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

[vsnet-grb-info 42260] The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44139 SUBJECT: The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart DATE: 26/03/29 11:11:13 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li, Runduo Liang (NAOC), Iair Arcav, Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of EP-WXT trigger 01709259209 with a Las Cumbres 1m telescope at Siding Spring Observatory, Australia, 6 mins after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical w-band. We find an uncataloged source at RA=181.3124, Dec=4.3516 within the EP-WXT error circle and measure the following preliminary photometry calibrated to the r band: Epoch 1: MJD 61128.446 Mag 18.7 Epoch 2: MJD 61128.450 Mag 17.1 The presented magnitudes are calibrated using Pan-STARRS sources in the field and are not corrected for Galactic extinction. We identify a faint source at this position in the Legacy Survey data, with r=24.08 mag. Additional follow-up observations are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/44139. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42259] GRID detection of GRB 260326A
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44138 SUBJECT: GRID detection of GRB 260326A DATE: 26/03/29 08:48:36 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Longhao Li, Xiangyi Wang, Chenyu Wang, Zirui Yang report on behalf of the GRID Collaboration: GRID-11B reports the detection of the long-duration GRB 260326A, which was also detected by Fermi-GBM (Fermi GBM team, GCN 44115; Pathak & Bala, GCN 44118). The event was triggered with GRID-11B on 2026-03-26 at 01:18:28 UTC. The measured burst duration (T90) in the 30-2000 keV range is approximately 13.3 +/- 0.6 seconds. 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/GRB260326A/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/44138. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42258] GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
by GCN Circulars 28 Mar '26

28 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44137 SUBJECT: GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features DATE: 26/03/28 14:25:31 GMT FROM: Brendan O'Connor at Carnegie Mellon University <boconno2(a)andrew.cmu.edu> B. O'Connor (CMU), S. Toshikage (Tohoku U.), M. Tanaka (Tohoku U.), X. J. Hall (CMU), D. Gruen (LMU), A. Palmese (CMU) report on behalf of a larger collaboration: We observed the optical counterpart (O’Neill et al. 2026, TNS Discovery Report 294132; Hinds et al., AstroNote 2026-65) of GRB 260310A (Hamburg & Meegan, GCN 43975; Salunke et al., GCN 43958) with GMOS mounted on Gemini-North starting on 2026-03-27 at 14:56:28 UT, corresponding to 17.4 d after the trigger. We obtained a spectral sequence of 2x1060 s exposures using the B480 grating. The observed spectrum has undergone a significant change compared to earlier epochs, and now displays the clear onset of supernova features. We confirm the report of de Ugarte Postigo et al. (GCN 44124) and the association of GRB 260310A to a massive star progenitor. We acknowledge the excellent support from the staff of the Gemini-North telescope, including Siyi Xu, Atsuko Nitta, Teo Mocnik, Jen Andrews, Sunny Stewart, and Denise Hung. View this GCN Circular online at https://gcn.nasa.gov/circulars/44137. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42257] EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
by GCN Circulars 28 Mar '26

28 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44136 SUBJECT: EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations DATE: 26/03/28 07:22:27 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z. H. Yang(IHEP), C. Y. Dai (NJU), Q. C. Zhao(IHEP), W. F. Wen(SZTU) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260327a was detected by the Wide-field X-ray Telescople (WXT) on board the Einstein Probe (EP) mission (Dai et al, GCN 44126). No reliable optical counterpart has been identified, and only upper limits have been reported (GCNs 44126, 44127, 44129, 44131, 44132, and 44135). The refined analysis of the WXT data shows that the event started at T0=2026-03-27 05:54:41 (UTC), and lasted for approximately 100 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 7.4×10^20 cm^-2, and a photon index of 1.2 (-0.4/+0.4). The derived average unabsorbed 0.5-4 keV flux is 1.9 (-0.4/+0.5) × 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP autonomously observed this source a few minutes after the on board trigger. The FXT observation started at 2026-03-27 05:56:22 (UTC, T0+109 s). The effective exposure time of the observation is around 2 ks. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 215.3694, DEC = 42.1379 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a fixed Galactic hydrogen column density of 7.4×10^20 cm^-2, and a photon index of 3.4 (-0.3/+0.3). The derived average unabsorbed 0.5-10 keV flux is 7.3 (-1.3/+1.3) × 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT follow-up observations have been arranged. 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/44136. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42256] EP260327a: SVOM/VT optical upper limits
by GCN Circulars 28 Mar '26

28 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44135 SUBJECT: EP260327a: SVOM/VT optical upper limits DATE: 26/03/28 02:55:40 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, L. P. Xin, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed a ToO observation of the field of EP260327a detected by Einstein Probe (Dai et al., GCN 44126). The observation started at 2026-03-27T06:41:45 UTC, i.e., about 47 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued optical source was detected at the FXT source position (Dai et al., GCN Circ. 44126) in our stacked images, compared to the Legacy Survey. The 3-sigma upper limits are: Mid_time Band Exposure time Magnitude (AB) 2.80 h VT_R 79*50 sec > 23.7 mag 2.80 h VT_B 66*50 sec > 23.5 mag The magnitudes are in the AB system and are not corrected for Galactic extinction. Our non-detection is consistent with the observations from MASTER (Lipunov et al., GCN 44127), Gemini-North (van Hoof et al., GCN 44129), COLIBRÍ (Guelfand et al., GCN 44131) and WINTER (Schneider et al., GCN 44132). 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/44135. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42255] SMA Detection of GRB 260310A / AT 2026fgk
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44134 SUBJECT: SMA Detection of GRB 260310A / AT 2026fgk DATE: 26/03/27 23:09:57 GMT FROM: Anna Y Q Ho at Cornell University <ayh24(a)cornell.edu> Anna Ho (Cornell), Garrett Keating (CfA), Kate Alexander (University of Arizona), Tanmoy Laskar (University of Utah), Raffaella Margutti (UC Berkeley) report on behalf of the POETS team: On UT 2026 March 26 the Submillimeter Array (SMA) observed the position of GRB 260310A / AT2026fgk (GCN 43951, 43958, 43974), a nearby (z=0.153; GCN 43977) gamma-ray burst with bright radio emission at cm (GCN 44005, 44045) and mm (GCN 44057) wavelengths. Observations were obtained as part of the SMA Large Program, POETS (Pursuit of Extragalactic Transients with the SMA; PI Berger). Using the COMPASS pipeline we measure a preliminary flux density of 5.67 +/- 0.23 mJy at 230 GHz. Further observations are planned. We thank the SMA staff for rapidly approving and scheduling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44134. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42254] GRB 260307B: ATCA Radio Upper Limits
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44133 SUBJECT: GRB 260307B: ATCA Radio Upper Limits DATE: 26/03/27 18:33:22 GMT FROM: Sarah Chastain at Texas Tech University <sarahichastain(a)gmail.com> S. I. Chastain (TTU), G. E. Anderson (CSIRO), S. Ryder (Macquarie), A. Gulati (USyd), A. J. van der Horst (GWU), J. K. Leung (UofT/HUJI), and L. Rhodes (TSI/McGill) on behalf of the ATCA PanRadio GRB collaboration: We observed the long GRB 260307B detected by SVOM (SVOM Team, GCN 43940) with the Australia Telescope Compact Array (ATCA) 0.9, 4.8, and 11 days post-burst. No radio source was detected within the SVOM MXT localization (SVOM Team, GRB43940). At 8 GHz we find 3-sigma upper limits of 36, 33, and 30 microJy/beam, at 0.9, 4.8, and 11 days post-burst respectively. 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/44133. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42253] EP260327a: WINTER J-band upper limit
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44132 SUBJECT: EP260327a: WINTER J-band upper limit DATE: 26/03/27 17:20:48 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of the EP260327a (Dai et al., GCN Circ. 44126) in the near-infrared with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations started on 2026-03-27 at 06:33:36 UT (38.92 min after the trigger) and consisted of 30 exposures of 120 s in the J-band. 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) and analysed with STDWeb/STDPipe (Karpov 2025). The photometric calibration was performed using nearby stars from the 2MASS catalog. The magnitude 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 FXT source position (Dai et al., GCN Circ. 44126) and derive the following 5-sigma upper limit: J > 19.6 We note that van Hoof et al., (GCN Circ. 44129) and Guelfand et al., (GCN Circ. 44131) report deep, early-time optical non-detections. 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/44132. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42252] EP260327a: COLIBRÍ optical upper limits
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44131 SUBJECT: EP260327a: COLIBRÍ optical upper limits DATE: 26/03/27 17:16:15 GMT FROM: Marion G <marion.guelfand(a)gmail.com> Marion Guelfand (CPPM), Enrique Moreno Méndez (UNAM), Jean-Grégoire Ducoin (CPPM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Benjamin Schneider (LAM), 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), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the X-ray transient EP260327a (Dai et al., GCN Circ. 44126) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-27 06:03:18 to 08:10:24 UTC (from 8.6 to 135 minutes after the trigger) and obtained 5760 seconds of simultaneous exposure in the r/z filters. The data were reduced and coadded with the COLIBRÍ ASU pipeline and the COLIBRÍ pipeline and analysed 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 stacked image, and after subtracting template images from the Subaru template images from Hyper Suprime-Cam Strategic Program (Aihara et al. 2021, doi:10.1093/pasj/psab122), we do not detect any new source at the FXT refined position (Dai et al., GCN Circ. 44126) down to the following 5-sigma limits: r > 24.4, z > 23.3. We do not find any optical transient at the position of the Gemini candidate (Rob Eyles-Ferris et al GCN Circ. 44129), although our observations started approximately three hours earlier. 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/44131. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42251] GRB 260327A: AstroSat CZTI detection of a long burst
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44130 SUBJECT: GRB 260327A: AstroSat CZTI detection of a long burst DATE: 26/03/27 16:41:15 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), S. Salunke (IUCAA), Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (Caltech/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 260327A which was also detected by Konus-Wind (IPN Notices). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve shows two emission episodes: a fainter episode preceding a brighter, longer episode by ~50 s. The brighter episode peaks at 2026-03-27 02:28:49.45 UTC. The measured peak count rate associated with the burst is 526 (+68, -68) counts/s above the background in the combined data of all quadrants, with a total of 7557 (+1305, -1387) counts. The local mean background count rate was 1236 (+5, -5) counts/s. We measure a T90 of 88 (+3, -4) s from the cumulative Veto light curve for both episodes. The source was also faintly detected in the 20-200 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/44130. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0