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[vsnet-grb-info 42231] EP260321a: J-band observations by the SYSU 80 cm infrared telescope
by GCN Circulars 25 Mar '26

25 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44110 SUBJECT: EP260321a: J-band observations by the SYSU 80 cm infrared telescope DATE: 26/03/25 09:38:42 GMT FROM: Rui-Chen Gao <ayxzxn0100(a)gmail.com> Rui-Chen Gao, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Wei-Sen Huang, Jin-Ji Li, Jia-Qi Lin, Pu Lin, Yun Shi, Hao-Nan Yang, Yan Yu, 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 fast X-ray transient EP260321a(Huang et. al, GCN 44068), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope. Our observations were carried out on 2026 Mar 24 18:57 UT, 78.4 hours after the trigger, using stacked images in the J band. We clearly detect the source at the position of the optical counterpart (Lee et al., GCN 44070; Tanvir et al., GCN 44082; Moran et al., GCN 44083, Ahumada et al., GCN 44084, Liu et al., GCN 44087, de Ugarte Postigo et al., GCN 44091, Xu et al., GCN 44092, Pankov et al. GCN 44103, Corcoran et al., GCN 44105, Rastinejad et al., GCN 44107), and we measure J = 17.489 +/- 0.232 Vega mag. The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction. Further observations are ongoing. 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/44110. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42230] GRID detection of GRB 260320A
by GCN Circulars 25 Mar '26

25 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44109 SUBJECT: GRID detection of GRB 260320A DATE: 26/03/25 01:52:27 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Longhao Li, Yuchen He, Chenyu Wang, Zirui Yang report on behalf of the GRID Collaboration: GRID-11B reports the detection of the long-duration GRB 260320A, which was also detected by Glowbug gamma-ray(C.C. Cheung et al.,GCN#44093), Insight-HXMT/HE (Xinghao Luo et al., GCN #44077) and NuSTAR (G. Waratkar et al., GCN #44064). The event was triggered with GRID on 2026-03-20 at 19:40:04.5 UTC. The measured burst duration (T90) in the 30-2000 keV range is approximately 9.9 +/- 1.8 seconds from GRID-11B . At present, only the GRID light curve is available. No spectral analysis is reported at this stage. The GRID light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260320A/GRID_260… GRID is a student-led project to monitor the transient gamma-ray sky with multiple detectors onboard different nanosatellites in the era of multi-messenger astronomy. For more information about GRID, please refer to the following references: https://doi.org/10.1007/s10686-019-09636-w and https://doi.org/10.1007/s10686-021-09819-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/44109. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42229] EP260321a: Gemini-South confirmation of a supernova
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44108 SUBJECT: EP260321a: Gemini-South confirmation of a supernova DATE: 26/03/24 18:32:10 GMT FROM: Jillian Rastinejad at University of Maryland <jillianrastinejad2024(a)u.northwestern.edu> Jillian Rastinejad, Gokul Srinivasaragavan (UMD), and Tomas Ahumada (NOIRLab) report on behalf of a larger collaboration: Following the detection of the putative optical counterpart (Lee et al., GCN 44070; Tanvir et al., GCN 44082; Moran et al., GCN 44083, Ahumada et al., GCN 44084, Liu et al., GCN 44087, de Ugarte Postigo et al., GCN 44091, Pankov et al. GCN 44103) of EP 260321a (Huang et al., GCN 44068), we obtained optical spectroscopy using the Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-South, under Program GS-2026A-Q-119. The mean time of the observation was 23:50 UT on 2026 Mar 23 (3.5 days post-burst). The total exposure time was 4x600 s using the B480 grating, and covered the wavelength range 3500-7500 AA. We clearly detect emission lines due to the underlying galaxy, which are well-matched to z = 0.0343 (Tanvir et al., GCN 44082). We also observe broad absorption features across a rest-frame wavelength range of 4200-5000 AA (assuming z=0.0343), consistent with the broad absorption lines observed in Type Ic-BL supernovae. Our observations confirm the presence of a supernova noted by Xu et al., GCN 44092 and Corcoran et al., GCN 44105. We thank the Gemini staff for the rapid scheduling and execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44108. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42228] EP260321a: Gemini-South confirmation of a supernova
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44107 SUBJECT: EP260321a: Gemini-South confirmation of a supernova DATE: 26/03/24 18:32:10 GMT FROM: Jillian Rastinejad at University of Maryland <jillianrastinejad2024(a)u.northwestern.edu> Jillian Rastinejad, Gokul Srinivasaragavan (UMD), and Tomas Ahumada (NOIRLab) report on behalf of a larger collaboration: Following the detection of the putative optical counterpart (Lee et al., GCN 44070; Tanvir et al., GCN 44082; Moran et al., GCN 44083, Ahumada et al., GCN 44084, Liu et al., GCN 44087, de Ugarte Postigo et al., GCN 44091, Pankov et al. GCN 44103) of EP 260321a (Huang et al., GCN 44068), we obtained optical spectroscopy using the Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-South, under Program GS-2026A-Q-119. The mean time of the observation was 23:50 UT on 2026 Mar 23 (3.5 days post-burst). The total exposure time was 4x600 s using the B480 grating, and covered the wavelength range 3500-7500 AA. We clearly detect emission lines due to the underlying galaxy, which are well-matched to z = 0.0343 (Tanvir et al., GCN 44082). We also observe broad absorption features across a rest-frame wavelength range of 4200-5000 AA (assuming z=0.0343), consistent with the broad absorption lines observed in Type Ic-BL supernovae. Our observations confirm the presence of a supernova noted by Xu et al., GCN 44092 and Corcoran et al., GCN 44105. We thank the Gemini staff for the rapid scheduling and execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44107. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42227] Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44106 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB DATE: 26/03/24 18:21:55 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 796060650/260324665 at 15:57:25.73 UT on 24 March 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to Local Particles due to SAA Entry." View this GCN Circular online at https://gcn.nasa.gov/circulars/44106. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42226] EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44105 SUBJECT: EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf DATE: 26/03/24 15:23:31 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> G. Corcoran (UCD), A. Martin-Carrillo (UCD), L. Izzo (INAF/OACN), A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud), M. De Pasquale (U. of Messina), N. R. Tanvir (U. Leicester), R. A. J. Eyles-Ferris (U. Leicester), A.J. Levan (Radboud) report on behalf of the Stargate collaboration: We observed the optical counterpart (Tanvir et al., GCN 44082; see also Lee et al., GCN 44070; Aryan et al., GCN 44081; Ahumada et al., GCN 44084; Liu et al., GCN 44087, Sankar et al., GCN 44089, de Ugarte Postigo et al., GCN 44091, Xu et al., GCN 44092, Pankov et al., GCN 44103), of EP260321a (Huang et al., GCNs 44068, 44075) with the FORS2 spectrograph on the ESO VLT UT1 (Antu) beginning on 2026-03-24 at 00:52 UT (2.515 days post-trigger). Our observations consisted of 3x300 s exposures in both the 300V and 300I grisms, spanning overall the wavelength range 3300-11000 AA. From the 30 s R-band acquisition image we measure a magnitude of r = 18.31 +/- 0.09 mag (AB) calibrated using nearby stars from the Pan-STARRS catalogue, not corrected for Galactic extinction and not corrected by the host galaxy contribution at that position. The acquired spectrum shows a good match to the spectrum of GRB-SN 2006aj (at 5 days pre-peak) using SNID SAGE (Stoppa in prep., https://github.com/FiorenSt/SNID-SAGE) Based on this similarity, we identify the supernova associated with EP260321a as a broad-lined type-Ic SN similar to other SNe accompanying GRBs and FXTs. This object is now named SN 2026gzf. A figure comparing our spectrum (blue line) to SN 2006aj (red line) is available at the following link: https://shorturl.at/DpROp. Further analyses and observations are ongoing. We acknowledge the excellent expert support from the observing staff in Paranal, in particular Linda Schmidtobreick, Alonso Luna Ruiz Fernandez, Lorena Faundez, and Marcela Espinoza. View this GCN Circular online at https://gcn.nasa.gov/circulars/44105. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42225] GRB 260310A: LBT optical observations
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44104 SUBJECT: GRB 260310A: LBT optical observations DATE: 26/03/24 14:51:33 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> Niccolo’ Passaleva, Yu-Han Yang, Narges Shahamt, Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: Following the detection of GRB 260310A by Fermi/GBM and AstroSat CZTI (Fermi GBM team, GCN 43951,43975; AstroSat CZTI collaboration, GCN 43958), we observed the likely counterpart AT2026fgk (discovered by GOTO; O’Neill et al. 2026, TNS Discovery Report 294132) in r and z filters with the Large Binocular Camera (LBC) mounted on the Large Binocular Telescope (LBT). Observations started at 2026-03-18T09:25:06 (~ 8.2 d after the GBM trigger) with an average airmass of 1.3. We detect the source with a preliminary magnitude of r~18.7 AB mag, calibrated using nearby stars from the Legacy Survey DR10 (Dey et al. 2019) catalogue, uncorrected for Galactic extinction. Our measurement is consistent with those at the same observing time reported by Perley et al. (GCN 44096), Volnova et al. (GCN 44060). We acknowledge excellent support from the LBTO and LBT-INAF staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/44104. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42224] EP260321A: Mondy optical observations
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44103 SUBJECT: EP260321A: Mondy optical observations DATE: 26/03/24 12:34:33 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> N. Pankov (IKI), A. Pozanenko (IKI), E. Shekotikhin (IKI), E. Klunko (ISTP), A. Volnova (IKI) report on behalf of IKI-GRB-Fun collaboration: We observed the localization of the EP260321A (Huang et. al, GCN 44068) with the AZT-33IK telescope of the Mondy observatory. We obtained series in the R filter on epochs 2026-03-21, 2026-03-22 and 2026-03-23. The source reported by the Kinder (Lee et al., GCN 44070) and observed till now by (Aryan et al., GCN 44081; Ma et al., GCN 44074; Aguilar-Ruiz et al., GCN 44076; Liang et al., GCN 44079; Aryan et al., GCN 44081; Tanvir et al., GCN 44082; Moran et al., GCN 44083; Ahumada et al., GCN 44084; Liu et al., GCN 44087; Sankar et al., GCN 44089; de Ugarte Postigo et al., GCN 44091; Xu et al., GCN 44092) is clearly visible in the co-add images on all epochs. The early brightening of the source is evident after subtracting the epochs (i.e., 2026-03-23 minus 2026-03-22). The photometry of the host galaxy + the source and observation details are listed below: Date UT start t-T0 Exp. Filter OT+host Err. UL(3sigma) (mid, days) (s) 2026-03-21 14:50:00 0.11785 30x120 R 18.09 0.02 22.7 2026-03-22 16:02:29 1.16819 30x120 R 17.77 0.02 22.7 2026-03-23 14:48:46 2.11561 28x120 R 17.29 0.02 22.8 The photometry was calibrated using nearby USNO-B1.0 stars (R2 mags) and has not been corrected for the Galactic extinction. The photometry of the 2026-03-23 epoch might be affected by the host very slightly, while for other epochs the photometry is significantly contaminated by the host. View this GCN Circular online at https://gcn.nasa.gov/circulars/44103. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42223] GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44102 SUBJECT: GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions DATE: 26/03/24 12:34:17 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Fredd Sánchez Álvarez (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), 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), 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), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) SVOM BA1 and SVOM BA2 report: We imaged the field of the SVOM GRB 260321A (Brunet et al., GCN Circ. 44071) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-03-22 06:35:41 to 09:32:17 UTC (from 12.39 to 15.34 hours after the trigger) and obtained 128 minutes of exposure in the r and z filters. A second comparison epoch was observed from 2026-03-24 06:16:18 to 09:07:59 UTC (from 60.07 to 62.93 hours after the trigger) again in r and z with 128 min of exposure. The data were reduced and coadded with the ASU pipeline, and analyzed with STDWeb/STDPipe (Karpov 2025). 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 comparison and subtraction of the two epochs, we do not detect any credible new source at any of the FXT source positions (Zou et al., GCN Circ. 44086) down to the following 3-sigma limit: r > 24.7 z > 23.6 These upper limits supersede the ones reported by de Ugarte Postigo et al. (GCN Circ. 44078). 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/44102. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42222] EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44101 SUBJECT: EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7 DATE: 26/03/24 10:20:29 GMT FROM: I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, A. J. Castro-Tirado, E. J. Fernandez-Garcia, M.D. Caballero-Garcia, S. Guziy, G. Garcia-Segura, R. Sanchez-Ramirez (IAA-CSIC), Y.-D. Hu (INAF-OAB), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), L. Hernandez-Garcia (Univ. de Valparaiso), M. Gritsevich (Univ. of Helsinki), S. Jeong (ADD, Daejeon), D. Hiriart (IA-UNAM, Ensenada), W. H. Lee (UNAM, Mexico DF), D.-R. Xiong (Yunnan Observatories of CAS), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of trigger 01709259112 by EP-WXT (Tang et al. GCN 44099), both the 0.6m robotic telescopes BOOTES-5/JGU robotic telescope at San Pedro Martir Observatory (Mexico) and BOOTES-7 at San Pedro de Atacama (Chile) responded to the alert on March 24, 5:17 UT (i.e. 1 min after notification and 26 min after the trigger). Within the reported EP-FXT error circle we find the star SCOCENSUS 132-087992 decreasing 2.3, 1.9 and 1.6 mag in g, r and i filters during a 3.5 hours time interval, confirming EP-WXT trigger 01709259112 as due to a stellar flare. We thank the staff at San Pedro de Atacama Celestial Observations and San Pedro Martir Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44101. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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