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

[vsnet-grb-info 42427] GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44305 SUBJECT: GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection DATE: 26/04/16 01:54:19 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> D. Xu (NAOC), B. P. Gompertz (U. Birmingham), S.Q. Jiang (NAOC) report on behalf of a large group: We performed a ToO observation at the location of GOTO26djh/AT2026jpw, a candidate orphan GRB afterglow (O'Neill et al., GCN 44301) with the Follow-up X-ray Telescope (FXT) onboard the Einstein Probe (EP) mission. The observation started at 18:49:01 on 2026-04-15 UT with a total exposure time of ~3000 s. An uncatalogued X-ray source, with a flux of ~ 1.7 x 10^-13 erg/cm^2/s (0.5-10 keV; observed), is detected at coordinates R.A.(J2000) = 13:22:13.34 Dec.(J2000) = +37:02:26.88 with an uncertainty of 15 arcsec, being consistent with the location of GOTO26djh/AT2026jpw, confirming it's the soft X-ray counterpart of GOTO26djh/AT2026jpw. The X-ray counterpart detection at ~ 3 days since the event happening favors its nature of an afterglow of a high-energy burst. Further EP-FXT observations are scheduled. View this GCN Circular online at https://gcn.nasa.gov/circulars/44305. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42426] GOTO26djh/AT2026jpw transient: SAO RAS optical observations
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44304 SUBJECT: GOTO26djh/AT2026jpw transient: SAO RAS optical observations DATE: 26/04/16 00:39:58 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin and O. I. Spiridonova (SAO RAS) report on behalf of GRB follow-up team. We observed the field of the fast-fading transient GOTO26djh/AT2026jpw (O'Neill et al., GCN 44301) with the Zeiss-1000 1m telescope of the SAO RAS on April 15/16 night. We obtained two series of images in Rc band. The OT (O'Neill et al., GCN 44301; Corcoran et al., GCN 44303) is clearly detected in the stacked images with the following brightness. Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2026-04-15T19:30:44 1.87945 8*300 Rc 21.6 +/- 0.1 23.3 2026-04-15T22:01:13 1.97747 13*300 Rc 22.0 +/- 0.1 23.8 This preliminary photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44304. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42425] NOT r-band observations of the transient GOTO26djh/AT2026jpw
by GCN Circulars 15 Apr '26

15 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44303 SUBJECT: NOT r-band observations of the transient GOTO26djh/AT2026jpw DATE: 26/04/15 23:26:03 GMT FROM: Laura Cotter at University College Dublin <laura.cotter(a)ucdconnect.ie> G. Corcoran (UCD), A. de Ugarte Postigo (LAM), L. Cotter (UCD), A. Martin-Carrillo (UCD), B. P. Gompertz (Birmingham), D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), N. Pyykkinen (NOT and UTU), report on behalf of a larger collaboration: We observed the field of the transient GOTO26djh/AT2026jpw (O'Neill et al., GCN 44301) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. Observations consisted of 3x500 s in the SDSS-r band starting at 21:01:12 UT on the 15th of April 2026 (45.73 hr after the GOTO discovery). In our stacked image, the transient is well detected. The calculated AB magnitude was found to be r = 21.85 +/- 0.05 (AB), calculated against the Pan-STARRS catalog, and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44303. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42424] GRB 260415B: NuSTAR detection of long prompt emission
by GCN Circulars 15 Apr '26

15 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44302 SUBJECT: GRB 260415B: NuSTAR detection of long prompt emission DATE: 26/04/15 22:13:57 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 260415B 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 2026-04-15T02:28:55.54 UTC, shows a detection of GRB 260415B, also detected by Fermi/GBM (Fermi GBM Team, GCN 44300) and CALET/GBM (Trigger 1460255329). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a ~30-s burst followed by a ~20-s burst after a ~20-s gap, consistent with CALET/GBM and the broad bright Fermi/GBM peak at ~200 s post-trigger. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see evidence in the signal above 100 keV in the CZT detectors. The Fermi/GBM localization (GCN 44300) at RA = 229.43, Dec = 24.94 implies an offset from the NuSTAR boresight of 71-deg (i.e. from the side of the instrument) and an offset from the geocenter of 107-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260415B 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/44302. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42423] GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
by GCN Circulars 15 Apr '26

15 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44301 SUBJECT: GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow DATE: 26/04/15 18:38:37 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, M. Wortley, M. Pursiainen, B. P. Gompertz, J. Lyman, R. Starling, G. Ramsay, K. Ackley, M. Dyer, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar, on behalf of GOTO collaboration, A. Aryan, T.-W. Chen, Y.-H. Lee, T. K. Ho Ngo, and H.-Y. Hsiao (all NCU), report: We report on the discovery of the rapidly-evolving transient GOTO26djh/AT2026jpw with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) during survey operations. The object was discovered at 2026-04-13 23:17:32 UT at co-ordinates: RA,DEC (J2000): = 13:22:13.21, +37:02:15.16, 200.555049, 37.03754 Observations consisted of 4 x 45s exposures taken in the L band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. The source was initially detected with L = 19.00 ± 0.08 AB mag at t0=2026-04-13 23:17:32 UT before fading to L = 19.61 ± 0.18 AB mag at 2026-04-14 03:21:27 UT (t0 +4.06h), suggesting a decay rate of ~3.5 mag/d. No underlying source is detected in either the Pan-STARRS or SDSS surveys that would suggest the presence of a host galaxy or stellar counterpart. Additionally, the high Galactic latitude (b = +78.15 deg) would be unusual for a local stellar origin. We performed follow-up observations with the 1 m Lulin One-meter Telescope (LOT) at Lulin Observatory, Taiwan, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86). The first epoch of LOT observations began at 2026-04-15 14:41 UT (MJD 61145.612, t0 +39.40h). The transient was detected with an r-band magnitude r=21.55 ± 0.07 AB mag. Using this combined dataset, the estimated decay index ranges from -1.6 < alpha < -1.1, assuming explosion times of 12h to 6h pre-discovery, consistent with the decay indices seen in GRB afterglows. GOTO26djh/AT2026jpw is not detected in the most recent pre-discovery GOTO observations taken at 2026-04-12 00:00 UT (t0 -47.29h) to a 3-sigma limiting magnitude of L > 20.5. This constrains its onset to a window of < 2 days before discovery. Despite the apparent lack of an underlying star and an evolution consistent with GRB afterglows, a local stellar origin cannot be definitively excluded with the current data. We encourage further follow-up to determine the nature of this transient. EP/FXT ToO observations have been scheduled. GOTO magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018). LOT magnitudes were calibrated using SDSS stars. Observations are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44301. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42422] GRB 260415B: Fermi GBM Final Localization
by GCN Circulars 15 Apr '26

15 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44300 SUBJECT: GRB 260415B: Fermi GBM Final Localization DATE: 26/04/15 05:51:24 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 02:25:33.80 UT on 15 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260415B (trigger 797912738/260415101). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 229.43, Dec = 24.94 (J2000 degrees, equivalent to J2000 15h 18m, +24d 56'), with a statistical uncertainty of 9.03 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/bn260415101/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260415101/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260415101/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44300. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42421] GRB 260415A: Fermi GBM Final Real-time Localization
by GCN Circulars 15 Apr '26

15 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44299 SUBJECT: GRB 260415A: Fermi GBM Final Real-time Localization DATE: 26/04/15 04:54:40 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 04:43:59 UT on 15 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260415A (trigger 797921044.314306 / 260415197). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 58.5, Dec = -24.0 (J2000 degrees, equivalent to J2000 03h 53m, -24d 00'), with a statistical uncertainty of 5.5 degrees. The angle from the Fermi LAT boresight is 92.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260415197/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260415197/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260415197/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44299. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42420] Fermi trigger No 797912738: Global MASTER-Net observations report
by GCN Circulars 15 Apr '26

15 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44298 SUBJECT: Fermi trigger No 797912738: Global MASTER-Net observations report DATE: 26/04/15 04:31:12 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 GRB260415.10 (trigger No 797912738,14h 44m 00.00s , +19d 21m 00.0s, R=6.21) errorbox 6140 sec after notice time and 6176 sec after trigger time at 2026-04-15 04:08:29 UT, with upper limit up to 19.8 mag. The observations began at zenith distance = 58 deg. The sun altitude is -29.0 deg. The galactic latitude b = 62 deg., longitude l = 22 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3252523 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 6206 | 2026-04-15 04:08:29 | MASTER-OAGH | (14h 36m 16.77s , +18d 18m 58.5s) | C | 60 | 19.6 | 6206 | 2026-04-15 04:08:29 | MASTER-OAGH | (14h 37m 29.78s , +17d 44m 59.9s) | C | 60 | 19.8 | 6277 | 2026-04-15 04:09:40 | MASTER-OAGH | (14h 44m 35.36s , +18d 17m 56.2s) | C | 60 | 19.6 | 6277 | 2026-04-15 04:09:40 | MASTER-OAGH | (14h 45m 47.91s , +17d 43m 56.2s) | C | 60 | 19.6 | 6414 | 2026-04-15 04:11:57 | MASTER-OAGH | (14h 30m 17.59s , +20d 12m 49.5s) | C | 60 | 19.6 | 6414 | 2026-04-15 04:11:57 | MASTER-OAGH | (14h 31m 31.50s , +19d 38m 52.0s) | C | 60 | 19.6 | 6486 | 2026-04-15 04:13:09 | MASTER-OAGH | (14h 38m 42.62s , +20d 11m 48.8s) | C | 60 | 19.7 | 6486 | 2026-04-15 04:13:09 | MASTER-OAGH | (14h 39m 56.27s , +19d 37m 50.5s) | C | 60 | 19.8 | 6827 | 2026-04-15 04:18:50 | MASTER-OAGH | (14h 36m 11.16s , +18d 19m 41.4s) | C | 60 | 19.7 | 6827 | 2026-04-15 04:18:50 | MASTER-OAGH | (14h 37m 24.26s , +17d 45m 44.5s) | C | 60 | 19.8 | 6900 | 2026-04-15 04:20:03 | MASTER-OAGH | (14h 44m 41.90s , +18d 18m 39.3s) | C | 60 | 19.6 | 6900 | 2026-04-15 04:20:03 | MASTER-OAGH | (14h 45m 54.73s , +17d 44m 41.1s) | C | 60 | 19.7 | 7036 | 2026-04-15 04:22:19 | MASTER-OAGH | (14h 30m 11.15s , +20d 13m 35.1s) | C | 60 | 19.6 | 7036 | 2026-04-15 04:22:19 | MASTER-OAGH | (14h 31m 25.61s , +19d 39m 38.3s) | C | 60 | 19.6 | 7108 | 2026-04-15 04:23:31 | MASTER-OAGH | (14h 38m 48.80s , +20d 12m 34.4s) | C | 60 | 19.8 | 7108 | 2026-04-15 04:23:31 | MASTER-OAGH | (14h 40m 03.05s , +19d 38m 36.8s) | C | 60 | 19.8 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44298. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42419] GRB 260414A: Glowbug gamma-ray detection
by GCN Circulars 14 Apr '26

14 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44297 SUBJECT: GRB 260414A: Glowbug gamma-ray detection DATE: 26/04/14 23:14:50 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260414A, which was detected by Fermi/GBM (GCN 44293). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-04-14 06:31:55.248 with a duration of 21.5 s and a total significance of about 21 sigma. The detection occurred during a time of high background as Glowbug was entering the northern radiation belt. The brightest peaks in the light curve are at ~T0+3.5s and ~T0+12.5s. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44297. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42418] EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
by GCN Circulars 14 Apr '26

14 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44296 SUBJECT: EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope DATE: 26/04/14 17:44:51 GMT FROM: Viraj Karambelkar at Indian Inst of Tech,Bombay <karambelkarvraj21197(a)gmail.com> V. Karambelkar, K. De (Columbia University), G. Mo (Carnegie/Caltech), S. Ibrahim, D. Schiminovich (Columbia University) We observed the field of the fast X-ray transient EP260409a (Jiang et al. 2026, GCN 44240) using the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3m telescope in the near-infrared J and Hs bands. Observations were carried out starting at UTC 2026-04-09T03:10:30 in the J-band and 2026-04-09T03:40:58 in the H-band, approximately three hours after the EP trigger. The exposures lasted for a total of 16 minutes in the J-band and 32 minutes in the H-band. We do not detect the counterpart reported by Quirola-Vasquez et al., GCN 44264 to 5-sigma limits of J >~ 19.5 mag (AB) Hs >~ 19.8 mag (AB) MIRAGE is a new YJHs-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44296. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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