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

[vsnet-grb-info 42265] EP260329b: LCO optical observations of the counterpart
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44144 SUBJECT: EP260329b: LCO optical observations of the counterpart DATE: 26/03/29 13:42:38 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), A. van Hoof (Radboud), G. Corcoran (UCD), J. Chácon (PUC), A. Martin-Carrillo (UCD), J. Quirola-Vasquez (Radboud), A. J. Levan (Radboud), F. E. Bauer (SSI and UTA) and P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260329b (Song et al., GCN 44142) with LCO 1m telescopes located at the Siding Spring Observatory (Australia) equipped with the SINISTRO instrument. We obtained 6 x 300 exposures in each of the r and z filters, starting from 2026-03-29 12:03:17 UT (t_mid = 1.74 hr and 1.78 hr post trigger respectively). We clearly detect the optical counterpart reported by Li et al. (GCN 44139) and Zhu et al. (GCN 44140) in our stacked images and measure the following AB magnitudes calibrated to Pan-STARRS and not corrected for Galactic extinction: r = 19.84 +/- 0.05 z = 19.38 +/- 0.05 Our measurements are >1 magnitude fainter than those reported by Li et al. (GCN 44139) and Zhu et al. (GCN 44140) indicating the counterpart is fading rapidly. View this GCN Circular online at https://gcn.nasa.gov/circulars/44144. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42264] GRB 260326A: Insight-HXMT/HE detection
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44143 SUBJECT: GRB 260326A: Insight-HXMT/HE detection DATE: 26/03/29 12:55:38 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Chao Zheng, Cheng-Kui Li and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team: At 2026-03-26T01:18:33.250 (T0), Insight-HXMT/HE detected the burst GRB 260326A, which is also detected by Fermi/GBM (Fermi GBM team, GCN #44115). The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 15 +1/-0.5 s. The 1s peak rate, measured from T0+0.75 s, is 6592 cnts/sec. Insight-HXMT/HE detected a total of 39437 counts from this burst. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260326A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/ View this GCN Circular online at https://gcn.nasa.gov/circulars/44143. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42263] EP260329b: Einstein Probe detection of an X-ray transient
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44142 SUBJECT: EP260329b: Einstein Probe detection of an X-ray transient DATE: 26/03/29 12:07:29 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> F.-F Song (YNAO, CAS), Guojiong Yang, Wei Chen, Yuan Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260329b. The transient triggered EP-WXT (ID: 01709259209) at 2026-03-29T10:36:00 (UTC). The WXT position of the source is R.A. = 181.309 deg, DEC = 4.362 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 181.3122 deg, DEC = 4.3526 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. 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/44142. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42262] EP260329a: Einstein Probe detection of an X-ray transient
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44141 SUBJECT: EP260329a: Einstein Probe detection of an X-ray transient DATE: 26/03/29 11:35:22 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Guojiong Yang (NAO, CAS), F.-F Song(YNAO, CAS), Wei Chen, Yuan Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260329a. The transient triggered EP-WXT (ID: 01709259198) at 2026-03-29T03:30:40 (UTC). The WXT position of the source is R.A. = 5.459 deg, DEC = 82.513 deg (J2000) with an uncertainty of 3.2 arcmin in radius (90% C.L. statistical and systematic). The WXT 0.5-4 keV spectrum can be described by an absorbed power law. Since the hydrogen column density is not well constrained by the current data, it was fixed at the Galactic value 0.1 x 10^22 cm^-2. The best-fit photon index is 2.23 (-0.69/+2.26). The derived 0.5-4 keV flux is 1.43 (-0.33/+0.40) x 10^-10 erg cm^-2 s^-1. A follow-up observation with the Follow-up X-ray Telescope (FXT) is scheduled. Further information will be updated when the telemetry data is received. 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/44141. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42261] EP-WXT trigger 01709259209: TRT optical counterpart detection
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44140 SUBJECT: EP-WXT trigger 01709259209: TRT optical counterpart detection DATE: 26/03/29 11:32:38 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z.P. Zhu (NAOC), S. Tinyanont, K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), J. An, X. Liu, S.Q. Jiang, L.B. He, N.C. Sun, W.X. Li, D. Xu (NAOC), S.Y. Fu (HUST) report on behalf of a large collaboration: We observed the field of EP260329a detected by the Einstein Probe (EP) (Trigger ID: 01709259209 ), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Sierra Remote Observatories in California. We obtained several exposure frames in the R filter. The optical counterpart located at: R.A. (J2000) = 12:05:14.95 () Dec.( J2000) = +4:21:05.8 with an uncertainty of ~ 0.8 arcsec. The uncatalogued source is clearly detected in the stacked image with the measured brightness of R = 18.4 +/- 0.1 at a mid-time of 10:47:20 UTC on 2026-03-29., consistant with the optical candidate reported by LCO (Li et al., GCN 44139), calibrated using nearby stars from the Pan-STARRS catalog and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44140. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[vsnet-grb-info 42250] EP260327a: Gemini-North optical upper limits
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44129 SUBJECT: EP260327a: Gemini-North optical upper limits DATE: 26/03/27 13:44:41 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> A. van Hoof (Radboud), G. Corcoran (UCD), J. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), A. J. Levan (Radboud), A. Martin-Carrillo (UCD), F. E. Bauer (SSI and UTA), J. Chácon (PUC) and P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260327a (Dai et al., GCN 44126) using the GMOS-N instrument mounted on the Gemini-North telescope. A series of 4x120 s exposures were taken in each of the r’ and z’ filters, starting at 2026-03-27 08:55:05 UT (3.00 hr after the trigger). We performed subtractions on our stacked images using template images from Hyper Suprime-Cam Strategic Program (Aihara et al. 2021, doi:10.1093/pasj/psab122) and compared the stacks and templates manually. Within the EP-FXT localisation (Dai et al., GCN 44126), we do not identify any new sources in our stacked images or subtractions in either band. For our stacked images, we calculate 3-sigma limits of r > 24.72 and z > 24.62 calibrated to nearby stars from PanSTARRS DR1 and not corrected for Galactic extinction. We do note the presence of a residual within the EP-FXT localisation in some of our subtractions at a position RA 215.3703, Dec 42.1406. This position is coincident with a DESI Legacy Survey object with a photometric redshift of 0.481 +/- 0.023. Given the magnitude of this object and depth of our images, we believe this to be a subtraction artefact rather than a real source. We thank the Gemini-North staff, particularly Denise Hung, for their rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44129. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42249] EP260324a: GROWTH-India Telescope optical observation
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44128 SUBJECT: EP260324a: GROWTH-India Telescope optical observation DATE: 26/03/27 10:14:57 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan (IITB), V. Swain (IITB), D. Eappachen (IIA), A.P. Saikia (IITB), S. Patil (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team: We observed the field of EP260324a (Wu et al., ATel 17728), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-03-26 18:34:45 (UTC), i.e., 2.48 days after the trigger, and obtained multiple exposures in the r' and g' filters. We detect the optical counterpart in our difference image at position reported by Anumarlapudi et al., GCN 44120. (ZTF26aapviim / [AT 2026hir](https://www.wis-tns.org/object/2026hir)) | MJD (mid) | Filter | tmid-t0 (days) | Exposure Time (sec) | Magnitude (AB) | | ------------ | ------ | -------------- | ------------------- | -------------- | | 61125.7835185| g' | 2.489 | 1x300 | 18.08 +- 0.09 | | 61125.7871875| r' | 2.493 | 1x300 | 18.34 +- 0.09 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our magnitude for the optical counterpart is consistent with other optical observations (Anumarlapudi et al., GCN 44120). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/44128. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42248] EP260327a: Global MASTER-Net observations report
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44127 SUBJECT: EP260327a: Global MASTER-Net observations report DATE: 26/03/27 08:54:22 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260327a ( EP Team et al., GCN 44126) errorbox 510 sec after trigger time at 2026-03-27 06:03:11 UT, with upper limit up to 20.3 mag. The observations began at zenith distance = 74 deg. The sun altitude is -55.4 deg. The galactic latitude b = 66 deg., longitude l = 77 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3214974 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 561 | 2026-03-27 06:03:11 | MASTER-OAFA | (14h 22m 35.11s , +42d 24m 43.5s) | C | 100 | 19.7 | 696 | 2026-03-27 06:03:11 | MASTER-OAFA | (14h 22m 35.11s , +42d 24m 43.5s) | C | 370 | 20.3 | Coadd 678 | 2026-03-27 06:04:58 | MASTER-OAFA | (14h 22m 35.03s , +42d 24m 50.5s) | C | 120 | 19.8 | 819 | 2026-03-27 06:07:04 | MASTER-OAFA | (14h 22m 34.92s , +42d 24m 58.1s) | C | 150 | 19.8 | 930 | 2026-03-27 06:09:40 | MASTER-OAFA | (14h 22m 34.83s , +42d 25m 03.4s) | C | 60 | 19.5 | 990 | 2026-03-27 06:09:40 | MASTER-OAFA | (14h 22m 34.83s , +42d 25m 03.4s) | C | 180 | 20.2 | Coadd 995 | 2026-03-27 06:10:46 | MASTER-OAFA | (14h 22m 34.77s , +42d 25m 06.2s) | C | 60 | 19.5 | 1060 | 2026-03-27 06:11:51 | MASTER-OAFA | (14h 22m 34.69s , +42d 25m 09.4s) | C | 60 | 19.5 | 1126 | 2026-03-27 06:12:57 | MASTER-OAFA | (14h 22m 34.62s , +42d 25m 12.2s) | C | 60 | 19.5 | 1186 | 2026-03-27 06:12:57 | MASTER-OAFA | (14h 22m 34.62s , +42d 25m 12.2s) | C | 180 | 20.2 | Coadd 1192 | 2026-03-27 06:14:02 | MASTER-OAFA | (14h 22m 34.55s , +42d 25m 15.1s) | C | 60 | 19.5 | 1257 | 2026-03-27 06:15:08 | MASTER-OAFA | (14h 22m 34.47s , +42d 25m 18.0s) | C | 60 | 19.5 | 1323 | 2026-03-27 06:16:14 | MASTER-OAFA | (14h 22m 34.40s , +42d 25m 21.0s) | C | 60 | 19.5 | 1383 | 2026-03-27 06:16:14 | MASTER-OAFA | (14h 22m 34.40s , +42d 25m 21.0s) | C | 180 | 20.0 | Coadd 1389 | 2026-03-27 06:17:20 | MASTER-OAFA | (14h 22m 34.35s , +42d 25m 24.2s) | C | 60 | 19.5 | 1455 | 2026-03-27 06:18:25 | MASTER-OAFA | (14h 22m 34.26s , +42d 25m 27.1s) | C | 60 | 19.5 | 1521 | 2026-03-27 06:19:31 | MASTER-OAFA | (14h 22m 34.17s , +42d 25m 30.0s) | C | 60 | 19.5 | 1581 | 2026-03-27 06:19:31 | MASTER-OAFA | (14h 22m 34.17s , +42d 25m 30.0s) | C | 180 | 20.2 | Coadd 1586 | 2026-03-27 06:20:36 | MASTER-OAFA | (14h 22m 34.09s , +42d 25m 32.9s) | C | 60 | 19.5 | 1651 | 2026-03-27 06:21:42 | MASTER-OAFA | (14h 22m 34.03s , +42d 25m 35.6s) | C | 60 | 19.4 | 1717 | 2026-03-27 06:22:47 | MASTER-OAFA | (14h 22m 33.95s , +42d 25m 38.2s) | C | 60 | 19.5 | 1777 | 2026-03-27 06:22:47 | MASTER-OAFA | (14h 22m 33.95s , +42d 25m 38.2s) | C | 180 | 20.2 | Coadd 1782 | 2026-03-27 06:23:53 | MASTER-OAFA | (14h 22m 33.88s , +42d 25m 41.1s) | C | 60 | 19.5 | 1848 | 2026-03-27 06:24:59 | MASTER-OAFA | (14h 22m 33.80s , +42d 25m 43.6s) | C | 60 | 19.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44127. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42247] EP260327a: Einstein Probe detection of an X-ray transient
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44126 SUBJECT: EP260327a: Einstein Probe detection of an X-ray transient DATE: 26/03/27 08:28:31 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Dai (NJU), Z. H. Yang, Q. C. Zhao (IHEP), W. F. Wen (SZTU), H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260327a. The transient triggered EP-WXT (ID: 01709259176) at 2026-03-27T05:54:41 (UTC). The WXT position of the source is R.A. = 215.371 deg, DEC = 42.130 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 215.3746 deg, DEC = 42.1396 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. 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/44126. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42246] GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44125 SUBJECT: GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova DATE: 26/03/27 08:14:57 GMT FROM: enriquemm(a)astro.unam.mx Marion Guelfand (CPPM), Enrique Moreno Méndez (UNAM), Rosa L. Becerra (UNAM), Antonio de Ugarte Postigo (LAM), Noémie Globus (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (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), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (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 Benjamin Schneider (LAM) and report: We imaged the field of the optical counterpart AT 2026fgk (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) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-27 02:46 to 03:59 UTC (from 16.90 to 16.95 days after the trigger) and obtained 1080 seconds in g, r, and i filters, and 3240 seconds of exposure in the z filter. The data were reduced, coadded and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, it is in the AB system, and it is not corrected for Galactic extinction. We have obtained spectral energy distributions at multiple epochs prior to T+12 days, all of which are well described by a single power law with a spectral index β ≈ −1. However, tonight we observe a significant increase in the g−r and g-i colours and a decrease in the i−z colour indicating the emergence of a thermal component in the spectral energy distribution. This behaviour suggests the onset of a supernova, in agreement with the report by de Ugarte Postigo et al. (GCN Circ. 44124) Further observations and analysis are ongoing. 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/44125. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42245] GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44124 SUBJECT: GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk DATE: 26/03/27 07:39:02 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> A. de Ugarte Postigo (LAM), S. Geier (GTC), L. Izzo (INAF/OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), D. González González (GTC) report: We observed the optical counterpart (AT2026fgk, a.k.a. GOTO26buh, 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) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. A total of 3 spectra of 900 s were secured, starting on 2026-03-27 at 04:25:40 UT (16.98 days after trigger), using grism R1000B. Continuum is visible over the full range 3610-7880 AA. The spectrum has evolved from the power-law continuum reported in de Ugarte Postigo et al. (GCN 43984) and now shows undulations expected in a SN spectrum. Indeed, using SNID to classify the SN we get a best match to a type Ic-BL SN close to maximum light. Our results allow us to conclusively identify the presence of a SN, linking the event to a massive stellar collapse. View this GCN Circular online at https://gcn.nasa.gov/circulars/44124. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42244] The EP-WXT trigger 01709259173 is likely a flaring star
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44123 SUBJECT: The EP-WXT trigger 01709259173 is likely a flaring star DATE: 26/03/27 04:19:32 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 EP-WXT trigger 01709259173 at the time of 2026-03-26T22:01:59, is likely a stellar flare associated with UCAC4 220-087219. The estimated flux of the flare is around 1.92e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4e+31 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/44123. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42243] GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
by GCN Circulars 27 Mar '26

27 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44122 SUBJECT: GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope DATE: 26/03/27 00:39:12 GMT FROM: Kishalay De at Columbia University <kde1(a)mit.edu> R. B. Effress, B. T. Gebreamlak, B. O. Goldman, T. Goodman, J. Kalish, L. Koo, T. Lack, S. A. Lawsky, S. L. Manyan, M. Nebart, K. N. Oqueli-White, A. Ramadorai, N. A. Rodgers, T. A. Sabin, E. Sharman, C. Wu, L. Zheng, R. Zheng, G. Mo, V. Karambelkar, S. Ibrahim, N. Aftab, D. Schiminovich, K. De (Columbia University) We observed the field of GRB 260310A detected by Fermi/GBM (Fermi GB team GCN 43951) and AstroSat CZTI (Salunke et al. GCN 43958), during commissioning operations of the MDM InfraRed Astronomy InGaAs Explorer (MIRAGE) instrument on the MDM 1.3m telescope. Observations were carried out starting at UTC 2026-03-22 08:50, approximately three weeks after the GRB trigger. We obtained a series of dithered exposures in J-band and Hs-band amounting to a total exposure time of 600 s each. Images were aligned, stacked and calibrated to the 2MASS catalog. Performing forced photometry at the position of the optical counterpart (AT2026fgk; Konno et al. GCN 43974, Hinds et al. AstroNote 2026-65; O’Neill et al. TNS Discovery Report 294132), we clearly detect a point source with magnitudes J = 18.40 +/- 0.14 Vega mag Hs = 17.07 +/- 0.16 Vega mag The measurements confirm continued infrared fading of the source (Gao et al. GCN 44110). Note that these measurements did not include image subtraction, though the host contamination is expected to be small. Further observations are planned and analysis is being improved. MIRAGE is a new YJH-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the commissioning observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44122. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42242] IPN triangulation of GRB 260320A
by GCN Circulars 26 Mar '26

26 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44121 SUBJECT: IPN triangulation of GRB 260320A DATE: 26/03/26 23:15:43 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, E. Burns on behalf of the IPN, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP), J. Wei (NAOC), B. Cordier (CEA) on behalf of the SVOM-GRM team, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP) on behalf of the Insight-HXMT team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The long-duration GRB 260320A (NuSTAR-ACS detection: Waratkar et al., GCN 44064; Insight-HXMT/HE detection: Luo et al., GCN 44077; Glowbug detection: Cheung et al., GCN 44093; GRID detection: Li et al., GCN 44109) was detected by NuSTAR (ACS), SVOM (GRM), Insight-HXMT(HE), Konus-Wind, Glowbug, GRID-11B, GRID-10B, and Mars-Odyssey (HEND) at about 70804 s UT (19:40:04). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 316.117 (21h 04m 28s) +6.388 ( +6d 23' 17") Corners: 318.993 (21h 15m 58s) +11.535 (+11d 32' 06") 313.686 (20h 54m 45s) -0.693 (+00d 41' 36") 313.683 (20h 54m 44s) -1.165 (-01d 09' 54") 318.941 (21h 15m 46s) +11.286 (+11d 17' 09") --------------------------------------------- The error box area is 1.3 sq. deg, and its maximum dimension is 13.8 deg (the minimum one is 5.7 arcmin). The Sun distance was 42 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB260320_T70801/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/44121. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42241] EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
by GCN Circulars 26 Mar '26

26 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44120 SUBJECT: EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir DATE: 26/03/26 21:32:04 GMT FROM: akashjanaki98(a)gmail.com Akash Anumarlapudi (UNC CH), Robert Stein (UMd), Tomas Ahumada (NOIRLab), Jillian Rastinejad (UMd), Mansi Kasliwal, Lin Yan (Caltech), D. Y. Li, C.C.Jin, W. Yuan (NAO, CAS) report, on behalf of the ZTF collaboration. Einstein Probe detected a long-lived X-ray transient (EP260324a; Wu et al., ATel #17728) beginning on 2026-03-24T07:04:20 (hereafter 't0') that triggered the Wide-field X-ray Telescope (WXT) multiple times over the following day. Subsequent observations with the Follow-up X-ray Telescope (FXT) proposed a likely association of this transient with the galaxy SDSS J084412.34+820110.9. Here, we report the Zwicky Transient Facility (ZTF; Bellm et al. 2019, Graham et al. 2019) discovery of the optical counterpart, ZTF26aapviim / AT2026hir. AT2026hir was detected by the ZTF survey on 2026-03-26T04:51:22, but forced photometry revealed an earlier detection at 2026-03-24T04:17:28. This first detection is ~3 hours before the first EP detection. The source thus exhibited a moderately fast rise (0.7 mag per day). ZTF light curve of AT2026hir is provided below: | Time (days since t0) | Band | Magnitude | Error | Limiting magnitude | | -------- | -------- | -------- | -------- | ------- | -0.12 | r | 20.14 | 0.15 | 20.52 | 0.07 | g | -- | -- | 17.93 | 1.91 | r | 18.71 | 0.11 | 19.42 | 2.07 | g | 18.38 | 0.08 | 19.49 | We note that AT2026hir was also reported to TNS by ATLAS (Tonry et al. 2018), with detections beginning at 2026-03-26T07:32:13.920 (~2 days after the EP discovery). The transient is 0.3" away from the nucleus (PS1 position) of the host galaxy identified by ATel #17728 (Wu et al.), so it may be nuclear. The host galaxy itself does not display any obvious evidence of being an AGN (W1-W2=0.2, no detection in milliquas (Flesch et al. 2023), and no previous significant ZTF detections). We are pursuing and encouraging follow-up observations to classify the source and validate the X-ray and optical association. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC. View this GCN Circular online at https://gcn.nasa.gov/circulars/44120. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42240] GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
by GCN Circulars 26 Mar '26

26 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44119 SUBJECT: GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope DATE: 26/03/26 13:15:35 GMT FROM: Y.C. Kang at Peking University <yckang(a)stu.pku.edu.cn> Yacheng Kang, Qiang Wang, Ruize Shi, Zexuan Wu, Zhuokai Liu, Yiming Dong, Ziming Wang, Chenxi Bao, Fangzhou Ren, Lijing Shao, Zhuo Li, Subo Dong (PKU) report on behalf of the PKU HiTF (High-energy Transients Follow-up) group: The field of GRB 260310A (Fermi GBM Team, GCN 43951; Salunke et al., GCN 43958) was observed with the PKU 60 cm optical telescope at Xinglong Observatory, NAOC. Observations began on 2026 Mar 18, corresponding to ~8.6 days after the GRB trigger, and were conducted over a total of three epochs. In the stacked R- and I-band images, we clearly detect the optical counterpart AT2026fgk (e.g., Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Malesani et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Gupta et al., GCN 44051; Passaleva et al., GCN 44058; Becerra et al., GCN 44059; Volnova et al., GCN 44060; Busmann et al., GCN 44061; Zheng et al., GCN 44065; Brosio et al., GCN 44067; Pankov et al. GCN 44073; Perley et al. GCN 44096; Passaleva et al. GCN 44104; Serrau et al. GCN 44112; O'Neill et al. 2026, TNS Discovery Report 294132). Preliminary photometry yields R-band magnitudes ranging from ~18.7 to ~18.9 mag and I ~ 18.5 mag, calibrated against nearby Pan-STARRS field stars and reported in the Vega system, without correction for Galactic extinction. The observation log is summarized below (T0 = 2026-03-10T04:57:10.81; GRB 260310A): | Date | Start_UT | T_mid − T0 (days) | Filter | Exposure (s) | Magnitude (Vega) | | :--------: | :---------: | :---------------: | :----: | :----------: | :--------------: | | 2026-03-18 | 20:23:26.87 | 8.66 | R | 4 * 600 | 18.66 +/- 0.03 | | 2026-03-19 | 16:22:31.97 | 9.53 | I | 15 * 600 | 18.45 +/- 0.03 | | 2026-03-19 | 18:57:02.55 | 9.63 | R | 14 * 600 | 18.90 +/- 0.03 | Further analysis and follow-up observations are ongoing. The 60 cm telescope is operated by the Department of Astronomy, School of Physics, Peking University. The PKU HiTF group is dedicated to rapid follow-up observations of high-energy transients. View this GCN Circular online at https://gcn.nasa.gov/circulars/44119. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42239] GRB 260326A: Fermi GBM Detection
by GCN Circulars 26 Mar '26

26 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44118 SUBJECT: GRB 260326A: Fermi GBM Detection DATE: 26/03/26 11:21:12 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> U. Pathak (IITB) and S. Bala (USRA) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 01:18:28.51 UT on 26 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260326A (trigger 796180713/260326054). The Fermi GBM real-time Localization is reported in GCN 44115. The angle from the Fermi LAT boresight is 76 degrees. The GBM light curve consists of two spikes from a single emission episode with a duration (T90) of about 50 s (50-300 keV). The time-averaged spectrum from T0-6.0 to T0+66.0 s is best fit by a Band function with Epeak = 275 +/- 1 keV, alpha = -1.040 +/- 0.004, and beta = -2.00 +/- 0.01. The event fluence (10-1000 keV) in this time interval is (5.37 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+7.0 s in the 10-1000 keV band is 32.6 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44118. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42238] EP260321a: JinShan near-infrared observations
by GCN Circulars 26 Mar '26

26 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44117 SUBJECT: EP260321a: JinShan near-infrared observations DATE: 26/03/26 07:29:39 GMT FROM: liuxing(a)nao.cas.cn Lin. B. He, X. Liu (NAOC), S.Y. Fu, A.D. Zhu, L. Lei, H.Z. Wu, W.H. Lei, Y.C. Zou (HUST), J. An, S.Q. Jiang, Z.P. Zhu, D. Xu (NAOC), J.Z. Liu (XAO), Zhong-Nan Dong, Bin Ma (Sun Yat-sen University) We observed the field of EP260321a (Huang et. al, GCN 44068) using the JinShan 100C telescope, equipped with the INS Mars640 SWIR Camera, located at Altay, Xinjiang, China. Observation started at 2026-03-25 15:12:02 UT, i.e., 4.11 days post-burst, and a series of J-band frames were obtained. 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; Gao et al., GCN 44110) was detected in our stacked J-band frame with magnitude J ~ 17.2 (Vega) at a mid-time 99.3 hrs post-burst. The magnitude was calibrated with the nearby 2MASS catalog and without the Galactic extinction correction. We acknowledge the excellent support from T.Q. Chen for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44117. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42237] GRB 260325A: Fermi GBM Final Localization
by GCN Circulars 26 Mar '26

26 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44116 SUBJECT: GRB 260325A: Fermi GBM Final Localization DATE: 26/03/26 02:06:55 GMT FROM: Suman Bala at USRA <sumanbala2210(a)gmail.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 23:39:37.55 UT on 25 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260325A (trigger 796174782/260325986). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 113.3, Dec = -59.7 (J2000 degrees, equivalent to J2000 7h 33m, -59d 43'), with a statistical uncertainty of 3.2 degrees. The angle from the Fermi LAT boresight is 134 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260325986/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260325986/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260325986/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44116. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42236] GRB 260326A: Fermi GBM Final Real-time Localization
by GCN Circulars 26 Mar '26

26 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44115 SUBJECT: GRB 260326A: Fermi GBM Final Real-time Localization DATE: 26/03/26 01:28:58 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 01:18:28 UT on 26 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260326A (trigger 796180713.505606 / 260326054). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 97.9, Dec = 25.4 (J2000 degrees, equivalent to J2000 06h 31m, 25d 23'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 76.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260326054/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260326054/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260326054/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44115. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42235] EP260321a: Upper limits from a neutrino search with IceCube
by GCN Circulars 25 Mar '26

25 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44114 SUBJECT: EP260321a: Upper limits from a neutrino search with IceCube DATE: 26/03/25 21:30:19 GMT FROM: Sam Hori at IceCube/U Wisc-Madison <sahori(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search for track-like muon neutrino events arriving from the direction of the X-ray transient EP260321a which was first detected by Einstein Probe (https://gcn.nasa.gov/circulars/events/ep260321a#gcn-circular-44068) to investigate possible neutrino emission associated with the shock breakout scenario proposed for this event. The position of the updated localization (https://gcn.nasa.gov/circulars/events/ep260321a#gcn-circular-44075) was searched over a time window covering the time range between [-3 hours, +1 hours] from Einstein Probe detection (2026-03-21 09:23:07 UTC to 2026-03-21 13:23:07 UTC), during which time IceCube was recording good quality data. The chosen time window is motivated by the shock breakout scenario, to account for possible high-energy neutrino emission produced during the shock propagation within the stellar envelope and in the immediate aftermath of the breakout. In this case, we report a p-value of 1.0, consistent with background expectation. We accordingly derive a time-integrated muon-neutrino flux upper limit for this source of E^2 dN/dE = 2.8 x 10^-2 GeV cm^-2 at 90% CL, under the assumption of an E^-2 power law. 90% of events IceCube would detect from a source at this declination with an E^-2 spectrum have energies in the approximate energy range between 1 TeV and 6 PeV. 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/44114. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42234] Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
by GCN Circulars 25 Mar '26

25 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44113 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB DATE: 26/03/25 17:59:12 GMT FROM: Daniel Fernandez at University of Alabama In Huntsville (UAH) <df0062(a)uah.edu> D. Fernandez (UAH) and L. Scotton (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 796145512/260325647 at 15:31:47.56 UT on 25 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/44113. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42233] GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
by GCN Circulars 25 Mar '26

25 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44112 SUBJECT: GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time DATE: 26/03/25 14:03:49 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Serrau, M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 260310 detected by Fermi/GBM (Fermi GBM team, GCN 43951) and AstroSat CZTI (Salunke et al., GCN 43958) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the ODK16 telescope at Observatoire Banon La Tuilerie, France operated by M. Serrau and the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+14.8 days and were taken with sdss-g and sdss-r filters. In our stacked frames, subtracted from the Legacy Survey DR10 template image, we detect the optical counterpart reported by GOTO (O'Neill et al. 2026, TNS Discovery Report 294132) and observed earlier (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978;Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980;de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996;Martin-Carrillo et al., GCN 44000; Moreno Méndez et al., GCN 43980; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Gupta et al., GCN 44051; Becerra et al., GCN 44059; Volnova et al., GCN 44060; Busmann et al., GCN 44061; Zheng et al., GCN 44065; Brosio et al., GCN 44067; Pankov et al. GCN 44073; Perley et al. GCN 44096; Passaleva et al. GCN 44104) We report part of our follow-up results in the table below +------------------+-----------+--------+----------------+-------------+ | Tmid-TGRB (days) | Exp (s) | Filter | Magnitude | Instrument | +==================+===========+========+================+=============+ | 14.83 | 16 x 300s | r (AB) | 19.96 +/- 0.09 | ODK16 | | 15.17 | 17 x 180s | r (AB) | 19.82 +/- 0.12 | TEC160FL | +------------------+-----------+--------+----------------+-------------+ The KNC members will keep monitoring the source in the coming days. All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/44112. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42232] IPN triangulation of GRB 260316B
by GCN Circulars 25 Mar '26

25 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44111 SUBJECT: IPN triangulation of GRB 260316B DATE: 26/03/25 13:33:31 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goyal, A. Arya, M. Tembhurnikar, G. Waratkar, V. Bhalerao, D. Bhattacharya, and S. Vadawale, on behalf of the Astrosat-CZTI team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The long-duration GRB 260316B (Ferm-GBM detection: The Fermi GBM team, GCN 44031; AstroSat-CZTI detection: Harsha et al., GCN 44035; SVOM-GRM detection: Zhang et al., GCN 44039; GECAM-B detection: Zhang et al., GCN 44040; CALET-GBM detection: Tamura et al., GCN 44100) was detected by Fermi (GBM trigger 795373977), Konus-Wind, Astrosat (CZTI), SVOM (GRM), GECAM-B, CALET (GBM), and Mars-Odyssey (HEND) at about 61973 s UT (17:12:53). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 345.026 (23h 00m 06s) -80.127 (-80d 07' 37") Corners: 292.551 (19h 30m 12s) -74.130 (-74d 07' 48") 293.015 (19h 32m 04s) -74.416 (-74d 24' 57") 32.817 (02h 11m 16s) -74.223 (-74d 13' 24") 32.021 (02h 08m 05s) -74.386 (-74d 23' 10") --------------------------------------------- The error box area is 1.7 sq. deg, and its maximum dimension is 24.2 deg (the minimum one is 4.3 arcmin). The Sun distance was 75 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB260316_T61972/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/44111. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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[vsnet-grb-info 42221] GRB 260316B: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44100 SUBJECT: GRB 260316B: CALET Gamma-Ray Burst Monitor detection DATE: 26/03/24 07:55:16 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> T. Tamura (Kanagawa U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The GRB 260316B (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 44031; AstroSat CZTI detection: Harsha et al., GCN Circ. 44035; SVOM/GRM observation: Wang et al., GCN Circ. 44039; GECAM-B observation: Wang et al., GCN Circ. 44040) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 17:12:52.15 UTC on 16 March 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1457716347/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a single pulse that starts at T+0.38 sec, peaks at T+1.25 sec, and ends at T+2.37 sec. The T90 and T50 durations measured by the SGM data are 1.75 +/- 0.18 sec and 0.75 +/- 0.13 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1457716347/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44100. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42220] The EP-WXT trigger 01709259112 is likely a flaring star
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44099 SUBJECT: The EP-WXT trigger 01709259112 is likely a flaring star DATE: 26/03/24 06:03:54 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. H. Tang, C. Y. Wang (THU), A. Li (BNU), Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709259112 at the time of 2026-03-24T04:51:45, is likely a stellar flare associated with Young stellar object SCOCENSUS 132-087992. The estimated flux of the flare is around 1.8×10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 2.8×10^32 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/44099. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42219] Fermi GRB 260323A: Global MASTER-Net observations report
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44098 SUBJECT: Fermi GRB 260323A: Global MASTER-Net observations report DATE: 26/03/24 00:15:25 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260323A ( Fermi GBM team, GCN 44097) errorbox 143 sec after notice time and 173 sec after trigger time at 2026-03-23 23:54:21 UT, with upper limit up to 20.1 mag. Observations started at twilight. The observations began at zenith distance = 43 deg. The sun altitude is -16.3 deg. The galactic latitude b = -27 deg., longitude l = 289 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3206970 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 188 | 2026-03-23 23:54:21 | MASTER-OAFA | (06h 02m 40.77s , -72d 38m 38.2s) | C | 30 | 18.8 | 229 | 2026-03-23 23:54:57 | MASTER-OAFA | (06h 02m 40.97s , -72d 38m 38.5s) | C | 40 | 18.9 | 280 | 2026-03-23 23:55:43 | MASTER-OAFA | (06h 02m 41.22s , -72d 38m 38.9s) | C | 50 | 19.2 | 341 | 2026-03-23 23:56:39 | MASTER-OAFA | (06h 02m 41.55s , -72d 38m 39.0s) | C | 60 | 19.3 | 650 | 2026-03-24 00:01:17 | MASTER-OAFA | (06h 42m 20.00s , -76d 51m 39.3s) | C | 120 | 20.1 | 786 | 2026-03-24 00:03:23 | MASTER-OAFA | (06h 42m 20.80s , -76d 51m 40.5s) | C | 140 | 20.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44098. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42218] GRB 260323A: Fermi GBM Final Real-time Localization
by GCN Circulars 24 Mar '26

24 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44097 SUBJECT: GRB 260323A: Fermi GBM Final Real-time Localization DATE: 26/03/24 00:02:09 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 23:51:27 UT on 23 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260323A (trigger 796002692.989066 / 260323994). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 100.1, Dec = -77.1 (J2000 degrees, equivalent to J2000 06h 40m, -77d 05'), with a statistical uncertainty of 5.5 degrees. The angle from the Fermi LAT boresight is 149.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260323994/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260323994/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260323994/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44097. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42217] GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44096 SUBJECT: GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days DATE: 26/03/23 22:07:59 GMT FROM: Daniel Perley at Liverpool JMU <d.a.perley(a)ljmu.ac.uk> GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days D. A. Perley (LJMU), Y. Wagh (LJMU), R. Jayaraman (Cornell), J. Sollerman (Stockholm), A. Y. Q. Ho (Cornell), K.-R. Hinds (Caltech), and A. Bochenek (LJMU) report: We used the SED Machine Rainbow Camera optical imager mounted on the Palomar 60-inch telescope to obtain observations of AT2026fgk (Hinds et al., TNS AstroNote 2026-65), the optical counterpart (Konno et al., GCN 43974) of the Fermi/GBM gamma-ray burst GRB260310A (Fermi GBM Team, GCN 43951; Hamburg & Meegan, GCN 43975). Observations began on the night of 2026-03-12 at 06:03 UT and have continued every night since in the SDSS g, r, and i filters; u-band imaging was also taken on certain nights. Photometry was performed following image subtraction of template images taken from Pan-STARRS survey imaging. For the first seven days after the GRB, the fading is generally consistent with a power-law evolution with a shallow temporal index of approximately -0.6. Beginning at around 7-8 days, the afterglow begins falling more sharply, with a decay index closer to -1.35. (A break in the X-ray light curve was seen at a similar time; Jayaraman et al., GCN 44095 ). Select photometry (AB, not corrected for extinction) is provided below: | UT date | dt (d) | filter | mag +/- unc | |---------------------|--------|--------|----------------| | 2026-03-12 06:03:41 | 2.047 | r | 18.14 +/- 0.04 | | 2026-03-13 06:33:38 | 3.067 | r | 18.19 +/- 0.03 | | 2026-03-15 06:08:19 | 5.050 | r | 18.59 +/- 0.03 | | 2026-03-18 06:01:43 | 8.045 | r | 18.83 +/- 0.03 | | 2026-03-23 05:20:09 | 13.016 | r | 19.58 +/- 0.04 | The behavior is consistent with other recent reports noting the continuation of the optical decay with no SN-like rebrightening yet (e.g., Volnova et al., GCN 44060; Bussman et al., GCN 44061). Accounting for Galactic extinction and converting to the equivalent host-frame bandpass, the absolute magnitude of the optical transient as of the most recent observation is M_V ~ -19.7. The fact that the light curve is still decaying steeply suggests that any associated supernova is likely to be significantly dimmer than the benchmark SN1998bw, which peaked at a similar magnitude and phase (e.g., Galama et al. 1998, Nature, 395, 670). The color of the afterglow indicates only modest dust extinction in the host galaxy, so the subluminous nature of the SN is likely intrinsic. A fainter SN comparable to SN2006aj is not yet ruled out, but will be tightly constrained by observations during the next 1-2 weeks. Additionally, we note that the optical afterglow is both extremely bright and very luminous at late times. To our knowledge only one[1] previous GRB (GRB030329 at z=0.168) has remained brighter than r=20 mag more than 10 observer-frame days after the event, excluding events dominated by the rebrightening of the SN on this timescale (see e.g., Kann et al. 2023, ApJL, 948, 12). The luminosity is also notable: despite its relatively weak prompt emission (E_iso ~ 10^51 erg: Minaev et al., GCN 44053), the afterglow luminosity of GRB260310A at the current time is at the upper end of the afterglow luminosity distribution at this time post-burst, comparable to many high-luminosity (E_iso ~ 10^54 erg) GRBs such as 080319B, 130427A, and 221009A. We encourage continued monitoring of this exceptional GRB afterglow (and any potential associated SN), which is likely to remain accessible to small- to medium-size optical facilities for many more weeks and possibly months. [1] GRB221009A would have been observed to have a similar apparent magnitude at this time but was heavily obscured by Galactic dust. Based on observations obtained with the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan, and the German Center for Astrophysics (DZA), Germany. Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA. DAP acknowledges the work, legacy, and friendship of D. Alexander Kann, who doubtless would have been tremendously excited by this GRB afterglow. View this GCN Circular online at https://gcn.nasa.gov/circulars/44096. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42216] GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44095 SUBJECT: GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data DATE: 26/03/23 21:59:34 GMT FROM: Rahul Jayaraman at Cornell University <rj438(a)cornell.edu> Rahul Jayaraman (Cornell), Gaurav Waratkar (Caltech), K-Ryan Hinds (Caltech), Yogesh Wagh (LJMU), Daniel Perley (LJMU), Anna Y. Q. Ho (Cornell), S. Y. Fu (HUST), R. D. Liang, M. J. Liu, Z. X. Ling, Hui Sun, Weimin Yuan (NAO, CAS), Genevieve Schroeder (Cornell), Xander J. Hall (CMU), Michael Coughlin (UMN), Aleksandra Bochenek (LJMU), and Jesper Sollerman (Stockholm) report: The Follow-up X-ray Telescope 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), which is associated with the optical transient AT2026fgk (Konno et al., GCN 43974; Hinds et al., AstroNote 2026-65). Observations with duration ~3 ks were taken at intervals of roughly every 2 days after the initial detection of this source in X-rays (Jayaraman et al., GCN 43994). With four further epochs of data since the initial detection, we find evidence for a steepening in the X-ray light curve at around 8 ± 2 days after the burst, with the decay slope steepening from roughly –0.3 to –1.6. The photon index measured by EP remains at roughly 1.5 throughout these observations. This steepening appears contemporaneous with an observed steepening at a similar epoch post-burst in r-band photometric data taken by the SED Machine on the Palomar P60 telescope, which will be reported in a forthcoming Circular. 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/44095. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42215] GRB 260322A: Fermi GBM Final Localization
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44094 SUBJECT: GRB 260322A: Fermi GBM Final Localization DATE: 26/03/23 17:56:30 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> The Fermi GBM team reports the detection of a likely SHORT GRB "At 10:45:40 UT on 22 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260322A (trigger 795869144/260322448). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 301.0, Dec = -61.8 (J2000 degrees, equivalent to J2000 20h 3m, -61d 46'), with a statistical uncertainty of 7.9 degrees. The angle from the Fermi LAT boresight is 59.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260322448/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260322448/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260322448/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44094. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42214] GRB 260320A: Glowbug gamma-ray detection
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44093 SUBJECT: GRB 260320A: Glowbug gamma-ray detection DATE: 26/03/23 17:34:44 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, confirms the detection of GRB 260320A, which was detected by NuSTAR (GCN 44064), SVOM/GRM (sb26032003), Insight-HXMT/HE (GCN 44077), and Konus-Wind (Trig_Time 19:40:01.257). The burst onset is at 2026-03-20 19:40:02, with a peak at ~T0+1.5s, and a burst duration of ~7s. Note that data throughout the detection interval suffered from deadtime in various detectors. 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/44093. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42213] EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44092 SUBJECT: EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344 DATE: 26/03/23 17:12:25 GMT FROM: nrt3(a)le.ac.uk D. Xu (NAOC), G. Corcoran (UCD), J. An (NAOC), L. Izzo (INAF/OACN), N. Habeeb (Leicester), N. R. Tanvir (Leicester), A. J. Levan (Radboud and Warwick), C. C. Thoene (AbAO), S. Schulze (Weizmann), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI), A. Saccardi (CEA/Irfu), A. Martin-Carrillo (UCD), G. Pugliese (API), A. de Ugarte Postigo (LAM), A. L. Thakur (INAF-IAPS) report on behalf of the Stargate collaboration: We observed the variable point source, AT2026gzf, (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) associated with X-ray transient EP260321a (Huang et al., GCN 44068) with the X-shooter spectrograph on the ESO VLT UT3 (Melipal) beginning on 2026-02-23 at 00:38 UT (36.1 hr post-trigger). Our observations consisted of 4x600 s exposures, and span the wavelength range 3000-20600 AA. Bright continuum flux is visible in all three arms of the spectrum. In addition to the blue continuum and narrow emission lines reported for the previous MUSE observation (Tanvir et al., GCN 44082), our X-shooter spectrum shows broad features below 5000 AA, similar to those seen in the early spectra of core-collapse supernovae, and inconsistent with those seen in typical young stellar populations. However, we caution that at this early phase there are limited templates for comparison, combined with some contribution from any underlying cluster light, and a search for matches within GELATO and SNID does not, at this time, yield a firm classification. Furthermore, the detection of narrow absorption features due to Ca II at z = 0.0344 conclusively excludes a Milky Way origin for this transient. We acknowledge excellent support of the ESO observing staff at Paranal, in particular Alonso Luna Ruiz Fernandez, Elyar Sedaghati, Lorena Faundez and Marcela Espinoza. View this GCN Circular online at https://gcn.nasa.gov/circulars/44092. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42212] EP260321a: COLIBRÍ further optical observations and brightening
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44091 SUBJECT: EP260321a: COLIBRÍ further optical observations and brightening DATE: 26/03/23 16:06:10 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Leonardo García García (UNAM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (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), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of EP260321a (Huang et al., GCN Circ. 44068, 44075) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope, following our previous observation (Aguilar-Ruiz et al. GCN Circ. 44076). We observed in two epochs between 2026-03-23 04:40 to 10:04 UTC (between 40.17 and 45.57 hours after the trigger) and obtained imaging in the g, r, i, z and y bands. The data were reduced and coadded with the ASU COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. From our first observation, at a mid epoch T+16.33 h after the EP detection, to the second epoch of last night, at a mid epoch of T+43.61 h, the transient reported by Lee et al. (GCN Circ. 44070), has increased in brightness in r-band by 1.3+/-0.1 mag consistently with the reported evolution of the source (Lee et al. GCN Circ. 44070, Aryan et al. GCN Circ. 44081, Tanvir et al. GCN Circ. 44082, Moran et al. GCN Circ. 44083, Ahumada et al. GCN Circ. 44084, Liu et al. GCN Circ. 44087 and Sankar et al. GCN Circ. 44089). Our latest photometric measurement is r = 18.67 +/- 0.02 mag but we caution that the value is likely affected by the contribution of the underlying galaxy. Further observations are planned. 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/44091. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42211] Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44090 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB DATE: 26/03/23 15:55:17 GMT FROM: Suman Bala at USRA <sumanbala2210(a)gmail.com> S. Bala (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 795918973/260323025 at 00:36:08.73 UT on 23 March 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to particle event." View this GCN Circular online at https://gcn.nasa.gov/circulars/44090. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42210] EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44089 SUBJECT: EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate DATE: 26/03/23 15:36:09 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Sankar.K, A. Aryan, T.-W. Chen, W.-J. Hou, C.-S. Lin (all NCU), S. Yang (HNAS), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), M. Nicholl (QUB), T. Moriya (NAOJ), M. Saillenfest (LTE, Paris Observatory), Y.-N. Lee (NTNU), M.-H. Lee, A. Dutta, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), Y. J. Yang (NYUAD), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz M. Huber, K. Chambers (all IfA, Hawaii) report: We obtained further optical observations of the field of the fast X-ray transient EP260321a (Huang et al., GCN 44068, 44075) using the 1m LOT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86; Aryan et al. 2025, ApJS, 281, 20). The new LOT observations started at UTC 12:42 on March 23rd 2026 (MJD 61122.5295), corresponding to 48.20 hr after the EP-WXT trigger. At the refined EP/FXT position, coincident with the blue variable source first noted by Lee et al. (GCN 44070) and further discussed by Tanvir et al. (GCN 44082), Ahumada et al. (GCN 44084), and Liu et al. (GCN 44087), we detect the source in the g band. We used the AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry for this object: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | Seeing | Airmass LOT | g | 61122.5295 | 48.20 | 300 * 1 | 18.30 +/- 0.03 | 1".02 | 1.14 The presented magnitude is calibrated using field stars from the ATLAS-RefCat2 catalog from MAST (Tonry et al. 2018, ApJ, 867, 105), is reported in the AB system, and is not corrected for the expected Galactic foreground extinction of A_g = 0.08 mag in the direction of the transient (Schlafly & Finkbeiner 2011). Compared with our previous LOT measurement of g = 18.77 +/- 0.04 mag at 23.99 hr post-trigger (Aryan et al., GCN 44081), the source has brightened by approximately 0.47 mag. This is also consistent with, and extends, the re-brightening trend reported by Liu et al. (GCN 44087), indicating that the source is still rising. Our time resolved monitoring of this source during the six hours after the FXT detection with the LOT (Lee et al., GCN 44070, Aryan et al., GCN 44081) indicates a sharp decline of 0.3 mag within the first 2 hours followed by a continued, monotonic rise, now at g = 18.3 at t-t0 = 48.2 hr. With the spectroscopic observation from Tanvir et al. (GCN 44082) indicating that the source may be associated the z = 0.0343, we propose the LOT optical lightcurve could be explained by the shock cooling and a rise from a supernovae associated with the blue point like source visible in the archive images, also proposed by Liu et al. (GCN 44087). At M_g ~ -17.7, this is now at supernova-like luminosities, which would be consistent with Huang et al. (GCN 44075) interpretaiton of the EP260321a as shock breakout signature. The luminosity of the blue progenitor source would be very large for a single star, lying between M_r = -15 to -16. Elevated, high luminosity has been seen in LBV type precursors (e.g. SN1961V, Kochanek et al. 2011, ApJ 737, 76; and other LBV precursors, Smith et al. 2010, AJ 139, 1451), but this case would be extreme. We note that long term Pan-STARRS monitoring shows this source to be variable over 7 years, with flux variations in the w-band difference imaging around 21 < w < 22. Further spectroscopic observations are required to determine if the transient shows high expansion velocities and lines that definitively place it in the z=0.0343 host. View this GCN Circular online at https://gcn.nasa.gov/circulars/44089. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42209] EP260214b: ATCA 6 GHz detection
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44088 SUBJECT: EP260214b: ATCA 6 GHz detection DATE: 26/03/23 15:25:11 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome <aishth(a)outlook.com> G. Gianfagna, G. Bruni, A. L. Thakur, M. Fanelli, L. Piro (INAF-IAPS) report: We re-observed the Fast X-ray Transient EP260214b (J Yang et al., GCN 43744, H Yang et al., GCN 43779) with the Australian Telescope Compact Array (ATCA) radio telescope using the 4-cm receiver. Observations were performed on March 20 2026 (at a mean epoch of ~34 days after the EP trigger and 17 days after our last observation; see Gianfagna et al., GCN 43924) for a total of 5 hours. Data were reduced and imaged with standard CASA procedures. The final 6 GHz image has an RMS of 12 uJy/beam. We detect radio emission at a flux density of ~0.04 mJy at a position consistent with the optical counterpart (He et al.). GCN 43745, Watson et al. GCN 43747, Le Floch et al. GCN 43749, Pérez-Fournon et al. GCN 43750, Russeil et al. 43752,Li et al. GCN 43755, Vijayjumar et al. GCN 43757, Becerra et al. GCN 43758, Yang et al. GCN 43760, Aaryan et al. GCN 43762, Bochenek et al. GCN 43764, Kar et al. GCN 43774, Volnova et al. GCN 43775). Further ATCA observations are planned. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (grid.421683.a), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. View this GCN Circular online at https://gcn.nasa.gov/circulars/44088. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42208] EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44087 SUBJECT: EP260321a: Early TRT rising followed by JinShan decaying and then re-rising DATE: 26/03/23 11:26:51 GMT FROM: liuxing(a)nao.cas.cn X. Liu, D. Xu (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan, K. Noysena (NARIT), J. An, Z.P. Zhu, N.C. Sun, W.X. Li, Z. Fan, S.Q. Jiang, L.B. He (NAOC), S.Y. Fu (HUST), J.Z. Liu (XAO) report on behalf of a large group: Upon the alert of EP260321a detected by Einstein Probe (Huang et al., GCN 44068), we observed the field of EP260321a using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO), and then using the 100B telescope of the JinShan project, located at Altay, Xinjiang, China. The TRT observation started at 12:52:13 UT on 2026-03-21, i.e., 21.9 mins after the EP-WXT trigger. No uncatalogued optical transient is detected within the EP-FXT error cicle (Huang et al., GCN 44068) down to R ~ 20.5 mag. We noticed the brightening of the catalogued blue point-like source (R.A. 09:59:42.880, Dec. 00:25:06.29, J2000), if compared with PanSTARRS and Legacy Survey, in the outskirt of the galaxy, SDSS J095942.88+002506.2, with a redshift z = 0.0343 in the DESI Legacy Survey DR1 spectroscopic catalogue, mentioned by Kinder (Lee et al., GCN 44070) and then spectroscopically confirmed at VLT/MUSE (Tanvir et al., GCN 44082). The point source has R ~ 19.0 (Vega) at a median time of 27.6 mins post-trigger, calibrated with PanSTARRS in which the source has r = 19.85 +/- 0.03 mag (AB). The JinShan 100B telescope observed the field in g- and r- bands in the nights of 2026-03-21 and 2026-03-22. In the first night, the blue source decayed a bit to g ~ 18.9 (AB and hereafter) at 2.3 hrs post-trigger and r ~ 19.3 mag at 2.8 hrs post-trigger. And the g-band brightening, if subtracted using the PanSTARS templates, is more prominent than in the r-band, suggesting the transient itself is also quite blue. Together with the rather deep ZTF pre-EP upper limit (Ahumada et al., GCN 44084), the TRT observation, and the Kinder first observation (Lee et al., GCN 44070), the transient shows a fast rising around the EP trigger time and then starts to decay around the first Kinder observation. The decaying behavior is consistent with the cooling of Shock Break-Out (SBO) of a SN-like event (Huang et al., GCN 44075) and a thermal-like spectrum at VLT/MUSE (Tanvir et al., GCN 44082). In the second night, the blue source re-brightened to g ~ 18.5 at 28.5 hrs post-trigger and r ~ 18.8 mag at 29.0 hrs post-trigger, which are also brighter than the second Kinder observation that is a bit earlier than the second JinShan (Aryan et al. GCN 44081). This indicates that a SN-like main component is emerging and will likely continue to brighten to a peak in the coming days. View this GCN Circular online at https://gcn.nasa.gov/circulars/44087. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42207] GRB 260321A: EP-FXT follow-up observation
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44086 SUBJECT: GRB 260321A: EP-FXT follow-up observation DATE: 26/03/23 03:51:16 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z.-C. Zou, Y. H. Jiang (NJU), J. P. Chen (SYSY), Y. J. Yi (BNU) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260321A (SVOM/sb26032123; Brunet et al., GCN 44071) starting at 2026-03-22T15:23:32 UTC, approximately 21 hours after the SVOM trigger, with a total exposure time of 4565 s. Four uncataloged sources are detected within the ECLAIRs error circle. Preliminary analysis on these sources is automatically conducted, and the details are listed as follows. EPF_J143847.8+314542 RA (J2000): 219.6990 Dec (J2000): 31.7616 Flux: 9.265 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 3.498 x 10^-14 erg/s/cm2 (1 sigma) EPF_J143759.7+314425 RA (J2000): 219.4989 Dec (J2000): 31.7404 Flux: 2.9252 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 1.2651 x 10^-14 erg/s/cm2 (1 sigma) EPF_J143833.9+314628 RA (J2000): 219.6440 Dec (J2000): 31.7719 Flux: 5.9349 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 2.0193 x 10^-14 erg/s/cm2 (1 sigma) EPF_J143845.7+313613 RA (J2000): 219.6902 Dec (J2000): 31.6037 Flux: 8.0698 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 1.9625 x 10^-14 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/44086. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42206] The EP-WXT trigger 01709259045 is likely a flaring star
by GCN Circulars 23 Mar '26

23 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44085 SUBJECT: The EP-WXT trigger 01709259045 is likely a flaring star DATE: 26/03/23 02:46:01 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.L. Hua (PMO, CAS), T. Zhao, W. Chen, Y. Liu (NAOC, CAS) on behalf of the Einstein Probe team The EP-WXT trigger 01709259045 at the time of 2026-03-22T23:47:38, is likely a stellar flare associated with 2MASS J15570856+2749007. The estimated flux of the flare is around 6e-11 erg/s/cm^2 in 0.5-4 keV, corresponding to an X-ray luminosity of around 4.31e+32 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/44085. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42205] EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44084 SUBJECT: EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a DATE: 26/03/22 23:06:20 GMT FROM: Tomas Ahumada <tomas.ahumada(a)noirlab.edu> T. Ahumada (NOIRLab), X. J. Hall (CMU), D. A. Perley (LJMU) on behalf of the Zwicky Transient Facility We report the Zwicky Transient Facility detection of ZTF26aaonmha (AT 2026gzf), the candidate optical counterpart to EP260321a (Huang et al., GCNs 44068, 44075) announced by Lee et al (GCN 44070, see also Aryan et al., GCN 44081, Tanvir et al. GCN 44082). The ZTF detection was observed at 2026-03-22 07:35:25 (~19 hr after the EP-trigger) in the ZTF-g band at a magnitude of 19.7 +/- 0.2 mag. The region was also observed in ZTF-r band at 2026-03-22 07:12:13, but resulted in a non-detection limit of 19.6 mag. The source has no previous activity in the ZTF survey, with the most recent upper limit of g = 20.2 mag on 2026-03-21 08:06:02 (4.5 hr before the X-ray detection). The ZTF non-detection prior to the EP detection, together with the post-EP ZTF trigger, strongly supports the optical association. We additionally note that the source is detected in the Rubin alert stream, although we caution that the alerts show a dipole structure and could be spurious detections. The variability in the Rubin data fluctuates in around r = 23.8 mag, with the most prominent pre-EP detection at r = 21.1 mag, ~25 days before the X-ray flare. The combined Rubin and ZTF lightcurve can be found at https://babamul.caltech.edu/objects/LSST/314003014107006318 We are pursuing and encouraging follow-up observations to classify the source and validate the X-ray and optical association. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC. View this GCN Circular online at https://gcn.nasa.gov/circulars/44084. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42204] EP260321a: GOTO detection of blue variable source
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44083 SUBJECT: EP260321a: GOTO detection of blue variable source DATE: 26/03/22 21:30:52 GMT FROM: Shane Moran at University of Leicester <shane.moran(a)leicester.ac.uk> S. Moran, A. Kumar, G. Ramsay, D. O'Neill, K. Ulaczyk, S. Moran, B. P. Gompertz, R. Starling, M. Wortley, M. Kennedy, K. Ackley, M. Dyer, J. Lyman, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, M. Pursiainen, on behalf of GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) that serendipitously covered the field of EP/WXT detected EP260321a (WXT01709259023; Huang et al., GCNs 44068, 44075). Observations covering the localisation area were taken at 2026-03-22 11:25:46 UT (+22.92h post trigger) utilising GOTO-South. Each observation consisted of 4x45s exposures in the GOTO L-band (400-700 nm). We detect the previously reported variable source (Lee et al. GCN 44070, Tanvir et al. GCN 44082) with L = 19.51 ± 0.1 AB mag. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44083. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42203] EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44082 SUBJECT: EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343 DATE: 26/03/22 19:50:53 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> N. R. Tanvir (Leicester), L. Izzo (INAF/OACN), A. J. Levan (Radboud and Warwick), D. Xu (NAOC), G. Corcoran (UCD), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), G. Pugliese (API), A. de Ugarte Postigo (LAM), K. Wiersema (Hertfordshire), report on behalf of the Stargate collaboration: We observed the field of EP260321a (Huang et al., GCNs 44068, 44075) with the ESO VLT UT1 (Antu) and UT4 (Yepun), obtaining R-band imaging with the FORS2 instrument (mid-time 00:44 UT on 2026-02-22; 12.23 hr after the EP trigger), and integral field spectroscopy with the MUSE instrument on UT4 (mid-time 05:29 UT on 2026-02-22; 16.98 hr after the EP trigger). Within the refined EP/FXT error circle (Huang et al., GCN 44075), the blue, historically variable source coincident with the outskirts of a galaxy at z = 0.0343, noted by Lee et al. (GCN 44070), is prominent. We measure a magnitude of R = 19.5, which is within the range of archival values, but is significantly brighter than reported by Lee et al. (GCN 44070). The source itself is consistent with being marginally resolved in 0.7" seeing imaging, though this may be due to contamination from the underlying galaxy. Our spectroscopy shows the variable source (covering the wavelength range 4750 - 9300 Å) to be characterised by a blue power-law continuum, with very strong narrow emission lines at z = 0.0343 (e.g., [O III] 5008 EW ~ 500 Å). No absorption features are detected at either z = 0 or z = 0.0343. While the emission lines are visible across the entire galaxy, they are strongly spatially concentrated at the location of the blue variable object, with fluxes approximately twenty times brighter than at the galaxy nucleus. This makes it unlikely for the source to be a random foreground superposition, suggesting that it lies itself within the galaxy at z = 0.0343. At this redshift, our measured flux corresponds to an absolute magnitude of approximately M_R = -16.8, and the past variability (Lee et al., GCN 44070) appears to be consistent with previous outbursts to a comparable flux level. It is possible that past variability was due to LBV-like outbursts from a star embedded within a dense, luminous cluster (as evidenced by the strong emission line component). The short-term variability following the outburst (Lee et al., GCN 44070; Aryan et al., GCN 44081), coupled with the location within the revised FXT error circle, suggest that this source is the optical counterpart of EP260321a. It is unclear if the current outburst is related to a further LBV flare or the terminal collapse of the star, as may be suggested by the possible shock breakout properties of the X-ray outburst (Huang et al., GCN 44075). Under this interpretation, this would make EP260321a the first example of an X-ray transient progenitor detected prior to explosion. We encourage further monitoring of this object at all wavelengths in order to clarify its enigmatic nature. We acknowledge excellent support of the ESO observing staff at Paranal, in particular Abel de Burgos Sierra, Alonso Luna Ruiz Fernandez, Elyar Sedaghati, Enrico Congiu, Israel Blanchard, and Rodrigo Palominos. We also thank the visitor observers on UT4, Silvia Piranomonte and Eleonora Parlanti, for generously allowing the execution of our observation. View this GCN Circular online at https://gcn.nasa.gov/circulars/44082. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42202] EP260321a: further Kinder optical observations
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44081 SUBJECT: EP260321a: further Kinder optical observations DATE: 26/03/22 15:49:58 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Aryan, M.-H. Lee, T.-W. Chen, W.-J. Hou (all NCU), S. Yang (HNAS), A. K. H. Kong (NTHU), T. Moriya (NAOJ), S. J. Smartt, J. Gillanders (both Oxford), Y. J. Yang (NYUAD), A. Dutta, Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, C.-S. Lin H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260321a (Huang et al., GCN 44068) using the 1m LOT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations started at 11:34 UTC on the 22nd of March 2026 (MJD 61121.482), 23.07 hr after the EP-WXT trigger. We used Kinder pipeline (Yang et al. A&A 646, A22) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image. In the difference image, we still detected this stellar source SDSS J095942.88+002506.2 (Lee et al., GCN 44070), but no other new transient has emerged. Moreover, we used AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry for this variable star (without template subtraction). The details of the observations and the measured magnitude (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | (med/avg.) Airmass LOT | r | 61121.482 | 23.07 | 300 * 6 | 19.18 +/- 0.04 | 0".96 | 1.27 LOT | g | 61121.520 | 23.99 | 300 * 2 | 18.77 +/- 0.04 | 1".11 | 1.17 Our 3-sigma upper limit for the observed field is r = 23.4 mag. EP260321a was identified as a possible supernova shock-breakout candidate in the EP refined analysis (Huang et al., GCN 44075). However, no optical counterpart has been reported to date (Lee et al., GCN 44070; Ma et al., GCN 44074; Aguilar-Ruiz et al., GCN 44076; Liang et al., GCN 44079). For comparison, in SN 2008D the optical counterpart was detected only ~1.4 hr after the initial X-ray detection (Soderberg et al. 2008). Given the similar X-ray duration to SN 2008D and the continued absence of any optical counterpart, we suspect that the EP260321a X-ray emission more likely originates from the variable star itself. If it is a Galactic X-ray binary, the spectrum suggests a supersoft (WD) accretor, but the X-ray flux is weak; a strong local stellar flare is also plausible. The presented magnitudes are calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105) and are not corrected for the expected Galactic foreground extinctions of A_r = 0.06 mag and A_g = 0.08 mag, in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission can be found in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44081. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42201] GRB 260321A: SVOM/VT optical upper limits
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44080 SUBJECT: GRB 260321A: SVOM/VT optical upper limits DATE: 26/03/22 14:10:30 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, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), M. Brunet (IRAP), O. Godet (IRAP) report on behalf of the SVOM/VT team. SVOM/VT performed an observation with automatic slew to the field of GRB 260321A triggered by SVOM/ECLAIRs (sb26032123, Brunet et al., GCN 44071). The observation started at 2026-03-21T18:57:18 UTC, i.e., about 45 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No credible sources were detected within the error box of ECLAIRs (Brunet et al., GCN 44071), compared to the Legacy survey catalog. The 5 sigma upper limits in AB magnitude are derived as follows: Mid time | Band | Exposure Time | 5 sigma upper limit 1.13 hour VT_B 53*50 sec > 22.7 mag 1.12 hour VT_R 42*50 sec > 22.5 mag More detailed analysis is still ongoing. 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/44080. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42200] EP260321a: Las Cumbres upper limit
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44079 SUBJECT: EP260321a: Las Cumbres upper limit DATE: 26/03/22 13:12:22 GMT FROM: aujust(a)mail.ustc.edu.cn Runduo Liang, Wenxiong Li (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of EP260321a (GCN 44068, GCN 44075) with a Las Cumbres 1m telescope at Cerro Tololo Inter-American Observatory, Chile, about 11.25 hours after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical r-band. We didn’t detect any uncataloged source within the EP-FXT refined position down to a 3-sigma limiting r-band mag of ~20.8. The presented magnitudes are calibrated with Pan-STARRS sources in the field and not corrected for Galactic extinction. Additional follow-up is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/44079. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42199] GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44078 SUBJECT: GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 26/03/22 08:47:42 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Edilberto Aguilar-Ruiz (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), M. Brunet, O. Godet (IRAP) 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 07:59:54 UTC (from 12.39 to 13.80 hours after the trigger) and obtained 61 minutes of exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ 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 stacked image, we do not detect any new source within the ECLAIRs source position (Brunet et al., GCN Circ. 44071), as compared to the Legacy Survey, down to the following 5-sigma limit: r > 23.7 mag z > 22.6 mag Further observations are ongoing. 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/44078. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42198] GRB 260320A: Insight-HXMT/HE detection
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44077 SUBJECT: GRB 260320A: Insight-HXMT/HE detection DATE: 26/03/22 08:44:50 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Chao Zheng, Cheng-Kui Li and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team: At 2026-03-20T19:40:04.700 (T0), Insight-HXMT/HE detected the burst GRB 260320A, which is also detected by NuSTAR (G. Waratkar et.al., GCN #44064). The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 4.4 +1.2/-0.8 s. The 1s peak rate, measured from T0-0.7 s, is 2511 cnts/sec. Insight-HXMT/HE detected a total of 5253 counts from this burst. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260320A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/ View this GCN Circular online at https://gcn.nasa.gov/circulars/44077. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42197] EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44076 SUBJECT: EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission DATE: 26/03/22 07:01:20 GMT FROM: Rosa L. Becerra at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Edilberto Aguilar-Ruiz (UNAM), Antonio de Ugarte Postigo (LAM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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), Fredd Sánchez Álvarez (UNAM), and Benjamin Schneider (LAM) report: We imaged the field of the Einstein Probe X-ray transient EP260321a (Huang et al., GCN Circ. 44068) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-22 03:48 to 05:50 UTC (from 15.3 to 17.4 hours after the trigger) and obtained 24, 65, and 89 minutes of exposure, respectively, in the g, r, and z filters. The data were reduced and coadded with the COLIBRÍ ASU 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 Legacy Survey DR10 (Dey et al. 2019) using STDWeb, we do not detect any new source at the FXT refined position (Huang et al., GCN Circ. 44075) down to the following 5-sigma limit: g > 23.8 r > 23.8 z > 22.8 Our upper limit in r is consistent with the ones reported by Lipunov et al. (GCN Circ. 44069) and Lee et al. (GCN Circ. 44070). We do see additional flux from the superposed star, also in agreement with Lee et al. In order to test the shock breakout scenario proposed by Huang et al. (GCN Circ. 44075), we compared our results against the light curve of the AT2016gkg (Bersten et al. 2018), shifted at the redshift of the galaxy 2dFGRS TGN352Z077 at z=0.034 (DESI Legacy Survey, Dey et al. 2019). At the time of our observations, we expect an AB magnitude about 19.2 at 570 nm, which lies between our g and r filters. Our upper limits are about 4.6 magnitudes fainter than this, and so we are unable to confirm the presence of a shock breakout. 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/44076. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42196] EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44075 SUBJECT: EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate DATE: 26/03/22 04:32:32 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. J. Huang (PMO, CAS), Z.-C. Zou (NJU), D. Y. Li, X. Mao, H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260321a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Huang et al., GCN 44068). The transient triggered WXT at T0=2026-03-21T12:23:07 (UTC). The WXT observation lasted for approximately 432 seconds, and was interrupted due to the autonomous follow-up observation. The WXT 0.5-4 keV spectrum was soft, and can be fitted with an absorbed black body with the absorption fixed at the Galactic value of 2.7 × 10^(20) cm^-2 and a temperature of 164 (-29/+40) eV. The derived average unabsorbed 0.5-4 keV flux is 8.0 (-1.9/+2.2) × 10^(-11) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-03-21T12:35:02 (UTC, T0+12min). The exposure time of this observation is 4266s. On-ground analysis of the FXT data found an uncatalogued fading source within the WXT error circle at R.A., Dec. = 149.9287, 0.4177 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). A significant decay was detected in the FXT light curve during the initial phase of FXT observation. The average 0.5-10 keV spectrum can be fitted with an absorbed black body with Galactic absorption and a temperature of 121 (-3/+3) eV. The derived average unabsorbed 0.5-10 keV flux is 9.8 (-0.3/+0.3) × 10^(-12) erg/s/cm^2. All quoted errors are at the 90% confidence level. We note that within the FXT error circle, there is a galaxy 2dFGRS TGN352Z077, at a redshift of 0.0345. If the transient is associated with this galaxy, the corresponding luminosity of the WXT detection would be approximately 2.2 × 10^(44) erg/s. Given its very soft spectrum, rapid decay and the corresponding luminosity at the assumed redshift, we tend to consider EP260321a as possibly a supernova shock breakout candidate. No optical counterpart of EP260321a has been detected so far (Lipunov et al., GCN 44069; Lee et al., GCN 44070; Ma et al., GCN 44074) , and further mutil-band follow-up observations are encouraged to explore the nature of EP260321a. A follow-up observation with the EP-FXT was planned, and further information will be updated when the telemetry data are received. 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/44075. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42195] EP260321a: SVOM/VT optical upper limit
by GCN Circulars 22 Mar '26

22 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44074 SUBJECT: EP260321a: SVOM/VT optical upper limit DATE: 26/03/22 02:34:27 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, H. L. Li, Z. H. Yao, Y. L. Qiu, C. Wu, L. P. Xin, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of EP260321a detected by EP/WXT (Huang et al., GCN 44068). SVOM/VT began observing the field at 2026-03-21T13:10:39 UTC, 0.673 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, no uncataloged source is found within the error box of FXT (Huang et al., GCN 44068) compared with DESI Legacy Survey at the mid time of 1.92 hours after trigger, VT_R > 22.8 mag with exposure time of 53*50 sec, VT_B > 23.0 mag with exposure time of 54*50 sec. The stellar source and the galaxy reported by Kinder (Lee et al., GCN 44070) are detected in our observations, with no significant variability. Our photometry was not corrected for Galactic extinction. 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/44074. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42194] GRB 260310A: continued optical observation at Mondy
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44073 SUBJECT: GRB 260310A: continued optical observation at Mondy DATE: 26/03/21 22:21:34 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (IKI), A. Volnova (IKI), E. Klunko (ISTP), A. S. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI) report on behalf of GRB IKI FuN. We continued observation the GRB260310A/AT2026fgk detected by Fermi/GBM (Fermi GBM team, GCN 43951) and AstroSat (Salunke et al., GCN 43958) with AZT-33IK telescope of Mondy observatory. We obtained series in B and R filters on 2026-03-21. The OT discovered by GOTO (O'Neill et al. 2026, TNS Discovery Report 294132) and observed earlier (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978;Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980;de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996;Martin-Carrillo et al., GCN 44000; Moreno Méndez et al., GCN 43980; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Gupta et al., GCN 44051; Becerra et al., GCN 44059; Volnova et al., GCN 44060; Busmann et al., GCN 44061; Zheng t al., GCN 44065) is clearly detected in our images. Preliminary photometry is the following Date UT_start t_mid - T0, exp, mag, err, filter, UL(3sigma) days s 2026-03-21 16:35:57 11.48526 30*120 B 20.19 0.04 23.3 2026-03-21 16:04:50 11.46366 15*120 R 19.21 0.04 23.4 The photometry is based on the nearby calibrations stars of PS1 catalogue converted to B, R using the Lupton (2005) transformations. The magnitudes of the AT2026fgk are not corrected for Galactic extinctions. The light curve obtained from our observations and GCNs can be found in https://heaiki.ru/lvc/GRB260310A/GRB260310A_LC.png We can assume that the light curve becomes steeper 9 days after long lasting plateau phase View this GCN Circular online at https://gcn.nasa.gov/circulars/44073. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42193] Fermi GBM Sub-Threshold Detection of GRB 260321A
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44072 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 260321A DATE: 26/03/21 22:15:38 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA) reports on behalf of the Fermi-GBM Team: SVOM/ECLAIRs detected GRB 260321A on 2026-03-21 at 18:12:08 UTC (GCN 44071). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates. The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient approximately 10 s after the ECLAIRs best image SNR time of 2026-03-21T18:11:48. The Targeted Search candidate was found most significantly on the 8 s timescale using the "normal" spectral template (i.e., Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) and has a false alarm rate of 3.7e-04 Hz. The Fermi-MET of this transient is 795809523.353 s. The Targeted Search localization is spatially consistent with the ECLAIRs location. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/44072. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42192] GRB 260321A: SVOM detection of a burst
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44071 SUBJECT: GRB 260321A: SVOM detection of a burst DATE: 26/03/21 18:39:15 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP) report on behalf of the SVOM mission team: At 2026-03-21T18:12:08 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260321A (SVOM burst-id sb26032123). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 2 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.37 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2026-03-21T18:11:48. The localization of the best alert is R.A., Dec. 219.574, 31.674 degrees: R.A. (J2000) = 14h38m17.65s Dec. (J2000) = 31d40m28.18s with a 90% confidence level (C.L.) radius of 8.45 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2026-03-21T18:12:08 with an SNR of 10.9. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 113.02 -18.24 / +74.15 (8-1100 keV). SVOM slewed to the burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Marius Brunet: mbrunet(a)irap.omp.eu. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44071. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42191] EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44070 SUBJECT: EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle DATE: 26/03/21 17:18:54 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> M.-H. Lee, A. Aryan, T.-W. Chen, W.-J. Hou (all NCU), S. Yang (HNAS), S. J. Smartt, J. Gillanders (both Oxford), A. K. H. Kong (NTHU), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, C.-S. Lin H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260321a (Huang et al., GCN 44068 using the 1m LOT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations started at 13:38 UTC on the 21st of March 2026 (MJD 61120.568), 1.13 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. In the difference image, we detected an obvious residual at RA, DEC = 09:59:42.82, 00:25:05.84. We noticed that this position coincides with a stellar source that sits close on top of a resolved galaxy detected in SDSS, Pan-STARRS1 and Legacy Surveys (SDSS J095942.88+002506.2). The stellar source has varying magnitudes in different catalogs (PS1 r = 20.42 +/- 0.25, SDSS r = 21.07 +/- 0.05, DESI r = 19.07). This is likely an unrelated variable star. Moreover, we used AutoPhOT to perform PSF photometry at the residual's position. The details of the observations and the measured magnitude (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 61120.568 | 1.13 | 300 * 6 | 20.97 +/- 0.04 | 1".02 | 1.09 Our 3-sigma upper limit for the observed field is r = 23.1 mag using the SDSS catalogue as the reference. The galaxy SDSS J095942.88+002506.2 is at z = 0.0343, as measured in 2dF and in the DESI Legacy Survey DR1 spectroscopic catalogue (TARGETID: 39627799320858502) lies within the EP FXT localisation region. If EP260321 is associated with this galaxy, then our detection limits imply there is no new source brighter than an absolute magnitude of M ~ -12.6 mag at t-t0 = 1.13 hours after the FXT trigger. A supernova or kilonova would still be rapidly rising in this phase; further observations are encouraged. The presented magnitude is calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105) and is not corrected for the expected Galactic foreground extinction of A_r = 0.06 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission can be found in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44070. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42190] EP260321a: Global MASTER-Net observations report
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44069 SUBJECT: EP260321a: Global MASTER-Net observations report DATE: 26/03/21 13:54:25 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP260321a ( EP Team et al., GCN 44068) errorbox 194 sec after notice time and 2105 sec after trigger time at 2026-03-21 13:05:23 UT, with upper limit up to 19.1 mag. Observations started at twilight. The observations began at zenith distance = 56 deg. The sun altitude is -16.9 deg. The galactic latitude b = 41 deg., longitude l = 239 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3200651 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 2135 | 2026-03-21 13:05:23 | MASTER-Tunka | (09h 57m 47.48s , +00d 56m 51.7s) | C | 60 | 18.8 | 2135 | 2026-03-21 13:05:23 | MASTER-Tunka | (09h 57m 34.12s , +01d 01m 05.4s) | C | 60 | 19.0 | 2208 | 2026-03-21 13:06:36 | MASTER-Tunka | (09h 57m 50.16s , +00d 58m 39.4s) | C | 60 | 18.8 | 2208 | 2026-03-21 13:06:36 | MASTER-Tunka | (09h 57m 36.78s , +01d 02m 53.3s) | C | 60 | 19.1 | 2283 | 2026-03-21 13:07:50 | MASTER-Tunka | (09h 57m 44.76s , +00d 57m 41.4s) | C | 60 | 18.9 | 2283 | 2026-03-21 13:07:50 | MASTER-Tunka | (09h 57m 31.35s , +01d 01m 55.6s) | C | 60 | 19.1 | 2354 | 2026-03-21 13:09:02 | MASTER-Tunka | (09h 57m 45.04s , +00d 58m 40.3s) | C | 60 | 18.8 | 2354 | 2026-03-21 13:09:02 | MASTER-Tunka | (09h 57m 31.61s , +01d 02m 54.6s) | C | 60 | 19.0 | 2429 | 2026-03-21 13:10:17 | MASTER-Tunka | (09h 57m 50.55s , +00d 57m 39.6s) | C | 60 | 18.8 | 2429 | 2026-03-21 13:10:17 | MASTER-Tunka | (09h 57m 37.10s , +01d 01m 53.7s) | C | 60 | 19.0 | 2502 | 2026-03-21 13:11:30 | MASTER-Tunka | (09h 57m 45.69s , +00d 56m 38.6s) | C | 60 | 18.9 | 2502 | 2026-03-21 13:11:30 | MASTER-Tunka | (09h 57m 32.22s , +01d 00m 52.6s) | C | 60 | 19.1 | 2575 | 2026-03-21 13:12:42 | MASTER-Tunka | (09h 57m 37.50s , +01d 01m 04.8s) | C | 60 | 19.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44069. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42189] EP260321a: Einstein Probe detection of an X-ray transient
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44068 SUBJECT: EP260321a: Einstein Probe detection of an X-ray transient DATE: 26/03/21 13:01:43 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q.J. Huang (PMO, CAS), Z. C. Zou (NJU), X. Mao, D. Y. Li, H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260321a. The transient triggered EP-WXT (ID: 01709259023) at 2026-03-21T12:30:18 (UTC). The WXT position of the source is R.A. = 149.894 deg, DEC = 0.397 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 149.9260 deg, DEC = 0.4181 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. 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/44068. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42188] GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44067 SUBJECT: GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations DATE: 26/03/21 11:45:32 GMT FROM: A. Brosio at ABObservatory Rosarno <antonino.brosio(a)gmail.com> A. Brosio (ABObservatory Rosarno), M. A. Tripodi (ABObservatory Rosarno), S. Savaglio (Università della Calabria), S. Benatti (INAF - Osservatorio Astronomico di Palermo), M. Basilicata, M. Rainer (INAF - Osservatorio Astronomico di Brera), S. Tosi (Università di Genova), A. Di Dato (INAF - Osservatorio Astronomico di Capodimonte), D. Liguori (Osservatorio "G. Galilei", Liceo Scientifico Cariati), A. Nastasi (GAL Hassin, Isnello), E. Pace, R. Stanga, L. Betti (Università di Firenze - Osservatorio Polifunzionale del Chianti), D. Ricci (INAF - Osservatorio Astronomico di Padova) and the NOCTIS Collaboration report: We observed the optical counterpart of GRB 260310A / AT 2026FGK, previously reported by several groups as the optical afterglow: (O'Neill et al. 2026, TNS Discovery Report 294132; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Gupta et al., GCN 44051; Salunke et al., GCN 43958; Becerra et al., GCN 44059; Volnova et al., GCN 44060; Busmann et al., GCN 44061). At JD 2461120.34019 (2026-03-20.84019 UT), we measured the source at: AT 2026FGK 18.92 +/- 0.10 Sloan r Photometric calibration was performed using the APASS catalog, adopting the comparison stars at coordinates RA(J2000) = 219.274765, Dec(J2000) = +71.914946; RA(J2000) = 219.311345, Dec(J2000) = +71.880330. View this GCN Circular online at https://gcn.nasa.gov/circulars/44067. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42187] GRB 260318A: Glowbug gamma-ray detection
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44066 SUBJECT: GRB 260318A: Glowbug gamma-ray detection DATE: 26/03/21 11:28:43 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 260318A, which was also detected by Fermi/GBM (GCN 44049), GECAM-B (GCN 44052), and SVOM/GRM (GCN 44055). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-03-18 22:35:52.696 with a duration of 7.7 s and a total significance of about 18.1 sigma. The light curve comprises two peaks at ~T0+2s and ~T0+6s. 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/44066. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42186] GRB 260310A / AT 2026fgk: KAIT optical observations
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44065 SUBJECT: GRB 260310A / AT 2026fgk: KAIT optical observations DATE: 26/03/21 06:49:53 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of GRB 251022A (Fermi GBM Team, GCN 43951; Salunke et al., GCN 43958) on March 13, 14, 18 19, 20 UT. A set of B, V, R, I and clear (roughly R) filter images were obtained. We clearly detected the optical afterglow (O'Neill et al. 2026, TNS Discovery Report 294132; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978;Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980;de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996;Martin-Carrillo et al., GCN 44000; Moreno Méndez et al., GCN 43980; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Gupta et al., GCN 44051; Salunke et al., GCN 43958; Becerra et al., GCN 44059; Volnova et al., GCN 44060; Busmann et al., GCN 44061) in our coadd images and photometry in R band gives the following result: t-t0(d) Mag err ------------------ 3.21 17.98 0.03 4.25 18.31 0.02 8.24 18.34 0.02 9.22 18.30 0.02 10.20 18.54 0.03 View this GCN Circular online at https://gcn.nasa.gov/circulars/44065. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42185] GRB 260320A: NuSTAR detection of prompt emission
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44064 SUBJECT: GRB 260320A: NuSTAR detection of prompt emission DATE: 26/03/21 04:53:08 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260320A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-03-20 19:40:03.9 UTC, shows a detection of GRB 260320A consistent with SVOM/GRM (GCN Notices). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single bright peak lasting for ~10-s. The peak count rate is ~2000-cps with a baseline rate of ~1000-cps during this time period. We do not see any evidence in the signal above 100 keV in the CdZnTe detectors. The SVOM/GRM localization (GCN Notices) at RA = 38.93, Dec = 16.64 implies an offset from the NuSTAR boresight of 92-deg (i.e. from the side of the instrument) and an offset from the geocenter of 14-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260320A Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44064. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42184] GRB 260310A / AT2026fgk: NuSTAR follow-up detection
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44063 SUBJECT: GRB 260310A / AT2026fgk: NuSTAR follow-up detection DATE: 26/03/21 04:50:06 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> Elias Kammoun (Caltech), Gaurav Waratkar (Caltech), Rahul Jayaraman (Cornell), K-Ryan Hinds (Caltech), Anna Y. Q. Ho (Cornell) report: In response to our NuSTAR DDT request (PI Waratkar), NuSTAR observed the position of GRB 260310A / AT2026fgk (Fermi GBM team, GCN 43951; Arya et al., GCN 43958; Konno et al., GCN 43974; Martin-Carrillo et al., GCN 43979, 44000; Méndez et al., GCN 43980; Becerra et al., GCN 43991; Jayaraman et al., GCN 43994; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Rhodes et al., GCN 44005; Moskvitin et al., GCN 44006; Romanov et al., GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Giarratana et al., GCN 44045; Gupta et al., GCN 44051; Ho et al., GCN 44057; Passaleva et al., GCN 44058; Becerra et al., GCN 44059; Volnova et al., GCN 44060), beginning at 2026-03-20T17:20:02 UTC with an exposure time of 7523 s. We performed a preliminary analysis of the NuSTAR spectrum in the 3-79 keV energy range from both the FPMA and FPMB modules by fitting an absorbed power law. We find a photon index of 1.76 ± 0.22 with an unabsorbed flux of (1.16 ± 0.15) x 10^-12 ergs/cm2/s (2-10 keV). All the uncertainties are 90% CL. At the reported redshift of 0.153 (Ugarte Postigo et al., GCN 43984; Hinds et al., GCN 43977), this would correspond to a luminosity (2-10 keV) of (7.2 ± 0.7) x 10^43 erg/s. We thank the entire NuSTAR Science & Mission operations teams for the rapid approval and execution of this DDT observation. NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44063. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42183] EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44062 SUBJECT: EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare DATE: 26/03/21 03:19:15 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, automatically responded to the EP-WXT trigger 01709258989 (Zhou et al. GCN 44054) starting at 04:57 UT, about 2.4 hours after the trigger. A set of clear (roughly R) filter images were obtained and lasted for ~2.5 hours. Photometry on the suggested flare star 1RXS J073101.9+460030 (confirmed by Perez-Garcia et al., GCN 44056) show that its brightness remain around 12.5 mag for about 1 hour, then another flare started at 06:05 UT (3.53 hours after trigger), brightened to ~12.0 mag at peak time of 06:11 UT, then decreased to ~12.4 mag around 06:23 UT. This confirming the EP X-ray trigger is related to the stellar flare. View this GCN Circular online at https://gcn.nasa.gov/circulars/44062. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42182] GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
by GCN Circulars 21 Mar '26

21 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44061 SUBJECT: GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening DATE: 26/03/21 01:42:34 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann, Daniel Gruen (LMU), Xander J. Hall, Brendan O'Connor, Antonella Palmese (CMU) report: We observed the optical/NIR counterpart of GRB 260310A (Fermi GBM team, GCN 43951; Salunke et al., GCN 43958), AT 2026fgk (e.g. O'Neill et al. 2026, TNS Discovery Report 294132; Konno et al., GCN 43974; Hinds et al., GCN 43977), with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the g, r, i, z, J, and Ks band starting at 2026-03-19T23:22:38 (9.77 days after the GRB trigger) and 2026-03-20T22:36:22 (10.74 after the GRB trigger). Unlike suggested by Becerra et al. (CGN 44059) we do not see signs of rebrightening in our observations in any filter (see also Volnova et al., GCN 44060). We thank Michael Schmidt and Silona Wilke for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44061. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42181] GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44060 SUBJECT: GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy DATE: 26/03/20 22:31:46 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> A. Volnova (IKI), N. Pankov (IKI), E. Klunko (ISTP), A. S. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI) report on behalf of GRB IKI FuN. We observed the field of GRB260310A/AT2026fgk detected by Fermi/GBM (Fermi GBM team, GCN 43951) and AstroSat(Salunke et al., GCN 43958) with AZT-33IK telescope of Mondy observatory. We obtained series in B and R filters starting on 2026-03-13. The OT discovered by GOTO (O'Neill et al. 2026, TNS Discovery Report 294132) and observed earlier (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978;Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980;de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996;Martin-Carrillo et al., GCN 44000; Moreno Méndez et al., GCN 43980; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044; Gupta et al., GCN 44051) is clearly detected in our images. Preliminary PSF photometry on some epochs is the following Date UT_start t_mid - T0, filter exp, mag err UL(3sigma) days s 2026-03-15 15:09:04 5.43535 15*120 B 19.18 0.05 23.0 2026-03-16 14:37:32 6.41345 15*120 B 19.05 0.05 22.6 2026-03-17 18:59:03 7.60549 30*120 B 19.18 0.05 22.7 2026-03-18 18:40:29 8.58565 19*120 B 19.47 0.06 21.7 2026-03-19 18:09:48 9.57128 30*120 B 19.61 0.06 23.2 2026-03-15 14:48:55 5.52493 11*120 R 18.27 0.05 23.0 2026-03-16 14:07:40 6.39202 13*120 R 18.22 0.05 22.8 2026-03-17 18:22:13 7.56948 15*120 R 18.29 0.06 22.8 2026-03-18 18:06:29 8.55786 15*120 R 18.60 0.06 22.4 2026-03-19 19:11:16 9.60355 15*120 R 18.71 0.07 22.7 The photometry is based on the nearby calibrations stars of PS1 catalogue converted to B, R using the Lupton (2005) transformations. The magnitudes are not corrected for Galactic extinctions. We do not observe the rebrightening reported in COLIBRÍ observations (Becerra et al., GCN 44059) up to the latest epoch (~9.6 days) in B,R - filters. Based on classification of the progenitor (Atteia et al., GCN 43981; Minaev et al., GCN 44053) we urge follow up observations to search for a supernova associated with GRB 260310A. View this GCN Circular online at https://gcn.nasa.gov/circulars/44060. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42180] GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44059 SUBJECT: GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening DATE: 26/03/20 20:08:08 GMT FROM: Rosa L. Becerra at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Noémie Globus (UNAM), Enrique Moreno Méndez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), 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), Antonio de Ugarte Postigo (LAM), and Benjamin Schneider (LAM) report: We reimaged the field of AT 2026fgk, first reported by Hinds et al. (AstroNote 2026-65) and followed-up by a large number of facilities across multiple wavelengths (GCNs Circ. 43951, 43954, 43958, 43974, 43975, 43977, 43978, 43979, 43980, 43981, 43984, 43986, 43990, 43991, 43993, 43994, 43996, 44000, 44001, 44002, 44003, 44004, 44005, 44006, 44020, 44021, 44022, 44043, 44044, 44045, 44051, 44053, 44057, 44058), as a possible counterpart to the Fermi GBM GRB 260310A (Fermi GBM Team, GCN Circ. 43951; Humburg & Meegan, GCN Circ. 43975), and also detected by AstroSat CZTI (Salunke et al., GCN Circ. 43958), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed several epochs from 2026-03-20 03:35 to 11:21 UTC (from 9.94 to 10.27 days after the GRB trigger) in the g, r, and z filters. The data were reduced, coadded, calibrated, and analysed with the ASU pipeline. 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 images, we continue to detect AT 2026fgk. Compared with the photometry acquired on 2026-03-19, we observe a rebrightening in all three filters throughout the night, with a temporal index of alpha > 1.5. We encourage extended follow-up observations. 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/44059. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42179] GRB 260310A/AT2026fgk: LBT near-infrared observations
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44058 SUBJECT: GRB 260310A/AT2026fgk: LBT near-infrared observations DATE: 26/03/20 17:40:46 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 J and K filters with the LUCI near-infrared imager mounted on the Large Binocular Telescope (LBT). Observations started at 2026-03-16T08:07:32 (~ 6.2 d after the GBM trigger) with an average airmass of 1.3. We detect the source with a preliminary magnitude of J~18.03 AB mag, calibrated using nearby stars from the 2MASS catalog (Skrutskie et al. 2006), uncorrected for Galactic extinction. Compared with previous near-infrared observations (Li et al., GCN 43993; Stein et al., GCN 43996; Brivio et al., GCN 44004), our measurement is consistent with a fading slope of 0.7. We acknowledge excellent support from the LBTO and LBT-INAF staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/44058. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42178] NOEMA Detection of GRB 260310A
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44057 SUBJECT: NOEMA Detection of GRB 260310A DATE: 26/03/20 14:52:58 GMT FROM: Anna Y Q Ho at Cornell University <ayh24(a)cornell.edu> Anna Y. Q. Ho (Cornell), Michael Bremer (IRAM), Genevieve Schroeder (Cornell) report on behalf of a larger collaboration: On UT 2026 March 20 the NOrthern Extended Millimeter Array (NOEMA) 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 wavelengths (GCN 44005, 44045). Observations were obtained in the new dual-band mode (100+230 GHz) as well as in Band 2 (150 GHz). With self-calibration, we measure a preliminary flux density of 17 mJy at 100 GHz, corresponding to a luminosity of 10^42 erg/s, typical for GRB afterglows at this epoch. Further observations are planned. We thank the NOEMA staff for rapidly approving and scheduling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44057. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42177] EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44056 SUBJECT: EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7 DATE: 26/03/20 10:46:01 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), 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 EP-WXT trigger 01709258989 (Zhou et al. GCN 44054), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) responded to the alert on Mar. 20, 02:39 UT (i.e. 6-min after trigger, 1 min after notification). Within the reported EP-FXT error circle we find the star 1RXS J073101.9+460030 decreasing 0.9, 0.5 and 0.4 mag in g, r and i filters during a 20 min time interval, confirming EP-WXT trigger 01709258989 as due to a stellar flare. We thank the staff at San Pedro de Atacama Celestial Observations for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44056. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42176] GRB 260318A: SVOM/GRM observation
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44055 SUBJECT: GRB 260318A: SVOM/GRM observation DATE: 26/03/20 06:30:30 GMT FROM: yzh807926(a)163.com SVOM/GRM team: Zheng-Hang Yu, Chao Zheng, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Hui Yang (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 260318A (SVOM trigger reference: sb26031805) at 2026-03-18T22:36:00.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44049). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a precursor followed by a main episode with two peaks a T90 of 28.5 +7.0/-8.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260318A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 303.6, DEC= 57.0 GCN#44049), is located at about 164 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-16 to T0+10 s is best fitted by a power law function. The power law index is -2.55 +0.17/-0.16. The event fluence (10-1000 keV) in this time interval is (6.72 +1.45/-1.02)E-05 erg/cm^2. 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: Zheng-Hang Yu(IHEP)(zhyu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44055. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42175] The EP-WXT trigger 01709258989 is likely a flaring star
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44054 SUBJECT: The EP-WXT trigger 01709258989 is likely a flaring star DATE: 26/03/20 03:33:53 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou, Y. Wang, Q. J. Huang (PMO, CAS), J. P. Chen (SYSU), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709258989 at the time of 2026-03-20T02:33:39 UTC, EP-FXT performed an automatic follow-up observation, and detected a source at RA: 112.7520 deg, Dec: 46.0075 deg, is likely a stellar flare associated with 1RXS J073101.9+460030. The estimated flux of the flare is around 1.0 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 3.6 x 10^31 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/44054. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42174] GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44053 SUBJECT: GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90 DATE: 26/03/20 01:38:39 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> P. Minaev (IKI) , A. Pozanenko (IKI) on behalf of GRB follow-up team We analyzed GRB 260310A (Hamburg et al., GCN 43975; Salunke et al., GCN 43958; Atteia et al., GCN 43981) using publicly available data of GBM/Fermi. The burst consists of several emission episodes with a total duration of T_90 = 86 s. Time integrated energy spectrum, constructed in the time interval (-4, 70) s since GBM trigger, is best described by Band model with E_p = 175 keV and fluence F = 1.74e-5 erg cm^-2 in 1 keV - 10 MeV range. Using z = 0.153 (Hinds et al., GCN 43977; de Ugarte Postigo et al., GCN 43984) we obtain E_iso = 9.8e50 erg. GRB 260310A is placed above the correlation fit for type II (long) bursts on Ep,i – Eiso diagram, as mentioned in (Atteia et al., GCN 43981), but it is inside 2 sigma correlation regions for both type I (short) and type II (long) bursts, therefore we cannot consider it as a clear outlier. Indeed, at the EH – T_90,i diagram (see [1-2] for details) GRB 260310A is well classified as type II (long) burst. The Ep,i – Eiso and EH - T90,i diagrams can be found at https://heaiki.ru/lvc/GRB260310A/ [1] - Minaev et al., MNRAS, 492, 1919, 2020 [2] - Minaev et al., Astronomy Letters, 46, 9, 573, 2020 View this GCN Circular online at https://gcn.nasa.gov/circulars/44053. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42173] GRB 260318A: GECAM-B observation
by GCN Circulars 19 Mar '26

19 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44052 SUBJECT: GRB 260318A: GECAM-B observation DATE: 26/03/19 15:47:49 GMT FROM: yzh807926(a)163.com Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260318A, at 2026-03-18T22:35:52.600 UTC (denoted as T0), which is also detected by Fermi/GBM ((Fermi GBM team, GCN #44049). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 19.5 +3.0/-2.5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260318A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44052. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42172] GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
by GCN Circulars 19 Mar '26

19 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44051 SUBJECT: GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT DATE: 26/03/19 14:57:05 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kumar Pranshu, Dhruv Jain, Debalina Kar, Pankaj Pawar, and Kuntal Misra (ARIES) report: We observed the field of GRB260310A/AT2026fgk detected by Fermi/GBM (Fermi GBM team, GCN 43951) and AstroSat(Salunke et al., GCN 43958) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-03-17 at 20:33:36.00 UT, i.e., ~ 7.65 days after the Fermi/GBM trigger. We have taken multiple frames with an exposure time of 300s in the I filter. We stacked the images after the alignment. We detect an optical afterglow in our stacked image. We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================ 2026-03-17 20:33:36.00 ~7.65 I 300s*3 18.01 +/-0.02 The optical detection of the burst is consistent with Lipunov et al., GCN 43954; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979, 44000; Moreno Méndez et al., GCN 43980; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044. The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/44051. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42171] Fermi GRB 260318A: Global MASTER-Net observations report
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44050 SUBJECT: Fermi GRB 260318A: Global MASTER-Net observations report DATE: 26/03/18 23:00:55 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260318A ( Fermi GBM team, GCN 44049) errorbox 572 sec after notice time and 596 sec after trigger time at 2026-03-18 22:45:44 UT, with upper limit up to 18.1 mag. The observations began at zenith distance = 62 deg. The sun altitude is -43.5 deg. The galactic latitude b = 12 deg., longitude l = 92 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3194853 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 657 | 2026-03-18 22:45:44 | MASTER-Kislovodsk | (20h 14m 11.39s , +56d 41m 32.7s) | P| | 120 | 17.6 | 797 | 2026-03-18 22:48:04 | MASTER-Kislovodsk | (20h 14m 11.18s , +56d 41m 32.8s) | P| | 120 | 17.4 | 938 | 2026-03-18 22:50:25 | MASTER-Kislovodsk | (20h 14m 11.08s , +56d 41m 36.1s) | P| | 120 | 18.1 | 1078 | 2026-03-18 22:52:45 | MASTER-Kislovodsk | (20h 14m 11.06s , +56d 41m 40.9s) | P| | 120 | 18.0 | The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44050. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42170] GRB 260318A: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44049 SUBJECT: GRB 260318A: Fermi GBM Final Real-time Localization DATE: 26/03/18 22:46:23 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 22:35:47 UT on 18 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260318A (trigger 795566152.456906 / 260318942). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 303.6, Dec = 57.0 (J2000 degrees, equivalent to J2000 20h 14m, 57d 00'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 17.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260318942/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260318942/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260318942/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44049. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42169] IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44048 SUBJECT: IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility DATE: 26/03/18 18:09:53 GMT FROM: Jannis Necker at DESY <jannis.necker(a)desy.de> Akshay Eranhalodi (DESY), Robert Stein (JSI), Jannis Necker (Leiden University), and Anna Franckowiak (Ruhr University Bochum) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-260315A (Zegarelli et. al, GCN 44017) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2026-03-15 07:45 UTC, approximately 5.4 hours after event time. We covered 93.7% (0.7 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019) . No candidate counterparts were detected. We do not recover the previously reported candidate counterpart AT 2026fpm (Lipunov et al. 2026, GCN 44023) because it lies outside of the 90% contianment area based on the publicly available probability map of the neutrino event localisation. As the source is also likely a known variable (Fortin et al. 2026, GCN 44026; Feng et al., GCN 44042) it is unlikely to be the neutrino counterpart. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; OKC, Sweden; DZA, Germany. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). Alert filtering is performed with the nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ). View this GCN Circular online at https://gcn.nasa.gov/circulars/44048. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42168] Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44047 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB DATE: 26/03/18 15:31:39 GMT FROM: oliver.roberts(a)universityofgalway.ie O.J. Roberts (Uni. of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger GRB 260313A (trigger 795096033/260312500) at 12:00:28.58 UT on 13 March 2026, tentatively classified as a GRB (GCN 43995, GCN 43987), is in fact unlikely to be a GRB. The nature of this trigger is uncertain." View this GCN Circular online at https://gcn.nasa.gov/circulars/44047. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42167] GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44046 SUBJECT: GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate DATE: 26/03/18 12:06:23 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), 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), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM) and Benjamin Schneider (LAM) report: We imaged the field of the GRB 260316A / EP260316a (Jiang et al., GCN Circ. 44027, GCN Circ. 44034) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-18 07:20:28 to 09:50:38 UTC (from 42.8 to 45.3 hours after the trigger) and obtained 111 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025) and the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We still detect the optical counterpart candidate that we previously reported in Fortin et al., GCN Circ. 44037. Template subtraction from 2026-03-17 to 2026-03-18 shows no significant residuals between the two epochs, and therefore does not allow us to conclude on the potential variability of this source. 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/44046. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42166] GRB 260310A / AT 2026fgk: radio detection with the VLA
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44045 SUBJECT: GRB 260310A / AT 2026fgk: radio detection with the VLA DATE: 26/03/18 09:14:01 GMT FROM: Stefano Giarratana at INAF-OAB <s.giarratana(a)ira.inaf.it> S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA), G. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.), N. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB), L. Nava (INAF-OAB) At 10:22:44 UT on 2026 March 14 (T_mid = 4.26 days post-burst) the Karl G. Jansky VLA observed the field of GRB 260310A / AT 2026fgk (Fermi GBM team, GCN 43951, 43975; AstroSat CZTI collaboration, GCN 43958) in three bands, with central frequencies of 6, 10 and 15 GHz. The standard 3C286 was used as bandpass and flux density calibrator, while J1435+7605 served as phase calibrator. From a preliminary analysis, an unresolved radio source (Rhodes et al., GCN 44005) is clearly detected at all frequencies at a position: RA: 14:37:16.1424 +- 0.001 Dec: +71:50:30.328 +- 0.01 consistent with the X-ray (Jayaraman et al., GCN 43994) and optical (Hinds et al., AstroNote 2026-65, GCN 43977; Konno et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979, 44000; Moreno Méndez et al, GCN 43980; Becerra et al., GCN 43991; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022) and infrared (Li et al., GCN 43993; Stein et al., GCN 43996; Brivio et al., GCN 44004) position of the transient. The preliminary analysis yields the following results: ================================================================ T_mid Freq Peak r.m.s. Beam PA [days] [GHz] [uJy/b] [uJy/b] [arcsec^2] [deg] ================================================================ 4.26 6 3894 8 0.39x0.29 -31 4.26 10 6368 13 0.24x0.19 3.9 4.26 15 9104 29 0.16x0.11 -11 ================================================================ We would like to thank the staff of the VLA for approving, executing, and processing the observations. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. These observations were carried out as part of project SF181027, approved in the framework of the Fermi - NRAO joint program agreement. View this GCN Circular online at https://gcn.nasa.gov/circulars/44045. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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