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[vsnet-grb-info 42629] IceCube-260504A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44502 SUBJECT: IceCube-260504A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/05/08 18:08:49 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(a)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-260504A (https://gcn.nasa.gov/circulars/44464) in a time range of 1000 seconds centered on the alert event time (2026-05-04 21:03:00.958 UTC to 2026-05-04 21:19:40.958 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-260504A. 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 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260504A 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 5e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-05-03 21:11:20.958 UTC to 2026-05-05 21:11:20.958 UTC). In this case, we report a p-value of 1.00, 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 1.9e-01 to 2.0e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260504A 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/44502. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42628] EP260507a: REM optical/NIR observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44501 SUBJECT: EP260507a: REM optical/NIR observations DATE: 26/05/08 15:30:56 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of EP260507a, detected by EP (Fu et al., GCN 44488) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried out in the g, r, i, z, and H bands, started on 2026-05-07 at 22:56:01 UT (i.e. 9.1 hr after the burst) and lasted for about 1 hour. From preliminary photometry, we do not detect the optical/NIR counterpart (Corcoran et al., GCN Circ. 44489; Sankar et al., GCN Circ. 44490; Jiang et al., GCN Circ. 44491; Kumar et al., GCN Circ. 44492; Eyles-Ferris et al., GCN Circ. 44495; Jiang et al., GCN Circ. 44496; Li et al., GCN 44497; Globus et al., GCN 44498) down to the following 3sigma limits: r > 19.8 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 10.0 hr after the trigger; H > 14.5 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 9.2 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44501. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42627] EP260507a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44500 SUBJECT: EP260507a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/05/08 13:33:09 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: The fast X-ray transient EP260507a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Fu et al., GCN 44488). The refined analysis of the WXT data shows that the event started at T0=2026-05-07T13:47:44.0 (UTC) and lasted for 15 s before the observation was interrupted by the autonomous follow-up observation (i.e. T90 > 15 s). The average 0.5–4 keV spectrum of WXT can be modeled with an absorbed power law, adopting a fixed Galactic hydrogen column density of 5.55 x 10^20 cm^-2 and an additional column density of 5.77 x 10^21 cm^-2. This additional absorption significantly improves the fit quality, yielding a photon index of 1.47 (+-0.79). The derived average unabsorbed 0.5-4 keV flux is 1.98 (-0.70/+2.20) x 10^(-8) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-05-07T13:51:52 (UTC), about 4 minutes after T0. The exposure time of this observation is 5046 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 206.899, -22.2364 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law adopting a fixed Galactic equivalent hydrogen column density of 5.55 x 10^20 cm^-2 and an additional column density of 8.33 x 10^20 cm^-2，yielding a photon index of 2.10 (+-0.06). The derived average unabsorbed 0.3-10 keV flux is 1.82 (-0.07/+0.08) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44500. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42626] GRB 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44499 SUBJECT: GRB 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection DATE: 26/05/08 06:22:37 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (ICE-CSIC and Radboud Univ.), P.G. Jonker (Radboud Univ.) and E. Burns (LSU), R. Hamburg (USRA), and P. Veres (UAH) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP260507a detected by EP (Fu et al., GCN 44488). There was no Fermi-GBM onboard trigger around the EP trigger time (T0 = 2026-05-07T13:47:57 UTC). The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+250] s from EP T0, seeking signals between 64 ms and 32.768 s in duration. A weak transient signal was found most significantly at ~T0-4 s on a 16 s timescale, with a false alarm rate of 1.7e-03 Hz. The localisation is consistent with the EP one, with a spatial association probability of 93.5%. Among the three spectral templates tested, the transient was best fit with a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/44499. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42625] EP260507a: COLIBRÍ optical observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44498 SUBJECT: EP260507a: COLIBRÍ optical observations DATE: 26/05/08 06:07:02 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Francis Fortin (IRAP), 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), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260507a (Fu et al., GCN Circ. 44488) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-08 04:59 to 05:50 UTC (from 15.19 to 16.06 hours after the trigger) and obtained 39 minutes of exposure in the r and z filters, respectively. The data were reduced and coadded 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 the optical candidate reported previously (Corcoran et al., GCN Circ. 44489; Sankar et al., GCN Circ. 44490; Jiang et al., GCN Circ. 44491; Kumar et al., GCN Circ. 44492; Bochenek et al., GCN Circ. 44494; Eyles-Ferris et al., GCN Circ. 44495; Jiang et al., GCN Circ. 44496) with preliminary magnitudes of: r = 23.37 +/- 0.14, z = 22.44 +/- 0.21. From a combined power-law fit including our data and previously reported GCN Circular measurements, we derive a temporal decay index of α ≈ 0.6. 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/44498. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42624] EP260507a: SVOM/VT optical observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44497 SUBJECT: EP260507a: SVOM/VT optical observations DATE: 26/05/08 03:08:14 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, 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, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic follow-up observations to the Xray transient EP260507a triggered by Einstein Probe (Fu et al., GCN 44488). The observation started at 2026-05-07T14:45:27 UTC, i.e. 57.5 minutes post trigger and lasted for 2 orbits (about 1.9 hours) in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Eyles-Ferris et al., GCN 44495; Jiang et al., GCN 44496) was clearly detected in both channels. The measurements in AB magnitude are as follows: Mid time | Band | Exposure Time | Brightness 1.35 h VT_B 56*50 s 21.92 +/- 0.12 mag 1.35 h VT_R 55*50 s 20.91 +/- 0.08 mag 2.96 h VT_B 56*50 s 22.29 +/- 0.14 mag 2.96 h VT_R 55*50 s 21.25 +/- 0.10 mag Our photometry was not corrected for Galactic extinction. 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/44497. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42623] EP260507a: NOT optical observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44496 SUBJECT: EP260507a: NOT optical observations DATE: 26/05/08 01:42:18 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang, L.B. He, Z.P. Zhu, J. An, X. Liu, D. Xu (NAOC), S.Y. Fu (HUST), J. P. U. Fynbo (DAWN/NBI), A. L. Bouquin (NOT) report: We observed the field of EP260507a detected by EP (Fu et al., GCN 44488), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 3 x 300 s frames in the Sloan g, r, i-band, respectively. The optical afterglow (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Eyles-Ferris et al., GCN 44495) is detected in our stacked images. Preliminary photometry results are as follows: Tmid-T0(hr) Mag MagErr Filter 9.54 23.04 0.12 r 9.82 23.61 0.17 g 10.10 22.77 0.17 i 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/44496. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42622] EP260507a: further Liverpool Telescope observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44495 SUBJECT: EP260507a: further Liverpool Telescope observations DATE: 26/05/08 01:20:37 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester) reports on behalf of a larger collaboration: We observed the field of EP260227a (Fu et al., GCN 44488) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x200s exposures in each of the SDSS r’ and z’ filters starting at 2026-05-07 22:51:45 UT, approximately 9.06 hours after the X-ray detection. We detect the optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Bochenek et al., GCN 44494) in both the r’ z’ bands and measure the following magnitudes: r’ = 22.76 +/- 0.21 z’ = 21.98 +/- 0.30 Our photometry is calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44495. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42621] EP260507a: Liverpool Telescope optical upper limits
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44494 SUBJECT: EP260507a: Liverpool Telescope optical upper limits DATE: 26/05/07 23:34:35 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of EP260507a (Fu et al., GCN 44488) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x100s exposures in SDSS g, r, and i filters, starting at 2026-05-07 22:20:09 UT, approximately 8.54 hours after trigger. We do not detect any sources at the position of the optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491, Kumar et al., GCN 44492) down to the 3-sigma limiting magnitude of g > 22.05, r > 21.92 and i > 22.07. Further observations are planned. The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44494. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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