TITLE:   GCN CIRCULAR
NUMBER:  37557
SUBJECT: LIGO/Virgo/KAGRA S240917cb: Updated Sky localization and EM Bright Classification
DATE:    24/09/19 12:42:50 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 S240917cb (GCN Circular 37534). 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/S240917cb

Based on posterior support from parameter estimation [1], under the assumption that the candidate S240917cb is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is <1%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] Both HasNS and HasRemnant consider the support of several neutron star equations of state. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.

For the Bilby.offline0.multiorder.fits,0 sky map, the 90% credible region is 8644 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 6657 +/- 3466 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
 [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe