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

[vsnet-grb-info 39857] Fermi GRB 250910B: Global MASTER-Net observations report
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41791 SUBJECT: Fermi GRB 250910B: Global MASTER-Net observations report DATE: 25/09/11 10:31:00 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) started inspect of the Fermi GRB 250910B ( Fermi GBM team, GCN 41778) errorbox 45057 sec after notice time and 45097 sec after trigger time at 2025-09-11 07:23:42 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 40 deg. The sun altitude is -41.7 deg. The galactic latitude b = -34 deg., longitude l = 252 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2989479 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 45128 | 2025-09-11 07:23:42 | MASTER-OAFA | (05h 21m 01.46s , -46d 16m 04.7s) | C | 60 | 19.9 | 45203 | 2025-09-11 07:24:58 | MASTER-OAFA | (05h 21m 06.25s , -46d 17m 02.2s) | C | 60 | 19.8 | 45277 | 2025-09-11 07:26:12 | MASTER-OAFA | (05h 21m 01.18s , -46d 17m 59.3s) | C | 60 | 19.9 | 45353 | 2025-09-11 07:27:28 | MASTER-OAFA | (05h 21m 05.78s , -46d 17m 54.0s) | C | 60 | 19.9 | 45428 | 2025-09-11 07:28:43 | MASTER-OAFA | (05h 21m 03.82s , -46d 16m 02.0s) | C | 60 | 19.8 | 45503 | 2025-09-11 07:29:58 | MASTER-OAFA | (05h 21m 03.84s , -46d 17m 30.1s) | C | 60 | 19.8 | 45579 | 2025-09-11 07:31:13 | MASTER-OAFA | (05h 21m 06.46s , -46d 16m 12.8s) | C | 60 | 19.8 | 45656 | 2025-09-11 07:32:31 | MASTER-OAFA | (05h 21m 00.95s , -46d 16m 45.4s) | C | 60 | 19.8 | 45734 | 2025-09-11 07:33:49 | MASTER-OAFA | (05h 21m 01.87s , -46d 15m 42.5s) | C | 60 | 19.8 | 45811 | 2025-09-11 07:35:06 | MASTER-OAFA | (05h 21m 07.33s , -46d 16m 40.1s) | C | 60 | 19.9 | 45888 | 2025-09-11 07:36:22 | MASTER-OAFA | (05h 21m 00.65s , -46d 17m 37.5s) | C | 60 | 19.8 | 45962 | 2025-09-11 07:37:36 | MASTER-OAFA | (05h 21m 07.79s , -46d 17m 14.3s) | C | 60 | 19.9 | 46036 | 2025-09-11 07:38:51 | MASTER-OAFA | (05h 21m 04.04s , -46d 15m 34.4s) | C | 60 | 19.9 | 46112 | 2025-09-11 07:40:06 | MASTER-OAFA | (05h 21m 04.05s , -46d 17m 27.2s) | C | 60 | 19.9 | 46187 | 2025-09-11 07:41:21 | MASTER-OAFA | (05h 21m 07.22s , -46d 15m 29.4s) | C | 60 | 19.9 | 46263 | 2025-09-11 07:42:38 | MASTER-OAFA | (05h 21m 00.93s , -46d 16m 25.0s) | C | 60 | 19.9 | 46340 | 2025-09-11 07:43:55 | MASTER-OAFA | (05h 21m 00.54s , -46d 15m 22.3s) | C | 60 | 19.9 | 46417 | 2025-09-11 07:45:11 | MASTER-OAFA | (05h 21m 06.25s , -46d 16m 20.5s) | C | 60 | 19.8 | 46495 | 2025-09-11 07:46:29 | MASTER-OAFA | (05h 21m 01.68s , -46d 17m 18.0s) | C | 60 | 19.9 | 46569 | 2025-09-11 07:47:43 | MASTER-OAFA | (05h 21m 06.17s , -46d 16m 51.8s) | C | 60 | 19.9 | 46645 | 2025-09-11 07:49:00 | MASTER-OAFA | (05h 21m 04.24s , -46d 15m 24.7s) | C | 60 | 19.9 | 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/41791. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39856] EP250911a: LCO optical counterpart discovery
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41790 SUBJECT: EP250911a: LCO optical counterpart discovery DATE: 25/09/11 10:23:38 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> J. A. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), L. Cotter (UCD), P. G. Jonker (Radboud), F. E. Bauer (SSI and UTA), and J. Chacón (PUC) report on behalf of a larger collaboration: We observed the location of EP250911a (Liang et al., GCN 41788) with the Sinistro instrument mounted on the 1-m telescopes at McDonald Observatory, available via the LCO network. 6 x 200 s exposures were obtained in the SDSS r filter at a start time of 2025-09-11 UT 09:35:35 (~37.1 min post trigger). Within the WXT and FXT error circles (Liang et al., GCN 41788) we locate a new source in our stacked r-band image, not visible in the archival Legacy Survey images. Its coordinates (0.5" error) are: RA(J2000): 23:50:04.83 DEC(J2000): +29:17:59.6 Calibrated to nearby stars from the Pan-STARRS catalog, we measure a magnitude r = 20.04 +/- 0.07 (AB), not corrected for Galactic extinction. Given the non-detection in the deeper archival images and the consistency with the FXT error circle, we suggest that this source is the optical counterpart of EP250911a. View this GCN Circular online at https://gcn.nasa.gov/circulars/41790. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39855] EP250910a: Global MASTER-Net observations report
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41789 SUBJECT: EP250910a: Global MASTER-Net observations report DATE: 25/09/11 10:09:24 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), 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 EP250910a ( EP Team et al., GCN 41776) errorbox 829 sec after trigger time at 2025-09-10 03:29:53 UT, with upper limit up to 19.6 mag. The observations began at zenith distance = 54 deg. The sun altitude is -60.2 deg. The galactic latitude b = -64 deg., longitude l = 248 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2989175 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 849 | 2025-09-10 03:29:53 | MASTER-OAFA | (02h 39m 03.43s , -39d 42m 17.1s) | C | 40 | 18.9 | 895 | 2025-09-10 03:30:38 | MASTER-OAFA | (02h 39m 03.40s , -39d 42m 15.3s) | C | 40 | 18.9 | 940 | 2025-09-10 03:31:24 | MASTER-OAFA | (02h 39m 03.42s , -39d 42m 13.6s) | C | 40 | 18.9 | 987 | 2025-09-10 03:32:10 | MASTER-OAFA | (02h 39m 03.36s , -39d 42m 11.4s) | C | 40 | 18.9 | 1032 | 2025-09-10 03:32:55 | MASTER-OAFA | (02h 39m 03.34s , -39d 42m 09.8s) | C | 40 | 18.9 | 1077 | 2025-09-10 03:33:41 | MASTER-OAFA | (02h 39m 03.29s , -39d 42m 08.0s) | C | 40 | 18.9 | 1123 | 2025-09-10 03:34:27 | MASTER-OAFA | (02h 39m 03.28s , -39d 42m 06.1s) | C | 40 | 18.9 | 1169 | 2025-09-10 03:35:13 | MASTER-OAFA | (02h 39m 03.23s , -39d 42m 04.7s) | C | 40 | 18.9 | 1215 | 2025-09-10 03:35:58 | MASTER-OAFA | (02h 39m 03.16s , -39d 42m 03.1s) | C | 40 | 18.8 | 1261 | 2025-09-10 03:36:45 | MASTER-OAFA | (02h 39m 03.15s , -39d 42m 01.5s) | C | 40 | 18.8 | 1306 | 2025-09-10 03:37:30 | MASTER-OAFA | (02h 39m 03.08s , -39d 41m 59.9s) | C | 40 | 18.9 | 1352 | 2025-09-10 03:38:15 | MASTER-OAFA | (02h 39m 03.06s , -39d 41m 58.1s) | C | 40 | 18.9 | 1398 | 2025-09-10 03:39:01 | MASTER-OAFA | (02h 39m 03.03s , -39d 41m 56.4s) | C | 40 | 18.9 | 1443 | 2025-09-10 03:39:46 | MASTER-OAFA | (02h 39m 03.00s , -39d 41m 55.0s) | C | 40 | 18.9 | 1488 | 2025-09-10 03:40:32 | MASTER-OAFA | (02h 39m 02.97s , -39d 41m 53.5s) | C | 40 | 18.9 | 1535 | 2025-09-10 03:41:19 | MASTER-OAFA | (02h 39m 02.93s , -39d 41m 52.0s) | C | 40 | 18.9 | 1580 | 2025-09-10 03:42:04 | MASTER-OAFA | (02h 39m 02.89s , -39d 41m 50.3s) | C | 40 | 18.9 | 1626 | 2025-09-10 03:42:50 | MASTER-OAFA | (02h 39m 02.87s , -39d 41m 49.0s) | C | 40 | 18.9 | 8775 | 2025-09-10 05:41:58 | MASTER-OAFA | (02h 39m 14.92s , -39d 38m 15.4s) | C | 40 | 19.0 | 8820 | 2025-09-10 05:42:44 | MASTER-OAFA | (02h 39m 15.02s , -39d 38m 14.6s) | C | 40 | 19.0 | 8866 | 2025-09-10 05:43:29 | MASTER-OAFA | (02h 39m 15.10s , -39d 38m 13.5s) | C | 40 | 19.0 | 8912 | 2025-09-10 05:44:16 | MASTER-OAFA | (02h 39m 15.16s , -39d 38m 12.2s) | C | 40 | 19.0 | 8958 | 2025-09-10 05:45:01 | MASTER-OAFA | (02h 39m 15.23s , -39d 38m 11.0s) | C | 40 | 19.0 | 9003 | 2025-09-10 05:45:46 | MASTER-OAFA | (02h 39m 15.27s , -39d 38m 09.8s) | C | 40 | 19.1 | 9050 | 2025-09-10 05:46:34 | MASTER-OAFA | (02h 39m 15.35s , -39d 38m 08.4s) | C | 40 | 19.2 | 9096 | 2025-09-10 05:47:19 | MASTER-OAFA | (02h 39m 15.36s , -39d 38m 07.0s) | C | 40 | 19.2 | 9141 | 2025-09-10 05:48:05 | MASTER-OAFA | (02h 39m 15.41s , -39d 38m 05.9s) | C | 40 | 19.2 | 9187 | 2025-09-10 05:48:51 | MASTER-OAFA | (02h 39m 15.48s , -39d 38m 04.6s) | C | 40 | 19.1 | 9233 | 2025-09-10 05:49:36 | MASTER-OAFA | (02h 39m 15.55s , -39d 38m 03.0s) | C | 40 | 19.2 | 9278 | 2025-09-10 05:50:22 | MASTER-OAFA | (02h 39m 15.61s , -39d 38m 01.9s) | C | 40 | 19.3 | 9601 | 2025-09-10 05:55:35 | MASTER-OAFA | (02h 33m 49.69s , -39d 37m 50.4s) | C | 60 | 19.4 | 9677 | 2025-09-10 05:56:51 | MASTER-OAFA | (02h 33m 54.50s , -39d 38m 48.0s) | C | 60 | 19.3 | 9755 | 2025-09-10 05:58:09 | MASTER-OAFA | (02h 33m 49.60s , -39d 39m 45.9s) | C | 60 | 19.4 | 9831 | 2025-09-10 05:59:24 | MASTER-OAFA | (02h 44m 18.55s , -39d 39m 18.6s) | C | 60 | 19.5 | 9907 | 2025-09-10 06:00:40 | MASTER-OAFA | (02h 44m 16.33s , -39d 37m 58.7s) | C | 60 | 19.5 | 9991 | 2025-09-10 06:02:05 | MASTER-OAFA | (02h 44m 16.40s , -39d 39m 33.5s) | C | 60 | 19.5 | 12839 | 2025-09-10 06:49:33 | MASTER-OAFA | (02h 44m 22.49s , -39d 36m 17.7s) | C | 60 | 18.5 | 12914 | 2025-09-10 06:50:48 | MASTER-OAFA | (02h 44m 16.60s , -39d 37m 14.4s) | C | 60 | 18.5 | 12995 | 2025-09-10 06:52:08 | MASTER-OAFA | (02h 44m 16.65s , -39d 36m 12.0s) | C | 60 | 18.5 | 21335 | 2025-09-10 09:11:08 | MASTER-OAFA | (02h 34m 24.31s , -39d 47m 18.9s) | C | 60 | 18.1 | 21411 | 2025-09-10 09:12:25 | MASTER-OAFA | (02h 44m 52.99s , -39d 48m 13.6s) | C | 60 | 18.2 | 21650 | 2025-09-10 09:16:23 | MASTER-OAFA | (02h 34m 27.58s , -39d 47m 23.8s) | C | 60 | 18.0 | 21725 | 2025-09-10 09:17:39 | MASTER-OAFA | (02h 44m 51.45s , -39d 48m 38.3s) | C | 60 | 18.3 | 21885 | 2025-09-10 09:20:18 | MASTER-OAFA | (02h 34m 24.84s , -39d 48m 09.4s) | C | 60 | 18.0 | 23662 | 2025-09-10 09:49:55 | MASTER-OAFA | (02h 44m 54.42s , -39d 48m 19.8s) | C | 60 | 18.1 | 23738 | 2025-09-10 09:51:12 | MASTER-OAFA | (02h 44m 57.09s , -39d 46m 48.8s) | C | 60 | 18.0 | 23814 | 2025-09-10 09:52:27 | MASTER-OAFA | (02h 44m 52.46s , -39d 47m 38.5s) | C | 60 | 17.9 | 108092 | 2025-09-11 09:17:15 | MASTER-OAFA | (02h 34m 29.12s , -39d 47m 30.9s) | C | 40 | 19.6 | 108137 | 2025-09-11 09:18:01 | MASTER-OAFA | (02h 34m 29.19s , -39d 47m 30.2s) | C | 40 | 19.5 | 108183 | 2025-09-11 09:18:46 | MASTER-OAFA | (02h 34m 29.25s , -39d 47m 29.8s) | C | 40 | 19.5 | 108235 | 2025-09-11 09:19:39 | MASTER-OAFA | (02h 34m 29.29s , -39d 47m 29.2s) | C | 40 | 19.5 | 108281 | 2025-09-11 09:20:24 | MASTER-OAFA | (02h 34m 29.36s , -39d 47m 28.6s) | C | 40 | 19.5 | 108326 | 2025-09-11 09:21:10 | MASTER-OAFA | (02h 34m 29.44s , -39d 47m 28.0s) | C | 40 | 19.6 | 108378 | 2025-09-11 09:22:02 | MASTER-OAFA | (02h 34m 29.50s , -39d 47m 27.5s) | C | 40 | 19.5 | 108424 | 2025-09-11 09:22:48 | MASTER-OAFA | (02h 34m 29.55s , -39d 47m 27.0s) | C | 40 | 19.5 | 108469 | 2025-09-11 09:23:33 | MASTER-OAFA | (02h 34m 29.62s , -39d 47m 26.2s) | C | 40 | 19.5 | 108521 | 2025-09-11 09:24:24 | MASTER-OAFA | (02h 34m 29.66s , -39d 47m 25.8s) | C | 40 | 19.5 | 108567 | 2025-09-11 09:25:10 | MASTER-OAFA | (02h 34m 29.74s , -39d 47m 25.1s) | C | 40 | 19.6 | 108612 | 2025-09-11 09:25:56 | MASTER-OAFA | (02h 34m 29.81s , -39d 47m 24.6s) | C | 40 | 19.5 | 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/41789. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39854] EP250911a: Einstein Probe detection of an X-ray transient
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41788 SUBJECT: EP250911a: Einstein Probe detection of an X-ray transient DATE: 25/09/11 09:56:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. F. Liang (PMO), Q. Y. Wu, W. D. Zhang(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 EP250911a. The transient triggered EP-WXT (ID: 01709240741) at 2025-09-11T08:58:28 (UTC). The WXT position of the source is R.A. = 357.532 deg, DEC = 29.286 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. = 357.5204 deg, DEC = 29.3018 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 are 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/41788. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39853] GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41787 SUBJECT: GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 DATE: 25/09/11 09:25:59 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) and D. B. Malesani (DAWN/NBI and Radboud) report: We carried out a full reduction of the spectrum of GRB 250404A / EP250404a observed with the GMG-2.4m telescope (Li et al., GCN 40084) using the most up-to-date calibrations and complete pipeline procedures. A Ly-alpha absorption feature at ~4400 AA was reported by the Xinglong-2.16 m telescope (Zhu et al., GCN 40061). In the GMG spectrum, the region around ~4400 AA exhibits a smooth continuum, and no typical Ly-alpha absorption feature is identified. However, we identified multiple metal absorption features, including Si IV at 1394 AA, Si IV at 1403 AA, Si II at 1527 AA, C IV at 1549 AA, Fe II at 1608 AA, Al II at 1671 AA, Al III at 1855 AA, Al III at 1863 AA, Zn II/Cr II at 2026 AA, Zn II/Cr II at 2062 AA, Fe II at 2344 AA, Fe II at 2374 AA, and Fe II at 2383 AA. These features consistently indicate a redshift of z = 1.88. In summary, we conclude that the redshift of the transient is z = 1.88 (see Figure B1 of Yin et al., 2025; doi:10.3847/2041-8213/adf552). We are grateful to D. B. Malesani for kindly pointing out the issue with the redshift determination. We apologize for any confusion that our preliminary report may have caused. View this GCN Circular online at https://gcn.nasa.gov/circulars/41787. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39852] LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41786 SUBJECT: LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate DATE: 25/09/11 08:46:44 GMT FROM: Iara Tosta e Melo at UniCT <iara.tosta.melo(a)dfa.unict.it> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250911ac during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-09-11 07:46:39.272 UTC (GPS time: 1441612017.272). The candidate was found by the Aframe [1], cWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines. S250911ac is an event of interest because its false alarm rate, as estimated by the online analysis, is 6e-09 Hz, or about one in 5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250911ac The initial classification of the GW signal, in order of descending probability, based on chirp-mass information only [5], is BBH (84%), NSBH (13%), Terrestrial (4%), or BNS (<1%). Noise transients (glitches) were present in LIGO Hanford detector data within two seconds of the event time, which may affect the parameters or the significance of the candidate. Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [7] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [7] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 7%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 27 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 1012 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1102 +/- 300 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] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010 [2] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [3] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [5] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [6] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [8] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41786. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39851] GRB 250903A: SVOM/ECLAIRs refined analysis
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41785 SUBJECT: GRB 250903A: SVOM/ECLAIRs refined analysis DATE: 25/09/11 08:37:06 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Nicolas Dagoneau (CEA), Jean-Luc Atteia (IRAP), Floriane Cangemi (APC), Tais Maiolino (LUPM), Claire Guépin-Detrigne (LUPM) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250903A (SVOM burst-id sb25090304). The burst that triggered ECLAIRs onboard (GCN 41677) was detected in the first trigger cycle that followed the SAA exit. Consequently, the precise duration of the event cannot be determined. The exposures in which the burst was detected onboard have durations spanning from 5.12 to 40.96 s starting from T0-13 s to T0+3 s (T0 = 2025-09-03T17:24:56 UTC). The time-averaged spectrum (from T0-8.7s to T0+7.5s) in the energy range 4-120 keV is best fit by a cutoff power-law with a photon index 1.28 +/- 0.22 and a peak energy Epeak 38 +/- 15 keV. With this model, the total fluence in the 4-120 keV band is (7.66 -5.78/+0.90)e-7 erg/cm^2. With a redshift of z = 1.59 (GCN 41691), the burst isotropic energy Eiso (from 1 keV to 10 MeV in its rest frame) is 6.4e51 erg. This is only a lower bound since we may have missed the beginning of the burst when SVOM was in the SAA. Still, this value makes this GRB consistent with type II GRBs in the 'Amati' relation diagram (Amati et al. 2002). The spectrum is also well fit by a simple power-law model with a photon index 1.62 +/- 0.08. With this model, the total fluence in the 4-120 keV band is (9.15 -1.74/+1.06) e-7 erg/cm^2. All the quoted errors are at the 90% 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. The SVOM/ECLAIRs point of contact for this burst is: Nicolas Dagoneau (CEA) (nicolas.dagoneau at cea.fr). View this GCN Circular online at https://gcn.nasa.gov/circulars/41785. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39850] GRB 250911A: Enhanced Swift-XRT position
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41784 SUBJECT: GRB 250911A: Enhanced Swift-XRT position DATE: 25/09/11 06:48:39 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 2239 s of XRT Photon Counting mode data and 6 UVOT images for GRB 250911A, 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 = 263.75012, -16.85418 which is equivalent to: RA (J2000): 17h 35m 00.03s Dec (J2000): -16d 51' 15.0" 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/41784. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39849] GRB 250911A: Swift-XRT observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41783 SUBJECT: GRB 250911A: Swift-XRT observations DATE: 25/09/11 05:16:58 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M. Perri (SSDC & INAF-OAR), P.A. Evans (U. Leicester) and J.A. Kennea (PSU) report on behalf of the Swift-XRT team: The XRT began observing the field of GRB 250911A at 02:25:07.6 UT, 3441.5 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 263.75102, -16.85448 which is equivalent to: RA(J2000) = 17h 35m 00.24s Dec(J2000) = -16d 51' 16.1" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 53 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (3.44 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 4.3 (+3.44/-2.88) x 10^21 cm^-2 (90% confidence). View this GCN Circular online at https://gcn.nasa.gov/circulars/41783. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39848] GRB 250911A: COLIBRÍ optical counterpart candidate
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41782 SUBJECT: GRB 250911A: COLIBRÍ optical counterpart candidate DATE: 25/09/11 03:50:26 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Camila Angulo (UNAM), Sarah Antier (OCA), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the Swift GRB 250911A (Palmer et al., GCN Circ. 41781) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed at 2025-09-11 02:41 UTC (1.2 hours after the trigger) and obtained 60 second exposures in the r and z filters. The data were 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. We detect an uncatalogued source consistent with the BAT 3.0 arcmin error circle (Palmer et al., GCN Circ. 41781) at: RA(J2000) = 17:35:00.05 = 263.75021 degrees Dec(J2000) = -16:51:14.40 = -16.8540 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitudes derived for that source are: r = 19.19 +/- 0.08 z = 18.46 +/- 0.10 We suggest that this source is the optical counterpart of the GRB. Further observations are ongoing. 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/41782. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0