Skip to main content
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 34148

LIGO/Virgo/KAGRA S230529ay: Updated Sky localization and EM Bright Classification
2023-07-06T14:20:32Z (9 months ago)
Sylvia Biscoveanu at MIT <>
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: 

We have conducted further offline analysis of the LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S230529ay (GCN Circular 33889). 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: 

Based on posterior support from parameter estimation [1], under the assumption that the candidate S230529ay is astrophysical in origin,the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is 98%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is 7%. [2] Both HasNS and HasRemnant consider the support of several neutron star equations of state. The probability that any one of the binary components lie between 3 to 5 solar mass (HasMassgap) is 73%. 

The upward revision in the HasRemnant value relative to that quoted in circular number 33891 is primarily due to an issue that was identified in the em-bright code rather than the updated choice of offline analysis settings. This issue has been fixed and does not affect any values from posterior samples reported in circulars for this event or other events in O4.

For the Bilby.offline0.multiorder.fits,0 sky map, the 90% credible region is 24534 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 197 +/- 62 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 <>. 

[1] Ashton et al. ApJS 241, 27 (2019)
[2] Chatterjee et al. The Astrophysical Journal 896, 1 (2020)
Looking for U.S. government information and services? Visit