April 2026 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 42328] EP260403a: LCO optical counterpart detection
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44207 SUBJECT: EP260403a: LCO optical counterpart detection DATE: 26/04/03 13:19:20 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), A. López-Oramas (IAC and ULL), and D. Aguado (IAC and ULL) Following the detection of the fast X-ray transient EP260403a (Guo et al., GCN circ. 44204) by the Wide-field X-ray Telescope (WXT) and the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission, we observed the field with one of the two Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Siding Spring Observatory near Coonabarabran, New South Wales, Australia. The observation, a single exposure of 180 sec in the SDSS r' filter, started on 2026-04-03 at 11:28:01 UT, about 58.8 hours after the EP WXT trigger. The optical counterpart, first reported by Antier et al. (GCN circ. 44206), is detected in our image with an AB magnitude of r' = 19.09 +/- 0.21, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026A-011, SGLF and Superluminous Supernovae surveys). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/44207. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42327] EP260403a: COLIBRÍ optical counterpart candidate
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44206 SUBJECT: EP260403a: COLIBRÍ optical counterpart candidate DATE: 26/04/03 12:26:56 GMT FROM: antier(a)ijclab.in2p3.fr Sarah Antier (IJCLAB), Noémie Globus (UNAM), Benjamin Schneider (LAM), Dalya Akl (NYUAD), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), 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), 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 Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260403a (Guo et al., GCN Circ. 44204) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-04 11:06:21 to 11:45:02 (from 37.20 to 76.87 min after the trigger) and obtained 29 min of simultaneous exposure in the r and z filters. The data were reduced and coadded with the ASU, COLIBRÍ pipelines and 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. We detect an uncatalogued and fading source (revealed by image subtraction using PanSTARRS as template) consistent with the FXT 20 arcsec error circle (Guo et al., GCN Circ. 44204) at: RA(J2000) = 14:36:37.44 = 219.1560 degrees Dec(J2000) = -25:30:14.2 = -25.5039 degrees The preliminary magnitude derived for that source is: r = 18.92 +/- 0.02 z = 18.70 +/- 0.02 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/44206. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42326] GRB 260330B: SVOM/VT optical candidate
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44205 SUBJECT: GRB 260330B: SVOM/VT optical candidate DATE: 26/04/03 12:11:54 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, J. R. Xu, 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. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. After the initial automatic follow-up (Li et al., GCN 44168), SVOM/VT performed ToO observations of the field of GRB 260330B detected by SVOM/ECLAIRs (sb26033003, Lan et al., GCN 44157), SVOM/GRM (Lan et al., GCN 44157) and Fermi/GBM with sub-threshold detection (Trigg et al., GCN 44159). The observations started at 2026-03-31T07:44:21 UTC, approximately 17.44 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. A catalogued optical candidate within the error box of the EP-FXT source #1 (Guillot et al., GCN 44203) was observed brightening in VT_R within 19 hours post trigger. It overlaps a faint source in the Legacy Survey, with magnitudes g=25.00, r=23.96, z=22.16. The position is at R.A., Dec. = 252.637034, 36.841008 degrees, equivalent to: R.A. (J2000) = +16:50:32.89 Dec. (J2000) = +36:50:27.63 with an uncertainty of 0.5 arcsec. The measurements in AB magnitude are as follows: Mid time | Band | Exposure Time | Brightness 1.00 h VT_R 34*50 sec >22.5 mag (5 sigma upper limit) 4.94 h VT_R 57*100 sec 22.67+/-0.20 mag 19.04 h VT_R 56*70 sec 22.12+/-0.15 mag Our photometry was not corrected for Galactic extinction. Further follow-up observation is scheduled. 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/44205. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42325] EP260403a: Einstein Probe detection of an X-ray transient
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44204 SUBJECT: EP260403a: Einstein Probe detection of an X-ray transient DATE: 26/04/03 11:41:00 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C.-L. Guo (NAO, CAS), R.-Z. Li (YNAO) and C.-Y. Dai (NJU) 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 EP260403a. The transient triggered EP-WXT (ID: 01709259505) at 2026-04-03T10:29:10 (UTC). The WXT position of the source is R.A. = 219.150 deg, DEC = -25.502 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. = 219.1572 deg, DEC = -25.5069 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 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/44204. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42324] GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44203 SUBJECT: GRB 260330B: EP-FXT follow-up and identification of candidate afterglow DATE: 26/04/03 10:26:00 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> S. Guillot, G. X. Lan (IRAP), D. Turpin, A. Saccardi (CEA/Irfu), report on behalf of the SVOM and EP collaborations: EP-FXT performed two follow-up observations of the SVOM/ECLAIRs-detected burst GRB 260330B (SVOM/sb26033003; Lan et al., GCN 44157), also detected as a sub-threshold event by Fermi/GBM (Trigg et al., GCN 44159). The first epoch started on 2026-03-31 at 16:39:42 UT, approximately 26.3 hours after the SVOM trigger, with a total exposure time of 3174 s. The second exposure started on 2026-04-02 at 19:48:54 UT, i.e., 77.5 hours after the SVOM trigger, with a total exposure time of 3200 s. Three uncataloged sources are detected within the ECLAIRs error circle in the first epoch: Source 1: EPF_J165032.7+365028 at RA, Dec (J2000) = 252.6363, 36.8413 with Fx=(1.20+/-0.32)e-13 erg/sec/cm2 from the FXT-B telescope. Source 2: EPF_J165010.3+364729 at RA, Dec (J2000) = 252.5430, 36.7914 with Fx=(2.40+/-0.43)e-13 erg/sec/cm2 from the FXT-B telescope. Source 3: EPF_J164951.2+365709 at RA, Dec (J2000) = 252.4635 36.9525 with Fx=(1.96+/-0.41)e-13 erg/sec/cm2 from the FXT-B telescope. All three sources detected by EP/FXT during the first visit are detected in the second epoch data set. However, in the second epoch EPF_J165032.7+365028 has faded by a factor ~4, down to a flux of (4.0 +/- 2.3)e-14 erg/sec/cm2, while the flux of the other sources remained constant within their uncertainties. The fading behavior of this X-ray source confirms it as the afterglow of GRB 260330B, localized at RA, Dec (J2000) = 252.6363, 36.8413 with an error radius of 10 arcsec. All fluxes are calculated in the 0.5-10 keV range with 1-sigma uncertainties. 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/44203. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42323] GRB 260403A: AstroSat CZTI detection
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44202 SUBJECT: GRB 260403A: AstroSat CZTI detection DATE: 26/04/03 10:09:38 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (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-duration GRB 260403A which was also detected by Fermi GBM team (GCN Circ. 44195). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-04-03 02:31:28.51 UTC. The measured peak count rate associated with the burst is 53 (+33, -2) counts/s above the background in the combined data of three quadrants (out of four), with a total of 604 (+338, -211) counts. The local mean background count rate was 221 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 34 (+4, -14) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 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/44202. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42322] EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44201 SUBJECT: EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/04/03 09:03:27 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Q. Zhao (USTC,PRIC), C. L. Guo, J. W. Hu, C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260402a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (GCN #44186), and temporally and spatially consistent with GRB 260402A (GCN #44181). The telemetry WXT data show that the flare started at 2026-04-02T10:29:33 (UTC) and exhibits a double-peaked burst lasting about 200 s. The average WXT 0.5-4 keV spectrum of the burst period can be fitted with an absorbed power law with a hydrogen column density of 0.76（-0.36/+0.41）×10^22 cm^-2 and a photon index of 2.09(-0.77/+0.84). The derived average unabsorbed 0.5-4 keV flux is 2.68 (-0.83/+1.97) ×10^(-9) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source at 2026-04-02T12:55:33 (UTC, T0+8760 s). The exposure time of this observation is 3.0ks. On-ground analysis of the FXT data found an uncatalogued source at R.A., Dec. = 170.9607, 63.6128 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 0.40 (-0.13/+0.14) × 10^22 cm^-2 and a photon index of 3.20 (-0.51/+0.55). The derived average unabsorbed 0.5-10 keV flux is 2.91 (-0.73/+1.46) × 10^(-12) erg/s/cm^2. The optical and near-infrared follow-up observations were performed by Antier et al. (GCN 44183), Carrasco et al. (GCN 44184), Freeberg et al. (GCN 44185), Wu et al. (GCN 44189), Li et al. (GCN 44190), Vijaykumar et al. (GCN 44191), Schneider et al. (GCN 44192) and He et al. (GCN 44199). 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/44201. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42321] GRB 260402B: GECAM-B observation
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44200 SUBJECT: GRB 260402B: GECAM-B observation DATE: 26/04/03 08:53:36 GMT FROM: zhangjinpeng(a)ihep.ac.cn Jin-Peng Zhang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B ground search was triggered by GRB 260402B, at 2026-04-02T22:57:17.100 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44193). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of one pulse, with a duration (T90) of 2.0 +0.5/-1.0 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260402B.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/44200. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42320] EP260402a/GRB 260402A: Jinshan near-infrared upper limit
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44199 SUBJECT: EP260402a/GRB 260402A: Jinshan near-infrared upper limit DATE: 26/04/03 08:06:20 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L. 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), Z.N. Dong, B. Ma (SYU) report: We observed the field of EP260402a/GRB 260402A detected by EP (Zhao et al., GCN 44186) and SVOM (Tan et al., GCN 44181; Gotz et al., GCN 44182), using the JinShan 100C telescope located at Altay, Xinjiang, China. Observation started at 2026-04-02 14:51:48 UT, i.e., 4.36 hrs post-burst, and a series of J-band frames were obtained. No new source is detected in the stacked image within the EP/FXT error circle, down to a 5-sigma limiting magnitude of J ~ 17.3 (Vega), calibrated with 2MASS stars in the field. This upper limit is consistent with that reported at WINTER (Schneider et al., GCN 44192). We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44199. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42319] GRB 260402C: NuSTAR detection of prompt emission
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44198 SUBJECT: GRB 260402C: NuSTAR detection of prompt emission DATE: 26/04/03 07:28:44 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 260402C 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 2026-04-02 13:13:00 UTC, shows a detection of GRB 260402C, consistent with AstroSat/CZTI (Tembhurnikar et al., GCN Circ. 44197). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a ~10-s burst consistent with the first bright peak in the AstroSat/CZTI light curve, with marginal evidence of a second peak consistent with the CZTI light curve. The peak count rate is ~2000-cps with a baseline rate of ~1000-cps during this time period. We do see marginal evidence in the signal above 100 keV in the CZT detectors. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260402C/ 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/44198. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0