GCN Circular 36735

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 S240621em (GCN Circular 36729
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). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.offline0.multiorder.fits, distributed via GCN Notice, is available for retrieval from the GraceDB event page:

https://gracedb.ligo.org/superevents/S240621em

After parameter estimation by RapidPE-RIFT [2], the updated classification of the GW signal, in order of descending probability, is BBH (96%), Terrestrial (4%), NSBH (<1%), or BNS (<1%).

For the Bilby.offline0.multiorder.fits sky map, the 90% credible region is 3069 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 7458 +/- 2672 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
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 and Morisaki et al. (2023) arXiv:2307.13380
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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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