TITLE: GCN CIRCULAR NUMBER: 26570 SUBJECT: LIGO/Virgo S191216ap: Updated Source Classification DATE: 19/12/23 18:27:02 GMT FROM: Brandon Piotrzkowski at U of Wisconsin-Milwaukee The LIGO Scientific Collaboration and the Virgo Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S191216ap (GCN Circular 26454). Assuming the candidate is astrophysical, the updated parameter estimation based classification of the GW signal, in order of descending probability, is BBH (>99%), MassGap (<1%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo Public Alerts User Guide . [1] Veitch et al. PRD 91, 042003 (2015)