August 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 39336] GRB 250806A: NOT z-band upper limit and host galaxy candidate
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41279 SUBJECT: GRB 250806A: NOT z-band upper limit and host galaxy candidate DATE: 25/08/08 08:32:02 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), L. Izzo (INAF/OAC and DARK/NBI), A. Martin-Carrillo (UCD), G. Corcoran (UCD), Dimple (Birmingham), A. Saccardi (CEA/Irfu), B. Schneider (LAM), D. Xu (NAOC) report on behalf of a larger collaboration: We observed the location of the SVOM/ECLAIRs GRB 250806A (Xie et al., GCN 41243) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A total of 25 exposures by 120 s each were secured in the SDSS z band, with mean epoch 2025 Aug 7.00 UT (16.05 hr after the trigger). There are two galaxies from the Legacy Survey that are consistent with the X-ray position currently listed at https://www.swift.ac.uk/xrt_positions/ (but slightly outside the preliminary error circle reported by Campana et al., GCN 41249). The first one (RA = 23:13:43.51, Dec = +01:21:22.0) is relatively bright, with (AB) magnitudes from the Legacy survey g = 22.64, r = 21.75, i = 21.45, z = 21.15, and a photometric redshift z = 0.51 +/- 0.09. This object is marginally detected in our NOT stacked z-band image. The second one (RA = 23:13:43.42, Dec = +01:21:19.8) is fainter (r = 24.10), and is not detected in the NOT image. No other objects are seen consistent with the XRT position in the NOT z-band images, down to a limiting magnitude z > 22.4 AB, calibrated against nearby Pan-STARRS objects. Given its low (<2%) chance-association probability with the X-ray source, the brighter galaxy is a promising host galaxy candidate for GRB 250806A, and we invite other observers (e.g., Wu et al., GCN 41244; Fortin et al., GCN 41245; Freeberg et al., GCN 41247; Zheng et al., GCN 41251; Schneider et al., GCN 41253) to examine their data and to monitor this galaxy in order to check for variability. A SN should be also detectable in the next couple of weeks, if the photometric redshift is approximately correct and there is no significant extinction. We acknowledge expert support from the NOT observing staff, in particular Tapio Pursimo and Laura Fuglsang. View this GCN Circular online at https://gcn.nasa.gov/circulars/41279. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39335] GRB 250807B: NTT optical observations
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41278 SUBJECT: GRB 250807B: NTT optical observations DATE: 25/08/08 08:10:05 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> J. N. D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), L. Cotter (UCD), M. Fraser (UCD), A. Martin-Carrillo (UCD), L. Galbany (IEEC-CSIC), T. Petrushevska (Nova Gorica), S. Srivastav (Oxford), L. Izzo (INAF/OAC and DARK/NBI), P. D'Avanzo (INAF/OAB), J. Anderson (ESO), T. Müller Bravo (Southampton), T.-W. Chen (NCU), M. Gromadzki (Warsaw), C. Inserra (Cardiff), E. Kankare (Turku), M. Nicholl (QUB), O. Yaron (Weizmann), D. Young (QUB), E. Zimmerman (Weizmann) report on behalf of the ePESSTO+ collaboration: We observed the optical counterpart of the Swift GRB 250807B (Klingler et al., GCN 41268) using the ESO NTT located in La Silla (Chile), equipped with the EFOSC2 camera. A total of 600 s imaging was secured in each of the Gunn r and g bands, with mean epoch 2025 Aug 8.15 UT (11.9 hr after the trigger). The optical afterglow is well detected in both filters. We measure the following J2000 coordinates (~0.3" error): RA = 01:02:33.04 Dec = -59:07:09.1 The object has a magnitude r = 20.4 +- 0.2 AB (calibrated against nearby stars from the SkyMapper catalog, and not corrected for Galactic extinction), where the error mostly stems from calibrators scatter. We acknowledge expert support from the NTT operator, Duncan Castex. View this GCN Circular online at https://gcn.nasa.gov/circulars/41278. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39334] EP250807a: EP-WXT detection of a fast X-ray transient
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41277 SUBJECT: EP250807a: EP-WXT detection of a fast X-ray transient DATE: 25/08/08 07:28:10 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> EP250807a: EP-WXT detection of a fast X-ray transient Y. Wang (PMO, CAS), Y. Q. Zhao (USTC,PRIC), H. Q. Cheng, Z. X. Ling (NAOC) 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 EP250807a. The transient triggered EP-WXT (ID: 15309198471) at 2025-08-07T23:33:02 (UTC). The WXT position of the source is R.A. = 281.311 deg, DEC = 14.383 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The duration of the flare is about 250 seconds, with a peak flux of 2.08 x 10^-8 ergs/s/cm^2. The WXT spectrum during the flare can be fitted with an absorbed power-law model, yielding best-fit absorption column density of 0.80 (-0.26, +0.27) x 10^22 cm^-2 and photon index of 1.99 (-0.11, +0.14). The 0.5-4 keV unabsorbed flux is 7.14 (-1.59, +2.71) x 10^-9 ergs/s/cm^2. Follow-up observations with EP-FXT are scheduled. 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/41277. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39333] EP 250807.979: GOTO optical upper limit
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41276 SUBJECT: EP 250807.979: GOTO optical upper limit DATE: 25/08/08 06:12:52 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> A. Kumar, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. O'Neill, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: The Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) serendipitously observed the field of EP-WXT triggered event (trigger 06800000803) at 2025-08-08 from 00:14:45 to 01:24:04 UT (from 43.89 min to 1.89 hours after the trigger, respectively). The observation was taken by GOTO-North, and consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. We do not identify any candidate optical counterparts within the EP/WXT localisation uncertainty region, down to a 3-sigma limiting magnitude of L >18.7 (AB). Also, a GOTO frame obtained at 4.36 minutes before the trigger shows no source to a 3-sigma limit of L >18.8 mag (AB). 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 and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/41276. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39332] EP 250807.979: COLIBRÍ optical upper limit
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41275 SUBJECT: EP 250807.979: COLIBRÍ optical upper limit DATE: 25/08/08 06:07:18 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Francis Fortin (IRAP), Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Alvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP X-ray transient EP 250807.979 using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-08-08 04:38 to 04:57 UTC (from 5.12 to 5.44 hours after the trigger) and obtained 16 minutes of exposure in the i-band filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with 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. In the stacked image, we do not detect any new source in the WXT uncertainty region, either in the direct image or after subtracting a Pan-STARRS DR2 template, down to the following 5-sigma limit: i > 21.67 We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. 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/41275. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39331] GRB 250807A: SVOM/VT optical observation
by GCN Circulars 08 Aug '25

08 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41274 SUBJECT: GRB 250807A: SVOM/VT optical observation DATE: 25/08/08 03:38:37 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of GRB 250807A detected by Swift-BAT（Klingler et al., GCN 41262; Evans et al., GCN 41270). The observation began at 2025-08-07T11:21:39.516 UTC, 35.52 minutes after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical afterglow (Evans et al., GCN 41262) is detected in both VT_R and VT_B using VT X-band data at R.A. = 51.448126 , DEC = -47.887663 degrees: RA (J2000) = 3:25:47.55 Dec (J2000) = -47:53:15.58 with an uncertainty of 0.5 arcsec. The magnitudes are: mid time (sec) | exposure time (s) | band | mag (AB) | mag err ---------------|-------------------|------|----------|-------- 2236 | 70 | VT_B | 20.52 | 0.08 14319 | 70 | VT_B | 21.07 | 0.10 2236 | 70 | VT_R | 18.98 | 0.03 14319 | 70 | VT_R | 19.29 | 0.03 Our photometry was not corrected for Galactic extinction. During our observations, the light curves exhibit an initial brightening followed by a decay phase. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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/41274. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39330] EP250806a: Upper limit from Fermi-GBM Observations
by GCN Circulars 07 Aug '25

07 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41273 SUBJECT: EP250806a: Upper limit from Fermi-GBM Observations DATE: 25/08/07 20:05:54 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio and P.G. Jonker (Radboud Univ.) on behalf of the Einstein Probe Team and E. Burns (LSU) on behalf of the Fermi-GBM Team, report: Fermi-GBM had full spatial coverage of the transient EP250806a detected by EP-WXT (Yang et al., GCN 41246). There was no Fermi-GBM onboard trigger around the refined EP starting time T0=2025-08-06T09:17:30 UTC (Liang et al., GCN 41256). The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50;T0+500] s, seeking signals between 64 ms and 32.768 s in duration. No signal consistent with the EP transient, both temporally and spatially, is identified, as confirmed also by visual inspection of the data. Assuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, we derive a flux upper limit of 3.7e-08 erg/cm2/s in the energy band 10-1000 keV. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/41273. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39329] GRB 250807B: Enhanced Swift-XRT position
by GCN Circulars 07 Aug '25

07 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41272 SUBJECT: GRB 250807B: Enhanced Swift-XRT position DATE: 25/08/07 19:34:25 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 1712 s of XRT Photon Counting mode data and 5 UVOT images for GRB 250807B, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 15.63710, -59.11896 which is equivalent to: RA (J2000): 01h 02m 32.90s Dec (J2000): -59d 07' 08.3" with an uncertainty of 2.4 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41272. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39328] Swift GRB250807.65: Global MASTER-Net observations report
by GCN Circulars 07 Aug '25

07 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41271 SUBJECT: Swift GRB250807.65: Global MASTER-Net observations report DATE: 25/08/07 18:44:25 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), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB250807.65 (trigger No 1340561,01h 02m 20.40s , -59d 05m 38.4s, R=0.05) errorbox 10317 sec after notice time and 10401 sec after trigger time at 2025-08-07 18:36:29 UT, with upper limit up to 17.8 mag. The observations began at zenith distance = 76 deg. The sun altitude is -32.1 deg. The galactic latitude b = -58 deg., longitude l = 300 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2963168 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 10491 | MASTER-SAAO | C | 180 | 17.1 | 10491 | MASTER-SAAO | C | 180 | 17.8 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41271. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39327] GRB 250807A: Enhanced Swift-XRT position
by GCN Circulars 07 Aug '25

07 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41270 SUBJECT: GRB 250807A: Enhanced Swift-XRT position DATE: 25/08/07 16:14:45 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 769 s of XRT Photon Counting mode data and 3 UVOT images for GRB 250807A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 51.44795, -47.88761 which is equivalent to: RA (J2000): 03h 25m 47.51s Dec (J2000): -47d 53' 15.4" with an uncertainty of 2.0 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41270. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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