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

[vsnet-grb-info 42359] GRB 260404A: Fermi GBM Final Localization
by GCN Circulars 08 Apr '26

08 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44238 SUBJECT: GRB 260404A: Fermi GBM Final Localization DATE: 26/04/08 19:07:24 GMT FROM: atrigg2(a)lsu.edu The Fermi GBM team reports the detection of a likely SHORT GRB "At 23:57:08.96 UT on 04 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260404A (trigger 797039833/260404998). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 165.79, Dec = -48.56 (J2000 degrees, equivalent to J2000 11h 03m, -48d 33'), with a statistical uncertainty of 18.12 degrees. The angle from the Fermi LAT boresight is 113 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260404998/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260404998/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260404998/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44238. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42358] GRB 260407A: Glowbug gamma-ray detection
by GCN Circulars 08 Apr '26

08 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44237 SUBJECT: GRB 260407A: Glowbug gamma-ray detection DATE: 26/04/08 14:32:22 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260407A, which was detected by Fermi/GBM (GCN 44226). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-04-07 09:11:06.112 with a duration of 4.1 s and a total significance of about 9.6 sigma. The light curve comprises a single peak. Additional lower-level emission up to ~T0+10s, as well as earlier emission beginning ~T0-2s, may be present in the Glowbug light curve at low significance. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44237. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42357] GRB 260402A: SVOM/ECLAIRs refined analysis
by GCN Circulars 08 Apr '26

08 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44236 SUBJECT: GRB 260402A: SVOM/ECLAIRs refined analysis DATE: 26/04/08 13:04:28 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O.Godet (IRAP), W.-J. Xie (NAOC), W. Tan, R. Li (IHEP), 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 260402A(SVOM burst-id sb26040203– GCN 44181, trigger time T0 = 2026-04-02T10:30:17 UTC), which was also detected by EP/WXT (GCN 44186). The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = (15.2 -3.9/+3.1) s in the 4-120 keV energy band. However, some emission is seen for 41 s from T0 up to T0 + 41 s in the 4-20 keV energy band through imaging. The time-averaged spectrum from T0 to T0+41s in the energy range 5-120 keV is best fitted by a powerlaw model with a photon index of -2.18 +0.09/-0.10. With this model, the 4-120 keV fluence is (5.40 +0.33/-0.57)e-7 erg/cm^2 and the 4-120 keV photon flux is 0.67 +0.03/-0.04 ph/cm^2/s. This GRB shows some spectral evolution. The spectrum from T0 to T0 + 1 s in the 5-120 keV energy range is best fitted by a power-law model with a photon index of -1.37 +/-0.12. With this model, the 4-120 keV flux is (8.9 +0.6/-1.7)e-8 erg/cm²/s. The spectrum from T0 + 1 s to T0 + 5 s in the 5-120 keV energy range is best fitted by a broken power-law model with the second photon index fixed at -3, which gives a first photon index of -0.85 +0.23/-0.20 and a break energy of 17.3 +2.0/-1.6 keV. With this model, the 4-120 keV flux is (4.6 +0.1/-1.1)e-8 erg/cm²/s. The spectrum from T0 + 5 s to T0 + 10 s in the 5-120 keV energy range is best fitted by a broken power-law model with the first photon index fixed at -0.85 and the second one fixed at -3, which gives a break energy of 8.6 +1.2/-0.8 keV. With this model, the 4-120 keV flux is (2.3 +0.1/-0.2)e-8 erg/cm²/s. The spectrum from T0 + 10 s to T0 + 41 s in the 5-50 keV energy range is best fitted by a power-law model with a photon index of -2.9 +0.3/-0.4. With this model, the 4-120 keV flux is (4.8 +0.3/-2.0)e-9 erg/cm²/s. All the quoted errors are at the 68% confidence level. 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) (mbrunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44236. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42356] GRB 260310A: Continued VLA Multi-frequency Radio Observations
by GCN Circulars 08 Apr '26

08 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44235 SUBJECT: GRB 260310A: Continued VLA Multi-frequency Radio Observations DATE: 26/04/08 02:27:55 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), D. A. Perley (LJMU), and T. Laskar (Utah) report on behalf of a larger collaboration: The Karl G. Jansky Very Large Array observed the location of the afterglow (Hinds et al., TNS AstroNote 2026-65; Konno et al., GCN 43974) associated with GRB 260310A (Fermi GBM Team, GCN 43951; Hamburg & Meegan, GCN 43975) using all available receivers from L-band to Q-band, providing nearly continuous spectral coverage from 1 to 50 GHz, as a part of our multi-frequency public campaign (Perley et al., GCN 44160). Observations were carried out on UT 2026-04-04 between 08:42 and 12:19 UT, approximately 25.2 days after the GRB. Preliminary flux densities are: | freq(GHz) | flux(mJy) | |-----------|----------------| | 1.5 | 1.74 +/- 0.06 | | 3 | 5.00 +/- 0.04 | | 6 | 8.39 +/- 0.05 | | 10 | 8.93 +/- 0.12 | | 15 | 8.16 +/- 0.22 | | 22 | 7.34 +/- 0.23 | | 33 | 6.14 +/- 0.19 | | 45 | 5.25 +/- 0.19 | Compared to previous radio observations (Rhodes et al., GCN 44005; Giarratana et al., GCN 44045; Ho et al., GCN 44057; Ho et al., GCN 44134, Perley et al., GCN 44160), the afterglow is brightening at lower frequencies (< 10 GHz) and fading at higher frequencies (> 10 GHz). We thank the NRAO staff for scheduling and executing these observations. Further observations are planned. View this GCN Circular online at https://gcn.nasa.gov/circulars/44235. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42355] GRB 260310A / AT2026fgk: X-ray rebrightening
by GCN Circulars 07 Apr '26

07 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44234 SUBJECT: GRB 260310A / AT2026fgk: X-ray rebrightening DATE: 26/04/07 17:22:52 GMT FROM: Rahul Jayaraman at Cornell University <rj438(a)cornell.edu> Rahul Jayaraman (Cornell), K-Ryan Hinds (Caltech), Gaurav Waratkar (Caltech), S. Y. Fu (HUST), R. D. Liang, M. J. Liu, Z. X. Ling, Hui Sun, Weimin Yuan (NAO, CAS), Anna Y. Q. Ho (Cornell), Genevieve Schroeder (Cornell) report: The Follow-up X-ray Telescope (FXT) on board the Einstein Probe has continued to monitor the X-ray afterglow of GRB 260310A (Fermi GBM team, GCN 43951; Arya et al., GCN 43958; Jayaraman et al., GCN 43994), associated with the optical transient AT2026fgk (Konno et al., GCN 43974; Hinds et al., AstroNote 2026-65), with 10 epochs of observations since the GRB. After the detection of a clear break (near-simultaneous steepening in both the X-ray and optical; Jayaraman et al., GCN 44095; Perley et al., GCN 44096), we observed two further epochs that were consistent with the steeper slope of -1.6 reported in GCN 44095. However, the most recent three epochs (which span 3 days) show a clear rebrightening, with a power-law index of α = 2.9 ± 0.5, where f ~ t^α. Further follow-up with FXT is planned. Launched on January 9, 2024, the Einstein Probe 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). EP is supported by the Strategic Priority Program on Space Sciénce of the Chinese Academy of Sciences, in collaboration with the European Space Agency, the Max-Planck-Institute for Extraterrestrial Physics (Germany), and the Centre National d'études Spatiales (France). View this GCN Circular online at https://gcn.nasa.gov/circulars/44234. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42354] EP260402a / GRB 260402A: Mephisto optical upper limits
by GCN Circulars 07 Apr '26

07 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44233 SUBJECT: EP260402a / GRB 260402A: Mephisto optical upper limits DATE: 26/04/07 15:20:03 GMT FROM: Chenxu Liu at Mephisto Team <cxliu(a)ynu.edu.cn> Chenxi Shang, Chenxu Liu, Guowang Du (SWIFAR, YNU), Jinghang Xue (NJU), Yuhui Zhang, Jialei Zheng, Tao Wang, Brajesh Kumar, Xueling Du, Xufeng Zhu, Yu Pan, Xingzhu Zou, Xinlei Chen, Yuan Fang, Jinghua Zhang (SWIFAR, YNU), Chao Wu (NAOC), Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: The 1.6-m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory, was triggered at 2026-04-02 19:52:10 UT (~9.4 hours after the Einstein Probe/WXT trigger; Zhao et al., GCN 44186) to observe the field of EP260402a. A set of simultaneous multi-band (u, g, v, r, i, z) images were collected with individual exposure times of 45 s per frame. Multiple exposures were obtained in each band and later stacked for analysis. The refined EP/FXT position (Zhao et al., GCN 44201) is fully covered by our field of view. Due to relatively poor seeing conditions during the observations (FWHM ~2.5–4.0 arcsec), the image quality is degraded compared to nominal performance, resulting in shallower limiting magnitudes. In our stacked images, no uncatalogued optical source is detected at the FXT position or within its error circle (radius ~10–20 arcsec). The corresponding 5-sigma limiting magnitudes (AB system, not corrected for Galactic extinction) are listed below: ---------------------------------------------------------------------------------------------- Start Time (UT) | Band | Exposure (s) | Mag / Limiting Mag ---------------------------------------------------------------------------------------------- 2026-04-02T19:52:10 | u | 45.0*2 | >19.77 2026-04-02T19:54:55 | v | 45.0*2 | >18.81 2026-04-02T19:52:23 | g | 45.0*2 | >20.21 2026-04-02T19:55:08 | r | 45.0*2 | >20.33 2026-04-02T19:52:13 | i | 45.0*2 | >20.23 2026-04-02T19:54:58 | z | 45.0*2 | >19.48 ---------------------------------------------------------------------------------------------- Our non-detection is consistent with previous optical and near-infrared upper limits reported by SVOM/COLIBRÍ (Antier et al., GCN 44183), MASTER (Carrasco et al., GCN 44184), Kilonova-Catcher (Freeberg et al., GCN 44185), SVOM/C-GFT (Wu et al., GCN 44189), SVOM/VT (Li et al., GCN 44190), WINTER (Schneider et al., GCN 44192), and Jinshan (He et al., GCN 44199). Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025 and presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. We note that the current data-processing pipeline is still at a preliminary stage, with flux calibration precision of about 2% in the u and v bands, about 1% in the g and r bands, and better than 1% in the i and z bands. View this GCN Circular online at https://gcn.nasa.gov/circulars/44233. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42353] EP-WXT01709259586: Xinglong optical upper limit
by GCN Circulars 07 Apr '26

07 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44232 SUBJECT: EP-WXT01709259586: Xinglong optical upper limit DATE: 26/04/07 15:12:09 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Min-He (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP-WXT01709258519, we observed the field of EP-WXT01709259586 (Wu et al. GCN 44213) using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s clear-band frames with a median time of 2026-04-07T12:58:22, 3 days after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (WXT01709259586), down to 3-sigma limiting magnitudes of 22.31 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/44232. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42352] EP260403a: Mephisto optical upper limits
by GCN Circulars 07 Apr '26

07 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44231 SUBJECT: EP260403a: Mephisto optical upper limits DATE: 26/04/07 15:11:25 GMT FROM: Chenxu Liu at Mephisto Team <cxliu(a)ynu.edu.cn> Chenxi Shang, Chenxu Liu, Guowang Du (SWIFAR, YNU), Jinghang Xue (NJU), Yuhui Zhang, Jialei Zheng, Tao Wang, Brajesh Kumar, Xueling Du, Xufeng Zhu, Yu Pan, Xingzhu Zou, Xinlei Chen, Yuan Fang, Jinghua Zhang (SWIFAR, YNU), Chao Wu (NAOC), Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: The 1.6-m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory, was triggered at 2026-04-03 17:53:31 UT (~7.4 hours after the Einstein Probe/WXT trigger; Guo et al., GCN 44204) to observe the field of EP260403a. A set of simultaneous multi-band (u, v, i, z) images were collected with individual exposure times of 45 s per frame. The observations consist of multiple exposures in each band, which were later stacked for analysis. In the stacked images, we did not detect the optical counterpart reported by Antier et al. (GCN 44206), Pérez-Fournon et al. (GCN 44207) and Quirola-Vasquez (GCN 44207). Our non-detection is consistent with the continued fading of the optical source at later epochs. The estimated 5-sigma limiting magnitudes (AB system, not corrected for Galactic extinction) are listed below: ---------------------------------------------------------------- Start_Time(UT) | Band | Exp(s) | LimMag (AB) ---------------------------------------------------------------- 2026-04-03T17:53:31 | u | 45.0*2 | >19.62 2026-04-03T17:55:57 | v | 45.0*2 | >18.79 2026-04-03T17:53:33 | i | 45.0*2 | >19.72 2026-04-03T17:56:00 | z | 45.0*2 | >19.16 ---------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025 and presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. We note that the current data-processing pipeline is still at a preliminary stage, with flux calibration precision of about 2% in the u and v bands, about 1% in the g and r bands, and better than 1% in the i and z bands. View this GCN Circular online at https://gcn.nasa.gov/circulars/44231. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42351] EP260402a/GRB 260402A: Xinglong optical upper limit
by GCN Circulars 07 Apr '26

07 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44230 SUBJECT: EP260402a/GRB 260402A: Xinglong optical upper limit DATE: 26/04/07 15:05:38 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Min-He (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Yuguang-Sun (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP260402a (Zhao et al., GCN 44186), we observed the field of EP260402a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s clear-band frames by using 2.16-m with a median time of 2026-04-07T12:58:22, 5 days after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 10 arcsec EP/FXT error circle (Zhao et al., GCN 44186), down to 3-sigma limiting magnitudes of Clear-band ~22.13 mag for for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/44230. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42350] EP260321a: Upper limits from VLA radio observations
by GCN Circulars 07 Apr '26

07 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44229 SUBJECT: EP260321a: Upper limits from VLA radio observations DATE: 26/04/07 14:50:36 GMT FROM: James Leung at U. Toronto / HUJI <jamesk.leung(a)utoronto.ca> J. K. Leung (U. Toronto/HUJI), L. Izzo (INAF-OACN), F. de Colle (UNAM), and M. R. Drout (U. Toronto) report on behalf of a larger collaboration: We report radio observations of EP260321a (Huang et al., GCN 44068) conducted on the Karl G. Jansky Very Large Array (VLA). The observations were centred at the position 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, Gao et al., GCN 44110, He et al., GCN 44117, Zhang et al., GCN44171), identified now as the broad-lined type-Ic supernova SN 2026gzf (Corcoran et al., GCN 44105, Rastinejad et al., GCN 44107). The radio observations were taken from UT05:12-07:42 on 2026-03-27 (~5.7 days post-trigger) at the central observing frequencies of 6, 10, 15 and 22 GHz. In our preliminary analysis, we detect no radio source at the position of the putative optical counterpart to EP260321a, giving a 3-sigma non-detection limit of <0.03 mJy/beam at each observing frequency band. We thank the VLA and NRAO staff for quickly scheduling and executing these observations. Further observations are planned. The National Radio Astronomy Observatory and Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc. View this GCN Circular online at https://gcn.nasa.gov/circulars/44229. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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