April 2026 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 42508] The EP-WXT trigger 01709260362 is likely a flaring star
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44386 SUBJECT: The EP-WXT trigger 01709260362 is likely a flaring star DATE: 26/04/22 01:30:57 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), J. P. Chen (SYSU), B. T. Wang (YNAO, CAS), R. D. Liang, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709260362 at the time of 2026-04-21T20:52:02, is likely a stellar flare associated with G 151-9. The estimated flux of the flare is around 2.8e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 2.7e31 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/44386. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42507] GOTO26djh/AT2026jpw: ATCA radio detection
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44385 SUBJECT: GOTO26djh/AT2026jpw: ATCA radio detection DATE: 26/04/22 00:39:54 GMT FROM: James Leung at U. Toronto / HUJI <jamesk.leung(a)utoronto.ca> J. K. Leung (U. Toronto/HUJI) We observed the field of the transient GOTO26djh/AT2026jpw (O'Neill et al., GCN 44301) with the Australia Telescope Compact Array (ATCA). We conducted the observation on 2026 April 19 at 15:30 - 16:30 UT. In our preliminary analysis, we detect an unresolved radio source coincident with the position of the transient (Rhodes et al., GCN 44379). The unresolved radio source had a flux density of ~0.2mJy at 10 GHz and a self-absorbed spectrum at and around this frequency. We thank the CSIRO Space and Astronomy staff for supporting these observations. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO. View this GCN Circular online at https://gcn.nasa.gov/circulars/44385. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42506] GRB 260421B: J-band upper limit with WINTER
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44384 SUBJECT: GRB 260421B: J-band upper limit with WINTER DATE: 26/04/21 23:32:26 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 260421B (Fermi GBM Team, GCN 44360; Preis et al., GCN 44361; Zhao et al., GCN 44362; Mukherjee et al., GCN 44382) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-04-21T04:36:00 UTC in the J band (~23 min after the GRB trigger) under poor conditions, consisting of 10 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We do not detect a source at the optical counterpart location (He et al., GCN 44363; Álvarez et al., GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366; Lipunov et al., GCN 44367; Schneider et al., GCN 44368; Li et al., GCN 44377; Pérez-Fournon et al., GCN 44383). We obtain the following 5-sigma upper limit: J = 16.4 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/44384. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42505] GRB 260421B: LCO optical counterpart detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44383 SUBJECT: GRB 260421B: LCO optical counterpart detection DATE: 26/04/21 23:18:19 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), A. López-Oramas (IAC and ULL), and D. Aguado (IAC and ULL) Following the detection of the long GRB 260421B by Fermi GBM (Fermi GBM team, GCN circ. 44360; Preis & Greiner, GCN circ. 44361; and Mukherjee, GCN circ. 44382) and by SVOM ECLAIRs, GBM, and MXT (Zhao et al., GCN circ. 44362), we observed the field with one of the two Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Siding Spring Observatory near Coonabarabran, New South Wales, Australia. The observation, a single exposure of 200 sec in the SDSS r' filter, started on 2026-04-21 at 13:40:22 UT, about 9.45 hours after the Fermi trigger. The optical counterpart, first reported by He et al. (GCN circ. 44363), is detected in our image with an AB magnitude of 21.55 +/- 0.21, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. Other optical detections or upper limits have been reported by Sánchez Álvarez et al. (GCN circ. 44364), Turpin et al. (GCN circ. 44365), Wu et al. (GCN circ. 44366), Lipunov et al. (GCN circ. 44367), Schneider et al. (GCN circ. 44368, redshift of z = 2.115), and Li et al. (GCN circ. 44377). This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026A-011, SGLF and Superluminous Supernovae surveys). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/44383. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42504] GRB 260421B: Fermi GBM Observation
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44382 SUBJECT: GRB 260421B: Fermi GBM Observation DATE: 26/04/21 19:36:16 GMT FROM: oindabimukherjee(a)gmail.com O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 04:13:21.17 UT on 21 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260421B (trigger 798437606/260421176), which was also detected by SVOM/ECLAIRs (Zhao et al. 2026, GCN 44362), and VLT/X-shooter with spectroscopic redshift z = 2.115 (Schneider et al. 2026, GCN 44368). The Fermi GBM on-ground location (GCN 44360) is consistent with the SVOM/ECLAIRs position. The angle from the Fermi LAT boresight is 58 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 18 s (50-300 keV). The time-averaged spectrum from T0-1.6 to T0+24.9 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.11 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 159 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (1.06 +/- 0.01)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+15 s in the 10-1000 keV band is 15.4 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 130 +/- 1 keV, alpha = -1 +/- 0.005 and beta = -2.31 +/- 0.02. 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/44382. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42503] Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44381 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB DATE: 26/04/21 19:24:18 GMT FROM: atrigg2(a)lsu.edu A. C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 798482368/260421694 at 16:39:23.09 UT on 21 April 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles (SAA Exit)." View this GCN Circular online at https://gcn.nasa.gov/circulars/44381. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42502] GRB 260421A: AstroSat CZTI detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44380 SUBJECT: GRB 260421A: AstroSat CZTI detection DATE: 26/04/21 15:59:15 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a short GRB 260421A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 44358). The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-21 02:12:43.91 UTC. The measured peak count rate associated with the burst is 251 (+66, -70) counts/s above the background in the combined data of all quadrants, with a total of 267 (+133, -138) counts. The local mean background count rate was 1340 (+8, -10) counts/s. Due to the intrinsic 1s binning of Veto data, we cannot reliably estimate T90 for this burst. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/44380. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42501] GOTO26djh/AT2026jpw: radio detection at 15GHz
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44379 SUBJECT: GOTO26djh/AT2026jpw: radio detection at 15GHz DATE: 26/04/21 15:44:07 GMT FROM: Lauren Rhodes at McGill <lauren.rhodes(a)mcgill.ca> Lauren Rhodes (McGill), Andrew Hughes, Rob Fender (Oxford), Dave Green, Dave Titterington (Cambridge) report: We observed the position of GOTO26djh/AT2026jpw (GCN 44301) with the Arcminute Microkelvin Imager Large-Array (AMI-LA) at 15.5 GHz beginning for three epochs starting 2026-04-16 22:18UTC; 2026-04-17 21:14UTC and 2026-04-18 21:38UTC, each epoch lasting 5, 6.5, and 7 hours, respectively. We detect an unresolved source, in each epoch with coordinates consistent with those of GOTO26djh/AT2026jpw. We measure a peak flux density of 0.28±0.07, 0.44±0.08, and 0.36±0.09mJy//beam in epochs 1, 2 and 3, respectively. We thank the staff at the Mullard Radio Astronomy Observatory for carrying out these observations and operating the AMI-LA. (edited) View this GCN Circular online at https://gcn.nasa.gov/circulars/44379. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42500] GRB 260412A: SVOM/ECLAIRs refined analysis
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44378 SUBJECT: GRB 260412A: SVOM/ECLAIRs refined analysis DATE: 26/04/21 13:31:47 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Marius Brunet (IRAP), Wenjin XIE (NAOC), Olivier Godet (IRAP), Ziqi Wang (GXU), Zhiyong Liu(GZNU) 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 260412A (SVOM burst-id sb26041206 – GCN 44276, trigger time T0 = 2026-04-12T06:13:35 UTC), which was also detected by Fermi (GCN 44275, 44279), GECAM (GCN 44281) and HXMT (GCN 44294). The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve with late peaks at around T0+80s and T0+160s. The burst duration is T90 = 165.0 +2.6/-1.6 s in the 4-120 keV energy band. The time-averaged spectrum from T0-3.5 s to T0+200.5 s in the energy range 4-120 keV is best fitted by a powerlaw model with best-fit parameters – alpha = -1.5 +/-0.3. With this model, the 4-120 keV fluence is 7.4 +/- 0.3 e-6 erg/cm^2. Using the same Fermi/GBM time window as in Palafox et al. (GCN 44279), we retrieve a consistent photon index value when using a cutoff model and fixing Epeak at 210 keV. 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/44378. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42499] GRB 260421B: SVOM/VT optical observations
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44377 SUBJECT: GRB 260421B: SVOM/VT optical observations DATE: 26/04/21 11:53:36 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, L. P. Xin, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), W. L. Zhang (PMO), Z. Y. Liu (GZNU) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic slew to the field of GRB 260421B triggered by SVOM/ECLAIRs (sb26042105, Zhao et al., GCN 44362). This burst was also detected by SVOM/GRM (Zhao et al., GCN 44362), SVOM/MXT (Zhao et al., GCN 44362), and Fermi-GBM (Fermi GBM team, GCN 44360; Preis & Greiner, GCN 44361). The observation started at 2026-04-21T04:18:32 UTC, i.e., approximately 5.1 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (He et al., GCN 44363; Sanchez-Alvarez, GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366) with redshift z=2.115 (Schneider et al., GCN 44368) was clearly detected in single frames in both channels. With X-band data available，the light curves showed a fast decay from 5.5 minutes to 50 minutes post trigger, following a plateau after 3.37 hours. The preliminary measurements are given in the AB magnitudes and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 5.53 min VT_B 50 sec 16.23+/-0.03 mag 5.53 min VT_R 50 sec 15.77+/-0.03 mag 3.599 hr VT_B 27*100 sec 20.94+/-0.07 mag 3.668 hr VT_R 22*100 sec 20.52+/-0.06 mag 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/44377. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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