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

[vsnet-grb-info 39586] GRB 250824A: Fermi GBM Final Real-time Localization
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41522 SUBJECT: GRB 250824A: Fermi GBM Final Real-time Localization DATE: 25/08/24 11:34:48 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 11:24:18 UT on 24 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250824A (trigger 777727463.376698 / 250824475). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 312.0, Dec = 49.5 (J2000 degrees, equivalent to J2000 20h 48m, 49d 30'), with a statistical uncertainty of 2.0 degrees. The angle from the Fermi LAT boresight is 61.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250824475/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250824475/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250824475/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41522. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39585] GRB 250823A: Swift/UVOT Detection
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41521 SUBJECT: GRB 250823A: Swift/UVOT Detection DATE: 25/08/24 09:33:50 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> Paul Kuin (UCL/MSSL) and M. H. Siegel (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250823A 126 s after the BAT trigger (Siegel et al., GCN Circ. 41511). A source consistent with the XRT position is detected in the initial UVOT exposures. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 126 1020 334 20.42 +/- 0.17 v 668 1244 78 18.43 +/- 0.28 b 594 1169 58 19.25 +/- 0.28 u 338 1317 304 >19.5 w1 718 1293 58 >19.1 m2 692 1268 58 >18.8 w2 644 1391 97 >19.3 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.111 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41521. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39584] GRB 250823A: NOT optical observations
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41520 SUBJECT: GRB 250823A: NOT optical observations DATE: 25/08/24 08:54:25 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), B. P. Gompertz (Birmingham), A de Ugarte Postigo (LAM), A. Henderson de la Fuente (NOT) report on behalf of a larger collaboration: We observed the optical counterpart (Gompertz & Dimple, GCN 41512; Fernandez-Garcia et al., GCN 41513; Strausbaugh & Cucchiara, GCN 41514) of the Swift and Fermi GRB 250823A (Siegel et al., GCN 41511; Smith et al., GCN 41517) using the Nordic Optical Telescope (NOT) located in La Palma (Canary Islands, Spain). Observations were carried out in the r and z filters. Calibrated against nearby Pan-STARRS pointlike objects, we report the following magnitudes: | Filter | Mean epoch (UT) | Time since trigger (hr) | Exp time (s) | Magnitude (AB) | | ------ | --------------- | ----------------------- | ------------ | -------------- | | r | 2025 Aug 24.022 | 4.36 | 3x300 | 21.89 +- 0.05 | | z | 2025 Aug 24.036 | 4.69 | 5x250 | 21.15 +- 0.12 | These values are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41520. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39583] LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41519 SUBJECT: LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz DATE: 25/08/24 07:14:08 GMT FROM: Sarah Antier at OCA <sarah.antier(a)oca.eu> S. Antier (OCA/IJCLAB), M. Pillas (Uliege), D. Akl (NYUAD), S. Karpov (FZU), M. Coughlin (UMN), P. Hello (IJCLAB), A. Jacquesson (IJCLAB) report on behalf on ZTF collaboration: We observed the optical transient AT2025ulz/ZTF25abjmnps (Stein et al., GCN 41414) over several nights, which has been reported by Stein et al., GCN 41414; Busmann et al., GCN 41421; Hall et al., GCN 41433; Karambelkar et al., GCN 41436; O’Connor et al., GCN 41452; Gillanders et al., GCN 41454; Liu et al., GCN 41461; Banerjee et al., GCN 41476; Perley et al., GCN 41480; D'Avanzo et al., GCN 41489; Malesani et al., GCN 41492; Smartt et al., GCN 41493; Bruni et al., GCN 41500; Santos et al., GCN 41501; Becerra et al., GCN 41502; An et al., GCN 41503, Angulo et al., GCN 41518 as a possible source to the Gravitational Wave Event S250818k (LVK collaboration GCN 41437; 41440). The observations were carried out using MegaCam on the CFHT. We report here our preliminary measurement in r-band taken around 2025-08-21 06:50 UTC by co-adding several images and analyzed with STDPipe (Karpov 2025) with photometric calibration against Pan-STARRS. The quality of the sky during that night was not ideal. r = 22.85 +/- 0.15 (AB) Differential image analysis against archival CFH data has been performed. Further observations are planned. We would like to thank the CFHT staff enabling these timely observations, in particular Nadine Manset and Heather Flewelling. View this GCN Circular online at https://gcn.nasa.gov/circulars/41519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39582] LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41518 SUBJECT: LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz DATE: 25/08/24 06:21:08 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Camila Angulo (UNAM), Alan M. Watson (UNAM), Damien Dornic (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd .Sánchez Álvarez (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the AT2025ulz (Stein et al., GCN Circ. 41414) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed at two epochs, from 2025-08-22 03:19 to 05:29 UTC (4.13 days after the trigger) and from 2025-08-24 03:29 to 05:41 UTC (6.14 days after the trigger). At both epochs we obtained 96 minutes of exposure in the i filter. The data were reduced and coadded with custom software and then analyzed in STDWeb (Karpov 2021). 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 a Pan-STARRS DR2 template image from our first epoch image (4.13 days after the trigger), we detect a source at the reported position of AT2025ulz with i = 23.1 +/- 0.25 After subtracting a Pan-STARRS DR2 template image from our second epoch image (6.14 days after the trigger), we detect a source at the reported position of AT2025ulz with i = 22.0 +/- 0.1 Subtracting the first epoch image from the second epoch image, we find a brightening that corresponds to Delta i = 22.7 +/- 0.2 We caution that these analyses are preliminary, especially the photometry after subtracting the shallower PS template images. Nevertheless, our results would appear to confirm the rebrightening reported by Freeburn et al. (GCN Circ. 41507). Further observations are planned. 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/41518. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39581] GRB 250823A: Fermi GBM Observation
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41517 SUBJECT: GRB 250823A: Fermi GBM Observation DATE: 25/08/24 02:09:14 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH), B. Mailyan (Florida Tech) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: At 20:10:10.67 UT on 23 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250823A (trigger 777672615/250823840), which was also detected by Swift BAT (M. H. Siegel et al. 2025, GCN 41511), and optical follow-up was first reported by Liverpool Telescope (B. P. Gompertz et al. 2025, GCN 41512). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 72 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 13 s (50-300 keV). The time-averaged spectrum from T0-6.1 to T0+10.2 s is best fit by a simple power law function with index -1.67 +/- 0.05. A power law function with an exponential high-energy cutoff fits equally well with power law index = -1.44 +/- 0.17 and Epeak = 206.5 +/- 95.8. The event fluence (10-1000 keV) in this time interval is (1.9 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.1 s in the 10-1000 keV band is 1.8 +/- 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/41517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39580] GRB 250818B: MeerKAT Detection
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41516 SUBJECT: GRB 250818B: MeerKAT Detection DATE: 25/08/24 01:11:07 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), W. Fong (Northwestern), T. Laskar (Utah), L. Rhodes (TSI/McGill) report: We observed the location of the SVOM short-duration GRB 250818B (Wang et al., GCN 41405) with a Swift/XRT counterpart (Ferro et al., GCN 41407) with the MeerKAT radio telescope under Director’s Discretionary program DDT-20250822-GS-01 (PI Schroeder) at 1.3 GHz and 3.1 GHz on 2025 August 23 (~5 days post burst). In preliminary analysis, we detect the radio afterglow (Ricci et al., GCN 41455) in the 3.1 GHz image, but not in 1.3 GHz (rms of 7 microJy/beam). We measure a flux density of ~30 microJy at 3.1 GHz. Further observations are planned. We thank Fernando Camilo for the rapid approval of the DDT proposal, and the staff at the South African Radio Astronomy Observatory for scheduling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41516. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39579] GRB 250823A: Enhanced Swift-XRT position
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41515 SUBJECT: GRB 250823A: Enhanced Swift-XRT position DATE: 25/08/24 01:08:20 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 950 s of XRT Photon Counting mode data and 1 UVOT images for GRB 250823A, 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 = 297.47814, -24.99557 which is equivalent to: RA (J2000): 19h 49m 54.75s Dec (J2000): -24d 59' 44.1" with an uncertainty of 2.2 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/41515. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39578] GRB 250823A: LCOGT Optical Detection
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41514 SUBJECT: GRB 250823A: LCOGT Optical Detection DATE: 25/08/24 00:24:31 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the Swift GRB 250823A field (Siegel et al., GCN 41511) with the LCOGT 1-meter Sinistro instrument at the Cerro Tololo Interamerican Observatory, Chile site, on August 23, from 23:17 to 23:49 UT (corresponding to 3.12 to 3.65 hours after the GRB trigger time) with the SDSS r and i filters. We performed a series of 3x300s exposures in i-band and r-band. We detect an uncatalogued source coincident with the XRT error region, and other optical detections (Gompertz et al., GCN 41512; Fernandez-Garcia et al., GCN 41513) in both bands. The following magnitudes are calculated using the PanSTARRS catalog as reference: r = 21.2 +/- 0.15 i = 22.5 +/- 0.55 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41514. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39577] GRB 250823A: BOOTES6/DPRT early optical detection
by GCN Circulars 23 Aug '25

23 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41513 SUBJECT: GRB 250823A: BOOTES6/DPRT early optical detection DATE: 25/08/23 23:11:13 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> E. Fernandez-Garcia, I. Perez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, S.-Y. Wu and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, Bloemfontein), A. Martin-Carrillo and L. Hanlon (UCD, Dublin), C. J. Perez del Pulgar (UMA, Malaga), Y.-D. Hu (GXI, Guangxi) and M. Gritsevich (Univ. of Helsinki), on behalf of a larger collaboration, report: Following the detection of GRB250823A by Fermi (Fermi GBM Team, GCN Circ. 41510) and Swift/BAT (Siegel et al., GCN Circ. 41511), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) automatically observed the Swift/XRT X-ray afterglow location starting on Aug. 23, 20:12:44 UT (i.e. 157 s after trigger). A series of images in clear filter were gathered and the optical counterpart reported by the LT (Gompertz et al., GCNC 41512) was detected at early times in our dataset. We measure a preliminary magnitude of 19.30 +- 0.15 on the co-added 10 s x 45 image (at 20:28:26 UT mid time). Further data analysis is ongoing. We thank the staff at Boyden Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/41513. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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