LIGO/Virgo/KAGRA S231231ag
GCN Circular 35445
Subject
LIGO/Virgo/KAGRA S231231ag: Identification of a GW compact binary merger candidate
Date
2023-12-31T16:10:22Z (a year ago)
From
Keita Kawabe at LIGO Hanford <kkawabe@caltech.edu>
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S231231ag during real-time processing of data from LIGO Hanford Observatory (H1) at 2023-12-31 15:40:16.670 UTC (GPS time: 1388072434.670). The candidate was found by the GstLAL [1] analysis pipeline.
S231231ag is an event of interest because its false alarm rate, as estimated by the online analysis, is 8.4e-15 Hz, or about one in 1e7 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S231231ag
The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%).
Assuming the candidate 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%.
Two sky maps are available at this time and can be retrieved from the GraceDB event page:
* bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 27 seconds after the candidate event time.
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 5 minutes after the candidate event time.
The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 24218 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1114 +/- 357 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/userguide/.
[1] Tsukada et al. PRD 108, 043004 (2023) and Ewing et al. arXiv:2305.05625 (2023)
[2] Chatterjee et al. ApJ 896, 54 (2020)
[3] Singer & Price PRD 93, 024013 (2016)
GCN Circular 35446
Subject
LIGO/Virgo/KAGRA S231231ag: Updated Sky localization and Source Classification
Date
2023-12-31T22:52:04Z (a year ago)
From
Aaron Zimmerman at U. of Texas at Austin <aaron.zimmerman@utexas.edu>
Via
Web form
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We have conducted further analysis of the LIGO Hanford Observatory (H1) data around the time of the compact binary merger (CBC) candidate S231231ag (GCN Circular 35445). 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/S231231ag
After parameter estimation by RapidPE-RIFT [2], the updated classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%).
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 27061 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1066 +/- 339 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/userguide/.
[1] Ashton et al. ApJS 241, 27 (2019) and Morisaki et al. arXiv:2307.13380 (2023)
[2] Rose et al. arXiv:2201.05263 (2022) and Pankow et al. PRD 92, 023002 (2015)