TITLE:   GCN CIRCULAR
NUMBER:  36733
SUBJECT: LIGO/Virgo/KAGRA S240621dy: Updated Sky localization and Source Classification
DATE:    24/06/22 12:07:22 GMT
FROM:    Nihar.Gupte@aei.mpg.de

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 S240621dy (GCN Circular  36727). 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:

https://gracedb.ligo.org/superevents/S240621dy

After parameter estimation by RapidPE-RIFT [2], the updated classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), BNS (<1%), or Terrestrial (<1%).

For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 22 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(03h12m, +45d20m, 3.53d, 1.95d, 105.53d)

Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1184 +/- 199 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. (2023) arXiv:2307.13380
[2] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002