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[vsnet-grb-info 42384] GRB 260411B: Fermi GBM Final Real-time Localization
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44262 SUBJECT: GRB 260411B: Fermi GBM Final Real-time Localization DATE: 26/04/11 08:15:05 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 08:04:35 UT on 11 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260411B (trigger 797587480.306254 / 260411337). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 83.2, Dec = 2.8 (J2000 degrees, equivalent to J2000 05h 32m, 2d 47'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 60.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411337/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411337/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411337/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44262. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42383] GRB 260411A: Fermi GBM Final Real-time Localization
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44261 SUBJECT: GRB 260411A: Fermi GBM Final Real-time Localization DATE: 26/04/11 06:46:58 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 06:36:28 UT on 11 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260411A (trigger 797582193.127706 / 260411275). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 153.6, Dec = 12.0 (J2000 degrees, equivalent to J2000 10h 14m, 12d 00'), with a statistical uncertainty of 9.6 degrees. The angle from the Fermi LAT boresight is 32.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411275/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411275/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411275/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42382] GRB 260410A: COLIBRÍ optical upper limit
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44260 SUBJECT: GRB 260410A: COLIBRÍ optical upper limit DATE: 26/04/11 06:40:10 GMT FROM: a.kuwata(a)irya.unam.mx Asuka Kuwata (UNAM), Damien Dornic (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (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), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), 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 imaged the field of the Fermi GRB 260410A (A. Holzmann Airasca et al., GCN Circ. 44253) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-11 03:50:46 to 04:47:10 UTC (from 20.7805 to 21.7371 hours after the trigger) and obtained 2460 seconds of simultaneous exposure in the r/z filters. The data were reduced, coadded, calibrated, and analyzed 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. In the stacked image, we do not detect any new source at the Fermi-LAT source position (A. Holzmann Airasca et al., GCN Circ. 44253) down to the following 5-sigma limit: r > 23.26 z > 21.83 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/44260. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42381] EP-WXT01709259790: Optical Upper limits with kinder observations
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44259 SUBJECT: EP-WXT01709259790: Optical Upper limits with kinder observations DATE: 26/04/11 02:08:30 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), S. Yang(HNAS), S. J. Smartt, J. Gillanders (both Oxford), A. Sankar.K, M.-H. Lee, A. Dutta, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, W.-J. Hou, H.-Y. Hsiao, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, K. W. Smith, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the WXT trigger 01709259790 using the 40cm SLT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations in r-band started at 12:10 UTC on 10th of April 2026 (MJD 61140.5068), 42 min after the EP-WXT detection. The EP-WXT transient was later identified as the star Gaia DR3 782359908221356544 during its flaring stage (Huang et al. GCN 44256). The star has an archival SDSS magnitude of r = 16.20. In our observations, we captured the stellar flare and the star varies from r = 15.561 +/- 0.042 in our first frame to r = 15.838 +/- 0.028 in the final (12th) image. The detailed photometric measurements using AutoPhOT are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude| SLT | r | 61140.5068 | 0.70 | 300 * 1 | 15.561 +/- 0.042 SLT | r | 61140.5104 | 0.78 | 300 * 1 | 15.582 +/- 0.048 SLT | r | 61140.5141 | 0.87 | 300 * 1 | 15.614 +/- 0.049 SLT | r | 61140.5177 | 0.96 | 300 * 1 | 15.718 +/- 0.043 SLT | r | 61140.5215 | 1.05 | 300 * 1 | 15.740 +/- 0.045 SLT | r | 61140.5251 | 1.14 | 300 * 1 | 15.750 +/- 0.038 SLT | r | 61140.5289 | 1.23 | 300 * 1 | 15.762 +/- 0.038 SLT | r | 61140.5326 | 1.31 | 300 * 1 | 15.786 +/- 0.041 SLT | r | 61140.5363 | 1.40 | 300 * 1 | 15.793 +/- 0.043 SLT | r | 61140.5400 | 1.49 | 300 * 1 | 15.805 +/- 0.035 SLT | r | 61140.5437 | 1.58 | 300 * 1 | 15.817 +/- 0.033 SLT | r | 61140.5473 | 1.67 | 300 * 1 | 15.838 +/- 0.028 We also utilized our Kinder Pipeline for the combined 300 sec*12 frames, we obtained an r-band limit of >20.6 mag at a median airmass of 1.13 and an average seeing of 1".5. Our limit is consistent with He et al. (GCN 44254). The presented magnitudes are calibrated using the field stars from the PanSTARRS catalog. The reported upper limit is not corrected for an expected galactic extinction of A_r = 0.02 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44259. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42380] GRB 260410B: SVOM/GRM detection of a short faint burst
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44257 SUBJECT: GRB 260410B: SVOM/GRM detection of a short faint burst DATE: 26/04/10 15:59:54 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chen-Wei Wang (IHEP), F. Piron (LUPM) and C. Lachaud (APC) report on behalf of the SVOM mission team: At 2026-04-10T12:22:27 UTC (T0), SVOM/GRM triggered on the gamma-ray burst GRB 260410B (SVOM burst-id sb26041001) on a timescale of 1 seconds and with a signal-to-noise ratio (SNR) of 5.90. This transient was also detected by Fermi/GBM (GCN Circulars #44255). At the time of this burst, SVOM/ECLAIRs was not taking data. With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that the short burst GRB 260410B consists a single pulse with T90 of 0.20 +0.12/-0.06 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260410B.png 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 Chenwei Wang: cwwang AT ihep.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44257. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42379] GRB 260410A: Fermi GBM Observation
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44258 SUBJECT: GRB 260410A: Fermi GBM Observation DATE: 26/04/10 17:00:13 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA), U. Pathak (IIT Bombay) and R. Sonawane (IISER TVM) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 07:03:57.00 UT on 10 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260410A (trigger 797497441/260410294), which was also detected by Fermi-LAT (Holzmann Airasca et al. 2026, GCN 44253) and SVOM/GRM (Wang et al. 2026, GCN 44257). The Fermi GBM real-time localization (GCN 44252) is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 49 degrees. The GBM light curve consists of a single bright emission episode with a duration (T90) of about 1 s (50-300 keV). The time-averaged spectrum from T0-0.07 to T0+0.30 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.17 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 960 +/- 30 keV. The event fluence (10-1000 keV) in this time interval is (1.33 +/- 0.01)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 12.0 +/- 1.0 ph/s/cm^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/44258. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42378] GRB 260410A: SVOM/GRM detection of a short faint burst
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44257 SUBJECT: GRB 260410A: SVOM/GRM detection of a short faint burst DATE: 26/04/10 15:59:54 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chen-Wei Wang (IHEP), F. Piron (LUPM) and C. Lachaud (APC) report on behalf of the SVOM mission team: At 2026-04-10T12:22:27 UTC (T0), SVOM/GRM triggered on the gamma-ray burst GRB 260410A (SVOM burst-id sb26041001) on a timescale of 1 seconds and with a signal-to-noise ratio (SNR) of 5.90. This transient was also detected by Fermi/GBM and Fermi/LAT (GCN Circulars #44252 and #44253). At the time of this burst, SVOM/ECLAIRs was not taking data. The SVOM/GRM light curve shows a single narrow peak structure with a duration of about 0.5 s. SVOM did not slew to the burst. An exceptional ToO observation has been scheduled which started about 3 hours after the trigger time. 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 Chenwei Wang: cwwang AT ihep.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44257. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42377] The EP-WXT trigger 01709259790 is likely a flaring star
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44256 SUBJECT: The EP-WXT trigger 01709259790 is likely a flaring star DATE: 26/04/10 15:22:03 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G. L. Huang, Z. X. Li, J. Y. Cao (IHEP, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709259790 at the time of 2026-04-10T11:27:58 (UTC), is likely a stellar flare associated with Gaia DR3 782359908221356544. The estimated flux of the flare is around 6 x 10^(-11) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 6x 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/44256. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42376] GRB 260410B: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44255 SUBJECT: GRB 260410B: Fermi GBM Final Real-time Localization DATE: 26/04/10 15:01:29 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 12:22:26 UT on 10 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260410B (trigger 797516551.925452 / 260410516). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 4.2, Dec = 37.7 (J2000 degrees, equivalent to J2000 00h 16m, 37d 42'), with a statistical uncertainty of 5.6 degrees. The angle from the Fermi LAT boresight is 90.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260410516/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260410516/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260410516/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44255. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42375] EP-WXT01709259790: Xinglong optical upper limit
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44254 SUBJECT: EP-WXT01709259790: Xinglong optical upper limit DATE: 26/04/10 14:18:44 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Min-He (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP-WXT01709259790, we observed the field of EP-WXT01709259790 using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s clear-band frames with a median time of 2026-04-10T12:16:23, 52 minutes after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (WXT01709259790), down to 3-sigma limiting magnitudes of 22.18 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/44254. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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