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

[vsnet-grb-info 42620] GRB 260507A: Fermi GBM Final Real-time Localization
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44493 SUBJECT: GRB 260507A: Fermi GBM Final Real-time Localization DATE: 26/05/07 20:38:34 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 20:28:00 UT on 7 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260507A (trigger 799878485.453562 / 260507853). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 287.5, Dec = -21.3 (J2000 degrees, equivalent to J2000 19h 10m, -21d 18'), with a statistical uncertainty of 2.4 degrees. The angle from the Fermi LAT boresight is 79.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260507853/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260507853/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260507853/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44493. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42619] EP260507a: GOTO optical counterpart detection
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44492 SUBJECT: EP260507a: GOTO optical counterpart detection DATE: 26/05/07 19:02:11 GMT FROM: Amit Kumar at The Open University, UK <amitkundu515(a)gmail.com> A. Kumar, S. Belkin, D. O'Neill, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, J. Casares, B. Godson, T. Killestein and M. Pursiainen on behalf of GOTO collaboration We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to EP-WXT triggered EP260507a (Fu et al., GCN 44488). The observations were conducted with GOTO-South at 2026-05-07 13:57:30 UT and 2026-05-07 15:04:48 UT (9.5 and 76.8 mins post-trigger, respectively), consisting of 4x90s exposures in the GOTO L-band (400-700 nm). Difference imaging was performed using deeper template observations of the same pointings. We detect the optical counterpart of EP260507a (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491) in the GOTO L-band at 2026-05-07 13:57:30 UT (9.5 mins post-trigger), with a measured magnitude of 19.56 ± 0.11 AB. The source is no longer detected at the next epoch obtained at 2026-05-07 15:04:48 UT (76.8 mins post-trigger), with a 3-sigma upper limit of 20.4 AB mag. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and 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/44492. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42618] EP260507a: TRT optical counterpart detection
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44491 SUBJECT: EP260507a: TRT optical counterpart detection DATE: 26/05/07 18:11:13 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), X. Liu, Z.P. Zhu, J. An, L.B. He, D. Xu (NAOC) report: We observed the field of EP260507a detected by EP (Fu et. al, GCN 44488), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observation started at 2026-05-07T14:27:55.509 UT, i.e., 39.98 mins post-burst, and a series of R-band frames were obtained. The optical afterglow (Corcoran et. al, GCN 44489; Sankar et. al, GCN 44490) is marginally detected in our stacked images with a brightness of R = 20.8 +/- 0.36 at a median time of 45.88 mins since trigger, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44491. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42617] EP260507a: Kinder optical counterpart candidate
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44490 SUBJECT: EP260507a: Kinder optical counterpart candidate DATE: 26/05/07 15:19:55 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Sankar.K, A. Aryan, Y.-H. Lee, T.-W. Chen, W.-J. Hou (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), S. Yang(HNAS), M.-H. Lee, A. Dutta, K. N.-T. Ho, 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 EP260507a (Fu et al., GCN 44488) using the 40cm SLT at the Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86). The first SLT epoch of observations started at 14:06 UTC on 7th May 2026 (MJD 61167.5837), 0.30 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. In the stacked frame as well as in the difference image, we detect an uncatalogued optical counterpart candidate at RA, DEC = 13:47:35.567, -22:14:08.38 with an uncertainty of 1". The optical counterpart candidate is well inside the EP-FXT error circle of 20". The details of the observations and measured PSF magnitude with template subtraction (in the AB system) of the possible counterpart of EP260507a are as follows: -------------------------------------------------------------------------------------------------- Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 61167.5837 | 0.30 | 300 * 6 | 20.64 +/- 0.07 | 2".07 | 1.44 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 = 0.16 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/44490. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42616] EP260507a: LCO optical counterpart
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44489 SUBJECT: EP260507a: LCO optical counterpart DATE: 26/05/07 15:16:19 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), J. A. Chácon (PUC), J. N. D. van Dalen (Radboud), F. E. Bauer (SSI and UTA), P. G. Jonker (Radboud), A. J. Levan (Radboud & Warwick) and D. B. Malesani (DAWN/NBI and Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260507a (Fu et al., GCN 44488) using an LCO 1m telescope located at the Siding Spring Observatory (Australia) equipped with the SINISTRO instrument. We obtained 6x300s exposures in the SDSS-r filter starting at 2026-05-07 14:34:48 (~47 minutes after the trigger). Within the EP/FXT error region (Fu et al., GCN 44488), we detect a likely optical counterpart at a position of (J2000): RA 13:47:35.57 (206.89822) Dec -22:14:08.40 (-22.23566) We measure a magnitude of r = 21.21 +/- 0.07 (AB) calibrated to PanSTARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42615] EP260507a: Einstein Probe detection of an X-ray transient
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44488 SUBJECT: EP260507a: Einstein Probe detection of an X-ray transient DATE: 26/05/07 14:40:02 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Y. Fu (HUST), Y. L. Wang (NAO, CAS; ICE, CSIC), C. L. Guo (NAO, CAS), X. Tian (GXU), W. D. Zhang (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 EP260507a. The transient triggered EP-WXT (ID: 01709261593) at 2026-05-07T13:47:57 (UTC). The WXT position of the source is R.A. = 206.895 deg, DEC = -22.243 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 206.8963 deg, DEC = -22.2361 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/44488. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42614] GRB 260504B: AstroSat CZTI detection
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44487 SUBJECT: GRB 260504B: AstroSat CZTI detection DATE: 26/05/07 14:19:14 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of GRB 260504B which is also detected by SVOM/GRM (Saccardi et al., GCN Circ. 44454), GECAM-B (Wang et al., GCN Circ. 44473), and Konus-Wind (Frederiks et. al., GCN Circ. 44474). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-04 09:31:16.450 UTC. The measured peak count rate associated with the burst is 1150 (+201, -203) counts/s above the background in the combined data of all four quadrants, with a total of 162 (+33, -36) counts. The local mean background count rate was 319 (+9, -11) counts/s. Using cumulative rates, we measure a T90 of 0.22 (+0.11, -0.07) 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 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/44487. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42613] GRB 260504B: SVOM/ECLAIRs refined analysis
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44486 SUBJECT: GRB 260504B: SVOM/ECLAIRs refined analysis DATE: 26/05/06 16:54:33 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> F. Piron (LUPM), M. Brunet (IRAP), N. Dagoneau (CEA), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), 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 260504B (SVOM burst-id sb26050402 – GCN 44454, trigger time T0 = 2026-05-04T09:31:19 UTC), which was also detected by SVOM/GRM (GCN 44470), GECAM-B (GCN 44473) and Konus-Wind (GCN 44474). The burst that triggered ECLAIRs onboard shows a single peak lightcurve. The burst duration is T90 = 0.46 -0.06/+0.09 s in the 4-120 keV energy band. The time-averaged spectrum from T0+0.40 s to T0+0.86 s in the energy range 5-120 keV is best fitted by a powerlaw model with best-fit parameters: alpha = -0.72 +/-0.06. With this model, the 4-120 keV fluence is (1.87 ± 0.09) e-7 erg/cm^2 and the 4-120 keV photon flux is 6.0 ± 0.3 ph/cm²/s. We note that the photon index is consistent with the one found by SVOM/GRM (GCN 44470). 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: Frédéric Piron (LUPM) (piron at in2p3.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44486. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42612] GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547)
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44485 SUBJECT: GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547) DATE: 26/05/06 14:01:40 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 799765648 at 13:07:23 on 06 May 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) = 280.7 deg Decl.(2000.0) = -6.1 deg The 1 sigma statistical error radius is 1.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260506547/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260506547/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260506547/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42611] GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547)
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44485 SUBJECT: GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547) DATE: 26/05/06 14:01:40 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 799765648 at 13:07:23 on 06 May 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) = 280.7 deg Decl.(2000.0) = -6.1 deg The 1 sigma statistical error radius is 1.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260506547/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260506547/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260506547/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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