TITLE: GCN CIRCULAR NUMBER: 36727 SUBJECT: LIGO/Virgo/KAGRA S240621dy: Identification of a GW compact binary merger candidate DATE: 24/06/21 20:30:11 GMT FROM: hsiang-yu.huang@ligo.org
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S240621dy during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2024-06-21 19:50:59.425 UTC (GPS time: 1403034677.425). The candidate was found by the CWB [1], GstLAL [2], MBTA [3], and PyCBC Live [4] analysis pipelines.
S240621dy is an event of interest because its false alarm rate, as estimated by the online analysis, is 4e-20 Hz, or about one in 1e12 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S240621dy
The classification of the GW signal, in order of descending probability, is BBH (>99%), BNS (<1%), NSBH (<1%), or Terrestrial (<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%. [5] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [5] 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 [6], distributed via GCN notice about 27 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [6], 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 well fit by an ellipse with an area of 37 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(03h12m, +44d49m, 4.90d, 2.40d, 97.02d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1181 +/- 249 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] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625 [3] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [4] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [5] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [6] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
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