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

[vsnet-grb-info 42555] EP260430a: LCO optical upper limits
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44432 SUBJECT: EP260430a: LCO optical upper limits DATE: 26/04/30 10:50:21 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> J. A. Chácon (PUC), F. E. Bauer (SSI and UTA), D. B. Malesani (DAWN/NBI and Radboud), J. Quirola-Vasquez (Radboud), A. J. Levan (Radboud & Warwick), P. G. Jonker (Radboud), R. A. J. Eyles-Ferris (Leicester), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260430a (Wang et al., GCN 44427) using LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) equipped with the SINISTRO instrument. A series of 6x300 s exposures was taken using the SDSS-r filter, starting at 2026-04-30 03:32:35 UT (~1 hr after the trigger). No new source is detected within or at the border of the EP/FXT uncertainty region (Wang et al., GCN 44427). From the stacked images, we obtain the following 3-sigma upper limit:  r > 22.1 This upper limit is in AB magnitudes, calibrated using nearby stars from the Pan-STARRS catalog, and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44432. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42554] GRB 260430A / EP260430a: COLIBRÍ optical upper limit
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44431 SUBJECT: GRB 260430A / EP260430a: COLIBRÍ optical upper limit DATE: 26/04/30 10:30:34 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Enrique Moreno Méndez (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), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), 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), 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 theEP GRB 260430A (Wang et al., GCN Circ. 44427) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-30 05:06:00 to 08:49:04 UTC (from 2.55 to 6.29 hours after the trigger) and obtained 43 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ ASU pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the WXT source position (Wang et al., GCN Circ. 44427) down to the following 3-sigma limit: r > 22.38 z > 21.78 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/44431. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42553] GRB 260429A: Fermi GBM Detection
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44430 SUBJECT: GRB 260429A: Fermi GBM Detection DATE: 26/04/30 07:10:23 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> L. Scotton (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:24:02.02 UT on 29 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260429A (trigger 799197847/260429975). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 283.92, Dec = 18.10 (J2000 degrees, equivalent to J2000 18h 55m, +18d 6'), with a statistical uncertainty of 2.61 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 76 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 0.16 s (50-300 keV). The time-averaged spectrum from T0-0.1 to T0+0.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 900 +/- 20 keV. The event fluence (10-1000 keV) in this time interval is (2.41 +/- 0.07)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 69 +/- 2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 600 +/- 20 keV, alpha = -0.92 +/- 0.03 and beta = -2 +/- 0.09. 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/44430. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42552] Fermi GRB 260429A: Global MASTER-Net observations report
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44429 SUBJECT: Fermi GRB 260429A: Global MASTER-Net observations report DATE: 26/04/30 06:31:44 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 260429A ( Fermi GBM team, GCN 44425) errorbox 24026 sec after notice time and 24067 sec after trigger time at 2026-04-30 06:05:09 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 65 deg. The sun altitude is -63.1 deg. The galactic latitude b = 7 deg., longitude l = 50 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3281490 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 24098 | 2026-04-30 06:05:09 | MASTER-OAFA | (18h 56m 08.86s , +18d 11m 55.3s) | C | 60 | 17.6 | 24177 | 2026-04-30 06:06:28 | MASTER-OAFA | (18h 56m 09.20s , +18d 12m 58.1s) | C | 60 | 17.6 | 24255 | 2026-04-30 06:07:47 | MASTER-OAFA | (18h 56m 14.55s , +18d 12m 00.2s) | C | 60 | 17.5 | 24363 | 2026-04-30 06:09:04 | MASTER-OAFA | (18h 56m 09.34s , +18d 11m 03.2s) | C | 120 | 17.7 | 24498 | 2026-04-30 06:11:20 | MASTER-OAFA | (18h 56m 15.66s , +18d 11m 31.9s) | C | 120 | 17.8 | 24636 | 2026-04-30 06:13:37 | MASTER-OAFA | (18h 56m 11.82s , +18d 12m 47.8s) | C | 120 | 17.9 | 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/44429. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42550] EP260430a: Global MASTER-Net observations report
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44428 SUBJECT: EP260430a: Global MASTER-Net observations report DATE: 26/04/30 04:09:48 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 EP260430a ( EP Team et al., GCN 44427) errorbox 320 sec after trigger time at 2026-04-30 02:38:07 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 23 deg. The sun altitude is -59.3 deg. The galactic latitude b = 50 deg., longitude l = 281 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3281929 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 350 | 2026-04-30 02:38:07 | MASTER-OAFA | (11h 53m 04.26s , -09d 58m 33.8s) | C | 60 | 18.5 | 420 | 2026-04-30 02:38:07 | MASTER-OAFA | (11h 53m 04.26s , -09d 58m 33.8s) | C | 200 | 18.8 | Coadd 426 | 2026-04-30 02:39:13 | MASTER-OAFA | (11h 53m 04.09s , -09d 58m 36.3s) | C | 80 | 15.7 | 1038 | 2026-04-30 02:49:35 | MASTER-OAFA | (11h 53m 02.59s , -09d 59m 04.2s) | C | 60 | 18.5 | 1104 | 2026-04-30 02:50:40 | MASTER-OAFA | (11h 53m 02.42s , -09d 59m 07.3s) | C | 60 | 18.5 | 1164 | 2026-04-30 02:50:40 | MASTER-OAFA | (11h 53m 02.42s , -09d 59m 07.3s) | C | 180 | 18.9 | Coadd 1170 | 2026-04-30 02:51:46 | MASTER-OAFA | (11h 53m 02.26s , -09d 59m 10.5s) | C | 60 | 18.5 | 1236 | 2026-04-30 02:52:52 | MASTER-OAFA | (11h 53m 02.09s , -09d 59m 13.9s) | C | 60 | 18.4 | 1301 | 2026-04-30 02:53:57 | MASTER-OAFA | (11h 53m 01.92s , -09d 59m 17.1s) | C | 60 | 18.5 | 1361 | 2026-04-30 02:53:57 | MASTER-OAFA | (11h 53m 01.92s , -09d 59m 17.1s) | C | 180 | 19.0 | Coadd 1366 | 2026-04-30 02:55:03 | MASTER-OAFA | (11h 53m 01.76s , -09d 59m 20.5s) | C | 60 | 18.5 | 1432 | 2026-04-30 02:56:09 | MASTER-OAFA | (11h 53m 01.60s , -09d 59m 24.0s) | C | 60 | 18.5 | 1498 | 2026-04-30 02:57:14 | MASTER-OAFA | (11h 53m 01.42s , -09d 59m 27.3s) | C | 60 | 18.4 | 1558 | 2026-04-30 02:57:14 | MASTER-OAFA | (11h 53m 01.42s , -09d 59m 27.4s) | C | 180 | 19.0 | Coadd 1564 | 2026-04-30 02:58:20 | MASTER-OAFA | (11h 53m 01.25s , -09d 59m 30.6s) | C | 60 | 18.4 | 1630 | 2026-04-30 02:59:27 | MASTER-OAFA | (11h 53m 01.08s , -09d 59m 34.3s) | C | 60 | 18.5 | 1696 | 2026-04-30 03:00:32 | MASTER-OAFA | (11h 53m 00.91s , -09d 59m 37.8s) | C | 60 | 18.5 | 1761 | 2026-04-30 03:01:38 | MASTER-OAFA | (11h 53m 00.74s , -09d 59m 41.3s) | C | 60 | 18.5 | 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/44428. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42549] EP260430a: Einstein Probe detection of an X-ray transient
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44427 SUBJECT: EP260430a: Einstein Probe detection of an X-ray transient DATE: 26/04/30 03:45:21 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. L. Wang (NAO, CAS; ICE, CSIC), Y. Wang (PMO), G. J. Yang, C.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 EP260430a. The transient triggered EP-WXT (ID: 01709261081) at 2026-04-30T02:32:47 (UTC). A follow-up observation with the Follow-up X-ray Telescope (FXT) on board EP was performed automatically following the WXT trigger. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 178.3341 deg, DEC = -10.2136 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/44427. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42551] EP260429a: EP-WXT detection of a fast X-ray transient
by GCN Circulars 30 Apr '26

30 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44426 SUBJECT: EP260429a: EP-WXT detection of a fast X-ray transient DATE: 26/04/30 03:05:55 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO), Y. L. Wang (NAO, CAS; ICE, CSIC), C.C Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260429a. The WXT light curve shows a single pulse with a duration of about 250 s. The transient started at 2026-04-29 14:41:11 UTC. The WXT position of the source is R.A. = 240.629 deg, DEC = -9.588 deg (J2000) with an uncertainty of 1.9 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5 - 4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 4.31 (-0.08/+0.09) x 10^21 cm^-2 and a photon index of 1.44 (-0.04/+0.04). The derived average unabsorbed 0.5-4 keV flux is 3.96 (-0.32/+0.37) x 10^-9 erg/s/cm^2. Follow-up observation with the Follow-up X-ray Telescope on board EP has been 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/44426. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42548] GRB 260429A: Fermi GBM Final Real-time Localization
by GCN Circulars 29 Apr '26

29 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44425 SUBJECT: GRB 260429A: Fermi GBM Final Real-time Localization DATE: 26/04/29 23:34:38 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 SHORT GRB At 23:24:02 UT on 29 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260429A (trigger 799197847.01658 / 260429975). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 283.9, Dec = 18.1 (J2000 degrees, equivalent to J2000 18h 55m, 18d 06'), with a statistical uncertainty of 2.6 degrees. The angle from the Fermi LAT boresight is 76.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260429975/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260429975/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260429975/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44425. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42545] GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
by GCN Circulars 29 Apr '26

29 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44424 SUBJECT: GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission DATE: 26/04/29 15:26:34 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Chao Zheng, Zheng-Hang Yu, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier GODET (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 260428A (SVOM trigger reference: sb26042803) at 2026-04-28T14:20:37.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#44415), AstroSat (A. Goyal et al., GCN#44421) and GECAM-B (Wang et al., GCN#44423). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of mutli-pulses hard spikes followed by a soft weak extended emission with a T90 of 4.1 +3.1/-2.1 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260428A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 277.0 deg, Dec = 1.9 deg, Err= 2.1 deg, GCN#44415), is located at about 100 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-1.4 to T0+8.4 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.11 +0.33/-0.25 and the cutoff energy, parameterized as Epeak, is 1380 +159/-66 keV. The event fluence (10-1000 keV) in this time interval is (4.82 +0.83/-0.79)E-06 erg/cm^2. GRB 260428A falls into the Type I region in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/svgrb260428A_amati.png With the brightness of the prompt emission, the predicted soft X-ray afterglow [1] is shown at: https://www.bursthub.cn//admin/static/svgrb260428A_xag_pre.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: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) [1] Chen-Wei Wang et al. ApJ 997 353 https://doi.org/10.3847/1538-4357/ae2eae View this GCN Circular online at https://gcn.nasa.gov/circulars/44424. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42543] GRB 260428A: GECAM-B detection of a possible long duration Type I burst
by GCN Circulars 29 Apr '26

29 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44423 SUBJECT: GRB 260428A: GECAM-B detection of a possible long duration Type I burst DATE: 26/04/29 15:24:26 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng, Zheng-Hang Yu (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a hard burst GRB 260428A at 2026-04-28T14:20:35.850 UTC (denoted as T0). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multi-pulses with a duration (T90) of 5.6 +6.8/-2.6 s, which is also detected by Fermi/GBM (Fermi GBM team, GCN#44415), AstroSat (A. Goyal et al., GCN#44421) and SVOM/GRM. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260428A.png The time-averaged spectrum from T0-0.6 s to T0+4.0 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.05 +0.24/-0.21 and the cutoff energy, parameterized as Epeak, is 1320 +690/-420 keV. The event fluence (10-1000 keV) in this time interval is (6.02 +0.42/-0.47)E-06 erg/cm^2. Thus GRB 260428A is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/gecambgrb260428A_amati.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/44423. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42544] IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 29 Apr '26

29 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44422 SUBJECT: IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/04/29 15:10:33 GMT FROM: Yuhua Yao at IceCube/UW-Madison <yyao255(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-260425A (https://gcn.nasa.gov/circulars/44409) in a time range of 1000 seconds centered on the alert event time (2026-04-24 23:58:43.540 UTC to 2026-04-25 00:15:23.540 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-260425A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.4e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260425A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 9e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-04-24 00:07:03.540 UTC to 2026-04-26 00:07:03.540 UTC). In this case, we report a p-value of 0.19, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.6e-01 to 1.7e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260425A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/44422. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42542] GRB 260428A: AstroSat CZTI detection
by GCN Circulars 29 Apr '26

29 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44421 SUBJECT: GRB 260428A: AstroSat CZTI detection DATE: 26/04/29 10:52:09 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 GRB 260428A which was also detected by Fermi GBM (Fermi GBM team, GCN Circ. 44415). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-04-28 14:20:35.79 UTC. The measured peak count rate associated with the burst is 135 (+30, -25) counts/s above the background in the combined data of three quadrants (out of four), with a total of 442 (+143, -149) counts. The local mean background count rate was 207 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 8.0 (+2.2, -5.7) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-28 14:20:36.03 UTC. The measured peak count rate associated with the burst is 480 (+68, -72) counts/s above the background in the combined data of all quadrants, with a total of 1659 (+414, -444) counts. The local mean background count rate was 1250 (+10, -10) counts/s. We measure a T90 of 7.6 (+3.3, -3.7) 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 data products like interactive and downloadable light curves for this GRB can be found at https://astrosat.iucaa.in/cift/cift_products/515082033.23/S515082033.23_det…. 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/44421. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42547] Fermi GRB 260428A: Global MASTER-Net observations report
by GCN Circulars 29 Apr '26

29 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44420 SUBJECT: Fermi GRB 260428A: Global MASTER-Net observations report DATE: 26/04/29 09:48:02 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260428A ( Fermi GBM team, GCN 44415) errorbox 64441 sec after notice time and 64478 sec after trigger time at 2026-04-29 08:15:13 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 49 deg. The sun altitude is -42.4 deg. The galactic latitude b = 6 deg., longitude l = 32 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3278426 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 64508 | 2026-04-29 08:15:13 | MASTER-OAGH | (18h 13m 31.74s , +02d 20m 54.0s) | C | 60 | 16.3 | 64580 | 2026-04-29 08:16:25 | MASTER-OAGH | (18h 21m 26.42s , +02d 19m 39.1s) | C | 60 | 17.1 | 64580 | 2026-04-29 08:16:25 | MASTER-OAGH | (18h 19m 40.92s , +02d 56m 34.7s) | C | 60 | 16.9 | 64723 | 2026-04-29 08:18:49 | MASTER-OAGH | (18h 18m 20.54s , +01d 02m 52.2s) | C | 60 | 18.4 | 64723 | 2026-04-29 08:18:49 | MASTER-OAGH | (18h 20m 05.93s , +00d 25m 55.1s) | C | 60 | 18.5 | 64795 | 2026-04-29 08:20:01 | MASTER-OAGH | (18h 16m 00.39s , +04d 14m 39.8s) | C | 60 | 17.9 | 64866 | 2026-04-29 08:21:11 | MASTER-OAGH | (18h 24m 02.21s , +04d 15m 27.1s) | C | 60 | 17.6 | 64866 | 2026-04-29 08:21:11 | MASTER-OAGH | (18h 22m 16.34s , +04d 52m 23.3s) | C | 60 | 17.4 | 65011 | 2026-04-29 08:23:36 | MASTER-OAGH | (18h 19m 59.66s , -01d 28m 30.2s) | C | 60 | 18.5 | 65011 | 2026-04-29 08:23:36 | MASTER-OAGH | (18h 18m 14.27s , -00d 51m 31.9s) | C | 60 | 18.4 | 65229 | 2026-04-29 08:27:15 | MASTER-OAGH | (18h 13m 26.99s , +02d 20m 32.5s) | C | 60 | 18.1 | 65301 | 2026-04-29 08:28:26 | MASTER-OAGH | (18h 21m 25.52s , +02d 21m 20.4s) | C | 60 | 17.2 | 65301 | 2026-04-29 08:28:26 | MASTER-OAGH | (18h 19m 39.54s , +02d 58m 17.0s) | C | 60 | 16.9 | 68807 | 2026-04-29 09:26:52 | MASTER-OAGH | (18h 16m 03.50s , +04d 15m 09.9s) | C | 60 | 18.8 | 68879 | 2026-04-29 09:28:04 | MASTER-OAGH | (18h 22m 20.90s , +04d 50m 32.1s) | C | 60 | 18.6 | 68879 | 2026-04-29 09:28:04 | MASTER-OAGH | (18h 24m 10.14s , +04d 13m 50.9s) | C | 60 | 18.9 | 69023 | 2026-04-29 09:30:29 | MASTER-OAGH | (18h 18m 11.84s , -00d 52m 17.0s) | C | 60 | 18.9 | 69024 | 2026-04-29 09:30:29 | MASTER-OAGH | (18h 20m 00.14s , -01d 29m 03.2s) | C | 60 | 19.0 | 69240 | 2026-04-29 09:34:05 | MASTER-OAGH | (18h 13m 34.50s , +02d 20m 44.0s) | C | 60 | 18.9 | 69311 | 2026-04-29 09:35:16 | MASTER-OAGH | (18h 19m 39.03s , +02d 56m 25.6s) | C | 60 | 18.6 | 69311 | 2026-04-29 09:35:16 | MASTER-OAGH | (18h 21m 27.49s , +02d 19m 41.1s) | C | 60 | 18.9 | 69457 | 2026-04-29 09:37:42 | MASTER-OAGH | (18h 18m 23.22s , +01d 02m 26.1s) | C | 60 | 19.0 | 69457 | 2026-04-29 09:37:42 | MASTER-OAGH | (18h 20m 11.48s , +00d 25m 40.2s) | C | 60 | 19.0 | 69530 | 2026-04-29 09:38:55 | MASTER-OAGH | (18h 16m 02.94s , +04d 12m 49.0s) | C | 60 | 19.0 | 69601 | 2026-04-29 09:40:06 | MASTER-OAGH | (18h 22m 22.25s , +04d 49m 23.6s) | C | 60 | 18.8 | 69601 | 2026-04-29 09:40:06 | MASTER-OAGH | (18h 24m 11.05s , +04d 12m 40.8s) | C | 60 | 18.9 | 69747 | 2026-04-29 09:42:32 | MASTER-OAGH | (18h 18m 09.51s , -00d 52m 18.5s) | C | 60 | 19.1 | 69747 | 2026-04-29 09:42:32 | MASTER-OAGH | (18h 19m 57.81s , -01d 29m 04.9s) | C | 60 | 19.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44420. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42546] EP260416a: Mondy and Terskol optical upper limits
by GCN Circulars 29 Apr '26

29 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44419 SUBJECT: EP260416a: Mondy and Terskol optical upper limits DATE: 26/04/29 08:29:18 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), I. Sokolov (INASAN), E. Klunko (ISTP), A. Pozanenko (IKI), N. Pankov (IKI) report on behalf of IKI GRB-FuN: We observed the field of the fast X-ray transient EP260416a (Hu et al., GCN 44307, 44324) at z = 1.909 (He et al., GCN 44336; An et al., GCN 44339) in R band with the Zeiss-2000 telescope of the Terskol observatory starting on 2026-04-25 (UT) 20:02:10 and with the AZT-33IK telescope of the Mondy observatory starting on 2026-04-26 (UT) 15:50:09. The optical counterpart (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334; He et al., GCN 44336; An et al., GCN 44339; Jelinek et al., GCN 44341; Guziy et al., GCN 44351; Ho et al., GCN 44354; Pawar et al., GCN 44373; Li et al., GCN 44376; Moskvitin et al., GCN 44395; Volnova et al., GCN 44398) is not detected in the stacked frames of every epoch. 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) 2026-04-25 20:02:10 9.63709 20*180 R n/d n/d 22.5 Terskol/Zeiss-2000 2026-04-26 15:50:09 10.45948 40*120 R n/d n/d 22.9 Mondy/AZT-33IK The photometry is based on nearby USNO-B1.0 stars (R2-magnitudes) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44419. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42541] GRB 260424B: Glowbug gamma-ray detection of a short burst
by GCN Circulars 28 Apr '26

28 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44418 SUBJECT: GRB 260424B: Glowbug gamma-ray detection of a short burst DATE: 26/04/28 21:25:44 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, confirms the detection of the short burst GRB 260424B, which was detected by SVOM/GRM (GCN 44410), Konus-Wind (GCN 44416), Mars-Odyssey (HEND), with an IPN triangulation (GCN 44411). The burst onset is at 2026-04-24 23:37:24.0 with a burst duration of ~0.6. The lightcurve comprises a double-peaked structure. 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/44418. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42540] GRB 260424B: COLIBRÍ optical upper limit
by GCN Circulars 28 Apr '26

28 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44417 SUBJECT: GRB 260424B: COLIBRÍ optical upper limit DATE: 26/04/28 19:07:11 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Massimiliano Lincetto (CPPM), Fredd Sánchez Álvarez (UNAM), 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), 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), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of GRB 260424B (SVOM/GRM Team et al., GCN Circ. 44410; Kozyrev et al., GCN Circ. 44411; Fermi GBM Team GCN Circ. 44413; Ridnaia et al., GCN Circ. 44416) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-28 10:43 to 11:45 UTC (from 3.80 to 3.84 days after the trigger) and obtained 48 minutes of simultaneous exposure in the i/z filters. The data were reduced and coadded with COLIBRÍ ASU pipeline and analysed in 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 performing image subtraction against PanSTARRS DR1 templates, we do not detect any new source at the IPN region (Kozyrev et al., GCN Circ. 44411) down to the following 5-sigma limits: i > 22.6 z > 21.9 Our images also include the bright galaxy PSO J348.1125+41.2291, centered at RA, Dec = 348.1125, 41.2290, with reported magnitudes of g=17.03, r=16.25, i=15.90, and z=15.61. This galaxy is just outside the IPN region. However, in image-subtraction analysis, we find no evidence for any additional component in the galaxy. We thank Chenwei Wang (SVOM/GRM) for the helpful communication, and the IPN team for their rapid analysis and prompt release of a refined position, which facilitated the observations of the region. 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/44417. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42538] Konus-Wind detection of GRB 260424B
by GCN Circulars 28 Apr '26

28 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44416 SUBJECT: Konus-Wind detection of GRB 260424B DATE: 26/04/28 15:28:08 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The short-duration GRB 260424B (SVOM/GRM detection: Wang et al., GCN Circ. 44410; IPN triangulation: Kozyrev et al., GCN Circ. 44411) triggered Konus-Wind at T0=85042.824 s UT (23:37:22.824). The burst light curve shows a multipeaked structure which starts at ~T0-0.1 s and has a total duration of ~0.6 s. The emission is seen up to ~3 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260424_T85042/ As observed by Konus-Wind, the burst had a fluence of 3.02(-0.30,+0.33)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0+0.198 s, of 1.89(-0.35,+0.38)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+0.256 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 = -0.67(-0.14,+0.16) and Ep = 756(-131,+170) keV (chi2 = 25/41 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.0 (chi2 = 24/40 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/44416. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42539] GRB 260428A: Fermi GBM Final Real-time Localization
by GCN Circulars 28 Apr '26

28 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44415 SUBJECT: GRB 260428A: Fermi GBM Final Real-time Localization DATE: 26/04/28 14:31:09 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 14:20:35 UT on 28 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260428A (trigger 799078840.683444 / 260428598). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 277.0, Dec = 1.9 (J2000 degrees, equivalent to J2000 18h 27m, 1d 53'), with a statistical uncertainty of 2.1 degrees. The angle from the Fermi LAT boresight is 88.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260428598/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260428598/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260428598/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44415. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42537] Fermi-LAT Gamma-ray Observations of IceCube-260425A
by GCN Circulars 28 Apr '26

28 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44414 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260425A DATE: 26/04/28 12:25:21 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260425A neutrino event (GCN 44409) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2026-04-25 at 00:07:03.54 UTC (T0) with J2000 position RA = 347.08 (+0.57, -0.58) deg, Decl. = 19.19 (+0.63, -0.60) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260425A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC260425A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260425A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 5.7e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <2.6e-08 (<8.7e-08) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/44414. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42536] GRB 260424B: Fermi GBM Final Localization
by GCN Circulars 27 Apr '26

27 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44413 SUBJECT: GRB 260424B: Fermi GBM Final Localization DATE: 26/04/27 21:13:35 GMT FROM: Angus Jameson <abj0023(a)uah.edu> The Fermi GBM team reports the detection of a likely SHORT GRB "At 15:30:22.50 UT on 24 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260424B (trigger 798737427/260424646). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 171.74, Dec = 20.24 (J2000 degrees, equivalent to J2000 11h 26m, +20d 14'), with a statistical uncertainty of 14.80 degrees. The angle from the Fermi LAT boresight is 41 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260424646/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260424646/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260424646/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44413. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42535] EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
by GCN Circulars 27 Apr '26

27 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44412 SUBJECT: EP260321a/SN 2026gzf: spectroscopy at Mondy observatory DATE: 26/04/27 15:01:46 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), I. Zaznobin (IKI), M. Eselevich (ISTP), A. Volnova (IKI), N. Pankov (IKI), A. Pozanenko (IKI), report on behalf of IKI-GRB-FuN: We observed the optical counterpart of the fast X-ray transient EP260321a (Huang et al., GCN 44068; GCN 44075) identified early as SN 2026gzf (Lee et al., GCN 44070; Ma et al., GCN 44074; Aguilar-Ruiz et al., GCN 44076; Aryan et al., GCN 44081; Tanvir et al., GCN 44082; Moran et al., GCN 44083; Ahumada et al., GCN 44084; Liu et al., GCN 44087; Sankar et al., GCN 44089; de Ugarte Postigo et al., GCN 44091; Xu et al., GCN 44092; Pankov et al., GCN 44103; Corcoran et al., GCN 44105; Rastinejad et al., GCN 44107; Gao et al., GCN 44110; Zhang et al., GCN 44171; Li et al., GCN 44284; Gupta et al., GCN 44348; also detected as NIR source: He et al., GCN 44117; Volnova et al., GCN 44295) with AZT-33IK telescope (Mondy) equipped with the ADAM spectrograph (Afanasiev et al., Astrophysical Bulletin, 2015, Vol. 71, Issue 4, p. 479; Burenin et al., Astronomy Letters, 2016, Vol. 42, Issue 5, p. 295). We obtained 4 x 900 sec spectra with VPHG600G grism (range 3600--7250AA, dispersion 3.6 A/pix) on 2026-04-13, 15:02:08--16:02:47 UT(t_mid - T0 = 23.1265 days). In the spectra we clearly detected host galaxy emission lines of Balmer series, [O III] 4959A, 5007A, 4363A, [O II] 3727A, [S II] 6717A and 6731A, He I 5876A at the redshift of z = 0.0343 which is consistent with other reported measurements (Tanvir et al., GCN 44082; Xu et al., GCN 44092; Corcoran et al., GCN 44105; Rastinejad et al., GCN 44107). We also detected broad lines of supernova SN 2026gzf which we interpreted as Fe II and Si II with the velocity of about 10000 km/s. Comparison with the SNID (Blondin & Tonry, 2007, ApJ, 666, 1024) showed best fit with SN 1997ef, SN 2006aj, SN 2002ap and SN 1998bw supernovae. View this GCN Circular online at https://gcn.nasa.gov/circulars/44412. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42534] IPN triangulation of GRB 260424B (short)
by GCN Circulars 27 Apr '26

27 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44411 SUBJECT: IPN triangulation of GRB 260424B (short) DATE: 26/04/27 14:52:38 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, E. Burns on behalf of the IPN, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP), J. Wei (NAOC), B. Cordier (CEA) on behalf of the SVOM-GRM team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The short-duration GRB 260424B (SVOM/GRM detection: Wang et al., GCN Circ. 44410) was detected by Konus-Wind, SVOM (GRM), and Mars-Odyssey (HEND) at about 85042 s UT (23:37:22). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 348.155 (23h 12m 37s) +41.208 (+41d 12' 30") Corners: 348.267 (23h 13m 04s) +41.301 (+41d 18' 04") 348.022 (23h 12m 05s) +41.176 (+41d 10' 32") 348.027 (23h 12m 06s) +41.107 (+41d 06' 24") 348.272 (23h 13m 05s) +41.232 (+41d 13' 56") --------------------------------------------- The error box area is 47 sq. arcmin, and its maximum dimension is 16 arcmin (the minimum one is 3.5 arcmin). The Sun distance was 48 deg. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB260424_T85042/IPN The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/44411. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42533] GRB 260424B: SVOM/GRM detection of a short burst
by GCN Circulars 27 Apr '26

27 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44410 SUBJECT: GRB 260424B: SVOM/GRM detection of a short burst DATE: 26/04/27 03:17:00 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a short burst GRB 260424B (SVOM trigger reference: sb26042404) at 2026-04-24T23:37:25.500 UTC (T0), which is also detected by Konus-Wind. With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a weak soft precursor followed by main emission with a T90 of 1.4 +0.6/-0.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260424B.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: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44410. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42532] IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 26 Apr '26

26 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44409 SUBJECT: IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/04/26 00:15:57 GMT FROM: Matthias Vereecken at Ghent University <matthias.vereecken(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2026-04-25 at 00:07:03.54 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 2.0413 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/142495_24231696.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 2026-04-25 Time: 00:07:03.54 UT RA: 347.08 (+0.57/-0.58 deg 90% PSF containment) J2000 Dec: 19.19 (+0.63/-0.6 deg 90% PSF containment) J2000 As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of this event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/44409. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42531] IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 26 Apr '26

26 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44409 SUBJECT: IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/04/26 00:15:57 GMT FROM: Matthias Vereecken at Ghent University <matthias.vereecken(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2026-04-25 at 00:07:03.54 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 2.0413 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/142495_24231696.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 2026-04-25 Time: 00:07:03.54 UT RA: 347.08 (+0.57/-0.58 deg 90% PSF containment) J2000 Dec: 19.19 (+0.63/-0.6 deg 90% PSF containment) J2000 As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of this event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/44409. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42530] GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
by GCN Circulars 25 Apr '26

25 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44408 SUBJECT: GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position DATE: 26/04/25 12:00:14 GMT FROM: yixing(a)shao.ac.cn Yi Xing, Wenfei Yu (SHAO, CAS) We report a likely detection of high-energy emission from GRB 260305A using Fermi-LAT data with our photon-cluster analysis method, which was initially applied to the search for gamma-ray flares from FRB 20240114A (ATel #16630; Xing et al. arXiv:2411.06996) and has successfully recovered approximately half of the previously reported LAT-detected GRBs with >1 GeV photons (doi:10.3847/1538-4357/ab1d4e). The GRB was discovered by Fermi-GBM (trigger 794371303.18619 / 260305112; GCN 43920). We found five LAT photons arriving within a 27.0 s interval starting at 2026-03-05 02:41:52.640 UTC (T0 + 14.45 s), with the interval ending just before the end of the GBM T90 interval (T90 start = T0 + 0.768 s; T90 = 41.473 s; Fermi GBM Burst Catalog). The highest-energy photon in the cluster arrived at T0 + 33.42 s and has a photon energy of 1.6 GeV. Using LAT data from T0 to T0 + 100 s, we performed standard likelihood analysis and obtained a best-fit position at RA, Dec = 218.73, 35.49 (J2000), with a 68% containment statistical error radius of 0.22 deg, much smaller than the 2.4 deg statistical uncertainty reported in the GBM final real-time localization (GCN 43920). This best-fit position is consistent with, though near the edge of, the GBM localization region. The estimated photon flux and photon index above 100 MeV over the 100-s interval are (9.95 +/- 5.18) x 10^-6 ph cm^-2 s^-1 and -1.80 +/- 0.38, respectively, with a TS of 23.7. View this GCN Circular online at https://gcn.nasa.gov/circulars/44408. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42529] IceCube Alert 260425A: Global MASTER-Net observations report
by GCN Circulars 25 Apr '26

25 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44407 SUBJECT: IceCube Alert 260425A: Global MASTER-Net observations report DATE: 26/04/25 11:13:28 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) was pointed to the IceCube Alert 260425A (trigger No 24231696,23h 08m 20.64s , +19d 12m 57.6s, R=0.51) errorbox 38282 sec after notice time and 38350 sec after trigger time at 2026-04-25 10:46:13 UT, with upper limit up to 19.6 mag. The observations began at zenith distance = 74 deg. The sun altitude is -23.1 deg. The galactic latitude b = -37 deg., longitude l = 93 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3270297 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 5768 | 2026-04-25 01:42:41 | MASTER- | (23h 08m 07.50s , +19d 12m 01.6s) | C | 60 | 14.4 | 38380 | 2026-04-25 10:46:13 | MASTER-OAGH | (23h 09m 51.08s , +18d 23m 56.6s) | C | 60 | 18.3 | 38440 | 2026-04-25 10:46:13 | MASTER-OAGH | (23h 09m 51.07s , +18d 23m 56.6s) | C | 180 | 19.2 | Coadd 38380 | 2026-04-25 10:46:13 | MASTER-OAGH | (23h 07m 55.11s , +19d 01m 13.2s) | C | 60 | 18.9 | 38440 | 2026-04-25 10:46:13 | MASTER-OAGH | (23h 07m 55.11s , +19d 01m 13.2s) | C | 180 | 19.6 | Coadd 38450 | 2026-04-25 10:47:23 | MASTER-OAGH | (23h 07m 55.20s , +18d 59m 50.2s) | C | 60 | 18.9 | 38450 | 2026-04-25 10:47:23 | MASTER-OAGH | (23h 09m 51.12s , +18d 22m 32.7s) | C | 60 | 18.4 | 38522 | 2026-04-25 10:48:35 | MASTER-OAGH | (23h 07m 57.46s , +19d 01m 32.3s) | C | 60 | 18.9 | 38522 | 2026-04-25 10:48:35 | MASTER-OAGH | (23h 09m 53.40s , +18d 24m 14.2s) | C | 60 | 18.4 | 39727 | 2026-04-25 11:08:10 | MASTER-OAGH | (23h 07m 52.40s , +19d 00m 52.4s) | C | 120 | 19.0 | 39727 | 2026-04-25 11:08:10 | MASTER-OAGH | (23h 09m 50.43s , +18d 23m 39.0s) | C | 120 | 18.6 | 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/44407. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42528] Fermi trigger No 798737427: Global MASTER-Net observations report
by GCN Circulars 25 Apr '26

25 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44406 SUBJECT: Fermi trigger No 798737427: Global MASTER-Net observations report DATE: 26/04/25 03:16:51 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB260424.65 (trigger No 798737427,11h 26m 57.60s , +20d 14m 24.0s, R=14.8) errorbox 41869 sec after notice time and 41891 sec after trigger time at 2026-04-25 03:08:33 UT, with upper limit up to 18.9 mag. Observations started at twilight. The observations began at zenith distance = 32 deg. The sun altitude is -16.0 deg. The galactic latitude b = 70 deg., longitude l = 229 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3269496 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 41921 | 2026-04-25 03:08:33 | MASTER-OAGH | (11h 47m 05.86s , +10d 42m 06.0s) | C | 60 | 18.6 | 41921 | 2026-04-25 03:08:33 | MASTER-OAGH | (11h 49m 08.48s , +10d 05m 44.8s) | C | 60 | 18.7 | 41994 | 2026-04-25 03:09:46 | MASTER-OAGH | (11h 55m 15.30s , +10d 43m 09.7s) | C | 60 | 18.6 | 41994 | 2026-04-25 03:09:46 | MASTER-OAGH | (11h 57m 17.68s , +10d 06m 46.1s) | C | 60 | 18.6 | 42066 | 2026-04-25 03:10:58 | MASTER-OAGH | (11h 43m 05.83s , +08d 46m 55.3s) | C | 60 | 18.8 | 42066 | 2026-04-25 03:10:58 | MASTER-OAGH | (11h 45m 07.84s , +08d 10m 31.3s) | C | 60 | 18.9 | 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/44406. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42527] GRB 260401A: cubesat Avion detection
by GCN Circulars 24 Apr '26

24 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44405 SUBJECT: GRB 260401A: cubesat Avion detection DATE: 26/04/24 23:43:29 GMT FROM: Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> From Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> Subject GRB 260401A: cubesat Avion detection A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report: At 2026-04-01 ~10:53:20 UT the long-duration GRB 260401A (Fermi GBM detection: GCN #44174, CALET detection: GCN #44177, GECAM-B detection: GCN #44187, SVOM detection: GCN #44188) was detected by the DeCoR-1 and DeCoR-3 instruments on the cubesat Avion of the Moscow University project “Sozvezdie-270” [1]. Total amount of photons detected by Avion is 256 (DeCoR-1, energy band 40-500 keV) and 526 (DeCoR-3, energy band >30 keV), it corresponds to a fluence of ~4.7*10^(-6) erg/cm^2 in the range 30-500 keV. LC in the energy range of 30-500 keV is a sharp peak of ~4 sec duration with a maximum flux of ~20 phot/(cm^2*s) at ~10:53:28 UT with increases of smaller amplitude before (10:53:20-10:53:24 UT) and after it (10:53:36-10:53:43 UT). А total duration (T90) of the burst is ~21 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260401A_LC_Avion.png Parameters of GRB 260401A as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion is one of 5 cubesats of the Moscow University project “Sozvezdie-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s. [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282 View this GCN Circular online at https://gcn.nasa.gov/circulars/44405. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42526] GRB 260424A: AstroSat CZTI detection of a long burst
by GCN Circulars 24 Apr '26

24 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44404 SUBJECT: GRB 260424A: AstroSat CZTI detection of a long burst DATE: 26/04/24 10:37:58 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), M. Tembhurnikar (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 GRB 260424A. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-04-24 00:22:01.50 UTC. The measured peak count rate associated with the burst is 91 (+33, -12) counts/s above the background in the combined data of all quadrants, with a total of 756 (+197, -209) counts. We caution that there is a 0.3 s readout dead time in CZT data during the burst which affects the calculated total counts. The local mean background count rate was 242 (+2.5, -3) counts/s. Using cumulative rates, we measure a T90 of 12.6 (+9.23, -2.96) s. 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 data products like interactive and downloadable light curves for this GRB can be found at https://astrosat.iucaa.in/cift/cift_products/514686101.74/S514686101.74_det… . All 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/44404. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42525] EP260321a: Upper limits from ATCA radio observations
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44403 SUBJECT: EP260321a: Upper limits from ATCA radio observations DATE: 26/04/23 17:14:05 GMT FROM: Nayana A J at University of California, Berkeley <nayan89deva(a)gmail.com> Nayana A.J., Eli Wiston, Raffaella Margutti, Itai Sfaradi, Ryan Chornock (UC Berkeley) report: We observed the field of EP260321a (Huang et al., GCN 44068) with the Australia Telescope Compact Array (ATCA) using the BIGCAT system. The observations were conducted on 2026 March 30.37 UT in the 15 mm band, utilizing a total instantaneous bandwidth of approximately 8 GHz, divided into four 2 GHz-wide sub-bands, each imaged independently. The resulting images have central observing frequencies of 17, 19, 21, and 23 GHz. In our preliminary analysis, we do not detect radio emission at the position of the optical counterpart (Lee et al., GCN 44070; Tanvir et al., GCN 44082). The corresponding 3-sigma flux density upper limits are 0.21, 0.15, 0.075, and 0.06 mJy at 17, 19, 21, and 23 GHz, respectively. We thank the ATCA operations staff for their prompt scheduling of these observations. The Australia Telescope Compact Array is part of the Australia Telescope National Facility, 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/44403. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42524] GRB 260421B: Kilonova-Catcher optical afterglow detection
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44402 SUBJECT: GRB 260421B: Kilonova-Catcher optical afterglow detection DATE: 26/04/23 15:46:39 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg, R. Hellot, M. Serrau (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 260421B detected by Fermi/GBM (Fermi GBM team, GCN 44360) and SVOM (Zhao et al., GCN 44362; Guo et al., GCN 44389) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot and the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+1.9 hours and were taken with sdss-r filter. In our stacked frames, subtracted from the Legacy Survey DR10 template image, we marginally detect the optical counterpart (He et al., GCN 44363; Álvarez et al., GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366; Lipunov et al., GCN 44367; Schneider et al., GCN 44368; Li et al., GCN 44377; Pérez-Fournon et al., GCN 44383; Mo et al., GCN 44384; and Shi et al., GCN 44388, Pawar et al., GCN 44396). We report our follow-up results in the table below: | Tmid-TGRB (hrs) | Exp (s) | Filter | Magnitude | Instrument | | ------------ | ------------ |------------ |------------ |------------ | | 2.48 | 20 x 180s | r (AB) | 21.12 +/- 0.30 | TEC160FL | | 3.87 | 9 x 300s | r (AB) | 20.94 (3 sig U.L.) | CDK17 | 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/44402. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42523] GRB 260421B: Insight-HXMT/HE detection
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44401 SUBJECT: GRB 260421B: Insight-HXMT/HE detection DATE: 26/04/23 14:06:52 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2026-04-21T04:13:23.400 (T0), Insight-HXMT/HE detected a long burst, GRB 260421B, which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44360), SVOM/ECLAIRs (D.Zhao et al., GCN #44362) and SVOM/GRM (Hao-Xuan Guo et al., GCN #44389). The Insight-HXMT/HE light curve mainly consists of multipe pulses with a total duration (T90) of 16.0 +3.0/-1.5 s. The 1s peak rate, measured from T0+12.75 s, is 3246 cnts/sec. Insight-HXMT/HE detected a total of 11625 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260421B.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/44401. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42522] The EP-WXT trigger 01709258652: Mondy optical observations
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44400 SUBJECT: The EP-WXT trigger 01709258652: Mondy optical observations DATE: 26/04/23 13:31:19 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> M. Chutchikova (HSE), A. Volnova (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the EP-WXT trigger 01709258652 (Yang et al., GCN 43849) with the AZT-33IK 1.5m telescope of the Mondy observatory starting on 2026-02-26 (UT) 21:07:17, i.e., ~8 hours after the trigger, and taking several 120-seconds frames in the R band. The photometry of suggested flare star LP 435-538 (High Proper Motion Star; Yang et al., GCN 43849; Wu et al., GCN 43857; Fang et al., GCN 43889) do no exhibit any significant variability within 1 hour of our observations. 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) 2026-02-26 21:07:17 0.32452 30*120 R 14.10 0.01 23.2 Mondy/AZT-33IK The photometry is based on nearby USNO-B1.0 stars (R2-magnitudes) and is not corrected for Galactic extinction. Our measured R magnitude is consistent with the photometry of the USNO-B1.0 star 1099-00207147 (R2 = 14.16) corresponding by the coordinates to LP 435-538. View this GCN Circular online at https://gcn.nasa.gov/circulars/44400. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42521] GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44399 SUBJECT: GRB 250328A: VLT host galaxy discovery and redshift z = 1.250 DATE: 26/04/23 12:50:54 GMT FROM: Nusrin Habeeb at University of Leicester <nh312(a)leicester.ac.uk> A. Saccardi (CEA/Irfu), B. Schneider (LAM), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud), N. Habeeb (U. Leicester), R. Brivio (INAF/OAB), G. Corcoran (UCD), J.-L. Atteia (IRAP), report on behalf of the Stargate collaboration: We observed the location of the optical/NIR counterpart (Schneider et al., GCN 39919, 39920; Li et. al, GCN 39923; Li et. al, GCN 39936; Kumar et. al, GCN 39946; Klingler et. al, GCN 39968; Pankov et al., GCN 40001) of the SVOM GRB 250328A (Brunet et al., GCN 39910), using the ESO VLT UT1 (Antu) equipped with the FORS2 imager. A 20 min exposure R-band observation was carried out at 04:05:01 UT on 2026 April 19 (386.46 days after the SVOM trigger). Consistent with the afterglow position, an object is clearly identified with a magnitude r = 24.51 +/- 0.09, calibrated against the Pan-STARRS catalog and not corrected for Galactic extinction. Its coordinates (J2000) are: RA = 14:23:50.45 Dec = +25:55:55.09 Given the spatial coincidence with the GRB afterglow (<0.5"), this is the likely host galaxy of GRB 250328A. Spectroscopic follow-up observations of this object were secured using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph, covering the wavelength range 3000-21000 AA. We obtained four spectra of 1200 s each starting at 03:28:04 on 2026 April 23, i.e. about 390.44 days after the SVOM trigger. Faint emission lines are detected in the visible and near-infrared arms, which we identify as the [O III] 4959,5007 doublet, H-beta, and the [O II] 3726,3729 doublet, all at a common redshift of z = 1.250. This is thus the redshift of the likely host galaxy of GRB 250328A. We acknowledge excellent support from the ESO staff in Paranal, in particular Boris Haeussler, Diego Parraguez, Felipe Gaete, Hannah Osborne, Luca Sbordone, Matias Jones, and Thomas Rivinius. View this GCN Circular online at https://gcn.nasa.gov/circulars/44399. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42520] EP260416a: Mondy optical observations
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44398 SUBJECT: EP260416a: Mondy optical observations DATE: 26/04/23 12:39:12 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP260416a (Hu et al., GCN 44307, 44324) at z = 1.909 (He et al., GCN 44336; An et al., GCN 44339) with the AZT-33IK 1.5m telescope of the Mondy observatory starting on 2026-04-21 (UT) 15:28:28 and taking several 120-seconds frames in the R band. The optical counterpart (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334; He et al., GCN 44336; An et al., GCN 44339; Jelinek et al., GCN 44341; Guziy et al., GCN 44351; Ho et al., GCN 44354; Pawar et al., GCN 44373; Li et al., GCN 44376) is clearly detected in the stacked frame. 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) 2026-04-21 15:28:28 5.43677 27*120 R 22.72 0.09 23.3 Mondy/AZT-33IK The photometry is based on nearby USNO-B1.0 stars (R2-magnitudes) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44398. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42519] GRB 260421A: SVOM/ECLAIRs refined analysis
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44397 SUBJECT: GRB 260421A: SVOM/ECLAIRs refined analysis DATE: 26/04/23 10:06:59 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP), L. Delfosse (CEA), O. Godet (IRAP), S. Schanne (CEA), W. L. Zhang (PMO), Z. Y. Liu (GZNU) 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 260421A (SVOM burst-id sb26042105 – GCN 44362, trigger time T0 = 2026-04-21T04:13:25 UTC), which was also detected by Fermi (GCN 44360, 44361, 44382) and SVOM/GRM (GCN 44389). The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = 26.3 +4.4/-6.0 s in the 4-120 keV energy band. The time-averaged spectrum from T0-12 s to T0+20 s in the energy range 5-120 keV is best fitted (chi²/dof = 20.1/16) by a broken powerlaw model with best-fit parameters: alpha = -1.00 +0.35/-0.11, beta = -1.42 +0.07/-0.06 and a break energy of 13.7 +2.7/-4.4 keV. With this model, the 4-120 keV fluence is (8.6 +0.1/-1.1)e-6 erg/cm^2 and the 4-120 keV photon flux is 6.4 +0.1/-0.7 ph/cm²/s. Using a simple powerlaw provides a bad fit (chi²/dof = 31.3/18). 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/44397. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42518] GRB 260421B: 3.6m DOT optical observation
by GCN Circulars 23 Apr '26

23 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44396 SUBJECT: GRB 260421B: 3.6m DOT optical observation DATE: 26/04/23 10:00:19 GMT FROM: pawarpankaj1492(a)gmail.com Pankaj Pawar, Anshika Gupta, Debalina Kar, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of GRB 260421B (Fermi GBM team, GCN 44360; Zhao et al., GCN 44362) using the 3.6m Devasthal Optical Telescope (DOT) located at Devasthal of the Aryabhatta Research Institute of observational sciencES (ARIES), India. The observations began on 2026-04-21 at 21:24:53 UT, approximately 17 hours after the trigger time. We obtained 2*300s frames in the SDSS r filter. We do not detect the optical counterpart (He et al., GCN 44363; Álvarez et al., GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366; Lipunov et al., GCN 44367; Schneider et al., GCN 44368; Li et al., GCN 44377; Pérez-Fournon et al., GCN 44383; Mo et al., GCN 44384; and Shi et al., GCN 44388) within the error circle, nor do we see a source at the reported location of the transient. The limiting magnitude in the stacked image is: r > 22.4 mag (AB) The magnitude is calibrated against the Pan-STARRS PS1 catalog. We thank the staff of Devasthal for their assistance during these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44396. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42517] EP260416a: ZTSh R band observations
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44395 SUBJECT: EP260416a: ZTSh R band observations DATE: 26/04/22 23:58:50 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), V. Rumyantsev (CrAO), A. Volnova, N. Pankov, A. Pozanenko (IKI), Tao An, Yuanqi Liu (SHAO), Ankur Ghosh, Soebur Razzaque (U. of Johannesburg, RSA) report on behalf of GRB follow-up collaboration. We observed the field of EP260416a (Hu et al., GCN 44307; GCN 44324) with 2.6-m ZTSh of CrAO equipped with BVRI photometer and FLI PL4240 camera. We obtained a series of images in R band on 2026-04-22, 21:11:50--22:14:42 UT (t_mid - T0 = 6.6762 days). The optical transient discovered by COLIBRÍ (Ducoin et al., GCN 44310; and also observed by Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334; He et al., GCN 44336; An et al., GCN 44339; Jelinek et al., GCN 44341; Guziy et al., GCN 44351; Ho et al., GCN 44354) is clearly detected in the stacked image with the following brightness. Date, UT_start, t_mid - T0, filter, exp, mag +/- err UL days s 2026-04-22T21:11:50 6.67620 R 30*120 23.12 +/- 0.17 24.1 This preliminary photometry is based on the nearby USNO-B1 stars and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44395. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42516] EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44394 SUBJECT: EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9 DATE: 26/04/22 18:53:47 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> Martin Jelinek, Jan Strobl and Filip Novotný (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Masek, Petr Janecek, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ) report: The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted robotically to the EP-WXT alert of trigger 01709260362 (Yang et al., GCN 44386), obtaining a series of 60 s unfiltered images starting at 21:24:16.6 UT on 2026-04-21, i.e. ~32.2 min post trigger (T0 = 2026-04-21T20:52:02.749 UTC, JD 2461152.36948). We clearly detect the flaring star G 151-9 identified by the EP team (Yang et al., GCN 44386). The source fades by approximately 0.25 mag over the course of our observations, which span from T0+32.2 min to T0+2h 13.6 min. The overall decay is consistent with a power-law of index alpha = 0.67 +/- 0.16, superimposed on the quiescent brightness of the star at an unfiltered magnitude of 12.12 +/- 0.07. This is consistent with the stellar flare interpretation. View this GCN Circular online at https://gcn.nasa.gov/circulars/44394. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42515] IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44393 SUBJECT: IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/04/22 17:38:53 GMT FROM: syan079(a)icecube.wisc.edu The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-Cascade 260418A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/142457_45845844.amon) in a time range of 1000 seconds centered on the alert event time (2026-04-18 01:29:34.206 UTC to 2026-04-18 01:46:14.206 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-Cascade 260418A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.3e-01 to 1.4e+00 GeV cm^-2 within the 90% spatial containment region of IceCube-Cascade 260418A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 3e+02 GeV and 6e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-04-17 01:37:54.206 UTC to 2026-04-19 01:37:54.206 UTC). In this case, we report a p-value of 0.21, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.5e-01 to 1.4e+00 GeV cm^-2 within the 90% spatial containment region of IceCube-Cascade 260418A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/44393. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42514] EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44392 SUBJECT: EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773 DATE: 26/04/22 15:48:38 GMT FROM: Nusrin Habeeb at University of Leicester <nh312(a)leicester.ac.uk> B. Schneider (LAM), A. Saccardi (CEA/Irfu), G. Corcoran (UCD), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud), J.-L. Atteia (IRAP), N. Habeeb (U. Leicester), R. Brivio (INAF/OAB), report on behalf of the Stargate collaboration: Underneath the position of the optical/NIR afterglow (Li et al., GCN 40443; Xin et al., GCN 40444; Busmann et al., GCN 40447) of EP250512a / GRB 250512B (EP/WXT: Zhao et al., GCN 40437; Yang et al., GCN 40448; SVOM/ECLAIRs: Maggi et al., GCN 40439; Konus-Wind: Svinkin et al. GCN 40460), an object is well detected in archival imaging taken using the MegaCam instrument on the CFHT in the broad "gri" filter (Bannister et al. 2016, doi:10.3847/0004-6256/152/3/70). The object magnitude is about 24.5 AB mag. Given the spatial coincidence, this is likely the host galaxy of EP250512a / GRB 250512B. Starting at 01:53:33 UT on 2026 April 20, i.e. about 342.6 days after the burst, we obtained four spectra of 1200 s each using the X-shooter instrument installed on the ESO VLT UT3 (Melipal), covering the wavelength range 3000-21000 AA. Our spectroscopy reveals a single, confidently detected emission line at 13,889 AA. Interpreting this feature as [O III] 5007 at z ~ 1.773, we note the presence of a second, fainter emission corresponding to the expected position of the [O II] doublet. At this redshift, Halpha falls in a region of very poor transparency, and no detection is expected. We note that the precise position of the [O III] emission is also affected by atmospheric opacity, which adds some uncertainty to the redshift (of the order of 0.001). Alternative interpretations of the line at 13,889 AA are disfavored because we would then expect to see other lines in regions of good atmospheric transparency, which are absent in our spectrum. We acknowledge excellent support from the ESO staff in Paranal, in particular Maria del Mar Carretero Castrillo, Francisco Caceres, Luciano Sbordone, and Thomas Rivinius. View this GCN Circular online at https://gcn.nasa.gov/circulars/44392. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42513] GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44391 SUBJECT: GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486 DATE: 26/04/22 15:42:23 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> A. Saccardi (CEA/Irfu), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud), R. Brivio (INAF/OAB), N. Habeeb (U. Leicester), J.-L. Atteia (IRAP) report on behalf of the Stargate collaboration: We observed the object visible in the Legacy Survey underlying the position of the optical/NIR afterglow (D'Avanzo et al., GCN 40588; Rayson et al. GCN 40589) of the SVOM GRB 250530A (Wang et al., GCN 40576) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. A spectrum covering the wavelength range 3000-21000 AA was secured, with a total exposure time of 4x600 s in each of the UVB, VIS, and NIR arms. Our observation started at 00:32:26 UT on 2026 April 22, i.e. about 326.75 days after the SVOM trigger. Clear emission lines are detected in the visible and near-infrared arms, which we identify as [N II] 6584, H-alpha, the [O III] 4959, 5007 doublet, H-beta, and the [O II] 3726, 3729 doublet, all at a common redshift of z = 1.486. We suggest this to be the redshift of the host galaxy of GRB 250530A. We acknowledge excellent support from the ESO staff in Paranal, in particular Matias Jones, Felipe Gaete, Luciano Sbordone, and Boris Haeussler. View this GCN Circular online at https://gcn.nasa.gov/circulars/44391. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42512] GRB 260419A: AstroSat CZTI detection
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44390 SUBJECT: GRB 260419A: AstroSat CZTI detection DATE: 26/04/22 09:33:20 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), G. Waratkar (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 260419A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 44346). The source was 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 2026-04-19 07:10:15 UTC. The measured peak count rate associated with the burst is 32 (+19, -2) counts/s above the background in the combined data of two quadrants (out of four), with a total of 715 (+297, -356) counts. The local mean background count rate was 137 (+19, -2) counts/s. Using cumulative rates, we measure a T90 of 47 (+11, -28) 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/44390. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42511] GRB 260421B: SVOM/GRM observation
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44389 SUBJECT: GRB 260421B: SVOM/GRM observation DATE: 26/04/22 08:31:00 GMT FROM: guohx(a)ihep.ac.cn SVOM/GRM team: Hao-Xuan Guo, Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier GODET (IRAP), Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260421B (SVOM trigger reference: sb26042105) at 2026-04-21T04:13:22.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44360) and SVOM/ECLAIRs (D.Zhao et al., GCN #44362). 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 21.5 +3.5/-2.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260421B.png In addition, the position of this burst, as determined by SVOM/ECLAIRs (RA = 190.0318, Dec = -17.7566, GCN #44362), is located at about 44 degrees from the SVOM optical axis, which is inside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-14.5 to T0+21.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.26 +0.07/-0.06 and the cutoff energy, parameterized as Epeak, is 162 +18/-14 keV. The event fluence (10-1000 keV) in this time interval is (1.19 +/-0.05)E-05 erg/cm^2. The 1s peak spectrum, measured from T0+14.0 to T0+15.0 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -0.72 +/-0.07 and the cutoff energy, parameterized as Epeak, is 200 +13/-12 keV. The flux (10-1000 keV) in this time interval is (2.27 +0.09/-0.08)E-06 erg/cm^2/s. With the measured redshift z=2.115 (B. Schneider et al., GCN 44368), we calculate the isotropic energy Eiso is about 1.5E53 erg. Thus GRB 260421B is well consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/svgrb260421B_amati.png The localization of GRB 260421B in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260421B_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: Hao-Xuan Guo (IHEP)(guohx(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44389. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42510] GRB260421B: J band upper limit by SYSU 80cm infrared telescope
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44388 SUBJECT: GRB260421B: J band upper limit by SYSU 80cm infrared telescope DATE: 26/04/22 07:24:57 GMT FROM: shiy228(a)mail2.sysu.edu.cn Yun Shi, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Rui-Chen Gao, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Jin-Ji Li, Hao-Nan Yang, Yan Yu, Hao-Ran Zhang, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team: We observed the field of the long GRB 260421B, detected by Fermi-GBM (Fermi GBM team, GCN 44360) and SVOM/ECLAIRs (Zhao et al., GCN 44362), and followed up by Einstein Probe/FXT (Wang et al., GCN 44387), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope. Early near-infrared follow-up observations have also been reported (Mo et al., GCN 44384). Our observations were carried out from 2026 Apr 21 15:25 UT to Apr 21 17:06 UT, corresponding to 11.2–12.9 hours after the GBM trigger (2026-04-21 04:13:21 UT), with a total exposure time of 5200 s in the J band, obtained under poor conditions. We do not detect any near-infrared counterpart at the position of the reported afterglow (He et al., GCN 44363; Sanchez-Alvarez, GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366; Li et al., GCN 44377; Pérez-Fournon et al., GCN 44383; Wang et al., GCN 44387). The 5-sigma limiting magnitude is approximately J ~ 16.9 Vega magnitudes. The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44388. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42509] GRB 260421B: EP-FXT follow-up observation
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44387 SUBJECT: GRB 260421B: EP-FXT follow-up observation DATE: 26/04/22 02:42:41 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B. T. Wang (YNAO, CAS), J. P. Chen (SYSU), D. Y. Li, and W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260421B (SVOM/sb26042105; Zhao et al., GCN 44362), also triggered by Fermi-GBM (Fermi GBM team, GCN 44360; Preis & Greiner, GCN 44361; Mukherjee et al., GCN 44382), starting at 2026-04-21T06:08:31UTC, approximately 1.9 hours after the SVOM trigger, with a total exposure time of 5994 s. One uncataloged source is detected within the ECLAIRs error circle, which is spatially consistent with the optical counterpart (He et al., GCN 44363; Sanchez-Alvarez, GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366, Li et al., GCN 44377; Pérez-Fournon et al., GCN 44383) at a redshift of z=2.115 (Schneider et al., GCN 44368). Preliminary analysis on this source is automatically conducted, and the details are listed as follows. EPF_J124000.4-174426 RA (J2000): 190.0018 Dec (J2000): -17.74055 Flux: 1.26e-11 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 6.27e-13 erg/s/cm2 (1 sigma) Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44387. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42508] The EP-WXT trigger 01709260362 is likely a flaring star
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44386 SUBJECT: The EP-WXT trigger 01709260362 is likely a flaring star DATE: 26/04/22 01:30:57 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), J. P. Chen (SYSU), B. T. Wang (YNAO, CAS), R. D. Liang, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709260362 at the time of 2026-04-21T20:52:02, is likely a stellar flare associated with G 151-9. The estimated flux of the flare is around 2.8e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 2.7e31 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/44386. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42507] GOTO26djh/AT2026jpw: ATCA radio detection
by GCN Circulars 22 Apr '26

22 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44385 SUBJECT: GOTO26djh/AT2026jpw: ATCA radio detection DATE: 26/04/22 00:39:54 GMT FROM: James Leung at U. Toronto / HUJI <jamesk.leung(a)utoronto.ca> J. K. Leung (U. Toronto/HUJI) We observed the field of the transient GOTO26djh/AT2026jpw (O'Neill et al., GCN 44301) with the Australia Telescope Compact Array (ATCA). We conducted the observation on 2026 April 19 at 15:30 - 16:30 UT. In our preliminary analysis, we detect an unresolved radio source coincident with the position of the transient (Rhodes et al., GCN 44379). The unresolved radio source had a flux density of ~0.2mJy at 10 GHz and a self-absorbed spectrum at and around this frequency. 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/44385. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42506] GRB 260421B: J-band upper limit with WINTER
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44384 SUBJECT: GRB 260421B: J-band upper limit with WINTER DATE: 26/04/21 23:32:26 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 GRB 260421B (Fermi GBM Team, GCN 44360; Preis et al., GCN 44361; Zhao et al., GCN 44362; Mukherjee et al., GCN 44382) 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 2026-04-21T04:36:00 UTC in the J band (~23 min after the GRB trigger) under poor conditions, consisting of 10 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 (He et al., GCN 44363; Álvarez et al., GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366; Lipunov et al., GCN 44367; Schneider et al., GCN 44368; Li et al., GCN 44377; Pérez-Fournon et al., GCN 44383). We obtain the following 5-sigma upper limit: J = 16.4 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/44384. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42505] GRB 260421B: LCO optical counterpart detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44383 SUBJECT: GRB 260421B: LCO optical counterpart detection DATE: 26/04/21 23:18:19 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 long GRB 260421B by Fermi GBM (Fermi GBM team, GCN circ. 44360; Preis & Greiner, GCN circ. 44361; and Mukherjee, GCN circ. 44382) and by SVOM ECLAIRs, GBM, and MXT (Zhao et al., GCN circ. 44362), 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 200 sec in the SDSS r' filter, started on 2026-04-21 at 13:40:22 UT, about 9.45 hours after the Fermi trigger. The optical counterpart, first reported by He et al. (GCN circ. 44363), is detected in our image with an AB magnitude of 21.55 +/- 0.21, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. Other optical detections or upper limits have been reported by Sánchez Álvarez et al. (GCN circ. 44364), Turpin et al. (GCN circ. 44365), Wu et al. (GCN circ. 44366), Lipunov et al. (GCN circ. 44367), Schneider et al. (GCN circ. 44368, redshift of z = 2.115), and Li et al. (GCN circ. 44377). 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/44383. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42504] GRB 260421B: Fermi GBM Observation
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44382 SUBJECT: GRB 260421B: Fermi GBM Observation DATE: 26/04/21 19:36:16 GMT FROM: oindabimukherjee(a)gmail.com O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 04:13:21.17 UT on 21 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260421B (trigger 798437606/260421176), which was also detected by SVOM/ECLAIRs (Zhao et al. 2026, GCN 44362), and VLT/X-shooter with spectroscopic redshift z = 2.115 (Schneider et al. 2026, GCN 44368). The Fermi GBM on-ground location (GCN 44360) is consistent with the SVOM/ECLAIRs position. The angle from the Fermi LAT boresight is 58 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 18 s (50-300 keV). The time-averaged spectrum from T0-1.6 to T0+24.9 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.11 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 159 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (1.06 +/- 0.01)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+15 s in the 10-1000 keV band is 15.4 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 130 +/- 1 keV, alpha = -1 +/- 0.005 and beta = -2.31 +/- 0.02. 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/44382. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42503] Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44381 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB DATE: 26/04/21 19:24:18 GMT FROM: atrigg2(a)lsu.edu A. C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 798482368/260421694 at 16:39:23.09 UT on 21 April 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles (SAA Exit)." View this GCN Circular online at https://gcn.nasa.gov/circulars/44381. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42502] GRB 260421A: AstroSat CZTI detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44380 SUBJECT: GRB 260421A: AstroSat CZTI detection DATE: 26/04/21 15:59:15 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (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 short GRB 260421A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 44358). The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-21 02:12:43.91 UTC. The measured peak count rate associated with the burst is 251 (+66, -70) counts/s above the background in the combined data of all quadrants, with a total of 267 (+133, -138) counts. The local mean background count rate was 1340 (+8, -10) counts/s. Due to the intrinsic 1s binning of Veto data, we cannot reliably estimate T90 for this burst. 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/44380. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42501] GOTO26djh/AT2026jpw: radio detection at 15GHz
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44379 SUBJECT: GOTO26djh/AT2026jpw: radio detection at 15GHz DATE: 26/04/21 15:44:07 GMT FROM: Lauren Rhodes at McGill <lauren.rhodes(a)mcgill.ca> Lauren Rhodes (McGill), Andrew Hughes, Rob Fender (Oxford), Dave Green, Dave Titterington (Cambridge) report: We observed the position of GOTO26djh/AT2026jpw (GCN 44301) with the Arcminute Microkelvin Imager Large-Array (AMI-LA) at 15.5 GHz beginning for three epochs starting 2026-04-16 22:18UTC; 2026-04-17 21:14UTC and 2026-04-18 21:38UTC, each epoch lasting 5, 6.5, and 7 hours, respectively. We detect an unresolved source, in each epoch with coordinates consistent with those of GOTO26djh/AT2026jpw. We measure a peak flux density of 0.28±0.07, 0.44±0.08, and 0.36±0.09mJy//beam in epochs 1, 2 and 3, respectively. We thank the staff at the Mullard Radio Astronomy Observatory for carrying out these observations and operating the AMI-LA. (edited) View this GCN Circular online at https://gcn.nasa.gov/circulars/44379. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42500] GRB 260412A: SVOM/ECLAIRs refined analysis
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44378 SUBJECT: GRB 260412A: SVOM/ECLAIRs refined analysis DATE: 26/04/21 13:31:47 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Marius Brunet (IRAP), Wenjin XIE (NAOC), Olivier Godet (IRAP), Ziqi Wang (GXU), Zhiyong Liu(GZNU) 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 260412A (SVOM burst-id sb26041206 – GCN 44276, trigger time T0 = 2026-04-12T06:13:35 UTC), which was also detected by Fermi (GCN 44275, 44279), GECAM (GCN 44281) and HXMT (GCN 44294). The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve with late peaks at around T0+80s and T0+160s. The burst duration is T90 = 165.0 +2.6/-1.6 s in the 4-120 keV energy band. The time-averaged spectrum from T0-3.5 s to T0+200.5 s in the energy range 4-120 keV is best fitted by a powerlaw model with best-fit parameters – alpha = -1.5 +/-0.3. With this model, the 4-120 keV fluence is 7.4 +/- 0.3 e-6 erg/cm^2. Using the same Fermi/GBM time window as in Palafox et al. (GCN 44279), we retrieve a consistent photon index value when using a cutoff model and fixing Epeak at 210 keV. 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/44378. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42499] GRB 260421B: SVOM/VT optical observations
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44377 SUBJECT: GRB 260421B: SVOM/VT optical observations DATE: 26/04/21 11:53:36 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, L. P. Xin, Y. L. Qiu, 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, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), W. L. Zhang (PMO), Z. Y. Liu (GZNU) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic slew to the field of GRB 260421B triggered by SVOM/ECLAIRs (sb26042105, Zhao et al., GCN 44362). This burst was also detected by SVOM/GRM (Zhao et al., GCN 44362), SVOM/MXT (Zhao et al., GCN 44362), and Fermi-GBM (Fermi GBM team, GCN 44360; Preis & Greiner, GCN 44361). The observation started at 2026-04-21T04:18:32 UTC, i.e., approximately 5.1 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (He et al., GCN 44363; Sanchez-Alvarez, GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366) with redshift z=2.115 (Schneider et al., GCN 44368) was clearly detected in single frames in both channels. With X-band data available，the light curves showed a fast decay from 5.5 minutes to 50 minutes post trigger, following a plateau after 3.37 hours. The preliminary measurements are given in the AB magnitudes and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 5.53 min VT_B 50 sec 16.23+/-0.03 mag 5.53 min VT_R 50 sec 15.77+/-0.03 mag 3.599 hr VT_B 27*100 sec 20.94+/-0.07 mag 3.668 hr VT_R 22*100 sec 20.52+/-0.06 mag 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/44377. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42498] EP260416a: J band upper limit by SYSU 80cm infrared telescope
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44376 SUBJECT: EP260416a: J band upper limit by SYSU 80cm infrared telescope DATE: 26/04/21 11:00:51 GMT FROM: lijj328(a)mail2.sysu.edu.cn Jin-Ji Li, Hao-Nan Yang, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Rui-Chen Gao, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Yun Shi, Yan Yu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team: We observed the field of the fast X-ray transient EP260416a (Hu et al., GCN 44307) using the Sun Yat-sen University (SYSU) 80cm infrared telescope. Our observations were carried out on 2026 Apr 19 18:39 UT, 85.1 hours after the trigger, using stacked images in the J band. We do not detect any counterpart at the position of the optical counterpart (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334, He et al. GCN 44336, An et al. GCN 44339, Jelinek et al. GCN 44341; Guziy et al., GCN 44351; Ho et al., GCN 44354), down to a 5-sigma depth of J ~ 18.1 Vega magnitudes. The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44376. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42497] GRB 260310A: Late-time Chandra X-ray Detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44375 SUBJECT: GRB 260310A: Late-time Chandra X-ray Detection DATE: 26/04/21 10:40:36 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang (U Rome), Eleonora Troja (U Rome), Yi-Han Iris Yin (HKU), Brendan O’Connor (CMU), Muskan Yadav (U Rome), Niccolo’ Passaleva (U Rome), Roberto Ricci (U Rome) report: We imaged the field of GRB 260310A (Fermi GBM team, GCN 43951,43975; AstroSat CZTI collaboration, GCN 43958) with the Chandra X-ray Observatory via a Director’s Discretionary Time (DDT) request (PI: Yang). Observations started at 2026-04-20T01:47:42 (~41 days after the trigger) using the ACIS-S instrument with a total exposure time of ~5 ks. Three sources are detected within a 1-arcmin radius centered on the optical counterpart (O’Neill et al. 2026, TNS Discovery Report 294132). The target afterglow is clearly identified with 89 counts, while two neighboring sources are marginal contributors, yielding only 5 and 9 counts, respectively. We performed a preliminary spectral analysis of the afterglow in the 0.5–8 keV range, adopting an absorbed power-law model with a fixed galactic absorption (N_H = 2.59e20/cm2) and intrinsic absorption (N_Hz = 1.7e21/cm2). We find a photon index of 2.07 ± 0.25 and a corresponding unabsorbed flux of (5.9+/-0.8)e-13 ergs/cm2/s (0.3-10 keV). Our observations confirm that the X-ray rebrightening (Jayaraman et al., GCN 44234; Waratkar et al.; GCN 44278) is intrinsic to the GRB afterglow and not contributed by nearby sources. Our temporal analysis indicates that the light curve is consistent with a late-time bump which is currently transitioning into a decay phase. We thank the Chandra director, Pat Slane, for awarding discretionary time and the observatory staff for rapidly scheduling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44375. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42496] GRB 260418A: Insight-HXMT/HE detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44374 SUBJECT: GRB 260418A: Insight-HXMT/HE detection DATE: 26/04/21 10:34:05 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 2026-04-18T04:49:35.000 (T0), Insight-HXMT/HE detected a short burst, GRB 260418A, which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44335). The Insight-HXMT/HE light curve mainly consists of a single pulse with a duration (T90) of 0.30 +0.55/-0.10 s. The 1s peak rate, measured from T0-0.475 s, is 361 cnts/sec. Insight-HXMT/HE detected a total of 292 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260418A.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/44374. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42495] EP260416a: 1.3m DFOT optical observation
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44373 SUBJECT: EP260416a: 1.3m DFOT optical observation DATE: 26/04/21 10:02:49 GMT FROM: pawarpankaj1492(a)gmail.com Pankaj Pawar, Anshika Gupta, Debalina Kar, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of EP260416a (Hu et al., GCN 44307) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of observational sciencES (ARIES), India. The observations began on 2026-04-20 at 15:58:17 UT, approximately ~106 hours after the trigger. We obtained a series of 300s exposures in the R filter. The frames were aligned and stacked to improve the signal-to-noise ratio. The optical counterpart (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334; He et al. GCN 44336; An et al. GCN 44339; Jelinek et al. GCN 44341; Guziy et al., GCN 44351; and Ho et al., GCN 44354) was not detected in the stacked image. The details of observations and measured upper limit are as follows: Date (UT) Start Time T_start-T0 (days) Filter Exposure (s) Magnitude (AB) ======================================================================================= 2026-04-20 15:58:17 ~4.44 R 300s*13 >22.6 The magnitude is calibrated using Pan-STARRS field stars. View this GCN Circular online at https://gcn.nasa.gov/circulars/44373. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42494] GRB 260415A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44372 SUBJECT: GRB 260415A: CALET Gamma-Ray Burst Monitor detection DATE: 26/04/21 09:56:37 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> 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), N. Cannady (GSFC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 260415A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN #44299; Insight-HXMT/HE detection: Ren et al., GCN #44311) at 04:43:58.34 UTC on 15 April 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1460263432/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a double-peaked structure starting at T-1.5 s, peaking at T+30.1 s, and ending at T+41.1 s. The T90 and T50 durations measured with the SGM data are 36.2 +/- 1.5 s and 19.9 +/- 1.9 s (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1460263432/ The CALET data used in this analysis were provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44372. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42493] GRB 260415B: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44371 SUBJECT: GRB 260415B: CALET Gamma-Ray Burst Monitor detection DATE: 26/04/21 09:51:16 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> P. S. Marrocchesi (U of Siena), 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), N. Cannady (GSFC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), and the CALET collaboration: The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 260415B (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN #44300; NuSTAR detection: Waratkar et al., GCN #44302; Glowbug gamma-ray detection: Woolf et al., GCN #44313) at 02:28:55.55 UTC on 15 April 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1460255329/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure starting at T-2.9 s, peaking at T+22.1 s, and ending at T+124.5 s. The T90 and T50 durations measured with the SGM data are 111.6 +/- 1.8 s and 50.7 +/- 1.0 s (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1460255329/ The CALET data used in this analysis were provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44371. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42492] Fermi GRB 260421C: Global MASTER-Net observations report
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44370 SUBJECT: Fermi GRB 260421C: Global MASTER-Net observations report DATE: 26/04/21 09:30:49 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260421C ( Fermi GBM team, GCN 44369) errorbox 165 sec after notice time and 186 sec after trigger time at 2026-04-21 08:28:26 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 51 deg. The sun altitude is -43.9 deg. The galactic latitude b = 19 deg., longitude l = 96 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3263342 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 217 | 2026-04-21 08:28:26 | MASTER-OAGH | (19h 25m 37.26s , +63d 45m 12.4s) | C | 60 | 19.6 | 217 | 2026-04-21 08:28:26 | MASTER-OAGH | (19h 28m 03.53s , +63d 11m 30.5s) | C | 60 | 19.8 | 290 | 2026-04-21 08:29:39 | MASTER-OAGH | (19h 43m 37.39s , +63d 44m 07.3s) | C | 60 | 19.6 | 290 | 2026-04-21 08:29:39 | MASTER-OAGH | (19h 46m 02.78s , +63d 10m 22.7s) | C | 60 | 19.9 | 518 | 2026-04-21 08:33:28 | MASTER-OAGH | (19h 26m 38.22s , +59d 56m 08.4s) | C | 60 | 20.0 | 518 | 2026-04-21 08:33:28 | MASTER-OAGH | (19h 28m 49.30s , +59d 22m 23.7s) | C | 60 | 20.2 | 736 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 39m 52.48s , +63d 57m 57.9s) | C | 120 | 19.9 | 856 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 39m 52.48s , +63d 57m 57.9s) | C | 360 | 20.5 | Coadd 736 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 42m 20.57s , +63d 24m 11.2s) | C | 120 | 20.1 | 856 | 2026-04-21 08:36:35 | MASTER-OAGH | (19h 42m 20.57s , +63d 24m 11.2s) | C | 360 | 20.5 | Coadd 936 | 2026-04-21 08:39:55 | MASTER-OAGH | (19h 39m 52.89s , +63d 57m 53.5s) | C | 120 | 19.9 | 936 | 2026-04-21 08:39:55 | MASTER-OAGH | (19h 42m 21.02s , +63d 24m 06.6s) | C | 120 | 20.1 | 1066 | 2026-04-21 08:42:05 | MASTER-OAGH | (19h 39m 58.99s , +63d 56m 50.1s) | C | 120 | 20.0 | 1066 | 2026-04-21 08:42:05 | MASTER-OAGH | (19h 42m 27.17s , +63d 23m 03.5s) | C | 120 | 20.2 | 1197 | 2026-04-21 08:44:16 | MASTER-OAGH | (19h 39m 53.32s , +63d 57m 47.2s) | C | 120 | 20.0 | 1197 | 2026-04-21 08:44:16 | MASTER-OAGH | (19h 42m 21.81s , +63d 24m 00.3s) | C | 120 | 20.2 | 1328 | 2026-04-21 08:46:27 | MASTER-OAGH | (19h 39m 59.23s , +63d 56m 43.3s) | C | 120 | 19.9 | 1328 | 2026-04-21 08:46:27 | MASTER-OAGH | (19h 42m 27.64s , +63d 22m 56.8s) | C | 120 | 20.2 | 2193 | 2026-04-21 09:01:22 | MASTER-OAGH | (19h 26m 48.80s , +59d 56m 20.2s) | C | 60 | 19.9 | 2193 | 2026-04-21 09:01:22 | MASTER-OAGH | (19h 29m 01.44s , +59d 22m 30.8s) | C | 60 | 20.0 | 2326 | 2026-04-21 09:03:35 | MASTER-OAGH | (19h 17m 11.76s , +61d 50m 25.1s) | C | 60 | 19.7 | 2326 | 2026-04-21 09:03:35 | MASTER-OAGH | (19h 19m 32.38s , +61d 16m 36.3s) | C | 60 | 19.9 | 2397 | 2026-04-21 09:04:46 | MASTER-OAGH | (19h 34m 03.19s , +61d 49m 16.1s) | C | 60 | 19.5 | 2397 | 2026-04-21 09:04:46 | MASTER-OAGH | (19h 36m 23.31s , +61d 15m 26.3s) | C | 60 | 19.9 | 2557 | 2026-04-21 09:06:57 | MASTER-OAGH | (19h 51m 54.15s , +63d 51m 04.9s) | C | 120 | 19.9 | 2557 | 2026-04-21 09:06:57 | MASTER-OAGH | (19h 54m 23.17s , +63d 17m 13.8s) | C | 120 | 20.0 | 2688 | 2026-04-21 09:09:07 | MASTER-OAGH | (19h 52m 00.00s , +63d 50m 02.0s) | C | 120 | 19.9 | 2688 | 2026-04-21 09:09:07 | MASTER-OAGH | (19h 54m 29.04s , +63d 16m 12.0s) | C | 120 | 19.9 | 2819 | 2026-04-21 09:11:18 | MASTER-OAGH | (19h 50m 19.75s , +64d 50m 59.2s) | C | 120 | 19.6 | 2819 | 2026-04-21 09:11:18 | MASTER-OAGH | (19h 52m 54.24s , +64d 17m 09.7s) | C | 120 | 19.6 | 2950 | 2026-04-21 09:13:29 | MASTER-OAGH | (19h 50m 26.43s , +64d 49m 56.1s) | C | 120 | 19.8 | 2950 | 2026-04-21 09:13:29 | MASTER-OAGH | (19h 53m 00.91s , +64d 16m 07.5s) | C | 120 | 19.8 | 3125 | 2026-04-21 09:16:54 | MASTER-OAGH | (19h 26m 53.60s , +59d 55m 26.9s) | C | 60 | 19.4 | 3125 | 2026-04-21 09:16:54 | MASTER-OAGH | (19h 29m 07.76s , +59d 21m 41.7s) | C | 60 | 19.4 | 3197 | 2026-04-21 09:18:06 | MASTER-OAGH | (19h 17m 13.13s , +61d 50m 46.4s) | C | 60 | 19.4 | 3197 | 2026-04-21 09:18:06 | MASTER-OAGH | (19h 19m 35.44s , +61d 17m 01.7s) | C | 60 | 19.5 | 3305 | 2026-04-21 09:19:24 | MASTER-OAGH | (19h 36m 06.37s , +65d 49m 10.5s) | C | 120 | 19.7 | 3305 | 2026-04-21 09:19:24 | MASTER-OAGH | (19h 38m 48.49s , +65d 15m 24.8s) | C | 120 | 19.8 | 3436 | 2026-04-21 09:21:35 | MASTER-OAGH | (19h 36m 10.81s , +65d 50m 43.9s) | C | 120 | 19.3 | 3436 | 2026-04-21 09:21:35 | MASTER-OAGH | (19h 38m 53.00s , +65d 16m 58.7s) | C | 120 | 19.5 | 3567 | 2026-04-21 09:23:46 | MASTER-OAGH | (19h 24m 08.88s , +65d 49m 56.4s) | C | 120 | 19.5 | 3567 | 2026-04-21 09:23:46 | MASTER-OAGH | (19h 26m 51.43s , +65d 16m 11.7s) | C | 120 | 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/44370. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42491] GRB 260421C: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44369 SUBJECT: GRB 260421C: Fermi GBM Final Real-time Localization DATE: 26/04/21 08:35:58 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 08:25:19 UT on 21 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260421C (trigger 798452724.59066 / 260421351). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 295.0, Dec = 64.2 (J2000 degrees, equivalent to J2000 19h 40m, 64d 12'), with a statistical uncertainty of 3.1 degrees. The angle from the Fermi LAT boresight is 59.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421351/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421351/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421351/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44369. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42490] GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44368 SUBJECT: GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115 DATE: 26/04/21 06:41:33 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> B. Schneider (LAM), A. Saccardi (CEA/Irfu), N. Habeeb (Leicester), R. Brivio (INAF/OAB), A. L. Thakur (INAF/IAPS), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of the Stargate collaboration: We observed the optical counterpart (He et al., GCN 44363; Sanchez-Alvarez, GCN 44364; Turpin et al., GCN 44365; Wu et al., GCN 44366) of the SVOM and Fermi GRB 260421B (Zhao et al., GCN 44362; Fermi GBM Team, GCN 44360) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-25000 AA, and consist of 4 exposures of 600 s each. The observation mid time was 05:39 UT on 2026 April 21 (1.42 hr after the SVOM/ECLAIRs trigger). In a 5-s acquisition image (taken 61 min after the SVOM/ECLAIRs trigger), the afterglow is detected with a magnitude r = 20.43 +/- 0.05 AB, calibrated against the single Pan-STARRS object lying in our field of view, and not corrected for Galactic extinction. In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. At the blue edge of the spectrum, we identify a broad trough at around 3786 AA, likely due to H I Lyman-alpha. Multiple absorption lines are also detected, which we interpret as due to, among others, S II, Si II, O I, Si II*, C II, C II*, Si IV, C IV, Fe II, Fe II*, Mg II, all at a common redshift z = 2.115. We consider this to be the redshift of GRB 260421B. We acknowledge the excellent expert support from the observing staff in Paranal, in particular Francisco Caceres and Matias Jones. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) We thank the COLIBRÍ (FM-GFT) team for alerting us of the afterglow prior to their GCN release. View this GCN Circular online at https://gcn.nasa.gov/circulars/44368. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42489] Fermi GRB 260421B: Global MASTER-Net observations report
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44367 SUBJECT: Fermi GRB 260421B: Global MASTER-Net observations report DATE: 26/04/21 05:45:38 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260421B ( Fermi GBM team, GCN 44360) errorbox 93 sec after notice time and 126 sec after trigger time at 2026-04-21 04:15:27 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 56 deg. The sun altitude is -28.9 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260421B errorbox 867 sec after notice time and 900 sec after trigger time at 2026-04-21 04:28:21 UT, with upper limit up to 20.2 mag. The observations began at zenith distance = 21 deg. The sun altitude is -70.7 deg. The galactic latitude b = 45 deg., longitude l = 298 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3262990 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 142 | 2026-04-21 04:15:27 | MASTER-OAGH | (12h 53m 10.93s , -17d 20m 23.6s) | C | 30 | 18.4 | 177 | 2026-04-21 04:15:27 | MASTER-OAGH | (12h 53m 10.93s , -17d 20m 23.5s) | C | 100 | 19.1 | Coadd 181 | 2026-04-21 04:16:07 | MASTER-OAGH | (12h 53m 17.82s , -17d 20m 17.3s) | C | 30 | 18.5 | 226 | 2026-04-21 04:16:47 | MASTER-OAGH | (12h 53m 13.89s , -17d 18m 44.5s) | C | 40 | 18.4 | 282 | 2026-04-21 04:17:37 | MASTER-OAGH | (12h 53m 13.81s , -17d 20m 10.6s) | C | 50 | 18.7 | 352 | 2026-04-21 04:17:37 | MASTER-OAGH | (12h 53m 13.81s , -17d 20m 10.6s) | C | 190 | 19.7 | Coadd 347 | 2026-04-21 04:18:38 | MASTER-OAGH | (12h 53m 17.74s , -17d 19m 02.7s) | C | 60 | 18.8 | 427 | 2026-04-21 04:19:48 | MASTER-OAGH | (12h 53m 11.54s , -17d 19m 39.5s) | C | 80 | 19.2 | 538 | 2026-04-21 04:21:28 | MASTER-OAGH | (12h 35m 06.04s , -17d 47m 57.6s) | C | 100 | 19.2 | 538 | 2026-04-21 04:21:28 | MASTER-OAGH | (12h 36m 24.29s , -18d 21m 51.5s) | C | 100 | 19.4 | 980 | 2026-04-21 04:28:11 | MASTER-OAGH | (12h 39m 45.91s , -17d 46m 54.8s) | P- | 180 | 17.5 | 980 | 2026-04-21 04:28:11 | MASTER-OAGH | (12h 41m 04.22s , -18d 20m 54.9s) | P| | 180 | 17.7 | 1160 | 2026-04-21 04:28:11 | MASTER-OAGH | (12h 41m 04.22s , -18d 20m 54.8s) | P| | 540 | 18.8 | Coadd 930 | 2026-04-21 04:28:21 | MASTER-OAFA | (12h 40m 14.08s , -17d 24m 25.2s) | C | 60 | 20.0 | 996 | 2026-04-21 04:29:26 | MASTER-OAFA | (12h 40m 14.11s , -17d 24m 23.6s) | C | 60 | 20.1 | 1061 | 2026-04-21 04:30:32 | MASTER-OAFA | (12h 40m 14.15s , -17d 24m 22.0s) | C | 60 | 20.1 | 1170 | 2026-04-21 04:31:21 | MASTER-OAGH | (12h 39m 52.24s , -17d 46m 46.8s) | P- | 180 | 17.7 | 1170 | 2026-04-21 04:31:21 | MASTER-OAGH | (12h 41m 10.67s , -18d 20m 47.4s) | P| | 180 | 18.1 | 1127 | 2026-04-21 04:31:38 | MASTER-OAFA | (12h 40m 14.20s , -17d 24m 20.9s) | C | 60 | 20.2 | 1193 | 2026-04-21 04:32:44 | MASTER-OAFA | (12h 40m 14.23s , -17d 24m 19.6s) | C | 60 | 20.1 | 1259 | 2026-04-21 04:33:49 | MASTER-OAFA | (12h 40m 14.26s , -17d 24m 18.2s) | C | 60 | 20.1 | 1361 | 2026-04-21 04:34:31 | MASTER-OAGH | (12h 39m 49.24s , -17d 45m 09.3s) | P- | 180 | 17.7 | 1361 | 2026-04-21 04:34:31 | MASTER-OAGH | (12h 41m 07.78s , -18d 19m 10.2s) | P| | 180 | 18.3 | 1325 | 2026-04-21 04:34:56 | MASTER-OAFA | (12h 40m 14.30s , -17d 24m 16.6s) | C | 60 | 20.0 | 1391 | 2026-04-21 04:36:01 | MASTER-OAFA | (12h 40m 14.36s , -17d 24m 15.7s) | C | 60 | 20.2 | 1456 | 2026-04-21 04:37:07 | MASTER-OAFA | (12h 40m 14.39s , -17d 24m 14.3s) | C | 60 | 20.1 | 1552 | 2026-04-21 04:37:43 | MASTER-OAGH | (12h 39m 49.10s , -17d 46m 59.8s) | P- | 180 | 17.9 | 1552 | 2026-04-21 04:37:43 | MASTER-OAGH | (12h 41m 07.75s , -18d 21m 00.3s) | P| | 180 | 18.3 | 1522 | 2026-04-21 04:38:13 | MASTER-OAFA | (12h 40m 14.44s , -17d 24m 13.3s) | C | 60 | 20.2 | 1588 | 2026-04-21 04:39:18 | MASTER-OAFA | (12h 40m 14.44s , -17d 24m 12.1s) | C | 60 | 20.1 | 1653 | 2026-04-21 04:40:24 | MASTER-OAFA | (12h 40m 14.48s , -17d 24m 10.8s) | C | 60 | 20.1 | 1742 | 2026-04-21 04:40:53 | MASTER-OAGH | (12h 39m 51.19s , -17d 45m 34.9s) | P- | 180 | 17.7 | 1742 | 2026-04-21 04:40:53 | MASTER-OAGH | (12h 41m 09.87s , -18d 19m 35.1s) | P| | 180 | 18.4 | 1720 | 2026-04-21 04:41:30 | MASTER-OAFA | (12h 40m 14.54s , -17d 24m 09.9s) | C | 60 | 20.1 | 1785 | 2026-04-21 04:42:36 | MASTER-OAFA | (12h 40m 14.54s , -17d 24m 08.9s) | C | 60 | 20.1 | 1850 | 2026-04-21 04:43:41 | MASTER-OAFA | (12h 40m 14.57s , -17d 24m 07.9s) | C | 60 | 20.0 | 1874 | 2026-04-21 04:44:05 | MASTER-OAGH | (12h 34m 22.11s , -17d 48m 09.2s) | C | 60 | 19.5 | 1874 | 2026-04-21 04:44:05 | MASTER-OAGH | (12h 35m 41.12s , -18d 22m 06.8s) | C | 60 | 19.7 | 1917 | 2026-04-21 04:44:48 | MASTER-OAFA | (12h 40m 14.60s , -17d 24m 07.3s) | C | 60 | 20.1 | 1946 | 2026-04-21 04:45:17 | MASTER-OAGH | (12h 25m 58.60s , -17d 47m 08.9s) | C | 60 | 19.3 | 1946 | 2026-04-21 04:45:17 | MASTER-OAGH | (12h 27m 17.78s , -18d 21m 05.4s) | C | 60 | 19.7 | 1982 | 2026-04-21 04:45:53 | MASTER-OAFA | (12h 40m 14.65s , -17d 24m 05.9s) | C | 60 | 20.1 | 2047 | 2026-04-21 04:46:58 | MASTER-OAFA | (12h 40m 14.66s , -17d 24m 04.9s) | C | 60 | 20.1 | 2113 | 2026-04-21 04:48:04 | MASTER-OAFA | (12h 40m 14.68s , -17d 24m 03.9s) | C | 60 | 20.1 | 2179 | 2026-04-21 04:49:09 | MASTER-OAFA | (12h 40m 14.72s , -17d 24m 02.9s) | C | 60 | 20.2 | 2245 | 2026-04-21 04:50:15 | MASTER-OAFA | (12h 40m 14.76s , -17d 24m 02.1s) | C | 60 | 20.2 | 2311 | 2026-04-21 04:51:22 | MASTER-OAFA | (12h 40m 14.77s , -17d 24m 00.8s) | C | 60 | 20.1 | 2376 | 2026-04-21 04:52:27 | MASTER-OAFA | (12h 40m 14.82s , -17d 24m 00.2s) | C | 60 | 20.2 | 2442 | 2026-04-21 04:53:32 | MASTER-OAFA | (12h 40m 14.86s , -17d 23m 59.2s) | C | 60 | 20.2 | 2474 | 2026-04-21 04:54:05 | MASTER-OAGH | (12h 34m 21.59s , -17d 48m 11.5s) | C | 60 | 19.4 | 2474 | 2026-04-21 04:54:05 | MASTER-OAGH | (12h 35m 40.80s , -18d 22m 07.1s) | C | 60 | 19.8 | 2508 | 2026-04-21 04:54:39 | MASTER-OAFA | (12h 40m 14.86s , -17d 23m 58.4s) | C | 60 | 20.1 | 2546 | 2026-04-21 04:55:17 | MASTER-OAGH | (12h 25m 58.36s , -17d 49m 11.4s) | C | 60 | 19.5 | 2546 | 2026-04-21 04:55:17 | MASTER-OAGH | (12h 27m 17.73s , -18d 23m 06.0s) | C | 60 | 19.7 | 2574 | 2026-04-21 04:55:44 | MASTER-OAFA | (12h 40m 14.88s , -17d 23m 57.6s) | C | 60 | 20.0 | 2640 | 2026-04-21 04:56:50 | MASTER-OAFA | (12h 40m 14.94s , -17d 23m 56.9s) | C | 60 | 20.1 | 2706 | 2026-04-21 04:57:57 | MASTER-OAFA | (12h 40m 14.96s , -17d 23m 55.9s) | C | 60 | 20.0 | 2771 | 2026-04-21 04:59:02 | MASTER-OAFA | (12h 40m 15.00s , -17d 23m 54.7s) | C | 60 | 20.0 | 2837 | 2026-04-21 05:00:08 | MASTER-OAFA | (12h 40m 15.01s , -17d 23m 53.9s) | C | 60 | 19.9 | 2903 | 2026-04-21 05:01:14 | MASTER-OAGH | (12h 34m 23.48s , -19d 42m 11.3s) | C | 60 | 18.8 | 2903 | 2026-04-21 05:01:14 | MASTER-OAGH | (12h 35m 43.55s , -20d 16m 06.9s) | C | 60 | 19.0 | 2903 | 2026-04-21 05:01:14 | MASTER-OAFA | (12h 40m 15.04s , -17d 23m 53.2s) | C | 60 | 20.0 | 2968 | 2026-04-21 05:02:19 | MASTER-OAFA | (12h 40m 15.06s , -17d 23m 52.6s) | C | 60 | 20.0 | 2974 | 2026-04-21 05:02:25 | MASTER-OAGH | (12h 42m 52.05s , -19d 41m 12.6s) | C | 60 | 18.6 | 2974 | 2026-04-21 05:02:25 | MASTER-OAGH | (12h 44m 12.00s , -20d 15m 09.4s) | C | 60 | 19.1 | 3034 | 2026-04-21 05:03:25 | MASTER-OAFA | (12h 40m 15.10s , -17d 23m 51.8s) | C | 60 | 20.0 | 3100 | 2026-04-21 05:04:31 | MASTER-OAFA | (12h 40m 15.14s , -17d 23m 51.1s) | C | 60 | 19.9 | 3106 | 2026-04-21 05:04:37 | MASTER-OAGH | (12h 34m 20.33s , -17d 47m 13.7s) | C | 60 | 19.1 | 3106 | 2026-04-21 05:04:37 | MASTER-OAGH | (12h 35m 39.73s , -18d 21m 08.6s) | C | 60 | 19.2 | 3166 | 2026-04-21 05:05:37 | MASTER-OAFA | (12h 40m 15.18s , -17d 23m 50.7s) | C | 60 | 20.0 | 3177 | 2026-04-21 05:05:47 | MASTER-OAGH | (12h 26m 02.37s , -17d 48m 11.9s) | C | 60 | 19.3 | 3177 | 2026-04-21 05:05:47 | MASTER-OAGH | (12h 27m 21.94s , -18d 22m 05.5s) | C | 60 | 19.6 | 3232 | 2026-04-21 05:06:42 | MASTER-OAFA | (12h 40m 15.19s , -17d 23m 50.1s) | C | 60 | 20.0 | 3298 | 2026-04-21 05:07:49 | MASTER-OAFA | (12h 40m 15.22s , -17d 23m 49.4s) | C | 60 | 20.1 | 3307 | 2026-04-21 05:07:58 | MASTER-OAGH | (12h 34m 24.99s , -15d 54m 14.3s) | C | 60 | 19.5 | 3307 | 2026-04-21 05:07:58 | MASTER-OAGH | (12h 35m 43.97s , -16d 28m 07.6s) | C | 60 | 19.6 | 3363 | 2026-04-21 05:08:54 | MASTER-OAFA | (12h 40m 15.24s , -17d 23m 48.3s) | C | 60 | 20.0 | 3378 | 2026-04-21 05:09:08 | MASTER-OAGH | (12h 42m 36.90s , -15d 55m 16.1s) | C | 60 | 19.3 | 3378 | 2026-04-21 05:09:08 | MASTER-OAGH | (12h 43m 55.82s , -16d 29m 09.9s) | C | 60 | 19.6 | 3429 | 2026-04-21 05:09:59 | MASTER-OAFA | (12h 40m 15.26s , -17d 23m 47.3s) | C | 60 | 20.0 | 3495 | 2026-04-21 05:11:05 | MASTER-OAFA | (12h 40m 15.29s , -17d 23m 46.6s) | C | 60 | 20.0 | 3509 | 2026-04-21 05:11:20 | MASTER-OAGH | (12h 34m 22.74s , -19d 41m 12.5s) | C | 60 | 19.6 | 3509 | 2026-04-21 05:11:20 | MASTER-OAGH | (12h 35m 43.08s , -20d 15m 06.9s) | C | 60 | 19.9 | 3560 | 2026-04-21 05:12:11 | MASTER-OAFA | (12h 40m 15.29s , -17d 23m 46.2s) | C | 60 | 20.0 | 3581 | 2026-04-21 05:12:32 | MASTER-OAGH | (12h 42m 57.79s , -19d 42m 14.3s) | C | 60 | 19.6 | 3581 | 2026-04-21 05:12:32 | MASTER-OAGH | (12h 44m 18.06s , -20d 16m 09.5s) | C | 60 | 19.7 | 3626 | 2026-04-21 05:13:17 | MASTER-OAFA | (12h 40m 15.31s , -17d 23m 45.6s) | C | 60 | 20.0 | 3692 | 2026-04-21 05:14:23 | MASTER-OAFA | (12h 40m 15.34s , -17d 23m 45.0s) | C | 60 | 20.0 | 3719 | 2026-04-21 05:14:50 | MASTER-OAGH | (12h 34m 21.06s , -17d 47m 14.4s) | C | 60 | 19.6 | 3719 | 2026-04-21 05:14:50 | MASTER-OAGH | (12h 35m 40.72s , -18d 21m 07.3s) | C | 60 | 19.9 | 3758 | 2026-04-21 05:15:29 | MASTER-OAFA | (12h 40m 15.36s , -17d 23m 44.7s) | C | 60 | 20.1 | 3791 | 2026-04-21 05:16:02 | MASTER-OAGH | (12h 26m 01.87s , -17d 48m 12.2s) | C | 60 | 19.3 | 3791 | 2026-04-21 05:16:02 | MASTER-OAGH | (12h 27m 21.65s , -18d 22m 03.8s) | C | 60 | 19.3 | 3823 | 2026-04-21 05:16:34 | MASTER-OAFA | (12h 40m 15.39s , -17d 23m 44.0s) | C | 60 | 20.1 | 3889 | 2026-04-21 05:17:40 | MASTER-OAFA | (12h 40m 15.43s , -17d 23m 43.4s) | C | 60 | 20.1 | 3930 | 2026-04-21 05:18:21 | MASTER-OAGH | (12h 34m 17.86s , -15d 53m 14.7s) | C | 60 | 19.4 | 3930 | 2026-04-21 05:18:21 | MASTER-OAGH | (12h 35m 37.05s , -16d 27m 06.0s) | C | 60 | 19.5 | 3955 | 2026-04-21 05:18:45 | MASTER-OAFA | (12h 40m 15.45s , -17d 23m 42.8s) | C | 60 | 20.2 | 4002 | 2026-04-21 05:19:32 | MASTER-OAGH | (12h 42m 42.14s , -15d 54m 17.4s) | C | 60 | 18.6 | 4002 | 2026-04-21 05:19:32 | MASTER-OAGH | (12h 44m 01.28s , -16d 28m 08.9s) | C | 60 | 18.9 | 4021 | 2026-04-21 05:19:51 | MASTER-OAFA | (12h 40m 15.46s , -17d 23m 42.1s) | C | 60 | 20.1 | 4087 | 2026-04-21 05:20:58 | MASTER-OAFA | (12h 40m 15.48s , -17d 23m 41.6s) | C | 60 | 20.1 | 4141 | 2026-04-21 05:21:51 | MASTER-OAGH | (12h 34m 22.53s , -19d 41m 12.5s) | C | 60 | 16.1 | 4141 | 2026-04-21 05:21:51 | MASTER-OAGH | (12h 35m 43.04s , -20d 15m 04.4s) | C | 60 | 15.7 | 4153 | 2026-04-21 05:22:04 | MASTER-OAFA | (12h 40m 15.50s , -17d 23m 41.3s) | C | 60 | 20.0 | 4212 | 2026-04-21 05:23:03 | MASTER-OAGH | (12h 42m 58.08s , -19d 42m 15.1s) | C | 60 | 18.5 | 4212 | 2026-04-21 05:23:03 | MASTER-OAGH | (12h 44m 18.55s , -20d 16m 07.7s) | C | 60 | 18.1 | 4219 | 2026-04-21 05:23:09 | MASTER-OAFA | (12h 40m 15.52s , -17d 23m 40.6s) | C | 60 | 20.1 | 4285 | 2026-04-21 05:24:15 | MASTER-OAFA | (12h 40m 15.55s , -17d 23m 40.1s) | C | 60 | 20.0 | 4341 | 2026-04-21 05:25:12 | MASTER-OAGH | (12h 34m 18.76s , -17d 47m 13.7s) | C | 60 | 18.2 | 4341 | 2026-04-21 05:25:12 | MASTER-OAGH | (12h 35m 38.65s , -18d 21m 04.7s) | C | 60 | 17.9 | 4350 | 2026-04-21 05:25:20 | MASTER-OAFA | (12h 40m 15.59s , -17d 23m 39.6s) | C | 60 | 20.0 | 4412 | 2026-04-21 05:26:23 | MASTER-OAGH | (12h 26m 01.58s , -17d 48m 10.3s) | C | 60 | 15.8 | 4412 | 2026-04-21 05:26:23 | MASTER-OAGH | (12h 27m 21.61s , -18d 22m 00.1s) | C | 60 | 16.0 | 4416 | 2026-04-21 05:26:26 | MASTER-OAFA | (12h 40m 15.62s , -17d 23m 39.2s) | C | 60 | 20.1 | 4482 | 2026-04-21 05:27:33 | MASTER-OAFA | (12h 40m 15.64s , -17d 23m 38.8s) | C | 60 | 19.9 | 4542 | 2026-04-21 05:28:33 | MASTER-OAGH | (12h 34m 16.69s , -15d 53m 12.9s) | C | 60 | 14.3 | 4547 | 2026-04-21 05:28:38 | MASTER-OAFA | (12h 40m 15.67s , -17d 23m 38.2s) | C | 60 | 20.0 | 4613 | 2026-04-21 05:29:44 | MASTER-OAGH | (12h 42m 41.80s , -15d 54m 16.3s) | C | 60 | 15.3 | 4613 | 2026-04-21 05:29:44 | MASTER-OAGH | (12h 44m 01.27s , -16d 28m 06.0s) | C | 60 | 14.9 | 4613 | 2026-04-21 05:29:44 | MASTER-OAFA | (12h 40m 15.70s , -17d 23m 37.8s) | C | 60 | 19.9 | 4679 | 2026-04-21 05:30:50 | MASTER-OAFA | (12h 40m 15.74s , -17d 23m 37.2s) | C | 60 | 20.0 | 4743 | 2026-04-21 05:31:54 | MASTER-OAGH | (12h 34m 21.40s , -19d 41m 10.3s) | C | 60 | 14.6 | 4743 | 2026-04-21 05:31:54 | MASTER-OAGH | (12h 35m 42.22s , -20d 15m 00.7s) | C | 60 | 14.5 | 4745 | 2026-04-21 05:31:55 | MASTER-OAFA | (12h 40m 15.77s , -17d 23m 37.0s) | C | 60 | 20.0 | 4810 | 2026-04-21 05:33:01 | MASTER-OAFA | (12h 40m 15.79s , -17d 23m 36.5s) | C | 60 | 20.1 | 4815 | 2026-04-21 05:33:05 | MASTER-OAGH | (12h 42m 56.35s , -19d 42m 13.4s) | C | 60 | 15.5 | 4815 | 2026-04-21 05:33:05 | MASTER-OAGH | (12h 44m 17.15s , -20d 16m 04.5s) | C | 60 | 15.2 | 4876 | 2026-04-21 05:34:07 | MASTER-OAFA | (12h 40m 15.81s , -17d 23m 36.3s) | C | 60 | 20.0 | 4941 | 2026-04-21 05:35:12 | MASTER-OAFA | (12h 40m 15.84s , -17d 23m 36.4s) | C | 60 | 20.0 | 4954 | 2026-04-21 05:35:24 | MASTER-OAGH | (12h 34m 19.16s , -17d 47m 10.7s) | C | 60 | 14.1 | 5007 | 2026-04-21 05:36:17 | MASTER-OAFA | (12h 40m 15.86s , -17d 23m 35.7s) | C | 60 | 20.0 | 5073 | 2026-04-21 05:37:24 | MASTER-OAFA | (12h 40m 15.87s , -17d 23m 35.3s) | C | 60 | 19.9 | 5138 | 2026-04-21 05:38:29 | MASTER-OAFA | (12h 40m 15.91s , -17d 23m 35.2s) | C | 60 | 19.9 | 5184 | 2026-04-21 05:39:15 | MASTER-OAGH | (12h 34m 16.09s , -15d 53m 00.5s) | C | 60 | 17.1 | 5184 | 2026-04-21 05:39:15 | MASTER-OAGH | (12h 35m 37.14s , -16d 26m 52.1s) | C | 60 | 17.1 | 5204 | 2026-04-21 05:39:35 | MASTER-OAFA | (12h 40m 15.93s , -17d 23m 34.8s) | C | 60 | 19.9 | 5256 | 2026-04-21 05:40:27 | MASTER-OAGH | (12h 42m 39.48s , -15d 54m 07.1s) | C | 60 | 17.1 | 5256 | 2026-04-21 05:40:27 | MASTER-OAGH | (12h 44m 00.43s , -16d 27m 59.1s) | C | 60 | 16.8 | 5270 | 2026-04-21 05:40:41 | MASTER-OAFA | (12h 40m 15.94s , -17d 23m 34.3s) | C | 60 | 19.9 | 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/44367. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42488] GRB 260421B: BOOTES-7 early optical afterglow detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44366 SUBJECT: GRB 260421B: BOOTES-7 early optical afterglow detection DATE: 26/04/21 05:37:53 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> S.-Y. Wu, M. Gritsevich, I. Perez-Garcia, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. of Malaga), Y.-D. Hu (GXU, Guanxi), B.-B. Zhang (Nanjing Univ.), and A. Maury (Space Obs., San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of GRB 260421B by Fermi (Fermi Team, GCN 44360, Preis and Greiner, GCN 44361) and SVOM (Zhao et al. GCN 44362), the BOOTES-7 telescope at the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) automatically observed the GRB location starting on Aug. 21, 04:28:36 UT (i.e. 15 min after GRB onset). A series of images in clear filter were gathered and we identify the fading optical afterglow reported by He et al. (GCN 44363) Sánchez-Álvarez et al. (GCN 44364) and Turpin et al. (GCN 44365) at coordinates RA: 12:40:00.50 Dec: -17:44:24.0 (+/- 0.5 “). Preliminary magnitude is 18. Further data analysis is ongoing. We would like to thank the staff at San Pedro de Atacama Space Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44366. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42487] GRB 260421B: LCO optical afterglow confirmation
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44365 SUBJECT: GRB 260421B: LCO optical afterglow confirmation DATE: 26/04/21 05:32:17 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), B. Cordier (CEA/Irfu), W.-L Zhang (PMO), Z.-Y Liu (GZNU), report on behalf of the SVOM mission team: We observed the field of GRB 260421B detected by SVOM (Zhao et al., GCN 44362) and Fermi/GBM (The Fermi GBM team, GCN 44360) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started at 2026-04-21T04:29:54.940 about 16.5 min after the SVOM/ECLAIRs trigger time. We obtained 3x200 s exposures in the SDSS r and PanSTARRS-z filters. An uncatalogued bright optical candidate is well detected in our single images at RA, dec (J2000) = 190.00203, -17.74017 (err = 0.5 arcsec). This position is consistent with the optical counterpart reported by the TRT telescope (He et al, GCN 44363) and the SVOM/COLIBRI FM-GFT (Álvarez et al. GCN 43646). We measure the following magnitude calibrated against the PanSTARRS DR1 catalog, and not corrected for Galactic extinction: r = 18.47 +/- 0.01 (AB) (Tmid - T0 = 18.2 min) z = 18.92 +/- 0.09 (AB) (Tmid - T0 = 30.7 min) This project is funded by the SVOM collaboration. Further observations are scheduled. View this GCN Circular online at https://gcn.nasa.gov/circulars/44365. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42486] GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44364 SUBJECT: GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart DATE: 26/04/21 05:28:06 GMT FROM: freddalvarez(a)astro.unam.mx Fredd Sánchez Álvarez (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), W.L. Zhang (PMO), and Z. Y. Liu (GZNU) report: We imaged the field of the SVOM/ECLAIRs and Fermin/GBM GRB 260421B (Zhao et al., GCN Circ. 44362; Fermi GBM Team, GCN Circ. 44360) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-21 04:15:13 to 04:30:07 (from 1.9 to 16.8 minutes after the trigger) and obtained 430 seconds of simultaneous exposure in the r/z filters. The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect an uncatalogued source consistent with the ECLAIRs localization at: RA(J2000) = 12:40:00.48 = 190.00200 degrees Dec(J2000) = -17:44:24.6 = -17.74015 degrees with an uncertainty of 0.5 arcsec. The source was detected in both r and z and was observed to fade from r ≈ 14.5 to r ≈ 18.3 during our observations. The color of the source was r - z ≈ 0.45 +/- 0.02, which is consistent with the expectations for an afterglow. We suggest this is the optical counterpart of the GRB. Subsequent imaging in the g/r/i/z/y filters show detections in all bands, indicating that the redshift is less than 3.5. We encourage spectroscopic observations of the source. 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/44364. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42485] GRB 260421B: TRT optical counterpart detection
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44363 SUBJECT: GRB 260421B: TRT optical counterpart detection DATE: 26/04/21 05:26:32 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), X. Liu, Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC) report: We observed the field of GRB 260421B detected by Fermi (GCN 44360) and SVOM (zhao et al., GCN 44362), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile (CTO). We obtained a series of frames in the r-band. An uncatalogued source is detected within the Fermi error circle at coordinates R.A. (J2000) = 12:40:00.5 Dec. (J2000) = -17:44:24.5 with an uncertainty of ~ 1.0 arcsec. The source had r = 19.14 +/- 0.07 mag, calibrated with Pan-STARRS DR2 and not corrected for Galactic extinction. No NEO would be at the above position at the observational time by checking MPC. We thus think the source is the optical counterpart of GRB 260421B. View this GCN Circular online at https://gcn.nasa.gov/circulars/44363. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42484] GRB 260421B: SVOM detection of a long burst
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44362 SUBJECT: GRB 260421B: SVOM detection of a long burst DATE: 26/04/21 05:20:23 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D.Zhao (NAOC), H.Goto (RIKEN), W. L. Zhang (PMO), Z. Y. Liu (GZNU) report on behalf of the SVOM mission team: At 2026-04-21T04:13:25 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260421B (SVOM burst-id sb26042105). The Fermi GBM also detected this burst (GCN 44360 & 44361). 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 13 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 30.71 in the [8-120] keV energy band over a time window of 20.48 seconds starting at 2026-04-21T04:13:17. The localization of the best alert is R.A., Dec. 189.9811, -17.7676 degrees (J2000) with a 90% confidence level (C.L.) radius of 3.21 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a multiple peak structure with a T90 duration of about 52.824 (-0.172 +0.169). This burst also triggered SVOM/GRM at 2026-04-21T04:13:21 on a timescale of 1 seconds with an SNR of 7.90. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 20.04 (-0.93 +3.07). SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-04-21T04:18:40 UTC, 315 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 190.0318, -17.7566 degrees: R.A. (J2000) = 12h40m07.62s Dec. (J2000) = -17d45m23.69s with a 90% C.L. radius of 97.27 arcseconds. This location is 2.97 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. 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 W. L. Zhang: wlzhang(a)pmo.ac.cn Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44362. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42483] GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44361 SUBJECT: GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176) DATE: 26/04/21 04:54:24 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 798437606 at 04:13:21 on 21 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) = 190.5 deg Decl.(2000.0) = -16.5 deg The 1 sigma statistical error radius is 2.2 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260421176/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260421176/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260421176/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44361. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42482] GRB 260421B: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44360 SUBJECT: GRB 260421B: Fermi GBM Final Real-time Localization DATE: 26/04/21 04:22:36 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 04:13:21 UT on 21 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260421B (trigger 798437606.166588 / 260421176). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 188.8, Dec = -17.8 (J2000 degrees, equivalent to J2000 12h 35m, -17d 48'), with a statistical uncertainty of 2.4 degrees. The angle from the Fermi LAT boresight is 58.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421176/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421176/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421176/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44360. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42481] Fermi GRB 260421A: Global MASTER-Net observations report
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44359 SUBJECT: Fermi GRB 260421A: Global MASTER-Net observations report DATE: 26/04/21 03:16:41 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260421A ( Fermi GBM team, GCN 44358) errorbox 3101 sec after notice time and 3131 sec after trigger time at 2026-04-21 03:04:55 UT, with upper limit up to 19.4 mag. Observations started at twilight. The observations began at zenith distance = 47 deg. The sun altitude is -16.0 deg. The galactic latitude b = 54 deg., longitude l = 118 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3262778 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 3162 | 2026-04-21 03:04:55 | MASTER-OAGH | (13h 20m 14.14s , +62d 00m 28.6s) | C | 60 | 18.8 | 3162 | 2026-04-21 03:04:55 | MASTER-OAGH | (13h 22m 34.25s , +61d 26m 33.6s) | C | 60 | 19.2 | 3234 | 2026-04-21 03:06:08 | MASTER-OAGH | (13h 37m 23.83s , +62d 00m 57.1s) | C | 60 | 18.8 | 3234 | 2026-04-21 03:06:08 | MASTER-OAGH | (13h 39m 43.36s , +61d 26m 60.0s) | C | 60 | 19.2 | 3426 | 2026-04-21 03:09:20 | MASTER-OAGH | (13h 07m 30.22s , +63d 21m 09.2s) | C | 60 | 19.4 | 3426 | 2026-04-21 03:09:20 | MASTER-OAGH | (13h 04m 59.80s , +63d 55m 03.4s) | C | 60 | 19.0 | 3497 | 2026-04-21 03:10:31 | MASTER-OAGH | (13h 25m 34.30s , +63d 20m 22.6s) | C | 60 | 19.4 | 3497 | 2026-04-21 03:10:31 | MASTER-OAGH | (13h 23m 04.46s , +63d 54m 18.8s) | C | 60 | 19.0 | 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/44359. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42480] GRB 260421A: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Apr '26

21 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44358 SUBJECT: GRB 260421A: Fermi GBM Final Real-time Localization DATE: 26/04/21 02:23:18 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 SHORT GRB At 02:12:44 UT on 21 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260421A (trigger 798430369.324586 / 260421092). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 198.8, Dec = 62.9 (J2000 degrees, equivalent to J2000 13h 15m, 62d 53'), with a statistical uncertainty of 8.2 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/bn260421092/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421092/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421092/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44358. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42479] EP260321a: VLA radio follow-up
by GCN Circulars 20 Apr '26

20 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44357 SUBJECT: EP260321a: VLA radio follow-up DATE: 26/04/20 21:56:06 GMT FROM: todwyer1(a)jh.edu Tanner O'Dwyer (JHU), Alessandra Corsi (JHU), Gokul Srinivasaragavan (UMD), S. Bradley Cenko (NASA GSFC), Shreya Anand (Stanford.U), Anna Ho (Cornell), Jesper Sollerman (U.Stockholm), Bei Zhou (FemiLab & U.Chicago), Marc Kamionkowski (JHU), Jillian Rastinejad (UMD) Following GCN 44239 we re-observed the field of EP260321a (Huang et al., GCN 44068) with the Karl G. Jansky Very Large Array (VLA) in its A-configuration. Our observations were conducted at about 22 days post trigger at a nominal central frequency of 6 GHz. We report no significant variation of the radio source at a position compatible with that of SN 2026gzf (Corcoran et al., GCN 44105, Rastinejad et al., GCN 44107). View this GCN Circular online at https://gcn.nasa.gov/circulars/44357. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42478] GRB 260412A: LCOGT Optical Upper Limits
by GCN Circulars 20 Apr '26

20 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44356 SUBJECT: GRB 260412A: LCOGT Optical Upper Limits DATE: 26/04/20 17:36:58 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the GRB260412A field (Fermi GBM Team, GCN 44275; Wang et al., GCN 44276) with the LCOGT 1-meter Sinistro instrument at the South African Astronomical Observatory, South Africa site, on April 12, from 17:13 to 17:26 UT (corresponding to 11.0 to 11.2 hours after the trigger time) and with the LCOGT 1-meter Sinistro instrument at the Cerro Tololo Interamerican Observatory, Chile site, from 23:20 to 23:52 (17.1 to 17.7 hours after the trigger time) with the Bessel I and R filters. We performed a series of 3x300s exposures in I-band and 1x100s exposure in R-band due to a scheduling interruption, and then 3x300s in I-band and R-band for the second epoch. We do not detect an uncatalogued source within the SVOM error region (Wang et al., GCN 44276), consistent with other optical upper limits (Lipunov et al., 44280). The following 5-sigma upper limits are calculated using the USNO-B1.0 catalog as reference: Epoch 1: I>20.7 R>17.3 Epoch 2: I>21.0 R>22.6 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44356. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42477] The EP-WXT trigger 01709260314 is likely a flaring star
by GCN Circulars 20 Apr '26

20 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44355 SUBJECT: The EP-WXT trigger 01709260314 is likely a flaring star DATE: 26/04/20 09:50:59 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. L. Wang (NAO, CAS; ICE, CSIC), J. P. Chen (SYSU), J. W. Hu, H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709260314 at the time of 2026-04-20T09:25:12, is likely a stellar flare associated with L 691-74. The estimated flux of the flare is around 1.6e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 6.2e30 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/44355. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42476] EP260416a: Optical follow-up observations with Kinder
by GCN Circulars 20 Apr '26

20 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44354 SUBJECT: EP260416a: Optical follow-up observations with Kinder DATE: 26/04/20 08:42:49 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> K. N.-T. Ho, A. Aryan, T.-W. Chen, W.-J. Hou (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), S. Yang(HNAS), A. Sankar.K, M.-H. Lee, A. Dutta, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, C.-S. Lin, J.-K. Guo (all NCU), 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. Nicholl, 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 EP260416a (Hu et al., GCN 44307) 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 r-band started at 11:48 UTC on the 16th of April 2026 (MJD 61146.4918), 6.32 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. Owing to the faint optical counterpart candidate (Ducoin et al., GCN 44310), the transient was not detected in our stacked image. After the reported optical rebrightening (Hua et al., GCN 44318), we performed another SLT epoch of observations starting at UTC 12:33 on April 18th, 2026 (61148.5228), 55.05 hr post the WXT discovery. The optical counterpart (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334, He et al. GCN 44336, An et al. GCN 44339, Jelinek et al. GCN 44341; and Guziy et al., GCN 44351) was detected in the stacked images. We observed the transient for one more epoch, starting at UTC 11:30 on April 19th, 2026 (61149.4790), about 78.0 hr since the WXT discovery. The optical counterpart candidate was not detected in the stacked image. 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 SLT | r | 61146.4918 | 6.31 | 300 * 24 | >21.3 | 2".13 | 1.26 SLT | r | 61148.5228 | 55.05 | 300 * 19 | 21.16 +/- 0.08 | 2".05 | 1.13 SLT | r | 61149.4790 | 78.00 | 300 * 18 | >20.9 | 2".66 | 1.35 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/upper-limits are not corrected for an expected galactic extinction of A_r = 0.04 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/44354. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42475] GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
by GCN Circulars 20 Apr '26

20 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44353 SUBJECT: GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient DATE: 26/04/20 06:51:39 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> N. Pankov (IKI), V. Rumyantsev (CrAO), E. Klunko (ISTP), A. Pozanenko (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN: We continued optical observations of the field of AT2026jpw (O'Neill et al., GCN 44301; Corcoran et al., GCN 44303; Moskvitin and Spiridonova, GCN 44304; Xu et al., GCN 44305; The COLIBRÍ team, GCN 44306; Sosnovskij et al., GCN 44309; Ma et at., GCN 44314; Pankov et al., GCN 44316) in the R band with the Shajn 2.6-meter telescope (ZTSh) of the Crimean Astrophysical Observatory (CrAO) and the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations began on 2026-04-16 20:53 UT, i.e. ~2.92 days since GOTO detection at CrAO and on 2026-04-18 14:47 UT (~4.67 days since GOTO detection) at Mondy. The series of 38x120s exposures were taken by ZTSh/CrAO and 35x120s exposures were taken by AZT-33IK/Mondy. The optical counterpart is clearly detected in the co-add image from CrAO, but not detected by AZT-33IK. The preliminary photometry and observation details are provided below: Date UT start t-T0 Exp. Filter OT Err. UL(3sigma) Telescope/Site (mid, days) (s) 2026-04-16 20:53:30 2.92638 38x120 R 22.11 0.02 23.7 ZTSH/CrAO 2026-04-18 14:47:18 4.66999 35x120 R n/d n/d 22.8 AZT-33IK/Mondy The photometry is calibrated using nearby stars from USNO-B1.0 (see Moskvitin and Spiridonova, GCN 44304) and has not been corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44353. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42474] EP-WXT trigger 01709260303: KAIT optical observations
by GCN Circulars 20 Apr '26

20 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44352 SUBJECT: EP-WXT trigger 01709260303: KAIT optical observations DATE: 26/04/20 06:33:01 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, automatically responded to the EP-WXT trigger 01709260303 (Yin et al., GCN 44350) starting at 10:53 UT, about 3.5 hours after the trigger. A set of B,V,R,I and clear (roughly R) filter images were obtained and lasted for ~0.9 hours. We performed photometry on the suggested flare star Gaia DR3 4524306802880186496 and did not find obvious variability on its brightness at 0.1 mag level. View this GCN Circular online at https://gcn.nasa.gov/circulars/44352. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42473] EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
by GCN Circulars 20 Apr '26

20 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44351 SUBJECT: EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring DATE: 26/04/20 04:03:59 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> S. Guziy, F. J. Aceituno, A. J. Castro-Tirado, M.D. Caballero-García, M. Gritsevich, I. Pérez-García, R. Sánchez-Ramírez, S.-Y. Wu (IAA-CSIC) and A. Fernández-Martin and M. M. Sánchez-Andújar (CAHA), on behalf of a larger collaboration,report: We observed EP260416a (Hu et al., GCN 44307) with both the 1.5m telescope at Observatorio de Sierra Nevada (OSN) and the 2.2m telescope at Calar Alto Observatory (CAHA), in Southern Spain. A series of 300 s BVRI exposures were obtained at the 1.5m OSN starting on Apr 17, 21:04 UT, complemented by one 100s i-band image at the 2.2m CAHA, on Apr 18, 01:04 UT., i.e. 39.6 h and 43.6 h respectively, after the initial trigger. The optical counterpart (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334, He et al. GCN 44336, An et al. GCN 44339, Jelinek et al. GCN 44341) is well detected in our images. We measure B = 21.08 +/- 0.14 and R = 20.99 +/- 0.07 on Apr 17, 21:15 UT and I = 19.82 +/-0.18 on Apr 18, 01:04 UT (none corrected for Galactic extinction). The night after, a second epoch BVRI observation was conducted at the 1.5m OSN, for which measure R = 21.59 +/- 0.10 on Apr 18, 20:14 UT. Our measurement is consistent with the continued fading of the afterglow. Further optical monitoring is being carried out. View this GCN Circular online at https://gcn.nasa.gov/circulars/44351. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42472] The EP-WXT trigger 01709260303 is likely a flaring star
by GCN Circulars 20 Apr '26

20 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44350 SUBJECT: The EP-WXT trigger 01709260303 is likely a flaring star DATE: 26/04/20 02:32:00 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (HKU), Z.-C. Zou (NJU), H.Q. Cheng and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709260303 at the time of 2026-04-19T07:22:35, is likely a stellar flare associated with Gaia DR3 4524306802880186496. The estimated flux of the flare is around 8e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 2.1e31 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/44350. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42471] GRB 260417A: SVOM/GRM observation
by GCN Circulars 19 Apr '26

19 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44349 SUBJECT: GRB 260417A: SVOM/GRM observation DATE: 26/04/19 16:33:14 GMT FROM: zhangjinpeng(a)ihep.ac.cn SVOM/GRM team: Jin-Peng Zhang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Sebastien Guillot (IRAP) Report on behalf of the SVOM team: SVOM/GRM detected GRB 260417A at 2026-04-17T00:10:11.500 (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44317), AstroSat CZTI (S. Salunke et al., GCN #44330) and possibly by EP (K. R. Ni et al., GCN #44337). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst mainly consists of a pulse with a T90 of 38 +15/-10 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260417A.png In addition, the position of this burst, according to Fermi/GBM localization (RA = 252.0, Dec = -19.8, error(stat) = 3.4, Fermi GBM Team, GCN #44317), is located at about 90.3 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-20 to T0+20 s is fitted by a power law function. The power law index is -1.77 +0.09/-0.09. The event fluence (10-1000 keV) in this time interval is (9.1 +1.0/-1.1)E-06 erg/cm^2. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Jin-Peng Zhang (IHEP) (zhangjinpeng(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44349. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42470] EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
by GCN Circulars 19 Apr '26

19 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44348 SUBJECT: EP260321A/AT2026gzf: Optical observation from 1.3m DFOT DATE: 26/04/19 09:06:27 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Pankaj Pawar, Divyanshu Janghel, Dhruv Jain, Debalina Kar, and Kuntal Misra (ARIES) report: We observed the field of EP260321A/AT2026gzf detected by EP-WXT (Huang, GCN 44068) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. Observations began on 2026-04-16 at 14:22:58 UT, i.e., ~26.07 days after the EP-WXT trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We detect an optical afterglow in our stacked image. We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================= 2026-04-16 14:22:58 ~26.07 R 300s*4 17.14 +- 0.01 The optical detection of the burst is consistent with Lipunov et al., GCN 44069; Lee et al., GCN 44070; Aryan et al., GCN 44081; Tanvir et al., GCN 44082; Moran et al., GCN 44083; Ahumada et al., GCN 44084; Liu et al., GCN 44087; Sankar et al. GCN 44089; de Ugarte Postigo et al., GCN 44091; Xu et al., GCN 44092; Pankov et al. GCN 44103; Corcoran et al., GCN 44105; Rastinejad et al., GCN 44107; Gao et al., GCN 44110; He et al., GCN 44117; Zhang et al., GCN 44171; Li et al., GCN 44284; Volnova et al., GCN 44295. The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/44348. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42469] GRB 260419B: Fermi GBM Final Real-time Localization
by GCN Circulars 19 Apr '26

19 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44347 SUBJECT: GRB 260419B: Fermi GBM Final Real-time Localization DATE: 26/04/19 08:00:23 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 07:49:50 UT on 19 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260419B (trigger 798277795.43596 / 260419326). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 137.1, Dec = -33.8 (J2000 degrees, equivalent to J2000 09h 08m, -33d 47'), with a statistical uncertainty of 9.6 degrees. The angle from the Fermi LAT boresight is 62.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260419326/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260419326/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260419326/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44347. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42468] GRB 260419A: Fermi GBM Final Real-time Localization
by GCN Circulars 19 Apr '26

19 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44346 SUBJECT: GRB 260419A: Fermi GBM Final Real-time Localization DATE: 26/04/19 07:20:17 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 07:09:40 UT on 19 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260419A (trigger 798275385.308626 / 260419298). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 317.4, Dec = -34.4 (J2000 degrees, equivalent to J2000 21h 09m, -34d 23'), with a statistical uncertainty of 2.3 degrees. The angle from the Fermi LAT boresight is 77.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260419298/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260419298/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260419298/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44346. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42467] Fermi trigger No 798275385: Global MASTER-Net observations report
by GCN Circulars 19 Apr '26

19 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44345 SUBJECT: Fermi trigger No 798275385: Global MASTER-Net observations report DATE: 26/04/19 07:16:07 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 GRB260419.30 (trigger No 798275385,20h 50m 14.40s , -47d 41m 24.0s, R=4.3) errorbox 42 sec after notice time and 75 sec after trigger time at 2026-04-19 07:10:56 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 52 deg. The sun altitude is -48.6 deg. The galactic latitude b = -40 deg., longitude l = 352 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3259527 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 86 | 2026-04-19 07:10:56 | MASTER-OAFA | (20h 49m 30.10s , -47d 58m 25.7s) | C | 20 | 19.4 | 112 | 2026-04-19 07:11:22 | MASTER-OAFA | (20h 49m 30.11s , -47d 58m 24.7s) | C | 20 | 19.3 | 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/44345. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42466] EP260417a: GROWTH-India Telescope optical upper limit
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44344 SUBJECT: EP260417a: GROWTH-India Telescope optical upper limit DATE: 26/04/18 23:25:30 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> A. Khade (IITB), A. Kumar (IITB), V. Vijaykumar (IITB), T. Mohan (IITB), V. Swain (IITB), D. Eappachen (IIA), S. Patil (IITB), A.P. Saikia (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 EP260417a detected by Einstein Probe (Wang et al., GCN 44325), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-04-18 21:01:23 (UTC), i.e., 1.86 days after the trigger, and obtained multiple exposures in the r' filter. No optical counterpart is detected at the position reported by He et al. (GCN 44326) in our stacked image. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | -------------- | ------------------- | ---------------- | | 61148.885 | r' | 44.85 | 4x360 | 20.64 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our upper limit is consistent with the reported optical measurements by He et al. (GCN 44326) and Lipunov et al. (GCN 44338). 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/44344. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42465] Fermi GRB 260417B: Global MASTER-Net observations report
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44343 SUBJECT: Fermi GRB 260417B: Global MASTER-Net observations report DATE: 26/04/18 23:15:27 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 260417B ( Fermi GBM team, GCN 44331) errorbox 66043 sec after notice time and 66079 sec after trigger time at 2026-04-18 10:05:14 UT, with upper limit up to 18.4 mag. Observations started at twilight. The observations began at zenith distance = 31 deg. The sun altitude is -11.6 deg. MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 260417B errorbox 1 days 23747 sec after notice time and 1 days 23783 sec after trigger time at 2026-04-18 22:20:18 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 48 deg. The sun altitude is -68.6 deg. The galactic latitude b = 1 deg., longitude l = 1 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3256668 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 23203 | 2026-04-17 22:10:08 | MASTER- | (17h 10m 25.00s , -22d 17m 31.5s) | C | 60 | 14.7 | 23280 | 2026-04-17 22:11:25 | MASTER- | (17h 25m 38.80s , -19d 39m 45.5s) | C | 60 | 13.2 | 23367 | 2026-04-17 22:12:52 | MASTER- | (17h 28m 29.57s , -18d 22m 14.8s) | C | 60 | 14.2 | 23445 | 2026-04-17 22:14:10 | MASTER- | (17h 09m 03.19s , -23d 33m 52.4s) | C | 60 | 14.9 | 24134 | 2026-04-17 22:25:39 | MASTER- | (17h 08m 12.30s , -24d 53m 35.2s) | C | 60 | 16.3 | 24217 | 2026-04-17 22:27:02 | MASTER- | (16h 56m 13.19s , -26d 09m 52.5s) | C | 60 | 15.3 | 66109 | 2026-04-18 10:05:14 | MASTER-OAFA | (17h 05m 41.45s , -21d 18m 08.8s) | C | 60 | 18.4 | 66184 | 2026-04-18 10:06:29 | MASTER-OAFA | (17h 14m 24.55s , -21d 19m 32.1s) | C | 60 | 18.0 | 66259 | 2026-04-18 10:07:44 | MASTER-OAFA | (17h 05m 42.90s , -21d 20m 07.9s) | C | 60 | 18.3 | 66335 | 2026-04-18 10:09:00 | MASTER-OAFA | (17h 14m 23.15s , -21d 20m 27.1s) | C | 60 | 18.0 | 66410 | 2026-04-18 10:10:14 | MASTER-OAFA | (17h 05m 44.83s , -21d 18m 07.3s) | C | 60 | 18.1 | 66561 | 2026-04-18 10:12:46 | MASTER-OAFA | (16h 54m 04.36s , -25d 06m 35.0s) | C | 60 | 17.9 | 110213 | 2026-04-18 22:20:18 | MASTER-SAAO | (17h 03m 25.97s , -21d 49m 48.4s) | C | 60 | 18.6 | 110399 | 2026-04-18 22:23:24 | MASTER-SAAO | (17h 17m 53.69s , -21d 35m 09.4s) | C | 60 | 18.1 | 110399 | 2026-04-18 22:23:24 | MASTER-SAAO | (17h 19m 53.70s , -21d 51m 16.9s) | C | 60 | 18.3 | 110492 | 2026-04-18 22:24:57 | MASTER-SAAO | (16h 59m 36.82s , -27d 32m 32.8s) | C | 60 | 17.5 | 110492 | 2026-04-18 22:24:57 | MASTER-SAAO | (16h 57m 30.65s , -27d 16m 26.2s) | C | 60 | 17.7 | 110586 | 2026-04-18 22:26:30 | MASTER-SAAO | (16h 59m 00.63s , -23d 27m 32.8s) | C | 60 | 18.7 | 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/44343. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42464] EP260417b: GROWTH-India Telescope optical upper limit
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44342 SUBJECT: EP260417b: GROWTH-India Telescope optical upper limit DATE: 26/04/18 22:00:13 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Vijaykumar (IITB), T. Mohan (IITB), V. Swain (IITB), D. Eappachen (IIA), S. Patil (IITB), A.P. Saikia (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 EP260417b detected by Einstein Probe (Ni et al., GCN 44323), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-04-18 19:04:51 (UTC), i.e., 1.74 days after the trigger, and obtained a single exposure in the r' filter. We did not detect any transient in our image within the uncertainty region of source position reported by EP. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | -------------- | ------------------- | ---------------- | | 61149.797 | r' | 41.78 | 420 | 19.3 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. 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/44342. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42463] EP260416a: Ondrejov D50 optical detection
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44341 SUBJECT: EP260416a: Ondrejov D50 optical detection DATE: 26/04/18 19:52:07 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> M. Jelinek, J. Strobl, F. Novotny, A. Malenakova and R. Hudec (ASU CAS Ondrejov, CZ) report: We observed the field of EP260416a (Hu et al., GCN 44307) with the 50 cm robotic telescope (D50) of the Astronomical Institute Ondrejov, near Prague, Czech Republic. We obtained a series of 120 s Sloan-r band exposures starting at 20:09 UT on 2026 April 17, i.e. 38.66 h after the initial trigger, and combined 68 frames with a mean exposure time of 40.03 h after the trigger. The optical counterpart (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328; Li et al., GCN 44334) is detected in the combined image. The preliminary AB magnitude of the object is r = 21.08 +/- 0.23, calibrated against the ATLAS catalog and not corrected for Galactic extinction. Our measurement is consistent with the continued fading of the afterglow. View this GCN Circular online at https://gcn.nasa.gov/circulars/44341. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42462] GRB 260418B: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44340 SUBJECT: GRB 260418B: Fermi GBM Final Real-time Localization DATE: 26/04/18 16:30:58 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 16:20:21 UT on 18 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260418B (trigger 798222026.725586 / 260418681). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 34.7, Dec = -40.5 (J2000 degrees, equivalent to J2000 02h 18m, -40d 30'), with a statistical uncertainty of 4.0 degrees. The angle from the Fermi LAT boresight is 47.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260418681/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260418681/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260418681/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44340. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42461] EP260416a: VLT/FORS2 spectroscopic redshift confirmation
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44339 SUBJECT: EP260416a: VLT/FORS2 spectroscopic redshift confirmation DATE: 26/04/18 12:32:28 GMT FROM: Laura Cotter at University College Dublin <laura.cotter(a)ucdconnect.ie> J. An (NAOC), A. Saccardi (CEA/Irfu), L. Cotter (UCD), D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), A. L. Thakur (INAF-IAPS) report on behalf of the Stargate collaboration: We observed the optical counterpart (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328; Li et al,. GCN 44334) of EP260416a (Hu et al., GCNs 44307, 44324) using the ESO VLT UT1 (Antu) equipped with the FORS2 spectrograph. Our observation started on 2026 April 18 at 03:04:13 UT (1.90 days after the EP trigger). A series of 3 spectra of 900 s each were obtained with the 300V grism, covering the wavelength range 3500-8600 AA. From a 60 s acquisition image (1.89 days after trigger), we measure a magnitude R = 20.99 +/- 0.06 (Vega), calibrated against nearby stars from the Pan-STARRS catalog using the Lupton (2005) transformations, and not corrected for Galactic extinction. In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. At the blue edge of the spectrum, even though the S/N is low, we identify a broad trough at around 3540 AA, likely due to H I. We also detect multiple absorption features including O I, C II, Si IV, C IV, Si II, Fe II, Al II, Al III, at a common redshift of z = 1.910, which we thus suggest to be the redshift of EP260416a. The lack of any further hydrogen absorption at higher redshift implies that the z = 1.910 system is indeed local to the GRB. Our results confirm the tentative redshift measurement reported by He et al. (GCN 44336). We acknowledge expert support from the ESO observing staff in Paranal, particularly Hannah Osborne and Diego Parraguez. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/44339. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42460] EP260417a: Global MASTER-Net observations report
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44338 SUBJECT: EP260417a: Global MASTER-Net observations report DATE: 26/04/18 09:45:27 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 EP260417a ( EP Team et al., GCN 44325) errorbox 12831 sec after trigger time at 2026-04-17 03:56:53 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 45 deg. The sun altitude is -67.6 deg. MASTER-OAGH robotic telescope located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) was pointed to the EP260417a errorbox 78480 sec after notice time and 1 days 33084 sec after trigger time at 2026-04-18 09:34:26 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 53 deg. The sun altitude is -36.9 deg. The galactic latitude b = 19 deg., longitude l = 355 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3256324 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 4312 | 2026-04-17 01:34:24 | MASTER- | (16h 25m 32.78s , -22d 27m 07.0s) | C | 60 | 16.8 | 12861 | 2026-04-17 03:56:53 | MASTER-OAFA | (16h 22m 03.10s , -23d 33m 17.7s) | C | 60 | 18.9 | 12921 | 2026-04-17 03:56:53 | MASTER-OAFA | (16h 22m 03.09s , -23d 33m 17.9s) | C | 180 | 19.7 | Coadd 13013 | 2026-04-17 03:59:24 | MASTER-OAFA | (16h 22m 05.31s , -23d 31m 13.7s) | C | 60 | 19.5 | 13243 | 2026-04-17 04:03:14 | MASTER-OAFA | (16h 22m 01.68s , -23d 31m 04.9s) | C | 60 | 19.4 | 13395 | 2026-04-17 04:05:46 | MASTER-OAFA | (16h 22m 02.65s , -23d 33m 00.6s) | C | 60 | 19.5 | 13455 | 2026-04-17 04:05:46 | MASTER-OAFA | (16h 22m 02.65s , -23d 33m 00.5s) | C | 180 | 19.9 | Coadd 15146 | 2026-04-17 04:34:57 | MASTER-OAFA | (16h 22m 04.82s , -23d 30m 29.9s) | C | 60 | 19.6 | 15221 | 2026-04-17 04:36:12 | MASTER-OAFA | (16h 22m 04.76s , -23d 32m 06.6s) | C | 60 | 19.7 | 15297 | 2026-04-17 04:37:28 | MASTER-OAFA | (16h 22m 07.64s , -23d 30m 28.6s) | C | 60 | 19.6 | 15357 | 2026-04-17 04:37:28 | MASTER-OAFA | (16h 22m 07.64s , -23d 30m 28.6s) | C | 180 | 19.9 | Coadd 15613 | 2026-04-17 04:42:44 | MASTER-OAFA | (16h 22m 02.17s , -23d 31m 58.9s) | C | 60 | 19.5 | 15688 | 2026-04-17 04:43:59 | MASTER-OAFA | (16h 22m 07.18s , -23d 31m 53.2s) | C | 60 | 19.5 | 15766 | 2026-04-17 04:45:17 | MASTER-OAFA | (16h 22m 04.70s , -23d 30m 07.5s) | C | 60 | 19.4 | 15826 | 2026-04-17 04:45:17 | MASTER-OAFA | (16h 22m 04.69s , -23d 30m 07.5s) | C | 180 | 19.9 | Coadd 17894 | 2026-04-17 05:20:45 | MASTER-OAFA | (16h 22m 01.37s , -23d 29m 11.6s) | C | 60 | 19.6 | 17967 | 2026-04-17 05:21:59 | MASTER-OAFA | (16h 22m 07.83s , -23d 30m 10.7s) | C | 60 | 19.6 | 18047 | 2026-04-17 05:23:18 | MASTER-OAFA | (16h 22m 00.60s , -23d 31m 09.3s) | C | 60 | 19.6 | 18107 | 2026-04-17 05:23:18 | MASTER-OAFA | (16h 22m 00.60s , -23d 31m 09.3s) | C | 180 | 19.5 | Coadd 18354 | 2026-04-17 05:28:26 | MASTER-OAFA | (16h 22m 07.10s , -23d 29m 32.0s) | C | 60 | 19.2 | 18433 | 2026-04-17 05:29:44 | MASTER-OAFA | (16h 22m 02.40s , -23d 30m 03.3s) | C | 60 | 18.9 | 18509 | 2026-04-17 05:31:00 | MASTER-OAFA | (16h 22m 00.62s , -23d 29m 01.8s) | C | 60 | 18.9 | 18569 | 2026-04-17 05:31:00 | MASTER-OAFA | (16h 22m 00.62s , -23d 29m 01.9s) | C | 180 | 19.4 | Coadd 21141 | 2026-04-17 06:14:52 | MASTER-OAFA | (16h 22m 06.99s , -23d 29m 57.4s) | C | 60 | 19.3 | 21216 | 2026-04-17 06:16:08 | MASTER-OAFA | (16h 22m 01.94s , -23d 30m 56.8s) | C | 60 | 19.2 | 21290 | 2026-04-17 06:17:21 | MASTER-OAFA | (16h 22m 08.44s , -23d 30m 33.6s) | C | 60 | 19.3 | 21350 | 2026-04-17 06:17:21 | MASTER-OAFA | (16h 22m 08.45s , -23d 30m 33.6s) | C | 180 | 19.6 | Coadd 21365 | 2026-04-17 06:18:36 | MASTER-OAFA | (16h 22m 04.86s , -23d 29m 08.6s) | C | 60 | 19.2 | 21439 | 2026-04-17 06:19:50 | MASTER-OAFA | (16h 22m 04.87s , -23d 30m 41.6s) | C | 60 | 18.7 | 21515 | 2026-04-17 06:21:07 | MASTER-OAFA | (16h 22m 08.53s , -23d 29m 14.9s) | C | 60 | 19.4 | 74895 | 2026-04-17 21:10:46 | MASTER- | (16h 16m 30.79s , -20d 56m 12.9s) | C | 60 | 13.1 | 110797 | 2026-04-18 07:09:09 | MASTER-OAFA | (16h 17m 04.14s , -21d 44m 07.5s) | C | 60 | 19.4 | 110874 | 2026-04-18 07:10:25 | MASTER-OAFA | (16h 25m 34.38s , -21d 45m 27.4s) | C | 60 | 19.5 | 110950 | 2026-04-18 07:11:42 | MASTER-OAFA | (16h 16m 57.59s , -21d 43m 52.3s) | C | 60 | 19.5 | 111028 | 2026-04-18 07:12:59 | MASTER-OAFA | (16h 25m 40.71s , -21d 45m 23.9s) | C | 60 | 19.5 | 111103 | 2026-04-18 07:14:15 | MASTER-OAFA | (16h 16m 57.41s , -21d 45m 48.8s) | C | 60 | 19.5 | 119575 | 2026-04-18 09:34:26 | MASTER-OAGH | (16h 20m 52.34s , -22d 05m 17.1s) | C | 180 | 19.2 | 119575 | 2026-04-18 09:34:26 | MASTER-OAGH | (16h 22m 13.44s , -22d 38m 32.3s) | C | 180 | 19.2 | 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/44338. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42459] EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44337 SUBJECT: EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations DATE: 26/04/18 08:34:24 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> K. R. Ni (CCNU), Y. L. Wang (NAO, CAS; ICE, CSIC), Y. Q. Zhao (USTC; PRIC) and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260417a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 44325) at 2026-04-17 00:23:02 (UTC). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.32 × 10^21 cm^-2, and a photon index of 0.78 (+/-0.27). The derived average unabsorbed 0.5-4 keV flux is 1.57 (+0.49/-0.39) × 10^(-10) erg/s/cm^2. Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-04-17T14:24:17 (UTC), ~14 hours after the WXT detection. The exposure time of the observation is around 3 ks. The on-ground analysis of the FXT data found an uncatalogued source at R.A. = 245.3232, DEC = -22.0249 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT light curve shows no significant variability. The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a free hydrogen column density of 1.54 (+/-0.4) × 10^21 cm^-2, and a photon index of 1.68 (+/-0.13). The derived average unabsorbed 0.5-10 keV flux is 7.79 (-0.76/+0.89) × 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. We note that the X-ray position determined from EP/FXT observation is ~6.6 degrees away from that of GRB 260417A, which is RA = 252.0, Dec = -19.8 (J2000) with a statistical uncertainty of 3.4 degrees, as reported by the Fermi GBM team (GCN 44317). The detection in X-rays by WXT was ~13 minutes later than the reported GBM detection time of GRB 260417A. Therefore it is possible that GRB 260417A is the Gamma-ray counterpart of EP260417a. 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/44337. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42458] EP260416a: NOT tentative spectroscopic redshift of z =1.909
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44336 SUBJECT: EP260416a: NOT tentative spectroscopic redshift of z =1.909 DATE: 26/04/18 05:02:56 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, X. Liu, Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC), S.Y. Fu (HUST), J. P. U. Fynbo (DAWN/NBI), L. Fuglsang (NOT) report: We observed the optical counterpart (e.g., Ducoin et al., 44310) of EP260416a (Hu et al., GCN 44307) using the Nordic Optical Telescope (NOT), equipped with the ALFOSC camera and spectrograph. Observations started at 2026-04-17T03:56:49, and 2x1800 s spectra were obtained, covering the wavelength range 3800-9000 AA. The trace has quite low signal-to-noise. The continuum is throughout the wavelength range. We identify two relatively prominent absorption lines as Mg II doublet at z = 1.909. Based on it, other weak lines as due to Fe II 2600, Fe II 2374, 2383, Al II 1671 are consistent with this redshift. We tentatively conclude that this is the redshift of EP260416a. View this GCN Circular online at https://gcn.nasa.gov/circulars/44336. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42457] GRB 260418A: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44335 SUBJECT: GRB 260418A: Fermi GBM Final Real-time Localization DATE: 26/04/18 05:00:17 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 SHORT GRB At 04:49:35 UT on 18 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260418A (trigger 798180580.203356 / 260418201). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 140.6, Dec = 29.3 (J2000 degrees, equivalent to J2000 09h 22m, 29d 18'), with a statistical uncertainty of 18.1 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/bn260418201/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260418201/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260418201/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44335. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42456] EP260416a: GMG Optical Observation
by GCN Circulars 18 Apr '26

18 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44334 SUBJECT: EP260416a: GMG Optical Observation DATE: 26/04/18 01:02:53 GMT FROM: Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi(a)ynao.ac.cn> R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, J.-G Wang and B. Wang (YNAO, CAS) report: We observed the field of EP260416a (Hu et al., GCN 44307, T0 at 2026-04-16T05:29:32) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2026-04-17T15:58:05, about 34.48 hours after the trigger. The optical counterpart of EP260416a (Ducoin et al., GCN 44310; Li et al., GCN 44315; Hua et al., GCN 44318; Lee et al., GCN 44319; Zheng et al., GCN 44321; Martin-Carrillo et al., GCN 44328) was well detected. The preliminary analysis results are shown as follows: +---------------+------------+----------+--------------+----------------+ | Tmid-T0 [h] | Exp. [s] | Filter | Mag | 5-sigma U.L. | +===============+============+==========+==============+================+ | 34.50 | 180 | r | 20.91 ± 0.07 | 22.3 | +---------------+------------+----------+--------------+----------------+ The given magnitudes are derived based on calibration against Pan-STARRS1 field stars, and are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.008 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/44334. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0