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

[vsnet-grb-info 36867] LIGO/Virgo/KAGRA S250109f: Identification of a GW compact binary merger candidate
by GCN Circulars 09 Jan '25

09 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38860 SUBJECT: LIGO/Virgo/KAGRA S250109f: Identification of a GW compact binary merger candidate DATE: 25/01/09 01:52:52 GMT FROM: 陳正敏 <cjhengmin(a)gmail.com> S250109f_circular The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250109f during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-01-09 01:05:41.482 UTC (GPS time: 1420419959.482). The candidate was found by the CWB [1], cWB BBH [2], GstLAL [3], MBTA [4], and PyCBC Live [5] analysis pipelines. S250109f is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.9e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250109f After parameter estimation by RapidPE-RIFT [6], 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 25 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 614 deg2. Marginalized over the whole sky, the posteriori luminosity distance estimate is 3259 +/- 876 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] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002 [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/38860. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36866] GRB 250108B: Swift-XRT refined Analysis
by GCN Circulars 09 Jan '25

09 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38859 SUBJECT: GRB 250108B: Swift-XRT refined Analysis DATE: 25/01/09 01:41:47 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M. Capalbi (INAF-IASFPA), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 8.5 ks of XRT data for GRB 250108B, from 97 s to 33.7 ks after the BAT trigger. The data comprise 608 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+5.5 ks) can be modelled with a power-law decay with a decay index of alpha=0.35 (+/-0.13). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.37 (+/-0.04). The best-fitting absorption column is 1.47 (+/-0.09) x 10^21 cm^-2, in excess of the Galactic value of 1.2 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.07 (+0.17, -0.16) and a best-fitting absorption column of 1.3 (+0.5, -0.4) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (4.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.3 (+0.5, -0.4) x 10^21 cm^-2 Galactic foreground: 1.2 x 10^20 cm^-2 Excess significance: 4.8 sigma Photon index: 2.07 (+0.17, -0.16) If the light curve continues to decay with a power-law decay index of 0.35, the count rate at T+24 hours will be 0.045 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.5 x 10^-12 (2.0 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01280056. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/38859. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36865] Swift GRB 250108B: Global MASTER-Net observations report
by GCN Circulars 08 Jan '25

08 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38858 SUBJECT: Swift GRB 250108B: Global MASTER-Net observations report DATE: 25/01/08 21:47:28 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-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 Swift GRB 250108B ( N. J. Klingler et al., GCN 38847) errorbox 35528 sec after notice time and 35573 sec after trigger time at 2025-01-08 20:16:00 UT, with upper limit up to 17.8 mag. The observations began at zenith distance = 84 deg. The sun altitude is -65.6 deg. The galactic latitude b = 82 deg., longitude l = 23 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2737810 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 35664 | MASTER-Kislovodsk | C | 180 | 16.7 | 35664 | MASTER-Kislovodsk | C | 180 | 16.7 | 35864 | MASTER-Kislovodsk | C | 180 | 16.7 | 35864 | MASTER-Kislovodsk | C | 180 | 16.7 | 36908 | MASTER-Kislovodsk | C | 180 | 17.5 | 36908 | MASTER-Kislovodsk | C | 180 | 17.5 | 38307 | MASTER-Kislovodsk | C | 180 | 17.6 | 38307 | MASTER-Kislovodsk | C | 180 | 17.6 | 38757 | MASTER-Kislovodsk | C | 120 | 17.6 | 38757 | MASTER-Kislovodsk | C | 120 | 17.6 | 39177 | MASTER-Kislovodsk | C | 120 | 17.5 | 39177 | MASTER-Kislovodsk | C | 120 | 17.5 | 39547 | MASTER-Kislovodsk | C | 180 | 17.8 | 39547 | MASTER-Kislovodsk | C | 180 | 17.8 | 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/38858. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36864] Fermi Gamma-ray Burst Monitor trigger 758061038/250108855 is not a GRB
by GCN Circulars 08 Jan '25

08 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38857 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 758061038/250108855 is not a GRB DATE: 25/01/08 21:33:43 GMT FROM: atrigg2(a)lsu.edu A. C. Trigg (LSU) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 758061038/250108855 at 20:30:33.28 UT on 08 January 2025 is not due to a GRB. This trigger is likely due to local particles. This trigger is not associated with LIGO/Virgo/KAGRA S250108ha (GCN 38856)" View this GCN Circular online at https://gcn.nasa.gov/circulars/38857. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36863] LIGO/Virgo/KAGRA S250108ha: Retraction of GW compact binary merger candidate
by GCN Circulars 08 Jan '25

08 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38856 SUBJECT: LIGO/Virgo/KAGRA S250108ha: Retraction of GW compact binary merger candidate DATE: 25/01/08 21:26:41 GMT FROM: Isaac McMahon at University of Zurich <isaac.mcmahon(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: The trigger S250108ha, initially reported because of a coincidence with Fermi/GBM trigger 758061038/250108855, is no longer considered to be a candidate of interest. That Fermi trigger is no longer classified as a GRB. Without this, the GW candidate’s significance is below our alert threshold. View this GCN Circular online at https://gcn.nasa.gov/circulars/38856. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36862] GRB 250108B: Gemini-North Candidate Optical Afterglow Detection
by GCN Circulars 08 Jan '25

08 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38855 SUBJECT: GRB 250108B: Gemini-North Candidate Optical Afterglow Detection DATE: 25/01/08 16:51:54 GMT FROM: Jillian Rastinejad at Northwestern Univ. <jillianrastinejad2024(a)u.northwestern.edu> Jillian Rastinejad (Northwestern), Andrew J. Levan (Radboud), Wen-fai Fong, Charlie Kilpatrick (Northwestern), Daniele B. Malesani (DAWN/ NBI and Radboud), Nial R. Tanvir (U. Leicester), Gavin P Lamb (LJMU), Benjamin P. Gompertz (U. Birmingham) and Brian D. Metzger (Columbia/CCA) report on behalf of a larger collaboration: We observed the location of the X-ray afterglow of GRB 250108B (Klinger et al., GCN 38847; Osborne et al., GCN 38848) with the Gemini Multi-Object Spectrograph (GMOS-N) mounted on Gemini-North under Program GN-2024B-Q-107. We obtained 15x120-s imaging in r-band at a mid-time of 2025-01-08 12:42:45.8 UT (2.33 hours post-burst), at a median airmass of 1.7 and seeing < 1.2''. We clearly detect a faint source not present in archival Legacy Survey DR10 r-band imaging but within the XRT localization at a position of RA (J2000) = 13:25:18.50 Dec (J2000) = 25:36:55.82 with an uncertainty of 0.7''. We suggest that this is the afterglow of GRB 250108B. We note that the candidate afterglow is 16.8'' offset from a bright galaxy (r = 19.5 AB mag). This galaxy has a Legacy Survey DR9 photometric redshift of z = 0.29 +/- 0.04 (Zhou et al., 2021) and an SDSS photometric redshift of z = 0.22 +/- 0.04 (Alam et al., 2015), corresponding to projected separations of 74 kpc and 60 kpc from the transient, respectively. We determine a probability of chance coincidence between this galaxy and the candidate afterglow of Pcc = 0.13 (Bloom et al., 2002). With present data we cannot rule out the presence of a faint, underlying host at the position of the transient. Calibrated to SDSS, we measure a preliminary brightness for the optical source of r = 23.4 +/- 0.1 AB mag, not corrected for Galactic extinction. At a redshift of z = 0.29, this corresponds to an optical luminosity of 2.1 x 10^42 erg/s. Further observations are planned to monitor the variability of the source. We thank Jen Miller, Leila Alamos, Brian Lemaux and additional Gemini staff for excellent support in the rapid planning and execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/38855. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36861] GRB 250103A: 1.6m Mephisto optical observations
by GCN Circulars 08 Jan '25

08 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38854 SUBJECT: GRB 250103A: 1.6m Mephisto optical observations DATE: 25/01/08 16:27:20 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Guowang Du, Jinghua Zhang, Yangwei Zhang, Brajesh Kumar, Xufeng Zhu, Fanchuan Kong, Chenxi Shang, Yuan Fang, Xinlei Chen, Xingzhu Zou, Yu Pan, Yuanpei Yang (all SWIFAR, YNU), Xuhui Han, Pinpin Zhang, Liping Xin, Chao Wu (all NAOC), Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of GRB 250103A (sb25010301) detected by SVOM/ECLAIRs (Wang et al. GCN 38786) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Simultaneous uvgriz band photometric observations were conducted starting from 11:35:51 2025-01-03 UT (~1.65 hr after the SVOM/ECLAIRs trigger) and several frames with different exposure times were taken. There is detection of the optical candidate (Li et al., GCN 38795; Qiu et al., GCN 38802; Xu et al., GCN 38808; Leonini et al., GCN 38811) in our r and i band single frames but not in the stacked images of uvgz bands. The preliminary photometry and 3 sigma upper limits are below: Start_Time(UT) | Band | Exp(s) | Mag/LimMag (AB) ---------------------------|--------|---------------- 2025-01-03T11:35:52 | u | 180*2 | >21.89 2025-01-03T11:43:02 | v | 180*2 | >22.28 2025-01-03T11:35:52 | g | 50*6 | >22.15 2025-01-03T11:43:03 | r | 50*1 | 20.91(+/-0.35) 2025-01-03T11:35:51 | i | 79*1 | 19.72(+/-0.32) 2025-01-03T11:43:02 | z | 79*4 | >20.46 ------------------------------------------------------------------------------------------------- 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/38854. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36860] GRB 250108A: Swift-XRT afterglow detection
by GCN Circulars 08 Jan '25

08 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38853 SUBJECT: GRB 250108A: Swift-XRT afterglow detection DATE: 25/01/08 16:18:44 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (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 the SVOM/ECLAIRs-detected burst GRB 250108A. We searched for X-ray sources in 2.7 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 3.2 ks, obtained between T0+16.1 ks and T0+34.4 ks. An uncatalogued X-ray source is detected within the estimated 3-sigma SVOM/MXTs error region (98 arcsec) and is above the LSXPS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 2670 s of PC mode data and 2 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 = 207.92093, +26.21642 which is equivalent to: RA (J2000): 13h 51m 41.02s Dec(J2000): +26d 12' 59.1" with an uncertainty of 4.1 arcsec (radius, 90% confidence). This position is 73 arcsec from the SVOM/MXTs position. The source has a mean count rate of 1.7e-02 ct/sec; we cannot determine at the present time whether it is fading. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021755. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021755. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/38853. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36859] GRB 250108A:SVOM/VT optical candidate
by GCN Circulars 08 Jan '25

08 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38852 SUBJECT: GRB 250108A:SVOM/VT optical candidate DATE: 25/01/08 16:14:39 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> SVOM/VT commissioning team: Y. L. Qiu, H. L. Li (NAOC), W. K. Zheng (UCB), Z. Q. Wang (GXU), X. H. Han, L. P. Xin, C. Wu, J. Wang, W. J. Xie, H. B. Cai, Y. Xu, Y. J. Xiao, P. P. Zhang, J. S. Deng, L. Lan, X. M. Lu, R. S. Zhang, Z. H. Yao (NAOC), J. Zhang, L. J. Dan, G. Y. Zou, C. J. Wang, Y. F. Du, C. Huang (XIOPM) SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Olivier Godet (IRAP), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Shao-Lin Xiong (IHEP), Bing Zhang (UNLV) report on behalf of the SVOM team: The SVOM/VT conducted follow-up observations of the GRB 250108A (Zheng et al., GCN 38845) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. With the X band downlinked data, an uncatalogued optical source was detected within the errorbox of MXT (Zheng et al., GCN 38845) in VT_R stacked image, compared to the DESI catalog. It is the only new source within the error box down to the 3 sigma limit of about 22.7 mag. The brightness of the source was estimated to be 22.1+/-0.2 mag in AB magnitude in VT_R image at the mid time of 1.516 hours post the burst, with a total exposure time of 8*100 seconds. The source can not be detected in VT_R 19*100 sec stacked image with a 3 sigma limit of 23.0 mag at the middle time of 3.978 hours. The source is located at RA, Dec = 207.89654, 26.23741, which is equivalent to: RA (J2000) : 13:51:35.17 Dec (J2000): +26:14:14.68 with an uncertainty of 0.5 arcsec. Additionally, no any new sources were detected within the errorbox of XRT #1 source (Phil Evans et al., GCN 38846). We proposed that this source is the candidate for the gamma-ray burst. More deep follow-ups are encouraged to confirm the nature of the source. 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/38852. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36858] LIGO/Virgo/KAGRA S250108eo: Identification of a GW compact binary merger candidate
by GCN Circulars 08 Jan '25

08 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38851 SUBJECT: LIGO/Virgo/KAGRA S250108eo: Identification of a GW compact binary merger candidate DATE: 25/01/08 16:01:16 GMT FROM: Isaac McMahon at University of Zurich <isaac.mcmahon(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250108eo during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-01-08 15:22:21.704 UTC (GPS time: 1420384959.704). The candidate was found by the CWB [1], cWB BBH [2], GstLAL [3], MBTA [4], and PyCBC Live [5] analysis pipelines. S250108eo is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.8e-11 Hz, or about one in 1e3 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250108eo After parameter estimation by RapidPE-RIFT [6], 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 32 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 938 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2826 +/- 750 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] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002 [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/38851. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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