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[vsnet-grb-info 42522] The EP-WXT trigger 01709258652: Mondy optical observations
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44400 SUBJECT: The EP-WXT trigger 01709258652: Mondy optical observations DATE: 26/04/23 13:31:19 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> M. Chutchikova (HSE), A. Volnova (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the EP-WXT trigger 01709258652 (Yang et al., GCN 43849) with the AZT-33IK 1.5m telescope of the Mondy observatory starting on 2026-02-26 (UT) 21:07:17, i.e., ~8 hours after the trigger, and taking several 120-seconds frames in the R band. The photometry of suggested flare star LP 435-538 (High Proper Motion Star; Yang et al., GCN 43849; Wu et al., GCN 43857; Fang et al., GCN 43889) do no exhibit any significant variability within 1 hour of our observations. Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-02-26 21:07:17 0.32452 30*120 R 14.10 0.01 23.2 Mondy/AZT-33IK The photometry is based on nearby USNO-B1.0 stars (R2-magnitudes) and is not corrected for Galactic extinction. Our measured R magnitude is consistent with the photometry of the USNO-B1.0 star 1099-00207147 (R2 = 14.16) corresponding by the coordinates to LP 435-538. View this GCN Circular online at https://gcn.nasa.gov/circulars/44400. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42521] GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44399 SUBJECT: GRB 250328A: VLT host galaxy discovery and redshift z = 1.250 DATE: 26/04/23 12:50:54 GMT FROM: Nusrin Habeeb at University of Leicester <nh312(a)leicester.ac.uk> A. Saccardi (CEA/Irfu), B. Schneider (LAM), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud), N. Habeeb (U. Leicester), R. Brivio (INAF/OAB), G. Corcoran (UCD), J.-L. Atteia (IRAP), report on behalf of the Stargate collaboration: We observed the location of the optical/NIR counterpart (Schneider et al., GCN 39919, 39920; Li et. al, GCN 39923; Li et. al, GCN 39936; Kumar et. al, GCN 39946; Klingler et. al, GCN 39968; Pankov et al., GCN 40001) of the SVOM GRB 250328A (Brunet et al., GCN 39910), using the ESO VLT UT1 (Antu) equipped with the FORS2 imager. A 20 min exposure R-band observation was carried out at 04:05:01 UT on 2026 April 19 (386.46 days after the SVOM trigger). Consistent with the afterglow position, an object is clearly identified with a magnitude r = 24.51 +/- 0.09, calibrated against the Pan-STARRS catalog and not corrected for Galactic extinction. Its coordinates (J2000) are: RA = 14:23:50.45 Dec = +25:55:55.09 Given the spatial coincidence with the GRB afterglow (<0.5"), this is the likely host galaxy of GRB 250328A. Spectroscopic follow-up observations of this object were secured using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph, covering the wavelength range 3000-21000 AA. We obtained four spectra of 1200 s each starting at 03:28:04 on 2026 April 23, i.e. about 390.44 days after the SVOM trigger. Faint emission lines are detected in the visible and near-infrared arms, which we identify as the [O III] 4959,5007 doublet, H-beta, and the [O II] 3726,3729 doublet, all at a common redshift of z = 1.250. This is thus the redshift of the likely host galaxy of GRB 250328A. We acknowledge excellent support from the ESO staff in Paranal, in particular Boris Haeussler, Diego Parraguez, Felipe Gaete, Hannah Osborne, Luca Sbordone, Matias Jones, and Thomas Rivinius. View this GCN Circular online at https://gcn.nasa.gov/circulars/44399. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42520] EP260416a: Mondy optical observations
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44398 SUBJECT: EP260416a: Mondy optical observations DATE: 26/04/23 12:39:12 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP260416a (Hu et al., GCN 44307, 44324) at z = 1.909 (He et al., GCN 44336; An et al., GCN 44339) with the AZT-33IK 1.5m telescope of the Mondy observatory starting on 2026-04-21 (UT) 15:28:28 and taking several 120-seconds frames in the R band. The optical counterpart (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334; He et al., GCN 44336; An et al., GCN 44339; Jelinek et al., GCN 44341; Guziy et al., GCN 44351; Ho et al., GCN 44354; Pawar et al., GCN 44373; Li et al., GCN 44376) is clearly detected in the stacked frame. Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-04-21 15:28:28 5.43677 27*120 R 22.72 0.09 23.3 Mondy/AZT-33IK The photometry is based on nearby USNO-B1.0 stars (R2-magnitudes) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44398. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42519] GRB 260421A: SVOM/ECLAIRs refined analysis
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44397 SUBJECT: GRB 260421A: SVOM/ECLAIRs refined analysis DATE: 26/04/23 10:06:59 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP), L. Delfosse (CEA), O. Godet (IRAP), S. Schanne (CEA), W. L. Zhang (PMO), Z. Y. 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 260421A (SVOM burst-id sb26042105 – GCN 44362, trigger time T0 = 2026-04-21T04:13:25 UTC), which was also detected by Fermi (GCN 44360, 44361, 44382) and SVOM/GRM (GCN 44389). The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = 26.3 +4.4/-6.0 s in the 4-120 keV energy band. The time-averaged spectrum from T0-12 s to T0+20 s in the energy range 5-120 keV is best fitted (chi²/dof = 20.1/16) by a broken powerlaw model with best-fit parameters: alpha = -1.00 +0.35/-0.11, beta = -1.42 +0.07/-0.06 and a break energy of 13.7 +2.7/-4.4 keV. With this model, the 4-120 keV fluence is (8.6 +0.1/-1.1)e-6 erg/cm^2 and the 4-120 keV photon flux is 6.4 +0.1/-0.7 ph/cm²/s. Using a simple powerlaw provides a bad fit (chi²/dof = 31.3/18). 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/44397. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42518] GRB 260421B: 3.6m DOT optical observation
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44396 SUBJECT: GRB 260421B: 3.6m DOT optical observation DATE: 26/04/23 10:00:19 GMT FROM: pawarpankaj1492(a)gmail.com Pankaj Pawar, Anshika Gupta, Debalina Kar, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of GRB 260421B (Fermi GBM team, GCN 44360; Zhao et al., GCN 44362) using the 3.6m Devasthal Optical Telescope (DOT) located at Devasthal of the Aryabhatta Research Institute of observational sciencES (ARIES), India. The observations began on 2026-04-21 at 21:24:53 UT, approximately 17 hours after the trigger time. We obtained 2*300s frames in the SDSS r filter. We do not detect the optical counterpart (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; Mo et al., GCN 44384; and Shi et al., GCN 44388) within the error circle, nor do we see a source at the reported location of the transient. The limiting magnitude in the stacked image is: r > 22.4 mag (AB) The magnitude is calibrated against the Pan-STARRS PS1 catalog. We thank the staff of Devasthal for their assistance during these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44396. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42517] EP260416a: ZTSh R band observations
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44395 SUBJECT: EP260416a: ZTSh R band observations DATE: 26/04/22 23:58:50 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), V. Rumyantsev (CrAO), A. Volnova, N. Pankov, A. Pozanenko (IKI), Tao An, Yuanqi Liu (SHAO), Ankur Ghosh, Soebur Razzaque (U. of Johannesburg, RSA) report on behalf of GRB follow-up collaboration. We observed the field of EP260416a (Hu et al., GCN 44307; GCN 44324) with 2.6-m ZTSh of CrAO equipped with BVRI photometer and FLI PL4240 camera. We obtained a series of images in R band on 2026-04-22, 21:11:50--22:14:42 UT (t_mid - T0 = 6.6762 days). The optical transient discovered by COLIBRÍ (Ducoin et al., GCN 44310; and also observed by Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334; He et al., GCN 44336; An et al., GCN 44339; Jelinek et al., GCN 44341; Guziy et al., GCN 44351; Ho et al., GCN 44354) is clearly detected in the stacked image with the following brightness. Date, UT_start, t_mid - T0, filter, exp, mag +/- err UL days s 2026-04-22T21:11:50 6.67620 R 30*120 23.12 +/- 0.17 24.1 This preliminary photometry is based on the nearby USNO-B1 stars and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44395. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42516] EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44394 SUBJECT: EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9 DATE: 26/04/22 18:53:47 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> Martin Jelinek, Jan Strobl and Filip Novotný (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Masek, Petr Janecek, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ) report: The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted robotically to the EP-WXT alert of trigger 01709260362 (Yang et al., GCN 44386), obtaining a series of 60 s unfiltered images starting at 21:24:16.6 UT on 2026-04-21, i.e. ~32.2 min post trigger (T0 = 2026-04-21T20:52:02.749 UTC, JD 2461152.36948). We clearly detect the flaring star G 151-9 identified by the EP team (Yang et al., GCN 44386). The source fades by approximately 0.25 mag over the course of our observations, which span from T0+32.2 min to T0+2h 13.6 min. The overall decay is consistent with a power-law of index alpha = 0.67 +/- 0.16, superimposed on the quiescent brightness of the star at an unfiltered magnitude of 12.12 +/- 0.07. This is consistent with the stellar flare interpretation. View this GCN Circular online at https://gcn.nasa.gov/circulars/44394. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42515] IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44393 SUBJECT: IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/04/22 17:38:53 GMT FROM: syan079(a)icecube.wisc.edu The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-Cascade 260418A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/142457_45845844.amon) in a time range of 1000 seconds centered on the alert event time (2026-04-18 01:29:34.206 UTC to 2026-04-18 01:46:14.206 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-Cascade 260418A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.3e-01 to 1.4e+00 GeV cm^-2 within the 90% spatial containment region of IceCube-Cascade 260418A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 3e+02 GeV and 6e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-04-17 01:37:54.206 UTC to 2026-04-19 01:37:54.206 UTC). In this case, we report a p-value of 0.21, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.5e-01 to 1.4e+00 GeV cm^-2 within the 90% spatial containment region of IceCube-Cascade 260418A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/44393. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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