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

[vsnet-grb-info 43421] EP260723a: SVOM/VT optical observation
by GCN Circulars 24 Jul '26

24 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45205 SUBJECT: EP260723a: SVOM/VT optical observation DATE: 26/07/24 12:08:26 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Z. H. Yao, J. R. Xu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of EP260723a detected by EP/WXT (Zhang et al., GCN 45201). SVOM/VT began observing the field at 2026-07-24T05:35:28 UTC, 10.658 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Eyles-Ferris et al., GCN 45202; He et al., GCN 45203; Basa et al., GCN 45204) was detected in both VT_B and VT_R bands. The AB magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) -------------|-------------------|------|--------------- 10.98 | 37*50 | VT_B | 22.1+-0.1 10.96 | 29*50 | VT_R | 21.9+-0.2 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/45205. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43420] EP260723a: COLIBRÍ optical observations
by GCN Circulars 24 Jul '26

24 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45204 SUBJECT: EP260723a: COLIBRÍ optical observations DATE: 26/07/24 10:38:47 GMT FROM: Stephane Basa at UAR Pytheas/OHP, LAM <stephane.basa(a)lam.fr> Stéphane Basa (UAR Pytheas), Enrique Moreno Méndez (UNAM), Jean-Grégoire Ducoin (CPPM), 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), Francis Fortin (IRAP), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Alan M. Watson (UNAM) We imaged the field of the EP260723a (Zhang et al., GCN 45201) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-07-24T07:43:35.559 to 2026-07-24T09:27:41.815 UTC (from 12.96 to 14.68 hours after the trigger) and obtained 64 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, and analysed with the COLIBRÍ 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. In the stacked images, we detect the optical counterpart reported by Eyles-Ferris et al. (GCN Circ. 45202) and He et al. (GCN Circ. 45203), with the following preliminary photometry: r = 22.25 +/- 0.09 z = 21.57 +/- 0.14 Further observations and analysis are ongoing. 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/45204. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43419] EP260723a: NOT optical conterpart confirmation
by GCN Circulars 24 Jul '26

24 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45203 SUBJECT: EP260723a: NOT optical conterpart confirmation DATE: 26/07/24 07:50:37 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, Z.P. Zhu, J. An, X. Liu, S.Q. Jiang, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), V. Vuolteenaho (NOT) report: We observed the field of EP260723a detected by EP (Zhang et al., GCN 45201) using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. An uncatalogued source is detected within the EP-WXT error circle at coordinates: R.A. (J2000): 00:11:54.04 (2.97518) Dec. (J2000): -12:05:54.6 (-12.09851) with an uncertainty of ~ 0.5 arcsec . The source had r = 22.10 +/- 0.05 at a median time of 10.18 hr post-trigger, calibrated with Pan-STARRS DR2 and not corrected for Galactic extinction. This position is consist with the previously reported optical conterpart (Eyles-Ferris et al., GCN 45202). We thus think this is the optical counterpart of EP260723a. View this GCN Circular online at https://gcn.nasa.gov/circulars/45203. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43418] EP260723a: Liverpool Telescope likely optical counterpart
by GCN Circulars 24 Jul '26

24 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45202 SUBJECT: EP260723a: Liverpool Telescope likely optical counterpart DATE: 26/07/24 07:25:20 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud) and R. L. C. Starling (Leicester) report on behalf of a larger collaboration: We observed the field of the Einstein Probe fast X-ray transient EP260723a (Zhang et al., GCN 45201) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 4x150 s and 5 x150 s exposures in each of the SDSS r’ and g’ filters respectively starting at 2026-07-24 04:35:57 UT, approximately 10.8 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. In our r-band subtraction and in the stacked image, we identify a new source within the EP/WXT localisation at a position of: RA 2.97513 (00:11:54.03) Dec -12.09839 (-12:05:54.2) We measure an AB magnitude of r = 21.86 +/- 0.11 and a g-band 5-sigma upper limit at the position of g > 22.25. Our photometry is calibrated to PanSTARRS and not corrected for Galactic extinction. We note the presence of a source in the Legacy Survey consistent with our candidate’s position at a magnitude of r = 23.62 +/- 0.15 and a photometric redshift of 0.91 +/- 0.13. We suggest this could be the host galaxy of EP260723a. View this GCN Circular online at https://gcn.nasa.gov/circulars/45202. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43417] EP260723a: EP-WXT detection of a fast X-ray transient
by GCN Circulars 24 Jul '26

24 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45201 SUBJECT: EP260723a: EP-WXT detection of a fast X-ray transient DATE: 26/07/24 06:57:32 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.J. Zhang (PKU), K. R. Ni (CCNU), X. H. Tang (THU), H. Sun (NAOC) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient, designated EP260723a (trigger ID: 11916655551), by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at 2026-07-23T18:56:01 (UTC) and lasted for about 100s, with a peak flux of ~ 1.4 x 10^(-9) erg cm^-2 s^-1 in 0.5-4 keV. The position of the transient is R.A. = 2.938 deg, Dec. = -12.112 (J2000), with an uncertainty radius of 3 arcmin in radius (90% confidence level, including both statistical and systematic uncertainties). The average WXT 0.5-4 keV spectrum can be fitted by an absorbed power-law model with a fixed Galactic hydrogen column density of 2.0×10^20 cm^-2 and a photon index of 1.4 (-0.8/+0.9). The derived average unabsorbed 0.5-4 keV flux is 4.1(-1.6/+2.7) x 10^(-10) erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters. Follow-up observations by EP-FXT will be arranged. Launched on 2024 January 9, Einstein Probe is a space-based X-ray observatory designed to monitor the dynamic X-ray sky and perform rapid follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/45201. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43416] GRB 260723A: Fermi GBM Final Localization
by GCN Circulars 23 Jul '26

23 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45200 SUBJECT: GRB 260723A: Fermi GBM Final Localization DATE: 26/07/23 21:06:26 GMT FROM: Suman Bala at USRA <sumanbala2210(a)gmail.com> The Fermi GBM team reports the detection of a likely LONG GRB. "At 13:54:48.40 UT on 23 July 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260723A (trigger 806507693/260723580). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 284.5, Dec = 7.7 (J2000 degrees, equivalent to J2000 18h 57m, +7d 42'), with a statistical uncertainty of 9.5 degrees. The angle from the Fermi LAT boresight is 87 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260723580/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260723580/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260723580/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/45200. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43415] IceCube-260722A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 23 Jul '26

23 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45199 SUBJECT: IceCube-260722A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/07/23 18:29:07 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-260722A (https://gcn.nasa.gov/circulars/45194) in a time range of 1000 seconds centered on the alert event time (2026-07-22 06:50:02.828 UTC to 2026-07-22 07:06:42.828 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-260722A. 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-260722A 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 7e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-07-21 06:58:22.828 UTC to 2026-07-23 06:58:22.828 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, is 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260722A 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/45199. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43414] IceCube-260722A: One candidate from the Zwicky Transient Facility (ZTF)
by GCN Circulars 23 Jul '26

23 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45198 SUBJECT: IceCube-260722A: One candidate from the Zwicky Transient Facility (ZTF) DATE: 26/07/23 18:22:44 GMT FROM: Jannis Necker at DESY <jannis.necker(a)desy.de> Jannis Necker (Leiden University), Akshay Eranhalodi (DESY), Robert Stein (JSI), Cristobal Zilleruelo Cañas (DESY), and Anna Franckowiak (Ruhr University Bochum) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-260722A (Zilleruelo Cañas et. al, GCN 45194) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2026-07-23 04:54 UTC, approximately 21.9 hours after event time. We covered 88.8% (2.3 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019). We are left with the following high-significance transient candidate by our pipeline, lying within the 90.0% localization of the skymap. +--------------------------------------------------------------------------------+ | ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr | +--------------------------------------------------------------------------------+ | ZTF26abjbxfs | AT 2026vts | 191.3022538 | +30.5970446 | r | 19.78 | 0.07 | +--------------------------------------------------------------------------------+ ZTF26abjbxfs / AT 2026vts was first detected on 2026-07-23, and is very blue (g-r = -0.2). It appears to lie on the edge of galaxy SDSS J124512.84+303550.1, with a spectroscopic redshift of z=0.0978. Assuming that this is the redshift of the transient, it has a current absolute magnitude of M=-18.8. ATLAS forced photometry reveals two marginal (3 sigma) detections in the ATLAS o-band at m= 19.6 +/- 0.2 mag, 3-4 days before the ZTF observations. This suggests that the transient is still blue more than four days after first detection. We encourage spectroscopic follow-up to determine its nature and assess potential high-energy neutrino emission scenarios. Further monitoring of this field will continue as part of the ZTF neutrino follow-up program (Stein et al. 2023) ZTF and GROWTH are worldwide collaborations comprising Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; OKC, Sweden; DZA, Germany. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). Alert filtering is performed with the nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ). View this GCN Circular online at https://gcn.nasa.gov/circulars/45198. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43413] IceCube Alert 260722A: Global MASTER-Net observations report
by GCN Circulars 22 Jul '26

22 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45197 SUBJECT: IceCube Alert 260722A: Global MASTER-Net observations report DATE: 26/07/22 17:40:06 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), M. Segura, 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-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) was pointed to the IceCube Alert 260722A (trigger No 47091427,12h 42m 12.00s , +31d 00m 00.0s, R=0.81) errorbox 36132 sec after notice time and 36189 sec after trigger time at 2026-07-22 17:01:32 UT, with upper limit up to 17.6 mag. Observations started at twilight. The observations began at zenith distance = 69 deg. The sun altitude is -14.7 deg. The galactic latitude b = 86 deg., longitude l = 145 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3438005 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 36220 | 2026-07-22 17:01:32 | MASTER-SAAO | (12h 41m 27.72s , +31d 36m 07.3s) | C | 60 | 17.6 | 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/45197. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43412] Konus-Wind detection of GRB 260721A
by GCN Circulars 22 Jul '26

22 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45196 SUBJECT: Konus-Wind detection of GRB 260721A DATE: 26/07/22 14:58:58 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, V. Panteleeva, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 260721A (NuSTAR-ACS detection: Grefenstette and Waratkar, GCN 45192) triggered Konus-Wind at T0=04620.710 s UT (01:17:00.710). The burst light curve shows a single pulse which starts at ~T0-0.6 s and has a total duration of ~33 s (75-1200 keV). The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260721_T04620/ As observed by Konus-Wind, the burst had the total fluence of 2.03(-0.14,+0.18)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+1.568 s, of 2.41(-0.44,+0.45)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+33.024 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.48(-0.11,+0.14), the high energy photon index beta = -2.69(-0.22,+0.19), the peak energy Ep = 161(-11,+10) keV (chi2 = 93/97 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = 0.02(-0.15,+0.17), the high energy photon index beta = -2.76(-0.27,+0.18), the peak energy Ep = 196(-12,+13) keV (chi2 = 84/82 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/45196. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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