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

[vsnet-grb-info 43063] GRB 260610B: TRT optical observation
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44909 SUBJECT: GRB 260610B: TRT optical observation DATE: 26/06/11 09:13:48 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z.-P. Zhu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), J. An (NAOC), X. Liu, S.-Q. Jiang, L.-B. He, D. Xu (NAOC), S.-Y. Fu (HUST) report: We observed the field of GRB260610B detected by Fermi (Fermi GBM team, GCN 44901) , using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO). Observation started at 2026-06-11 08:22:08 UT, i.e., ~ 0.36 days post-burst, and a series of R-band frames were obtained. The previously reported optical counterpart (O'Neill et al., GCN 44903; Watson et al., GCN 44905) is clearly detected in our stacked images with a brightness of R = 18.92 +/- 0.05, 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/44909. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43062] EP260610a: refined analysis of the EP-WXT and follow-up EP-FXT observations
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44908 SUBJECT: EP260610a: refined analysis of the EP-WXT and follow-up EP-FXT observations DATE: 26/06/11 08:52:18 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Y. Ren, C. L. Guo, Z. X. Ling (NAO, CAS), H.Z. Wu (HUST, CAS), on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260610a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission at 2026-06-10T04:41:46 (UTC). We note that the trigger time reported in Wu et al., GCN 44889 was incorrect. The correct trigger time is 2026-06-10T04:49:21 (UTC). The WXT light curve lasted for around 450 seconds before the interruption of the autonomous follow-up. The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model with a fixed Galactic hydrogen column density of 0.46 × 10^21 cm^−2 and a photon index of 0.89 (+0.60/−0.57). The derived average unabsorbed 0.5–4 keV flux is 2.71 (+1.21/−0.70) × 10^−10 erg s^−1 cm^−2. The autonomous follow-up observation with the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-06-10T04:52:19 (UTC). The exposure time was approximately 3.5 ks. The on-ground analysis of the FXT data detected an uncatalogued X-ray source at R.A. = 306.1022 deg, DEC = −25.9045 deg (J2000), with an uncertainty of 10 arcsec in radius (90% C.L., including statistical and systematic uncertainties). The average FXT 0.5–10 keV spectrum can be fitted with an absorbed power-law model with a fixed Galactic hydrogen column density of 0.46 × 10^21 cm^−2 and a photon index of 1.95 (+0.07/−0.07). The derived average unabsorbed 0.5–10 keV flux is 0.82 (+0.06/−0.05) × 10^−11 erg s^−1 cm^−2. The uncertainties quoted above are at the 90% confidence level. We note that follow-up observations were carried out with COLIBRÍ (de Ugarte Postigo et al., GCN 44890) and SVOM/VT (Li et al., GCN 44896), but no optical counterpart was detected in these observations. Launched on January 9, 2024, EP is a space X-ray observatory designed 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/44908. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43061] GRB 260611A: Fermi GBM Final Real-time Localization
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44907 SUBJECT: GRB 260611A: Fermi GBM Final Real-time Localization DATE: 26/06/11 08:12:44 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 08:00:16 UT on 11 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260611A (trigger 802857621.474604 / 260611334). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 126.4, Dec = -41.2 (J2000 degrees, equivalent to J2000 08h 25m, -41d 12'), with a statistical uncertainty of 18.7 degrees. The angle from the Fermi LAT boresight is 111.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260611334/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260611334/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260611334/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44907. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43060] EP260610b: COLIBRÍ optical observations
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44906 SUBJECT: EP260610b: COLIBRÍ optical observations DATE: 26/06/11 06:56:12 GMT FROM: enriquemm(a)astro.unam.mx Enrique Moreno Méndez (UNAM), Dalya Akl (NYUAD), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (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), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260610b (Wu et al., GCN Circ. 44895) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-11 05:16 to 06:32 UTC (from 16.48 to 17.73 hours after the trigger) and obtained 54 minutes of simultaneous exposure in the r/z filters. The data were reduced and coadded with the ASU 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. We marginally detect the optical counterpart reported by Levan et al., GCN Circ. 44897, in the r band, at a preliminary magnitude of: r ≈ 23.7, In z, we do not detect the source down to the following 3-sigma limit: z > 22.0. These values are consistent with those reported by Gemini (Levan et al., GCN Circ. 44897), SVOM/VT (Xin et al., GCN Circ. 44900), NOT (Zhu et al., GCN Circ. 44902) and MAO/AZT-22 (Burkhonov et al., GCN Circ. 44904). 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/44906. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43059] GRB 260610B: DDOTI optical observations
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44905 SUBJECT: GRB 260610B: DDOTI optical observations DATE: 26/06/11 06:31:15 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Rosa L. Becerra (UNAM), Nat Butler (ASU), Tsvetelina Dimitrova (ASU), William H. Lee (UNAM), and Margarita Pereyra (UNAM) report: We observed the field of GRB 260610B (Fermi Team, GCN Circ. 44901) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2026-06-11 04:53 to 05:44 UTC (5.1 to 5.9 hours after the trigger) obtaining total exposure of 27 minutes. We detect the candidate afterglow GOTO26fua/AT2026owq reported by O'Neill et al. (GCN Circ. 44903) with a preliminary AB magnitude of: w = 18.82 +/- 0.04 Compared to the observations reported by O'Neill et al. at 0.21 hours, the candidate continues to fade and has an estimated temporal decay index of approximately −0.6, in agreement with that measured by O'Neill et al. between 0.21 and 1.4 hours. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/44905. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43058] EP260610b: MAO/AZT-22 optical observations
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44904 SUBJECT: EP260610b: MAO/AZT-22 optical observations DATE: 26/06/11 04:37:49 GMT FROM: Yodgor Rajabov at UBAI <rajabov(a)astrin.uz> O. Burkhonov, Y. Rajabov, B.Abidkhanov, S. Ehgamberdiev, Y. Tillayev, T. Boyqobilov, A. Shaymanov report on behalf of UBAI team. We observed the field of EP transient EP260610b (Wu et al., GCN 44895), with the AZT-22 1.5m telescope of the Maidanak Observatory (MAO) starting on 2026-06-10 at 20:09:52 UT. In total we obtained 6x300 s exposures in the R-band using 4kx4k CCD SNUCAM camera (Im et al., 2010). The optical counterpart (Levan et al., GCN 44897; Xin et al., GCN 44900; Zhu et al., GCN 44902) is detected in the stacked frame. Preliminary photometry is the following: Date MidTime Exptime t-T0 Filter OT Err. UL SNR Site/Telescope (nxs) (mid, days) 2026-06-10T20:24:52 6x300 0,317072 R 22.85 0.15 23.26 6.4 MAO/AZT-22 All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022) web interface called STDweb (Karpov et al., 2025). Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog. The data has not corrected for the Galactic extinction. Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/) View this GCN Circular online at https://gcn.nasa.gov/circulars/44904. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43057] EP260610b: NOT optical observation
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44902 SUBJECT: EP260610b: NOT optical observation DATE: 26/06/11 02:42:23 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z.-P. Zhu, X. Liu, L.-B. He, J. An, S.-Q. Jiang, D. Xu (NAOC), S.-Y. Fu (HUST) reports on behalf of a large collaboration: We observed the field of EP260610b detected by EP (Wu et al., GCN 44895), using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observation started at 2026-06-10 22:20:33 UT, i.e., about 0.4 days post-burst, and a series of r-band frames were obtained. The previously reported optical counterpart (Levan et al., GCN 44897; Xin et al., GCN 44900) is detected in our stacked images with a preliminary brightness of r ~ 22.5, 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/44902. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43056] GRB 260610B: GOTO optical counterpart candidate
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44903 SUBJECT: GRB 260610B: GOTO optical counterpart candidate DATE: 26/06/11 02:49:52 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, J. Mills, M. Pursiainen, J. Lyman, K. Ackley, M. Dyer, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, R. Starling, B. Gompertz, B. Godson, T. Killestein, A. Kumar, on behalf of GOTO collaboration We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the Fermi/GBM alert GRB 260610B (GCN #44901). Observations covering the localisation area began at 2026-06-10 23:58:04 UT, (+0.2h post trigger) and continued through to 2026-06-11 00:31:39 UT (+0.76h post trigger). 63 images were taken, across 10 unique pointings, covering 241.5 sq. deg within the 90% localisation contour. ~89.6% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.6 mag. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks (Lyman et al. 2026). A new optical source GOTO26fua/AT2026owq is identified within the GBM 90% localisation region (25% contour) with co-ordinates: RA,DEC (J2000) = 218.159414, 27.004935, 14:32:38.26, +27:00:17.76 The source was detected with L = 16.66 ± 0.01 AB mag (+0.21h) before fading to L = 17.83 ± 0.03 AB mag (+1.4h) with the light curve consistent with a decay index t^-0.56. We find no evidence of the source prior to the GRB trigger time in previous GOTO observations, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021) at m_o > 19.45 mag (-38.99h). The temporal and spatial coincidence along with the power-law like decay strongly suggests this is the optical counterpart of GRB 260610B. 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/44903. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43055] EP260610b: NOT optical observation
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44902 SUBJECT: EP260610b: NOT optical observation DATE: 26/06/11 02:42:23 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z.-P. Zhu, X. Liu, L.-B. He, J. An, S.-Q. Jiang, D. Xu (NAOC), S.-Y. Fu (HUST) reports on behalf of a large collaboration: We observed the field of EP260610b detected by EP (Wu et al., GCN 44895), using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observation started at 2026-06-10 22:20:33 UT, i.e., about 0.4 days post-burst, and a series of r-band frames were obtained. The previously reported optical counterpart (Levan et al., GCN 44897; Xin et al., GCN 44900) is detected in our stacked images with a preliminary brightness of r ~ 22.5, 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/44902. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43054] GRB 260610B: GOTO optical counterpart candidate
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44903 SUBJECT: GRB 260610B: GOTO optical counterpart candidate DATE: 26/06/11 02:49:52 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, J. Mills, M. Pursiainen, J. Lyman, K. Ackley, M. Dyer, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, R. Starling, B. Gompertz, B. Godson, T. Killestein, A. Kumar, on behalf of GOTO collaboration We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the Fermi/GBM alert GRB 260610B (GCN #44901). Observations covering the localisation area began at 2026-06-10 23:58:04 UT, (+0.2h post trigger) and continued through to 2026-06-11 00:31:39 UT (+0.76h post trigger). 63 images were taken, across 10 unique pointings, covering 241.5 sq. deg within the 90% localisation contour. ~89.6% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.6 mag. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks (Lyman et al. 2026). A new optical source GOTO26fua/AT2026owq is identified within the GBM 90% localisation region (25% contour) with co-ordinates: RA,DEC (J2000) = 218.159414, 27.004935, 14:32:38.26, +27:00:17.76 The source was detected with L = 16.66 ± 0.01 AB mag (+0.21h) before fading to L = 17.83 ± 0.03 AB mag (+1.4h) with the light curve consistent with a decay index t^-0.56. We find no evidence of the source prior to the GRB trigger time in previous GOTO observations, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021) at m_o > 19.45 mag (-38.99h). The temporal and spatial coincidence along with the power-law like decay strongly suggests this is the optical counterpart of GRB 260610B. 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/44903. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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