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

[vsnet-grb-info 39496] LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
by GCN Circulars 20 Aug '25

20 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41433 SUBJECT: LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz DATE: 25/08/20 01:24:57 GMT FROM: xjh(a)andrew.cmu.edu Xander J. Hall (Carnegie Mellon U.), Malte Busmann (LMU), Daniel Gruen (LMU), Brendan O’Connor (Carnegie Mellon U.), and Antonella Palmese (Carnegie Mellon U.) report: We observed the source AT 2025ulz reported by Stein et al. (GCN 41414) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the g, r, i, z, and J bands starting at 2025-08-19T20:09:46 for 22 x 180 s. We took 11 observations in the giJ configuration and 11 in the rzJ configuration. In the difference imaging with templates from the Legacy Survey, we detect AT 2025ulz at g = (22.08 +/- 0.09) AB mag, r = (21.83 +/- 0.06) AB mag. We note significant reddening and fading from our previous report (GCN 41421), with the g band dropping 0.83 AB mag in 24.6 hours and r band now being brighter than g. The magnitudes are calibrated against the PS1 catalog and not corrected for Galactic extinction. Further analysis is underway. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41433. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39495] GRB 250820A: Fermi GBM Final Real-time Localization
by GCN Circulars 20 Aug '25

20 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41432 SUBJECT: GRB 250820A: Fermi GBM Final Real-time Localization DATE: 25/08/20 00:42:49 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 00:32:21 UT on 20 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250820A (trigger 777342746.588176 / 250820022). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 28.0, Dec = -70.8 (J2000 degrees, equivalent to J2000 01h 52m, -70d 47'), with a statistical uncertainty of 1.1 degrees. The angle from the Fermi LAT boresight is 169.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250820022/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250820022/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250820022/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41432. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39494] GCN Announcement: Client Credential Expiration Policy
by GCN Announcements 19 Aug '25

19 Aug '25

The GCN Team is announcing a new policy on https://gcn.nasa.gov. For security purposes, we will disable client credentials that you have not used to connect to a Kafka broker for the past 30 days. We will email you reminders 9 days before client credentials will expire. Once disabled, a client credential cannot be used again. To prevent a credential from expiring and being disabled, simply use it to connect to a Kafka broker. You may create new client credentials at any time. To review, create, delete, and manage your client credentials, see your account client credential settings (https://gcn.nasa.gov/user/credentials) For more details on this new feature and an archive of GCN news and announcements, see https://gcn.nasa.gov/news. For questions, issues, or bug reports, please contact us via: - Contact form: https://gcn.nasa.gov/contact - GitHub issue tracker: https://github.com/nasa-gcn/gcn.nasa.gov/issues --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39493] GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
by GCN Circulars 19 Aug '25

19 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41431 SUBJECT: GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq) DATE: 25/08/19 14:54:41 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> A. Kumar (RHUL), D. O’Neill (Birmingham), N. Rawat (SAAO), R. A. J. Eyles-Ferris (U. Leicester), R. Dastidar (UNAB), D. Buckley (SAAO), D. Steeghs (Warwick), J. R. Maund (RHUL), R. L. C. Starling (U. Leicester) and G. Ramsay (Armagh) report: We observed the optical afterglow GOTO25fzq (Kumar et al. GCN 41406) associated with GRB 250818B (Wang et al., GCN 41405), also reported by Yao et al. (GCN 41409), Zheng et al. (GCN 41417), Bendtsen et al. (GCN 41426), Moskvitin et al. (GCN 41428), and An et al. (GCN 41430). The observations are conducted using the 1-m Lesedi telescope at the South African Astronomical Observatory (SAAO), Sutherland, South Africa, between 2025-08-19 00:51:24 UT and 2025-08-19 04:05:00 UT (between 21.37 and 24.60 hours post-trigger) in g’, r’, i’, and z’ bands (6×450s in g and z, 6×400s in r and i bands). OT was clearly detected in the stacked g’- and r’-band images, whereas i’ and z’ images are severely affected by trailing. Preliminary aperture photometry yields the following magnitudes in the g’ and r’ bands: DATE-OBS (Start_time) T-T0 (hrs) Filter Exp (s) Magnitude (AB) -------------------------------------------------------------------------------------- 2025-08-19 00:51:24 UT 21.37 g’ 6x450s 21.39 ± 0.09 2025-08-19 01:36:43 UT 22.13 r’ 6x400s 21.58 ± 0.47 Although our r'-band image is also significantly affected by trailing, aperture photometry confirms a low-significance detection, yielding the reported magnitude. Photometric calibration was performed using reference stars from the SDSS catalogue. Magnitudes are not corrected for Galactic extinction. Follow-up observations are ongoing, and further analysis is in progress. Data were obtained using the 1-m Lesedi robotic telescope at the SAAO, equipped with the Mookodi low-resolution spectrograph and imager operating in fully robotic imaging mode. We thank the SAAO Instrumentation and Operations (IO) team for their continued support. View this GCN Circular online at https://gcn.nasa.gov/circulars/41431. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39492] GRB 250818B: TRT Optical Observation
by GCN Circulars 19 Aug '25

19 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41430 SUBJECT: GRB 250818B: TRT Optical Observation DATE: 25/08/19 13:29:47 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> J. An (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), X. Liu, Z.P. Zhu, S.Q. Jiang, L.B. He, D. Xu (NAOC) report on behalf of a large collaboration: We carried out two-epoch observations of GRB 250818B (Wang et al., GCN 41405), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO) and New South Wales, Australia (SBO), respectively. And we obtained several frames in the B, V, R & I band. The optical afterglow (Kumar et al., GCN 41406; Yao et al., GCN 41409; Zheng et al., GCN 41417; Bendtsen et al., GCN 41426; Moskvitin et al., GCN 41428) was clearly detected in our stack frames. The photometric results are presented in the following table: |mid time(h)|filter|mag(Vega)|site| |--|--|--|--| |7.75|R|19.98+/-0.06|SRO| |12.64|R|20.23+/-0.06|SBO| The presented magnitudes are calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41430. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39491] Fermi GRB 250816A: Global MASTER-Net observations report
by GCN Circulars 19 Aug '25

19 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41429 SUBJECT: Fermi GRB 250816A: Global MASTER-Net observations report DATE: 25/08/19 09:47:47 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250816A ( Fermi GBM team, GCN 41397) errorbox 16 sec after notice time and 43 sec after trigger time at 2025-08-16 01:30:54 UT, with upper limit up to 12.5 mag. Observations started at twilight. The observations began at zenith distance = 68 deg. The sun altitude is -8.5 deg. The galactic latitude b = 50 deg., longitude l = 151 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2969505 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 49 | 2025-08-16 01:30:54 | MASTER-Kislovodsk | (10h 24m 32.65s , +60d 44m 23.8s) | C | 10 | 12.5 | 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/41429. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39490] GRB 250818B: SAO RAS optical observations
by GCN Circulars 19 Aug '25

19 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41428 SUBJECT: GRB 250818B: SAO RAS optical observations DATE: 25/08/19 08:13:33 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova, V. Vlasyuk, Yu. Sotnikova (SAO RAS), Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) report on behalf of a larger collaboration. We observed the field of the SVOM short GRB 250818B (Wang et al., GCN 41405; also detected by Swift/XRT, Ferro et al., GCN 41407 and EP-FXT, Li et al., GCN 41424) with the 1-m SAO RAS telescope Zeiss-1000 equipped with CCD-photometer. We obtained 13 x 300 sec. images in Rc band on August 18, 23:15:02 -- August 19, 00:33:37 UT (t_mid - T0 = 20.4196 hours = 0.85082 days). The OT (Kumar et al., GCN 41406; Yao et al., GCN 41409; Zheng et al., GCN 41417; Fong et al., GCN 41419; Bendtsen et al., GCN 41426) is clearly detected in the stacked image with the brightness of R = 20.88 +/- 0.04 (R_lim = 23.0). This preliminary photometry is based on nearby Pan-STARRS objects (magnitudes were converted with the Lupton 2005 equations) and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41428. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39489] Swift GRB 250818A: Global MASTER-Net observations report
by GCN Circulars 19 Aug '25

19 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41427 SUBJECT: Swift GRB 250818A: Global MASTER-Net observations report DATE: 25/08/19 05:30:35 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 250818A ( S. B. Cenko et al., GCN 41403) errorbox 30 sec after notice time and 64 sec after trigger time at 2025-08-18 01:32:26 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 52 deg. The sun altitude is -43.8 deg. The galactic latitude b = 3 deg., longitude l = 314 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2971328 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 69 | MASTER-OAFA | C | 10 | 17.6 | 90 | MASTER-OAFA | C | 20 | 17.4 | 116 | MASTER-OAFA | C | 20 | 17.6 | 148 | MASTER-OAFA | C | 30 | 18.0 | 184 | MASTER-OAFA | C | 30 | 18.1 | 225 | MASTER-OAFA | C | 40 | 18.3 | 276 | MASTER-OAFA | C | 50 | 18.1 | 337 | MASTER-OAFA | C | 60 | 18.4 | 408 | MASTER-OAFA | C | 70 | 18.1 | 494 | MASTER-OAFA | C | 90 | 18.1 | 601 | MASTER-OAFA | C | 110 | 18.2 | 722 | MASTER-OAFA | C | 120 | 18.1 | 848 | MASTER-OAFA | C | 120 | 18.0 | 974 | MASTER-OAFA | C | 120 | 18.1 | 1100 | MASTER-OAFA | C | 120 | 18.1 | 1226 | MASTER-OAFA | C | 120 | 18.1 | 1352 | MASTER-OAFA | C | 120 | 18.1 | 1478 | MASTER-OAFA | C | 120 | 18.1 | 1604 | MASTER-OAFA | C | 120 | 18.0 | 1730 | MASTER-OAFA | C | 120 | 18.1 | 1856 | MASTER-OAFA | C | 120 | 18.3 | 1982 | MASTER-OAFA | C | 120 | 18.1 | 2108 | MASTER-OAFA | C | 120 | 18.1 | 2234 | MASTER-OAFA | C | 120 | 18.1 | 2361 | MASTER-OAFA | C | 120 | 18.0 | 2487 | MASTER-OAFA | C | 120 | 18.0 | 2613 | MASTER-OAFA | C | 120 | 17.9 | 2739 | MASTER-OAFA | C | 120 | 17.8 | 2865 | MASTER-OAFA | C | 120 | 17.9 | 2992 | MASTER-OAFA | C | 120 | 17.8 | 3118 | MASTER-OAFA | C | 120 | 17.9 | 3244 | MASTER-OAFA | C | 120 | 18.1 | 3370 | MASTER-OAFA | C | 120 | 18.1 | 3496 | MASTER-OAFA | C | 120 | 18.0 | 3622 | MASTER-OAFA | C | 120 | 18.1 | 3748 | MASTER-OAFA | C | 120 | 18.0 | 3874 | MASTER-OAFA | C | 120 | 18.1 | 4000 | MASTER-OAFA | C | 120 | 18.0 | 4126 | MASTER-OAFA | C | 120 | 18.0 | 4253 | MASTER-OAFA | C | 120 | 18.0 | 4379 | MASTER-OAFA | C | 120 | 18.1 | 4505 | MASTER-OAFA | C | 120 | 18.1 | 4631 | MASTER-OAFA | C | 120 | 17.9 | 4757 | MASTER-OAFA | C | 120 | 18.0 | 4884 | MASTER-OAFA | C | 120 | 18.0 | 5010 | MASTER-OAFA | C | 120 | 18.1 | 5135 | MASTER-OAFA | C | 120 | 18.0 | 5261 | MASTER-OAFA | C | 120 | 18.1 | 5388 | MASTER-OAFA | C | 120 | 18.1 | 5515 | MASTER-OAFA | C | 120 | 18.0 | 5640 | MASTER-OAFA | C | 120 | 18.0 | 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/41427. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39488] GRB 250818B: NOT optical observations
by GCN Circulars 19 Aug '25

19 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41426 SUBJECT: GRB 250818B: NOT optical observations DATE: 25/08/19 04:07:05 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> Jonas Broe Bendtsen (SDU), Johanne Hein Pedersen (SDU), Isabella Alexandra Koch (SDU), Sophie Lund Wagner (SDU), Julie Magaard Knudsen (SDU), Roar Holmberg Rasmussen (NOT and Aarhus), Kostas Valeckas (NOT and NBI), Johan P. U. Fynbo (DAWN/NBI), Daniele B. Malesani (DAWN/NBI and Radboud Univ.), Antonio de Ugarte Postigo (LAM), report on behalf of a larger collaboration: We observed the optical counterpart (Kumar et al., GCN 41406; Yao et al., GCN 41409; Zheng et al., GCN 41417; Fong et al., GCN 41419) of the short SVOM GRB 250818B (Wang et al., GCN 41405) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried in the SDSS r band out using the ALFOSC camera, for a total exposure time of 3x300 s. The optical afterglow is clearly detected in our images. Its coordinates, calibrated against the Gaia catalog, are: RA(J2000) = 03:04:13.483 Dec(J2000) = -03:07:30.74 with an error of 0.1". At a mean epoch 2025 Aug 19.128 UT (23.60 hr after the trigger), we measure r = 21.15 +- 0.04 (AB), calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41426. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39487] GRB 250818A: Swift-XRT refined Analysis
by GCN Circulars 19 Aug '25

19 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41425 SUBJECT: GRB 250818A: Swift-XRT refined Analysis DATE: 25/08/19 04:02:04 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.5 ks of XRT data for GRB 250818A, from 86 s to 83.2 ks after the trigger. The data comprise 247 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+4.4 ks) can be modelled with a power-law decay with a decay index of alpha=1.15 (+/-0.04). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.18 (+/-0.06). The best-fitting absorption column is 1.63 (+/-0.08) x 10^22 cm^-2, in excess of the Galactic value of 6.8 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.76 (+0.17, -0.16) and a best-fitting absorption column of 1.69 (+0.25, -0.23) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.6 x 10^-11 (1.2 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.69 (+0.25, -0.23) x 10^22 cm^-2 Galactic foreground: 6.8 x 10^21 cm^-2 Excess significance: 7.2 sigma Photon index: 1.76 (+0.17, -0.16) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01343270. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41425. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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