TITLE: GCN CIRCULAR NUMBER: 39776 SUBJECT: LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate DATE: 25/03/19 07:43:35 GMT FROM: sreedevi_p230198ph@nitc.ac.in
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S250319bu during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-03-19 06:25:36.479 UTC (GPS time: 1426400754.479). The candidate was found by the GstLAL [1], MBTA [2], and SPIIR [3] analysis pipelines.
S250319bu is an event of interest because its false alarm rate, as estimated by the online analysis, is 4.7e-10 Hz, or about one in 67 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S250319bu
The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%).
The LIGO Hanford detector lost its working point about two seconds after the merger time. That has been carefully investigated by the LVK rapid response team and should have no impact on the significance of the signal nor on its classification or skymap.
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%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [4] 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%.
Three 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 [5], distributed via GCN notice about 23 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [5], distributed via GCN notice about 28 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [5], 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 2057 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4372 +/- 1308 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] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [3] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
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