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[vsnet-grb-info 43622] GRB 260818B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 19 Aug '26

19 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45401 SUBJECT: GRB 260818B: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 26/08/19 11:53:08 GMT FROM: Marion G <marion.guelfand(a)gmail.com> Marion Guelfand (CPPM), Diego López-Cámara (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), 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), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM) and Clare Plasse (HKU) report: We imaged the field of the SVOM GRB 260818B (Cordier et al., GCN Circ. 45398) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-08-19 08:03:24 to 10:40:40 UTC (from 11.87 to 14.51 hours after the trigger) and obtained 118 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded and analysed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the ECLAIRs source position (Cordier et al., GCN Circ. 45398) down to the following 10-sigma limit: r > 23.8 z > 22.4 This is consistent with the non-detection reported by the LCO 1m telescope (Shi et al., GCN 45399). 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/45401. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43621] GRB260818A: EP-FXT follow-up observation
by GCN Circulars 18 Aug '26

18 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45400 SUBJECT: GRB260818A: EP-FXT follow-up observation DATE: 26/08/19 03:49:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z.M. Wang(BNU), C.Y. Dai(NJU), D. F. Hu(PMO,CAS) and H.W. Pan(NAOC) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of GRB 260818A detected by SVOM/ECLAIRs (Yin et al., GCN 45391). The observation started at 2026-08-18 02:43:32(UTC), about 1.67 hr after the SVOM trigger, with a total exposure time of around 4.6 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_J232025.8-320549 | 350.1077 | -32.0971 | 6.101382 | 1.3205e-13 EPF_J231936.3-320537 | 349.9012 | -32.0935 | 6.582593 | 5.9746e-14 EPF_J231953.3-320838 | 349.9729 | -32.1449 | 6.812141 | 2.0801e-13 EPF_J231912.9-320034 | 349.8036 | -32.0095 | 10.701601 | 1.0260e-12 EPF_J231953.3-320838 | 349.9722 | -32.1440 | 6.770902 | 2.0112e-13 EPF_J232037.7-320633 | 350.1572 | -32.1093 | 8.604395 | 4.5878e-14 with uncertainties of 10 arcsec (radius, 90% C.L. statistical and systematic). 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/45400. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43620] GRB 260818B: LCO optical upper limits
by GCN Circulars 18 Aug '26

18 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45399 SUBJECT: GRB 260818B: LCO optical upper limits DATE: 26/08/19 03:42:13 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y.Y. Shi (GXU), C. Wu, L.P. Xin (NAOC), A. Saccardi, D. Turpin (CEA/Irfu), Bertrand Cordier (CEA), Hatsune Goto (RIKEN, CEA), report on behalf of the SVOM mission team: We observed the field of GRB 260818B (SVOM burst-id sb26081807) detected by SVOM (Cordier et al., GCN 45398) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2026-08-18 at 23:44:55 UT (about 3.56 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and PS1 zs filter. In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limits calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r > 21.9 AB (5-sigma, mid-time 3.65 hr after the trigger), z > 19.7 AB (5-sigma, mid-time 3.65 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/45399. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43619] GRB 260818B: SVOM detection of a short burst
by GCN Circulars 18 Aug '26

18 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45398 SUBJECT: GRB 260818B: SVOM detection of a short burst DATE: 26/08/18 21:18:05 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Bertrand Cordier (CEA), Hatsune Goto (RIKEN, CEA) report on behalf of the SVOM mission team: At 2026-08-18T20:11:12 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260818B (SVOM burst-id sb26081807). 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 Count-Rate Trigger (CRT), which produced a sequence of 2 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 18.60 in the [8-120] keV energy band over a time window of 0.08 seconds starting at 2026-08-18T20:11:12. The localization of the best alert is R.A., Dec. 44.9407, 7.4547 degrees: R.A. (J2000) = 2h59m45.76s Dec. (J2000) = 7d27m16.93s with a 90% confidence level (C.L.) radius of 4.60 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a single peak structure with a duration of about 1 second. This burst also triggered SVOM/GRM at 2026-08-18T20:11:12 on a timescale of 0.10 seconds with an SNR of 31.10. Due to a platform constraint, no immediate slew was performed on this burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. We will schedule a SVOM ToO observation for this burst. 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 Bertrand Cordier: bcordier(a)cea.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/45398. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43618] SVOM trigger sb26081806 is not a GRB
by GCN Circulars 18 Aug '26

18 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45397 SUBJECT: SVOM trigger sb26081806 is not a GRB DATE: 26/08/18 17:10:59 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> B. Cordier, D. Götz (CEA Saclay) report on behalf of the SVOM mission team: At 2026-08-18T14:46:57 SVOM issued an alert with burst-id: sb26081806. This event is not a GRB but most likely an outburst from V* V934 Her. We apologize for any inconvenience this may have caused. The Burst Advocate (BA) on shift for this alert is Bertrand Cordier: bcordier(a)cea.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/45397. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43617] EP260806a: SAO RAS multicolor optical observations
by GCN Circulars 18 Aug '26

18 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45396 SUBJECT: EP260806a: SAO RAS multicolor optical observations DATE: 26/08/18 15:10:31 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> N. Pankov (IKI), A. Moskvitin (SAO RAS), A. Pozanenko (IKI), O. Spiridonova (SAO RAS), S. Kaisin (SAO RAS) report on behalf of IKI-GRB-FuN: We observed the field of the X-ray transient EP260806a detected by EP (Li et al., GCN Circ. 45299) with the Zeiss-1000 1-meter and the BTA 6-meter telescopes of Special Astrophysical Observatory (SAO RAS) on six epochs between 2026-08-07T00:56:47 and 2026-08-10T23:19:45 UT. We have applied image subtraction using PS1 g,r images as reference and clearly detected the optical counterpart (He et al., GCN 45300; de Ugarte Postigo et al., GCN 45302; Eyles-Ferris et al., GCN 45303; Ma et al., GCN 45304; de Ugarte Postigo et al., GCN 45306; Anumarlapudi et al., GCN 45312; Abidkhanov et al., GCN 45354; Hua et al., GCN 45385; Maksut et al., GCN 4538) at each epoch. The observational summary and preliminary photometry are presented below: Date UTstart t-T0 Exp. Filter Mag Err. Telescope (mid, d) (n*s) 2026-08-07 00:56:47 0.08539 7*120 Rc 19.519 0.030 Zeiss-1000 2026-08-07 23:18:25 1.01898 4*300 Rc 18.842 0.055 Zeiss-1000 2026-08-08 23:18:25 2.02679 5*300 Rc 18.783 0.043 Zeiss-1000 2026-08-10 02:53:28 3.16181 12*20 r 18.877 0.008 BTA-6m 2026-08-10 04:25:25 3.22439 2*20 g 17.650 0.140 BTA-6m 2026-08-10 00:57:26 3.08632 3*300 Rc 18.618 0.007 Zeiss-1000 2026-08-10 23:19:45 4.02827 6*300 Rc 18.935 0.084 Zeiss-1000 2026-08-11 23:26:37 5.02719 6*300 Rc 18.618 0.007 Zeiss-1000 The photometry is based on set of nearby stars from USNO-B1.0 (for Rc) and PS1 (for g,r) filters, respectively. No correction for the Galactic extinction was applied. The plot of the light curve derived from own data and GCN photometry is available online at: https://heaiki.ru/lvc/r/GRBs/EP260806a/EP260806a_lc.png. We observe a significant g-r color evolution from -0.24 +/- 0.13 at ~0.5 days (Anumarlapudi et al., GCN 45312) to -1.23 +/- 0.16 at ~3.2 days since trigger. The observed light curve behavior is consistent with an AGN outburst, as was suggested by de Ugarte Postigo et al. (GCN 45302). View this GCN Circular online at https://gcn.nasa.gov/circulars/45396. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43616] GRB 260818A: LCO optical upper limits
by GCN Circulars 18 Aug '26

18 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45395 SUBJECT: GRB 260818A: LCO optical upper limits DATE: 26/08/18 15:08:30 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y.Y. Shi (GXU), C. Wu, L.P. Xin (NAOC), A. Saccardi, D. Turpin (CEA/Irfu), Clara Plasse (HKU), Donghua Zhao (NAOC), report on behalf of the SVOM mission team: We observed the field of GRB 260818A (SVOM burst-id sb26081801) detected by SVOM (Yin et al., GCN 45391) with the LCO 1m telescope at Teide Observatory and South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2026-08-18 at 01:46:28.00 UT (about 41.87 min after the trigger) and we obtained 6x200 s exposures in the SDSS r and 3x200 s exposures in the PS1 zs filter. No credible uncatalogued source was detected in our stacked frames in the ECLAIRs localization region as also reported by SVOM/COLIBRÍ (Ducoin et al., GCN 45393). We measure the following upper limits calibrated against the DESI Legacy Imaging Surveys DR10 catalog, and not corrected for Galactic extinction: r > 21.8 AB (5-sigma, mid-time 1.01 hr after the trigger), z > 20.5 AB (5-sigma, mid-time 1.14 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/45395. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43615] EP260812a: AbAO optical upper limit
by GCN Circulars 18 Aug '26

18 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45394 SUBJECT: EP260812a: AbAO optical upper limit DATE: 26/08/18 14:36:58 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> N. Pankov (IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI), M. Zhuzhunadze (AbAO) report on behalf of IKI-GRB-FuN: We observed the field of the Einstein Probe fast X-ray transient EP260812a (Liu et al., GCN 45362) with the AS-32 telescope of Abastumani Observatory (AbAO). The observations were conducted on 2026-08-13 starting at 17:12:50 UT, i.e. ~1.267 days since trigger. The series of 66x60 sec exposures was taken in the R-filter using CCD-photometer. No new sources was identified within the X-ray error circle (Yang et al., GCN 45373). A faint optical source found in the NOT and LT observations (Corcoran et al., GCN 45376) is not detected in our observations. The observation summary and preliminary upper limit are provided below: Date UTstart t-T0 Exp. Filter UL (mid, d) (n*s) (3sigma) 2026-08-13 17:12:50 1.26723 65x60 R 22.1 The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes) and has not been corrected for the Galactic extinction. Our results are consistent with the upper limits reported by Yin et al. (GCN 45372), Corcoran et al. (GCN 45376), and Mirzakulov et al. (GCN 45387). View this GCN Circular online at https://gcn.nasa.gov/circulars/45394. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43614] GRB 260818A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 18 Aug '26

18 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45393 SUBJECT: GRB 260818A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 26/08/18 09:54:29 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Jean-Grégoire Ducoin (CPPM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (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), Alan M. Watson (UNAM), and Clara Plasse report: We imaged the field of the SVOM GRB 260818A (Yin et al., GCN Circ. 45391) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-08-18T07:52:19 to 2026-08-18T08:35:21 UTC (from 6.82 to 7.54 hours after the trigger) and obtained 32 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded and analysed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the SkyMapper DR4 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the ECLAIRs source position (Yin et al., GCN Circ. 45391) down to the following 10-sigma limit: r > 22.3 z > 20.4 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/45393. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43613] GRB 260810A: Insight-HXMT/HE detection
by GCN Circulars 18 Aug '26

18 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45392 SUBJECT: GRB 260810A: Insight-HXMT/HE detection DATE: 26/08/18 06:57:05 GMT FROM: yzh807926(a)163.com Zheng-Hang Yu, Chao Zheng, and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team: At 2026-08-10T19:09:43.350 (T0), Insight-HXMT/HE detected GRB 260810A, which is also detected by AstroSat CZTI (A. Arya et al., GCN #45363), and Glowbug (C.C. Cheung et al., GCN #45365) The Insight-HXMT/HE light curve mainly consists of two pulses with a T90 of 18.0 +7.0/-5.5 s. The 1 s peak rate, measured from T0+0.25 s, is 4028 cnts/sec. Insight-HXMT/HE detected a total of 15728 counts from this burst. The Insight-HXMT/HE light curve can be found here: https://www.bursthub.cn/gcn/2026/hxmtgrb260810A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the Normal 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://hxmten.ihep.ac.cn View this GCN Circular online at https://gcn.nasa.gov/circulars/45392. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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