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[vsnet-grb-info 42514] EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44392 SUBJECT: EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773 DATE: 26/04/22 15:48:38 GMT FROM: Nusrin Habeeb at University of Leicester <nh312(a)leicester.ac.uk> B. Schneider (LAM), A. Saccardi (CEA/Irfu), G. Corcoran (UCD), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud), J.-L. Atteia (IRAP), N. Habeeb (U. Leicester), R. Brivio (INAF/OAB), report on behalf of the Stargate collaboration: Underneath the position of the optical/NIR afterglow (Li et al., GCN 40443; Xin et al., GCN 40444; Busmann et al., GCN 40447) of EP250512a / GRB 250512B (EP/WXT: Zhao et al., GCN 40437; Yang et al., GCN 40448; SVOM/ECLAIRs: Maggi et al., GCN 40439; Konus-Wind: Svinkin et al. GCN 40460), an object is well detected in archival imaging taken using the MegaCam instrument on the CFHT in the broad "gri" filter (Bannister et al. 2016, doi:10.3847/0004-6256/152/3/70). The object magnitude is about 24.5 AB mag. Given the spatial coincidence, this is likely the host galaxy of EP250512a / GRB 250512B. Starting at 01:53:33 UT on 2026 April 20, i.e. about 342.6 days after the burst, we obtained four spectra of 1200 s each using the X-shooter instrument installed on the ESO VLT UT3 (Melipal), covering the wavelength range 3000-21000 AA. Our spectroscopy reveals a single, confidently detected emission line at 13,889 AA. Interpreting this feature as [O III] 5007 at z ~ 1.773, we note the presence of a second, fainter emission corresponding to the expected position of the [O II] doublet. At this redshift, Halpha falls in a region of very poor transparency, and no detection is expected. We note that the precise position of the [O III] emission is also affected by atmospheric opacity, which adds some uncertainty to the redshift (of the order of 0.001). Alternative interpretations of the line at 13,889 AA are disfavored because we would then expect to see other lines in regions of good atmospheric transparency, which are absent in our spectrum. We acknowledge excellent support from the ESO staff in Paranal, in particular Maria del Mar Carretero Castrillo, Francisco Caceres, Luciano Sbordone, and Thomas Rivinius. View this GCN Circular online at https://gcn.nasa.gov/circulars/44392. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42513] GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44391 SUBJECT: GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486 DATE: 26/04/22 15:42:23 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> A. Saccardi (CEA/Irfu), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud), R. Brivio (INAF/OAB), N. Habeeb (U. Leicester), J.-L. Atteia (IRAP) report on behalf of the Stargate collaboration: We observed the object visible in the Legacy Survey underlying the position of the optical/NIR afterglow (D'Avanzo et al., GCN 40588; Rayson et al. GCN 40589) of the SVOM GRB 250530A (Wang et al., GCN 40576) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. A spectrum covering the wavelength range 3000-21000 AA was secured, with a total exposure time of 4x600 s in each of the UVB, VIS, and NIR arms. Our observation started at 00:32:26 UT on 2026 April 22, i.e. about 326.75 days after the SVOM trigger. Clear emission lines are detected in the visible and near-infrared arms, which we identify as [N II] 6584, H-alpha, the [O III] 4959, 5007 doublet, H-beta, and the [O II] 3726, 3729 doublet, all at a common redshift of z = 1.486. We suggest this to be the redshift of the host galaxy of GRB 250530A. We acknowledge excellent support from the ESO staff in Paranal, in particular Matias Jones, Felipe Gaete, Luciano Sbordone, and Boris Haeussler. View this GCN Circular online at https://gcn.nasa.gov/circulars/44391. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42512] GRB 260419A: AstroSat CZTI detection
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44390 SUBJECT: GRB 260419A: AstroSat CZTI detection DATE: 26/04/22 09:33:20 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), 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 long GRB 260419A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 44346). The source was detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-04-19 07:10:15 UTC. The measured peak count rate associated with the burst is 32 (+19, -2) counts/s above the background in the combined data of two quadrants (out of four), with a total of 715 (+297, -356) counts. The local mean background count rate was 137 (+19, -2) counts/s. Using cumulative rates, we measure a T90 of 47 (+11, -28) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. 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/44390. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42511] GRB 260421B: SVOM/GRM observation
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44389 SUBJECT: GRB 260421B: SVOM/GRM observation DATE: 26/04/22 08:31:00 GMT FROM: guohx(a)ihep.ac.cn SVOM/GRM team: Hao-Xuan Guo, Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier GODET (IRAP), Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260421B (SVOM trigger reference: sb26042105) at 2026-04-21T04:13:22.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44360) and SVOM/ECLAIRs (D.Zhao et al., GCN #44362). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 21.5 +3.5/-2.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260421B.png In addition, the position of this burst, as determined by SVOM/ECLAIRs (RA = 190.0318, Dec = -17.7566, GCN #44362), is located at about 44 degrees from the SVOM optical axis, which is inside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-14.5 to T0+21.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.26 +0.07/-0.06 and the cutoff energy, parameterized as Epeak, is 162 +18/-14 keV. The event fluence (10-1000 keV) in this time interval is (1.19 +/-0.05)E-05 erg/cm^2. The 1s peak spectrum, measured from T0+14.0 to T0+15.0 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -0.72 +/-0.07 and the cutoff energy, parameterized as Epeak, is 200 +13/-12 keV. The flux (10-1000 keV) in this time interval is (2.27 +0.09/-0.08)E-06 erg/cm^2/s. With the measured redshift z=2.115 (B. Schneider et al., GCN 44368), we calculate the isotropic energy Eiso is about 1.5E53 erg. Thus GRB 260421B is well consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/svgrb260421B_amati.png The localization of GRB 260421B in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260421B_yonetoku.png 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Hao-Xuan Guo (IHEP)(guohx(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44389. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42510] GRB260421B: J band upper limit by SYSU 80cm infrared telescope
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44388 SUBJECT: GRB260421B: J band upper limit by SYSU 80cm infrared telescope DATE: 26/04/22 07:24:57 GMT FROM: shiy228(a)mail2.sysu.edu.cn Yun Shi, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Rui-Chen Gao, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Jin-Ji Li, Hao-Nan Yang, Yan Yu, Hao-Ran Zhang, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team: We observed the field of the long GRB 260421B, detected by Fermi-GBM (Fermi GBM team, GCN 44360) and SVOM/ECLAIRs (Zhao et al., GCN 44362), and followed up by Einstein Probe/FXT (Wang et al., GCN 44387), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope. Early near-infrared follow-up observations have also been reported (Mo et al., GCN 44384). Our observations were carried out from 2026 Apr 21 15:25 UT to Apr 21 17:06 UT, corresponding to 11.2–12.9 hours after the GBM trigger (2026-04-21 04:13:21 UT), with a total exposure time of 5200 s in the J band, obtained under poor conditions. We do not detect any near-infrared counterpart at the position of the reported afterglow (He et al., GCN 44363; Sanchez-Alvarez, GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366; Li et al., GCN 44377; Pérez-Fournon et al., GCN 44383; Wang et al., GCN 44387). The 5-sigma limiting magnitude is approximately J ~ 16.9 Vega magnitudes. The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44388. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42509] GRB 260421B: EP-FXT follow-up observation
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44387 SUBJECT: GRB 260421B: EP-FXT follow-up observation DATE: 26/04/22 02:42:41 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B. T. Wang (YNAO, CAS), J. P. Chen (SYSU), D. Y. Li, and W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260421B (SVOM/sb26042105; Zhao et al., GCN 44362), also triggered by Fermi-GBM (Fermi GBM team, GCN 44360; Preis & Greiner, GCN 44361; Mukherjee et al., GCN 44382), starting at 2026-04-21T06:08:31UTC, approximately 1.9 hours after the SVOM trigger, with a total exposure time of 5994 s. One uncataloged source is detected within the ECLAIRs error circle, which is spatially consistent with the optical counterpart (He et al., GCN 44363; Sanchez-Alvarez, GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366, Li et al., GCN 44377; Pérez-Fournon et al., GCN 44383) at a redshift of z=2.115 (Schneider et al., GCN 44368). Preliminary analysis on this source is automatically conducted, and the details are listed as follows. EPF_J124000.4-174426 RA (J2000): 190.0018 Dec (J2000): -17.74055 Flux: 1.26e-11 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 6.27e-13 erg/s/cm2 (1 sigma) 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/44387. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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