TITLE: GCN CIRCULAR NUMBER: 34786 SUBJECT: LIGO/Virgo/KAGRA S230928cb: Updated Sky localization DATE: 23/10/01 22:27:17 GMT FROM: Colm Talbot at University of Chicago talbotcolm@gmail.com

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 S230928cb (GCN Circular 34781). 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/S230928cb

For the Bilby.offline0.multiorder.fits,0 sky map, the 90% credible region is 3102 deg2. Marginalized over the whole sky, the a posterior luminosity distance estimate is 4060 +/- 1553 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)

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