TITLE: GCN CIRCULAR NUMBER: 42026 SUBJECT: LIGO/Virgo/KAGRA S250929c: Updated Sky localization DATE: 25/09/29 14:29:17 GMT FROM: Aditya Vijaykumar aditya.vijaykumar@ligo.org

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

We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250929c (GCN Circular 42023). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:

https://gracedb.ligo.org/superevents/S250929c

For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 1828 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3796 +/- 1511 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] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040

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