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[vsnet-grb-info 39877] EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41811 SUBJECT: EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84 DATE: 25/09/12 09:59:04 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), A. J. Levan (Radboud and Warwick), G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), A. L. Cabrera Lavers (GTC), D. Reverte-Payá (GTC), A. Pérez-Romero (GTC) report for a larger collaboration: We observed the afterglow (Quirola-Vasquez et al., GCN 41790; Angulo et al., GCN 41793; Lai et al., GCN 41801; Evans et al., GCN 41802; Moskvitin & Spiridonova, GCN 41805; Ma et al., GCN 41807) of EP250911a (Liang et al. GCN 41788; Liang et al., GCN 41809) using the Gran Telescopio Canairas (GTC) equipped with the OSIRIS+ instrument. In a sequence of images taken in the r and z filters (mean times 13.97 and 14.12 hr after the trigger time, respectively), we measure magnitudes r = 22.0 +/- 0.1, z = 21.4 +/- 0.1 (all AB, calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction). A sequence of 4 spectra with 1200 s exposure time each was obtained using the R1000B grism, covering the wavelength range 3700-7700 AA (mean time 15.4 hr after trigger). Inspection of the combined spectrum shows a weak continuum. A broad trough is observed around 5890 AA, which is interpreted as a DLA feature at a redshift z ~ 3.84. This is confirmed by the detection of a few metal absorption lines at a consistent redshift, among which we identify S II / Si II 1260, O II / Si II 1303, C II 1334, Si IV 1394, C IV 1548,1550. We also detect a continuum break around 4400 AA, which corresponds to the Lyman limit at this redshift. Note that, despite some temporal and spatial proximity, this redshift is inconsistent with the distance (~1.1 Gpc) derived for the LVK GW source S250911ac (LVK collaboration, GCNs 41786, GCN 41795), excluding an association between the two events. View this GCN Circular online at https://gcn.nasa.gov/circulars/41811. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39876] LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41810 SUBJECT: LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate DATE: 25/09/12 07:24:18 GMT FROM: Trang Nguyen <trang.nguyen(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250912f during real-time processing of data from LIGO Livingston Observatory (L1) and Virgo Observatory (V1) at 2025-09-12 06:40:08.840 UTC (GPS time: 1441694426.840). The candidate was found by the GstLAL [1] and SPIIR [2] analysis pipelines. S250912f is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.9e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250912f 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%. [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 <1%. The source chirp mass falls with highest probability in the bin (44.0, 88.0) 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,1, an initial localization generated by BAYESTAR [4], distributed via GCN and SCiMMA notices about 27 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [4], 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,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 393 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2870 +/- 784 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] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [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/41810. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39875] EP250911a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41809 SUBJECT: EP250911a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/09/12 05:02:03 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: The fast X-ray transient EP250911a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Liang et al., GCN 41788), and followed by Swift/XRT (Evans et al., GCN 41802) and several optical telescopes (Quirola-Vasquez et al., GCN 41790 , Angulo et al., GCN 41793, Lai et al., GCN 41801, Moskvitin et al., GCN 41805, Ma et al., GCN 41807). The refined analysis of the WXT data shows that the event started at T0=2025-09-11T08:57:55 (UTC) and lasted for 34 s with the peak flux of 9.3 x 10^(-9) erg/s/cm^2, before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 4.79 x 10^20 cm^-2 and a photon index of 0.77 (-/+0.95). The derived average unabsorbed 0.5-4 keV flux is 3.4 (-1.5/+3.1) x 10^(-9) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2025-09-11T09:03:21 (UTC), about six minutes after T0. The exposure time of this observation is 3856 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 357.5194, 29.2999 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 4.79 x 10^20 cm^-2 and a photon index of 2.02 (-/+0.22). The derived average unabsorbed 0.5-10 keV flux is 7.5 (-1.1/+1.4) 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/41809. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39874] GRB 250910B: SVOM/GRM observation
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41808 SUBJECT: GRB 250910B: SVOM/GRM observation DATE: 25/09/12 04:13:28 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 250910B (SVOM trigger reference: sb25091008) at 2025-09-10T18:52:06.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #41778). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 10.0 +4.5/-1.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250910B.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 80.2, Dec = -46.4, GCN #41778), is located at about 54 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. ECLAIRs was not collecting data at the time of this burst. With the localization from Fermi/GBM, the time-averaged spectrum from T0-3 to T0+8.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.75 +0.12/-0.11 and the cutoff energy, parameterized as Epeak, is 218 +29/-22 keV. The event fluence (10-1000 keV) in this time interval is (5.77 +0.38/-0.36)E-06 erg/cm^2. The 'Amati' relation diagram of GRB 250910B is shown at: https://www.bursthub.cn//admin/static/svgrb250910B_amati.png 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41808. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39873] EP250911a: SVOM/VT optical observation
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41807 SUBJECT: EP250911a: SVOM/VT optical observation DATE: 25/09/12 03:27:06 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, L. P. Xin, Z. H. Yao, 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 EP250911a detected by EP/WXT (Liang et al., GCN 41788). SVOM/VT began observing the field at 2025-09-11T15:33:30 UTC, 6.584 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Quirola-Vasquez et al., GCN 41790, Angulo et al., GCN 41793; Lai et al., GCN 41801; Moskvitin & Spiridonova, GCN 41805) at a location consistent with Swift XRT position (Evans et al., GCN 41802) was clearly detected in both VT_B and VT_R bands. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 6.945 | 27*100 | VT_B | 22.06 | 0.08 6.945 | 27*100 | VT_R | 20.87 | 0.05 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/41807. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39872] GRB 250911A: MASTER optical counterpart observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41806 SUBJECT: GRB 250911A: MASTER optical counterpart observations DATE: 25/09/12 00:53:31 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.M.Lipunov (Lomonosov MSU, Moscow), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (OAFA), A.Kuznetsov, A.Sankovich, G.Antipov, P.Balanutsa, E.Gorbovskoy, N.Tiurina, M.Shilova, A.Chasovnikov, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko (Lomonosov MSU), D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A.Sosnovskij (Crao RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru,Argentina started Swift GRB 250911A (Klingler et al. GCN 41781) observations automatically at 2025-09-11 02:25:44UT and in own planner mode befor it. There is GRB optical counterpart MASTER OT J173500.02-165114.40 with mOT~18.81 at Swift position (XRT Perri et al. GCN 41783, Beardmore et al. GCN 41784, Dichiara et al. GCN 41804; UVOT Siegel et al. GCN 41800), first reported by COLIBRI (Angula et al. GCN 41782). All images reduction will be continued. The message may be cited. References 1) Lipunov et al. 2010, MASTER Robotic Net, Advances in Astronomy, vol. 2010, p.30L 2) Lipunov,V.G. Kornilov, E.S. Gorbovskoy, N.V. Tyurina, A.S. Kuznetsov, "ASTRONOMICAL ROBOTIC NETWORKS and OPERATIVE MULTICHANNEL ASTROPHYSICS. Based on the example of the global MASTER network.", The Moscow State University Publishing House. In the series "Works of Outstanding Scientists of Moscow State University", http://www.pereplet.ru/lipunov/625.html#625) View this GCN Circular online at https://gcn.nasa.gov/circulars/41806. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39871] EP250911a: SAO RAS optical observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41805 SUBJECT: EP250911a: SAO RAS optical observations DATE: 25/09/11 23:47:13 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO RAS) report on behalf of GRB follow-up collaboration. We observed the field of EP250911a (Liang et al., GCN 41788, Evans et al., GCN 41802) with the 1-m SAO RAS telescope Zeiss-1000 equipped with CCD-photometer. We obtained 9 x 300 sec. images in Rc band on September 11, 21:38:05--22:34:14 UT (t_mid - T0 = 13.12819 hours = 0.547008 days). The OT (Quirola-Vasquez et al., GCN 41790, Angulo et al., GCN 41793; Lai et al., GCN 41801) is clearly detected in the stacked image with the brightness of R = 21.90 +/- 0.11 (R_lim = 23.0 mag). This preliminary photometry is based on nearby SDSS stars (magnitudes were converted with the Lupton 2005 equations) and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41805. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39870] GRB 250911A: Swift-XRT refined Analysis
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41804 SUBJECT: GRB 250911A: Swift-XRT refined Analysis DATE: 25/09/11 20:18:36 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.6 ks of XRT data for GRB 250911A, from 3.4 ks to 48.4 ks after the trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.52 (+/-0.08). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+0.16, -0.15). The best-fitting absorption column is 3.9 (+1.0, -0.5) x 10^21 cm^-2, consistent with the Galactic value of 3.4 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 4.5 x 10^-11 (6.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.9 (+1.0, -0.5) x 10^21 cm^-2 Galactic foreground: 3.4 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.80 (+0.16, -0.15) If the light curve continues to decay with a power-law decay index of 1.52, the count rate at T+24 hours will be 0.015 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.8 x 10^-13 (9.5 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/01348587. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41804. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39869] GRB 250910C: Fermi GBM Final Localization Correction
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41803 SUBJECT: GRB 250910C: Fermi GBM Final Localization Correction DATE: 25/09/11 18:28:00 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 23:50:11.34 UT on 10 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250910C (trigger 779241016/250910993). This trigger was initially classified as Unreliable location by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 47.58, Dec = -35.77 (J2000 degrees, equivalent to J2000 3h 10m, -35d 46'), with a statistical uncertainty of 10.95 degrees. The angle from the Fermi LAT boresight is 46 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910993/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910993/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910993/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41803. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39868] EP250911a: Swift-XRT observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41802 SUBJECT: EP250911a: Swift-XRT observations DATE: 25/09/11 17:36:52 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 EP250911a (Liang et al., GCN Circ 41788), collecting 1.7 ks of Photon Counting (PC) mode data between T0+5.5 ks and T0+11 ks after the trigger. We have detected 1 source consistent with the EP/FXT position (Liang et al., GCN Circ 41788). This has been automatically classified as an uncatalogued X-ray source. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J235004.5+291757): ================================== RA (J2000.0): 357.5191 = 23 50 04.58 Dec (J2000.0): +29.2992 = +29 17 57.1 Error: 4.6 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 62 arcsec from the Einstein Probe/WXT position. Mean rate: 0.0239 +/- 0.0047 ct s^-1 Mean flux: (8.3 +/- 1.6)e-13 erg cm^-2 s^-1 Peak rate: 0.0239 +/- 0.0047 ct s^-1 Peak flux: (8.3 +/- 1.6)e-13 erg cm^-2 s^-1 ECF: 3.47e-11 erg cm^-2 ct^-1 assuming NH=5.84e+20 cm^-2, gamma=1.92 determined from a spectral fit. XMM UL: 7.6e-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. 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. We note that source 1 also matches the position of the optical counterpart to EP250911a reported by Quirola-Vasquez et al. (GCN Circ. 41790) and Angulo et al. (GCN Circ. 41793). 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_FIELD00073. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41802. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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