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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[vsnet-grb-info 39847] GRB 250911A: Swift detection of a burst
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41781 SUBJECT: GRB 250911A: Swift detection of a burst DATE: 25/09/11 01:43:39 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> N. J. Klingler (GSFC/UMBC/CRESSTII), S. Dichiara (PSU), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:27:46 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250911A (trigger=1348587). Due to an observing constraint Swift did not immediately slew to the burst. The BAT on-board calculated location is RA, Dec 263.762, -16.844 which is RA(J2000) = 17h 35m 03s Dec(J2000) = -16d 50' 36" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 20 sec. The peak count rate was ~1200 counts/sec (15-350 keV), at ~3 sec after the trigger. Due to an observing constraint, Swift will not slew until T0+50 minutes. There will be no XRT or UVOT data until this time. Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41781. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39846] LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41780 SUBJECT: LIGO/Virgo/KAGRA S250906ca: Updated Sky localization DATE: 25/09/10 19:56:00 GMT FROM: natalie.williams(a)uni-potsdam.de The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250906ca (GCN Circular 41745). 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/S250906ca For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 516 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1121 +/- 266 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/41780. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39845] GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41779 SUBJECT: GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786) DATE: 25/09/10 19:25:58 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 779223130 at 18:52:05 on 10 Sept. 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 74.2 deg Decl.(2000.0) = -47.5 deg The 1 sigma statistical error radius is 3.6 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250910786/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250910786/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250910786/json View this GCN Circular online at https://gcn.nasa.gov/circulars/41779. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39844] GRB 250910B: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41778 SUBJECT: GRB 250910B: Fermi GBM Final Real-time Localization DATE: 25/09/10 19:02:42 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 18:52:05 UT on 10 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250910B (trigger 779223130.045678 / 250910786). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 80.2, Dec = -46.4 (J2000 degrees, equivalent to J2000 05h 20m, -46d 23'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 35.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910786/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910786/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910786/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41778. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39843] GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41777 SUBJECT: GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations DATE: 25/09/10 11:26:08 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> M. Garnichey (LUX-Paris Obs.), V. D'Elia (ASI-SSDC), B. Schneider (LAM), A. J. Levan (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF-IAPS), S. D. Vergani (LUX-Paris Obs.) report on behalf the Stargate collaboration: We observed the field of GRB 250910A / EP250910a (Ma et al., GCN 41769; Götz et al. GCN 41770; Wu et al., GCN 41772; Li et al., GCN 41774; Liu et al., GCN 41776) using the ESO VLT UT4 (Yepun) equipped with the HAWK-I NIR camera. We obtained 15 min imaging in the J band, beginning on 2025-09-10 at 08:28 UT (5.2 hr post-trigger). Within the 20"-radius EP/FXT error circle (Liu et al., GCN 41776), several objects are visible in the stack of our data. All have an archival optical counterpart in the Legacy Survey (and they are thus not high-redshift candidates). Any of these sources could in principle contain an afterglow contribution, but a new template image is required to isolate any transient flux that might be present in our image. Further observations are planned with HAWK-I. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Julien Drevon. View this GCN Circular online at https://gcn.nasa.gov/circulars/41777. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39842] EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41776 SUBJECT: EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient DATE: 25/09/10 09:08:42 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), H. N. Yang, H. W. Pan (NAO,CAS) on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient, designated EP250910a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2025-09-10T03:16:04 (UTC). The position of the source is R.A. = 39.797 deg, DEC = -39.686 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic). The trigger time and position of this X-ray transient are consistent with that of GRB 250910A (GCN 41769, GCN 41770). The 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.74 x 10^20 cm^-2 and a photon index of 0.8 (+0.3/-0.3) during the flare. The estimated unabsorbed 0.5-4 keV flux of the flare is 1.2 (+0.3/-0.2) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The transient event lasts for 160 seconds. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 39.8048 deg, DEC = -39.6966 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). 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/41776. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39841] GRB 250909B: AstroSat CZTI detection of a long burst
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41775 SUBJECT: GRB 250909B: AstroSat CZTI detection of a long burst DATE: 25/09/10 08:58:31 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long and bright GRB 250909B which was also detected by Konus-Wind (IPN notices). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-09 17:49:11.50 UTC. The measured peak count rate associated with the burst is 701 (+50, -52) counts/s above the background in the combined data of all quadrants, with a total of 3971 (+218, -234) counts. The local mean background count rate was 282 (+4, -4) counts/s. Using cumulative rates, we measure a T90 of 10.1 (+0.9, -0.4) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-09 17:49:10.32 UTC. The measured peak count rate associated with the burst is 1432 (+86, -93) counts/s above the background in the combined data of all quadrants, with a total of 5850 (+337, -369) counts. The local mean background count rate was 1344 (+7, -8) counts/s. We measure a T90 of 9.4 (+0.5, -0.3) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/41775. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39840] GRB 250910A: SVOM/VT optical upper limit
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41774 SUBJECT: GRB 250910A: SVOM/VT optical upper limit DATE: 25/09/10 08:53:25 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> H. L. Li, Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, 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, D. H. Zhao (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Ma et al., GCN 41769). SVOM/VT began observing the field at 2025-09-10T04:00:48 UTC, 0.739 hours after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No credible candidate was detected in our single or stacked images at the SVOM/MXT position (Götz et al., GCN 41770), the three sigma limits are: mid-time | exposure time (s) | band | upper limit (AB) ---------|-------------------|------|----------------- 1.08h | 16*50 | VT_B | 22.8 1.08h | 16*50 | VT_R | 23.3 Our results are consistent with LCO (Wu et al., GCN 41772). The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center 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/41774. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39839] EP250908C: GROND observation of the fading optical counterpart
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41773 SUBJECT: EP250908C: GROND observation of the fading optical counterpart DATE: 25/09/10 08:48:05 GMT FROM: Arne Rau at MPE <arau(a)mpe.mpg.de> Arne Rau (MPE) reports: We observed the position of EP250908C (Zhang et al., GCN 41754) using the Gamma-Ray burst Optical Near-infrared Detector (GROND, Greiner et al. 2008) mounted to the MPG 2.2m telescope at ESO’s La Silla Observatory on 2025-09-10 07:24 UT, i.e. 31.5 hours after the Einstein Probe trigger. The candidate optical counterpart reported by Malesani et al. (GCN 41760) was detected with r’= 23.0+/-0.2 i’ = 22.8+/-0.2 indicating clear fading. The magnitudes are in the AB magnitude system and calibrated against nearby SkyMapper sources. We acknowledge the excellent support of the 2.2m staff, in particular Angel Hempel. View this GCN Circular online at https://gcn.nasa.gov/circulars/41773. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39838] GRB 250910A: LCO optical upper limit
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41772 SUBJECT: GRB 250910A: LCO optical upper limit DATE: 25/09/10 07:43:10 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), A. Saccardi (CEA/Irfu), L. P. Xin (NAOC), J. T. Palmerio (CEA/Irfu), B. Cordier (CEA/Irfu), Y. N. Ma (NAOC), D. Zhao (NAOC) report on behalf of the SVOM mission team: We observed the field of the GRB 250910A detected by SVOM/ECLAIRs (Ma et al., GCN 41769) with the LCO 1m telescope at Cerro Tololo Interamerican Observatory equipped with the Sinistro instrument. Our observation started on 2025-09-10 at 05:03:46 UT (~1.79 hr after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/MXT position (Götz et al., GCN 41770). We derived the following upper limit r > 20.8 mag (5-sigma) calibrated using nearby stars from the UCAC4 catalog and not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41772. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39837] GRB 250909A: AstroSat CZTI detection
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41771 SUBJECT: GRB 250909A: AstroSat CZTI detection DATE: 25/09/10 06:35:24 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long-duration GRB 250909A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41753). The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a burst peak of emission at 2025-09-09 02:33:32.44 UTC. The measured peak count rate associated with the burst is 228 (+61, -66) counts/s above the background in the combined data of all quadrants, with a total of 663 (+255, -303) counts. The local mean background count rate was 1258 (+7, -5) counts/s. We measure a T90 of 8.2 (+2.5, -4.0) s from the cumulative Veto light curve. The source was also faintly detected in the CZT detectors in the 20-200 keV energy range. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/41771. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39836] GRB 250910A: SVOM/MXT possible afterglow detection
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41770 SUBJECT: GRB 250910A: SVOM/MXT possible afterglow detection DATE: 25/09/10 06:18:14 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Götz (CEA), C. Van Hove (IJCLab), M. Moita (CEA) F. Robinet (IJCLab), P. Maggi (ObAS), H. Goto (Kanazawa Univ./CEA), C. Plasse (CEA) , report of behalf of the SVOM/MXT Team: GRB 250910A (Ma et al. GCN# 41769) was observed by SVOM/MXT after an automatic SVOM slew, but due to Earth constraints the observation started at 2025-09-10T05:37:38, about 88 minutes after Tb. Using the on board automatic detection software, MXT detects a faint source at the coordinates R.A. (J2000) = 02h39m18s, Dec (J2000) = -39d39m39s with a 90% C.L. radius of 2.5 arc min (including 25 arc sec systematic error added in quadrature). This position is at 2.8 arc min from the ECLAIRs position. At this time we cannot evaluate the variability of the source. We hence encourage follow-up with other X-ray facilities. The Space 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. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The Burst Advocate (BA) on shift for this alert is Yinuo Ma: mayn(a)bao.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41770. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39835] GRB 250910A: SVOM detection of a faint burst
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41769 SUBJECT: GRB 250910A: SVOM detection of a faint burst DATE: 25/09/10 04:10:10 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Yinuo MA, Donghua ZHAO, Wenjin XIE (NAOC), Li ZHANG (IHEP), Charlotte VAN HOVE(IJCLab) report on behalf of the SVOM mission team: At 2025-09-10T03:16:30 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250910A (SVOM burst-id sb25091001). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 8 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.02 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2025-09-10T03:16:10. The localization of the best alert is R.A., Dec. 39.7665, -39.6758 degrees: R.A. (J2000) = 2h39m03.96s Dec. (J2000) = -39d40m32.94s with a 90% confidence level (C.L.) radius of 9.80 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM/GRM had no significant detection. SVOM slewed to the burst. SVOM/MXT and SVOM/VT were occulted by the Earth. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Yinuo Ma: mayn(a)bao.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41769. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39834] LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41768 SUBJECT: LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate DATE: 25/09/10 00:42:32 GMT FROM: Trang Nguyen <trang.nguyen(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: The trigger S250910b is no longer considered to be a candidate of interest. This candidate was initially identified by one or more early-warning analyses by matching partial signal templates to the data. Analysis of additional data up to the putative merger time, with full signal templates, did not make a significant detection, indicating that the initial candidate was likely due to transient noise. View this GCN Circular online at https://gcn.nasa.gov/circulars/41768. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39833] GRB 250702B: Late time Chandra observations
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41767 SUBJECT: GRB 250702B: Late time Chandra observations DATE: 25/09/09 20:42:37 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (U of Leicester), A. J. Levan (Radboud and Warwick), A. Martin-Carrillo (UCD), P. T. O’Brien (U of Leicester), M. De Pasquale (Univ. Messina), B. P. Gompertz (U. Birmingham), T. Laskar (Utah), D. B. Malesani (DAWN/NBI and Radboud), J. C. Rastinejad (Maryland), S. Schulze (Northwestern), N. R. Tanvir (U of Leicester), P. G. Jonker (Radboud) and D. Watson (DAWN/NBI) report on behalf of a larger collaboration: We observed the position of the gamma-ray and X-ray transient GRB 250702B/EP250702a (Fermi GBM Team, GCNs 40883, 40886, 40890; Cheng et al., GCN 40906) with the Chandra X-ray Observatory through a Director’s Discretionary Time request (PI: Eyles-Ferris) using ACIS-S. Our observation started at 2025-09-05 23:26:41 UT, approximately 65 days after the initial Fermi trigger, and lasted 39.55 ks. At the position of GRB 250702B, we detect the X-ray counterpart (Cheng et al., GCN 40906; Kennea et al., GCN 40919; O’Connor et al., GCN 41309) with a preliminary count rate of ~3.1e-4 ct/s. Assuming the same spectrum as derived from Swift/XRT observations, this corresponds to a flux ~6.7e-15 erg/cm^2/s. This is broadly consistent with the alpha ~ 1.9 decay slope measured in both the Swift/XRT light curve and previous Chandra observations (O’Connor et al., GCN 41309). Further analysis of these data is ongoing. We thank Pat Slane and the Chandra X-ray Center team for approving and scheduling our DDT request. View this GCN Circular online at https://gcn.nasa.gov/circulars/41767. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39832] EP250908b/EP#01709240653: Swift/UVOT Detection
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41766 SUBJECT: EP250908b/EP#01709240653: Swift/UVOT Detection DATE: 25/09/09 20:26:09 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk> A.A. Breeveld (UCL-MSSL) and M. Ferro (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of the EP/WXT detected burst EP250908b (Yin et al., GCN Circ. 41752) 1103 s after the trigger. The afterglow reported by Ma et al. (GCN Circ. 41758) and also detected as source 1 in the Swift/XRT (Evans et al., GCN Circ. 41765), is detected in the initial U-band exposure. The preliminary magnitude using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposure is: Filter T_start(s) T_stop(s) Exp(s) Mag u 1103 2836 1706 20.0 +/- 0.14 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.048 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41766. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39831] EP#01709240653: Swift-XRT observations
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41765 SUBJECT: EP#01709240653: Swift-XRT observations DATE: 25/09/09 16:05:43 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 EP#01709240653, collecting 1.8 ks of Photon Counting (PC) mode data between T0+859 s and T0+6.8 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 2 uncatalogued X-ray sources * 0 known X-ray sources Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J194954.4-572931): ================================== RA (J2000.0): 297.4769 = 19 49 54.46 Dec (J2000.0): -57.4921 = -57 29 31.6 Error: 5.7 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 1.6 arcmin from the Einstein Probe/WXT position. Mean rate: 0.0334 [+0.0053, -0.0052] ct s^-1 Mean flux: (8.9 +/- 1.4)e-13 erg cm^-2 s^-1 Peak rate: 0.085 +/- 0.025 ct s^-1 Peak flux: (2.25 +/- 0.66)e-12 erg cm^-2 s^-1 ECF: 2.65e-11 erg cm^-2 ct^-1 assuming NH=4.43e+20 cm^-2, gamma=2.38 determined from a spectral fit. XMM UL: 2.1e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 0.3-sigma above this 3-sigma upper limit. The source may be fading, at the 1.9-sigma level. There are 2 2MASS objects within the source's 3-sigma error radius. Source 5 (SWIFT J194951.3-573147): ================================== RA (J2000.0): 297.4638 = 19 49 51.31 Dec (J2000.0): -57.5299 = -57 31 47.6 Error: 6.8 (arcsec, radius, 90% confidence). Detect flag: POOR Distance: 1.8 arcmin from the Einstein Probe/WXT position. Mean rate: (-1.0 +/- -1.0)e0 ct s^-1 Mean flux: (-4.3 +/- -4.3)e-11 erg cm^-2 s^-1 Peak rate: (6.0 [+4.5, -3.2])e-3 ct s^-1 Peak flux: (2.6 [+1.9, -1.4])e-13 erg cm^-2 s^-1 XMM UL: 1.9e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. There is 1 2MASS object within the source's 3-sigma error radius. 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_FIELD00071. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41765. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39830] The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41764 SUBJECT: The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg DATE: 25/09/09 10:10:04 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, M. H. Zhang (NAO, CAS), Y.-H. I. Yin (NJU), X. X. Sun, T. Y. Liu, H. Y. Ren, H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709240674 at the time of 2025-09-09T09:16:57 is associated with the cataclysmic binary SS Cyg. The estimated flux of the flare is around 2.6 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4.0 x 10^32 erg/s. 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/41764. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39829] EP250908c: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41763 SUBJECT: EP250908c: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/09/09 10:00:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. H. Zhang, X. X. Sun, M. J. Liu, H. Y. Ren, T. Y. Liu (NAO, CAS), Y.-H. I. Yin (NJU), H. Sun (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250908c was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 41754). Refined analysis of the WXT data shows that the event started at T0=2025-09-08 23:49:53 (UTC) and lasted for about 62 s before the interruption of the autonomous follow-up. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.6 x 10^20 cm^-2 and a photon index of 0.3 (-0.6/+0.6). The derived average unabsorbed 0.5-4 keV flux is 6.2 (-1.4/+2.2) x 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 277 s after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 8.2167, DEC = -50.4612 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent positionally with the WXT transient. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.6 x 10^20 cm^-2 and a photon index of 1.59 (-0.07/+0.07). The absorption from the host galaxy cannot be constrained. The derived average unabsorbed 0.5-10 keV flux is 8.16 (-0.17/+0.21) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/41763. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39828] GRB 250907A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41762 SUBJECT: GRB 250907A: CALET Gamma-Ray Burst Monitor detection DATE: 25/09/09 07:19:26 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> M. L. Cherry (LSU), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 250907A (GECAM-B detection: Wang et al., GCN Circ. 41749) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 22:00:54.59 UTC on 7 September 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1441317257/index.html) The burst signal was seen by all CGBM detectors. Because of a problem with the ground alert processing script, the GCN notice was not distributed automatically for this event. The burst light curve shows a single pulse that starts at T-0.9 sec, peaks at T+0.4 sec, and ends at T+5.9 sec. The T90 and T50 durations measured by the SGM data are 6.0 +/- 0.6 sec and 3.0 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1441317257/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/41762. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39827] EP250908c: SVOM/VT optical observation
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41761 SUBJECT: EP250908c: SVOM/VT optical observation DATE: 25/09/09 05:22:53 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 performed a Target of Opportunity observation of EP250908c detected by EP/WXT (Zhang et al., GCN 41754). SVOM/VT began observing the field at 2025-09-09T00:29:02 UTC, 0.636 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data availible, the optical counterpart (Malesani et al., GCN 41760) was clearly detected in both VT_B and VT_R. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 0.987 | 16*50 | VT_B | 20.73 | 0.05 0.987 | 15*50 | VT_R | 19.76 | 0.04 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center 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/41761. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39826] EP250908c: VLT/FORS2 optical counterpart identification
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41760 SUBJECT: EP250908c: VLT/FORS2 optical counterpart identification DATE: 25/09/09 04:22:14 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), M. Garnichey (LUX-Paris Obs.), D. Xu (NAOC), L. Cotter (UCD), J. A. Chacon (PUC), L. Izzo (INAF/OACn and DARK/NBI), J. An (NAOC), report on behalf the Stargate collaboration: We observed the field of the fast X-ray transient EP250908c (Zhang et al., GCN 41754) using the ESO VLT UT1 (Antu) equipped with the FORS2 instrument. In a 150 s I-band observation with mid-time 2.76 hr after the high-energy trigger, we detect an uncatalogued object at J2000 coordinates: RA = 00:32:52.18 Dec = -50:27:39.8 This position is consistent with the EP/FXT X-ray location (Zhang et al., GCN 41754) and nothing is visible at this location in archival imaging from the Legacy Survey. We thus conclude that this is the optical afterglow of EP250908c. Using nearby calibrator stars from the SkyMapper catalog, we measure for the counterpart a magnitude i = 20.40 +/- 0.1 (AB), where most of the error is due to calibration scatter. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Marcela Espinoza, Julien Drevon, Marco Berton and Jonathan Smoker. View this GCN Circular online at https://gcn.nasa.gov/circulars/41760. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39825] EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41759 SUBJECT: EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758) DATE: 25/09/09 03:54:18 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 performed a Target of Opportunity observation of EP250908b detected by EP/WXT (Yin et al., GCN 41752). SVOM/VT began observing the field at 2025-09-08T19:29:58 UTC, 1.061 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data availible, an uncatalogued fading optical candidate (Ma et al., GCN 41758) within the error box of EP/FXT, compared to Legacy survey, was clearly detected in both VT_B and VT_R at R.A., Dec 297.476836, -57.4930538 degrees: RA (J2000) = 19:49:54.44 Dec (J2000) = -57:29:34.99 with an uncertainty of 0.5 arcsec. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 1.491 | 57*50 | VT_B | 21.13 | 0.06 3.103 | 32*50 | VT_B | 22.5 | 0.2 1.484 | 60*50 | VT_R | 20.66 | 0.06 3.103 | 32*50 | VT_R | 21.4 | 0.1 Our photometry was not corrected for Galactic extinction. We proposed that this is the optical candidate for the trigger. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center 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/41759. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39824] EP250908b: SVOM/VT optical candidate
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41758 SUBJECT: EP250908b: SVOM/VT optical candidate DATE: 25/09/09 03:20:04 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 performed a Target of Opportunity observation of EP250908b detected by EP/WXT (Yin et al., GCN 41752). SVOM/VT began observing the field at 2025-09-08T19:29:58 UTC, 1.061 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data availible, an uncatalogued fading optical candidate within the error box of EP/FXT, compared to Legacy survey, was clearly detected in both VT_B and VT_R. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 1.491 | 57*50 | VT_B | 21.13 | 0.06 3.103 | 32*50 | VT_B | 22.5 | 0.2 1.484 | 60*50 | VT_R | 20.66 | 0.06 3.103 | 32*50 | VT_R | 21.4 | 0.1 Our photometry was not corrected for Galactic extinction. We proposed that this is the optical candidate for the trigger. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center 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/41758. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39823] The EP-WXT trigger EP250908a/01709240652 is not a real source
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41757 SUBJECT: The EP-WXT trigger EP250908a/01709240652 is not a real source DATE: 25/09/09 03:14:28 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Zhou (HUST), Y. H. Cheng (SWIFAR, YNU), S. L. Wang (YNU), T. Y. Liu, H. Q. Cheng, C. C. Jin (NAO, CAS) report on behalf of the Einstein Probe (EP) team The EP-WXT trigger EP250908a/01709240652 at the time of 2025-09-08T15:43:42 is not a real source based on ground data analysis. View this GCN Circular online at https://gcn.nasa.gov/circulars/41757. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39822] EP250908c: Global MASTER-Net observations report
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41756 SUBJECT: EP250908c: Global MASTER-Net observations report DATE: 25/09/09 03:01:15 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 EP250908c ( EP Team et al., GCN 41754) errorbox 385 sec after trigger time at 2025-09-08 23:57:19 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 66 deg. The sun altitude is -21.0 deg. The galactic latitude b = -67 deg., longitude l = 309 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2987645 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 426 | 2025-09-08 23:57:19 | MASTER-OAFA | (00h 32m 33.78s , -50d 34m 25.0s) | C | 80 | 19.4 | 517 | 2025-09-08 23:58:46 | MASTER-OAFA | (00h 32m 33.61s , -50d 34m 21.6s) | C | 90 | 19.4 | 623 | 2025-09-09 00:00:22 | MASTER-OAFA | (00h 32m 33.35s , -50d 34m 18.6s) | C | 110 | 19.4 | 704 | 2025-09-09 00:02:17 | MASTER-OAFA | (00h 32m 33.16s , -50d 34m 16.5s) | C | 40 | 19.0 | 750 | 2025-09-09 00:03:03 | MASTER-OAFA | (00h 32m 33.01s , -50d 34m 15.4s) | C | 40 | 19.0 | 795 | 2025-09-09 00:03:49 | MASTER-OAFA | (00h 32m 32.90s , -50d 34m 14.1s) | C | 40 | 19.0 | 842 | 2025-09-09 00:04:35 | MASTER-OAFA | (00h 32m 32.81s , -50d 34m 12.7s) | C | 40 | 18.9 | 887 | 2025-09-09 00:05:20 | MASTER-OAFA | (00h 32m 32.71s , -50d 34m 11.3s) | C | 40 | 19.0 | 932 | 2025-09-09 00:06:06 | MASTER-OAFA | (00h 32m 32.57s , -50d 34m 10.1s) | C | 40 | 19.0 | 978 | 2025-09-09 00:06:51 | MASTER-OAFA | (00h 32m 32.42s , -50d 34m 09.1s) | C | 40 | 19.0 | 1023 | 2025-09-09 00:07:37 | MASTER-OAFA | (00h 32m 32.31s , -50d 34m 08.0s) | C | 40 | 18.9 | 1069 | 2025-09-09 00:08:23 | MASTER-OAFA | (00h 32m 32.23s , -50d 34m 06.6s) | C | 40 | 18.9 | 1116 | 2025-09-09 00:09:09 | MASTER-OAFA | (00h 32m 32.14s , -50d 34m 05.4s) | C | 40 | 18.9 | 1161 | 2025-09-09 00:09:55 | MASTER-OAFA | (00h 32m 32.02s , -50d 34m 04.0s) | C | 40 | 18.9 | 1207 | 2025-09-09 00:10:40 | MASTER-OAFA | (00h 32m 31.90s , -50d 34m 03.0s) | C | 40 | 19.0 | 1253 | 2025-09-09 00:11:26 | MASTER-OAFA | (00h 32m 31.80s , -50d 34m 01.9s) | C | 40 | 19.0 | 1298 | 2025-09-09 00:12:12 | MASTER-OAFA | (00h 32m 31.67s , -50d 34m 01.1s) | C | 40 | 18.9 | 1344 | 2025-09-09 00:12:57 | MASTER-OAFA | (00h 32m 31.57s , -50d 33m 59.7s) | C | 40 | 18.9 | 1390 | 2025-09-09 00:13:43 | MASTER-OAFA | (00h 32m 31.45s , -50d 33m 58.3s) | C | 40 | 19.0 | 1436 | 2025-09-09 00:14:29 | MASTER-OAFA | (00h 32m 31.33s , -50d 33m 57.1s) | C | 40 | 18.9 | 1481 | 2025-09-09 00:15:15 | MASTER-OAFA | (00h 32m 31.23s , -50d 33m 56.1s) | C | 40 | 19.0 | 1528 | 2025-09-09 00:16:01 | MASTER-OAFA | (00h 32m 31.11s , -50d 33m 54.9s) | C | 40 | 18.9 | 1573 | 2025-09-09 00:16:46 | MASTER-OAFA | (00h 32m 31.00s , -50d 33m 53.6s) | C | 40 | 18.9 | 1618 | 2025-09-09 00:17:32 | MASTER-OAFA | (00h 32m 30.90s , -50d 33m 52.2s) | C | 40 | 18.8 | 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/41756. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39821] Fermi GRB 250909A: Global MASTER-Net observations report
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41755 SUBJECT: Fermi GRB 250909A: Global MASTER-Net observations report DATE: 25/09/09 02:45:32 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-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 250909A ( Fermi GBM team, GCN 41753) errorbox 31 sec after notice time and 68 sec after trigger time at 2025-09-09 02:34:37 UT, with upper limit up to 15.3 mag. Observations started at twilight. The observations began at zenith distance = 17 deg. The sun altitude is -7.8 deg. The galactic latitude b = 1 deg., longitude l = 168 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2987637 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 74 | 2025-09-09 02:34:37 | MASTER-Tavrida | (05h 35m 20.66s , +41d 15m 12.7s) | C | 10 | 14.4 | 91 | 2025-09-09 02:34:50 | MASTER-Tavrida | (05h 35m 20.96s , +41d 15m 12.4s) | C | 20 | 15.1 | 124 | 2025-09-09 02:35:22 | MASTER-Tavrida | (05h 23m 43.51s , +41d 45m 12.1s) | C | 20 | 15.2 | 154 | 2025-09-09 02:35:22 | MASTER-Tavrida | (05h 23m 43.50s , +41d 45m 12.1s) | C | 80 | 15.3 | Coadd 199 | 2025-09-09 02:35:22 | MASTER-Tavrida | (05h 23m 43.51s , +41d 45m 12.2s) | C | 170 | 15.3 | Coadd 152 | 2025-09-09 02:35:45 | MASTER-Tavrida | (05h 23m 43.26s , +41d 45m 11.6s) | C | 30 | 15.0 | 184 | 2025-09-09 02:36:17 | MASTER-Tavrida | (05h 23m 43.04s , +41d 45m 10.9s) | C | 30 | 14.6 | 221 | 2025-09-09 02:36:50 | MASTER-Tavrida | (05h 23m 42.76s , +41d 45m 10.4s) | C | 40 | 15.1 | 276 | 2025-09-09 02:36:50 | MASTER-Tavrida | (05h 23m 42.74s , +41d 45m 10.4s) | C | 150 | 14.7 | Coadd 269 | 2025-09-09 02:37:32 | MASTER-Tavrida | (05h 23m 42.35s , +41d 45m 09.7s) | C | 50 | 15.1 | 327 | 2025-09-09 02:38:25 | MASTER-Tavrida | (05h 23m 41.85s , +41d 45m 08.4s) | C | 60 | 14.7 | 395 | 2025-09-09 02:39:28 | MASTER-Tavrida | (05h 23m 41.29s , +41d 45m 06.9s) | C | 70 | 14.5 | 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/41755. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39820] EP250908c: Einstein Probe detection of an X-ray transient
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41754 SUBJECT: EP250908c: Einstein Probe detection of an X-ray transient DATE: 25/09/09 02:45:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. H. Zhang, M. J. Liu (NAO, CAS), Y.-H. I. Yin (NJU), X. X. Sun, T. Y. Liu, H. Y. Ren, H. Sun (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 EP250908c. The transient triggered EP-WXT (ID: 01709240659) at 2025-09-08T23:50:54 (UTC). The WXT position of the source is R.A. = 8.226 deg, DEC = -50.447 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. = 8.2170 deg, DEC = -50.4633 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 is 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/41754. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39819] GRB 250909A: Fermi GBM Final Real-time Localization
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41753 SUBJECT: GRB 250909A: Fermi GBM Final Real-time Localization DATE: 25/09/09 02:43:59 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 02:33:28 UT on 9 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250909A (trigger 779078013.882702 / 250909107). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 78.8, Dec = 39.5 (J2000 degrees, equivalent to J2000 05h 15m, 39d 30'), with a statistical uncertainty of 3.3 degrees. The angle from the Fermi LAT boresight is 85.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250909107/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250909107/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250909107/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41753. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39818] EP250908b: EP-WXT detection of a fast X-ray transient and EP-FXT observation
by GCN Circulars 09 Sep '25

09 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41752 SUBJECT: EP250908b: EP-WXT detection of a fast X-ray transient and EP-FXT observation DATE: 25/09/09 02:42:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (NJU), M. H. Zhang, M. J. Liu, X. X. Sun, T. Y. Liu, H. Y. Ren, H. Sun (NAO, CAS), 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 EP250908b. The transient triggered EP-WXT (ID: 01709240653) at 2025-09-08T18:26:19 (UTC). The WXT position of the source is R.A. = 297.534 deg, DEC = -57.505 deg (J2000) with an uncertainty of 2.5 arcmin in radius (90% C.L. statistical and systematic). The WXT data shows that the event started at T0=2025-09-08T18:26:08 (UTC) and lasted for about 13 s before the interruption of the autonomous follow-up. The WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 1.59 x 10^21 cm^-2 and a photon index of 1.14 (-0.45/+0.45). The derived peak unabsorbed 0.5-4 keV flux is 8.14 (-1.60/+2.00) x 10^-9 erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 164s after T0. On-ground analysis of the FXT data found a fading uncatalogued source at R.A. = 297.4784, DEC = -57.4938 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 1.59 (-0.76/+0.76) x 10^21 cm^-2 and a photon index of 2.02 (-0.23/+0.23). The derived average unabsorbed 0.5-10 keV flux is 1.10 (-0.09/+0.09) x 10^-12 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/41752. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39817] EP#01709240652 (possibly EP250908a): FTW optical and NIR observations
by GCN Circulars 08 Sep '25

08 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41751 SUBJECT: EP#01709240652 (possibly EP250908a): FTW optical and NIR observations DATE: 25/09/08 23:54:00 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Xander Hall (Carnegie Mellon U.), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the 90% localization of EP/WXT trigger 01709240652 (possibly EP250908a) for 10 x 180 s in the r, i, and J-band simultaneously with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW). Our observations started at 2025-09-08T21:33:56 (0.23 days after trigger). We performed difference imaging with i-band templates from PS1 and J-band templates from UKIDSS. We do not detect any new sources in the difference images. The mean 3-sigma depth of our J band difference is J > 20.4 AB mag, calibrated against the 2MASS catalog and not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41751. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39816] LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
by GCN Circulars 08 Sep '25

08 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41750 SUBJECT: LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate DATE: 25/09/08 15:54:52 GMT FROM: Mayara Hilgert Pacheco at LIGO <mayara.pacheco(a)inpe.br> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250908y during real-time processing of data from LIGO Hanford Observatory (H1) and Virgo Observatory (V1) at 2025-09-08 14:34:28.958 UTC (GPS time: 1441377286.958). The candidate was found by the GstLAL [1] analysis pipeline. S250908y is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.1e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250908y The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%). 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%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] 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 <1%. 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 [3], distributed via GCN and SCiMMA notices about 45 minutes after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 50 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 11002 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1280 +/- 403 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] 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 [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41750. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39815] GRB 250907A: GECAM-B detection
by GCN Circulars 08 Sep '25

08 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41749 SUBJECT: GRB 250907A: GECAM-B detection DATE: 25/09/08 15:18:41 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a bright long burst GRB 250907A at 2025-09-07T22:00:52.850 UTC (denoted as T0), which is also detected by Konus-Wind. According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 36.5 +0.5/-3.0 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb250907A.png GECAM-B localized this burst to the following position (J2000): Ra: 337.2 deg Dec: -9.0 deg Err: 1.3 deg (1-sigma, statistical only) The time-averaged spectrum from T0-5 s to T0+40 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.08 +0.14/-0.12 and the cutoff energy, parameterized as Epeak, is 535 +192/-129 keV. The event fluence (10-1000 keV) in this time interval is (7.57 +0.51/-0.61)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 250907A is shown at: https://www.bursthub.cn//admin/static/gecambgrb250907A_amati.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/41749. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39814] GRB 250905A: Swift-BAT refined analysis
by GCN Circulars 08 Sep '25

08 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41748 SUBJECT: GRB 250905A: Swift-BAT refined analysis DATE: 25/09/08 15:16:06 GMT FROM: D. R. Sadaula at NASA GSFC <dev.r.sadaula(a)nasa.gov> T. Parsotan (GSFC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250905A (trigger #1347265) (Brivio, et al., GCN Circ. 41714). The BAT ground-calculated position is RA, Dec = 232.943, 0.789 deg which is RA(J2000) = 15h 31m 46.3s Dec(J2000) = +00d 47' 19.6" with an uncertainty of 3.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 74%. The BAT light curve showed a complex structure with multiple peaks. The burst lasted about 70 sec. T90 (15-350 keV) is 48.00 +- 50.60 sec (estimated error including systematics). The time-averaged spectrum from T-15.10 to T+64.89 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.65 +- 0.67. The fluence in the 15-150 keV band is 4.1 +- 1.4 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+8.40 sec in the 15-150 keV band is 0.27 +- 0.16 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1347265 View this GCN Circular online at https://gcn.nasa.gov/circulars/41748. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39813] Fermi-LAT Gamma-ray Observations of IceCube-250905A
by GCN Circulars 08 Sep '25

08 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41747 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250905A DATE: 25/09/08 12:34:22 GMT FROM: chiara.bartolini-1(a)unitn.it C.Bartolini (Univ. of Trento & INFN Bari), L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250905A neutrino event (GCN 41731) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2025-09-05 at 20:08:36.00 UTC (T0) with J2000 position RA = 348.31 (+0.93, -1.09)deg, Decl. = 38.87 (+0.78, -0.86) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250905A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC250905A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250905A best-fit position, the >100 MeV flux upper limit (95% confidence) is <3.4e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <1.7e-08 (<1.5e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is C. Bartolini (chiara.bartolini at ba.infn.it). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/41747. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39812] GRB 250903A: Swift-XRT afterglow detection
by GCN Circulars 08 Sep '25

08 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41746 SUBJECT: GRB 250903A: Swift-XRT afterglow detection DATE: 25/09/08 09:47:11 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Perri (SSDC & INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 250903A. We searched for X-ray sources in 2.4 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 6.3 ks, obtained between T0+12.7 ks and T0+344.1 ks. Four uncatalogued X-ray sources are detected within the estimated 3-sigma SVOM/ECLAIRs error region (509 arcsec), of which one ("Source 1") is fading with >3-sigma significance and its position is consistent with the optical afterglow (An et al., GCN 41679). Therefore, this is the GRB afterglow. Using 2370 s of PC mode data and 3 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 356.79798, -75.96644 which is equivalent to: RA (J2000): 23h 47m 11.52s Dec(J2000): -75d 57' 59.2" with an uncertainty of 3.0 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=0.9 (+/-0.9). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.95 (+0.73, -0.21). The best-fitting absorption column is consistent with the Galactic value of 4.7 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4 (+/-10) x 10^20 cm^-2 Galactic foreground: 4.7 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.95 (+0.73, -0.21) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/03000070. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00034. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41746. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39811] LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
by GCN Circulars 07 Sep '25

07 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41745 SUBJECT: LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate DATE: 25/09/07 18:01:44 GMT FROM: Mayara Hilgert Pacheco at LIGO <mayara.pacheco(a)inpe.br> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250906ca during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-06 12:23:59.099 UTC (GPS time: 1441196657.099). Automated LVK preliminary notices as well as this initial circular were delayed by a day due to the consequences of a power outage in our main computing center for processing low-latency alerts. The candidate was found by the GstLAL [1] and MBTA [2] analysis pipelines. S250906ca is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.1e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250906ca The classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<1%), or BNS (<1%). 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%. [3] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [3] 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 6%. 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 [4], distributed via GCN and SCiMMA notices about a day after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [4], distributed via GCN and SCiMMA notices about a day 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 520 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1195 +/- 307 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] 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 [2] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [3] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [4] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41745. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39810] IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 07 Sep '25

07 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41744 SUBJECT: IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/09/07 03:51:25 GMT FROM: Yuhua Yao at IceCube/UW-Madison <yyao255(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-250905A (https://gcn.nasa.gov/circulars/41731) in a time range of 1000 seconds centered on the alert event time (2025-09-05 20:00:16.000 UTC to 2025-09-05 20:16:56.000 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-250905A.We report a p-value of 1.00 in this time window. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250905A is 1.5e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 6e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-09-04 20:08:36.000 UTC to 2025-09-06 20:08:36.000 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90%spatial containment region of IceCube-250905A ranges from 1.7e-01 to 1.8e-01 GeV cm^-2 in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/41744. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39809] SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41743 SUBJECT: SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40 DATE: 25/09/06 22:06:11 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. G. Bernardini (INAF, LUPM), M. Gnaoui (IAP), S. Schanne, N. Dagoneau (CEA/Irfu), F. Piron (LUPM), M. Moita (CEA/Irfu) At 2025-09-06T21:18:30 UTC (T0), SVOM/ECLAIRs triggered and located an X-ray transient (SVOM burst-id sb25090605) from the LMXB 4U 0513-40, which is not present in the trigger onboard catalog. The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The source was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 11 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 14.14 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2025-09-06T21:18:25. The localization of the best alert is R.A., Dec. 78.5709, -40.0751 degrees (J2000) with a 90% confidence level (C.L.) radius of 5.8 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the source. SVOM/MXT began observing the field at 2025-09-06T21:21:09 UTC, 159 seconds after T0. Using onboard processed data we found an X-ray source located at R.A., Dec. 78.5386, -40.0520 degrees: R.A. (J2000) = 5h14m09.26s Dec. (J2000) = -40d03m07.30s with a 90% C.L. radius of 50 arcseconds (including systematic error). This location is 2 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. The MXT position is consistent with the position of LMXB 4U 0513-40, located at 44 arcseconds. VT began observing the field after the slew. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Maria Grazia Bernardini: maria.bernardini(a)inaf.it. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41743. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39808] EP250905a: Liverpool Telescope i-band upper limits
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41742 SUBJECT: EP250905a: Liverpool Telescope i-band upper limits DATE: 25/09/06 21:23:03 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of the fast X-ray transient EP250905a (Liu et al., GCN 41574) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS i’ filter starting at 2025-09-05 22:06:03 UT, approximately 10.9 hours after the trigger. We performed image subtraction of the stacked images against Pan-STARRS using PSF matching with the help of PSFEx. We do not detect the reported optical counterpart (He et al., GCN 41732, as well as GCN 41734) nor any new objects within the EP/FXT error region of the transient (Cheng et al., GCN 41725; Wang et al., GCN 41737). The 3-sigma limiting magnitude on the stacked images is i > 22.6 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/41742. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39807] LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41741 SUBJECT: LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates DATE: 25/09/06 17:01:35 GMT FROM: Xander J Hall at Carnegie Mellon University <xjh(a)andrew.cmu.edu> Xander J. Hall (CMU), Lei Hu (CMU), Tomás Cabrera (CMU), James Freeburn (UNC), Antonella Palmese (CMU), Brendan O’Connor (CMU), Igor Andreoni (UNC), Keerthi Kunnumkai (CMU), on behalf of the Gravitational Wave MultiMessenger Astronomy DECam Survey (GW-MMADS) team report: DECam observed the high probability area of the LVK gravitational wave candidate S250830bp (GCN 41606) using the wide-field Dark Energy Camera (DECam) on the 4m Blanco telescope. Observations started at 2025-09-05T04:12:03 UTC (Prop ID: 2025B-485252; PI Soares-Santos) and covered the highest 90% probability region of the event (GCN 41607). We run the SFFT difference imaging (Hu et al. 2022) on the available images, filter out likely stars and moving objects, and then visually inspect the remaining transients. We report on TNS 13 newly identified transients within the LVK 99% CI area. We report the new transient AT 2025xab as a likely supernova and note that none of our nuclear transients show any compelling evolution. A crossmatch with Gaia reveals AT 2025wzv and AT 2025wzw (McMahon et al. GCN 41739) as galactic sources, thus we conclude these are not associated with S250830bp (GCN 41607). We also provide updates on previously announced candidates: We report that AT 2025wpk has shown little to no color evolution or brightness change since its last observation and that AT 2025wpv has shown a slow decline in brightness, dropping ~0.1 mag/day. Finally, we report on AT 2025wpq (GCN 41643), which was observed by SOAR at 2025-09-04T05:32:07 UTC (PI Andreoni). We clearly see broad Halpha and Hbeta securing its classification as a quasar at a z ~ 0.4, thus, we therefore conclude this candidate is far too distant to be associated with S250830bp (GCN 41607). Further analysis is underway. We thank the CTIO and NOIRLab staff for supporting these observations and the data calibration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41741. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39806] EP250905b: EP-FXT follow-up observation
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41740 SUBJECT: EP250905b: EP-FXT follow-up observation DATE: 25/09/06 15:00:37 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. Mao (NAO,CAS), Q. C. Liu (THU), Y. H. Cheng (SWIFAR,YNU), G. J. Yang, Y. Liu (NAO,CAS) on behalf of the Einstein Probe team: EP-FXT performed a follow-up observation of EP250905b (GCN 41735) at 2025-09-06T05:05:21 (UTC), about 10 hours after the WXT detection, with an exposure time of 3.2 ks. FXT detected a weak uncatalogued source within the WXT error circle at R.A. = 90.7297, DEC = -54.1582 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). Assuming a powerlaw spectrum with the absorption fixed at the Galactic value of 7.64x10^20 cm^-2 and the photon index of 2, the flux in 0.5-10 keV is derived to be approximately 2x10^-14 erg/s/cm2 from the FXT count rate. Further follow-up observations are encouraged to identify the nature of this source. 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/41740. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39805] LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41739 SUBJECT: LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates DATE: 25/09/06 13:37:14 GMT FROM: Isaac McMahon at University of Zürich <isaac.mcmahon(a)ligo.org> Isaac McMahon, Sean MacBride, Marcelle Soares-Santos (UZH), Lillian Joseph (Benedictine U.), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team: At 2025-09-06 04:12:03 UTC, the Dark Energy Camera (DECam) conducted the second epoch of observations in response to the LVK alert issued for the candidate gravitational-wave event S250830bp (GCN 41606). We observed the same fields as epoch 1 (GCN 41640) and employed the same analysis. The average limiting magnitudes achieved for epoch 2 were 20.7 in g, 21.4 in r, and 21.3 in i, and 21.1 in z. We report the following seven candidates which have multiple good detections on both days of observation. The candidate reported previously, AT2025wpk, is confirmed to be variable and dimming with good detections in all four bands. The other six candidates are all nuclear-type transients at the centers of previously detected objects. | ID | ATNAME | RA | DEC | MAG_G | MAG_G_ERR | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR | |--------- |-------- |------------ |----------- |------- |----------- |------- |----------- |------- |----------- |------- |----------- | | DESGW_3336579 | AT2025wpk | 329.476163 | -77.412560 | 22.43 | 0.24 | 21.58 | 0.19 | 21.30 | 0.13 | 21.05 | 0.09 | | DESGW_3336526 | AT2025wzu | 325.368195 | -77.603585 | N/A | N/A | 21.16 | 0.09 | N/A | N/A | 21.76 | 0.17 | | DESGW_3336621 | AT2025wzw | 323.031060 | -77.708095 | 23.21 | 0.49 | 21.74 | 0.23 | 21.52 | 0.10 | 20.68 | 0.07 | | DESGW_3336660 | AT2025wzv | 328.307211 | -78.281736 | 15.94 | 0.01 | N/A | N/A | N/A | N/A | N/A | N/A | | DESGW_3336681 | AT2025wpr | 321.643320 | -77.755092 | N/A | N/A | 21.07 | 0.08 | 21.72 | 0.14 | 20.98 | 0.10 | | DESGW_3336921 | AT2025wpo | 323.141341 | -78.204743 | 20.22 | 0.06 | 20.27 | 0.06 | 20.32 | 0.06 | 20.38 | 0.06 | | DESGW_3337296 | AT2025wzx | 321.552602 | -78.046756 | N/A | N/A | 21.77 | 0.16 | 20.95 | 0.07 | 21.65 | 0.19 | In particular, AT2025wzv seems to be very luminous and actively brightening in g-band but shows little to no transient activity in other bands. This behavior makes it an interesting transient but unlikely to be associated with S250830bp. We also recover the transient AT2025wpq reported in Hall et al (GCN 41643), although we note that the redshift reported for the host AGN by the Quaia catalog (Storey-Fisher et al 2024) is z = 0.43 +- 0.06, outside of the confidence volume for S250830bp. We do not recover the transient AT2025wpv. Further observations are ongoing and we encourage followup of the event region and the above candidates. The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41739. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39804] EP250905a: Liverpool Telescope observations
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41738 SUBJECT: EP250905a: Liverpool Telescope observations DATE: 25/09/06 13:20:01 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris and N. Habeeb (U of Leicester) report on behalf of a larger collaboration: We observed the field of EP250905a with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS r’ and SDSS g’ filters starting at 2025-09-05 22:20:05 UT, approximately 11.1 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. We detect no new sources in either the subtractions or stacked images. At the position of the optical source proposed as the counterpart by He et al. (GCN 41732) and GCN 41734, we use forced photometry to measure r = 22.6 +/- 0.4. We therefore identify no significant variability. We derive 3-sigma upper limits of r’ > 22.5 and g’ > 21.5 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41738. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39803] EP250905a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41737 SUBJECT: EP250905a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/09/06 11:24:15 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO), Y.H.Cheng (SWIFAR,YNU), R. D. Liang, W. D. Zhang (NAOC) on behalf of the Einstein Probe (EP) team: The X-ray transient EP250905a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (GCN 41725), with several multi-wavelength follow-up observations (GCN 41727, GCN 41732, GCN 41734). The refined WXT data shows that the flare started at about 2025-09-05 11:07:08 UTC (T0). WXT detected the source from T0 to before the slew with a peak flux of 1.4 x 10^(-9) erg/s/cm^2. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.0 x 10^20 cm^-2 and a photon index of 1.7 (+/-0.4). The derived average unabsorbed 0.5-4 keV flux is around 5.7 (-1.3/+1.6) x 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 405 s after T0. On-ground analysis of the FXT data found an fading source at R.A. = 4.4504 deg, DEC = 37.4697 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.0 x 10^20 cm^-2 and a photon index of 2.3(+/-0.4). The derived average unabsorbed 0.5-10 keV flux is around 4.5(-1.0/+1.5) x 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/41737. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39802] EP250905b: Global MASTER-Net observations report
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41736 SUBJECT: EP250905b: Global MASTER-Net observations report DATE: 25/09/06 08:27:35 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 EP250905b ( EP Team et al., GCN 41735) errorbox 2238 sec after notice time and 46512 sec after trigger time at 2025-09-06 08:13:40 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 43 deg. The sun altitude is -33.0 deg. The galactic latitude b = -28 deg., longitude l = 262 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2985909 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 46542 | 2025-09-06 08:13:40 | MASTER-OAFA | (06h 03m 11.78s , -54d 19m 04.9s) | C | 60 | 19.5 | 46618 | 2025-09-06 08:14:56 | MASTER-OAFA | (06h 03m 19.42s , -54d 18m 45.3s) | C | 60 | 19.5 | 46697 | 2025-09-06 08:16:14 | MASTER-OAFA | (06h 03m 15.86s , -54d 17m 05.6s) | C | 60 | 19.5 | 46771 | 2025-09-06 08:17:29 | MASTER-OAFA | (06h 03m 15.93s , -54d 18m 30.1s) | C | 60 | 19.5 | 46837 | 2025-09-06 08:18:35 | MASTER-OAFA | (06h 03m 15.94s , -54d 18m 27.8s) | C | 60 | 19.5 | 46903 | 2025-09-06 08:19:41 | MASTER-OAFA | (06h 03m 15.97s , -54d 18m 25.3s) | C | 60 | 19.5 | 46981 | 2025-09-06 08:20:59 | MASTER-OAFA | (06h 03m 19.09s , -54d 17m 19.1s) | C | 60 | 19.5 | 47047 | 2025-09-06 08:22:05 | MASTER-OAFA | (06h 03m 19.11s , -54d 17m 16.9s) | C | 60 | 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/41736. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39801] EP250905b: EP-WXT detection of a fast X-ray transient
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41735 SUBJECT: EP250905b: EP-WXT detection of a fast X-ray transient DATE: 25/09/06 07:35:38 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), Y. H. Cheng (SWIFAR,YNU), X. Mao, G. J. Yang, Y. Liu (NAO,CAS) on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient, designated EP250905b, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2025-09-05T19:18:28 (UTC). The position of the source is R.A. = 90.724 deg, DEC = -54.167 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The transient event lasts for nearly 200 seconds. No automated X-ray follow-up observation was performed due to the solar angle constraint. The average 0.5-4 keV spectrum can be fitted by an absorbed power law with a photon index of 1.4 (+0.6/-0.6). The column density is fixed at the Galactic value of 7.64 x 10^20 cm^-2. The derived average unabsorbed 0.5-4 keV flux is 7 (+4/-2) x 10^-10 erg/s/cm^2. The peak flux is around 2.9 x 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Follow-up observations with the Follow-up X-ray Telescope (FXT) on board EP have been scheduled, and further information will be updated when the telemetry data 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/41735. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39800] EP250905a: FTW one optical and multiple NIR counterpart candidates
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41734 SUBJECT: EP250905a: FTW one optical and multiple NIR counterpart candidates DATE: 25/09/06 02:50:51 GMT FROM: xjh(a)andrew.cmu.edu We observed the localization of the x-ray flare EP250905a (GCN 41725), with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands starting at 2025-09-05T20:12:28 UTC (0.38 days after the X-ray flare) for 52 x 180s. In the difference imaging with templates from PS1, we detect no new sources down to r ~ 23.2 and i ~ 23.1. However, our image depth is far deeper (r ~ 24.5, i ~ 24.3, J ~ 23.2). By eye, we compare to PS1 and 2MASS catalogs and present 5 potential new sources within the 20” error circle: | id | ra | dec | mag_J | mag_J_err | mag_r | mag_r_err | | ----------- | ------------- | ------------- | ---- | --- | ----- | ---- | | EP250905a_2 | 00:17:47.9940 | +37:28:19.306 | 21.3 | 0.1 | 22.14 | 0.04 | EP250905a_2 was reported by He et al. (GCN 41732), however in our difference imaging we see no source. In our science image, we note a distinct point source there below the galaxy. We report a noticeably brighter r ~ 22.14 than reported by He et al. (GCN 41732), but there is significant bleed from the nearby galaxy. There also appears to be a faint source at that position in the PS1 template. We note that these following four sources are not detected above our three sigma limit in r or i band photometry, but have clear sources in J. | id | ra | dec | mag_J | mag_J_err | | ----------- | ------------- | ------------- | ---- | ----| | EP250905a_1 | 00:17:47.4836 | +37:28:25.975 | 22.1 | 0.1 | | EP250905a_3 | 00:17:46.8641 | +37:28:16.316 | 21.40 | 0.06 | | EP250905a_4 | 00:17:47.4834 | +37:28:07.901 | 21.9 | 0.1 | | EP250905a_5 | 00:17:47.4630 | +37:28:05.478 | 21.9 | 0.1 | We encourage continued follow-up to determine the variable nature of these sources. The magnitudes are reported in AB and calibrated against the PS1 and 2MASS catalog and not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41734. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39799] GRB 250905A: Swift-XRT refined Analysis
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41733 SUBJECT: GRB 250905A: Swift-XRT refined Analysis DATE: 25/09/06 02:25:05 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 4.7 ks of XRT data for GRB 250905A, from 140 s to 27.9 ks after the trigger. The data comprise 26 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=5.2 (+0.4, -0.3). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.9 (+0.8, -0.6). The best-fitting absorption column is 1.8 (+3.2, -1.2) x 10^21 cm^-2, consistent with the Galactic value of 5.5 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.1 x 10^-11 (5.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.8 (+3.2, -1.2) x 10^21 cm^-2 Galactic foreground: 5.5 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.9 (+0.8, -0.6) If the light curve continues to decay with a power-law decay index of 5.2, the count rate at T+24 hours will be 2.5 x 10^-14 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x 10^-24 (1.3 x 10^-24) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01347265. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41733. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39798] EP250905a: JinShan likely optical counterpart detection
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41732 SUBJECT: EP250905a: JinShan likely optical counterpart detection DATE: 25/09/06 01:19:57 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> L.B. He, X. Liu, J. An, D. Xu, S.Q. Jiang, Z.P. Zhu (NAOC), S.Y. Fu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of EP250905a detected by Einstein Probe (Cheng et al., GCN 41725), using the 100C telescope of the JinShan project, located at Altay, Xinjiang, China. We obtained 40 x 180 s Sloan i-band frames, starting from 2025-09-05 13:56:23 UT, i.e., 2.74 hrs since the EP trigger. A new source is detected positionally in a known GLADE galaxy (GLADE+ #2980788) via image subtraction, which is within the EP-FXT 20-arcsec error circle , at coordinates R.A. (J2000) = 0:17:48.01 Dec. (J2000) = +37:28:19.44 with an uncertainty of ~ 0.6 arcsec. The source has r ~ 22.9 mag, calibrated with PanSTARRS. We think the source is very likely the counterpart of EP250905a. In this case, the galaxy is the host with a redshfit of z ~ 0.28 from GLADE. Further observations are planned and encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/41732. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39797] IceCube-250905A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41731 SUBJECT: IceCube-250905A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/09/05 22:22:56 GMT FROM: Erik Blaufuss at University of Maryland, College Park <blaufuss(a)umd.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2025-09-05 20:08:36.01 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 0.41 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/141315_25569816.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 2025-09-05 Time: 20:08:36.01 UT RA: 348.31 (+0.93, -1.09 deg 90% PSF containment) J2000 Dec: 38.87 (+0.78, -0.86 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/41731. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39796] GRB 250904A: Swift-BAT refined analysis
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41730 SUBJECT: GRB 250904A: Swift-BAT refined analysis DATE: 25/09/05 21:28:22 GMT FROM: D. R. Sadaula at NASA GSFC <dev.r.sadaula(a)nasa.gov> D. M. Palmer (LANL), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250904 A (trigger #1347179) (Salvaggio, et al., GCN Circ. 41704). The BAT ground-calculated position is RA, Dec = 84.377, 3.575 deg which is RA(J2000) = 05h 37m 30.5s Dec(J2000) = +03d 34' 29.9" with an uncertainty of 1.0 arcmin (radius, sys+stat, 90% containment). The partial coding was 100%. The BAT light curve showed a complex structure with a duration of about 50 sec. T90 (15-350 keV) is 37.11 +- 13.89 sec (estimated error including systematics). The time-averaged spectrum from T-19.68 to T+54.44 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.40 +- 0.11. The fluence in the 15-150 keV band is 1.7 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+5.11 sec in the 15-150 keV band is 1.1 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1347179 View this GCN Circular online at https://gcn.nasa.gov/circulars/41730. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39795] IceCube Alert 250905.84: Global MASTER-Net observations report
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41729 SUBJECT: IceCube Alert 250905.84: Global MASTER-Net observations report DATE: 25/09/05 20:39:22 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 IceCube Alert 250905.84 (trigger No 25569816,23h 15m 48.96s , +38d 16m 19.2s, R=0.51) errorbox 34 sec after notice time and 87 sec after trigger time at 2025-09-05 20:10:03 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 80 deg. The sun altitude is -47.4 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the IceCube Alert 250905.84 errorbox 48 sec after notice time and 101 sec after trigger time at 2025-09-05 20:10:17 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 15 deg. The sun altitude is -38.6 deg. The galactic latitude b = -21 deg., longitude l = 104 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2985645 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 97 | 2025-09-05 20:10:03 | MASTER-SAAO | (23h 13m 56.30s , +37d 51m 11.7s) | C | 20 | 16.2 | 97 | 2025-09-05 20:10:03 | MASTER-SAAO | (23h 11m 44.72s , +38d 07m 09.5s) | C | 20 | 16.4 | 111 | 2025-09-05 20:10:17 | MASTER-Kislovodsk | (23h 14m 08.98s , +38d 35m 46.0s) | P- | 20 | 15.4 | 136 | 2025-09-05 20:10:17 | MASTER-Kislovodsk | (23h 14m 08.98s , +38d 35m 46.1s) | P- | 70 | 16.2 | Coadd 141 | 2025-09-05 20:10:42 | MASTER-SAAO | (23h 13m 56.43s , +37d 51m 17.0s) | C | 30 | 16.4 | 141 | 2025-09-05 20:10:42 | MASTER-SAAO | (23h 11m 44.83s , +38d 07m 15.6s) | C | 30 | 16.7 | 151 | 2025-09-05 20:10:57 | MASTER-Kislovodsk | (23h 14m 08.82s , +38d 35m 44.8s) | P- | 20 | 15.4 | 195 | 2025-09-05 20:11:31 | MASTER-SAAO | (23h 13m 56.59s , +37d 51m 22.5s) | C | 40 | 16.6 | 195 | 2025-09-05 20:11:31 | MASTER-SAAO | (23h 11m 44.98s , +38d 07m 20.6s) | C | 40 | 16.9 | 196 | 2025-09-05 20:11:37 | MASTER-Kislovodsk | (23h 14m 08.65s , +38d 35m 44.0s) | P- | 30 | 15.8 | 252 | 2025-09-05 20:12:27 | MASTER-Kislovodsk | (23h 14m 08.46s , +38d 35m 43.3s) | P- | 40 | 15.8 | 312 | 2025-09-05 20:12:27 | MASTER-Kislovodsk | (23h 14m 08.45s , +38d 35m 43.5s) | P- | 160 | 16.6 | Coadd 259 | 2025-09-05 20:12:30 | MASTER-SAAO | (23h 13m 56.76s , +37d 51m 27.4s) | C | 50 | 16.7 | 259 | 2025-09-05 20:12:30 | MASTER-SAAO | (23h 11m 45.14s , +38d 07m 24.6s) | C | 50 | 17.0 | 317 | 2025-09-05 20:13:27 | MASTER-Kislovodsk | (23h 14m 08.26s , +38d 35m 43.2s) | P- | 50 | 15.8 | 333 | 2025-09-05 20:13:39 | MASTER-SAAO | (23h 13m 56.93s , +37d 51m 32.0s) | C | 60 | 16.8 | 333 | 2025-09-05 20:13:39 | MASTER-SAAO | (23h 11m 45.32s , +38d 07m 27.8s) | C | 60 | 17.1 | 397 | 2025-09-05 20:14:37 | MASTER-Kislovodsk | (23h 14m 08.05s , +38d 35m 43.6s) | P- | 70 | 16.0 | 412 | 2025-09-05 20:14:58 | MASTER-SAAO | (23h 13m 57.13s , +37d 51m 36.8s) | C | 60 | 16.8 | 412 | 2025-09-05 20:14:58 | MASTER-SAAO | (23h 11m 45.54s , +38d 07m 31.7s) | C | 60 | 17.1 | 497 | 2025-09-05 20:16:07 | MASTER-Kislovodsk | (23h 14m 07.75s , +38d 35m 44.0s) | P- | 90 | 16.2 | 612 | 2025-09-05 20:16:07 | MASTER-Kislovodsk | (23h 14m 07.76s , +38d 35m 44.0s) | P- | 320 | 17.0 | Coadd 617 | 2025-09-05 20:17:58 | MASTER-Kislovodsk | (23h 14m 07.43s , +38d 35m 44.9s) | P- | 110 | 16.4 | 753 | 2025-09-05 20:20:09 | MASTER-Kislovodsk | (23h 14m 07.06s , +38d 35m 46.5s) | P- | 120 | 16.4 | 893 | 2025-09-05 20:22:28 | MASTER-Kislovodsk | (23h 14m 06.67s , +38d 35m 47.7s) | P- | 120 | 16.3 | 1013 | 2025-09-05 20:22:28 | MASTER-Kislovodsk | (23h 14m 06.67s , +38d 35m 47.7s) | P- | 360 | 17.0 | Coadd 1035 | 2025-09-05 20:24:51 | MASTER-Kislovodsk | (23h 14m 06.26s , +38d 35m 49.4s) | P- | 120 | 16.4 | 1175 | 2025-09-05 20:27:11 | MASTER-Kislovodsk | (23h 14m 05.86s , +38d 35m 51.3s) | P- | 120 | 16.4 | 1315 | 2025-09-05 20:29:31 | MASTER-Kislovodsk | (23h 14m 05.49s , +38d 35m 53.3s) | P- | 120 | 16.4 | 1456 | 2025-09-05 20:31:52 | MASTER-Kislovodsk | (23h 14m 05.12s , +38d 35m 55.7s) | P- | 120 | 16.4 | 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/41729. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39794] GRB 250905A: Swift/UVOT Upper Limits
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41728 SUBJECT: GRB 250905A: Swift/UVOT Upper Limits DATE: 25/09/05 20:04:34 GMT FROM: Samantha Oates at University of Birmingham <samantha.oates(a)alumni.ucl.ac.uk> S. R. Oates (Lancaster Uni.) and R. Brivio (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250905A 140 s after the BAT trigger (Brivio et al., GCN Circ. 41714). No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 41722) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag/3sigUL white (FC) 140 290 147 >21.0 u (FC) 300 405 103 >19.8 v 4973 16058 1082 >20.3 b 5794 5978 181 >20.3 u 5588 27905 1036 >21.1 uvw1 5383 27038 1082 >20.4 uvm2 5178 16867 989 >20.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.054 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41728. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39793] EP250905a: Global MASTER-Net observations report
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41727 SUBJECT: EP250905a: Global MASTER-Net observations report DATE: 25/09/05 18:09:28 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 EP250905a ( EP Team et al., GCN 41725) errorbox 18309 sec after notice time and 24012 sec after trigger time at 2025-09-05 17:52:01 UT, with upper limit up to 17.2 mag. The observations began at zenith distance = 51 deg. The sun altitude is -23.2 deg. The galactic latitude b = -25 deg., longitude l = 116 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2985447 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 24043 | 2025-09-05 17:52:01 | MASTER-Kislovodsk | (00h 16m 34.13s , +37d 41m 06.2s) | C | 60 | 17.2 | 24633 | 2025-09-05 18:01:52 | MASTER-Kislovodsk | (00h 16m 32.36s , +37d 38m 50.7s) | C | 60 | 17.2 | 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/41727. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39792] GRB 250901A - SVOM/ECLAIRs refined analysis
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41726 SUBJECT: GRB 250901A - SVOM/ECLAIRs refined analysis DATE: 25/09/05 13:34:45 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Tais Maiolino (LUPM), Frédéric Piron (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 250901A (SVOM burst-id sb25090101). The burst that triggered ECLAIRs (GCN #41634) consists of a single pulse structure with a duration of T90 = 16 +1/-3 s in the 4-120 keV energy band. The time-averaged spectrum from T0-8 s to T0+10 s (T0 = 2025-09-01T18:14:22.916) in the energy range 5-120 keV is best fitted by a power-law model with photon index -1.15 +/- 0.09. With this model, the 4-120 keV fluence is (1.4 +/- 0.1) e-06 erg/cm^2. All the quoted errors are at the 68% confidence level. We note that the calibration of SVOM/ECLAIRs is undergoing thus these results are preliminary 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Tais Maiolino (LUPM) (tais.maiolino at lupm.in2p3.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/41726. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39791] EP250905a: Einstein Probe detection of an X-ray transient
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41725 SUBJECT: EP250905a: Einstein Probe detection of an X-ray transient DATE: 25/09/05 12:44:26 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.H. Cheng (SWIFAR,YNU), Y. Wang (PMO), R. D. Liang, W. D. Zhang (NAOC) 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 EP250905a. The transient triggered EP-WXT (ID: 01709201261) at 2025-09-05T11:11:49 (UTC). The WXT position of the source is R.A. = 4.441 deg, DEC = 37.493 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. = 4.4517 deg, DEC = 37.4728 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/41725. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39790] GRB 250905B: Fermi GBM Final Localization
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41724 SUBJECT: GRB 250905B: Fermi GBM Final Localization DATE: 25/09/05 11:17:13 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> The Fermi GBM team reports the detection of a likely LONG GRB "At 08:14:40.87 UT on 05 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250905B (trigger 778752885/250905344). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 123.82, Dec = -19.65 (J2000 degrees, equivalent to J2000 8h 15m, -19d 38'), with a statistical uncertainty of 11.91 degrees. The angle from the Fermi LAT boresight is 90 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250905344/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250905344/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250905344/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41724. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39789] GRB250904A: Liverpool Telescope upper limits
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41723 SUBJECT: GRB250904A: Liverpool Telescope upper limits DATE: 25/09/05 11:14:38 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of GRB250904A (Salvaggio et al., GCN 41704) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x120s exposures in the SDSS i’ filter starting at 2025-09-05 05:47:54 UT, approximately 12.2 hours after the trigger. We do not detect the reported optical counterpart (Fu et al., GCN 41709; Oates et al., GCN 41721) or any new source near the XRT position (Evans et al., GCN 41706; Goad et al., GCN 41711). The 3-sigma limiting magnitude on the stacked images is i > 22.4 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/41723. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39788] GRB 250905A: Enhanced Swift-XRT position
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41722 SUBJECT: GRB 250905A: Enhanced Swift-XRT position DATE: 25/09/05 10:52:49 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 233 s of XRT Photon Counting mode data and 1 UVOT images for GRB 250905A, 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 = 233.00557, +0.79370 which is equivalent to: RA (J2000): 15h 32m 01.34s Dec (J2000): +00d 47' 37.3" with an uncertainty of 2.5 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/41722. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39787] GRB 250904A: Swift/UVOT Detection
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41721 SUBJECT: GRB 250904A: Swift/UVOT Detection DATE: 25/09/05 10:09:45 GMT FROM: Samantha Oates at University of Birmingham <samantha.oates(a)alumni.ucl.ac.uk> S. R. Oates (Lancaster Uni.) and C. Salvaggio (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250904A 86 s after the BAT trigger (Salvaggio et al., GCN Circ. 41704). A source consistent with the XRT position (Goad et al., GCN Circ. 41711) is detected in white and marginally in u. 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/3sigUL white (FC) 86 235 147 20.23+\-0.36 u (FC) 298 441 141 19.14+\-0.41 (2.7 sigma) white 4990 10603 1097 20.60+\-0.16 v 5401 5601 197 >19.5 b 4786 6421 393 >20.4 u 6016 6215 197 >19.6 uvw1 5811 6011 197 >19.5 uvm2 5606 5806 197 >19.4 uvw2 5196 10942 524 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.284 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41721. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39786] GRB 250903A: Swift/UVOT detection
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41720 SUBJECT: GRB 250903A: Swift/UVOT detection DATE: 25/09/05 09:51:33 GMT FROM: s.shilling(a)lancaster.ac.uk S. P. R. Shilling (Lancaster U.) reports on behalf of the Swift/UVOT team: Swift/UVOT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 250903A. Swift/UVOT observed the field of GRB 250903A (Maiolino et al., GCN 41677) for 2.3 ks in the U-band starting at 20:57:46 UT, 3.5 hours after the detection by SVOM/ECLAIRs. A source consistent with the TRT optical counterpart position (An et al., GCN 41679), within the SVOM/ECLAIRs error circle, is detected and is fading. The preliminary detection magnitude reported below is calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373). Filter T_start(s) T_stop(s) Exp(s) Mag u 12770 24862 2330 19.71 +/- 0.11 View this GCN Circular online at https://gcn.nasa.gov/circulars/41720. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39785] GRB 250904A: Swift-XRT refined Analysis
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41719 SUBJECT: GRB 250904A: Swift-XRT refined Analysis DATE: 25/09/05 09:20:44 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.0 ks of XRT data for GRB 250904A, from 66 s to 45.6 ks after the trigger. The data comprise 9 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=0.85 (+0.05, -0.04). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.05 (+0.27, -0.25). The best-fitting absorption column is 4.4 (+1.4, -1.0) x 10^21 cm^-2, consistent with the Galactic value of 3.3 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (6.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4.4 (+1.4, -1.0) x 10^21 cm^-2 Galactic foreground: 3.3 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 2.05 (+0.27, -0.25) If the light curve continues to decay with a power-law decay index of 0.85, the count rate at T+24 hours will be 7.0 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.8 x 10^-13 (4.5 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01347179. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41719. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39784] LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41718 SUBJECT: LIGO/Virgo/KAGRA S250904cv: Updated Sky localization DATE: 25/09/05 08:02:39 GMT FROM: Michael J. Williams at University of Portsmouth <michael.williams(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 S250904cv (GCN Circular 41700). 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/S250904cv For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 980 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1806 +/- 595 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/41718. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39783] LIGO/Virgo/KAGRA S250904br: Updated Sky localization
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41717 SUBJECT: LIGO/Virgo/KAGRA S250904br: Updated Sky localization DATE: 25/09/05 08:01:58 GMT FROM: Michael J. Williams at University of Portsmouth <michael.williams(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), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250904br (GCN Circular 41692). 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/S250904br For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 232 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(15h39m, +13d59m, 21.87d, 3.41d, 70.39d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2547 +/- 578 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/41717. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39782] The EP-WXT trigger 01709201259: a brightening of LMXB 1ES 1735-26.9
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41716 SUBJECT: The EP-WXT trigger 01709201259: a brightening of LMXB 1ES 1735-26.9 DATE: 25/09/05 07:07:13 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang (NAOC), Y. Wang (PMO), Y.H.Cheng (SWIFAR,YNU), W. D. Zhang (NAOC) on behalf of the Einstein Probe (EP) team: We report on the detection of X-ray brightening of Low Mass X-ray Binary (LMXB) 1ES 1735-26.9 by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The burst triggered EP-WXT (ID: 01709201259) at the time of 2025-09-05T05:11:45 UTC. The WXT position of the source is R.A. = 264.569 deg, DEC = -26.997 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The estimated flux in the 0.5-4 keV band is around 5 x 10^-10 erg/cm^2/s, which is an order of magnitude higher than the previous detection. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. An X-ray source was detected at R.A. = 264.5679 deg, DEC = -26.9927 (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic), which is consistent with the position of known LMXB 1ES 1735-26.9. The estimated flux in the 0.5-10 keV band is around 2 x 10^-10 erg/cm^2/s. 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/41716. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39781] GRB 250905A: KAIT optical upper limit
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41715 SUBJECT: GRB 250905A: KAIT optical upper limit DATE: 25/09/05 04:51:12 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of Swift GRB 250905A (Brivio et al., GCN 41714) starting at 03:14 UT, ~64 minutes after the burst. A set of 34x60s clear (roughly R) filter images were obtained under twilight condition. We do not detect any new optical counterpart candidate within the XRT error circles (Brivio et al., GCN 41714), down to an upper limit of about 20.0 (Vega) mag at a mid time of 94 minutes after the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/41715. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39780] GRB 250905A: Swift detection of a burst
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41714 SUBJECT: GRB 250905A: Swift detection of a burst DATE: 25/09/05 02:25:34 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> R. Brivio (INAF-OAB), S. Dichiara (PSU), D. M. Palmer (LANL), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 02:09:54 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250905A (trigger=1347265). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 233.047, +0.777 which is RA(J2000) = 15h 32m 11s Dec(J2000) = +00d 46' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Due to a telemetry gap, the BAT lightcurve is not immediately available. The XRT began observing the field at 02:12:11.4 UT, 136.6 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 233.00629, 0.79395 which is equivalent to: RA(J2000) = 15h 32m 01.51s Dec(J2000) = +00d 47' 38.2" with an uncertainty of 3.4 arcseconds (radius, 90% containment). This location is 158 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 5.50 x 10^20 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 140 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.054. Burst Advocate for this burst is R. Brivio (riccardo.brivio AT inaf.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41714. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39779] Swift GRB250905.09: Global MASTER-Net observations report
by GCN Circulars 05 Sep '25

05 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41713 SUBJECT: Swift GRB250905.09: Global MASTER-Net observations report DATE: 25/09/05 02:16:50 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 GRB250905.09 (trigger No 1347265,15h 32m 11.28s , +00d 46m 37.2s, R=0.05) errorbox 18 sec after notice time and 87 sec after trigger time at 2025-09-05 02:11:22 UT, with upper limit up to 16.0 mag. The observations began at zenith distance = 78 deg. The sun altitude is -49.0 deg. The galactic latitude b = 43 deg., longitude l = 6 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2985121 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 97 | MASTER-OAFA | C | 20 | 16.0 | 124 | MASTER-OAFA | C | 20 | 15.9 | 155 | MASTER-OAFA | C | 30 | 16.0 | 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/41713. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39778] Swift GRB 250904A: Global MASTER-Net observations report
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41712 SUBJECT: Swift GRB 250904A: Global MASTER-Net observations report DATE: 25/09/04 23:11:08 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-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB 250904A ( C. Salvaggio et al., GCN 41704) errorbox 19454 sec after notice time and 19494 sec after trigger time at 2025-09-04 23:01:57 UT, with upper limit up to 15.5 mag. The observations began at zenith distance = 81 deg. The sun altitude is -35.9 deg. The galactic latitude b = -14 deg., longitude l = 201 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2984839 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 19585 | MASTER-Tavrida | C | 180 | 15.5 | 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/41712. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39777] GRB 250904A: Enhanced Swift-XRT position
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41711 SUBJECT: GRB 250904A: Enhanced Swift-XRT position DATE: 25/09/04 19:57:22 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 343 s of XRT Photon Counting mode data and 1 UVOT images for GRB 250904A, 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 = 84.38044, +3.58445 which is equivalent to: RA (J2000): 05h 37m 31.31s Dec (J2000): +03d 35' 04.0" with an uncertainty of 2.5 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/41711. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39776] IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41710 SUBJECT: IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/09/04 19:32:11 GMT FROM: Yuhua Yao at IceCube/UW-Madison <yyao255(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-Cascade 250903A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/141309_814805.amon) in a time range of 1000 seconds centered on the alert event time (2025-09-03 17:21:14.210 UTC to 2025-09-03 17:37:54.210 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-Cascade 250903A.We report a p-value of 1.00 in this time window. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-Cascade 250903A ranges from 1.3e-01 to 1.6e+00 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 3e+02 GeV and 7e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-09-02 17:29:34.210 UTC to 2025-09-04 17:29:34.210 UTC). In this case, we report a p-value of 0.83, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-Cascade 250903A ranges from 1.5e-01 to 1.6e+00 GeV cm^-2 in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/41710. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39775] GRB 250904A: TRT optical counterpart detection
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41709 SUBJECT: GRB 250904A: TRT optical counterpart detection DATE: 25/09/04 18:36:01 GMT FROM: syfu(a)nao.cas.cn S.Y. Fu (HUST), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), L.B. He, X. Liu, Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250904A (Salvaggio et al., GCN 41704), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 17:49:41.450 UTC on 2025-09-04, i.e., ~ 12.6 min after the Swift/BAT trigger and a series of frames in the R band were obtained. An uncatalogued source is detected in our stacked image within the enhanced Swift/XRT error circle (Evans et al., GCN 41706) with magnitude of R = 20.1 +/- 0.2 (AB) at 18.97 min post-trigger, calibrated with Pan-STARRS1 DR2 catalog converted using Lupton (2005) equations and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41709. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39774] EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41708 SUBJECT: EP250827a and EP250827b: Upper limit from Fermi-GBM Observations DATE: 25/09/04 18:18:09 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), C. M. Hui (NASA MSFC) and R. Hamburg (USRA) on behalf of the Fermi-GBM Team, report: Fermi-GBM had full spatial coverage of the transients EP250827a (Hua et al., GCN 41553, Ni et al., GCN 41573) and EP250827b (Schroeder et al., GCN 41635) detected by EP-WXT. There was no Fermi-GBM onboard trigger around both EP trigger times (T0=2025-08-27T07:39:01 UTC for EP250827a, and T0=2025-08-27T06:22:27 UTC for EP250827b). 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 transients, 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 3.5e-08 erg/cm2/s for EP250827a, and a flux upper limit of 3.0e-08 erg/cm2/s for EP250827b, 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/41708. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39773] GRB 250902B: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41707 SUBJECT: GRB 250902B: CALET Gamma-Ray Burst Monitor detection DATE: 25/09/04 18:04:18 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> N. Cannady (GSFC/UMBC), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 250902B (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 41660; SVOM/GRM observation: Wang et al., GCN Circ. 41668; AstroSat CZTI detection: Tembhurnikar et al., GCN Circ. 41678) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 18:45:35.15 UTC on 2 September 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1440873547/index.html) The burst signal was seen by all CGBM detectors. Because of a problem with the ground alert processing script, the GCN notice was not distributed automatically for this event. The burst light curve shows a multi-peaked structure that starts at T-2.4 sec, peaks at T+9.6 sec, and ends at T+17.4 sec. The T90 and T50 durations measured by the SGM data are 17.4 +/- 0.7 sec and 8.8 +/- 0.6 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1440873547/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/41707. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39772] GRB 250904A: Prompt enhanced Swift-XRT position
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41706 SUBJECT: GRB 250904A: Prompt enhanced Swift-XRT position DATE: 25/09/04 18:01:38 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Using 343 s of promptly downlinked XRT event data for GRB 250904A, we find an enhanced XRT position of the afterglow: RA, Dec: 84.38029, 3.58466 which is equivalent to: RA (J2000) = 05 37 31.27 Dec (J2000) = +03 35 04.8 with an uncertainty of 2.2 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1347179. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41706. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39771] EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41705 SUBJECT: EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova DATE: 25/09/04 17:53:57 GMT FROM: Brendan O'Connor at Carnegie Mellon University <boconno2(a)andrew.cmu.edu> Brendan O’Connor (CMU), Xander J. Hall (CMU), Antonella Palmese (CMU), Daniel Gruen (LMU), Gokul Srinivasaragavan (UMD), Anna Y. Q. Ho (Cornell): We observed the optical transient AT2025wkm, associated with EP250827b (Schroeder et al., GCN 41635), using GMOS mounted on Gemini-North (PI: O’Connor). Observations started on 2025-09-02 at 13:36:55 UT (6.3 d) and 2025-09-04 at 10:58:00 UT (8.2 d). At each epoch, we obtained 2x600 s exposures using the B480 grating covering 3950-8210 AA. The spectra show a steep blueward slope (likely due to shock cooling) and display broad features that are consistent with ejecta moving at a high velocity (see also Corcoran et al., GCN 41670 and Ho et al., GCN 41639). We identify blueshifted Fe II absorption features in both spectra, indicative of ejecta velocities ~ 40,000 km/s. The Fe II absorption features in combination with the lack of broad Hydrogen and Helium features associated with the transient itself allow us to confirm the classification of a Ic-BL supernova as initially reported by Corcoran et al. (GCN 41670). In addition, we identify numerous narrow emission lines, including the [O II] doublet, multiple [Ne III] lines, the entire Balmer series between Hbeta and Halpha, He I lines, [N II], [S II], and [Ar III], that identify the host galaxy as highly star forming. Further observations are planned and encouraged. We thank the staff of the Gemini Observatory, in particular Brian Lemaux, Eunchong Kim, Teo Mocnik, and Aleksandar Cikota for their assistance in planning and obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41705. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39770] GRB 250904A: Swift detection of a burst
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41704 SUBJECT: GRB 250904A: Swift detection of a burst DATE: 25/09/04 17:49:36 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> C. Salvaggio (INAF-OAB), R. Brivio (INAF-OAB), S. Dichiara (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), K. L. Page (U Leicester), D. M. Palmer (LANL) and T. Sbarrato (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team: At 17:37:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250904A (trigger=1347179). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 84.358, +3.584 which is RA(J2000) = 05h 37m 26s Dec(J2000) = +03d 35' 04" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single complex peak structure with a duration of about 50 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~8 sec after the trigger. The XRT began observing the field at 17:38:25.4 UT, 82.4 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 84.38001, 3.58520 which is equivalent to: RA(J2000) = 05h 37m 31.20s Dec(J2000) = +03d 35' 06.7" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 79 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 consistent with the Galactic value of 3.34 x 10^21 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 85 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.292. Burst Advocate for this burst is C. Salvaggio (chiara.salvaggio AT inaf.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41704. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39769] GRB 250902A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41703 SUBJECT: GRB 250902A: CALET Gamma-Ray Burst Monitor detection DATE: 25/09/04 16:50:35 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> T. Tamura (Kanagawa U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 250902A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 41648; SVOM/GRM observation: Wang et al., GCN Circ. 41653; Fermi GBM Detection: Bala et al., GCN Circ. 41662; GECAM-B detection: Zheng et al., GCN Circ. 41687; VZLUSAT-2 detection: Ripa et al., GCN Circ. 41701) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 01:30:01.56 UTC on 2 September 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1440811415/index.html) The burst signal was seen by all CGBM detectors. Because of a problem with the ground alert processing script, the GCN notice was not distributed automatically for this event. The burst light curve shows a multi-peaked structure that starts at T-0.6 sec, peaks at T+2.9 sec, and ends at T+6.8 sec. The T90 and T50 durations measured by the SGM data are 6.1 +/- 0.3 sec and 2.5 +/- 0.3 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1440811415/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/41703. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39768] LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41702 SUBJECT: LIGO/Virgo/KAGRA S250904ae: Updated Sky localization DATE: 25/09/04 16:44:30 GMT FROM: Michael J. Williams at University of Portsmouth <michael.williams(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), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250904ae (GCN Circular 41689). 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/S250904ae For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 931 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3545 +/- 913 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/41702. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39767] GRB 250902A: VZLUSAT-2 detection
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41701 SUBJECT: GRB 250902A: VZLUSAT-2 detection DATE: 25/09/04 15:29:58 GMT FROM: Jakub Ripa <ripa.jakub(a)gmail.com> J. Ripa, M. Dafcikova (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250902A (Fermi/GBM detection GCN 41662; NuSTAR detection trigger time 2025-09-02 01:29:54 UTC; SVOM detection GCN 41653; GECAM-B detection GCN 41687) was detected by the GRB detectors on board the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/) The data acquisition was performed by the GRB detector unit no. 1. The detection was confirmed at the peak time 2025-09-02 01:30:02 UTC. The T90 duration is 8 s and the significance during T90 reaches 29 sigma. The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250902A_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/41701. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39766] LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41700 SUBJECT: LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate DATE: 25/09/04 14:40:32 GMT FROM: Lorenzo Aiello at University of Roma Tor Vergata <lorenzo.aiello(a)roma2.infn.it> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250904cv during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-09-04 13:49:52.532 UTC (GPS time: 1441029010.532). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], PyCBC Live [6], and SPIIR [7] analysis pipelines. S250904cv is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250904cv The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). 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%. [8] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [8] 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 <1%. The source chirp mass falls with highest probability in the bin (11.0, 22.0) 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 [9], distributed via GCN and SCiMMA notices about 2 minutes after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 7 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 1237 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2414 +/- 670 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] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [4] 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 [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [9] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41700. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39765] GRB 250903A: Swift-XRT observations
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41699 SUBJECT: GRB 250903A: Swift-XRT observations DATE: 25/09/04 13:38:46 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 SVOM/ECLAIRs-detected source GRB 250903A, collecting 2.4 ks of Photon Counting (PC) mode data between T0+12 ks and T0+24 ks after the trigger. We have detected 2 sources inside the ECLAIRs error region. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 2 uncatalogued X-ray sources * 0 known X-ray sources Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J234712.1-755757): ================================== RA (J2000.0): 356.8008 = 23 47 12.19 Dec (J2000.0): -75.9660 = -75 57 57.6 Error: 4.3 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 2.7 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.0387 [+0.0049, -0.0047] ct s^-1 Mean flux: (1.33 [+0.17, -0.16])e-12 erg cm^-2 s^-1 Peak rate: 0.052 +/- 0.014 ct s^-1 Peak flux: (1.80 +/- 0.47)e-12 erg cm^-2 s^-1 ECF: 3.42e-11 erg cm^-2 ct^-1 assuming NH=4.68e+20 cm^-2, gamma=1.95 determined from a spectral fit. XMM UL: 2.0e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. The source may be fading, at the 0.8-sigma level. Source 2 (SWIFT J234819.4-755214): ================================== RA (J2000.0): 357.0812 = 23 48 19.49 Dec (J2000.0): -75.8707 = -75 52 14.5 Error: 6.4 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.8 arcmin from the SVOM/ECLAIRs position. Mean rate: (8.6 [+2.9, -2.4])e-3 ct s^-1 Mean flux: (1.06 [+0.36, -0.30])e-11 erg cm^-2 s^-1 Peak rate: (8.6 [+2.9, -2.4])e-3 ct s^-1 Peak flux: (1.06 [+0.36, -0.30])e-11 erg cm^-2 s^-1 ECF: 1.23e-09 erg cm^-2 ct^-1 assuming NH=4.41e+20 cm^-2, gamma=-2.35 determined from a spectral fit. XMM UL: 1.9e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 2.7-sigma above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `LEDA 242511' is 4.1" away. There is 1 2MASS object within the source's 3-sigma error radius. 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. Source 1 position is consistent with the optical counterpart discovered by TRT (GCN 41679). 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/SVOM/SVOM_FIELD00034. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41699. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39764] EP250903a: Swift-XRT observations
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41698 SUBJECT: EP250903a: Swift-XRT observations DATE: 25/09/04 13:34:42 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 EP250903a, collecting 3.7 ks of Photon Counting (PC) mode data between T0+1.3 ks and T0+35 ks after the trigger. We have detected 1 source inside the EP/WXT error region. This has been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 1 uncatalogued X-ray source * 0 known X-ray sources Uncatalogued X-ray sources -------------------------- Source 2 (SWIFT J223627.0-495113): ================================== RA (J2000.0): 339.1126 = 22 36 27.02 Dec (J2000.0): -49.8538 = -49 51 13.7 Error: 7.1 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 37 arcsec from the Einstein Probe/WXT position. Mean rate: (3.8 [+1.4, -1.2])e-3 ct s^-1 Mean flux: (2.20 [+0.83, -0.67])e-13 erg cm^-2 s^-1 Peak rate: (3.8 [+1.4, -1.2])e-3 ct s^-1 Peak flux: (2.20 [+0.83, -0.67])e-13 erg cm^-2 s^-1 ECF: 5.78e-11 erg cm^-2 ct^-1 assuming NH=1.17e+20 cm^-2, gamma=1.15 determined from a spectral fit. XMM UL: 1.9e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. There are 2 2MASS objects within the source's 3-sigma error radius. 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 position of Source 2 is consistent with the optical counterpart detected by LCO (GCN 41680) and SVOM/VT (GCN 41683). 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_FIELD00068. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41698. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39763] EP#01709201209: Swift-XRT observations
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41697 SUBJECT: EP#01709201209: Swift-XRT observations DATE: 25/09/04 13:30:47 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 EP#01709201209, collecting 1.4 ks of Photon Counting (PC) mode data between T0+4.0 ks and T0+15 ks after the trigger. We have detected 1 source inside the EP/WXT error region. This source coincides with the known source 1RXS J020013.6-084106 and the burst is likely a stellar flare from this object, as reported also in GCN 41690. Known X-ray sources ------------------- Source 1 (SWIFT J020012.7-084052): ================================== RA (J2000.0): 30.0530 = 02 00 12.72 Dec (J2000.0): -8.6811 = -08 40 52.0 Error: 3.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 52 arcsec from the Einstein Probe/WXT position. Mean rate: 1.949 +/- 0.079 ct s^-1 Mean flux: (6.57 +/- 0.27)e-11 erg cm^-2 s^-1 Peak rate: 5.8 +/- 1.3 ct s^-1 Peak flux: (1.95 +/- 0.44)e-10 erg cm^-2 s^-1 ECF: 3.37e-11 erg cm^-2 ct^-1 assuming NH=1.53e+21 cm^-2, gamma=2.08 determined from a spectral fit. This matches a catalogued X-ray source CXO J020012.8-084051 in the Chandra/2CSC catalogue. Details: Separation: 1.1" from the XRT source Cat Rate: 0.0e+00 +/- 0.0e+00 ct s^-1 Cat Flux: 0.0e+00 +/- 0.0e+00 erg cm^-2 s^-1 (0.3-10 keV) so the source is not above the catalogued flux. The source IS FADING at the 4.1-sigma level. A SIMBAD object `1RXS J020013.6-084106' is 0.7" away. There is 1 2MASS object within the source's 3-sigma error radius. 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_FIELD00069. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41697. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39762] EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41696 SUBJECT: EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart DATE: 25/09/04 13:25:08 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. J. Levan (Radboud and Warwick), J. A. Quirola-Vasquez (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radbound), F. E. Bauer (SSI and UTA), and J. Chacón (PUC) report on behalf of a larger collaboration: We observed again the field of the fast X-ray transient EP250903a (Zhao et al., GCN 41674). Our first observation was carried out with LCO/Sinistro (3x300 s exposure, mean epoch 0.68 hr after the trigger) and was reported by Levan et al. (GCN 41680). We obtained a second, deeper observation with LCO/Sinistro (9x300 s exposure, mean epoch 3.79 hr after the trigger), and a follow-up observation with Gemini/GMOS-S (4x60 s exposure, mean epoch 19.38 hr after the trigger). Besides, a more accurate X-ray localization of EP250903a is now available, thanks to both Swift/XRT (https://www.swift.ac.uk/EP/) and EP/FXT (Zhang et al., GCN 41693). The candidate afterglow proposed by Levan et al. (GCN 41680) is outside both the XRT and FXT error circles. Furthermore, image subtraction with respect to the Legacy Survey leaves no detectable residual. The magnitudes of this object reported by Xin et al. (GCN 41683) using SVOM/VT are also consistent with the Legacy Survey archival values (r = 21.49, g = 21.95). Given the low S/N of the original detection, the most likely explanation is that there was no flux excess, and we hereby retract this afterglow candidate. Inspection of the second (deeper) LCO epoch and Gemini images reveals however an object not visible in the Legacy survey, at a position consistent with both the Swift/XRT and EP/FXT X-ray localization, at coordinates: RA(J2000) = 22:36:27.02 Dec(J2000) = -49:51:14.1 The estimated error is 0.5". This object is seen to fade between the two observations, and is not detected in (deeper) images from the Legacy Survey. We conclude that this is the actual optical afterglow of EP250903a. We report for the transient the following r-band magnitudes, calibrated against the SkyMapper catalog and not corrected for Galactic extinction: | Time since trigger (hr) | Telescope | Magnitude (AB) | | ----------------------- | --------- | -------------- | | 0.68 | LCO | > 21.7 | | 3.79 | LCO | 23.2 +- 0.3 | | 19.38 | Gemini | 24.3 +- 0.2 | | N/A | Legacy | > 24.8 | We apologize for any inconvenience that our previous announcement may have caused. We acknowledge excellent support from the Gemini staff, in particular Roque Ruiz. View this GCN Circular online at https://gcn.nasa.gov/circulars/41696. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39761] EP-WXT trigger 01709201209: Liverpool Telescope upper limits
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41695 SUBJECT: EP-WXT trigger 01709201209: Liverpool Telescope upper limits DATE: 25/09/04 13:04:23 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris, N. Habeeb and R. L. C. Starling (U of Leicester) report on behalf of a larger collaboration: We observed the field of the EP-WXT trigger 01709201209 with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS r’ and SDSS g’ filters starting at 2025-08-29 04:15:08 UT, approximately 51 minutes after the X-ray detection. We compared the stacked images to reference images from Pan-STARRS. We also used the reference images to perform image subtraction but note that there is significant artefacting due to the bright stars in the centre of the field. We detect no new sources in either the subtractions or stacked images. This is consistent with 01709201209 being a stellar flare (Li et al., GCN 41690). We derive 3-sigma upper limits of r’ > 22.2 and g’ > 22.5 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41695. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39760] GRB 250830C: VZLUSAT-2 detection
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41694 SUBJECT: GRB 250830C: VZLUSAT-2 detection DATE: 25/09/04 12:09:10 GMT FROM: Jakub Ripa <ripa.jakub(a)gmail.com> J. Ripa, M. Dafcikova (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250830C (Konus-Wind detection trigger at 2025-08-30 14:52:17.865 UT; AstroSat detection: GCN 41628; GECAM-B detection: 41630; Insight-HXMT detection: 41632) was detected by the GRB detectors on board the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/) The data acquisition was performed by the GRB detector units no. 0 and no. 1. The detection was confirmed at the peak time 2025-08-30 14:52:19 UTC. The T90 duration is 9 s (8 s) and the significance during T90 reaches 32 sigma (18 sigma) for detector unit no. 0 (no. 1). The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250830C_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/41694. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39759] EP250903a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41693 SUBJECT: EP250903a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/09/04 11:34:49 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. J. Zhang (THU), T. Zhao, Y. J. Song, H. Sun(NAO, CAS), on behalf of the Einstein Probe (EP) team: The X-ray transient EP250903a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhao et al., GCN 41674), with several multi-wavelength follow-up observations (O'Neill et al., GCN 41672; An et al., GCN 41675; Lipunov et al., GCN 41676; Levan et al., GCN 41680; Xin et al., GCN 41683). The refined WXT data shows that the event started at T0=2025-09-03T13:59:40 (UTC) and lasted for about 200 s before the interruption of the autonomous follow-up. WXT detected the source during its rising phase with a peak flux of 6 x 10^(-10) erg/s/cm^2. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.0 x 10^20 cm^-2 and a photon index of 1.6 (+/-0.6). The derived average unabsorbed 0.5-4 keV flux is around 1.0 (-0.5/+1.1) x 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 428s after T0. On-ground analysis of the FXT data found an fading source at R.A. = 339.1101, DEC = -49.8541 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.0 x 10^20 cm^-2 and a photon index of 2.6(+/-0.1). The derived average unabsorbed 0.5-10 keV flux is around 4.3(+/-0.3) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/41693. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39758] LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41692 SUBJECT: LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate DATE: 25/09/04 11:17:57 GMT FROM: Lorenzo Aiello at University of Roma Tor Vergata <lorenzo.aiello(a)roma2.infn.it> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250904br during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-04 10:22:08.022 UTC (GPS time: 1441016546.022). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], and PyCBC Live [6] analysis pipelines. S250904br is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250904br The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). 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 <1%. The source chirp mass falls with highest probability in the bin (22.0, 44.0) 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: * amplfi.multiorder.fits,0, an initial localization generated by AMPLFI [8], distributed via GCN and SCiMMA notices about 26 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [9], 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 373 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2748 +/- 681 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] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [4] 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 [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [8] Chatterjee et al. MLST 5, 045030 (2024) doi:10.1088/2632-2153/ad8982 [9] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41692. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39757] GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41691 SUBJECT: GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590 DATE: 25/09/04 09:50:16 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> A. Saccardi (CEA/Irfu), J. An (NAOC), A. Martin-Carrillo (UCD), G. Corcoran (UCD), N. Habeeb (Leicester), A. J. Levan (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud), G. Pugliese (API), B. Schneider (LAM), S. D. Vergani (LUX-Paris Obs.), D. Xu (NAOC) report on behalf of the Stargate collaboration: We observed the optical counterpart (An et al., GCN 41679; Xin et al., GCN 41684; Pérez-Fournon et al., GCN 41685; Saccardi et al., GCN 41686) of GRB 250903A detected by SVOM/ECLAIRs (Maiolino et al., GCN 41677), using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. From the 30 s X-Shooter acquisition image at 2025-09-04 01:36 UT (~8.18 hr post-trigger), the optical afterglow is well detected with a magnitude of r ~ 20.5 (AB) calibrated against SkyMapper nearby stars and not corrected by Galactic extinction. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 900 s each. Observations started on 2025-09-04 at approximately 01:38 UT (~8.22 hr after the SVOM/ECLAIRs trigger). In a preliminary reduction of the spectra, we detect a continuum over the entire covered wavelength range. From detection in the blue down to ~3190 AA we set a redshift upper limit z < 1.62. Furthermore, we detect several absorption lines due to C IV, Si IV, Si II, Fe II, Al II, Mg II, Mg I, from which we infer a redshift of z = 1.590. While the lack of fine-structure lines formally prevents us from securely associating the z = 1.590 system to the GRB, the lack of any unidentified features (and the reasonable S/N of the spectra), coupled with the tight redshift upper limit, indicate that most likely GRB 250903A was indeed at z = 1.590. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Cecilia Bustos, Martina Baratella, and Rob Van Holstein. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/41691. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39756] The EP-WXT trigger 01709201209 is likely a flaring star
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41690 SUBJECT: The EP-WXT trigger 01709201209 is likely a flaring star DATE: 25/09/04 05:01:21 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), H. Z. Wu (HUST), M. J. Liu and H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709201209 at the time of 2025-09-04T03:24:02, is likely a stellar flare associated with 1RXS J020013.6-084106. The estimated flux of the flare is around 4x10^-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 6.5x10^31 erg/s. 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/41690. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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