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

[vsnet-grb-info 43051] 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…

1 0

[vsnet-grb-info 43050] 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…

1 0

[vsnet-grb-info 43049] 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…

1 0

[vsnet-grb-info 43048] 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…

1 0

[vsnet-grb-info 43047] 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…

1 0

[vsnet-grb-info 43046] 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…

1 0

[vsnet-grb-info 43045] 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…

1 0

[vsnet-grb-info 43044] 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…

1 0

[vsnet-grb-info 43043] 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…

1 0

[vsnet-grb-info 43042] 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…

1 0

[vsnet-grb-info 43041] 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 43040] 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 43039] 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 43038] 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 43037] 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 43036] 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 43035] 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 43034] GRB 260610B: Fermi GBM Final Localization
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44901 SUBJECT: GRB 260610B: Fermi GBM Final Localization DATE: 26/06/11 01:29:13 GMT FROM: Matt Godwin <msg0028(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 23:46:14.25 UT on 10 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260610B (trigger 802827979/260610990). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 218.66, Dec = 23.94 (J2000 degrees, equivalent to J2000 14h 34m, +23d 56'), with a statistical uncertainty of 2.77 degrees. The angle from the Fermi LAT boresight is 84 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610990/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610990/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610990/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44901. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43033] EP260610b: SVOM/VT optical confirmation with blue color
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44900 SUBJECT: EP260610b: SVOM/VT optical confirmation with blue color DATE: 26/06/11 01:25:37 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> L. P. Xin, H. L. Li, C. Wu, Y. L. Qiu, J. R. Xu,, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations to the field of EP260610b triggered by Einstein Probe (Wu et al., GCN 44895). The observation started at 2026-06-10T13:47:19 UTC, 59.5 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Levan et al., GCN 44897) was detected by VT in both channels. The following measurements are in the AB magnitude without correction for Galactic extinction: Mid time | Band | Exposure Time | Brightness 2.13 h VT_B 91*50 s 22.6 +/- 0.2 mag 2.13 h VT_R 80*50 s 23.0 +/- 0.3 mag We note the source has a blue color in VT observations. 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/44900. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43032] IceCube-260610A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 11 Jun '26

11 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44899 SUBJECT: IceCube-260610A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/06/11 01:17:40 GMT FROM: janeth.phd(a)gmail.com The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-06-10 at 20:02:41.03 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD alert stream. The average astrophysical neutrino purity for Gold alerts is 50%. Given the path through the IceCube detector (track traversing only a limited instrumented volume), the detector does not observe the full energy deposition as well as it would for a track crossing a larger portion of the array. This leads to some uncertainty in the p_astro value, circulated via GCN notice. Regardless, this track remains a strong candidate for an astrophysical neutrino event. This alert has an estimated false alarm rate of 0.1495 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/142709_10606089.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-06-10 Time: 20:02:41.03 UT RA: 309.20 (+2.04/-2.06 deg 90% PSF containment) J2000 Dec: 37.22 (+0.96/-0.93 deg 90% PSF containment) J2000 As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. Two gamma-ray sources from the Fermi 4FGL-DR4 catalog are located within the 90% uncertainty region of this event. The closest source is 4FGL J2035.0+3632 (PSR J2034+3632), at RA = 308.7571° and Dec = 36.5371° (J2000), with an angular separation of 0.77° from the best-fit event position. The second-closest source is 4FGL J2030.0+3641 (PSR J2030+3641), at RA = 307.5086° and Dec = 36.6872° (J2000), with an angular separation of 1.45° from the best-fit event position. 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/44899. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43031] GRB 260515A: SOAR optical observations
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44898 SUBJECT: GRB 260515A: SOAR optical observations DATE: 26/06/10 20:40:46 GMT FROM: James Freeburn at University of North Carolina at Chapel Hill <jamesfreeburn54(a)gmail.com> Kira Nolan, James Freeburn, Anirudh Salgundi, Igor Andreoni (UNC Chapel Hill): We observed the field of GRB 260515A (Brunet et al., GCN 44622) using the Goodman High Throughput Spectrograph instrument on the 4.1m Southern Astrophysical Research (SOAR) Telescope, in imaging mode. We obtained 3x300s exposures respectively in the SDSS r and i filters, starting at 2026-06-08T02:01:28 UTC, approximately 23 days after the GRB trigger. We confirm the late-time emission (Li et al., GCN 44821) of the optical counterpart previously reported by He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Lipunov et al., GCN 44627; Wu et al., GCN 44628; Malesani et al., GCN 44629, Dennefeld et al., GCN 44633; Li et al., GCN 44634; Wang et al., GCN 44642; Antier et al., GCN 44643; Pérez-Fournon et al., GCN 44645; Dimple et al. GCN 44646; Moskvitin et al., GCN 44652; Bochenek et al., GCN 44658. We measure the following measurements and the magnitude limit is quoted at the 5 sigma level: | MJD (mid) | T - T_0 | Filter | Mag. (AB) | | --------- | -------- | - | ----- | | 61199.088 | 23.271 d | r | >23.6 | | 61199.099 | 23.282 d | i | 23.1 +/- 0.2 | Photometry is calibrated against nearby PanSTARRS-1 DR2 catalog stars and not corrected for extinction. As this location does not have i-band coverage in Legacy Survey DR10 (Dey et al., 2019), the detected emission may include contributions from the host galaxy. View this GCN Circular online at https://gcn.nasa.gov/circulars/44898. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43030] EP260610b: Gemini North optical counterpart candidate
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44897 SUBJECT: EP260610b: Gemini North optical counterpart candidate DATE: 26/06/10 16:54:45 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> A. J. Levan (Radboud & Warwick), J. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), G. Corcoran (UCD), A. P. C. van Hoof (Radboud), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), J. Chacón (PUC), H. Sun (NAO, CAS), F. E. Bauer (SSI and UTA) report on behalf of a larger collaboration: We observed the localisation region of EP260610b (Wu et al. 2026, GCN 44895) with the Gemini North Telescope and the GMOS-N instrument on Mauna Kea, Hawaii, USA. Observations began at 13:36:51 UT on 10 June 2026 and consisted of 7 × 100 s exposures in the SDSS r band (~0.81 hr after T0) and 3 × 100 s exposures in the SDSS z band (~1.08 hr after T0). By comparison with the Legacy Survey images, we identify a candidate optical counterpart at the following coordinates (J2000): RA = 17:50:29.72 Dec = +46:32:10.6 Photometry performed on the stacked images yields r = 22.23 ± 0.03 and z = 22.19 ± 0.05 AB mag, calibrated against nearby stars from the Pan-STARRS catalog and not corrected for Galactic extinction. We acknowledge the excellent support from the Gemini North staff in the execution of these challenging observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44897. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43029] EP260610a: SVOM/VT optical upper limits
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44896 SUBJECT: EP260610a: SVOM/VT optical upper limits DATE: 26/06/10 14:40:01 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, J. R. Xu,, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed a ToO observation of the field of EP260610a triggered by Einstein Probe (Wu et al., GCN 44889). The observation started at 2026-06-10T05:47:51 UTC, i.e., about 1.18 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued optical source was detected at the FXT source position (Wu et al., GCN 44889) in our stacked images, compared to the Legacy Survey. The 3-sigma upper limits are: Mid_time Band Exposure Time Magnitude (AB) 2.27 h VT_B 83*50 s > 23.8 mag 2.27 h VT_R 84*50 s > 23.4 mag The magnitudes are in the AB system and are not corrected for Galactic extinction. Our non-detection is consistent with the observation from COLIBRÍ (Postigo et al., GCN 44890). 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/44896. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43028] EP260610b: Einstein Probe detection of an X-ray transient
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44895 SUBJECT: EP260610b: Einstein Probe detection of an X-ray transient DATE: 26/06/10 13:28:05 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Z. Wu, (HUST, CAS),C. L. Guo, H. Y. Ren, Z. X. Ling (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 EP260610b. The transient triggered EP-WXT (ID: 01709268876) at 2026-06-10T12:48:17 (UTC). The WXT position of the source is R.A. = 267.601 deg, DEC = 46.534 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. = 267.6268 deg, DEC = 46.5388 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/44895. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43027] Konus-Wind detection of GRB 260601A
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44894 SUBJECT: Konus-Wind detection of GRB 260601A DATE: 26/06/10 13:16:20 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The short-duration GRB 260601A (Fermi-GBM detection: Fermi GBM team, GCN 44755, Holzmann Airasca et al., GCN 44760; Glowbug detection: Cheung et al., GCN 44763; GECAM-B detection: Wang et al., GCN 44778; SVOM-GRM detection: Wang et al., GCN 44793; CALET-GBM detection: Yamaoka et al., GCN 44817; IPN triangulation: Svinkin et al., GCN 44893) triggered Konus-Wind at T0=39609.166 s UT (11:00:09.166). The burst light curve shows a multipeaked structure which starts at ~T0 and has a total duration of ~0.2 s. 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/GRB260601_T39609/ As observed by Konus-Wind, the burst had the total fluence of 3.05(-0.27,+0.29)x10^-6 erg/cm2, and the 16-ms peak flux, measured from T0+0.078 s, of 4.04(-0.53,+0.55)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+0.192 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.44(-0.13,+0.14) and Ep = 780(-91,+107) keV (chi2 = 36/39 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.6 (chi2 = 36/38 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/44894. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43026] IPN triangulation of GRB 260601A (short/hard)
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44893 SUBJECT: IPN triangulation of GRB 260601A (short/hard) DATE: 26/06/10 13:06:10 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng, Cheng-Kui Li (IHEP) on behalf of GECAM team, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP), J. Wei (NAOC), B. Cordier (CEA) on behalf of the SVOM-GRM team, K. Yamaoka (Nagoya U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), on behalf of the CALET collaboration, report: The short-duration GRB 260601A (Fermi-GBM detection: The Fermi GBM team, GCN 44755; Holzmann Airasca, GCN 44760; Glowbug detection: Cheung et al., GCN 44763; GECAM-B detection: Y. Wang et al., GCN 44778; SVOM-GRM detection: Y. Wang et al., GCN 44793; CALET-GBM detection: Yamaoka et al., GCN 44817) was detected by Fermi (GBM trigger 802004417), CALET (GBM trigger 1464346716), Konus-Wind, Glowbug, SVOM (GRM), and GECAM-B at about 39612 s UT (11:00:12). We have triangulated it to the 3 sigma localization region whose area is 2.8 sq. deg, and its maximum dimension is 73 deg (the minimum one is 2.7 arcmin). A triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB260601_T39609/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/44893. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43025] GRB 260610b: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44892 SUBJECT: GRB 260610b: Fermi GBM Final Real-time Localization DATE: 26/06/10 10:19:57 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 10:07:46 UT on 10 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260610b (trigger 802778871.805202 / 260610422). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 354.7, Dec = 8.4 (J2000 degrees, equivalent to J2000 23h 38m, 8d 24'), with a statistical uncertainty of 10.5 degrees. The angle from the Fermi LAT boresight is 102.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44892. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43024] GRB 260610b: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44891 SUBJECT: GRB 260610b: Fermi GBM Final Real-time Localization DATE: 26/06/10 10:18:35 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 10:07:46 UT on 10 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260610b (trigger 802778871.805202 / 260610422). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 354.7, Dec = 8.4 (J2000 degrees, equivalent to J2000 23h 38m, 8d 24'), with a statistical uncertainty of 10.5 degrees. The angle from the Fermi LAT boresight is 102.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260610422/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44891. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43023] GRB 260610a: COLIBRÍ optical upper limits
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44890 SUBJECT: GRB 260610a: COLIBRÍ optical upper limits DATE: 26/06/10 10:12:50 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Diego López-Cámara (UNAM), 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), 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), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) report: We imaged the field of EP260610a (Wu et al., GCN Circ. 44889) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-10 08:23:40 to 09:56:22 UTC (from 3.78 to 5.32 hours after the trigger) and obtained 69 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded and analysed 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. In the stacked image, we do not detect any new source at the FXT source position (Wu et al., GCN Circ. 44889) down to the following 5-sigma limits: r > 24.0 mag z > 22.6 mag 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/44890. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43022] EP260610a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 10 Jun '26

10 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44889 SUBJECT: EP260610a: Einstein Probe detection of a fast X-ray transient DATE: 26/06/10 06:22:59 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Z. Wu, (HUST, CAS),C. L. Guo, H. Y. Ren, Z. X. Ling (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 EP260610a. The transient triggered EP-WXT (ID: 01709268833) at 2026-06-10 04:37:09(UTC). The WXT position of the source is R.A. = 306.104 deg, DEC = -25.926 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 at 2026-06-10T04:49:21(UTC). Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 306.1055 deg, DEC = -25.9057 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). 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/44889. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43021] GRB 260609A: Fermi GBM Final Localization
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44888 SUBJECT: GRB 260609A: Fermi GBM Final Localization DATE: 26/06/09 21:40:53 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 20:05:42.61 UT on 09 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260609A (trigger 802728347/260609837). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 42.43, Dec = -7.99 (J2000 degrees, equivalent to J2000 2h 49m, -7d 59'), with a statistical uncertainty of 8.05 degrees. The angle from the Fermi LAT boresight is 86 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260609837/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260609837/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260609837/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44888. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43020] Konus-Wind detection of GRB 260604C
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44887 SUBJECT: Konus-Wind detection of GRB 260604C DATE: 26/06/09 16:52:29 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260604C (Fermi-GBM detection: Fermi GBM team, GCN 44822, Neights et al., GCN 44831; SVOM-ECLAIRs detection: Gotz et al., GCN 44823, Brunet et al., GCN 44883; GECAM-B detection: Luo et al., GCN 44854; AstroSat-CZTI detection: Arya et al., GCN 44885) triggered Konus-Wind at T0=73128.568 s UT (20:18:48.568). The burst light curve shows a single pulse which starts at ~T0-3.2 s and has a duration of ~8.5 s. The emission is seen up to ~4 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260604_T73128/ As observed by Konus-Wind, the burst had the total fluence of 3.60(-0.26,+0.26)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+3.056 s, of 2.25(-0.18,+0.18)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+12.032 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 = -0.92(-0.05,+0.06), the high energy photon index beta = -2.33(-0.19,+0.13), the peak energy Ep = 421(-37,+40) keV (chi2 = 82/89 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+3.840 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 = -0.73(-0.06,+0.06), the high energy photon index beta = -2.07(-0.07,+0.06), the peak energy Ep = 374(-32,+35) keV (chi2 = 60/71 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/44887. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43019] GRB 260608A: Fermi GRB Observation
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44886 SUBJECT: GRB 260608A: Fermi GRB Observation DATE: 26/06/09 16:34:28 GMT FROM: Padraig McDermott at University College Dublin <padraig.mcdermott(a)ucdconnect.ie> Padraig Mc Dermott (UCD) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 11:35:31.06 UT on 08 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260608A (trigger 802611336/260608483). which was also detected by SVOM ECLAIRs (M.Brunet et al. 2026, GCN 44870, GCN 44882). The Fermi GBM on-ground location is consistent with the SVOM ECLAIRs position. The angle from the Fermi LAT boresight is 31 degrees. The GBM light curve consists of a main emission followed by a smaller peak with a duration (T90) of about 50 s (50-300 keV). The time-averaged spectrum from T0-6.7 to T0+43.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.35 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 93 +/- 3 keV. The event fluence (10-1000 keV) in this time interval is (2.83 +/- 0.11)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.83 s in the 10-1000 keV band is 2.1 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44886. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43018] GRB 260604C: AstroSat CZTI detection
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44885 SUBJECT: GRB 260604C: AstroSat CZTI detection DATE: 26/06/09 13:26:28 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), Harsha K. H. (IUCAA), S. Salunke (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 a long GRB 260604C which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44822) and SVOM/ECLAIRs (D. Gotz et.al., GCN Circ. 44823). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-06-04 20:18:49 UTC. The measured peak count rate associated with the burst is 1274 (+126, -136) counts/s above the background in the combined data of all quadrants, with a total of 1904 (+116, -105) counts. The local mean background count rate was 282 (+4, -7) counts/s. Using cumulative rates, we measure a T90 of 2.7 (+0.5, -0.2) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-06-04 20:18:48 UTC. The measured peak count rate associated with the burst is 3712 (+112, -126) counts/s above the background in the combined data of all quadrants, with a total of 8150 (+207, -252) counts. The local mean background count rate was 1332 (+7, -6) counts/s. We measure a T90 of 3.3 (+0.2, -0.1) s from the cumulative Veto light curve. 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 data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/ET20260604T201844/ET20260604T2… 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/44885. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43017] IPN triangulation of GRB 260601B / EP260601a
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44884 SUBJECT: IPN triangulation of GRB 260601B / EP260601a DATE: 26/06/09 12:41:20 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, Chen-Wei Wang (IHEP), Shao-Lin Xiong (IHEP), Shuang-Nan Zhang (IHEP) on behalf of the Insight-HXMT team, Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng, Cheng-Kui Li (IHEP) on behalf of GECAM team, E. Burns on behalf of the IPN, S. Sugita, A. Yoshida, T. Sakamoto, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena) on behalf of the CALET collaboration, A. Arya (IITB), G. Waratkar (Caltech/IITB), V. Bhalerao (IITB) on behalf of AstroSat/CZTI team, report: The long-duration GRB 260601B (GECAM-B detection: Yu et al., GCN 44767; NuSTAR-ACS detection: Waratkar et al., GCN 44771; CALET-GBM detection: Sugita et al., GCN 44773; Insight-HXMT detection: Wang et al., GCN 44785; Glowbug detection: Cheung et al., GCN 44801; Konus-Wind detection: Ridnaia et al., GCN 44806; AstroSat-CZTI detection: Arya et al., GCN 44839) was detected by GECAM-B, NuSTAR (ACS), CALET (GBM trigger 1464376270), Insight-HXMT (HE), Glowbug, AstroSat (CZTI), and Konus-Wind, at about 69168 s UT (19:12:48). We have triangulated it to the 3 sigma IPN localization region whose area is 55 sq. deg, and its maximum dimension is 39 deg (the minimum one is 1.3 deg). The fast X-ray transient EP260601a (Yang et al., GCN 44766) is inside the IPN localization strengthen the association of the transient and GRB 260601B. A triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB260601_T69173/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. View this GCN Circular online at https://gcn.nasa.gov/circulars/44884. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43016] GRB 260604C: SVOM/ECLAIRs refined analysis
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44883 SUBJECT: GRB 260604C: SVOM/ECLAIRs refined analysis DATE: 26/06/09 11:58:07 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP), N. Dagoneau, D. Gotz, D. Adrien, S. Bisero (CEA) 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 260604C (SVOM burst-id sb26060404 – GCN 44823, trigger time T0 = 2026-06-04T20:21:59 UTC), which was also detected by Fermi/GBM (GCN 44822, 44831) and GECAM-B (GCN 44854). The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is estimated to be around 255 s in the 4-20 keV energy band through imaging. The refined burst localization is RA, Dec = 224.396, 28.742 degrees: RA (J2000) = 14h57m35.0s Dec (J2000) = 28d44m31.2s with a 90% C.L. radius of 8.6 arcmin (including systematic error of 2 arcmin added in quadrature). This localization is consistent with the one of the afterglow (MASTER OT detection, GCN 44827). The time-averaged spectrum, before the slew (from T0-56.3 s to T0+41.9 s) in the 5-120 keV energy range is best fitted by a powerlaw model with alpha = -2.02 +0.17/-0.19. With this model, the 4-120 keV fluence is (4.5 +0.5/-1.3)e-7 erg/cm² and the 4-120 keV photon flux is 0.21 +0.01/-0.05 ph/cm²/s. The time-averaged spectrum after the slew (from T0+100 s to T0+200 s) in the 5-120 keV energy range is best fitted by a powerlaw model with alpha = -2.09 +0.35/-0.48. With this model, the 4-120 keV fluence is (2.2 +0.2/-1.3 )e-7 erg/cm² and the 4-120 keV photon flux is 0.10 +0.01/-0.05 ph/cm²/s. Fermi/GBM trigger occurred at T0-195 s at a time when ECLAIRs was not collecting data. So ECLAIRs missed the main part of the burst prompt emission. The spectral parameters we obtained may indicate that ECLAIRs observed the transition from the prompt to afterglow emission. All the quoted errors are at the 68% confidence level. 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: M. Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44883. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43015] GRB 260608A: SVOM/ECLAIRs refined analysis
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44882 SUBJECT: GRB 260608A: SVOM/ECLAIRs refined analysis DATE: 26/06/09 11:54:47 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, L. Bouchet (IRAP), C.-W. Wang (IHEP) D.-F. Kong (GXU) 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 260608A (SVOM burst-id sb260608A – GCN 44870, trigger time T0 = 2026-06-08T11:35:32 UTC), which was also detected by Fermi/GBM (GCN 44868). The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = 57.4 +3.8/-2.6 s in the 4-120 keV energy band. The time-averaged spectrum from T0-5.2 s s to T0+52.0 s in the 5-120 keV energy range is best fitted by a powerlaw model with alpha = -1.51 +/- 0.04. With this model, the 4-120 keV fluence is (3.1 +/- 0.1)e-6 erg/cm^2 and the 4-120 keV photon flux is 1.55 +/- 0.04 ph/cm^2/s. All the quoted errors are at the 68% confidence level. 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: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44882. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43014] Konus-Wind detection of GRB 260607B
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44881 SUBJECT: Konus-Wind detection of GRB 260607B DATE: 26/06/09 11:26:57 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260607B (Fermi-GBM detection: Fermi-GBM team, GCN 44859; Neights & Palafox, GCN 44861; Fermi-LAT detection: Holzmann Airasca et al., GCN 44860; AstroSat CZTI detection: Harsha et al., GCN 44871; GECAM-B detection: Wang et al., GCN 44880) triggered Konus-Wind at T0=47968.353 s UT (13:19:28.353). The burst light curve shows a bright multipeaked structure which starts at ~T0-6.8 s and ends at ~T0+50 s, which is followed by a weaker decaying emission with a 'bump' around ~T0+190 s. The total duration of the burst is ~209.8 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260607_T47968/ As observed by Konus-Wind, the burst had the total fluence of 4.55(-0.09,+0.09)x10^-4 erg/cm2, and the 64-ms peak flux, measured from T0+29.456 s, of 3.33(-0.27,+0.27)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+57.600 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 = -0.88(-0.02,+0.02), the high energy photon index beta = -2.87(-0.14,+0.11), the peak energy Ep = 622(-15,+16) keV (chi2 = 103/97 dof). The spectrum near the maximum count rate (measured from T0+29.184 to T0+30.720 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 = -0.74(-0.06,+0.06), the high energy photon index beta = -2.80(-0.37,+0.22), the peak energy Ep = 686(-51,+55) keV (chi2 = 48/62 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/44881. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43013] GRB 260607B: GECAM-B observation
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44880 SUBJECT: GRB 260607B: GECAM-B observation DATE: 26/06/09 05:54:44 GMT FROM: Yue Wang <m18509381757(a)163.com> Yue Wang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260607B at 2026-06-07T13:19:30.100 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44859) and Feimi/LAT (Airasca et. al., GCN #44860). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of muplti-pulses with a duration (T90) of 46.3 +0.1/-0.1 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260607B.png Using the localization reported by Fermi/LAT (Ra = 54.68 deg, Dec = 30.45 deg, Err = 0.40 deg, GCN #44860) , the time-averaged spectrum from T0-0 s to T0+55 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.03 +0.03/-0.03 and the cutoff energy, parameterized as Epeak, is 768 +49/-45 keV. The event fluence (10-1000 keV) in this time interval is (3.09 +/-0.03)E-04 erg/cm^2. The 'Amati' relation diagram of GRB 260607B is shown at: https://www.bursthub.cn//admin/static/gecambgrb260607B_amati.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44880. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43012] GRB 260608C: Fermi GBM Final Real-time Localization
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44879 SUBJECT: GRB 260608C: Fermi GBM Final Real-time Localization DATE: 26/06/09 00:09:29 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 23:54:23 UT on 8 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260608C (trigger 802655668.086186 / 260608996). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 245.4, Dec = 47.8 (J2000 degrees, equivalent to J2000 16h 21m, 47d 47'), with a statistical uncertainty of 9.6 degrees. The angle from the Fermi LAT boresight is 122.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608996/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608996/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608996/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44879. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43011] GRB 260608C: Fermi GBM Final Real-time Localization
by GCN Circulars 09 Jun '26

09 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44878 SUBJECT: GRB 260608C: Fermi GBM Final Real-time Localization DATE: 26/06/09 00:06:51 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 23:54:23 UT on 8 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260608C (trigger 802655668.086186 / 260608996). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 245.4, Dec = 47.8 (J2000 degrees, equivalent to J2000 16h 21m, 47d 47'), with a statistical uncertainty of 9.6 degrees. The angle from the Fermi LAT boresight is 122.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608996/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608996/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608996/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44878. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43010] GRB 260604C: further SAO RAS optical observations
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44877 SUBJECT: GRB 260604C: further SAO RAS optical observations DATE: 26/06/08 22:27:43 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI), A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team We observed the field of long GRB 260604C discovered by Fermi (The Fermi GBM team, GCN 44822; Neights & Meegan, GCN 44831); SVOM (Gotz et al., GCN 44823) and GECAM-B (Luo et al., GCN 44854) with the Zeiss-1000 1-m telescope of SAO RAS equipped with the CCD photometer. We obtained 12 x 300 sec. images in Rc band on June 08, 20:01:14--21:07:58 UT. The OT (Lipunov, GCN 44827; Konno et al., GCN 44828; GCN 44836; Zhu et al., GCN 44832; Becerra et al., GCN 44834; Hellot et al., GCN 44835; Gompertz et al., GCN 44837; Gompertz et al., GCN 44843; Chen et al., GCN 44851; Moskvitin et al., GCN 44852; Sasaki et al., GCN 44857; Pankov et al., GCN 44858; Pankov et al., GCN 44862; Burkhonov et al., GCN 44865; Lincetto et al., GCN 44873) is detected in our stacked image with the following brightness: Date UTstart t-T0 Exp. Filter Mag +/- Err. UL (mid,d) (n*s) (3-sigma) 2026.06.08 20:01:14 4.01102 12*300 Rc 23.08 +/- 0.18 23.8 The preliminary photometry is based on nearby SDSS stars (R-magnitudes were obtained using Lupton 2005 transformation equations) as in Moskvitin et al., GCN 44852, and was not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44877. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43009] GRB 260607A: AT2026ong (GOTO26fqf) is a type-Ia SN
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44876 SUBJECT: GRB 260607A: AT2026ong (GOTO26fqf) is a type-Ia SN DATE: 26/06/08 18:46:23 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> G. Corcoran (UCD), L. Izzo (INAF/OAC and DARK/NBI), B. Schneider (LAM), J. An (NAOC), B. P. Gompertz (Birmingham), V. Abril-Melgarejo (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of the Stargate collaboration: We observed the transient AT2026ong (GOTO26fqf; Gompertz et al., GCN 44864; He et al., GCN 44866; Lincetto et al., GCN 44875), proposed to be associated with the Fermi GBM GRB 260607A (Fermi GBM team, GCN 44855) using the ESO Very Large Telescope (VLT) UT3 (Melipal) equipped with the X-shooter telescope. Our spectra cover the wavelength range 3000-25000 AA, and consist of 2 exposures of 600 s each. The observation mid time was 2026 Jun 8.40 UT (20.87 hr after the GRB). In the acquisition image, we measure an AB magnitude r = 19.49 +- 0.03 (calibrated against Pan-STARRS, not corrected for Galactic extinction). The slit also covers the galaxy just east of the transient (Gompertz et al., GCN 44864), its likely host galaxy. From detection of multiple emission (Halpha, [N II], [S II]) and absorption (Ca II, G band) features, we measure for the galaxy a redshift of z = 0.111. The spectrum of the transient reveals a clear continuum with broad undulations across the entire optical range, markedly different from GRB afterglow spectra. Template matching via SNID-SAGE (Stoppa et al. 2026, doi:10.48550/arXiv.2603.28741) indicates a good agreement with a type-Ia SN, at a redshift consistent with the galaxy redshift. GOTO26fqf is thus not related to GRB 260607A and has been now named SN 2026ong. The UVB and VIS spectra of the transient are available via TNS at https://www.wis-tns.org/object/2026ong. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange and Francisco Caceres, for rapidly executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44876. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43008] GRB 260607A / GOTO26fqf / AT2026ong: COLIBRÍ optical observations
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44875 SUBJECT: GRB 260607A / GOTO26fqf / AT2026ong: COLIBRÍ optical observations DATE: 26/06/08 18:24:05 GMT FROM: Massimiliano Lincetto at Aix Marseille Univ, CNRS/IN2P3, CPPM <lincetto(a)cppm.in2p3.fr> Massimiliano Lincetto (CPPM), Leonardo García García (UNAM), Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), 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), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), 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) and Antonio de Ugarte Postigo (LAM) report: We imaged the candidate optical counterpart GOTO26fqf / AT2026ong (Gompertz et al., GCN Circ. 44864) of the Fermi GRB 260607A (Fermi GBM, GCN Circ. 44855) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-08 09:42 to 09:58 UTC (23 hours after the trigger) and obtained 840 seconds of simultaneous exposure in the r/z filters. The data were reduced and coadded with the COLIBRÍ ASU pipeline and analysed in STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. After subtracting template Pan-STARRS images, we detected the optical counterpart reported by Gompertz et al., GCN Circ. 44864, at preliminary magnitudes of: r = 19.72 +/- 0.01 z = 20.05 +/- 0.04 The measurement is consistent with a no-evolution scenario with reference to the GOTO measurement taken 14.7h after the trigger. The color r-z = -0.33 indicates a blue object, not consistent with typical GRB afterglows. 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/44875. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43007] GRB 260608B: Fermi GBM Final Localization
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44874 SUBJECT: GRB 260608B: Fermi GBM Final Localization DATE: 26/06/08 17:54:52 GMT FROM: oindabimukherjee(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 12:41:28.68 UT on 08 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260608B (trigger 802615293/260608529). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 56.98, Dec = 64.15 (J2000 degrees, equivalent to J2000 3h 47m, +64d 9'), with a statistical uncertainty of 3.78 degrees. The angle from the Fermi LAT boresight is 116 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608529/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608529/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608529/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44874. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43006] GRB 260604C: SVOM/COLIBRÍ (FM-GFT) colour evolution and confirmation of the late rebrightening
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44873 SUBJECT: GRB 260604C: SVOM/COLIBRÍ (FM-GFT) colour evolution and confirmation of the late rebrightening DATE: 26/06/08 15:49:40 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Massimiliano Lincetto (CPPM), Leonardo García García (UNAM), Rosa L. Becerra (UNAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Sarah Antier (IJCLAB), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), 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 Sofia Bisero (CEA Saclay) report: We re-imaged the field of GRB 260604C (Fermi GBM Team, GCN Circ. 44822, Gotz et al., GCN Circ. 44823) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-08 06:37 to 09:24 UTC (from 3.43 to 3.54 days after the trigger) and obtained 64, 63, and 127 minutes of exposure in the g, r, and z filters respectively. The data were reduced, coadded and analysed 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. In our first epoch reported by Becerra et al. (GCN Circ. 44827), we measured: g-r = 0.13 +/- 0.07 g-z = 0.48 +/- 0.10 In this epoch, we measured: g-r = 0.47 +/- 0.06 g-z = 0.86 +/- 0.09 Our measurements indicate a significant reddening of the source between the two epochs. Moreover, we also observe the rebrightening first reported by the Mondy team (Pankov et al., GCN Circ. 44862). The rise began approximately 30 hours after the trigger and lasted for about 30 hours. 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/44873. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43005] GRB 260604C: SVOM/C-GFT upper limit
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44872 SUBJECT: GRB 260604C: SVOM/C-GFT upper limit DATE: 26/06/08 15:20:05 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), Z. Kang (CHO), L.P. Xin（NAOC), S.J. Yin (GXU), X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC), N. Dagoneau, S. Bisero (CEA Saclay) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 260604C (SVOM burst-id sb26060404) detected by SVOM/ECLAIRs (GCN 44823) with LATIOS on SVOM/C-GFT. Observations started at 2026-06-05T15:54:29 UTC, ~19.54 h after the trigger. We obtained 9X90s exposures in the SDSS g filter. After preliminary analysis，we do not detect the optical counterpart (Lipunov et al., GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832, Becerra et al., GCN 44834; Hellot et al., GCN 44835; Gompertz et al., GCN 44837; Gompertz et al., GCN 44843; Saccardi et al., GCN 44844; Chen et al., GCN 44851; Moskvitin et al., GCN 44852; Sasaki et al., GCN 44857 ; Pankov et al., GCN 44858 ; Pankov et al., GCN 44862 ; Burkhonov et al., GCN 44865 ) in the stacked image. The upper limit is measured as follows: g > 21.1 AB (3-sigma, mid-time 19.68 h after the trigger). The photometry was calibrated against Pan-STARRS1 DR1 catalog and no correction for Galactic dust extinction was applied. We thank the observation assistants Hong-Xu Xue and Bo-Wen Li at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/44872. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43004] GRB 260607B: AstroSat CZTI detection
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44871 SUBJECT: GRB 260607B: AstroSat CZTI detection DATE: 26/06/08 13:00:00 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), 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 a long GRB 260607B which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 44859), Fermi LAT (Airasca et. al. , GCN Circ. 44860). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-06-07 13:19:41.91 UTC. The measured peak count rate associated with the burst is 508 (+45, -30) counts/s above the background in the combined data of all quadrants, with a total of 8523 (+313, -323) counts. The local mean background count rate was 280 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 45.8 (+0.2, -0.6) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.The light curve showed multiple peaks of emission with the strongest peak at 2026-06-07 13:19:41.36 UTC. The measured peak count rate associated with the burst is 4613 (+124, -120) counts/s above the background in the combined data of all quadrants, with a total of 79352 (+766, -730) counts. The local mean background count rate was 1278 (+4, -5) counts/s. We measure a T90 of 45.8 (+0.1, -0.1) s from the cumulative Veto light curve. 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 data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/ET20260607T131928/ET20260607T1… 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/44871. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43003] GRB 260608A: SVOM detection of a burst
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44870 SUBJECT: GRB 260608A: SVOM detection of a burst DATE: 26/06/08 12:08:17 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, L. Bouchet (IRAP), C.-W. Wang (IHEP) D.-F. Kong (GXU) report on behalf of the SVOM mission team: At 2026-06-08T11:35:32 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260608A (SVOM burst-id sb26060803), which is also detected by Fermi/GBM (GCN 44868). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 34 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 24.71 in the [8-120] keV energy band over a time window of 81.92 seconds starting at 2026-06-08T11:35:14. The localization of the best alert is R.A., Dec. 81.3711, -48.3879 degrees: R.A. (J2000) = 5h25m29.07s Dec. (J2000) = -48d23m16.62s with a 90% confidence level (C.L.) radius of 3.70 arcmin (including systematic error of 2 arcmin added in quadrature). TThe SVOM/ECLAIRs light curve showed a multiple peak structure with a T90 duration of about 46.839 (-2.959 +3.411) s. This burst was also detected by SVOM/GRM with a significance of 18.20. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 53.73 (-2.457 +2.459) s. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260608A.png Due to Sun constraint, no X-ray observation could be performed by SVOM/MXT and no optical observation could be performed by SVOM/VT for the time being. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Chenwei Wang: cwwang(a)ihep.ac.cn Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44870. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43002] GRB 260608A: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44869 SUBJECT: GRB 260608A: Fermi GBM Final Real-time Localization DATE: 26/06/08 11:47:57 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 11:35:31 UT on 8 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260608A (trigger 802611336.05914 / 260608483). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 78.4, Dec = -45.2 (J2000 degrees, equivalent to J2000 05h 13m, -45d 12'), with a statistical uncertainty of 3.2 degrees. The angle from the Fermi LAT boresight is 29.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608483/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608483/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608483/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44869. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43001] GRB 260608A: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44868 SUBJECT: GRB 260608A: Fermi GBM Final Real-time Localization DATE: 26/06/08 11:46:30 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 11:35:31 UT on 8 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260608A (trigger 802611336.05914 / 260608483). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 78.4, Dec = -45.2 (J2000 degrees, equivalent to J2000 05h 13m, -45d 12'), with a statistical uncertainty of 3.2 degrees. The angle from the Fermi LAT boresight is 29.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608483/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608483/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260608483/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44868. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43000] EP260605a: EP-FXT follow-up observation
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44867 SUBJECT: EP260605a: EP-FXT follow-up observation DATE: 26/06/08 10:47:23 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A.Li (BNU), C. Y. Wang (THU), Z.-C. Zou (NJU), X. H. Tang (THU), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260605a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Li et al., GCN 44847) at 2026-06-05T09:31:00 (UTC). Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-06-06T10:39:36(UTC), ~25 hours after the WXT detection. The exposure time of the observation is around 6 ks. The on-ground analysis of the FXT data found an uncatalogued source within the error circle of WXT at R.A. = 273.298 deg, DEC = -40.3945 deg (J2000) with an uncertainty of 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 with a fixed Galactic hydrogen column density of 1.03 x 10^21 cm^-2, and a photon index of 3.3 (-0.6, +0.5). The derived average unabsorbed 0.5-10 keV flux is 1.1 (-0.4, +0.9) ×10^(-13) 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/44867. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42999] GRB 260607A: TRT optical observations
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44866 SUBJECT: GRB 260607A: TRT optical observations DATE: 26/06/08 10:34:45 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), J. An, X. Liu, Z.P. Zhu, S.Q. Jiang, L.B. He, D. Xu (NAOC), S.Y. Fu (HUST) report: We observed the optical counterpart candidate, AT2026ong, (Gompertz et. al., GCN 44864) of GRB 260607A detected by Fermi GBM (Fermi GBM Team, GCN 44855), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO). A series of frames in the R-band were obtained. AT2026ong is clearly detected in our stacked image with a brightness of R = 19.2 +/- 0.2 at a median time of ~20.5 hrs post-trigger, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. There is no decay between the GOTO and TRT observations. The previously reported potential host galaxy of AT2026ong (Gompertz et. al., GCN 44864) has a redshift of z ~ 0.126 from the [REGALADE](https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=J/A%2bA/706/A284/regalade&-out.add=.) catalog (Tranin et al., 2026). View this GCN Circular online at https://gcn.nasa.gov/circulars/44866. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42998] GRB 260604C: GRANDMA further observations
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44865 SUBJECT: GRB 260604C: GRANDMA further observations DATE: 26/06/08 09:38:41 GMT FROM: antier(a)ijclab.in2p3.fr O. Burkhonov (UBAI), M. Pillas (IAP), T. Leandro de Almeida (LNA), E. Elhosseiny (NRIAG), N. Kochiashvili (AbAO), L. Chen (TSU), A. Simon (TShNU of Kyiv), S. Antier (IJCLAB), M. Coughlin (UMN), S. Ehgamberdiev (UBAI), Y. Rajabov (UBAI), Y. Tillayev (UBAI), N. Sasaki (UEA,LNA), R. Inasaridze (AbAO), V. Zhuzhunadze (AbAO), A. Takey (NRIAG), W. Corradi (LNA), I. Abdusamatjan (TNOT) on behalf of GRANDMA: We conducted further follow-up observations of GRB 260604C (Fermi Team, GCN Circ. 44822, Gotz et al., GCN Circ. 44823) with GRANDMA up to now. We observed a possible re-brightening in r, i, and R thanks to further observations from Two-meter Twin Telescope (TTT) sited at the Teide Observatory, UBAI-AZT-22 at Madainak Observatory, AbAO-T1.5m at Abastumani Observatory, KAO-1.88m at Kottamia Astronomical Observatory, and OPD-1.6m at Observatório do Pico dos Dias (Sasaki et al GCN 44857). This is shown in the public site group of the public ACME service Skyportal/ICARE https://skyportal-icare.ijclab.in2p3.fr/source/GCN-260604_202037. To access, one simply needs to create an account using your ORCID id. Our measurements are aligned with Mondy's report (Pankov GCN 44862). The observations are performed under the P7 campaign of GRANDMA to monitor SVOM alerts and LSST alerts from explosive fast transients filtered by BOOM/Babamul and FINK. GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (kilonovacatcher.in2p3.fr). Astrophysics Center for Multimessenger studies in Europe is supported Skyportal/ICARE (contact camille.douzet(a)ijclab.in2p3.fr, skyportal.io). The TTT Observing Time Rights (DTO) used were provided by Light Bridges, SL. View this GCN Circular online at https://gcn.nasa.gov/circulars/44865. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42997] GRB 260607A: GOTO tentative optical counterpart candidate GOTO26fqf / AT2026ong
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44864 SUBJECT: GRB 260607A: GOTO tentative optical counterpart candidate GOTO26fqf / AT2026ong DATE: 26/06/08 09:15:55 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz, M. Shrestha, R. Starling, A. Kumar, G. Ramsay, K. Ackley, M. Dyer, J. Lyman, 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, D. O'Neill and M. Pursiainen report 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 short GRB 260607A (Fermi GBM Team, GCN 44855). Targeted observations from GOTO-N covering the localisation area began at 2026-06-07 23:38:04 UT, (+10.81h post trigger) and continued through to 2026-06-08 03:49:33 UT (+15.0h post trigger). 260 images were taken, across 11 unique pointings, covering 417.3 sq. deg within the 90% localisation contour. ~82.7% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.5 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. We identify one candidate optical counterpart contained within the 90% probability contour: +--------------------------------------------------------------------------+ | Internal name | IAU name | RA (J2000) | dec (J2000) | AB mag | +--------------------------------------------------------------------------+ | GOTO26fqf | AT2026ong | 314.468601 | 34.277287 | 19.54 ± 0.10 | +--------------------------------------------------------------------------+ We find no evidence of this source prior to the GRB trigger time in the previous GOTO epoch, taken at 04:13:23 UT on 2026-06-07 (t0 - 8.6h) to a 3-sigma limiting magnitude of L > 20.1 (AB). We also find no evidence for the source prior to the GRB in the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). Its position is on the 63% probability contour of the GBM localisation map. GOTO26fqf / AT2026ong was detected in 3 epochs with magnitudes of L = 19.54 ± 0.10 (t0 + 12.1h), L = 19.83 ± 0.14 (t0 + 13.4h) and L = 19.84 ± 0.14 (t0 + 14.7h), which is consistent with a power-law temporal decay with an index of t^[-1.60 ± 0.64]. However, we caution that epochs 2 and 3 are consistent with no evolution. The candidate counterpart is spatially coincident with an extended object in PanSTARRS archival imaging, which we suggest is the host galaxy of the unidentified transient. We are unable to robustly relate GOTO26fqf / AT2026ong to GRB 260607A based on available observations but further follow-up, especially spectroscopic classification, is encouraged. 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/44864. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42996] GRB 260604A: SVOM/GRM detection
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44863 SUBJECT: GRB 260604A: SVOM/GRM detection DATE: 26/06/08 09:07:17 GMT FROM: yzh807926(a)163.com SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier GODET (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by a burst GRB 260604A at 2026-06-04T02:24:27.200 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44812). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst mainly consists of multiple pulses with a T90 of 4.0 +4.2/-2.2 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260604A.png In addition, the position of this burst, according to Fermi/GBM localization (RA = 60.4 deg, Dec = -12.8 deg, Err = 9.8 deg, Fermi GBM Team, GCN #44812), is located at about 71 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0+0 to T0+4 s is fitted by a power law function. The power law index is -1.69 +0.12/-0.11. The event fluence (10-1000 keV) in this time interval is (1.01 +0.17/-0.16)E-06 erg/cm^2. 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Zheng-Hang Yu (IHEP) (zhyu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44863. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42995] GRB 260604C: Mondy optical observations: evidence of a possible brightening
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44862 SUBJECT: GRB 260604C: Mondy optical observations: evidence of a possible brightening DATE: 26/06/08 09:03:44 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> N. Pankov (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), A. Moskvitin (SAO RAS), A. Volnova (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 260604C (The Fermi GBM team, GCN 44822; Neights & Meegan, GCN 44831; Gotz et al., GCN 44823) with the AZT-33IK 1.6-m telescope of the Sayan Solar Observatory (Mondy). The observations were conducted starting on 2026-06-07 16:34 UT, i.e. ~2.86 days since GRB. We aquired 30x120 sec exposures in the R-band using a CMOS-photometer. The optical afterglow (Lipunov, GCN 44827; Konno et al., GCN 44828; GCN 44836; Zhu et al., GCN 44832; Becerra et al., GCN 44834; Hellot et al., GCN 44835; Konno et al., GCN 44836; Gompertz et al., GCNs 44837, 44843; Chen et al., GCN 44851; Moskvitin et al., GCN 44852; Sasaki et al., GCN 44857; Pankov et al., GCN 44858) is clearly detected in the co-add image and displays an evidence of a brightening in comparison with previous epochs of observations (Moskvitin et al., GCN 44852; Sasaki et al., GCN 44857; Pankov et al., GCN 44858). The observations details and preliminary photometry are summarized below: Date UTstart t-T0 Exp. Filter Mag Err. UL (mid,d) (n*s) (3-sigma) 2026-06-07 16:34:49 2.86396 28x120 R 21.18 0.06 23.2 The photometry is based on nearby SDSS stars (R-magnitudes were obtained using Lupton 2005 transformation equations) as in Moskvitin et al., GCN 44852, and was not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44862. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42994] GRB 260607B: Fermi GBM Observation
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44861 SUBJECT: GRB 260607B: Fermi GBM Observation DATE: 26/06/08 02:49:06 GMT FROM: eliza.neights(a)gmail.com E. Neights (GWU, NASA GSFC) and E. Palafox (INAOE-Mexico) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 13:19:28.70 UT on 07 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260607B (trigger 802531173/260607555), which was also detected by Fermi LAT (Holzmann Airasca et al. 2026, GCN 44860). The Fermi GBM on-ground location is consistent with the Fermi LAT position. The angle from the Fermi LAT boresight is 72 degrees. The GBM light curve consists of multiple emission episodes, with a duration (T90) of about 47 s (50-300 keV). The time-averaged spectrum from T0+2.9 to T0+57.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.92 +/- 0.004 and the cutoff energy, parameterized as Epeak, is 728 +/- 2 keV. The event fluence (10-1000 keV) in this time interval is (2.999 +/- 0.006)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+53 s in the 10-1000 keV band is 66.9 +/- 0.5 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44861. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42993] GRB 260607B: Fermi-LAT detection
by GCN Circulars 08 Jun '26

08 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44860 SUBJECT: GRB 260607B: Fermi-LAT detection DATE: 26/06/08 00:59:52 GMT FROM: N. Di Lalla at Stanford University <niccolo.dilalla(a)stanford.edu> A. Holzmann Airasca (UniTrento and INFN Bari), R. Gupta (NASA/GSFC) and N. Di Lalla (Stanford University) report on behalf of the Fermi-LAT team: At 13:19:28.70 UT on June 7th, 2026 Fermi-LAT detected high-energy emission from GRB 260607B, which was also detected by Fermi-GBM (trigger 802531173/260607555, GCN #44859). The best LAT on-ground location is found to be RA, Dec = 54.68, 30.45 (J2000) with an error radius of 0.40 deg (90 % containment, statistical error only). This was 72 deg from the LAT boresight at the time of the trigger. The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 0 - 1.2 ks after the GBM trigger is (2.22 ± 0.50)E-5 ph/cm2/s. The estimated photon index above 100 MeV is -1.98 ± 0.15. The highest energy photon has an energy of 4.7 GeV and occurs at 120 s after trigger time. The Fermi-LAT point of contact for this burst is Niccolò Di Lalla (niccolo.dilalla(a)stanford.edu) The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/44860. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42992] GRB 260607B: Fermi GBM Final Localization Correction
by GCN Circulars 07 Jun '26

07 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44859 SUBJECT: GRB 260607B: Fermi GBM Final Localization Correction DATE: 26/06/07 21:01:33 GMT FROM: Eva M. Palafox at INAOE <eva.palafox(a)gmail.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 13:19:28.70 UT on 07 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260607B (trigger 802531173/260607555). This trigger was initially classified as Distant Particles by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 55.11, Dec = 26.90 (J2000 degrees, equivalent to J2000 +03h 40m, +26d 54'), with a statistical uncertainty of 1.00 degree. The angle from the Fermi LAT boresight is 68 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607555/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607555/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607555/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44859. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42991] GRB 260604C: Simeiz Zeiss-1000 optical observations of the afterglow
by GCN Circulars 07 Jun '26

07 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44858 SUBJECT: GRB 260604C: Simeiz Zeiss-1000 optical observations of the afterglow DATE: 26/06/07 19:31:45 GMT FROM: Nicolai Pankov at IKI <colinsergesen(a)gmail.com> N. Pankov (IKI), A. Pozanenko (IKI), A. Novichonok (KIAM), A. Moskvitin (SAO RAS), I. Nikolenko (INASAN), A. Volnova (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 260604C (The Fermi GBM team, GCN 44822; Neights & Meegan, GCN 44831; Gotz et al., GCN 44823) with the Zeiss-1000 1-m telescope of the Simeiz Observatory (mnt. Koshka) of INASAN. The observations were conducted on 2026-06-05 and 2026-06-06 epochs using a CCD-photometer and the R-filter. The optical afterglow (Lipunov, GCN 44827; Konno et al., GCN 44828; GCN 44836; Zhu et al., GCN 44832; Becerra et al., GCN 44834; Hellot et al., GCN 44835; Konno et al., GCN 44836; Gompertz et al., GCNs 44837, 44843; Chen et al., GCN 44851; Moskvitin et al., GCN 44852; Sasaki et al., GCN 44857) is clearly detected in the co-add images obtained on both epochs. The observations details and preliminary photometry are summarized below: Date UTstart t-T0 Exp. Filter Mag Err. UL (mid,d) (n*s) (3-sigma) 2026-06-05 21:31:13 1.07291 26x150 R 21.35 0.14 22.4 2026-06-06 20:09:21 2.03341 46x150 R 21.53 0.19 22.3 The photometry is based on nearby SDSS stars (R-magnitudes were obtained using Lupton 2005 transformation equations) as in Moskvitin et al., GCN 44852, and was not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44858. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42990] GRB 260604C: OPD1.6m - GRANDMA observations - detection
by GCN Circulars 07 Jun '26

07 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44857 SUBJECT: GRB 260604C: OPD1.6m - GRANDMA observations - detection DATE: 26/06/07 13:35:13 GMT FROM: Nelio Sasaki at NEPA-UEA <nsasaki(a)uea.edu.br> Nélio Sasaki (UEA-Parintins), Wagner Corradi (LNA), Leandro de Almeida (LNA), Felipe Navarete (LNA), S. Antier (OCA/IJCLAB), I. Tosta e Melo (IFN), A. Simon (TshNU of Kyiv), L. Chen (TSU), M. Coughlin (UMN) and P. Hello (IJCLAB) on behalf of Observatório do Pico dos Dias (OPD/LNA/Brazil) and the GRANDMA collaboration, report follow-up observations of GRB 260604C (Fermi Team, GCN Circ. 44822, Gotz et al., GCN Circ. 44823, Chen et al., GCN 44851; Moskvitin et al., GCN 44852) performing photometry of the GRB260604C source with SPARC4 in the Sloan bands (g,r,i,z), using exposures of 40 × 180 s in (g), 120 × 60 s in (r), 120 × 60 s in (i), and 120 × 60 s in (z). The observations began on 2026-06-07T00:18:36.036 UTC, corresponding to JD 2461198.512917. The recentered position of the source is: RA = 14:57:49.54, Dec = +28:49:03.96 The measured magnitudes of the target are: Filter | Mag (AB) g | 22.0938 ± 0.0008 (Magnitude limit: 24.6925) r | 21.7162 ± 0.0005 (Magnitude limit: 23.9245) i | 21.5773 ± 0.0008 (Magnitude limit: 25.1456) z | 21.4418 ± 0.0006 (Magnitude limit: 23.8440) Photometric calibration was performed using Gaia DR3 field stars. For each comparison star, the Gaia magnitude (G) and color (G_BP-G_RP) were transformed to Sloan-type magnitudes (g,r,i,z). The photometric zero point in each filter was then obtained from the difference between the transformed magnitudes from the catalog and the instrumental magnitudes of the comparison stars, and applied to the instrumental magnitude of the target. The transformations in (g,r,i) follow the Gaia-SDSS color relationships of Evans et al. (2018), while the magnitude in (z) was estimated using the (G-g) versus (g-z) relationship of Jordi et al. (2010). The Gaia DR3 catalog is from Gaia Collaboration et al. / Vallenari et al. (2023). The observations are performed under the P7 campaign of GRANDMA to monitor SVOM alerts and LSST alerts from explosive fast transients filtered by BOOM/Babamul and FINK. GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (kilonovacatcher.in2p3.fr). Astrophysics Center for Multimessenger studies in Europe is supported by Skyportal/ICARE (contact camille.douzet(a)ijclab.in2p3.fr, skyportal.io) View this GCN Circular online at https://gcn.nasa.gov/circulars/44857. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42989] GRB 260607A: Fermi GBM Final Real-time Localization
by GCN Circulars 07 Jun '26

07 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44856 SUBJECT: GRB 260607A: Fermi GBM Final Real-time Localization DATE: 26/06/07 13:01:39 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 SHORT GRB At 12:49:18 UT on 7 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260607A (trigger 802529363.702736 / 260607534). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 304.2, Dec = 36.5 (J2000 degrees, equivalent to J2000 20h 16m, 36d 30'), with a statistical uncertainty of 7.3 degrees. The angle from the Fermi LAT boresight is 57.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44856. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42988] GRB 260607A: Fermi GBM Final Real-time Localization
by GCN Circulars 07 Jun '26

07 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44856 SUBJECT: GRB 260607A: Fermi GBM Final Real-time Localization DATE: 26/06/07 13:01:39 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 SHORT GRB At 12:49:18 UT on 7 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260607A (trigger 802529363.702736 / 260607534). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 304.2, Dec = 36.5 (J2000 degrees, equivalent to J2000 20h 16m, 36d 30'), with a statistical uncertainty of 7.3 degrees. The angle from the Fermi LAT boresight is 57.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44856. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42987] GRB 260607A: Fermi GBM Final Real-time Localization
by GCN Circulars 07 Jun '26

07 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44855 SUBJECT: GRB 260607A: Fermi GBM Final Real-time Localization DATE: 26/06/07 13:00:13 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 SHORT GRB At 12:49:18 UT on 7 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260607A (trigger 802529363.702736 / 260607534). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 304.2, Dec = 36.5 (J2000 degrees, equivalent to J2000 20h 16m, 36d 30'), with a statistical uncertainty of 7.3 degrees. The angle from the Fermi LAT boresight is 57.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607534/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44855. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42986] GRB 260604C: GECAM-B observation
by GCN Circulars 07 Jun '26

07 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44854 SUBJECT: GRB 260604C: GECAM-B observation DATE: 26/06/07 12:57:24 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260604C, at 2026-06-04T20:18:44.600 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44822), and SVOM/ECLAIRs (D. Gotz et.al., GCN#44823). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 7 +/-0.5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260604C.png In addition, the position of this burst, is determined by SVOM/ECLAIRs (RA=224.3461 , DEC=28.6558, with a 90% confidence level raiuds of 9.6 arcmins , D.Gotz et.al., GCN #43647). With this localization, the time-averaged spectrum from T0-0.5 to T0+7.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.41 +0.12/-0.09 and the cutoff energy, parameterized as Epeak, is 759 +342/-210 keV. The event fluence (10-1000keV) in this time interval is (2.88 +0.086/-0.11)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 260604C is shown at: https://www.bursthub.cn//admin/static/gecambgrb260604C_amati.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44854. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42985] GRB 260604C: 6 GHz VLA observations
by GCN Circulars 07 Jun '26

07 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44853 SUBJECT: GRB 260604C: 6 GHz VLA observations DATE: 26/06/07 10:22:39 GMT FROM: Roberto Ricci at INAF-IRA <ricci(a)ira.inaf.it> R. Ricci, M. Yadav, E. Troja (U Rome) report: We observed the field of GRB 260604C which triggered Fermi-GBM (Fermi-GBM team, GCN 44822) and SVOM (Gotz et al., GCN 44823) with Very Large Array in C-band at the centre frequency of 6 GHz with a bandwidth of 4 GHz on June 04th 2026 (38 hours after the trigger). Data were calibrated and imaged using standard procedures in CASA (v6.6.1). 1331+305 (3C286) was used for flux density and bandpass calibration and J1513+2338 was used for complex gain calibration. No radio source was detected at the optical transient position (Lipunov et al., GCN 44827) down to a preliminary 3-sigma upper limit of ~24 uJy/beam. Further observations are planned. We thank the VLA staff for executing the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44853. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42984] GRB 260504C: SAO RAS optical observations
by GCN Circulars 06 Jun '26

06 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44852 SUBJECT: GRB 260504C: SAO RAS optical observations DATE: 26/06/06 20:42:04 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI), A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team We observed the field of long GRB 260604C discovered by Fermi (The Fermi GBM team, GCN 44822; Neights & Meegan, GCN 44831) and SVOM (Gotz et al., GCN 44823) with the Zeiss-1000 1-m telescope of SAO RAS equipped with the CCD photometer. We obtained 12 x 300 sec. images in Rc band on June 05, 22:25:58--23:33:55 UT. The OT (Lipunov, GCN 44827; Konno et al., GCN 44828; GCN 44836; Zhu et al., GCN 44832; Becerra et al., GCN 44834; Hellot et al., GCN 44835; Gompertz et al., GCN 44837; Gompertz et al., GCN 44843; Chen et al.б GCN 44851) is clearly detected in our stacked image with the following brightness: Date UTstart t-T0 Exp. Filter Mag +/- Err. UL (mid,d) (n*s) (3-sigma) 2026.06.05T22:25:58 1.11195 12*300 Rc 21.65 +/- 0.07 23.4 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44852. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42983] GRB 260604C: GRANDMA observations
by GCN Circulars 06 Jun '26

06 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44851 SUBJECT: GRB 260604C: GRANDMA observations DATE: 26/06/06 17:16:35 GMT FROM: antier(a)ijclab.in2p3.fr L. Chen (TSU), N. Sasaki (UEA,LNA), A. Simon (TShNU of Kyiv), S. Antier (IJCLAB), M. Coughlin (UMN) O. Burkhonov (UBAI), S. Ehgamberdiev (UBAI), Y. Rajabov (UBAI), Y. Tillayev (UBAI), R. Inasaridze (AbAO), N. Kochiashvili (AbAO), V. Zhuzhunadze (AbAO), A. Klotz (IRAP), P. Put (NARIT), K. Noysena (NARIT), A. Manasanun (NARIT), M. Freeberg (KNC), E. Elhosseiny (NRIAG), A. Takey (NRIAG), M. Pillas (IAP), W. Corradi (LNA), T. Leandro de Almeida (LNA), I. Abdusamatjan (TNOT) on behalf of GRANDMA: We conducted follow-up observations of GRB 260604C (Fermi Team, GCN Circ. 44822, Gotz et al., GCN Circ. 44823) with GRANDMA from 0.05 h post T0 (MJD 61195.84859954) up to now. To do this, we have collected data from KNC (Hellot et al., GCN 44835), TAROT/TCH, UBAI-NT60, UBAI-AZT22, AbAO-T70, KAO-1.8m, TRT-SRO, OPD-60, TTT and NOWT. GRB 260604C optical afterglow (reported by Lipunov et al., GCN 44827) is detected at several epochs and a subset of the photometry corrected for Galactic extinction is reported in the public site group of the public ACME service Skyportal/ICARE https://skyportal-icare.ijclab.in2p3.fr/source/GCN-260604_202037. To access, one simply needs to create an account using your ORCID id. Our measurements are in agreement with Lipunov et al., GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832, Becerra et al., GCN 44834; GCN 44835; Gompertz et al., 44843,Saccardi et al. 44844. The observations are performed under the P7 campaign of GRANDMA to monitor SVOM alerts and LSST alerts from explosive fast transients filtered by BOOM/Babamul and FINK. GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (kilonovacatcher.in2p3.fr). Astrophysics Center for Multimessenger studies in Europe is supported Skyportal/ICARE (contact camille.douzet(a)ijclab.in2p3.fr, skyportal.io) View this GCN Circular online at https://gcn.nasa.gov/circulars/44851. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42982] GRB 260604B: SVOM/GRM detection
by GCN Circulars 06 Jun '26

06 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44850 SUBJECT: GRB 260604B: SVOM/GRM detection DATE: 26/06/06 14:28:23 GMT FROM: zhangjinpeng(a)ihep.ac.cn SVOM/GRM team: Jin-Peng Zhang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier GODET (IRAP) Report on behalf of the SVOM team: SVOM/GRM detected GRB 260604B during the routine ground search at 2026-06-04T08:45:56.000 (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44818). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst mainly consists of multiple pulses with a T90 of 17 +9/-5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260604B.png In addition, the position of this burst, according to Fermi/GBM localization (RA = 173.4, Dec = -19.9, Fermi GBM Team, GCN #44818), is located at about 82 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-15 to T0+25 s is fitted by a power law function. The power law index is -1.67 +0.10/-0.11. The event fluence (10-1000 keV) in this time interval is (3.8 +0.8/-0.8)E-06 erg/cm^2. 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Jin-Peng Zhang (IHEP) (zhangjinpeng(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44850. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42981] GRB 260605A: Insight-HXMT/HE detection
by GCN Circulars 06 Jun '26

06 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44849 SUBJECT: GRB 260605A: Insight-HXMT/HE detection DATE: 26/06/06 14:02:12 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2026-06-05T01:04:27.850 (T0), Insight-HXMT/HE detected a long burst, GRB 260605A, which is also detected by SVOM/GRM. The Insight-HXMT/HE light curve mainly consists of a single pulse with a duration (T90) of 11.0 +2.5/-1.0 s. The 1s peak rate, measured from T0+1.75 s, is 6386 cnts/sec. Insight-HXMT/HE detected a total of 22324 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260605A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/ View this GCN Circular online at https://gcn.nasa.gov/circulars/44849. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42980] GRB260603A: SVOM/ECLAIRs refined analysis
by GCN Circulars 06 Jun '26

06 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44848 SUBJECT: GRB260603A: SVOM/ECLAIRs refined analysis DATE: 26/06/06 09:24:50 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP),N. Dagoneau (CEA), Donghua ZHAO, Wenjin Xie (NAOC), Ruizhi Li (YNAO), Ziming Wang (BNU) 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 260603A (SVOM burst-id sb26060303 – GCN 44787, trigger time T0 = 2026-06-03T05:38:16 UTC). The burst that triggered ECLAIRs onboard shows a single peak lightcurve. The burst duration is T90 = 101 +4/-7 s in the 4-120 keV energy band. The time-averaged spectrum from T0-51.0 s to T0+50.7 s in the 5-120 keV energy range is best fitted by a powerlaw model with alpha = -1.75 +0.08/-0.09. With this model, the 4-120 keV fluence is (1.33 +0.11/-0.12)e-6 erg/cm^2 and the 4-120 keV photon flux is 0.47 +0.02/-0.03 ph/cm^2/s. All the quoted errors are at the 68% confidence level. 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: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44848. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42979] EP260605a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 06 Jun '26

06 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44847 SUBJECT: EP260605a: Einstein Probe detection of a fast X-ray transient DATE: 26/06/06 06:30:27 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A.Li (BNU), C. Y. Wang (THU), Z.-C. Zou (NJU), X. H. Tang (THU), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260605a. The transient was identified during ground-based telemetry analysis. The WXT light curve started at 2026-06-05T09:31:00 (UTC). The WXT position of the source is R.A. = 273.360 deg, DEC = -40.392 deg (J2000) with an uncertainty of 3.2 arcmin in radius (90% C.L. statistical and systematic). The duration of the event is around 500 s. The WXT spectrum can be fitted with an absorbed power-law, with the absorption fixed at the Galactic value of 1.03 x 10^21 cm^-2, and a photon index of 1.76 (-0.58, +0.61). The unabsorbed 0.5-4 keV flux is 4.3 (-1.3, +1.6) x 10^-11 erg/s/cm2. All uncertainties are reported in 90% C.L. We have arranged follow-up observation with the Follow-up X-ray Telescope onboard EP and will update the information upon receiving the data. 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/44847. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42978] EP260603a: COLIBRÍ optical upper limit
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44846 SUBJECT: EP260603a: COLIBRÍ optical upper limit DATE: 26/06/05 22:08:07 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Enrique Moreno Méndez (UNAM), Dalya Akl (NYUAD), Rosa L. Becerra (UNAM), Alan M. Watson (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 EP260603a (Liang et al., GCN Circ. 44814) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-04 06:09 to 06:25 UTC (from 12.30 to 12.58 hours after the trigger) and obtained 14 minutes of simultaneous exposure in the r/z filters. The data were reduced, coadded and analysed 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. In the stacked image, we do not detect any new source within the WXT source region (Liang et al., GCN Circ. 44814) down to the following 5-sigma limit: r > 22.5 z > 21.3 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/44846. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42977] GRB 260604A: Glowbug gamma-ray detection
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44845 SUBJECT: GRB 260604A: Glowbug gamma-ray detection DATE: 26/06/05 22:03:48 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 260604A, which was also detected by Fermi/GBM (GCN 44812). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-06-04 02:24:24.648 with a duration of 4.1 s and a total significance of about 9.8 sigma. The light curve comprises a single peak. Note that data from ~T0-5s to +1s suffered from deadtime in various detectors. 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/44845. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42976] GRB 260604C: LCO optical upper limit
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44844 SUBJECT: GRB 260604C: LCO optical upper limit DATE: 26/06/05 21:22:48 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), S. Bisero (CEA/Irfu) report on behalf of the SVOM mission team: We observed the field of GRB 260604C (Fermi GBM Team, GCN 44822; Gotz et al., GCN 44823) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2026-06-05 at 20:08:32 UT (about 1 day after the trigger) and we obtained 3x200 s exposures in the SDSS r filter. In the stacked image we do not detect the optical counterpart (Lipunov et al., GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832, Becerra et al., GCN 44834; Hellot et al., GCN 44835; Gompertz et al., GCN 44837; Gompertz et al., GCN 44843). We measure the following upper limit calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction: r > 21.8 AB (3-sigma, mid-time 0.997 days after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44844. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42975] GRB 260604C: Liverpool Telescope optical detection
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44843 SUBJECT: GRB 260604C: Liverpool Telescope optical detection DATE: 26/06/05 14:01:06 GMT FROM: Dimple at University of Birmingham <dimplepanchal96(a)gmail.com> B. P. Gompertz (U. Birmingham), D. B. Malesani (DAWN/NBI and Radboud) and Dimple (U. Birmingham) report on behalf of a larger collaboration: We conducted follow-up observations of GRB 260604C (Fermi Team, GCN Circ. 44822, Gotz et al., GCN Circ. 44823) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 00:14:01 UT on 2026-06-05, ~3.92 hr after the burst, and consisted of 5 x 120 s exposures in each of the SDSS r, g, i and z filters. We detect the optical counterpart (Lipunov et al., GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832, Becerra et al., GCN 44834; Hellot et al., GCN 44835; Gompertz et al. 44837) in all the filters, and measure an AB magnitude of r = 18.60 ± 0.05. Magnitudes are calibrated against nearby Pan-STARRS stars and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44843. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42974] The EP-WXT trigger 01709267001 is likely a flaring star
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44842 SUBJECT: The EP-WXT trigger 01709267001 is likely a flaring star DATE: 26/06/05 12:57:39 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO), X. Tian (GXU), C.-L. Guo and C.-C. Jin (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709267001 at the time of 2026-06-05T12:42:11, is likely a stellar flare associated with RX J1431.6+0047 (High Proper Motion Star). The estimated flux of the flare is around 1.8 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4.8 x 10^(31) erg/s. 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/44842. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42973] EP260602d: EP-FXT follow-up observation
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44841 SUBJECT: EP260602d: EP-FXT follow-up observation DATE: 26/06/05 12:47:27 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J.Y. Cao, Z. X. Li, G. L. Huang, (IHEP, CAS), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260602d was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Cao et al., GCN 44796) at 2026-06-02T21:13:25 (UTC). Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-06-04T04:27:19(UTC), ~31 hours after the WXT detection. The exposure time of the observation is around 4 ks. The on-ground analysis of the FXT data found a source within the error circle of WXT at R.A. = 267.9681 deg, DEC = 18.1658 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic) which have no historical X-ray source within 10 arcsec. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 6.7×10^20 cm^-2, and a photon index of 0.8 (-0.3, +0.4). The derived average unabsorbed 0.5-10 keV flux is 3.2 (-1.2, +1.8) ×10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Since this source is below the RASS upper limit and shows no significant fading, we cannot identify it as the counterpart of EP260602d at present. The optical and infrared follow-up observations were performed by A. Aryan et al. (GCN 44813) and Tanishk Mohan et al. (GCN 44830) without detection. 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/44841. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42972] EP260602c: EP-FXT follow-up observation
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44840 SUBJECT: EP260602c: EP-FXT follow-up observation DATE: 26/06/05 11:56:50 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> EP260602c: EP-FXT follow-up observation J.Y. Cao, Z. X. Li, G. L. Huang, (IHEP, CAS), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260602c was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Cao et al., GCN 44792) at 2026-06-02T09:06:44 (UTC). Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-06-03T18:37:43(UTC), ~33 hours after the WXT detection. The exposure time of the observation is around 4 ks. The on-ground analysis of the FX-A data found three sources within the error circle of WXT. Source 1 is at R.A. = 134.8551 deg, DEC = -75.673 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). This position is 12 arcsec from a known X-ray source 1eRASS J085924.9-754010 with the historical flux of 1.8 ×10^(-14) erg/s/cm^2 in 0.3-2.3 keV band. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 8×10^20 cm^-2, and a photon index of 1.9 (-1.2, +1.2). The observed 0.5-10.0 keV flux is 9.1 (+/-2.9) ×10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Source 2 is at R.A. = 134.5839 deg, DEC = -75.7147 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). This position is 5 arcsec from a known X-ray source 1eRASS J085820.6-754257 with the historical flux of 2.0 ×10^(-14) erg/s/cm^2 in 0.3-2.3 keV band. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 8×10^20 cm^-2, and a photon index of 0.13 (-0.68, +0.61). The observed 0.5-10.0 keV flux is 5.1 (+/-2.0) ×10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Source 3 is at R.A. = 134.5079 deg, DEC = -75.6493 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic) which have no historical X-ray source within 10 arcsec. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 8×10^20 cm^-2, and a photon index of 3.1 (-1.3, +1.7). The observed 0.5-10.0 keV flux is 3.51 (+/-1.6) ×10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Since none of them is significantly above the eRASS1 upper limit or shows fading trends, we cannot identify the counterpart of EP260602c at present. 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/44840. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42971] GRB 260601B / EP260601a: AstroSat CZTI detection
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44839 SUBJECT: GRB 260601B / EP260601a: AstroSat CZTI detection DATE: 26/06/05 11:44:11 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (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 a long GRB 260601B, associated with EP260601a, which was also detected by Einstein Probe / WXT (Yang et. al., GCN Circ. 44766), GECAM-C (Yu et al., GCN Circ. 44767), NuSTAR (Waratkar et. al. , GCN Circ. 44771), CALET (Sugita et. al., GCN Circ. 44773), and Insight HXMT (Wang et. al., GCN Circ. 44785). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-06-01 19:12:50.54 UTC. AstroSat was departing the South Atlantic Anomaly (SAA) region and hence the background rates were higher. The measured peak count rate associated with the burst is 498 (+39, -46) counts/s above the background in the combined data of three quadrants (out of four), with a total of 12100 (+491, -799) counts. The local mean background count rate was 278 (+4, -4) counts/s. Using cumulative rates, we measure a T90 of 54 (+2, -2) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-06-01 19:12:50.66 UTC. The measured peak count rate associated with the burst is 1468 (+92, -129) counts/s above the background in the combined data of four quadrants, with a total of 29202 (+2008, -3307) counts. The local mean background count rate was 1805 (+20, -8) counts/s. We measure a T90 of 51 (+1, -2) s from the cumulative Veto light curve. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/ET20260601T191246/ET20260601T1… 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/44839. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42970] GRB 260527A/EP260527a: 6 GHz VLA observations
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44838 SUBJECT: GRB 260527A/EP260527a: 6 GHz VLA observations DATE: 26/06/05 10:05:25 GMT FROM: muskan.yadav(a)students.uniroma2.eu M. Yadav, R. Ricci, E. Troja (U Rome) report: We observed the field of EP260527a (Yang et al., GCN 44718), likely associated with the short GRB 260527A (Svinkin et al., GCN 44722, Yu et al., GCN 44724; Kawakubo et al., GCN 44726, Wang et al., GCN 44735, Svinkin et al., GCN 44744, Cheung et al., GCN 44757) with Very Large Array in C-band at the centre frequency of 6 GHz with a bandwidth of 4 GHz in two epochs on May 29th 2026 (2.01 days after the trigger) and June 4th 2026 (8.05 days after the trigger). Data were calibrated and imaged using standard procedures in CASA (6.6.6.18). 1331+305 (3C286) was used for flux density and bandpass calibration and J1224+0330 was used for complex gain calibration. The radio source reported by Schroeder et al. (GCN 44740) is detected in our first epoch at a consistent position and flux level, and is seen to fade below detection threshold in our second epoch, yielding a preliminary 3-sigma upper limit of ~30 uJy/beam. We therefore confirm this source as the radio counterpart of EP260527a. We thank the VLA staff for executing the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44838. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42969] GRB 260604C: GOTO detections of the optical afterglow
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44837 SUBJECT: GRB 260604C: GOTO detections of the optical afterglow DATE: 26/06/05 09:47:43 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz, S. Moran, D. O’Neill, A. Kumar, G. Ramsay, R. Starling, K. Ackley, M. Dyer, J. Lyman, 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 and M. Pursiainen, on behalf of the 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 GRB 260604C, discovered by Fermi/GBM and SVOM (Fermi GBM Team, GCN 44822; Gotz et al., GCN 44823). Observations were taken in the GOTO-L filter (400 - 700nm) with 4x90s exposures. Images were processed immediately after acquisition using the GOTO pipeline. The optical counterpart (Lipunov et al., GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832, Becerra et al., GCN 44834; Hellot et al., GCN 44835) was detected in three epochs: | mid-time(UT) | t-t0(hr) | ABmag | | 2026-06-04 23:46:15 | 3.46 | 18.45 ± 0.04 | | 2026-06-05 00:54:05 | 4.59 | 18.70 ± 0.08 | | 2026-06-05 02:00:28 | 5.70 | 19.06 ± 0.12 | 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/44837. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42968] GRB 260604C: Correction to GCN 44828
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44836 SUBJECT: GRB 260604C: Correction to GCN 44828 DATE: 26/06/05 08:46:15 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) report on behalf of the LAST Collaboration. This is a correction to the GCN Circular "GRB 260604C: LAST detection of optical counterpart candidate" (GCN 44828). The photometry within the circular was erroneously listed in the reverse order. The correct photometry is | Tmid-T0 (h) | Mag (AB) | | ------------ | ------------ | | 0.33 | 16.42 +/- 0.02 | | 0.45 | 16.63 +/- 0.02 | | 0.57 | 16.85 +/- 0.02 | | 0.75 | 17.12 +/- 0.02 | A correction of the archival circular has been requested, apologies for any confusion. View this GCN Circular online at https://gcn.nasa.gov/circulars/44836. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42967] GRB 260604C: Kilonova-Catcher optical afterglow detection
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44835 SUBJECT: GRB 260604C: Kilonova-Catcher optical afterglow detection DATE: 26/06/05 08:27:06 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> R. Hellot, D. Christen, M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 260604C detected by Fermi/GBM (Fermi GBM team, GCN 44822) and SVOM (Götz et al., GCN 44823) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot and D. Cristen and the A1 CDK17 telescope located at the Alnitak Observatory operated by M. Freeberg. Our observations started at TGRB+1.0 hours and were taken with sdss-r and Rc filters. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we clearly detect the optical counterpart (Lipunov et al., GCN 44825; GCN 44826; GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832; Becerra et al., GCN 44834). We report part of our follow-up results in the table below : | Tmid-TGRB (hrs) | Exp (s) | Filter | Magnitude | Instrument | | ------------ | --------- |------------ |---------------- |------------ | | 1.47 | 15 x 180s | Rc (Vega) | 17.43 +/- 0.03 | A1/CDK17 | | 3.17 | 8 x 300s | r (AB) | 18.41 +/- 0.05 | AITP/CDK17 | | 4.01 | 11 x 180s | Rc (Vega) | 18.43 +/- 0.06 | A1/CDK17 | All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/44835. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42966] GRB 260604C: Kilonova-Catcher optical afterglow detection
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44835 SUBJECT: GRB 260604C: Kilonova-Catcher optical afterglow detection DATE: 26/06/05 08:27:06 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> R. Hellot, D. Christen, M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 260604C detected by Fermi/GBM (Fermi GBM team, GCN 44822) and SVOM (Götz et al., GCN 44823) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot and D. Cristen and the A1 CDK17 telescope located at the Alnitak Observatory operated by M. Freeberg. Our observations started at TGRB+1.0 hours and were taken with sdss-r and Rc filters. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we clearly detect the optical counterpart (Lipunov et al., GCN 44825; GCN 44826; GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832; Becerra et al., GCN 44834). We report part of our follow-up results in the table below : | Tmid-TGRB (hrs) | Exp (s) | Filter | Magnitude | Instrument | | ------------ | --------- |------------ |---------------- |------------ | | 1.47 | 15 x 180s | Rc (Vega) | 17.43 +/- 0.03 | A1/CDK17 | | 3.17 | 8 x 300s | r (AB) | 18.41 +/- 0.05 | AITP/CDK17 | | 4.01 | 11 x 180s | Rc (Vega) | 18.43 +/- 0.06 | A1/CDK17 | All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/44835. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42965] GRB 260604C: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44834 SUBJECT: GRB 260604C: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 26/06/05 04:19:38 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Sarah Antier (IJCLAB), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), 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), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Sofia Bisero (CEA Saclay) report: We imaged the field of GRB 260604C (Fermi Team, GCN Circ. 44822, Gotz et al., GCN Circ. 44823) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-05 03:41 to 03:51 UTC (from 7.34 to 7.52 hours after the trigger) and obtained 3, 3, 3, 3 and 6 minutes of exposure in the g, r, i, z and y filters respectively. The data were reduced, coadded and analysed 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 detected the optical counterpart reported by Lipunov et al. (GCN Circ. 44827), at preliminary magnitudes of: g = 19.69 +/- 0.04 r = 19.56 +/- 0.03 i = 19.38 +/- 0.04 z = 19.21 +/- 0.06 y = 19.26 +/- 0.08 These values are consistent with those reported by MASTER (Lipunov et al., GCN Circ. 44827), LAST (Gotz et al., GCN Circ. 44828), Jinshan (Zhu et al., GCN Circ. 44832). Comparing to the observations with LAST at about 0.75 hours, we estimate a temporal decay index of about -1.2. Moreover, the detections in all filters and the values in the colours, suggest a low-redshift event. We also notice the presence of a red galaxy with g = 21.69 +/- 0.02, r = 20.15 +/- 0.01, z = 19.10 +/- 0.01 and a photo-z = 0.343 +/- 0.031 (DESI Legacy Survey catalog; Dey et al. 2019) at 18.9" from the optical counterpart position. This corresponds to a Pcc ≈ 0.16 and a projected offset of 95 kpc, which makes an association very unlikely. We also comment that the light curve and analysis reported by the Fermi/GBM Team (GCN Circ. 44822, 44831) suggests hard emission with a duration that cannot completely rule out a Type I burst. 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/44834. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42964] The EP-WXT trigger 01709266798 is likely a flaring star
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44833 SUBJECT: The EP-WXT trigger 01709266798 is likely a flaring star DATE: 26/06/05 03:12:02 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO), X. Tian (GXU), C.-L. Guo and C.-C. Jin (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709266798 at the time of 2026-06-05T02:51:45, is likely a stellar flare associated with BD+33 2401 (High Proper Motion Star). The estimated flux of the flare is around 1.6 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 7.1 x 10^(31) erg/s. 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/44833. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42963] GRB 260604C: Jinshan optical observations
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44832 SUBJECT: GRB 260604C: Jinshan optical observations DATE: 26/06/05 02:52:57 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z.P. Zhu, X. Liu, D. Xu, J. An,S.Q. Jiang, L.B. He (NAOC), S.Y. Fu, A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report: We observed the field of GRB260604C detected by Fermi-GBM (Fermi GBM team, GCN 44822) and SVOM (Gotz et al, GCN 44823), using the JinShan 100B telescope located at Altay, Xinjiang, China. Observation started at 2026-06-04T20:32:14 UT, i.e., about 13 min post-burst, and a series of r-band frames were obtained. The previously reported optical counterpart (Lipunov et al, GCN 44827; Konno et al, GCN 44828) is detected in our first single frame with a brightness of R = 16.1 +/- 0.1, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. We acknowledge the excellent support from T.Q. Chen, and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44832. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42962] GRB 260604C: Fermi GBM Observation
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44831 SUBJECT: GRB 260604C: Fermi GBM Observation DATE: 26/06/05 02:49:32 GMT FROM: eliza.neights(a)gmail.com E. Neights (GWU, NASA GSFC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 20:18:44.41 UT on 04 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260604C (trigger 802297129/260604846), which was also detected by SVOM ECLAIRs (Gotz et al. 2026, GCN 44823), MASTER (Lipunov et al. 2026, GCN 44827), and LAST (Konno et al. 2026, GCN 44828). The Fermi GBM on-ground location is consistent with the SVOM ECLAIRs position. The angle from the Fermi LAT boresight is 102 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 6.4 s (50-300 keV). The time-averaged spectrum from T0-2.2 to T0+12.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.03 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 551 +/- 2 keV. The event fluence (10-1000 keV) in this time interval is (2.55 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+4.5 s in the 10-1000 keV band is 44.1 +/- 0.6 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 394 +/- 3 keV, alpha = -0.95 +/- 0.01 and beta = -2 +/- 0.03. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44831. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42961] EP260602d: J-band upper limit with WINTER
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44830 SUBJECT: EP260602d: J-band upper limit with WINTER DATE: 26/06/05 01:19:18 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Tanishk Mohan (IITB), Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (NOIRLab), Benjamin Schneider (LAM), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of EP260602d (Cao et al., GCN 44796) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-06-03T08:06:13 UTC in the J band (10.88 hr after the EP trigger), consisting of 15*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We do not detect any new source in the WXT localization (Aryan et al., GCN 44813; Cao et al., GCN 44796) after image subtraction performed relative to J-band images from the UKIRT Hemisphere survey (Dye et al., 2017). We obtain the following 5-sigma upper limit: J = 19.4 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/44830. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42960] EP260602b: J-band upper limit with WINTER
by GCN Circulars 05 Jun '26

05 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44829 SUBJECT: EP260602b: J-band upper limit with WINTER DATE: 26/06/05 01:18:25 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Tanishk Mohan (IITB), Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (NOIRLab), Benjamin Schneider (LAM), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of EP260602b (Wu et al., GCN 44786; Wu et al., GCN 44802) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-06-03T04:53:16 UTC in the J band (~11 hr after the EP trigger), consisting of 15*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We do not detect a source at the optical counterpart location (He et al., GCN 44780; Eyles-Ferris et al., GCN 44809; Bochenek et al., GCN 44811). We obtain the following 5-sigma upper limit: J = 19.1 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/44829. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42959] GRB 260604C: LAST detection of optical counterpart candidate
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44828 SUBJECT: GRB 260604C: LAST detection of optical counterpart candidate DATE: 26/06/04 23:52:38 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) report on behalf of the LAST Collaboration. We report observations of GRB 260604C, detected by Fermi-GBM (Fermi GBM team, GCN 44822) and SVOM (Gotz et al, GCN 44823). Observations were conducted with the Large Array Survey Telescope (LAST; Ofek et al. 2023, PASP 135, 5001; Ben-Ami et al. 2023, PASP 135, 5002). Observations of GRB 260604C were taken over 4 sequential epochs in clear band (similar to the Gaia Bp band). The first epoch began at 2026-06-04 20:35:04 UTC (T-T0 = 0.275 h). Each epoch consists of 20x20s exposures per telescope. We detect one credible optical transient within the field reported by SVOM (Gotz et al, GCN 44823) consistent with the position of AT 2026ofi (TNS Report No. 307026) reported by MASTER (Lipunov et al, GCN 44827). The transient is well detected within each epoch and shows a rapid decay, consistent with afterglow emission. | Tmid-T0 (h) | Mag (AB) | | ------------ | ----------- | | 0.33 | 17.12 | | 0.45 | 16.85 | | 0.57 | 16.63 | | 0.75 | 16.42 | Previous observations of the field yield no detections on the source positions up to 2026-06-01 20:46:47 UTC (T0-T = 3d) with a 5-sigma limiting magnitude of 20.15 (AB). We encourage further follow-up observations. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/) View this GCN Circular online at https://gcn.nasa.gov/circulars/44828. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42958] GRB 260604C: MASTER OT J145749.59+284903.0 optical counterpart discovery
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44827 SUBJECT: GRB 260604C: MASTER OT J145749.59+284903.0 optical counterpart discovery DATE: 26/06/04 22:45:21 GMT FROM: Vladimir Lipunov at Lomonosov Moscow State University <lipunov(a)sai.msu.ru> MASTER OT J145749.59+284903.0 discovery MASTER-Tavrida auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered OT source at (RA, Dec) = 14h 57m 49.59s +28d 49m 03.0s on 2026-06-04.86020 UT. The OT magnitude (unfiltered) is 17.5m at04.86020UT (mlim=19.4). The OT is seen in 14 images. There is no minor planet at this place. We have reference image on 2020-09-17.71399 UT with unfiltered mlim= 18.1m. Spectral observations are required. View this GCN Circular online at https://gcn.nasa.gov/circulars/44827. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42957] Fermi GRB 260604C: Global MASTER-Net observations report
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44826 SUBJECT: Fermi GRB 260604C: Global MASTER-Net observations report DATE: 26/06/04 21:20:24 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-Tavrida robotic telescope [1] located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 260604C ( Fermi GBM team, GCN 44822) errorbox 68 sec after notice time and 121 sec after trigger time at 2026-06-04 20:20:45 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 13 deg. The sun altitude is -20.4 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260604C errorbox 2607 sec after notice time and 2660 sec after trigger time at 2026-06-04 21:03:04 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 28 deg. The sun altitude is -23.8 deg. The galactic latitude b = 65 deg., longitude l = 54 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3361051 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 132 | 2026-06-04 20:20:45 | MASTER-Tavrida | (14h 45m 39.13s , +34d 23m 10.1s) | C | 20 | 18.2 | 159 | 2026-06-04 20:21:08 | MASTER-Tavrida | (14h 45m 39.22s , +34d 23m 08.2s) | C | 30 | 18.5 | 201 | 2026-06-04 20:21:45 | MASTER-Tavrida | (14h 45m 39.31s , +34d 23m 05.7s) | C | 40 | 18.7 | 244 | 2026-06-04 20:22:28 | MASTER-Tavrida | (14h 45m 39.40s , +34d 23m 03.5s) | C | 40 | 18.7 | 292 | 2026-06-04 20:23:11 | MASTER-Tavrida | (14h 45m 39.48s , +34d 23m 00.9s) | C | 50 | 18.9 | 351 | 2026-06-04 20:24:05 | MASTER-Tavrida | (14h 45m 39.57s , +34d 22m 58.3s) | C | 60 | 19.0 | 424 | 2026-06-04 20:25:08 | MASTER-Tavrida | (14h 45m 39.70s , +34d 22m 55.4s) | C | 80 | 19.9 | 512 | 2026-06-04 20:26:31 | MASTER-Tavrida | (14h 45m 39.83s , +34d 22m 52.2s) | C | 90 | 18.1 | 616 | 2026-06-04 20:28:05 | MASTER-Tavrida | (14h 45m 39.93s , +34d 22m 49.5s) | C | 110 | 18.8 | 753 | 2026-06-04 20:30:17 | MASTER-Tavrida | (14h 41m 46.90s , +33d 53m 19.6s) | C | 120 | 19.3 | 2690 | 2026-06-04 21:03:04 | MASTER-Kislovodsk | (14h 31m 34.56s , +34d 00m 31.5s) | C | 60 | 18.4 | 2780 | 2026-06-04 21:04:34 | MASTER-Kislovodsk | (14h 41m 05.21s , +33d 59m 44.5s) | C | 60 | 18.5 | 2868 | 2026-06-04 21:06:02 | MASTER-Kislovodsk | (14h 36m 52.22s , +35d 55m 19.9s) | C | 60 | 18.3 | 2957 | 2026-06-04 21:07:31 | MASTER-Kislovodsk | (14h 46m 41.72s , +35d 54m 08.3s) | C | 60 | 18.4 | 3046 | 2026-06-04 21:09:00 | MASTER-Kislovodsk | (14h 45m 53.08s , +34d 00m 34.0s) | C | 60 | 18.5 | 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/44826. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42956] Fermi GRB 260604C: Global MASTER-Net observations report
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44825 SUBJECT: Fermi GRB 260604C: Global MASTER-Net observations report DATE: 26/06/04 21:18:02 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-Tavrida robotic telescope [1] located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 260604C ( Fermi GBM team, GCN 44822) errorbox 68 sec after notice time and 121 sec after trigger time at 2026-06-04 20:20:45 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 13 deg. The sun altitude is -20.4 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260604C errorbox 2607 sec after notice time and 2660 sec after trigger time at 2026-06-04 21:03:04 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 28 deg. The sun altitude is -23.8 deg. The galactic latitude b = 65 deg., longitude l = 54 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3361051 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 132 | 2026-06-04 20:20:45 | MASTER-Tavrida | (14h 45m 39.13s , +34d 23m 10.1s) | C | 20 | 18.2 | 159 | 2026-06-04 20:21:08 | MASTER-Tavrida | (14h 45m 39.22s , +34d 23m 08.2s) | C | 30 | 18.5 | 201 | 2026-06-04 20:21:45 | MASTER-Tavrida | (14h 45m 39.31s , +34d 23m 05.7s) | C | 40 | 18.7 | 244 | 2026-06-04 20:22:28 | MASTER-Tavrida | (14h 45m 39.40s , +34d 23m 03.5s) | C | 40 | 18.7 | 292 | 2026-06-04 20:23:11 | MASTER-Tavrida | (14h 45m 39.48s , +34d 23m 00.9s) | C | 50 | 18.9 | 351 | 2026-06-04 20:24:05 | MASTER-Tavrida | (14h 45m 39.57s , +34d 22m 58.3s) | C | 60 | 19.0 | 424 | 2026-06-04 20:25:08 | MASTER-Tavrida | (14h 45m 39.70s , +34d 22m 55.4s) | C | 80 | 19.9 | 512 | 2026-06-04 20:26:31 | MASTER-Tavrida | (14h 45m 39.83s , +34d 22m 52.2s) | C | 90 | 18.1 | 616 | 2026-06-04 20:28:05 | MASTER-Tavrida | (14h 45m 39.93s , +34d 22m 49.5s) | C | 110 | 18.8 | 753 | 2026-06-04 20:30:17 | MASTER-Tavrida | (14h 41m 46.90s , +33d 53m 19.6s) | C | 120 | 19.3 | 2690 | 2026-06-04 21:03:04 | MASTER-Kislovodsk | (14h 31m 34.56s , +34d 00m 31.5s) | C | 60 | 18.4 | 2780 | 2026-06-04 21:04:34 | MASTER-Kislovodsk | (14h 41m 05.21s , +33d 59m 44.5s) | C | 60 | 18.5 | 2868 | 2026-06-04 21:06:02 | MASTER-Kislovodsk | (14h 36m 52.22s , +35d 55m 19.9s) | C | 60 | 18.3 | 2957 | 2026-06-04 21:07:31 | MASTER-Kislovodsk | (14h 46m 41.72s , +35d 54m 08.3s) | C | 60 | 18.4 | 3046 | 2026-06-04 21:09:00 | MASTER-Kislovodsk | (14h 45m 53.08s , +34d 00m 34.0s) | C | 60 | 18.5 | 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/44825. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42955] SVOM GRB260604.85: Global MASTER-Net observations report
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44824 SUBJECT: SVOM GRB260604.85: Global MASTER-Net observations report DATE: 26/06/04 20:48:54 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-Tavrida robotic telescope [1] located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the SVOM GRB260604.85 (trigger No 1780604437,14h 57m 12.77s , +28d 36m 26.6s, R=0.1738) errorbox 43 sec after notice time and 713 sec after trigger time at 2026-06-04 20:32:30 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 18 deg. The sun altitude is -21.0 deg. The galactic latitude b = 62 deg., longitude l = 43 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3361056 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 774 | 2026-06-04 20:32:30 | MASTER-Tavrida | (14h 57m 09.62s , +29d 05m 58.4s) | C | 120 | 19.4 | 897 | 2026-06-04 20:34:33 | MASTER-Tavrida | (14h 57m 09.73s , +29d 05m 54.0s) | C | 120 | 19.4 | 1019 | 2026-06-04 20:36:36 | MASTER-Tavrida | (14h 57m 09.83s , +29d 05m 50.2s) | C | 120 | 19.4 | 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/44824. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42954] GRB 260604C: SVOM detection of a long burst
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44823 SUBJECT: GRB 260604C: SVOM detection of a long burst DATE: 26/06/04 20:43:09 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Gotz, D. Adrien, N. Dagoneau, S. Bisero (CEA Saclay) report on behalf of the SVOM mission team: At 2026-06-04T20:21:59 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260604C (SVOM burst-id sb26060404). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 4 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.23 in the [5-20] keV energy band over a time window of 163.84 seconds starting at 2026-06-04T20:19:56 UTC. The localization of the best alert is R.A., Dec. 224.3461, 28.6558 degrees: R.A. (J2000) = 14h57m23s Dec. (J2000) = 28d39m20s with a 90% confidence level (C.L.) radius of 9.6 arcmin (including systematic error of 2 arcmin added in quadrature). This position is compatible with the GRB detected by Fermi/GBM GCN 44822 . SVOM slewed to the burst position. No X-ray observation could be performed by SVOM/MXT for the time being. Optical observations by VT will be published in a further circular. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Sofia Bisero: sofia.bisero(a)cea.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44823. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42953] GRB 260604C: Fermi GBM Final Real-time Localization
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44822 SUBJECT: GRB 260604C: Fermi GBM Final Real-time Localization DATE: 26/06/04 20:31:01 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 20:18:44 UT on 4 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260604C (trigger 802297129.411688 / 260604846). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 220.5, Dec = 33.4 (J2000 degrees, equivalent to J2000 14h 41m, 33d 23'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 108.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604846/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604846/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604846/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44822. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42952] GRB 260515A: SVOM/VT optical detection at about 18 days post trigger
by GCN Circulars 04 Jun '26

04 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44821 SUBJECT: GRB 260515A: SVOM/VT optical detection at about 18 days post trigger DATE: 26/06/04 15:44:09 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, J. R. Xu, Y. N. Ma, Z. H. Yao, 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, A. Saccardi and D. Gotz (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed further ToO observations of GRB260515A triggered by SVOM/ECLAIRs (sb26051504, Brunet et al., GCN 44622, GCN 44666). The burst was also detected by Konus-Wind (Frederiks et al., GCN 44647). The observation started at 2026-06-03T02:02:18 UTC, i.e., 18.28 days post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Lipunov et al., GCN 44627; Wu et al., GCN 44628; Dennefeld et al., GCN 44633; Li et al., GCN 44634; Wang et al., GCN 44642; Antier et al., GCN 44643; Pérez-Fournon et al., GCN 44645; Dimple et al. GCN 44646; Moskvitin et al., GCN 44652; Bochenek et al., GCN 44658) with redshift z=0.764 (Malesani et al., GCN 44629) was faintly detected VT_R. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 18.38 d VT_R 108*70 s 23.5 +/- 0.3 mag 18.38 d VT_B 110*70 s >24.0 mag (3 sigma upper limit) 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/44821. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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