vsnet-grb-info September 2025

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

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[vsnet-grb-info 39691] LIGO/Virgo/KAGRA S250830m: Updated Sky localization
by GCN Circulars 01 Sep '25

01 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41626 SUBJECT: LIGO/Virgo/KAGRA S250830m: Updated Sky localization DATE: 25/09/01 08:29:41 GMT FROM: alexandresebastien.goettel(a)LIGO.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S250830m (GCN Circular 41601). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250830m For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 3194 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3731 +/- 1474 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/41626. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39690] EP250831a: EP-FXT follow-up observation
by GCN Circulars 01 Sep '25

01 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41625 SUBJECT: EP250831a: EP-FXT follow-up observation DATE: 25/09/01 07:35:09 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), X. Tian (GXU), D. Y. Li, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of EP250831a (GCN 41619) at 2025-08-31T15:30:41 (UTC), about 6 hours after the WXT detection, with an exposure time of 2.9 ks. The source was also followed by Swift-XRT (GCN 41624). FXT detected an uncatalogued source within the WXT error circle at R.A. = 42.9816, DEC = -36.1872 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with the absorption fixed at the Galactic value of 1.9x10^20 cm^-2, and a photon index of 1.4(-0.8, +0.8). The derived unabsorbed 0.5-10 keV flux is approximately 1.84x10^-13 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. We noted that EP-FXT also detected the uncatalogued X-ray source outside the WXT error circle detected by Swift-XRT. 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/41625. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39689] EP250831a: Swift-XRT observations
by GCN Circulars 01 Sep '25

01 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41624 SUBJECT: EP250831a: Swift-XRT observations DATE: 25/09/01 04:39:35 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected source EP250831a, collecting 1.8 ks of Photon Counting (PC) mode data between T0+24 ks and T0+30 ks after the trigger. We have detected 1 source 4.6 arcmin from the WXT position, somewhat outside the 90% error region of 2.9 arcmin (GCN 41619). This has been automatically classified as an uncatalogued X-ray source. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J025130.9-360728): ================================== RA (J2000.0): 42.8789 = 02 51 30.94 Dec (J2000.0): -36.1245 = -36 07 28.2 Error: 5.0 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.6 arcmin from the Einstein Probe/WXT position. Mean rate: (7.6 [+2.8, -2.3])e-3 ct s^-1 Mean flux: (1.97 [+0.73, -0.59])e-13 erg cm^-2 s^-1 Peak rate: (7.6 [+2.8, -2.3])e-3 ct s^-1 Peak flux: (1.97 [+0.73, -0.59])e-13 erg cm^-2 s^-1 ECF: 2.58e-11 erg cm^-2 ct^-1 assuming NH=3.05e+20 cm^-2, gamma=2.54 determined from a spectral fit. LSXPS UL: 1.7e-02 ct/sec, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/EP/EP_FIELD00066. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41624. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39688] LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
by GCN Circulars 01 Sep '25

01 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41623 SUBJECT: LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations DATE: 25/09/01 03:03:21 GMT FROM: Hitoshi Negoro at Nihon University/MAXI team <negoro.hitoshi(a)nihon-u.ac.jp> H. Negoro, M. Nakajima, K. Takagi (Nihon U.), N. Kawai, T. Mihara, (RIKEN), S. Sugita, M. Serino, Y. Kawakubo, H. Hiramatsu, Y. Kondo (AGU) report on behalf of the MAXI team: We examined MAXI/GSC all-sky X-ray images (2-20 keV) after compact binary merger candidate S250831cc at 2025-08-31 12:30:48.228 UTC. At the trigger time of S250831cc, the high-voltage of MAXI/GSC was on, but the FOV was out of the 90% credible region of the bayestar skymap. The first one-orbit (92 min) scan observation with GSC after the event covered 48% of the 90% credible region of the bayestar skymap from 13:12:46 to 13:24:01 UTC (T0+2518 to T0+3193 sec). No significant new source was found in the region in the one-orbit scan observation. A typical 1-sigma averaged upper limit obtained in one scan observation is 20 mCrab at 2-20 keV. If you require information about X-ray flux by MAXI/GSC at specific coordinates, please contact the submitter of this circular by email. View this GCN Circular online at https://gcn.nasa.gov/circulars/41623. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39687] IceCube Alert 250831.75: Global MASTER-Net observations report
by GCN Circulars 01 Sep '25

01 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41622 SUBJECT: IceCube Alert 250831.75: Global MASTER-Net observations report DATE: 25/09/01 00:39:34 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) was pointed to the IceCube Alert 250831.75 (trigger No 5972385,07h 02m 33.60s , +05d 02m 24.0s, R=0.53) errorbox 20982 sec after notice time and 21045 sec after trigger time at 2025-08-31 23:51:31 UT, with upper limit up to 17.3 mag. The observations began at zenith distance = 83 deg. The sun altitude is -26.9 deg. The galactic latitude b = 5 deg., longitude l = 210 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2980982 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21075 | 2025-08-31 23:51:31 | MASTER-Kislovodsk | (07h 00m 41.24s , +05d 07m 13.0s) | C | 60 | 15.9 | 21135 | 2025-08-31 23:51:31 | MASTER-Kislovodsk | (07h 00m 41.26s , +05d 07m 12.7s) | C | 180 | 16.4 | Coadd 21075 | 2025-08-31 23:51:31 | MASTER-Kislovodsk | (07h 00m 37.35s , +04d 44m 38.4s) | C | 60 | 15.9 | 21155 | 2025-08-31 23:52:51 | MASTER-Kislovodsk | (07h 00m 43.33s , +05d 08m 51.7s) | C | 60 | 15.8 | 21155 | 2025-08-31 23:52:51 | MASTER-Kislovodsk | (07h 00m 39.47s , +04d 46m 16.8s) | C | 60 | 15.8 | 21235 | 2025-08-31 23:54:11 | MASTER-Kislovodsk | (07h 00m 38.32s , +05d 08m 20.3s) | C | 60 | 15.7 | 21235 | 2025-08-31 23:54:11 | MASTER-Kislovodsk | (07h 00m 34.57s , +04d 45m 45.1s) | C | 60 | 15.9 | 21315 | 2025-08-31 23:55:31 | MASTER-Kislovodsk | (07h 00m 37.37s , +05d 09m 24.8s) | C | 60 | 15.9 | 21375 | 2025-08-31 23:55:31 | MASTER-Kislovodsk | (07h 00m 37.37s , +05d 09m 24.7s) | C | 180 | 16.4 | Coadd 21315 | 2025-08-31 23:55:31 | MASTER-Kislovodsk | (07h 00m 33.70s , +04d 46m 50.1s) | C | 60 | 16.0 | 21395 | 2025-08-31 23:56:50 | MASTER-Kislovodsk | (07h 00m 44.34s , +05d 08m 27.2s) | C | 60 | 15.9 | 21395 | 2025-08-31 23:56:50 | MASTER-Kislovodsk | (07h 00m 40.78s , +04d 45m 52.4s) | C | 60 | 15.9 | 21474 | 2025-08-31 23:58:10 | MASTER-Kislovodsk | (07h 00m 39.37s , +05d 07m 32.4s) | C | 60 | 16.0 | 21475 | 2025-08-31 23:58:10 | MASTER-Kislovodsk | (07h 00m 35.89s , +04d 44m 57.5s) | C | 60 | 16.0 | 22440 | 2025-09-01 00:13:15 | MASTER-Kislovodsk | (07h 00m 37.64s , +05d 10m 27.0s) | C | 180 | 17.1 | 22440 | 2025-09-01 00:13:15 | MASTER-Kislovodsk | (07h 00m 39.06s , +04d 47m 32.5s) | C | 180 | 17.3 | 23039 | 2025-09-01 00:23:14 | MASTER-Kislovodsk | (07h 00m 37.10s , +04d 48m 25.8s) | C | 180 | 17.0 | 23039 | 2025-09-01 00:23:14 | MASTER-Kislovodsk | (07h 00m 38.51s , +05d 11m 07.6s) | C | 180 | 16.9 | 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/41622. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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