TITLE: GCN CIRCULAR NUMBER: 35422 SUBJECT: LIGO/Virgo/KAGRA S231223j: Updated Sky localization DATE: 23/12/23 23:55:45 GMT FROM: Aaron Zimmerman at U. of Texas at Austin aaron.zimmerman@utexas.edu

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 S231223j (GCN Circular 35420). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.offline0.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page:

https://gracedb.ligo.org/superevents/S231223j

For the Bilby.offline0.multiorder.fits,0 sky map, the 90% credible region is 3520 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4468 +/- 1602 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/userguide/.

[1] Ashton et al. ApJS 241, 27 (2019) and Morisaki et al. arXiv:2307.13380 (2023)

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