GCN Circular 36473

The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:

We identified the compact binary merger candidate S240514c during real-time processing of data from LIGO Livingston Observatory (L1) at 2024-05-14 08:03:21.048 UTC (GPS time: 1399709019.048). The candidate was found by the GstLAL [1] analysis pipeline.

S240514c is an event of interest because its false alarm rate, as estimated by the online analysis, is 9.6e-09 Hz, or about one in 3 years. The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S240514c

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%).

Low-frequency excess of noise was present in LIGO Livingston detector at the time of the event, which 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%.

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 [4], distributed via GCN notice about 28 seconds after the candidate event time.
 * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [4], distributed via GCN notice about 47 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 24219 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3762 +/- 1324 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
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 and Ewing et al. (2023) arXiv:2305.05625
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 [2] Rose et al. (2022) arXiv:2201.05263
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 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002
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 [3] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
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 [4] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013
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