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GCN Circular 33816

LIGO/Virgo/KAGRA S230518h: Updated Sky localization and EM Bright Classification
2023-05-18T17:30:57Z (a year ago)
Keita Kawabe at LIGO Hanford <>
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:

We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S230518h (GCN Circular 33813). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page:

Based on posterior support from parameter estimation [1], under the assumption that the candidate S230518h is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is >99%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] Both HasNS and HasRemnant consider the support of several neutron star equations of state. The probability that any one of the binary components lie between 3 to 5 solar mass (HasMassgap) is <1%.

For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 666 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 278 +/- 68 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 <>.

 [1] Ashton et al. ApJS 241, 27 (2019)
 [2] Chatterjee et al. ApJ 896, 1 (2020)

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