to T0+43s in the 5-120 keV energy range is best fitted by a powerlaw model with alpha = -1.96 +0.14/-0.16. With this model, the 4-120 keV fluence is 6.4 +/-0.9 e-7 erg/cm^2 and the 4-120 keV photon flux is 0.32 +/-0.03 ph/cm^2/s. The possible precursor is too faint to extract any significant spectral parameters. 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: L. Bouchet (IRAP) (laurent.bouchet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/45333. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43551] EP260809a:refined analysis of the EP-WXT and autonomous EP-FXT observation
by GCN Circulars 09 Aug '26

09 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45332 SUBJECT: EP260809a:refined analysis of the EP-WXT and autonomous EP-FXT observation DATE: 26/08/09 17:58:56 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. X. Sun(NAO, CAS), Q. J. Huang (PMO, CAS), K. J. Zhang(YNU), J. P. Chen (SYSU), Z. X. Ling(NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260809a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Sun et al., GCN 45321) and followed by several optical telescopes (Adami et al., GCN 45324; Jiang et al., GCN 45325; Basa et al., GCN 45326 ) . The refined analysis of the WXT data shows that the event started at T0=2026-08-09T00:38:21(UTC) and lasted for 34 s before the observation was interrupted by the autonomous follow-up observation.The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model (tbabs*tbabs*cflux*powerlaw), with the Galactic hydrogen column density fixed at 8.24 × 10^20 cm^-2. The best-fit photon index is 1.74 (-0.63/+0.88), and the additional hydrogen column density is 1.25 (-1.25/+2.23) × 10^21 cm^-2. The derived average unabsorbed 0.5–4 keV flux is 3.32 (-0.77/+0.98) × 10^-9 erg s^-1 cm^-2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-08-09T01:25:57(UTC), about 47.6 minutes after T0. The exposure time of this observation is 3020 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 328.5791, 17.6054 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 8.24 × 10^20 cm^-2 and a photon index of 2.00 (-0.28/+0.29), and the intrinsic hydrogen column density is 0.08 (-/+0.08) × 10^22 cm^-2. The derived average unabsorbed 0.5-10 keV flux is 1.27(-0.12/+0.14)× 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/45332. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43550] GRB 260809A: SVOM detection of a faint burst
by GCN Circulars 09 Aug '26

09 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45331 SUBJECT: GRB 260809A: SVOM detection of a faint burst DATE: 26/08/09 15:24:53 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP), F. Piron (LUPM), D.Gotz (CEA), A. Saccardi (CEA) report on behalf of the SVOM mission team: At 2026-08-09T14:57:33 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260809A (SVOM burst-id sb26080907). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 2 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 7.20 in the [8-120] keV energy band over a time window of 20.48 seconds starting at 2026-08-09T14:57:13. The localization of the best alert is R.A., Dec. 356.820, 20.969 degrees (J2000) with a 90% confidence level (C.L.) radius of 10.88 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-08-09T15:00:23 UTC, 170 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 356.9664, 21.0347 degrees: R.A. (J2000) = 23h47m51s Dec. (J2000) =21d02m04s with a 90% C.L. radius of 94 arcseconds. This location is 9.09 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Frédéric Piron: piron(a)in2p3.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/45331. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43549] GRB 260808B: Liverpool Telescope optical observations
by GCN Circulars 09 Aug '26

09 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45330 SUBJECT: GRB 260808B: Liverpool Telescope optical observations DATE: 26/08/09 12:05:07 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of GRB 260808B (Bouchet et al., GCN 45316) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x120s exposures in SDSS griz filters, starting at 2026-08-09 00:32:11 UT, approximately 10.17 hours after SVOM/ECLAIRS trigger. We detect a source in the stacked images at the counterpart position reported by Turpin et al. (GCN 45318), Li et al. (GCN 45320), also observed by Wang et al. (GCN 45322), Adami et al. (GCN 45323), Saccardi et al. (GCN 45328), and Schneider et al. (GCN 45329), with preliminary photometry given below: MJD (mid) T_mid-T_0 Filter Mag. (AB) 61261.02909 10.35 h i 22.50 ± 0.23 61261.04320 10.88 h z 21.96 ± 0.28 61261.05760 11.03 h g 22.95 ± 0.25 61261.07154 11.37 h r 22.74 ± 0.19 The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/45330. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43548] GRB 260808B: NOT optical observations
by GCN Circulars 09 Aug '26

09 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45329 SUBJECT: GRB 260808B: NOT optical observations DATE: 26/08/09 09:53:05 GMT FROM: luca.izzo(a)inaf.it B. Schneider (LAM), L. Izzo (INAF/OACN and DARK/NBI), A. Saccardi (CEA/Irfu), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), D. O’Neill (U. Birmingham), report on behalf of a larger collaboration: We observed the field of GRB 260808B detected by SVOM/ECLAIRs (Bouchet et al., GCN 45316; see also Wang et al., GCN 45322), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 3x300 s exposures in the SDSS r-band and 5x200s in the SDSS z-band at mid time 2026 Aug 09.1158 UT (12.43 hr after the trigger). In the stacked images, we clearly detect the optical afterglow (Turpin et al., GCN 45318; Li et al., GCN 45320; Adami et al., GCN 45323; Saccardi et al., GCN 45328). We measure a preliminary AB magnitude of r = 22.72 +/- 0.17 mag, and z = 22.19 +/- 0.24 mag, 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/45329. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43547] GRB 260808B: LCO optical observations
by GCN Circulars 09 Aug '26

09 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45328 SUBJECT: GRB 260808B: LCO optical observations DATE: 26/08/09 09:46:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), S. J. Yin (GXU), C. Wu (NAOC), D. Turpin (CEA/Irfu), M. Dinatolo (U. Milano), report on behalf of the SVOM mission team: We observed the field of GRB 260808B detected by SVOM/ECLAIRs (Bouchet et al., GCN 45316; see also Wang et al., GCN 45322) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2026-08-08 at 20:29:25 UT (about 6.14 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical counterpart (Turpin et al., GCN 45318; Li et al., GCN 45320; Adami et al., GCN 45323) is detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction: r = 22.13 +/- 0.23 AB (5-sigma, mid-time 6.23 hr after the trigger). z > 20.74 AB (3-sigma, mid-time 7.44 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/45328. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43546] GRB 260808A: NuSTAR detection of prompt emission
by GCN Circulars 09 Aug '26

09 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45327 SUBJECT: GRB 260808A: NuSTAR detection of prompt emission DATE: 26/08/09 07:43:36 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260808A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-08-08T02:51:42.310 UTC, shows a detection of GRB 260808A, also detected by Fermi-GBM (GCN 45313). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single episode with two peaks lasting for about 20-s. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see any evidence in the signal above 100 keV in the CZT detectors. The Fermi-GBM localization (GCN 45313) at RA = 341.8, Dec = 14.1 implies an offset from the NuSTAR boresight of 76-deg (i.e. from the side) and an offset from the geocenter of 135-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260808A Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/45327. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43545] EP260809a: COLIBRÍ optical observations
by GCN Circulars 09 Aug '26

09 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45326 SUBJECT: EP260809a: COLIBRÍ optical observations DATE: 26/08/09 07:27:51 GMT FROM: Stephane Basa at UAR Pytheas/OHP, LAM <stephane.basa(a)lam.fr> EP260809a: COLIBRÍ optical observations Stéphane Basa (UAR Pytheas), Edilberto Aguilar-Ruiz (UNAM), William H. Lee (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), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM) and Alan M. Watson (UNAM) report: We imaged the field of the EP260809a (Sun et al., GCN 45321) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-08-09 05:19:54 to 05:49:15 (from 4.683 to 5.172 hours after the trigger) and obtained 20 minutes of exposure in the z filter. The data were reduced and coadded with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS catalog, is in the AB system, and is not corrected for Galactic extinction. We clearly detected the optical counterpart (Adami et al., GCN 45324 and Jiang et al., GCN 45325) at a preliminary magnitude of: z = 22.04 +/- 0.19 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/45326. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43544] EP260809a: LCO optical observation
by GCN Circulars 08 Aug '26

08 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45325 SUBJECT: EP260809a: LCO optical observation DATE: 26/08/09 05:04:21 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang, L.B. He, J. An, X. Liu, Z.P. Zhu, Z. Fan, W.X. Li, D. Xu(NAOC), S.Y. Fu (HUST), Y.L. Hua (PMO) report: We observed the field of EP260809a detected by EP (Sun et al., GCN 45321), using an LCO 1m telescope located at the Teide Observatory (Spain) equipped with the SINISTRO instrument. Observation started at 2026-08-09T03:55:09.359 UT, i.e., 3.27 hr after the trigger, and 3x200 s Sloan r-band frames were obtained. The optical counterpart (Adami et al., GCN 45324) is marginally detected in our stacked image with a brightness of r ~ 22 at a median time of 3.36 hr since trigger, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/45325. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43543] EP260809a: OHP/T193 optical observations
by GCN Circulars 08 Aug '26

08 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45324 SUBJECT: EP260809a: OHP/T193 optical observations DATE: 26/08/09 03:43:07 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), B. Schneider (LAM), A. Saccardi (CEA/Irfu), S. Basa (LAM/OHP/Pytheas/AMU) report on behalf of a larger collaboration: We observed the field of EP260809a (Sun et al., GCN45321) using the T193cm telescope at Observatoire de Haute-Provence (France) with the MISTRAL spectro-imager. We obtained 4x10 minutes of exposure in the r-band under a 2.3arcsec seeing, starting at 20260809_020201UT (1.4 hr after the Sun et al. trigger) and ending at 20260809_025709UT (2.3 hr after the Bouchet et al. trigger). In the preliminary stacked images, we detect an object not present in PanStarr images at RA (J2000): 21:54:19.2 DEC (J2000): +17:36:23 with a preliminar magnitude of: r = 21.53 +/- 0.10 mag The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction. We acknowledge the excellent support from Observatoire de Haute-Provence and in particular Stephane Favard. View this GCN Circular online at https://gcn.nasa.gov/circulars/45324. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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