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

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44182 SUBJECT: GRB 260402A: SVOM/MXT candidate X-ray afterglow DATE: 26/04/02 11:12:18 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Gotz (CEA Saclay) on behalf of the SVOM MXT team reports: MXT observed the field of GRB 260402A at 10:53:24 U.T., about 23 minutes after the ECLAIRs trigger. The automatic on board software detects a faint source at R.A.= 170.806 deg (J2000) Dec.= +63.627 deg (J2000) with a R90 uncertainty (incdluding systematics) of 114 arc sec. This position is at 4.7 arc min from the ECLAIRs position reported by Tan et al. (GCN 44181). Further data will be needed to confirm the afterglow nature of this candidate source. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Wenjun Tan: tanwj at ihep.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44182. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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

02 Apr '26

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

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

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44180 SUBJECT: Fermi GRB 260401A: Global MASTER-Net observations report DATE: 26/04/02 06:00:50 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260401A ( Fermi GBM team, GCN 44174) errorbox 63483 sec after notice time and 63518 sec after trigger time at 2026-04-02 04:32:04 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 29 deg. The sun altitude is -63.7 deg. The galactic latitude b = 38 deg., longitude l = 337 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3225119 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 33732 | 2026-04-01 20:15:08 | MASTER- | (14h 42m 26.86s , -15d 41m 21.2s) | C | 60 | 12.9 | 63549 | 2026-04-02 04:32:04 | MASTER-OAFA | (14h 25m 14.66s , -15d 38m 17.7s) | C | 60 | 18.4 | 63609 | 2026-04-02 04:32:04 | MASTER-OAFA | (14h 25m 14.66s , -15d 38m 17.8s) | C | 180 | 19.0 | Coadd 63624 | 2026-04-02 04:33:19 | MASTER-OAFA | (14h 25m 11.96s , -15d 36m 34.5s) | C | 60 | 18.3 | 63700 | 2026-04-02 04:34:36 | MASTER-OAFA | (14h 25m 12.06s , -15d 37m 47.2s) | C | 60 | 18.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44180. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44179 SUBJECT: GRB 260401A: Fermi GBM Observation DATE: 26/04/01 23:33:42 GMT FROM: Daniel Fernandez at University of Alabama In Huntsville (UAH) <df0062(a)uah.edu> D. Fernandez (UAH), M. Dafčíková (MUNI) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 10:53:26.00 UT on 01 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260401A (trigger 796733611/260401454), which was also detected by MAXI (T. Usuki et al. 2026, GCN 44176). The Fermi GBM on-ground location (GCN 44174) is consistent with the MAXI position. The angle from the Fermi LAT boresight is 60 degrees. The GBM light curve consists of a bright emission episode with multiple peaks with a duration (T90) of about 27 s (50-300 keV). The time-averaged spectrum from T0-0.8 to T0+32.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.78 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 239 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (1.80 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+7.5 s in the 10-1000 keV band is 21.1 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44179. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44178 SUBJECT: GRB 260401A: NuSTAR detection of prompt emission DATE: 26/04/01 23:21:40 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260401A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-04-01 10:53:26.0 UTC, shows a detection of GRB 260401A, consistent with Fermi/GBM (Fermi GBM team, GCN Circ. 44174, MAXI/GSC (Usuki et al., GCN Circ. 44176), CALET/GBM (Cannady et al., GCN Circ. 44177) and SVOM/GRM (GCN Notices). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single peak lasting for ~10-s which is consistent with the bright part of the burst as seen in the GBM lightcurve. The peak count rate is ~3000-cps with a baseline rate of ~1000-cps during this time period. We do not see any evidence in the signal above 100 keV in the CZT detectors. The GBM localization (GCN Circular 44174) at RA = 219.5, Dec = -17.4 implies an offset from the NuSTAR boresight of 42-deg (i.e. from the side of the instrument) and an offset from the geocenter of 73-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260401A/ Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44178. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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

01 Apr '26

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

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

01 Apr '26

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

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

01 Apr '26

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

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

01 Apr '26

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

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

01 Apr '26

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

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