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[vsnet-grb-info 42342] The EP-WXT trigger 01709259621 is likely a flaring star
by GCN Circulars 06 Apr '26

06 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44221 SUBJECT: The EP-WXT trigger 01709259621 is likely a flaring star DATE: 26/04/06 02:18:37 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Tian-Yu Liu, R.H. Yao, Chen Wang and C.C. Jin (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709259621 at the time of 2026-04-05T 22:38:24, is likely a stellar flare associated with LP 368-99. The estimated flux of the flare is around 1e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.27e31 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/44221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42341] EP260405.149 / EP-WXT 11900672904: COLIBRÍ optical upper limits
by GCN Circulars 05 Apr '26

05 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44220 SUBJECT: EP260405.149 / EP-WXT 11900672904: COLIBRÍ optical upper limits DATE: 26/04/05 16:04:19 GMT FROM: Massimiliano Lincetto at Aix Marseille Univ, CNRS/IN2P3, CPPM <lincetto(a)cppm.in2p3.fr> Massimiliano Lincetto (CPPM), Alan M. Watson (UNAM), Jean-Grégoire Ducoin (CPPM), 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), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), 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 the EP-WXT transient EP260405.149 using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. Observation started within 30 seconds from the alert reception. We observed on 2026-04-05 from 09:51:17 to 10:30:32 UTC (from 6.25 to 7 hours after the trigger T0) and obtained 1920 seconds of simultaneous exposure in the r and z filters. The data were reduced and co-added with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR2 catalog, 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 WXT source position down to the following 3-sigma limit: r > 21.11 z > 20.57 Further observations may be 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/44220. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42340] The EP-WXT trigger 01709259615 is likely a flaring star
by GCN Circulars 05 Apr '26

05 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44219 SUBJECT: The EP-WXT trigger 01709259615 is likely a flaring star DATE: 26/04/05 12:27:55 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO), Y. J. Yi (BNU), H.Q. Cheng and Z.-X. Ling (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709259615 at the time of 2026-04-05T12:01:49, is likely a stellar flare associated with RX J1411.0+0751. The estimated flux of the flare is around 1e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.4e31 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/44219. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42339] Fermi trigger No 797039833: Global MASTER-Net observations report
by GCN Circulars 05 Apr '26

05 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44218 SUBJECT: Fermi trigger No 797039833: Global MASTER-Net observations report DATE: 26/04/05 11:00:42 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 GRB260404.99 (trigger No 797039833,12h 09m 43.20s , -35d 10m 48.0s, R=16.55) errorbox 21767 sec after notice time and 21798 sec after trigger time at 2026-04-05 06:00:27 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 19 deg. The sun altitude is -58.3 deg. The galactic latitude b = 27 deg., longitude l = 294 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3232826 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21859 | 2026-04-05 06:00:27 | MASTER-OAFA | (12h 59m 32.15s , -41d 01m 29.5s) | C | 120 | 18.4 | 23083 | 2026-04-05 06:21:21 | MASTER-OAFA | (12h 37m 40.74s , -42d 05m 50.7s) | C | 60 | 17.6 | 23143 | 2026-04-05 06:21:21 | MASTER-OAFA | (12h 37m 40.75s , -42d 05m 50.7s) | C | 180 | 18.7 | Coadd 23163 | 2026-04-05 06:22:42 | MASTER-OAFA | (12h 48m 26.86s , -42d 07m 29.9s) | C | 60 | 17.5 | 23240 | 2026-04-05 06:23:58 | MASTER-OAFA | (12h 37m 42.77s , -42d 05m 40.4s) | C | 60 | 18.3 | 23334 | 2026-04-05 06:25:32 | MASTER-OAFA | (12h 48m 27.14s , -42d 06m 12.0s) | C | 60 | 19.2 | 23409 | 2026-04-05 06:26:48 | MASTER-OAFA | (12h 37m 39.06s , -42d 07m 24.1s) | C | 60 | 19.1 | 23525 | 2026-04-05 06:28:43 | MASTER-OAFA | (12h 35m 41.78s , -40d 12m 31.0s) | C | 60 | 18.5 | 23585 | 2026-04-05 06:28:43 | MASTER-OAFA | (12h 35m 41.77s , -40d 12m 31.0s) | C | 180 | 19.5 | Coadd 23600 | 2026-04-05 06:29:59 | MASTER-OAFA | (12h 46m 10.91s , -40d 11m 40.1s) | C | 60 | 19.2 | 23676 | 2026-04-05 06:31:14 | MASTER-OAFA | (12h 35m 48.78s , -40d 12m 30.1s) | C | 60 | 19.2 | 23761 | 2026-04-05 06:32:39 | MASTER-OAFA | (12h 46m 18.29s , -40d 12m 02.0s) | C | 60 | 19.1 | 23837 | 2026-04-05 06:33:55 | MASTER-OAFA | (12h 35m 41.12s , -40d 12m 28.9s) | C | 60 | 19.1 | 23932 | 2026-04-05 06:35:30 | MASTER-OAFA | (12h 49m 34.20s , -47d 48m 23.1s) | C | 60 | 19.1 | 24013 | 2026-04-05 06:36:51 | MASTER-OAFA | (13h 01m 25.31s , -47d 50m 17.4s) | C | 60 | 19.1 | 24089 | 2026-04-05 06:38:07 | MASTER-OAFA | (12h 49m 34.19s , -47d 49m 47.0s) | C | 60 | 19.1 | 35699 | 2026-04-05 09:51:38 | MASTER-OAFA | (12h 18m 08.46s , -19d 48m 02.5s) | C | 60 | 16.7 | 35759 | 2026-04-05 09:51:38 | MASTER-OAFA | (12h 18m 08.45s , -19d 48m 02.5s) | C | 180 | 17.1 | Coadd 35765 | 2026-04-05 09:52:43 | MASTER-OAFA | (12h 18m 08.49s , -19d 48m 02.4s) | C | 60 | 16.6 | 35830 | 2026-04-05 09:53:49 | MASTER-OAFA | (12h 18m 08.48s , -19d 48m 02.4s) | C | 60 | 16.5 | 35896 | 2026-04-05 09:54:55 | MASTER-OAFA | (12h 18m 08.55s , -19d 48m 02.6s) | C | 60 | 16.5 | 35956 | 2026-04-05 09:54:55 | MASTER-OAFA | (12h 18m 08.55s , -19d 48m 02.7s) | C | 180 | 16.6 | Coadd 35962 | 2026-04-05 09:56:00 | MASTER-OAFA | (12h 18m 08.56s , -19d 48m 02.5s) | C | 60 | 16.4 | 36028 | 2026-04-05 09:57:06 | MASTER-OAFA | (12h 18m 08.63s , -19d 48m 02.7s) | C | 60 | 16.2 | 36095 | 2026-04-05 09:58:13 | MASTER-OAFA | (12h 18m 08.72s , -19d 48m 03.5s) | C | 60 | 16.0 | 36155 | 2026-04-05 09:58:13 | MASTER-OAFA | (12h 18m 08.72s , -19d 48m 03.6s) | C | 180 | 16.3 | Coadd 36160 | 2026-04-05 09:59:18 | MASTER-OAFA | (12h 18m 08.73s , -19d 48m 03.4s) | C | 60 | 16.0 | 36225 | 2026-04-05 10:00:24 | MASTER-OAFA | (12h 18m 08.80s , -19d 48m 03.7s) | C | 60 | 15.8 | 36291 | 2026-04-05 10:01:30 | MASTER-OAFA | (12h 18m 08.89s , -19d 48m 03.9s) | C | 60 | 15.7 | 36357 | 2026-04-05 10:02:35 | MASTER-OAFA | (12h 18m 08.96s , -19d 48m 04.3s) | C | 60 | 15.5 | 36423 | 2026-04-05 10:03:41 | MASTER-OAFA | (12h 18m 09.09s , -19d 48m 04.8s) | C | 60 | 15.3 | 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/44218. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42338] GRB 260403A: GECAM-B observation of a long burst
by GCN Circulars 05 Apr '26

05 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44217 SUBJECT: GRB 260403A: GECAM-B observation of a long burst DATE: 26/04/05 07:34:52 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260433A, at 2026-04-03T02:31:29.500 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44195) and AstroSat CZTI (A. Goyal et.al., GCN#44202). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 24.5 +3.0/-4.0 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260403A.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/44217. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42337] EP260324A / AT 2026hir: COLIBRÍ further optical observations
by GCN Circulars 05 Apr '26

05 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44216 SUBJECT: EP260324A / AT 2026hir: COLIBRÍ further optical observations DATE: 26/04/05 05:38:58 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Massimiliano Lincetto (CPPM), Rosa L. Becerra (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), 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), 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 observed AT2026hir/ZTF26aapviim, the optical counterpart (Anumarlapudi et al., GCN Circ. 44120, Stein et al., GCN Circ. 44194, Globus et al., GCN Circ. 44196) of EP260324a (Wu et al., Atel #17728), with the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-05 03:10 to 03:26 UTC (from 11.95 to 11.96 days after the discovery time reported in the TNS record and from 11.84 to 11.85 days after the EP trigger) and obtained 5 minutes of exposure in each of the g, r, i filters, and 15 minutes of simultaneous exposure in the z filter. The data were reduced and coadded 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 image, we detect the optical counterpart. The preliminary PSF-fitting magnitudes after performing image subtraction using PanSTARRS DR1 images as a template are: r = 18.01 +/- 0.01, z = 18.54 +/- 0.02. Compared to our previous observations from 2026-04-03 (Globus et al., GCN Circ. 44196), we see an apparently achromatic fading of: delta r = 0.28 +/- 0.01, delta z = 0.28 +/- 0.03. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/44216. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42336] Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
by GCN Circulars 04 Apr '26

04 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44215 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB DATE: 26/04/04 07:18:24 GMT FROM: Rushikesh Sonawane at IISER, TVM <rushikesh23(a)iisertvm.ac.in> R. Sonawane (IISER, TVM) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 796972356/260404217 at 05:12:31.90 UT on 04 April 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to Local Particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/44215. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42335] EP260403a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 04 Apr '26

04 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44214 SUBJECT: EP260403a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/04/04 06:09:17 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C.-Y. Dai (NJU), R.-Z. Li (YNAO), C.-L. Guo, and W.-D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260403a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Guo et al., GCN 44204). Optical follow-up of EP260403a revealed a fading counterpart, first identified by COLIBRÍ (Antier et al., GCN 44206) and subsequently confirmed by LCO (Pérez-Fournon et al., GCN 44207; Quirola-Vasquez et al., GCN 44209). The burst beginning at T0 = 2026-04-03 10:27:45 (UTC). The WXT observation lasted for approximately 50 seconds, and was interrupted due to the autonomous follow-up observation. The WXT light curve exhibits a single-peaked structure. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value of 5.6×10^20 cm^-2 and a photon index of 0.3 (-0.3/+0.3). The derived average unabsorbed flux in the 0.5-4 keV band is 1.6 (-0.3/+0.3) × 10^-9 erg s^-1 cm^-2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-04-03 10:33:22 (UTC, T0+337 s). The exposure time of this observation is 3.6 ks. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 219.1556, -25.5045 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value and a photon index of 1.94 (-0.02/+0.02). The derived average unabsorbed flux in the 0.5-10 keV band is 6.4 (-0.1/+0.1)×10^-11 erg s^-1 cm^-2. 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/44214. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42334] The EP-WXT trigger 01709259586 is likely a flaring star
by GCN Circulars 04 Apr '26

04 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44213 SUBJECT: The EP-WXT trigger 01709259586 is likely a flaring star DATE: 26/04/04 06:05:02 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q.Y. Wu, X.X. Sun, W. Chen (NAO,CAS), Y.J. Yi (BNU), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709259586 at the time of 2026-04-04T05:19:38, is likely a stellar flare associated with UCAC4 498-055345. The estimated flux of the flare is around 8 x 10^-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1 x 10^33 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/44213. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42333] GRB 260330B: SVOM/VT further optical observation
by GCN Circulars 04 Apr '26

04 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44212 SUBJECT: GRB 260330B: SVOM/VT further optical observation DATE: 26/04/04 05:24:23 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, 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. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed a second ToO observation 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 2026-04-03T12:56:07 UTC, approximately 3.94 days post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical candidate (Li et al., GCN 44205) was detected in VT_R. The measurements in AB magnitude are as follows: Mid time | Band | Exposure Time | Brightness 4.019 d VT_R 82*70 sec 22.7+/-0.2 mag 4.019 d VT_B 87*70 sec >24.0 mag Our photometry was in the AB magnitude and was not corrected for Galactic extinction. We note the current brightness may be contaminated by the catalogued extended source (Li et al., GCN 44205). Combined with our previous observations (Li et al., GCN 44205), the candidate brightened and then faded in our observations. Further observations are encouraged to confirm the nature of this source. 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/44212. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42332] Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44211 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB DATE: 26/04/03 19:38:24 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 796931884/260403749 at 17:57:59.85 UT on 03 April 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to charge particles. View this GCN Circular online at https://gcn.nasa.gov/circulars/44211. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42331] GRB 260330B: SVOM/ECLAIRs refined analysis
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44210 SUBJECT: GRB 260330B: SVOM/ECLAIRs refined analysis DATE: 26/04/03 19:30:32 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Authors: S. Guillot, M. Brunet, F. Triot, H. Yang, O. Godet, G. Lan (IRAP) report on behalf of the SVOM/ECLAIRs team Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260330B (SVOM burst-id sb26033003 – GCN 44157, trigger time T0 = 2026-03-30T14:19:57 UTC), which was also detected by Fermi GBM as a sub-threshold event (GCN 44159). The burst that triggered ECLAIRs onboard shows a multiple-peak lightcurve. The burst duration is T90 = 58.7 (+9.4)(-4.9) s s in the 4-120 keV energy band. The time-averaged spectrum from T0-23.0 s to T0+43.04 s in the energy range 4-120 keV is best fitted by a cutoff powerlaw model with alpha = -1.21 (+0.18)(-0.170), with Epeak = 24.9 (+11.5)(-8.8) keV. With this model, the 4-120 keV fluence is 1.32 (0.02)(-0.32) e-6 erg/cm^2 and the 4-120 keV photon flux is 0.85 +0.01/-0.14 ph/cm^2/s. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Sebastien Guillot (IRAP) (sebastien.guillot1 at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44210. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42330] EP260403a: LCO optical observations of the counterpart
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44209 SUBJECT: EP260403a: LCO optical observations of the counterpart DATE: 26/04/03 14:56:19 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> J. Quirola-Vasquez (Radboud), A. Martin-Carrillo (UCD), J. N. D. van Dalen (Radboud), 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 EP260403a (Guo et al., GCN 44204) with the LCO 1m telescope located at Siding Spring Observatory equipped with the SINISTRO instrument. We obtained 6 x 60 exposures in r-band, starting on 2026-04-03 at 12:19:37.245 UT (~1.84 hr post the EP trigger). In our stacked images, we detect the optical counterpart reported by Antier et al., GCN 44206 and Pérez-Fournon et al. GCN 44207 with an AB magnitude of r = 19.35 +/- 0.05, calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction. Our observations confirm that the counterpart is fading rapidly. View this GCN Circular online at https://gcn.nasa.gov/circulars/44209. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42329] GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44208 SUBJECT: GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring DATE: 26/04/03 13:30:44 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We have continued to observe the field of GRB 260310A 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) over the past week mainly in Rc and sdssr filters (One observation every night). Our last night observations were performed with a CDK17 telescope operated by M. Freeberg. Our observations started at TGRB+23.9 days and were taken with Rc filters. In our stacked frames, subtracted from the Legacy Survey DR10 template image, we still detect the optical counterpart reported by many teams (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; 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; Kang et al;, GCN 44119; Effress et al., GCN 44122; de Ugarte Postigo et al., GCN 44124; Guelfand et al. GCN 44125; O'Connor et al., GCN 44137; Liu et al., GCN 44172) We report our last 3 nights follow-up results in the table below: +------------------+-----------+-----------+----------------+--------------+ | Tmid-TGRB (days) | Exp (s) | Filter | Magnitude | Instrument | +==================+===========+===========+================+==============+ | 21.82 | 44 x 180s | Rc (Vega) | 19.92 +/- 0.12 | CDK17 | | 22.82 | 50 x 180s | Rc (Vega) | 20.01 +/- 0.15 | CDK17 | | 23.95 | 50 x 180s | Rc (Vega) | 20.22 +/- 0.12 | CDK17 | +------------------+-----------+-----------+----------------+--------------+ The KNC members will keep monitoring the source as long as it stays detectable. All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Johnson-Cousins filters were calibrated using the GAIA DR3 Synphot 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/44208. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[vsnet-grb-info 42318] GRB 260402C: AstroSat CZTI detection of a long burst
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44197 SUBJECT: GRB 260402C: AstroSat CZTI detection of a long burst DATE: 26/04/03 07:19:42 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), 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 260402C. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-04-02 13:13:05.78 UTC. The measured peak count rate associated with the burst is 254 (+34, -26) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1786 (+230, -307) counts. The local mean background count rate was 210 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 27 (+4, -3) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-04-02 13:13:05.08 UTC. The measured peak count rate associated with the burst is 570 (+82, -42) counts/s above the background in the combined data of all quadrants, with a total of 3647 (+569, -635) counts. The local mean background count rate was 1405 (+6, -7) counts/s. We measure a T90 of 25 (+4, -1) s from the cumulative Veto light curve. 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/44197. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42317] EP260324A / AT 2026hir: COLIBRÍ optical observations
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44196 SUBJECT: EP260324A / AT 2026hir: COLIBRÍ optical observations DATE: 26/04/03 05:33:45 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Sarah Antier (IJCLAB), Rosa L. Becerra (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), 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), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We observed AT2026hir/ZTF26aapviim, the optical counterpart (Anumarlapudi et al., GCN Circ. 44120, Stein et al., GCN Circ. 44194) associated to EP260324a (Wu et al., Atel #17728) with the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-03 03:09:08 to 03:26:20 UTC (from 9.95 to 9.96 days after the discovery time reported in the TNS entry and from 9.84 to 9.85 days after the EP trigger) and obtained 5 minutes of exposure in the g, r, i filters, and 15 minutes of simultaneous exposure in the z filter. In the stacked image, we detect the optical counterpart. The data were reduced and coadded 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. The preliminary PSF magnitudes revealed after performing image subtraction using PanSTARRS DR1 as template are: r = 17.73 +/- 0.01, z = 18.26 +/- 0.02. 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/44196. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42316] GRB 260403A: Fermi GBM Final Real-time Localization
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44195 SUBJECT: GRB 260403A: Fermi GBM Final Real-time Localization DATE: 26/04/03 02:41:58 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 02:31:27 UT on 3 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260403A (trigger 796876292.704364 / 260403105). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 236.2, Dec = -31.0 (J2000 degrees, equivalent to J2000 15h 44m, -31d 00'), with a statistical uncertainty of 5.0 degrees. The angle from the Fermi LAT boresight is 86.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260403105/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260403105/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260403105/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44195. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42315] EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44194 SUBJECT: EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph DATE: 26/04/03 00:03:49 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Robert Stein (UMD/JSI/NASA GSFC), Kaustav Das (Caltech), Christoffer Fremling (Caltech), Tomas Ahumada (NOIRLab), Akash Anumarlapudi (UNC CH), Ryan Chornock (UC Berkeley),Michael C. Davis (UMN), K-Ryan Hinds (Caltech), Mansi Kasliwal (Caltech), Jillian Rastinejad (UMD), Gokul Srinivasaragavan (UMD) and Yuhan Yao (UC Berkeley) report, on behalf of the ZTF collaboration: We observed AT2026hir/ZTF26aapviim, the optical counterpart (Anumarlapudi et al, GCN #44120) to EP260324A (Wu et al., ATEL #17728), with the Next Generation Palomar Spectrograph (NGPS; AstroNote 2024-340) on the Palomar 5.1m Hale Telescope (P200). Our observations began on 2026-03-27T03:51:37 (~3 days after the EP trigger), and data were reduced using the standard NGPS pipeline. The spectrum was extremely blue, as also noted by Zhu et al. (Astronote #2026-87). From our spectrum, in addition to the continuum, we see an excess that would be consistent with broad He II with a velocity of ~15000 km / s. However, we have not performed host galaxy subtraction, and we caution that the SNR is insufficient to be certain whether this broad feature is real. In any case, given the nuclear location (GCN #44120) and blue spectrum which is either featureless or has broad He, our observations would be consistent with a TDE-F or TDE-He classification for this source. However, we plan for and encourage additional multi-wavelength observations to secure the classification. The transient is bright (mg=17.3 in the latest ZTF data), so remains accessible to a wide variety of ground-based telescopes. View this GCN Circular online at https://gcn.nasa.gov/circulars/44194. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42314] GRB 260402B: Fermi GBM Final Real-time Localization
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44193 SUBJECT: GRB 260402B: Fermi GBM Final Real-time Localization DATE: 26/04/02 23:07:38 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 22:57:17 UT on 2 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260402B (trigger 796863442.54282 / 260402956). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 238.4, Dec = 0.2 (J2000 degrees, equivalent to J2000 15h 53m, 0d 12'), with a statistical uncertainty of 11.4 degrees. The angle from the Fermi LAT boresight is 72.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260402956/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260402956/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260402956/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44193. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42313] GRB 260402A: WINTER J-band upper limit
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44192 SUBJECT: GRB 260402A: WINTER J-band upper limit DATE: 26/04/02 18:08:21 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Geoffrey Mo (Caltech/Carnegie), Robert Stein (UMD), Viraj Karambelkar (Columbia), Tomas Ahumada (NOIRLab), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 260402A detected by SVOM/ECLAIRs (Tan et al., GCN 44181) and EP/WXT (Zhao et al., GCN Circ. 44186) 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 2026-04-02 at 10:58:52 UT (28.58 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) 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 position (Zhao et al., GCN Circ. 44186) or MXT position (Gotz et al., GCN Circ. 44182) and derive the following 5-sigma upper limit: J > 18.9 Our upper limit is consistent with previously reported optical upper limits from Antier et al. (GCN Circ. 44183), Carrasco et al. (GCN Circ. 44184), Freeberg et al. (GCN Circ. 44185), Wu et al. (GCN Circ. 44189), Li et al. (GCN Circ. 44190), and Vijaykumar et al. (GCN Circ. 44191). 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/44192. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42312] GRB260402A: GROWTH-India Telescope optical upper limit
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44191 SUBJECT: GRB260402A: GROWTH-India Telescope optical upper limit DATE: 26/04/02 17:45:27 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Vijaykumar, A. Khade, R. Arya, V. Swain, S. Patil, A.P. Saikia, T. Mohan, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team: We observed the field of GRB260402A detected by SVOM/ECLAIRs (SVOM, GCN 44181), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-04-02 14:10:35 (UTC), i.e., 3.65 hours after the trigger, and obtained multiple exposures in the r' filter. We do not detect any transient in our image within the uncertainty region of source position reported by ECLAIRs and MXT (Tan et al., GCN Circ. 44181, Gotz et al., GCN Circ.44182). The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Magnitude (AB) | | ------------ | ------ | -------------- | ------------------- | -------------- | | 61132.590| r' | 3.92 | 5x360 | 20.5 | 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 (GCN 44190 Li et al.; GCN 44189 Wu et al.; GCN 44185 Freeberg et al.; GCN 44184 Carrasco et al.; GCN 44183 Antier et al.) 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/44191. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42311] GRB 260402A / EP260402a: SVOM/VT optical upper limits
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44190 SUBJECT: GRB 260402A / EP260402a: SVOM/VT optical upper limits DATE: 26/04/02 16:30:34 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, Y. L. Qiu, L. P. Xin, Y. N. Ma, Z. H. Yao, 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. Palmerio (CEA/Irfu), W. Tan (IHEP) and R. Li (YNAO) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic slew to the field of GRB 260402A triggered by SVOM/ECLAIRs (sb26032123, Tan et al., GCN 44181), SVOM/GRM (Tan et al., GCN 44181) and Einstein Probe (EP260402a, Zhao et al., GCN 44186). The observation started at 2026-04-02T10:44:07 UTC, approximately 13.8 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued sources are detected in single or stacked images within the error box of SVOM/MXT (Gotz et al., GCN 44182) or EP-FXT (Zhao et al., GCN 44186), compared to the Legacy Survey. The 3-sigma limit magnitudes are VT_B ~ 23.1 mag and VT_R ~ 23.0 mag at 31.3 minutes post trigger. Our result is consistent with the non-detection reports from SVOM/COLIBRÍ (Antier et al., GCN 44183), MASTER (Carrasco et al., GCN 44184), Kilonova-Catcher (Freeberg et al., GCN 44185) and SVOM/C-GFT (Wu et al., GCN 44189). Given the early optical non-detection, near-infrared follow-up observations are encouraged. 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/44190. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42310] EP260402a/GRB 260402A: SVOM/C-GFT upper limit
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44189 SUBJECT: EP260402a/GRB 260402A: SVOM/C-GFT upper limit DATE: 26/04/02 15:30:47 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), Z. Kang (CHO), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC) , W. Tan, R. Li (IHEP) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 260402A (SVOM burst-id sb26040203) detected by SVOM/ECLAIRs (Tan et al., GCN 44181) with LATIOS on SVOM/C-GFT. Observations started at 2026-04-02T12:50:51 UTC, ~2.34 hr after the trigger. We obtained i-band follow-up imaging. After preliminary analysis，no credible candidate was detected within the error box provided by SVOM/MXT (Gotz et al., GCN 44182) and EP/MXT (Zhao et al., GCN 44186) in our stacked image. The 3-sigma upper limit is: | Mid_t - T0 (hr) | Exposure Time (s) | Band | Upper Limit (AB) | |----------------|-------------------|------|------------------| | 2.69 | 30×30 | i | 19.0 | The photometry was calibrated against Pan-STARRS1 stars and no correction for Galactic dust extinction was applied. This result is consistent with Antier et al. (GCN 44183) and Freeberg et al.(GCN 44185). We thank the observation assistants Ying-huai Hao and Chun-lei Guo at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/44189. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42309] GRB 260401A: SVOM/GRM observation
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44188 SUBJECT: GRB 260401A: SVOM/GRM observation DATE: 26/04/02 15:06:11 GMT FROM: renyz16607(a)163.com SVOM/GRM team: Yang-Zhao Ren, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, 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 GRB 260401A (SVOM trigger reference: sb26040101) at 2026-04-01T10:53:33.600 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44174), MAXI/GSC (Usuki et. al., GCN #44176), CALET/GBM (Cannady et al., GCN #44177), NuSTAR (Waratkar et al., GCN #44178), and GECAM-B (Ren et al., GCN #44187). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 24 +2/-2 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260401A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 219.5, Dec = -17.4, GCN #44174), is located at about 74 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst still clearly detected by ECLAIRs through the shield. With this localization, the time-averaged spectrum from T0-10 to T0+10 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.64 +0.06/-0.06 and the cutoff energy, parameterized as Epeak, is 321 +141/-77 keV. The event fluence (10-1000 keV) in this time interval is (1.44 +0.06/-0.07)E-05 erg/cm^2. The 1s peak spectrum, measured from T0-0.1 to T0+0.9 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.26 +0.07/-0.07 and the cutoff energy, parameterized as Epeak, is 391 +84/-59 keV. The flux (10-1000 keV) in this time interval is (3.28 +0.14/-0.15)E-06 erg/cm^2/s. The localization of GRB 260401A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260401A_amati.png The localization of GRB 260401A in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260401A_yonetoku.png 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: Yang-Zhao Ren (IHEP)(renyz(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44188. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42308] GRB 260401A: GECAM-B observation
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44187 SUBJECT: GRB 260401A: GECAM-B observation DATE: 26/04/02 15:01:22 GMT FROM: renyz16607(a)163.com Yang-Zhao Ren, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 260401A, at 2026-04-01T10:53:29.200 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44174), MAXI/GSC (Usuki et. al., GCN #44176), CALET/GBM (Cannady et al., GCN #44177), and NuSTAR (Waratkar et al., GCN #44178). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 28.8 +0.1/-0.2 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260401A.png The time-averaged spectrum from T0 to T0 + 15 s is best fitted by a power law function. The power law index is -1.51 +0.08/-0.07. The event fluence (10-1000 keV) in this time interval is (2.20 +0.11/-0.10) E-05 erg/cm^2. 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/44187. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42307] EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44186 SUBJECT: EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient DATE: 26/04/02 14:16:37 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: 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 EP260402a. The transient triggered EP-WXT (ID: 01709259488) at 2026-04-02T10:30:41 (UTC). The WXT position of the source is R.A. = 170.994 deg, DEC = 63.604 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). EP260402a is temporally and spatially consistent with GRB 260402A (GCN #44181). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically triggered by SVOM GRB detection, began at 2026-04-02T12:55:33Z. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 170.9607 deg, DEC = 63.6128 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/44186. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42306] GRB 260402A: Kilonova-Catcher optical upper limit
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44185 SUBJECT: GRB 260402A: Kilonova-Catcher optical upper limit DATE: 26/04/02 13:09:54 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (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 260402A detected by SVOM/ECLAIRs (Tan et al., GCN 44181) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+20.8 min and were taken with the sdssr filter. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we do not detect any optical counterpart in the SVOM/ECLAIRs error radius. We report our follow-up results in the table below: +----------------+----------+---------+---------------+--------------+ | Tmid-TGRB (min)| Exp (s) | Filter | Magnitude | Instrument | +================+==========+=========+===============+==============+ | 29.97 | 5 x 180s | r (AB) | 19.5 (5 sigma)| TEC160FL | +----------------+----------+---------+---------------+--------------+ 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/44185. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42305] GRB 260402A: MASTER optical observations
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44184 SUBJECT: GRB 260402A: MASTER optical observations DATE: 26/04/02 12:22:04 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez, A.R.Corella, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) V.Lipunov, A.Kuznetsov, I.Panchenko, P.Balanutsa, G.Antipov, E.Gorbovskoy, N.Tiurina, V.Senik, A.Chasovnikov, Ya.Kechin, V.Topolev, D.Vlasenko, A.Sankovich,Yu.Tselik (Lomonosov MSU), M.J. Segura, C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), N.Budnev, O.Gress (ISU), A.Sosnovskij (CrAO), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) MASTER-OAGH robotic telescope of MASTER Global Robotic Net [1-4] started SVOM GRB 260302A (Tan et al. GCN 44181, Gotz et al. GCN 44182 Ttrigger=2026-04-02 10:30:17UT) at 2026-04-02 10:55:46UT (25min after trigger time) with m_lim=19.1m(unfiltered) at 1st image. We didn't find new object inside error-box at single images.Observations and reduction will be continued. Error-box altitude was 34deg, the sun_alt=-28deg, the FULL moon (0.99) alt=27deg (in 75 deg from erro-box) Cover map is available here https://master.sai.msu.ru/site/master2/event.php?id=3227188 [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/44184. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42304] GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44183 SUBJECT: GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 26/04/02 12:17:52 GMT FROM: antier(a)ijclab.in2p3.fr Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), 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), 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), Antonio de Ugarte Postigo (LAM), W. Tan (IHEP), R. Li (IHEP) report: We imaged the field of the SVOM GRB 260402A (Tan et al., GCN Circ. 44181) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-04-02 10:37:04 to 11:52:05 UTC (from 7 minutes after the trigger) and obtained about 45 min of exposure in the r/z filters. The data were reduced and coadded with the ASU and Colibri 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 image, we do not detect any new source at the ECLAIRs and MXT source position (Tan et al., GCN Circ. 44181, Gotz et al., GCN Circ.44182) and down to the following 3-sigma limit: r > 22.6 z > 22.0 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/44183. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42303] GRB 260402A: SVOM/MXT candidate X-ray afterglow
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44182 SUBJECT: GRB 260402A: SVOM/MXT candidate X-ray afterglow DATE: 26/04/02 11:12:18 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Gotz (CEA Saclay) on behalf of the SVOM MXT team reports: MXT observed the field of GRB 260402A at 10:53:24 U.T., about 23 minutes after the ECLAIRs trigger. The automatic on board software detects a faint source at R.A.= 170.806 deg (J2000) Dec.= +63.627 deg (J2000) with a R90 uncertainty (incdluding systematics) of 114 arc sec. This position is at 4.7 arc min from the ECLAIRs position reported by Tan et al. (GCN 44181). Further data will be needed to confirm the afterglow nature of this candidate source. 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 Wenjun Tan: tanwj at ihep.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44182. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42302] GRB 260402A: SVOM detection of a burst
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44181 SUBJECT: GRB 260402A: SVOM detection of a burst DATE: 26/04/02 10:51:18 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W. Tan, R. Li (IHEP), M. Brunet, O. Godet (IRAP), D. Gotz (CEA), report on behalf of the SVOM mission team: At 2026-04-02T10:30:17 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260402A (SVOM burst-id sb26040203). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 17 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 18.74 in the [5-20] keV energy band over a time window of 10.20 seconds starting at 2026-04-02T10:30:17. The localization of the best alert is R.A., Dec. 170.982, 63.622 degrees: R.A. (J2000) = 11h23m55s Dec. (J2000) = 63d37m18s with a 90% confidence level (C.L.) radius of 4.57 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a broad peak structure with a T90 duration of 15.17 (-1.27 / +5.86) s in the 5-120 keV energy band. This burst was also detected by SVOM/GRM with a significance of 7.20. SVOM slewed to the burst. No prompt X-ray observation could be performed by SVOM/MXT for the time being. VT began observing the field after the slew. The analysis of the data will be published in a future circular. 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 Wenjun Tan: tanwj at ihep.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44181. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42301] Fermi GRB 260401A: Global MASTER-Net observations report
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44180 SUBJECT: Fermi GRB 260401A: Global MASTER-Net observations report DATE: 26/04/02 06:00:50 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 260401A ( Fermi GBM team, GCN 44174) errorbox 63483 sec after notice time and 63518 sec after trigger time at 2026-04-02 04:32:04 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 29 deg. The sun altitude is -63.7 deg. The galactic latitude b = 38 deg., longitude l = 337 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3225119 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 33732 | 2026-04-01 20:15:08 | MASTER- | (14h 42m 26.86s , -15d 41m 21.2s) | C | 60 | 12.9 | 63549 | 2026-04-02 04:32:04 | MASTER-OAFA | (14h 25m 14.66s , -15d 38m 17.7s) | C | 60 | 18.4 | 63609 | 2026-04-02 04:32:04 | MASTER-OAFA | (14h 25m 14.66s , -15d 38m 17.8s) | C | 180 | 19.0 | Coadd 63624 | 2026-04-02 04:33:19 | MASTER-OAFA | (14h 25m 11.96s , -15d 36m 34.5s) | C | 60 | 18.3 | 63700 | 2026-04-02 04:34:36 | MASTER-OAFA | (14h 25m 12.06s , -15d 37m 47.2s) | C | 60 | 18.4 | 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/44180. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42300] GRB 260401A: Fermi GBM Observation
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44179 SUBJECT: GRB 260401A: Fermi GBM Observation DATE: 26/04/01 23:33:42 GMT FROM: Daniel Fernandez at University of Alabama In Huntsville (UAH) <df0062(a)uah.edu> D. Fernandez (UAH), M. Dafčíková (MUNI) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 10:53:26.00 UT on 01 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260401A (trigger 796733611/260401454), which was also detected by MAXI (T. Usuki et al. 2026, GCN 44176). The Fermi GBM on-ground location (GCN 44174) is consistent with the MAXI position. The angle from the Fermi LAT boresight is 60 degrees. The GBM light curve consists of a bright emission episode with multiple peaks with a duration (T90) of about 27 s (50-300 keV). The time-averaged spectrum from T0-0.8 to T0+32.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.78 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 239 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (1.80 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+7.5 s in the 10-1000 keV band is 21.1 +/- 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/44179. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42299] GRB 260401A: NuSTAR detection of prompt emission
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44178 SUBJECT: GRB 260401A: NuSTAR detection of prompt emission DATE: 26/04/01 23:21:40 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 260401A 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 2026-04-01 10:53:26.0 UTC, shows a detection of GRB 260401A, consistent with Fermi/GBM (Fermi GBM team, GCN Circ. 44174, MAXI/GSC (Usuki et al., GCN Circ. 44176), CALET/GBM (Cannady et al., GCN Circ. 44177) and SVOM/GRM (GCN Notices). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single peak lasting for ~10-s which is consistent with the bright part of the burst as seen in the GBM lightcurve. The peak count rate is ~3000-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 CZT detectors. The GBM localization (GCN Circular 44174) at RA = 219.5, Dec = -17.4 implies an offset from the NuSTAR boresight of 42-deg (i.e. from the side of the instrument) and an offset from the geocenter of 73-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260401A/ 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/44178. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42298] GRB 260401A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44177 SUBJECT: GRB 260401A: CALET Gamma-Ray Burst Monitor detection DATE: 26/04/01 16:20:41 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> N. Cannady (GSFC), 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, T. Tamura (Kanagawa U), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 260401A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 44174; BALROG localization: Preis et al., GCN Circ 44175; MAXI/GSC detection: Usuki et al., GCN Circ 44176) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 10:53:31.52 UTC on 1 April 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1459075956/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a single pulse that starts at T+1.4 sec, peaks at T+2.2 sec, and ends at T+6.3 sec. The T90 and T50 durations measured by the SGM data are 4.4 +/- 0.6 sec and 2.0 +/- 0.3 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1459075956 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/44177. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42297] GRB 260401A: MAXI/GSC detection
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44176 SUBJECT: GRB 260401A: MAXI/GSC detection DATE: 26/04/01 14:47:29 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> T. Usuki (Ehime U.), K. Fujiwara (Kyoto U.), M. Serino, Y. Kawakubo (AGU), M. Nakajima, H. Negoro, K. Takagi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, Y. Kondo, D. Iijima, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto, M. Uenishi, S. Yatsuzuka (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 10:53:19 UT on 2026 April 1. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (219.942 deg, -17.349 deg) = (14 39 46, -17 20 56) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.06 deg and 0.02 deg, respectively. The roll angle of long axis from the north direction is 15.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 5700 +- 200 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (R.A., Dec) = (220.028, -17.391) deg = (14 40 06, -17 23 27) (J2000) (R.A., Dec) = (220.046, -17.270) deg = (14 40 11, -17 16 11) (J2000) (R.A., Dec) = (219.512, -17.198) deg = (14 38 02, -17 11 52) (J2000) (R.A., Dec) = (219.494, -17.319) deg = (14 37 58, -17 19 08) (J2000) There was no significant excess flux in the previous transit at 09:20 UT and in the next transit at 12:26 UT with an upper limit of 20 mCrab for each. This event is spatially and temporally consistent with GRB 260401A, which was also detected by Fermi/GBM (GCN #44174, #44175). View this GCN Circular online at https://gcn.nasa.gov/circulars/44176. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42296] GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44175 SUBJECT: GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454) DATE: 26/04/01 12:11:04 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 796733611 at 10:53:26 on 01 April 2026 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 220.7 deg Decl.(2000.0) = -16.9 deg The 1 sigma statistical error radius is 1.3 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260401454/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260401454/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260401454/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44175. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42295] GRB 260401A: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44174 SUBJECT: GRB 260401A: Fermi GBM Final Real-time Localization DATE: 26/04/01 11:02:02 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 10:53:26 UT on 1 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260401A (trigger 796733611.002678 / 260401454). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 219.5, Dec = -17.4 (J2000 degrees, equivalent to J2000 14h 37m, -17d 23'), with a statistical uncertainty of 1.6 degrees. The angle from the Fermi LAT boresight is 60.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260401454/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260401454/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260401454/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44174. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42294] EP260329b: Mondy and Assy-Turgen optical upper limits
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44173 SUBJECT: EP260329b: Mondy and Assy-Turgen optical upper limits DATE: 26/04/01 09:25:28 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), E. Klunko (ISTP), D. Anarbek (FAI), M. Krugov (FAI), A. Pozanenko (IKI), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP260329b (Song et al., GCN 44142; EP Team, GCN 44155) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) taking several 40-second expositions in R-band, and with the AZT-20 telescope of Assy-Turgen observatory taking several 30-second exposures in r' filter on Mar. 29. In the stacked frames we do not detect the optical counterpart reported previously (Li et al., GCN 44139; Zhu et al., GCN 44140; Eyles-Ferris et al., GCN 44144; Aryan et al., GCN 44147; Lipunov et al., GCN 44150; Mo et al., GCN 44163; O'Neill et al., GCN 44169). Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-03-29 15:24:19 0.22110 90*40 R n/d n/d 21.1 Mondy/AZT-33IK 2026-03-29 19:57:04 0.40444 80*30 r n/d n/d 21.6 Assy-Turgen/AZT-20 The photometry is based on several nearby stars from the SDSS-DR16 catalogue (Lupton transformations were used for the R-band values) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44173. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42293] GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44172 SUBJECT: GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng DATE: 26/04/01 07:07:05 GMT FROM: Y.C. Kang at Peking University <yckang(a)stu.pku.edu.cn> Zhuokai Liu, Zexuan Wu, Chenxi Bao, Yacheng Kang (PKU) report on behalf of the Interestar Collaboration and the PKU HiTF (High-energy Transients Follow-up) group: We observed the field of GRB 260310A, detected by Fermi/GBM (GCN 43951; T0 = 2026-03-10T04:57:10.81) and AstroSat/CZTI (Salunke et al., GCN 43958), using a 28cm optical telescope located in Daocheng, Sichuan, China. Observations began on 2026 Mar 17, approximately ~ 7.4 days after the GRB trigger, and spanned six epochs in the Luminance filter. In the stacked Luminance-band images, we detect the optical counterpart at a position consistent with AT2026fgk, the reported GRB afterglow candidate at z = 0.153 (O'Neill et al. 2026, TNS Discovery Report 294132; Hinds et al., AstroNote 2026-65; Konno et al., GCN 43974; Hinds et al., GCN 43977), later found to show Type Ic-BL SN features (de Ugarte Postigo et al., GCN 44124; Guelfand et al., GCN 44125; O'Connor et al., GCN 44137). Preliminary photometry was calibrated using nearby catalogued field stars and is reported as approximate AB-equivalent magnitudes, without correction for Galactic extinction. Our measurements show that the optical counterpart continues to fade, from ~ 19.0 mag to ~ 19.8 mag between 7.4 and 14.3 days after the GRB trigger. The observation log is summarized below: | Date | Start_UT | T_mid - T0 (days) | Filter | Exposure (s) | Magnitude (AB) | | :--------: | :------: | :---------------: | :-------: | :----------: | :------------: | | 2026-03-17 | 13:28:40 | 7.40 | Luminance | 7400 | 19.02 +/- 0.04 | | 2026-03-18 | 13:52:51 | 8.42 | Luminance | 7600 | 19.10 +/- 0.04 | | 2026-03-19 | 14:14:50 | 9.42 | Luminance | 6000 | 19.18 +/- 0.04 | | 2026-03-20 | 12:37:02 | 10.36 | Luminance | 7400 | 19.39 +/- 0.04 | | 2026-03-21 | 12:39:41 | 11.35 | Luminance | 5000 | 19.65 +/- 0.05 | | 2026-03-24 | 12:33:31 | 14.33 | Luminance | 2200 | 19.84 +/- 0.08 | Further analysis and follow-up observations are ongoing. The 28cm optical telescope is located in Daocheng, Sichuan, China, and is operated by the Interestar Collaboration. 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/44172. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42292] EP260321a :Xinglong optical observations
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44171 SUBJECT: EP260321a :Xinglong optical observations DATE: 26/04/01 05:05:57 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Yu-Zhang(NAOC), Junjie-Jin(NAOC), Haiyang-Mu(NAOC), Yuguang-Sun(NAOC), Pengliang-Du (NAOC), Jie-Zheng(NAOC), Zhou-Fan(NAOC), Hong-Wu(NAOC) report on behalf of a large collaboration: We performed optical observations of the field of a fast X-Ray transient EP260321a(Q.J. Huang et al., GCN 44068) in the g, r and i filter using Tsinghua-NAOC 0.8-m telescope (TNT) located at Xinglong, Hebei, China. A series of 300-s exposures were obtained on three epochs (March 25, 26, and 27, 2026), with the first observation at 2026-03-25T14:37:57, approximately 4 days after the EP FXT trigger (2026-03-21T12:30:18). We measure a preliminary magnitude calibrated against nearby stars from the Pan-STARRS catalog. We summarize our observation results as follows: Obs. No. | Time (UTC) | Exposure Time (s) | Filter | Apparent mag (AB) | Telescope Name 1 | 2026-03-25T14:37:57 | 300 s | g |17.70 +/- 0.24| Tsinghua-NAOC 0.8-m telescope (TNT) 2 | 2026-03-25T14:53:18 | 300 s | r |17.69 +/- 0.20| Tsinghua-NAOC 0.8-m telescope (TNT) 3 | 2026-03-25T15:08:39 | 300 s | i |17.42 +/- 0.25| Tsinghua-NAOC 0.8-m telescope (TNT) 4 | 2026-03-26T16:00:16 | 300 s | g |17.17 +/- 0.24| Tsinghua-NAOC 0.8-m telescope (TNT) 5 | 2026-03-26T16:15:37 | 300 s | r |17.30 +/- 0.23| Tsinghua-NAOC 0.8-m telescope (TNT) 6 | 2026-03-26T16:40:01 | 300 s | i |17.38 +/- 0.30| Tsinghua-NAOC 0.8-m telescope (TNT) 7 | 2026-03-27T13:25:21 | 300 s | g |16.61 +/- 0.01| Tsinghua-NAOC 0.8-m telescope (TNT) 8 | 2026-03-27T13:40:42 | 300 s | r |16.53 +/- 0.01| Tsinghua-NAOC 0.8-m telescope (TNT) 9 | 2026-03-27T13:56:03 | 300 s | i |16.43 +/- 0.02| Tsinghua-NAOC 0.8-m telescope (TNT) View this GCN Circular online at https://gcn.nasa.gov/circulars/44171. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42291] EP260327a: Xinglong optical upper limit
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44170 SUBJECT: EP260327a: Xinglong optical upper limit DATE: 26/04/01 04:32:23 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Yu-Zhang(NAOC), Junjie-Jin(NAOC), Haiyang-Mu(NAOC), Junjun-Jia(NAOC), Jie-Zheng(NAOC), Zhou-Fan(NAOC), Hong-Wu(NAOC) report on behalf of a large collaboration: Following the detection of EP260327a by EP-WXT (C. Y. Dai, GCN 44126), we observed the field of EP260327a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 6x300s clear-band frames with a median time of 2026-03-27T14:06:25 i.e., 8.2 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 20 arcsec EP/FXT error circle (C. Y. Dai, GCN 44126), down to 3-sigma limiting magnitudes of clear ~ 20.87 mag, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/44170. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42290] EP260329b: GOTO detection of optical counterpart
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44169 SUBJECT: EP260329b: GOTO detection of optical counterpart DATE: 26/03/31 17:39:44 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, R. Starling, A. Kumar, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Gompertz, 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) in response to the EP/WXT alert EP260329b (Song et al; GCN 44142). We detect the counterpart candidate previously reported (Li et al., GCN 44139; Eyles-Ferris et al., GCN 44144; Magnani et al., GCN 44146; Aryan et al., GCN 44147; Lipunov et al., GCN 44150) with an L-band magnitude of 18.73 ± 0.09 AB mag (+0.74h) at 2026-03-29 11:20:38 UT. We find no evidence of the source prior to the GRB trigger time in previous GOTO observations taken at 2026-03-28 11:41:26 (-22.91h) down to a 3-sigma depth of L>20.10 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/44169. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42289] GRB 260330B: SVOM/VT optical upper limits
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44168 SUBJECT: GRB 260330B: SVOM/VT optical upper limits DATE: 26/03/31 15:25:54 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), G. X. Lan, S. Guillot (IRAP) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic slew to the field of GRB 260330B detected by SVOM/ECLAIRs and SVOM/GRM (sb26033003, Lan et al., GCN 44157). It was also a sub-threshold detection by Fermi/GBM (Trigg et al., GCN 44159). The observation started at 2026-03-30T15:06:18 UTC, i.e., about 46 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 (Lan et al., GCN 44157), compared to the Legacy Survey. The 5 sigma upper limits in AB magnitude are derived as follows: Mid time | Band | Exposure Time | 5 sigma upper limit 1.03 hour VT_B 38*50 sec > 22.7 mag 1.00 hour VT_R 34*50 sec > 22.5 mag Our photometry was in AB magnitude and was not corrected for Galactic extinction. This result is consistent with the nondetection report by LCO (Turpin et al., GCN 44158). More detailed analysis is 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/44168. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42288] Konus-Wind detection of GRB 260320A
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44167 SUBJECT: Konus-Wind detection of GRB 260320A DATE: 26/03/31 13:34:05 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260320A (NuSTAR detection: Waratkar et al., GCN 44064, Insight-HXMT/HE detection: Luo et al., GCN 44077, Glowbug gamma-ray detection: Cheung et al., GCN 44093, GRID detection: Li et al., GCN 44109, IPN triangulation: Kozyrev et al., GCN 44121) triggered Konus-Wind at T0=70801.257 s UT (19:40:01.257). The burst light curve shows a single pulse which starts at ~T0-0.4 s and has a total duration of ~13.1 s. The emission is seen up to ~1 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260320_T70801/ As observed by Konus-Wind, the burst had the total fluence of 1.88(-0.20,+0.19)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+0.896 s, of 6.92(-0.78,+0.80)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+16.640 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.18(-0.10,+0.10), the high energy photon index beta = -2.44(-0.43,+0.18), the peak energy Ep = 267(-32,+45) keV (chi2 = 86/91 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.33(-0.06,+0.06) and Ep = 359(-36,+44) keV (chi2 = 82/77 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.29 (chi2 = 82/76 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44167. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42287] Konus-Wind detection of GRB 260316B
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44166 SUBJECT: Konus-Wind detection of GRB 260316B DATE: 26/03/31 13:32:31 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260316B (Fermi-GBM detection: The Fermi GBM team, GCN 44031; AstroSat CZTI detection: Harsha et al., GCN 44035, SVOM/GRM detection: Wang et al., GCN 44039, GECAM-B detection: Wang et al., GCN 44040, CALET-GBM detection: Tamura et al., GCN 44100, IPN triangulation: Kozyrev et al., GCN 44111) triggered Konus-Wind at T0=61972.457 s UT (17:12:52.457). The burst light curve shows a single pulse which starts at ~T0-0.9 s and has a total duration of ~2.5 s. The emission is seen up to ~5 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260316_T61972/ As observed by Konus-Wind, the burst had the total fluence of 2.66(-0.45,+0.56)x10^-6 erg/cm2, and the 64-ms peak flux, measured from T0+0.230 s, of 2.87(-0.74,+0.85)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.24(-0.65,+0.76), the high energy photon index beta = -2.64(-7.36,+0.34), the peak energy Ep = 123(-22,+58) keV (chi2 = 64/77 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44166. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42286] Konus-Wind detection of GRB 260316B
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44165 SUBJECT: Konus-Wind detection of GRB 260316B DATE: 26/03/31 13:32:29 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260316B (Fermi-GBM detection: The Fermi GBM team, GCN 44031; AstroSat CZTI detection: Harsha et al., GCN 44035, SVOM/GRM detection: Wang et al., GCN 44039, GECAM-B detection: Wang et al., GCN 44040, CALET-GBM detection: Tamura et al., GCN 44100, IPN triangulation: Kozyrev et al., GCN 44111) triggered Konus-Wind at T0=61972.457 s UT (17:12:52.457). The burst light curve shows a single pulse which starts at ~T0-0.9 s and has a total duration of ~2.5 s. The emission is seen up to ~5 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260316_T61972/ As observed by Konus-Wind, the burst had the total fluence of 2.66(-0.45,+0.56)x10^-6 erg/cm2, and the 64-ms peak flux, measured from T0+0.230 s, of 2.87(-0.74,+0.85)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.24(-0.65,+0.76), the high energy photon index beta = -2.64(-7.36,+0.34), the peak energy Ep = 123(-22,+58) keV (chi2 = 64/77 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44165. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42285] GRB 260321A: SVOM/ECLAIRs refined analysis
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44164 SUBJECT: GRB 260321A: SVOM/ECLAIRs refined analysis DATE: 26/03/31 12:06:20 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O.Godet, F. Triot, J.-L. Atteia (IRAP), report on behalf of the SVOM/ECLAIRs team Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260321A (SVOM burst-id sb26032123 – GCN 44071, trigger time T0 = 2026-03-21T18:12:08 UTC), which was also detected by Fermi/GBM as a sub-threshold event (GCN 44072). The burst that triggered ECLAIRs onboard shows a single peak lightcurve, followed by a featureless emission tail. The burst duration is estimated to be around 57 s in the 4-50 keV energy band through imaging. The ECLAIRs light curve can be found here: https://docs.google.com/document/d/1aA9Ams6NNpz7RKQksAyu6mulcFsYo2OPOXFnpyy… The time-averaged spectrum from T0-16 s to T0+34.92 s in the 5-120 keV energy range is best fitted by a broken power-law model with a first photon index of -0.65 +0.32/-0.25, a second photon index of -2.71 +0.77/-1.59 and a break energy of 33.4 +4.6/-4.7 keV. With this model, the 4-120 keV fluence is (4.9 +0.6/-3.6)e-7 erg/cm^2 and the 4-120 keV photon flux is 0.23 +0.20/0.17 ph/cm^2/s. This GRB shows some spectral evolution. The spectrum from T0-16s s to T0 in the 5-120 keV energy range is best fitted by a power-law model with a photon index of -1.06 +/-0.13. With this model, the 4-120 keV flux is (2.3 +0.1/-0.6)e-8 erg/cm²/s. The spectrum from T0 to T0+34.92 s in the 5-120 keV energy range is well fitted using a broken power-law model, fixing the first photon index to -1 and the second to -3, with a break energy of 35.7 +12.6/-10.4 keV. With this model, the 4-120 keV flux is (0.7 +/-0.1)e-9 erg/cm²/s. The position of GRB 260321A in the Amati relation diagram is compatible with those of Type-II GRBs if it is at a redshift larger than 3. The non detection of an optical afterglow even with early deep observations (SVOM/Colibri upper limit, GCN 44078 & GCN 44102 and SVOM/VT upper limit GCN 44080) may also favor a high redshift origin for this burst. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44164. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42284] EP260329b: J-band upper limits with WINTER
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44163 SUBJECT: EP260329b: J-band upper limits with WINTER DATE: 26/03/31 00:28:16 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (NOIRLab), Benjamin Schneider (LAM), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of EP260329b (Song et al., GCN 44142, GCN 44155) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-03-30T04:09:30 UTC in the J band (~17.6 hr after the GRB trigger), consisting of 15 x 120 s exposures. 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) We do not detect a source at the optical counterpart location (Li et al., GCN 44139; Eyles-Ferris et al., GCN 44144; Magnani et al., GCN 44146; Aryan et al., GCN 44147; Lipunov et al., GCN 44150). We obtain the following 5-sigma upper limit: J = 19.3 mag (AB). 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/44163. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42283] EP260329a: J-band upper limit with WINTER
by GCN Circulars 31 Mar '26

31 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44162 SUBJECT: EP260329a: J-band upper limit with WINTER DATE: 26/03/31 00:27:44 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of EP260329a (Yang et al., GCN 44141) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-03-29T11:11:03 UTC in the J band (~7.7 hr after the GRB trigger), consisting of 15 x 120 s exposures. 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) We do not detect a source at the optical counterpart location (Sankar et al., GCN 44145; He et al., GCN 44152; Yang et al., GCN 44153; Angulo et al., GCN 44154). We obtain the following 5-sigma upper limit: J = 18.0 mag (AB). 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/44162. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42282] GRB 260330A: Glowbug gamma-ray detection
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44161 SUBJECT: GRB 260330A: Glowbug gamma-ray detection DATE: 26/03/30 21:27:51 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 260330A, which was detected by Fermi/GBM (GCN 44151). The burst onset is at 2026-03-30 03:40:18.4 with a burst duration of ~16s. The lightcurve comprises an initial faint peak at ~T0+0.2s, followed by bright multi-peaked structures from ~T0+3s to +6s and ~T0+9s to +15.5s. 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/44161. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42281] GRB 260310A: VLA Multi-frequency Radio Observations
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44160 SUBJECT: GRB 260310A: VLA Multi-frequency Radio Observations DATE: 26/03/30 20:08:21 GMT FROM: Daniel Perley at Liverpool JMU <d.a.perley(a)ljmu.ac.uk> D. A. Perley (LJMU), G. Schroeder (Cornell), and T. Laskar (Utah) report on behalf of a larger collaboration: The Karl G. Jansky Very Large Array observed the location of the afterglow (Hinds et al., TNS AstroNote 2026-65; Konno et al., GCN 43974) associated with GRB 260310A (Fermi GBM Team, GCN 43951; Hamburg & Meegan, GCN 43975) using all available receivers from S-band to Q-band, providing nearly continuous spectral coverage from 2 to 50 GHz. Observations were carried out on UT 2026-03-27 between 07:45 and 11:06 UT, approximately 17.2 days after the GRB. Consistent with previous reports (Rhodes et al., GCN 44005; Giarratana et al., GCN 44045; Ho et al., GCN 44057; Ho et al., GCN 44134) we detect very strong radio emission from the afterglow. Preliminary flux densities are: | freq(GHz) | flux(mJy) | |-----------|----------------| | 3 | 2.90 +/- 0.04 | | 6 | 7.52 +/- 0.05 | | 10 | 11.11 +/- 0.11 | | 15 | 11.73 +/- 0.16 | | 33 | 9.58 +/- 0.39 | | 45 | 7.98 +/- 0.27 | This indicates that the afterglow has brightened at low frequencies since the observations of Giarratana et al. and Rhodes et al. at ~4 days post-GRB, and that the peak of the f_nu spectral energy distribution during our observations was at approximately 15 GHz. We thank the NRAO for rapidly approving our DDT request for a public multifrequency campaign on this exceptional GRB, and Heidi Medlin for assistance with checking the SBs. Further observations are planned. View this GCN Circular online at https://gcn.nasa.gov/circulars/44160. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42280] Fermi GBM Sub-Threshold Detection of GRB 260330B
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44159 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 260330B DATE: 26/03/30 19:48:13 GMT FROM: atrigg2(a)lsu.edu A.C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi-GBM Team: SVOM/ECLAIRs detected GRB 260330B on 2026-03-30 at 14:19:57 UTC (GCN 44157). 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 16 s after the ECLAIRs best image SNR time of 2026-03-30T14:19:31. The Targeted Search candidate was found most significantly on the 32 s timescale using the "soft" spectral template (i.e., Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) and has a false alarm rate of 1.0-04 Hz. The Fermi-MET of this transient is 796573176.806 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/44159. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42279] GRB 260330B: LCO optical upper limits
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44158 SUBJECT: GRB 260330B: LCO optical upper limits DATE: 26/03/30 18:58:32 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), G. X. Lan (IRAP), S. Guillot (IRAP), report on behalf of the SVOM mission team: We observed the field of GRB 260330B detected by SVOM (Lan et al., GCN 44157) with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument. Our observation started on 2026-03-30 at 17:05:41 UT (about 2.76 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limit calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r > 20.4 AB (5-sigma, mid-time 2.85 hr after the trigger); z > 19.2 AB (5-sigma, mid-time 2.86 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44158. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42278] GRB 260330B: SVOM detection of a burst
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44157 SUBJECT: GRB 260330B: SVOM detection of a burst DATE: 26/03/30 14:50:52 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> G. X. Lan, S. Guillot, H. Yang, O. Godet (IRAP), report on behalf of the SVOM mission team: At 2026-03-30T14:19:57 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260330B (SVOM burst-id sb26033003). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 9 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 12.13 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2026-03-30T14:19:31. The localization of the best alert is R.A., Dec. 252.555, 36.862 degrees: R.A. (J2000) = 16h50m13s Dec. (J2000) = 36d51m44s with a 90% confidence level (C.L.) radius of 6.66 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed multiple broad peak structures with a T90 duration of about 20.844 (-3.025 / +7.55) s. This burst was also detected by SVOM/GRM with a significance of 9.10. 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 Guangxuan Lan: glan(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/44157. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42277] EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44156 SUBJECT: EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope DATE: 26/03/30 13:44:34 GMT FROM: Y.C. Kang at Peking University <yckang(a)stu.pku.edu.cn> Yacheng Kang, Zexuan Wu, Qiang Wang, Ruize Shi, Xinmiao Zhao, Zhuokai Liu, Chenxi Bao, Yiming Dong, Ziming Wang, Fangzhou Ren, Lijing Shao, Zhuo Li, Subo Dong, Xian Chen (PKU) report on behalf of the PKU HiTF (High-energy Transients Follow-up) group: We observed the field of EP260324a (Wu et al., ATel 17728; T0 = 2026-03-24T07:04:20) using the PKU 60cm telescope at Xinglong Observatory, NAOC. Observations began on 2026 Mar 27, corresponding to ~ 3.4 days after the EP-WXT detection, and spanned two epochs. In the stacked g- and r-band images, we detect the optical counterpart in the difference image at a position consistent with that of ZTF26aapviim / AT2026hir (Anumarlapudi et al., GCN 44120; Mohan et al., GCN 44128). Preliminary photometry is calibrated against nearby Pan-STARRS field stars and reported in the AB magnitude system, without correction for Galactic extinction. The observation log is summarized below: | Date | Start_UT | T_mid − T0 (days) | Filter | Exposure (s) | Magnitude (AB) | | :--------: | :---------: | :---------------: | :----: | :----------: | :------------: | | 2026-03-27 | 16:33:34.32 | 3.41 | g | 4 * 600 | 17.88 +/- 0.02 | | 2026-03-27 | 17:16:14.28 | 3.44 | r | 4 * 600 | 18.22 +/- 0.03 | Further analysis and follow-up observations are ongoing. The PKU 60cm Telescope is operated by the Department of Astronomy, 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/44156. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42276] EP260329b: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44155 SUBJECT: EP260329b: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/03/30 13:25:23 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> The fast X-ray transient EP260329b triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Song et al., GCN 44142) , and followed by several optical telescopes (Li et al., GCN 44139, Zhu et al., GCN 44140, Eyles-Ferris et al., GCN 44144, Magnani et al., GCN 44146, Aryan et al., GCN 44147, Lipunov et al., GCN 44150). The refined analysis of the WXT data shows that the event started at T0=2026-03-29T10:35:25 (UTC) and lasted for 35 s with a single pulse, before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.51 x 10^20 cm^-2 and a photon index of 1.42 +/- 0.65. The derived average unabsorbed 0.5-4 keV flux is 1.07 (-0.37/+0.56) x 10^(-9) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-03-29T10:38:50.16 (UTC), about 3 minutes after T0. The exposure time of this observation is 4388 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 181.3131, 4.3505 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT detected a sharp pulse lasting about 200 s. About 400 s after the end of the pulse, the light curve started to rise again. The rising phase was slower than that of the initial pulse and lasted for roughly 800 s, until the observation was interrupted due to Earth occultation. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 1.51 x 10^20 cm^-2 and a photon index of 1.91 +/-0.04. The derived average unabsorbed 0.5-10 keV flux is 1.54 +/-0.05 x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/44155. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42275] EP260329a: COLIBRÍ optical upper limit
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44154 SUBJECT: EP260329a: COLIBRÍ optical upper limit DATE: 26/03/30 07:26:18 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), 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), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260329a (Yang et al., GCN Circ. 44141) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-29 11:41:47 to 12:23:53 UTC (from 8.19 to 8.89 hours after the trigger, starting 1.3 hours after the notice) and obtained 29 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded 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 image, we do not detect any new source at the position of the two EP/FXT sources (assuming a 10″ error) reported by Yang et al. (GCN Circ. 44153), as well as at the position of the optical counterpart reported by NOT (He et al., GCN Circ. 44152), down to the following 3-sigma limit: r > 22.45 z > 21.06 Our non-detection, together with the FXT observation, is consistent with the candidate reported by NOT (He et al., GCN Circ. 44152) being a plausible optical counterpart of EP260329A. 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/44154. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42274] EP260329a: EP-FXT follow up observation
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44153 SUBJECT: EP260329a: EP-FXT follow up observation DATE: 26/03/30 06:40:23 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: The fast X-ray transient EP260329a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Yang et al., GCN 44141). Early optical follow-up observations reported only upper limits (Sankar et al., GCN 44145). A possible uncatalogued optical counterpart was reported by later optical observations (He et al., GCN 44152). EP-FXT performed a follow-up observation starting at 2026-03-29T14:47:27 UTC, approximately 11.3 hours after the WXT trigger, with a total exposure time of 5934 s. Two uncataloged sources are detected within the WXT error circle. Preliminary analysis on these sources is automatically conducted, and the details are listed as follows. EPF_J002151.2+822924 RA (J2000): 5.4918, Dec (J2000): 82.4881 Flux: 4.9e-14 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 1.3e-14 erg/s/cm^2 (1 sigma) EPF_J002212.3+823200 RA (J2000): 5.5758 Dec (J2000): 82.5335 Flux: 5.3e-14 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 1.5e-14 erg/s/cm^2 (1 sigma) We note that the position of EPF_J002151.2+822924 is consistent with the optical uncatalogued counterpart reported by GCN 44152 (He et al.) 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/44153. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42273] EP260329a: NOT optical counterpart candidate
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44152 SUBJECT: EP260329a: NOT optical counterpart candidate DATE: 26/03/30 06:09:01 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, S.Q. Jiang, Z.P. Zhu, J. An, X. Liu, D. Xu (NAOC), S.Y. Fu (HUST), J. P. U. Fynbo (DAWN/NBI), K. Valeckas (NOT) report: We observed the field of EP260329a detected by Einstein Probe (EP), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 3 x 300 s frames in the Sloan r-band. An uncatalogued optical source is detected within the EP-WXT error circle (Yang et al., GCN 44141) at coordinates R.A. (J2000) = 5.4770 (deg) Dec. (J2000) = 82.4894 (deg) with an uncertainty of ~ 0.5 arcsec. The source has r ~ 21.6 mag (AB) at a median time of 45 mins after the EP trigger, calibrated with nearby PanSTARRS1-dr2 catalog and not corrected for Galactic extinction. No source is present at the above position in PanSTARRS down to a 5-sigma limit of r ~22.3 mag. No NEO object would be at the above position at the NOT observational time by checking MPC. We thus think the source could be the optical counterpart of EP260329a. View this GCN Circular online at https://gcn.nasa.gov/circulars/44152. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42272] GRB 260330A: Fermi GBM Final Real-time Localization
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44151 SUBJECT: GRB 260330A: Fermi GBM Final Real-time Localization DATE: 26/03/30 03:48:27 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 03:40:19 UT on 30 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260330A (trigger 796534824.63566 / 260330153). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 93.6, Dec = -44.6 (J2000 degrees, equivalent to J2000 06h 14m, -44d 36'), with a statistical uncertainty of 2.8 degrees. The angle from the Fermi LAT boresight is 63.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260330153/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260330153/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260330153/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44151. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42271] EP260329b: Global MASTER-Net observations report
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44150 SUBJECT: EP260329b: Global MASTER-Net observations report DATE: 26/03/29 23:45:30 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 EP260329b ( EP Team et al., GCN 44142) errorbox 41172 sec after notice time and 46747 sec after trigger time at 2026-03-29 23:35:07 UT, with upper limit up to 17.2 mag. Observations started at twilight. The observations began at zenith distance = 75 deg. The sun altitude is -13.8 deg. The galactic latitude b = 65 deg., longitude l = 277 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3219325 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 46777 | 2026-03-29 23:35:07 | MASTER-OAFA | (12h 05m 25.47s , +04d 20m 43.8s) | C | 60 | 16.4 | 46837 | 2026-03-29 23:35:07 | MASTER-OAFA | (12h 05m 25.47s , +04d 20m 43.7s) | C | 180 | 17.2 | Coadd 46852 | 2026-03-29 23:36:21 | MASTER-OAFA | (12h 05m 25.71s , +04d 21m 49.7s) | C | 60 | 16.6 | 46927 | 2026-03-29 23:37:36 | MASTER-OAFA | (12h 05m 33.10s , +04d 20m 55.0s) | C | 60 | 16.7 | 47124 | 2026-03-29 23:40:54 | MASTER-OAFA | (12h 05m 30.36s , +04d 21m 51.8s) | C | 60 | 16.9 | 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/44150. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42270] Fermi trigger No 796485221: Global MASTER-Net observations report
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44149 SUBJECT: Fermi trigger No 796485221: Global MASTER-Net observations report DATE: 26/03/29 23:31:14 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-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB260329.58 (trigger No 796485221,19h 47m 48.00s , -55d 55m 12.0s, R=7.59) errorbox 33703 sec after notice time and 33736 sec after trigger time at 2026-03-29 23:15:52 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 69 deg. The sun altitude is -60.5 deg. The galactic latitude b = -30 deg., longitude l = 342 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3219478 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 33796 | 2026-03-29 23:15:52 | MASTER-SAAO | (19h 42m 30.66s , -55d 55m 47.3s) | C | 120 | 18.7 | 33796 | 2026-03-29 23:15:52 | MASTER-SAAO | (19h 45m 45.76s , -56d 11m 20.9s) | C | 120 | 18.7 | 33948 | 2026-03-29 23:18:24 | MASTER-SAAO | (19h 42m 36.60s , -55d 56m 48.4s) | C | 120 | 18.8 | 33948 | 2026-03-29 23:18:24 | MASTER-SAAO | (19h 45m 51.90s , -56d 12m 19.9s) | C | 120 | 18.8 | 34100 | 2026-03-29 23:20:56 | MASTER-SAAO | (19h 17m 26.52s , -55d 57m 25.2s) | C | 120 | 18.6 | 34100 | 2026-03-29 23:20:56 | MASTER-SAAO | (19h 20m 42.35s , -56d 12m 54.8s) | C | 120 | 18.9 | 34252 | 2026-03-29 23:23:28 | MASTER-SAAO | (19h 17m 32.63s , -55d 57m 06.4s) | C | 120 | 18.6 | 34252 | 2026-03-29 23:23:28 | MASTER-SAAO | (19h 20m 48.48s , -56d 12m 34.7s) | C | 120 | 18.8 | 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/44149. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42269] GRB 260327A: Insight-HXMT/HE detection
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44148 SUBJECT: GRB 260327A: Insight-HXMT/HE detection DATE: 26/03/29 15:18:30 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2026-03-27T02:28:50.350 (T0), Insight-HXMT/HE detected a long burst, GRB 260327A, which is also detected by AstroSat CZTI (A. Arya et. al., GCN #44130) and Konus-Wind (IPN notice). The Insight-HXMT/HE light curve mainly consists of two emission episodes with a total duration (T90) of 98 +14/-6 s. The 1s peak rate, measured from T0-1 s, is 2435 cnts/sec. Insight-HXMT/HE detected a total of 22378 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260327A.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/44148. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42268] EP260329b: Optical follow-up with Kinder observations
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44147 SUBJECT: EP260329b: Optical follow-up with Kinder observations DATE: 26/03/29 14:47:29 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Aryan, A. Sankar.K, T.-W. Chen, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), M. Nicholl (QUB), M.-H. Lee, A. Dutta, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, W.-J. Hou, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Fulton, K. W. Smith, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260329b (Song et al., GCN 44142) using the 1m LOT at the Lulin observatory, 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 in r-band started at 12:01 UTC on 29th of March 2026 (MJD 61128.501), 1.42 hr after the EP-WXT detection. 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. Our images were strongly affected by moonlight, and are therefore relatively shallow. In the stacked r-band image at t_mid - t_0 =1.80 hr, we did detect a very faint source (SNR 3.4) at the reported position of the optical counterpart candidate (Wenxiong et al., GCN 44139; Zhu et al., GCN 44140; and Eyles-Ferris et al., GCN 44144). Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and measured photometry/the 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | Med. Airmass LOT | r | 61128.501 | 1.42 | 300 * 8 | 20.19+/-0.14 |1".71 | 1.54 LOT | g | 61128.536 | 2.26 | 300 * 7 | >19.9 |1".50 | 1.34 Our observations confirm the rapidly fading nature of the optical counterpart candidate. The presented magnitudes are calibrated using the field stars from ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported magnitudes are not corrected for an expected galactic extinction of A_g = 0.06 mag and A_r = 0.04, 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 are presented 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/44147. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42267] EP 260329b: COLIBRÍ optical observations
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44146 SUBJECT: EP 260329b: COLIBRÍ optical observations DATE: 26/03/29 14:45:02 GMT FROM: Francesco at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Noémie Globus (UNAM), Rosa L. Becerra (UNAM), 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), 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), 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 EP 260329b (Song et al., GCN Circ. 44142) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-29 11:21 to 11:41 UTC (from 45.7 to 65.0 minutes after the trigger) and obtained 16 minutes of exposure in the r and z filters, respectively. The data were reduced and coadded with 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. We detected the optical counterpart reported by LCO (Li et al., GCN Circ. 44139, Eyles-Ferris et al., GCN Circ. 44144) and TRT (Zhu et al., GCN Circ 44140), at preliminary magnitudes of: r = 18.85 +/- 0.08 z = 18.53 +/- 0.13 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/44146. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42266] EP260329a: Optical upper limit with Kinder observations
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44145 SUBJECT: EP260329a: Optical upper limit with Kinder observations DATE: 26/03/29 14:40:17 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Sankar.K, A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), S. Yang (HNAS), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), M. Nicholl (QUB), M.-H. Lee, A. Dutta, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, W.-J. Hou, 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 observed the field of the EP260329a (Yang et al., GCN 44141) using the 40cm SLT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations in g-band started at 11:03 UTC on 29th of March 2026 (MJD 61128.460), 7.54 hr after the EP-WXT detection. 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 used the Python-based AutoPhOT package (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction of the Pan-STARRS1 3Pi archive image (Chambers et al., 2016, arXiv:1612.05560) using the 'SFFT' (Hu et al., 2022, ApJ, 936, 157) algorithm. Neither in the stacked nor in the difference image did we detect any signature of a new or uncatalogued source within the EP-WXT localization circle (3.2'). Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude| avg. Seeing | Med. Airmass SLT | r | 61128.460 | 7.54 | 300 * 9 | >21.1 | 2".36 | 3.02 The presented magnitudes are calibrated using the field stars from the PanSTARRS catalog. The reported upper limit is not corrected for an expected galactic extinction of A_r = 0.44 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 are presented 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/44145. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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