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

[vsnet-grb-info 37526] EP250226a/GRB 250226A: refined analysis of the EP-WXT and FXT observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39513 SUBJECT: EP250226a/GRB 250226A: refined analysis of the EP-WXT and FXT observations DATE: 25/02/27 09:18:11 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang (NAO, CAS), B.-T. Wang (YNAO, CAS), H. Z. Wu (HUST), T. Zhao, Y. J. Song, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250226a/GRB 250226A triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Jiang et al., GCN 39482), which is also detected by Fermi/GBM (Fermi GBM team, GCN 39479), GECAM-B (Zhang et al., GCN 39492) and INTEGRAL/SPI-ACS (triNum #11070), and followed by several optical telescopes (An et al., GCN 39486, Magnani et al., GCN 39488, Li et al., GCN 39489, Aryan et al., GCN 39509, Zou et al., GCN 39511) at the redshift of 3.315 (Zhu et al., GCN 39487). The refined analysis of the WXT data shows that the event started at 2025-02-26T06:34:54 (UTC) and lasted for 22 s with the peak flux of 9.8 x 10^(-9) erg/s/cm^2, before the observation was interrupted by the autonomous follow-up observation. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed about 44 minutes later as blocked by the Earth. The on-ground analysis shows that an uncatalogued source was detected at R.A. = 224.2641, DEC = 20.9754 (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 Galactic equivalent hydrogen column density of 3.7 x 10^20 cm^-2 and a photon index of 2.07 (-/+0.06). The derived average unabsorbed 0.5-10 keV flux is 2.89 (-/+0.08) x 10^(-11) erg/s/cm^2. Further FXT observation performed at about 11.9 hours after the trigger showed an average unabsorbed 0.5-10 keV flux is 1.83 (-/+0.18) 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/39513. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37525] EP250225a: TRT optical upper limits
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39512 SUBJECT: EP250225a: TRT optical upper limits DATE: 25/02/27 09:15:26 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z.P. Zhu, J. An, X. Liu, S.Q. Jiang, S.Y. Fu (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of EP250225a (Jiang et al., GCN 39475) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 02:45:51 UTC on 2025-02-26, 6 x 300 s and 5 x 300s frames were obtained in Sloan-r and Sloan-z band, respectively. No new optical source is detected in the stacked images within or beside the ~ 2.8 arc min EP/WXT error circle (Jiang et al., GCN 39475), consistent with the non-detection (Li et al., GCN 39477; Lipunov et al., GCN 39478), down to a 5-sigma limiting magnitude of r ~ 21.8 and z ~ 19.5, calibrated with Pan-STARRS sources in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39512. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37524] EP250226a/GRB 250226A: 1.6m Mephisto observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39511 SUBJECT: EP250226a/GRB 250226A: 1.6m Mephisto observations DATE: 25/02/27 08:51:56 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Xingzhu Zou, Brajesh Kumar, Wenqiang Fan, Tao Wang, Jiayu Qi, Yuan Fang, Guowang Du, Jinghua Zhang, Helong Guo, Edoardo P. Lagioia, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of EP250226a/GRB 250226A (Jiang et al., GCN 39482; The Fermi team, GCN 39479) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Three exposures of 300s each in the MEPHISTO u, v, g, and r bands were simultaneously (ug, vr) obtained starting from 2025-02-26T17:59:42 (~ 11.5h after the trigger). In our stacked g and r band images, we detect a source at the position of the optical candidate (An et. al., GCN 39486; Zhu et. al., GCN 39487; Magnani et al., GCN 39488; Li et. al., GCN 39489; Aryan et al., GCN 39509) but not in u, v bands. The preliminary magnitudes and the 3-sigma upper limits are below: Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB) --------------------|------|--------|--------------- 2025-02-26T17:59:42 | u | 300*3 | > 22.6 2025-02-26T18:17:11 | v | 300*3 | > 23.0 2025-02-26T17:59:42 | g | 300*3 | 22.2 +/- 0.2 2025-02-26T18:17:11 | r | 300*3 | 21.2 +/- 0.1 ------------------------------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ------------------------------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/39511. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37523] LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39510 SUBJECT: LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations DATE: 25/02/27 08:37:53 GMT FROM: Yue Wang <m18509381757(a)163.com> Yue Wang, Chen-Wei Wang, Shao-Lin Xiong, Shi-Jie Zheng, Ping Wang (IHEP) and Ce Cai (HEBNU) report on behalf of the SVOM team: At the event time 2025-02-06T21:25:30.439 (UTC) of S250206dm (GCN 39175; GCN 39178; GCN 39231), SVOM/GRM was observing normally and monitored 96.6% of the localization probability region of this GW event. There was no SVOM/GRM in-flight trigger around the event time of S250206dm. The routine blind search of SVOM/GRM data also found no burst candidate. Considering three typical GRB spectral models (i.e. soft, normal and hard Band functions), three timescales and the center region of GW localization (RA= 38.21°, Dec = 53.47°), the 3 sigma upper limits of the GRB energy flux (15 keV-5000 keV, in units of 10^-7 erg/s/cm^2) are reported below: |Timescale (s) | Soft | Normal | Hard| | ------------ | ------------ | ------------ | ------------ | |0.1| 0.63 | 1.36 | 17.09 | |1| 0.20 | 0.43 | 5.40 | |10| 0.06 | 0.14 | 1.71 | With the median luminosity distance of 373 Mpc from the GW detection (GCN 39231), we further calculate the following upper limits of the GRB intrinsic luminosity (1 keV-10 MeV, in units of 10^49 erg/s): |Timescale (s) | Soft | Normal | Hard| | ------------ | ------------ | ------------ | ------------ | |0.1| 0.17 |0.25|4.35| |1| 0.05 |0.08|1.38| |10| 0.01 |0.03|0.44| We note that all these results are preliminary and refined analysis will be reported. 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/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/39510. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37522] EP250226a/GRB 250226A: Kinder optical follow-up observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39509 SUBJECT: EP250226a/GRB 250226A: Kinder optical follow-up observations DATE: 25/02/27 05:20:39 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, T.-W. Chen, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, M.-H. Lee, H.-C. Lin, C.-H. Lai, C.-S. Lin, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP250226a/GRB 250226a (Jiang et al., GCN 39482; The Fermi team, GCN 39479) using the Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first LOT epoch of observations in the g band started at 19:34 UT on the 26th of February 2025 (MJD = 60732.815), ~12.98 hrs after the EP trigger; while the first LOT epoch of observations in the r band started at 19:59 UT on the 26th of February 2025 (MJD = 60732.826), ~13.25 hrs after the EP trigger. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked r-band image, we marginally detected the optical counterpart candidate proposed by An et al. (GCN 39486) and confirmed by several other observations (e.g., Zhu et al., GCN 39487; Magnani et al., GCN 39488; and Li et al., GCN 39489). We employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on our stacked frames. The details of the observations and measured photometry (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | g | 60732.815 | 12.98 | 300 * 3 | >21.1 | 0".92 | 1.02 LOT | r | 60732.826 | 13.25 | 300 * 3 | 21.73 +/- 0.17 | 0".91 | 1.01 The presented magnitudes were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_g = 0.16 mag and A_r = 0.11 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/39509. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37521] LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39508 SUBJECT: LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501) DATE: 25/02/27 03:06:58 GMT FROM: yqzhang_cl(a)163.com Ce Cai (HEBNU), Shao-Lin Xiong, Xiao-Bo Li, Shu-Xu Yi, Shuang-Nan Zhang (IHEP) report on behalf of the Insight-HXMT team: At the event time (T0 = 2025-02-23T12:01:15.360 UTC) of the LIGO/Virgo/KAGRA S250223dk event, which was reported to be possibly associated with a sub-threshold burst candidate by Swift/BAT (GCN 39443, 39499), Insight-HXMT was observing 99.97% of the localization probability region based on the combined skymap and there is no Insight-HXMT/HE triggers from the on-ground automated blind search around this event. Thus, we implemented a targeted search [1] for sub-threshold burst signals within the window of T0+/-30 s using the central region of the joint LVK-Swift/BAT localization probability map (i.e. RA = 85.341 deg, Dec = -47.554 deg) and three types of GRB spectra. Our targeted search detected a burst candidate (named as HEB 250223501) with about 4 sigma on the 1-second timescale, starting at T0 - 9.50 s. We note that the time of this Insight-HXMT/HE burst candidate is well consistent with the start time of the Swift/BAT candidate (T0 - 10.240 s, GCN 39443), but the duration is much shorter, which could be explained as the detection energy band of Insight-HXMT/HE is higher than that of Swift/BAT in terms of GRB observation. We note that these results are very preliminary. Refined analysis will be reported later. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/. [1] Cai, C., Xiong, S. L., Li, C. K., et al. 2021, MNRAS, 508, 3910S View this GCN Circular online at https://gcn.nasa.gov/circulars/39508. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37520] LIGO/Virgo/KAGRA S250227y: Retraction of GW compact binary merger candidate
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39507 SUBJECT: LIGO/Virgo/KAGRA S250227y: Retraction of GW compact binary merger candidate DATE: 25/02/27 01:38:00 GMT FROM: chl20171(a)outlook.com The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: The trigger S250227y 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/39507. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37519] LIGO/Virgo/KAGRA S250227e: Identification of a GW compact binary merger candidate
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39506 SUBJECT: LIGO/Virgo/KAGRA S250227e: Identification of a GW compact binary merger candidate DATE: 25/02/27 00:59:12 GMT FROM: chl20171(a)outlook.com The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250227e during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-02-27 00:12:45.474 UTC (GPS time: 1424650383.474). The candidate was found by the GstLAL [1] analysis pipeline. S250227e is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.6e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250227e After parameter estimation by RapidPE-RIFT [2], the classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%). There is evidence for excess noise in L1 coinciding with the merger time. There is evidence for nonstationary noise in V1 around the event time. These data quality issues may affect the parameters or the significance of the candidate. Assuming the candidate is astrophysical in origin, the probability that the lighter compact object 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. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. 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 notice about 26 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [4], distributed via GCN notice 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 500 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2077 +/- 642 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. (2023) arXiv:2305.05625 [2] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002 [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/39506. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37518] Fermi GRB 250226B: Global MASTER-Net observations report
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39505 SUBJECT: Fermi GRB 250226B: Global MASTER-Net observations report DATE: 25/02/26 23:31:13 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 250226B ( Fermi GBM team, GCN 39503) errorbox 99 sec after notice time and 134 sec after trigger time at 2025-02-26 22:32:37 UT, with upper limit up to 16.4 mag. Observations started at twilight. The observations began at zenith distance = 75 deg. The sun altitude is -13.9 deg. The galactic latitude b = -7 deg., longitude l = 24 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2792989 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 150 | 2025-02-26 22:32:37 | MASTER-Tunka | (18h 59m 50.08s , -12d 13m 54.5s) | C | 30 | 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/39505. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37517] LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39504 SUBJECT: LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate DATE: 25/02/26 23:30:23 GMT FROM: chl20171(a)outlook.com The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250226dl during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-02-26 22:48:38.699 UTC (GPS time: 1424645336.699). The candidate was found by the CWB [1], CWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines. S250226dl is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.2e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250226dl 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 the lighter compact object 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. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. 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 notice about 28 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN notice 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 1479 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3587 +/- 1101 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] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [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. (2023) arXiv:2305.05625 [4] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [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/39504. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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